In 1998, Singh & Shaner (Weed Technol. 12: 527‒530) proposed a method which allows one to differentiate whether a plant was resistant or not to glyphosate by measuring shikimate levels, before and after herbicide application. In 2011, Rojano et al. (Talanta 82: 1757‒1762) proposed another method with the same finality, but with reference to glyoxylate levels (intrinsic metabolite in plants). The aim of this study is to compare both based on response time and application rate of the herbicide required. For that, two biotypes of Conyza canadensis were used, susceptible (S) and resistant (R) to glyphosate, whose ED₅₀ were 39.00 and 226.74 g a.e. ha^-1, respectively. For this purpose, two experiments were conducted in which, either varying the response time (3, 6, 9, 12, 24 and 48 HDT) using a fixed dose of application at 222 g a.e. ha^-1 or different doses (18.5, 37, 74, 148, 222, 296, 444 and 592 g a.e. ha^-1) were applied maintaining the response time fixed at 24 HDT. The results indicate that although both methods can differentiate between R and S biotypes, when the herbicide application rate was 222 the response time was 48 hours for shikimate and only 3 hours for glyoxylate, whereas when the time application was 24 HDT the herbicide dose required was 222 g a.e. ha^-1 for shikimate and 37 g a.e. ha^-1 for glyoxylate. Thus we have concluded that the analysis of glyoxylate could be an interesting procedure to detect glyphosate resistance in plants, as it presents advantages compared to the method based on shikimate, because it requires less time for the assay, and a lower dose of glyphosate application.

Fails in the control of Leptochloa virgata with the glyphosate herbicide in a Persian lime orchard was reported in Veracruz, México. Two suspiciously resistant (R) and one susceptible (S) biotype were collected with the aim to determine the resistance level. For this purpose, dose-response assays and shikimic acid accumulation were carried out. Results showed a Resistance Factor [ED₅₀ (R)/ED₅₀ (S)] of 1.7 and 3.5 for biotypes R1 and R2 respectively. At 96 h after treatment with 360 g ai ha^-1, both resistant biotypes accumulated significantly lesser amounts of shikimic acid compared with the susceptible one. This is the first confirmed case of glyphosate resistance in L. virgata from México.

Winter annual grass weeds are a major concern in the production of winter cereals. Many of the herbicides registered for winter annual grass weed control in winter wheat are not labeled for use in winter barley. Flufenacet is not labeled for use on barley in the US, but it is in the United Kingdom. Thus, it could potentially be used in the US on winter barley. Three winter barley varieties were planted in Moscow (dryland) and Kimberly (irrigated), ID during fall 2010. Flufenacet/metribuzin and flufenacet were applied to the soil before barley emergence. Rates used were 0.5, 1, and 1.5 times the use rate of flufenacet/metribuzin which is 0.3 kg ai/ha flufenacet. Pinoxaden at 0.06 kg ai/ha and an untreated check were included for comparison. The experimental design was a split block design with four replications.  Plots were harvested at maturity. Yield, test weight, plumps and thins were measured. Grain yield was lower with all treatments containing flufenacet compared to the untreated check at Moscow, but grain yield at Kimberly was lower than the check with the 1.5 use rates only. Grain yield from pinoxaden treated plots was not different from the untreated at either location. Test weight, plumps and thins were not different among flufenacet herbicides and the untreated check at either location. All varieties responded similarly to herbicide treatments, although yield and quality was different among varieties. Yield was highest with Eight twelve and lowest with Charles at Moscow. At Kimberly, Endeavor yield was highest and Eight twelve yield was lowest. Test weight of Endeavor was higher than the other two varieties at Kimberly, but test weight did not differ among varieties at Moscow. Eight twelve had lower plumps and more thins than Charles or Endeavour at both locations.

Pyroxasulfone (Zidua®) is a new chemistry being evaluated for preemergence (PRE) residual weed control in glyphosate-resistant corn.  Field experiments were conducted at the Southern Agricultural Research Center in Huntley, MT, and at a grower’s field in Yellowstone County, MT, in 2011, to evaluate crop safety and weed control efficacy of pyroxasulfone in comparison to other standard PRE herbicide programs in glyphosate-resistant corn.  Experiments were conducted in a randomized complete block design with four replications.  Treatments included: 1) a nontreated control, 2) pyroxasulfone (Zidua®) alone at 0.149 kg ai ha^-1, 3) pyroxasulfone (Zidua®) alone at 0.298 kg ai ha^-1, 4) dimethenamid (Outlook®) alone at 0.840 kg ai ha^-1, 5) saflufenacil + dimethenamid-P (Verdict®) at 0.737 kg ai ha^-1, 6) acetochlor (Harness®) alone at 1.960 kg ai ha^-1, 7) pyroxasulfone at 0.119 kg ai ha^-1 + pendimethalin (Prowl H₂O®) at 1.064 kg ai ha^-1, and 8) dimethenamid-P at 0.840 kg ai ha^-1 + pendimethalin at 1.064 kg ai ha^-1, 9) saflufenacil + dimethenamid-P at 0.737 kg ai ha^-1 + pendimethalin at 1.064 kg ai ha^-1.  Herbicides were applied with a hand-held boom calibrated to deliver 94 L ha^-1 at 276 kPa.  Corn injury and weed control were visually estimated at 3, 5, and 9 wk after application (WAA) using a scale of 0 to 100, 0 being no injury or no control and 100 being plant death or complete control.  No crop injury was observed with any of the herbicide programs, including pyroxasulfone.  Kochia control 5 WAA with the tank-mix application of pyroxasulfone + pendimethalin was 92%, which was superior to all other treatments, except saflufenacil + dimethenamid-P + pendimethalin mixture.  Kochia control 5 WAA did not differ between 0.149 kg ai ha^-1 (low) and 0.298 kg ai ha^-1 (high) rates of pyroxasulfone applied alone, and averaged 72%, which was no different from saflufenacil + dimethenamid-P treatment.  Dimethenamid alone and acetochlor alone were the least effective treatments for kochia control, which averaged 55% at 5 WAA.  Common lambsquarters control 5 WAA with pyroxasulfone + pendimethalin mixture and dimethenamid-P + pendimethalin mixture averaged 82%, and was higher than pyroxasulfone alone or dimethenamid-P alone treatment.  With pyroxasulfone alone, common lambsquarters control was 69% at the high rate compared with 46% control at the low rate.  Acetochlor was the least effective treatment for common lambsquarters control.  Tank-mix of saflufenacil + dimethenamid-P + pendimethalin provided the most effective control (82%) of wild buckwheat 5 WAA, although it did not differ from the saflufenacil + dimethenamid-P treatment.  Wild buckwheat control 5 WAA with pyroxasulfone alone at the high rate was 46%, and was higher than the 16% average control obtained from pyroxasulfone alone at the low rate and dimethenamid-P alone treatment.  Acetochlor provided < 5% control of wild buckwheat 5 WAA.  Corn yield with pendimethalin-containing herbicide programs, pyroxasulfone (0.298 kg ai ha^-1) alone, and saflufenacil + dimethenamid-P averaged 7109 kg ha^-1, which was 36% higher compared with the average yields obtained from dimethenamid-P alone and pyroxasulfone (0.149 kg ai ha^-1) alone treatments, and 91% higher than the acetochlor alone treatment.  In conclusion, pyroxasulfone applied PRE at 0.298 kg ai ha^-1 would be a valuable tool for residual weed control in glyphosate-resistant corn.

Late emerging broadleaf and grass weeds are a common problem in corn (Zea mays L.) production systems with suppression typically achieved using glyphosate applications.  However, glyphosate-resistant weed biotypes have become problematic.  In addition, baling of corn residue has become a common practice in South Dakota (SD).  This negatively impacts protective cover for wildlife and soil, and reduces grazing opportunities for livestock.  Introducing a cover crop mix, planted after the critical weed free period of corn, may help ameliorate these impacts.  However, cold fall temperatures and dry conditions do not allow for establishment of cover crops after corn harvest.  The objectives of this study were to determine if a cover crop mixture could be established in the corn canopy to suppress late-emerging weeds without negatively affecting corn yield and determine how much cover crop remains in the late fall during corn harvest.  A mixture of lentil (Lens culinaris), winter wheat (Triticum aestivum), and crimson clover (Trifolium incarnatum) was interseeded at the V3 and V5 corn growth stages using broadcast and drilled techniques at a no-till summit (NTS) and, footslope (NTF), and in a conventional tillage (CT) location.  Plants that remained in the late fall were harvested just prior to corn grain harvest.  Biomass samples were separated into cover crop and weed (broadleaf and grass), dried, and weighed.  Data were analyzed by using PROC GLM in SAS.  In August, all cover crop species were present in the canopy.  However, in late fall, crimson clover was the predominant species that remained at NTS and NTF locations, whereas winter wheat was predominant at the CT location.  At fall harvest, due to the early seedling and more water, cover crops seeded at V3 had 20% greater biomass than those seeded at V5.  The drilled application of the cover crops had 35% (V3) and 71% (V5) more biomass when compared with broadcast application.  Cover crops interseeded at the V5 NTF location increased yield by 11%, however there was no other impacts on yield due to cover crops.  Cover crops broadcast at the NTF V5 reduced broadleaf weed biomass by 18% but, if drilled, broadleaf biomass increased about 8% compared with no cover crop areas in this treatment.  Grass weed biomass was reduced at both broadcast and drilled V5 interseedings at the NTS and NTF sites.  Furthermore, grass weed biomass was reduced at the V3 and drilled V5 interseedings at the CT site.  However, the broadcast V5 at the CT site demonstrated an increase in grass weed biomass.  These data suggest that cover crop mixtures may only need a limited number of species, since only one species was dominant at each location.  Furthermore, these data show that cover crops can reduce grass weed biomass without negatively impacting corn yield.

Two of the greatest factors, following genetics, impacting production and yield in agronomic crops are fertility and weed management.  The uptake efficiency of nitrogen is dependent upon many factors including tillage system, soil type, crop, weeds, and the amount and type of nitrogen fertilizer applied.  The relationship and interaction between crops and weeds is important, and determining how North Carolina corn production may be impacted by different fertilizers could improve nitrogen use efficiency and overall corn yields.  Field studies were conducted in 2011 at the Upper Coastal Plains Research Station near Rocky Mount, NC and at the Central Crops Research Station in Clayton, NC.  Treatment factors included N source, N rate and weed removal time with a factorial treatment arrangement.  The N sources included urea ammonium nitrate (UAN), chicken litter (CCL), and sulfur coated urea (SCU) with rates of 0 kg N/A, 27.22 kg N/A, 54.43 kg N/A, and 81.65 kg N/A.  Weed removal times were at 0 (weed-free), 7.62, and 15.24 cm heights.  Significant location, nitrogen source, and weed removal height effects were observed for corn yield.  When weeds were allowed to remain in the field with corn, the weeds were able to compete with the corn for nitrogen over a greater time period therefore reducing corn yield potential which showed the importance of the critical period of weed removal.  The interaction between location and source of nitrogen is due to the differences in soil types at the two research stations with Clayton having a lighter, sandier soil which is better known for leaching and Rocky Mount having a heavier soil with greater clay content.  The increased corn yield corresponding with an increase in applied nitrogen is expected, as nitrogen is an essential nutrient in corn production and is partially due to the increase in Nitrogen Uptake Efficiency with greater nitrogen rates applied. 

Dow AgroSciences is currently developing Enlist^TM corn with anticipated U.S. commercial launch in 2013, pending regulatory approvals.  Enlist corn contains the aad-1 gene which conveys robust tolerance to 2,4-D.  Enlist corn has a single copy of the aad-1 gene which has been shown to be stable over multiple generations with normal Mendelian segregation.  A quantitative ELISA assay has been developed to quantify expression of the AAD-1 protein in the plant.  Key to the characterization of Enlist corn is to ensure the protein is present and expression level is consistent across hybrids.  Additionally, characterization of the agronomics and crop tolerance of Enlist corn across environments in multiple genetic backgrounds is needed. 

Studies were conducted to evaluate the level of AAD-1 protein expression across 7 hybrids at the V4 and V7 growth stages.   Five of the seven hybrids were produced from one AAD-1 inbred while the remaining two hybrids were produced from a second AAD-1 inbred.  The results of this study show that AAD-1 protein expression is similar across all hybrids at the V4 and V7 growth stages.   

Protein expression in AAD-1 corn was determined in the leaves by taking four leaf punches from the highest leaf with a fully exposed leaf collar.  Samples were taken at V3, V7, V12 and VT stages.  Expression in the reproductive tissue of the cob, kernel, silk and pollen was determined.   Expression results show AAD-1 protein present in all leaves sampled and in all the reproductive tissues. 

Agronomic trials were conducted in 2010 to compare growth, development and yield of Enlist corn.  The first study consisted of 6 hybrids adapted for North America Corn Belt Zone 7 produced from common AAD-1 inbred.  Data were summarized across 10 locations within zone 7 with 2 reps per location.  The second study consisted of 5 hybrids adapted for North America Corn Belt Zone 5 produced from common AAD-1 inbred.  Data were summarized across 12 locations within zone 5 with 2 reps per location.  No significant difference in growth, development and yield was observed between Enlist hybrids and the isogenic hybrids.

A third experiment evaluated yield response of spraying 2,4-D on multiple Enlist hybrids in zones 5 and 7.  Trials were designed as split plot with the whole plot factors being 2,4-D DMA at 0 and 2240 g ae/ha and the sub-plot being hybrid genotypes.   Zone 5 hybrids were evaluated at 3 locations and zone 7 hybrids at four locations.  Twelve Enlist hybrids were evaluated in zones 5 and 7 for a total of 24 unique hybrids.  2,4-D applications were made at the V6 growth stage with CO2 backsprayer calibrated to delivery 15 GPA.  The rate of 2,4-D is 2X the anticipated maximum use rate for a single POST application. Results show no significant differences in yield with the Enlist corn hybrids between 2,4-D treated and non-treated controls.  

^™Enlist is a trademark of Dow AgroSciences LLC.  Components of the Enlist Weed Control System have not yet received regulatory approvals; approvals are pending.   The information provided here is not an offer for sale. ©2012 Dow AgroSciences LLC.

Fifteen field trials were established during 2009 to 2011 at various locations in Ontario, Canada and Michigan, USA to determine the effect of late emerging weeds on the yield of glyphosate-resistant corn. Data were separated into two environments based on the impact of treatment on corn yield. Environments were kept constant throughout the analysis for ease of interpretation.  There were no differences among corn height for any treatments or between environments. Environment 1 (4/15 sites) had yield loss if weeds were allowed to emerge after glyphosate application at the 2 leaf stage of corn, but not if weeds were allowed to emerge after glyphosate application at the 4, 6, 8, or 10 stage of the corn.  Environment 2 (11/15 sites) had no yield loss if weeds emerged after a glyphosate application at the 2 leaf corn. The most prominent weeds were ABUTH, AMARE, AMBEL, CHEAL and SETVI. While weeds were allowed to emerge after various corn leaf stages they did not necessarily impact yield, it is probable that weed seeds were added to the soil seed bank for weeds emerging at corn 2 leaf and 4 leaf corn stage (also supported by visual ratings). Weeds emerging after 6, 8, and 10 leaf corn were small (low biomass/seedlings) and most likely did not reach reproductive maturity. Based on this study, corn must be maintained weed free up to the 4-leaf stage. Any weeds emerging after that do not influence corn yield.

Two separate field trials were conducted near Columbia, Missouri in 2011 to determine the effects of herbicide, fungicide, and slow release N fertilizer co-applications on corn injury and yield.  Both trials were arranged in a RCB design with six replications.  In the first experiment, the herbicides rimsulfuron plus mesotrione, thiencarbazone-methyl plus tembotrione, S-metolachlor plus glyphosate plus mesotrione, glyphosate plus thiencarbazone-methyl plus tembotrione, glyphosate plus atrazine, mesotrione, glyphosate, and glufosinate were applied alone or in combination with the fungicides prothioconazole plus trifloxystrobin, azoxystrobin plus propiconazole, and pyraclostrobin plus metconazole.  In the second experiment, the herbicides glyphosate plus thiencarbazone-methyl plus tembotrione, S-metolachlor plus glyphosate plus mesotrione, glyphosate, and glufosinate were also applied alone or in combination with these same three fungicides, and all of these herbicide-fungicide combinations were also applied with or without a slow-release N fertilizer. Treatments containing rimsulfuron plus mesotrione and thiencarbazone-methyl plus tembotrione resulted in height reductions of up to 19 and 22% of the non-treated control 7 days after treatment (DAT), respectively.  In the first experiment, corn yields ranged from 6156 to 7594 kg/Ha, and there were few differences in yield among herbicide-fungicide combinations compared to the non-treated control.  When averaged across all fungicides, treatments that contained thiencarbazone-methyl plus tembotrione, glyphosate plus thiencarbazone-methyl plus tembotrione, and rimsulfuron plus mesotrione resulted in lower yields than the weed-free, non-treated control and mesotrione.  All other herbicide treatments provided similar yields as the weed-free, non-treated control.  When averaged across all herbicides, there were no differences in corn yield between the fungicide treatments and the non-treated control.  Similar responses were observed in the second experiment, and when averaged across all herbicide and fungicide treatments, there were no differences in corn yield between treatments that contained a slow-release N fertilizer compared to those that did not.  Disease severity, SPAD meter readings, and stalk strength evaluations were similar for all herbicide and fungicide treatments in comparison to the non-treated control.  Overall, results from both experiments indicate that certain early-season herbicide plus fungicide or herbicide plus fungicide plus slow-release N fertilizer combinations can cause significant reductions in corn height and are not likely to provide increases in corn yield.   

  Field studies were conducted from 2007 to 2009 in East Lansing, Michigan, to evaluate  three residual herbicide programs, three postemergence (POST) herbicide application timings, and two POST herbicides in glyphosate- and glufosinate- resistant
corn.  Herbicide programs included a residual preemergence herbicide followed by (fb) POST application (residual fb
POST), a residual herbicide tank-mixed with a POST herbicide (residual + POST), and a non-residual POST.  Three POST herbicide application timings included early POST (EP), mid-POST (MP), and late POST (LP) at an average weed canopy height of 7, 14, and 21 cm, respectively. The two herbicides evaluated were glyphosate and glufosinate.  Control of common lambsquarters, redroot pigweed, giant foxtail, and common ragweed was visually evaluated 28 days after the LP application. Weed control was generally greatest when glyphosate or glufosinate was applied in combination with a residual herbicide.  Glyphosate and glufosinate resulted in similar weed control when used in combination with a residual herbicide, but glyphosate often provided greater weed control than glufosinate when applied without a residual herbicide.  Later application timings resulted in greater weed control, which may be attributed to control of late-emerging weeds.  The effect of residual herbicide program, POST herbicide, and POST application timing on corn grain yield varied by year.  In 2007, the use of glyphosate resulted in higher grain yield compared to glufosinate.  In 2008, corn grain yield was the highest in the PRE fb POST program and with POST applications at EP and MP.  To provide the most consistent weed control and minimize the likelihood of grain yield reductions, a PRE fb POST program applied from EP to MP is recommended.

With the adoption of no-till practices, winter annual weed populations have become more prominent in Nebraska. Winter annual weeds use soil moisture and sequester nutrients that would normally be accessible for the production of corn, soybeans or sorghum. They can also form dense mats that may physically interfere with a planter’s ability to function properly. Field pansy (Viola bicolor) has become a more prevalent species in the winter annual weed complex in Southeast Nebraska fields. The objective of this study was to observe field pansy efficacy of common soybean burndown and PRE herbicides, when fall and spring applied. The experiments were conducted in Richardson and Nemaha Counties in Southeast Nebraska, in the fall/spring of 2009/2010 and 2010/2011. An untreated control was maintained to estimate efficacy. Visual estimations of injury, for both the fall and spring timings, were recorded at 28 days after the spring herbicide application. Fall applications of clorimuron (22.77 g a.i. ha^-1), imazethapyr (70.05 g a.i. ha^-1), sulfentrazone (280.21 g a.i. ha^-1) and flumioxazin (107.18 g a.i. ha^-1) provided 95, 86, 78 and 75% control, respectively. Spring applications of glyphosate (866 g a.e. ha^-1) and paraquat (756.57 g a.i. ha^-1) provided 97 and 87 % control, respectively. 2,4-D and dicamba consistently provided the lowest level of control at both application timings. Results demonstrate that different products should be considered if making fall or spring applications for field pansy control.

Palmer amaranth has become a driving force in weed management decisions in North Carolina due to widespread glyphosate and ALS-inhibitor resistance in the state. Growers are continually looking for options in soybeans to increase control and ensure high yields. The pending introduction of pyroxasulfone for use as a preemergence herbicide in North Carolina soybean production has led to investigations into its ability to control Palmer amaranth in a variety of environments. Studies were initiated to investigate pyroxasulfone control of Palmer amaranth at two on-farm locations in Moore County, NC. Weed control varied by location with generally greater control where timely rainfall occurred for activation. Overall control increased with increasing rates with little injury observed on soybean. Residual control of Palmer amaranth is an important consideration when selecting a preemergence program in North Carolina, and pyroxasulfone showed excellent residual activity, even on deep sands.

Two field studies were conducted in the spring/summer of 2011 at the NC State research stations in Clayton, NC and Rocky Mount, NC to evaluate the effectiveness of burndown programs for horseweed (Conyza Canadensis) management in soybeans. Since the first reported case of glyphosate resistant (GR) horseweed in the US in 2000 in Delaware, 19 states have reported GR resistant horseweed, including North Carolina in 2003. While the Clayton research station appears to still be free of GR horseweed, the Rocky Mount field station has approximately 50% GR horseweed. It is essential to find new programs to control this program because current methods provide inconsistent control and horseweed growth characteristics enable it to proliferate and spread quickly. These field studies aim to evaluate and compare multiple burndown programs for control of horseweed in soybeans.

 Treatment combinations at burndown consisted of glyphosate alone and  in combination with the following: 2,4-D Ester at 540 g a.e. ha^-1, saflufenacil at 25 g a.i. ha^-1, saflufenacil at 37.5 g a.i. ha^-1,  saflufenacil at 25 g a.i. ha^-1 + 2,4-D at 540 g a.e. ha^-1, saflufenacil at 25 g a.i. ha^-1 + glufosinate at 600 g a.i. ha^-1, saflufenacil at 25 g a.i. ha^-1 + imazaquin at 140 g a.i. ha^-1, saflufenacil at 25 g a.i. ha^-1 + dimethanamid-p at 220 g a.i. ha^-1, saflufenacil at 25 g a.i. ha^-1 + pendimethalin at 1380 g a.i. ha^-1, sulfentrazone at 85 g a.i. ha^-1 + chloransulam-methyl at 11 g a.i. ha^-1, and flumioxazin at 71 g a.i. ha^-1 + 2,4-D ester at 540 g a.e. ha^-1. All treatments received a post application of glyphosate at 840 g a.e. ha^-1. Methylated seed oil and ammonium sulfate were added to all saflufenacil and flumioxazin containing treatments. Nonionic surfactant and ammonium sulfate were added to all other treatments. Fields were rated for percent control of horseweed at 14 and 28 days after the burndown application. Horseweed control was greatest where saflufenacil was applied in combination with glyphosate. Control was less than 80% at Rocky Mount and less than 50% at Clayton with a single application of glyphosate, indicating a resistant population was present. Additionally, the standard treatment for most of North Carolina, 2,4-D + flumioxazin + glyphosate, failed to provide acceptable control around the state and in these studies.

The registration of flumioxazin as a dry bean desiccant and the recent changes to shorten the rotational restrictions of certain crops have caused concerns about the actual crop safety of rotational crops that may be impacted by these recent label changes.  Therefore, a field study was conducted for 3 years to determine the crop safety of the rotational crops, sugarbeet, winter wheat, and winter wheat frost seeded with clover after a desiccation application of flumioxazin.  Flumioxazin at 71 g ha^-1 (typical desiccation rate) and 107 g ha^-1 (maximum labeled desiccation rate), glyphosate (0.84 kg ae ha^-1), and paraquat (0.56 kg ha^-1) were the four desiccation treatments examined.  These treatments were applied in mid-September of 2008, 2009, and 2010.  Within 7 days after treatment (DAT) all plots were harvested and the rotational crops were planted at the designated planting intervals. The rotational crops planted were: 1) winter wheat planted 7 DAT, 2) winter wheat planted 14 DAT, 3) winter wheat planted 14 DAT and frost-seeded with red clover in mid-March, 4) sugarbeet planted no-till in the spring, and 5) sugarbeet planted conventional tillage in the spring.  There were no signs of winter wheat being affected by any of the desiccation treatments in the springs of 2009 and 2010. In fact, there were no differences in winter wheat yield.  However, in the spring of 2011 winter wheat showed signs of injury in the form of stunting and leaf discoloration from all flumioxazin treatments.  Injury tended to be greater at the higher flumioxazin application rate (>25%).  However, by the end of the season treatment differences were not apparent and there was no difference in winter wheat yield.  Due to significant stand loss of sugarbeet by Rhizoctonia solani, data for sugarbeet was only collected in 2009 and 2011.  Intervals between desiccant applications and sugarbeet planting were 7 month and 16 d in 2009 and 7 month and 5 d in 2011.  There was not a significant year by treatment interaction, so sugarbeet data are combined over the two years. In both conventional tillage and no-tillage sugarbeet flumioxazin applied at the 71 and 107 g ha^-1 caused significant injury and reduced stand compared with either the glyphosate or paraquat treatments.  Differences in injury and sugarbeet stand between the treatments were greatest in the no-till sugarbeet plots, with the higher rate of flumioxazin causing as much as 86% stand loss.  In the conventional tillage plots sugarbeet stand at harvest was 25 and 50% lower when flumioxazin was applied at the 71 and 107 g ha^-1 rates, respectively, compared with either glyphosate or paraquat. In no-till sugarbeet, recoverable white sucrose per hectare (RWSH) was lower at both rates of flumioxazin compared with glyphosate and paraquat. The current rotation restrictions for no-till sugarbeet are 8 and 10 months for the 71 and 107 g ha^-1 rates, respectively. In our research sugarbeet were planted earlier than both of these restrictions. Differences in RWSH were not as apparent in the conventional tillage system and RWSH was only different between flumioxazin at the higher rate of 107 g ha^-1 compared with glyphosate. Currently the flumioxazin rotation restrictions for sugarbeet that are tilled prior to planting are 4 and 5 months for the 71 and 107 g ha^-1 rates, respectively. While the crop rotation restrictions were met for both of these rates, we did observe significant injury and sugarbeet stand loss.

Planting in narrower rows is a practice that has been associated with improved canopy closure, weed suppression, and higher yields in many crops. The development of upright, short-vine black and small red bean varieties has expanded the opportunities for dry bean growers to plant in narrower rows.  If yield differences between row widths or lack of yield differences between planting populations are observed, this must be explained in terms of a change in one or more components of yield in individual plants: seeds per plant, seeds per pod, or seed weight, possibly coupled with changes in plant architecture.  Therefore, field studies were conducted in 2010 and 2011 at two locations in Michigan to examine the effect of varying row width and bean populations on: 1) yield, 2) components of yield, and 3) plant architecture.  Varieties examined were ‘Zorro’ black and ‘Merlot’ small red beans; both are new upright varieties.  Each variety was planted in: 1) 38-, 2) 51-, and 3) 76-cm rows at one location and only 38- and 76-cm rows at the other. Black bean populations were 1) 196,400-, 2) 261,800-, and 3) 327,300 plants ha^-1; small red bean populations were 1) 148,200-, 2) 196,400-, and 3) 261,800-plants ha^-1.  Yield was obtained using direct harvest by combine.  Dry bean plants were hand-harvested from each plot, and on each plant, height was measured, branches and pods were counted, and pods were separated into main stem and branch fractions and then were separated by number of seeds per pod.  One hundred seeds from each plot were weighed.  While the results were not consistent across all site-years, narrow rows were found to result in higher yields than wide rows in 4 out of 8 dry bean class-site-year combinations; increases in yield were observed equally in each class.  Planting population had little or no impact on yield.  The yield component that was most sensitive to row width and population was number of pods per plant, which was often increased in narrow rows and always increased at low populations.  Branch pods were more responsive to row width and population than main-stem pods, and a higher percentage of pods were formed on branches in narrow rows and at low populations.  Average number of beans per pod was occasionally higher in narrow rows and at low populations, but differences were small. Under drought conditions, average number of beans per pod decreased in narrow rows.  Main-stem and branch pods tended to have similar average numbers of seeds per pod, and neither fraction was clearly more responsive to row width or population than the other.  Differences in average seed weight between treatments were rare and small.  Number of branches usually increased in narrow rows and always increased at low populations; this presumably both facilitated the higher numbers of branch pods in narrow rows and at low populations and enabled plants to spread outward and efficiently close the canopy.  Row width and population had little effect on plant height.  Thus, yield increases in narrow rows consisted largely in an increase in the number of pods per plant, especially on the branches, which was facilitated both by the greater efficiency inherent in narrow rows and the increase in branching.  Likewise, the failure of high planting populations to increase yield was due to the fact that at lower populations, dry beans compensate by forming more branches, thus providing the energy to form more pods per plant, especially on the branches.

The grains of the common bean (Phaseolus vulgaris L.) crop are very important food staple in Brazil. A research program was established by three Universities (UFRGS-UFSM-UTFPR) to determine the intensity of weed impact on this crop. The objective of this work was to determine the effect of three weed species on common bean productivity. The weed species and the location of the experiments were: Urochloa plantaginea (Link) R. D. Webster, in Eldorado do Sul, RS; Digitaria horizontalis Willd., in Frederico Westfalen, RS; and Euphorbia heterophylla L., in Pato Branco, PR. The additive method was used. From the emergence of the crop plants, different densities of each weed were established. Crop management decisions followed the procedures adopted by the farmers of each region, targeting very high grain yield productivity. By the end of the season, the crop grain was harvested and the reduction of crop yield due to weeds was determined. A classical rectangular hyperbole curve was fitted to the weed density-yield reduction data. The value of the parameter “i” was used to indicate the impact of each weed plant on the bean crop yield. The grass weeds were less harmful to the crop than the dicot weed. At low weed densities, each plant of U. plantaginea and of D. horizontalis reduced about 1% the common bean grain yield. Each E. heterophylla reduced as much as 3% of the crop yield. Several weed management strategies are needed to achieve season long weed control and to avoid common bean yield losses.

2,4-D is a synthetic auxin herbicide used for the control of broadleaf weeds in several crops, including field corn, grain sorghum, and small grains.  2,4-D resistance is currently being developed in cotton and soybeans.  Peanuts are often grown in close proximity to cotton and soybeans in southern states. The adoption of the 2,4-D resistance technologies will likely increase the risk of 2,4-D damage to peanuts by drift and/or sprayer contamination.  The objective of this study was to evaluate peanut response to simulated drift rates of 2,4-D.

In 2011, two field trials were conducted in at the Ponder Research Farm near Ty Ty, Georgia and the Attapulgus Research and Education Center.  Peanut, variety ‘GA-06G’, was planted in early May at both locations and grown under weed-free conditions.  2,4-D amine (Agristar® 2,4-D 3.8SL) at rates of 0, 2, 4, 8, 16, and 32 oz/A was applied at 30, 60, and 90 days after planting (DAP). Herbicides were applied using a CO₂-pressurized backpack sprayer calibrated to deliver 15 GPA.  Treatments were replicated four times in a split-plot design. Whole plots were time of application and sub-plots were 2,4-D rates.  Data collected included visual estimates of peanut injury, yield, 100 pod weights, and 100 seed weights. Only yield data are reported.  All data were subjected to ANOVA and means separated by Fisher’s Protected LSD Test (P=0.10).  A significant interaction between time of application and 2,4-D rate was observed at each location.

At the Ponder farm, 2,4-D applied at 30 DAP reduced peanut yield 11% and 29% when applied at 16 and 32 oz/A. When applied 60 DAP, 2,4-D reduced peanut yields 17%, 26%, and 51% at the 8, 16, and 32 oz/A rates respectively.  At this location, there were no significant yield reductions when 2,4-D was applied at 90 DAP, regardless of rate. In Attapulgus, 2,4-D applied at 30 DAP reduced peanut yields 36% at the 32 oz/A rate. 2,4-D applied 60 DAP reduced peanut yields 4% and 32%  at the 2 oz/A  32 oz/A rates, respectively. There were no yield reductions when 2,4-D was applied 90 DAP, regardless of rate at this location.    

To improve grain quality and thus  provide greater antioxidant activity, much of the action should be adopted in the pre-harvest, although it may be acting in post-harvest. In the crop sunflower, one of the most important factors is competition between plants, which impacts on the availability of environmental factors such as light, nutrients and water. Based on that, the objective of this study was to study the alteration on phenolic compounds, carotenoids and total antioxidant capacity in sunflower grains as affected by competition with wild radish. The experiment consisted of two factors: the coexistence periods and control periods of wild radish with sunflower cultivation. In the period of coexistence, the culture was maintained in the presence of wild radish for increasing periods of time at 0, 7, 14, 24, 28, 35 and 120 (the whole crop cycle) days after emergence (DAE), from which were controlled. In the control period, the culture was kept free of weeds for the same periods described above and wild radish plants emerged after these breaks were no longer controlled. Evaluated the phenolic compounds and total carotenoids and total antioxidant capacity. The total phenols were not significantly different for treatments and obtained a general average of 32.75 mg g^-1 EAG. The presence of wild radish in the initial period 0 DAE, from which were controlled, indicated a higher content of carotenoids, resulting in a higher antioxidant capacity.

Effective weed control in sugarbeet is important to eliminate competition for water, light and nutrients.  Nitrogen is an important nutrient applied to sugarbeet to obtain high yields; however too much nitrogen reduces sugar quality.  Early-season weed control may reduce the amount of nitrogen that is required to achieve maximum yields and sugar quality.  Field experiments were conducted at the Saginaw Valley Research and Extension Center near Richville, Michigan and at the Michigan State Agronomy Farm in East Lansing, Michigan during the 2010 and 2011 growing seasons.  The objectives of the experiment were to: 1) determine the amount of nitrogen removed by weeds, 2) determine the height at which weeds need to be controlled in order to maximize sugarbeet yield and quality, and 3) determine if split nitrogen application reduces weed competition with sugarbeet.  The experiment was a strip-plot design with nitrogen rate as the main-plot factor and weed removal timing as the sub-plot factor.  Nitrogen was applied prior to planting at 0, 67, 100, and 134 kg ha^-1.  An additional treatment of 134 kg ha^-1 was split-applied preplant and at 4 to 6 leaf sugarbeet.  Weeds were controlled using applications of glyphosate at 0.84 kg ae ha^-1 plus 2% w/w of ammonium sulfate when they were <2, 8, 15, and 30-cm tall.  All plots were maintained weed-free after the initial glyphosate application.  At the time of glyphosate applications, sugarbeet and weeds were collected from the field and their total nitrogen content was determined using the Total Kjeldahl Nitrogen (TKN) procedure.   At both locations, the amount of nitrogen removed by weeds increased at the later control timings.  Weeds that were controlled when they were 30-cm tall removed up to 30 kg ha^-1 of nitrogen, while weeds that were controlled at the 8-cm tall timing removed less than 5 kg ha^-1 of nitrogen.  The amount of nitrogen applied to sugarbeet also affected the amount of nitrogen removed by weeds.  At East Lansing, weeds removed more nitrogen when it was applied as the split application (67:67 kg ha^-1) compared with the preplant applications of 0, 67, and 100 kg ha ^-1 of nitrogen.  Sugarbeet yield and recoverable white sucrose per hectare (RWSH) were affected by the time of weed removal at East Lansing (2010 & 2011) and at Richville in 2010.  Sugarbeet yield and RWSH were the greatest when weeds were controlled prior to 2 cm in height.  Nitrogen application rate also impacted sugarbeet yield and RWSH.  Both sugarbeet yield and RWSH increased as nitrogen application rate increased at Richville; however, nitrogen application did not play a significant role in sucrose production at East Lansing for either year.    

Flumioxazin is being increasingly utilized as a preplant burndown herbicide in cotton production.  This herbicide is most commonly used in fields with glyphosate resistant Palmer amaranth.  The pattern of flumioxazin use is 0.03 to 0.06 lb/A and must be applied 14 or 21 days prior to cotton planting, respectively.  However, it is unknown whether cotton injury and subsequent yield reduction will be observed if flumioxazin is applied closer to planting.  Therefore, experiments were planted in Citra, FL, and Jay, FL from 2009 through 2011.  Flumioxazin was applied at 0.03 and 0.06 lb/A in 2009 and 0.03, 0.06, and 0.09 lb/A in 2010-2011.  Applications were made 30, 20, 15, 10, 5 and 0 days before planting (DBP).  Cotton emergence per 10’ of row was counted at 2 and 3 weeks after planting (WAP), cotton height was measured at 4 and 6 WAP, and cotton yield was determined at end of season.  For the Jay, FL location, no reductions in cotton stand, height, or yield was observed.  At the Citra, FL location, no reductions were observed in 2009.  In 2010-11, cotton stand and yield was reduced when flumioxazin at 0.06 and 0.09 lb/A was applied at 0 DBP. 

Palmer amaranth (Amaranthus palmeri) is the most common weed on the Texas High Plains.  Residual herbicides are typically used in conjunction with glyphosate to control this weed, but weed shifts have been observed following continued use of glyphosate.  Weeds such as ivyleaf morningglory (Ipomoea hederacea) are now problematic in parts of this region.  GlyTol® + LibertyLink® (GL) cotton offers opportunities to manage weeds such as ivyleaf morningglory while maintaining effective control of Palmer amaranth.  However, there are concerns about antagonism between glyphosate and glufosinate when tank-mixed.

Field trials were conducted in Lubbock, TX in 2010 and 2011 to evaluate tank-mix combinations of glyphosate and glufosinate-ammonium in GL cotton for control of Palmer amaranth and ivyleaf morningglory.  Field trials included glyphosate and glufosinate applied at varying tank-mix rates (1X:1X, 1X:0.75X, 1X:0.5X, 1X:0.25X and 1X:0X for each herbicide).  The 1X rate of glyphosate corresponded to 0.84 kg ae/ha (22 oz/A) while the 1X rate of glufosinate corresponded to 0.58 kg ai/ha (29 oz/A).  All treatments were applied postemergence (POST) to 5 to 10 cm weeds.  Treatments were made using a CO₂-presurized backpack sprayer calibrated to deliver 94 l/ha.  FM 9250GL was planted on May 20 in 2010 and May 23 in 2011 on 102 cm rows.  Plots were 4 rows by 9.14 m in length with three replications.  Weed control was visually estimated based on a standard scale of 0 to 100% where 0 = no weed control and 100 = complete weed control and verified with weed counts. 

Greenhouse studies were conducted in 2011 to quantify antagonistic or synergistic effects.  Locally harvested glyphosate-susceptible Palmer amaranth and ivyleaf morningglory were planted in 8 by 8 cm pots and thinned to two plants per pot after germination.  Pots were arranged in a randomized complete block design with four replications.  Treatments included an untreated control; glyphosate at 0.84, 0.63, 0.42, and 0.21 kg ae/ha; glufosinate at 0.58, 0.44, 0.29, and 0.15 kg ai/ha; and all tank-mix combinations of each herbicide rate.  Treatments were applied when plants were 5 to 10 cm with a CO₂-pressurized spray chamber calibrated to deliver 94 l/ha.  Fourteen days after treatment, above-ground portions of plants were harvested and dried.  Dry weights were recorded and converted to percent growth (calculated as a percent of the untreated control mean).  Percent growth values for each rate of the two herbicides alone were then used to calculate expected responses of tank-mix combinations using Colby’s Method.  Expected values were then compared to observed percent growth values using an augmented mixed-model methodology.

Results of field studies indicated that tank-mixes of glyphosate and glufosinate were less effective at controlling Palmer amaranth (50-93%) than glyphosate applied alone (98-99%).  The addition of any rate of glufosinate to a 1X rate of glyphosate reduced Palmer amaranth control (70-93%) compared to glyphosate alone (98-99%).  Greenhouse studies confirmed antagonism seen in the field.  All tank-mix treatments except one (glyphosate 0.42 + glufosinate 0.44) provided less control than calculated expected response values. 

Tank mixes of glyphosate and glufosinate were as effective at controlling ivyleaf morningglory (82-95%) as glufosinate alone (85-88%).  The addition of any rate of glyphosate to a 1X rate of glufosinate did not affect control of ivyleaf morningglory.  Greenhouse studies showed low levels of antagonism with some tank-mix treatments and no antagonism in other treatments.  The data from field and greenhouse studies on ivyleaf morningglory suggest some antagonism with glyphosate/glufosinate tank-mixes, but not to the degree seen in Palmer amaranth.  These results indicate that sequential applications of these two herbicides are a better option for Palmer amaranth and ivyleaf morningglory weed management.

Glyphosate is the major component of chemical weed control in glyphosate-resistant crops and in fallow in Kansas. Proliferation of kochia (Kochia scoparia) control failure with glyphosate-centered herbicide systems in western Kansas has occurred in the past few years. We conducted a visual survey to determine the level of kochia infestation, examine the control practice employed by farmers, and evaluate herbicidal control effectiveness in nearly 1,600 wheat stubble fields in the western half of Kansas in 2011.  By the first week of August, 49% of wheat stubble fields had been sprayed with herbicides and 30% of the fields had been tilled. Nothing had been done to manage weeds post-harvest in 21% of the fields. A high proportion of the non-controlled fields had been sprayed with herbicide by the end of August, whereas the proportion of the tilled fields remained nearly the same. Of the sprayed fields, 4% were heavily infested, 52% were moderately infested, and 44% were lightly infested with kochia. Control of kochia in 1, 28, and 71% of infested fields was rated poor, fair, and good or excellent, respectively. Herbicidal kochia control failure in a significant number of fields and the higher-than-expected percentage of tilled fields, collectively, may indicate a shift to increased use of tillage to control kochia. A shikimate accumulation assay to determine resistance to glyphosate was performed on excised leaf discs of four kochia plants from each of 44 randomly sampled fields. All four plants from four fields were resistant to glyphosate and none of the plants in 21 sampled fields were resistant to glyphosate. Three-fourth, one-half, and one-fourth of the plants in six, eight, and five sampled fields, respectively, were resistant to glyphosate. Sites with glyphosate resistant kochia were widely distributed throughout approximately the western one-third of Kansas. This study shows pervasiveness of kochia in western Kansas with high presence of glyphosate resistance.

Weed management in wheat has primarily focused on post emergence applications either in the fall or spring, with applications being made in the presence of weeds.   Preemergence herbicides are currently limited in their functionality in wheat, likely due to moisture limitations around application time and the economic commitment.  Utilization of preemergence herbicides has been commonplace for corn and soybean growers with over 40% receiving a preemergence herbicide application. However, little is known about early season yield loss in wheat and subsequent potential for preemergence herbicides to minimize (or prevent) yield loss.  Previous research has only examined single weed species interference with wheat yield.  Very few studies examined the impact of multiple weed species thus limiting the applicability to fields that contain more than one weed competing with the crop.     

Therefore, our objectives were to 1. Evaluate the efficacy and crop safety of flumioxazin in winter wheat and 2. Determine wheat yield as affected by grass and broadleaf interference.    

Seven trials were conducted at Hays, Larned, and Manhattan, KS between 2008 and 2011 to evaluate the utility of flumioxazin as a preemergence herbicide.   Applications were made 30, 14, 7 and 0 days before winter wheat planting with efficacy, crop injury, and yield recorded.  Efficacy of flumioxazin improved as the application timing was closer to planting; however, wheat injury also tended to increase.  No crop injury was observed from the application made 30 days before planting, but increased to 0 to 20% with the at planting application with visible stunting and necrosis.   Crop injury, however, did not necessarily translate to yield loss.   Yields were equal or higher than standards at harvest.     

Natural populations of weeds in farmers’ fields were used to determine wheat yield in response to interference.  Forty 1-m^-2 quadrats were randomly located in each field.  Weed species, density, growth stage in addition to wheat density and growth stage were observed on a bi-weekly basis from planting through the growing season and then harvested.  Dominant weed species were henbit (Lamium amplexicaule L.) and downy brome (Bromus tectorum L.) at the Flush, KS location and only henbit was present at the Clay Center, KS location.  Henbit density ranged from 0 to 156 plants m^-2 while downy brome ranged from 0 to 44 plants m^-2.  Regression analysis was used to determine the effect of weed density on wheat yield.   Henbit, regardless of density, had no affect on wheat yield.  Downy brome density was correlated with wheat yield with the greatest yield loss occurring between the densities of 1 and 10 plants m^-2. 

These results suggest that flumioxazin does have potential as a preemergence herbicide in Kansas winter wheat production.   Flumioxazin applied prior to planting can provide control of winter annuals and some annual grasses, including downy brome, thus preventing yield loss associated with early season weed competition.          

drefsell@ksu.edu

There is an increasing interest among producers to sow wheat with a 38-cm row planter vs. a traditional 18-cm row drill equipment. Wheat yield impacts and weed emergence patterns are unknown with this relatively new concept.  The objectives of this study were to evaluate weed emergence, weed competition, and wheat yield effects when sowing wheat with a 38-cm row planter vs. 18-cm row drill equipment.  Wheat was sowed October 21^st, 2010 at the Ottawa experiment field.  A high seeding rate of 3.7 million seeds ha^-1 and low seeding rate of 2.5 million seeds ha^-1 were sowed with the 18-cm row drill and the 38-cm row planter.  Treatments were replicated four times in a pyroxsulam treated and untreated block.  Henbit (Lamium amplexicaule L.), Carolina foxtail (Alopecurus carolinianus Walt.), and smallflowered bittercress (Cardamine parviflora L.) emergence was greater in the 38-cm wheat rows vs. the 18-cm wheat rows.  The increase in emergence in the 38-cm wheat rows is likely because of less shading by the wheat.  Seeding rate didn’t affect weed emergence in the drilled wheat, however, significant differences in weed emergence did occur in the planted wheat.  Henbit in the 38-cm wheat row at the low seeding rate emerged more than at the high wheat seeding rate at 152 vs. 109 plants m^-2, respectively.  Smallflowered bittercress emergence was greater in the high seeding rate vs. low seeding rate in 38-cm row wheat at 70 vs. 45 plants m^-2, respectively.  Wheat sowed with the 38-cm row planter in the pyroxsulam treated block yielded 5470 kg ha^-1 less than wheat sowed with the 18-cm row drill. Wheat sowed with the 38-cm row planter in the untreated pyroxsulam block yielded 3832 kg ha^-1 less than wheat sowed with the 18-cm row drill.  Yield losses for the wheat in 38-cm rows in both herbicide treatment blocks are attributed to too wide of a row spacing to maximize yields. dshoup@ksu.edu

Initial Clearfield wheat cultivars were characterized as having only a single gene for tolerance to imidazolinone herbicides, which inhibit acetolactate synthesis (ALS). Having the single gene led to efficacy problems with increased wheat injury when spray solutions were applied with methylated seed oil (MSO). Imidazolinone herbicides combined with MSO improve weed control and thus led to Clearfield cultivars having two ALS tolerance genes. With subsequent conventional breeding, soft red winter wheat cultivars have been developed containing two ALS resistant genes. Studies were conducted to compare an ALS susceptible cultivar (AGS 2000), a single gene cultivar (AGS CL7), and two gene wheat breeding lines. Herbicide treatments were nontreated, imazamox at 105 g ai/ha tank mixed with either 0.25% V/V NIS, or 1% V/V MSO. All treatments included 1.5% V/V urea ammonium nitrate solution. For all studies, AGS 2000 was always susceptible with complete death by harvest. AGS CL7 exhibited 17 to 38% injury when MSO was applied in combination with imazamox, but injury was 4 to 17% to AGS CL7 when applied with NIS.  This indicates that the single gene did not provide acceptable tolerance.  Cultivars with two ALS genes little to no injury from any treatment with yield similar to the nontreated controls. 

Pyroxasulfone is a new herbicide being developed for weed control in corn, soybean and other crops prior to crop emergence. There is little information on the tolerance of spring planted cereals to pyroxasulfone under Ontario environmental conditions. Four field studies were conducted in Ontario over a three year period (2009 to 2011) to evaluate the tolerance of spring planted barley, durum wheat, oats, and wheat to pyroxasulfone applied preemergence (PRE) at 62.5, 125, 250, and 500 g ai/ha. Regression equations were used to calculate the predicted pyroxasulfone doses (g ai/ha) that resulted in 5, 10 or 20% injury, or a 5, 10 or 20% reduction in height and yield. The dose of pyroxasulfone that caused 5% injury in spring planted barley, durum wheat, oats, and wheat was as low as 23, 14, 7, and 164 g ai/ha at 1 WAE; 40, 13, 7, and 127 g ai/ha at 2 WAE; 33, 132, 110, and 472 g ai/ha at 4 WAE; and 38, 74, 32, and >500 g ai/ha at 8 WAE, respectively. The dose of pyroxasulfone that caused 5, 10, and 20% reduction in height was 80, 160, and 321 g ai/ha in barely; 30, 58, and 128 g ai/ha in durum wheat; 16, 30, and 59 g ai/ha in oats; and 149, 299, and >500 g ai/ha in wheat, respectively. The dose of pyroxasulfone that caused 5, 10, and 20% reduction in yield was as low as 31, 63, and 126 g ai/ha in barely; 25, 49, and 98 g ai/ha in durum wheat; 8, 16, and 34 g ai/ha in oats; and 122, 244, and 489 g ai/ha in wheat, respectively. Based on this study, in general among spring planted cereals evaluated, wheat is more tolerant than barley followed by durum wheat followed by oats.

The Pacific Northwest (PNW) supplied 65%, or 2.1 million metric tons, of the forage imported by Asian Pacific Rim countries in 2007.  Sixteen percent of the timothy hay produced in the PNW was exported to Pacific Rim countries in 2004. These countries have specific quality specifications for imported forages, which, in part, require production of hay in fields with few or no weeds. In addition to reducing stand life of forage crops, weeds reduce the nutritional quality, color (green hue) and palatability and, thus the marketability of a forage crop. Currently, only a few broadleaf herbicides, and no grass herbicides, are registered for use in timothy grown for hay. Ventenata, downy brome, and rattail fescue are annual grass weeds that commonly infest timothy hay fields. The purpose of this study was to identify herbicides that will selectively control these annual grass weeds in timothy grown for hay. In 2010 and 2011, herbicide studies were initiated in established timothy fields in Latah, Nez Perce, and Boundary Co., ID to evaluate ventenata, downy brome, and rattail fescue control. Timothy response to herbicide treatments also was evaluated at weed-free sites for forage production in both years. The experimental design was a randomized complete block with four replications and included an untreated check. Herbicides were applied preemergence or early postemergence in the fall and included aminopyralid, diclofop, diuron, ethofumesate, flucarbazone, flufenacet/metribuzin, metolachlor, oxyfluorfen, primisulfuron, pyroxsulam, sulfosulfuron, and terbacil. Herbicides were applied alone or as specific combination treatments. Weed control and timothy injury was evaluated visually where 0% represented no control or injury and 100% represented complete weed control or crop death. Timothy was swathed and a wet in-field total weight was measured at the weed-free locations. A subsample was collected, weighed and dried to determine percent moisture to calculate a dry forage weight. Ventenata control was 90% or greater with all treatments in 2010, except aminopyralid and sulfosulfuron applied alone and flucarbazone alone or plus primisulfuron. Ventenata control in 2011 was 80% or greater with pyroxsulam, oxyfluorfen plus diuron, diclofop, and all flufenacet/metribuzin combinations except aminopyralid. Flufenacet/metribuzin combined with terbacil, sulfosulfuron, or primisulfuron controlled downy brome 88 to 96% in 2010. In 2011, no treatment controlled downy brome due to a dense weed infestation and a very poor stand of timothy hay. All flufenacet/metribuzin combinations, except with diclofop or primisulfuron, controlled rattail fescue 90 to 99% in 2010. Flufenacet/metribuzin applied alone at the highest rate or in combination, except with diclofop, controlled rattail fescue 80 to 96% in 2011. Oxyfluorfen plus diuron controlled all three grass species 95% or more in 2010 and ventenata and rattail fescue 94% or more in 2011. Timothy plants were visually injured 15 to 20% with sulfosulfuron and flufenacet/metribuzin treatments in 2010 and 20 to 21% with diclofop in 2011. Dry forage weight did not differ among treatments including the untreated check during both years.

Field and laboratory studies were conducted to evaluate fertility-based clomazone injury remediation in hybrid rice. Hybrid rice was drill seeded in two field locations near Eagle Lake and Ganado, TX at 39 kg/ha. In the first objective of the field study, clomazone was applied PRE at 6 different rates (0.11, 0.22, 0.34, 0.45, 0.56, and 0.67 kg a.i./ha) to produce a standard curve of clomazone herbicide injury. Visual injury ratings and plant heights were recorded at four timings between clomazone application and physiological maturity. Tissue samples were also collected at each rating event for chlorophyll content analysis in the laboratory. In the second objective of the field study, clomazone was applied uniformly to field plots at 0.45 kg a.i./ha. Another application of clomazone at 0.45 kg a.i./ha was needed EPOST to further induce injury symptoms. After initial visual injury ratings were recorded at the 4- to 6-leaf growth stage, tissue samples were collected and fertility treatments were applied. Treatments consisted of two recommended forms of nitrogen fertilizer (ammonium sulfate and urea) and two foliar-applied micronutrient fertilizers (iron sulfate and magnesium sulfate) at different rate combinations and application timings. Visual injury ratings and plant heights were recorded at four timings between herbicide application and physiological maturity. Tissue samples were collected at each visual assessment for chlorophyll content analysis. For lab procedures used to determine chlorophyll content, rice leaf tissue was weighed and placed in glass vials containing 7 ml of dimethyl sulfoxide (DMSO). Extraction procedures included 1-hour submersion of the vials in a 65°C water bath, and three vortex events every 15 minutes during the extraction. Following the extraction, liquid in the vials was transferred to graduated test tubes and brought to a 10-ml volume with DMSO and vortexed. Sample aliquots were analyzed for absorbance values at 663 nm and 645 nm, the absorbance values for chlorophyll a and chlorophyll b, respectively. Values were read against a DMSO blank and samples reading higher than 0.7 were diluted using a 90% DMSO-10% water solution and re-analyzed. Chlorophyll content was then determined by using the following equation – Total Chlorophyll (a +b) = 8.02A663 + 20.20A645. Values reported are in milligrams of chlorophyll per gram of fresh weight. At the conclusion of the study, yield data was taken from all plots. Initial visual injury ratings for the standard curve plots near Eagle Lake were statistically different with the highest injury ratings in plots that received higher rates of clomazone.  Later visual injury ratings and plant height measurements were not different. Yield data showed that only control plots receiving no clomazone application were statistically different. Visual injury ratings and yield showed no difference in the herbicide injury remediation plots. Plant height was different in plots receiving only foliar-applied micronutrient fertilizers when compared to plots receiving nitrogen fertilizers.  Visual injury ratings for the standard curve plots near Ganado were different with the highest injury ratings in plots that received higher rates of clomazone. There were no differences in plant height or yield throughout the study. Visual injury ratings were not different in the herbicide injury remediation plots at Ganado. Plant height measurements were different and plots receiving the highest rates of nitrogen produced taller plants. Yield data showed differences with the highest yield occurring in plots that received the highest rates of nitrogen. Initial laboratory results from chlorophyll extraction and quantification show that chlorophyll content decreases linearly as the rate of clomazone increases. 

Crawfish producers prefer rice to remain in the vegetative stage in order to provide forage for a longer period of time into the fall and winter. However, when rice is allowed to head the plant matures and foliage desiccates; therefore, reducing the total amount of forage available to crawfish. Previous research indicated that reduced spray volume results in higher activity of glyphosate when applied at reduced rates. Based on herbicide drift research conducted at the LSU AgCenter, it was observed that rice maturity would delay or fail to advance into the reproductive stage when treated with drift rates of glyphosate and with a low carrier volume. With this in mind, a study was conducted at the LSU AgCenter Rice Research Station near Crowley, Louisiana in 2011 to evaluate the effects of glyphosate on ‘Jupiter’ rice.

The experimental design was a randomized complete block with four replications in an augmented two-factor factorial arrangement of treatments.  A nontreated was added for comparison.  The study was conducted at two locations in 2011. Factor A consisted of application timings at two different growth stages: EARLY BOOT and BOOT SPLIT. The EARLY BOOT timing corresponds to the panicle being totally enclosed within the flag leaf sheath, and BOOT SPLIT is when the flag leaf sheath begins to separate open due to swelling of the panicle. Factor B consisted of herbicide rate.  Glyphosate in the formulation of Honcho Plus was applied at rates of 53, 105, 160, and 210 g ae ha^-1. Each treatment was made with a CO₂-pressurized backpack sprayer calibrated to deliver a constant carrier volume of 84 L ha^-1. Two plant heights were taken: overall plant canopy height and height from the ground to the tip of the extended panicle. Percent rice panicle emergence, rough rice yield, 100 count seed weights, and percent seed germination of harvested seed were determined. Percent germination was determined by calculating the total number of germinated seed out of a hundred, held at 19 C for 14 days. Injury was visually assessed at 4, 14, and 28 DAT; however, injury did not exceed 15% at all evaluation dates.

An application timing by glyphosate rate interaction occurred for heading, plant height to extended panicle, and germination. At 4, 14, and 28 days after the BOOT SPLIT application, rice panicle emergence was reduced when rice was treated with 105, 160, and 210 g ha^-1 of glyphosate applied at the EARLY BOOT timing. Rice treated with glyphosate at 210 g ha^-1 at the EARLY BOOT timing reduced panicle emergence approximately 95% compared with rice treated with 53 g ha^-1. However, rice panicle emergence was not reduced with any of the glyphosate rates applied at the BOOT SPLIT timing. Rice treated with 105, 160, and 210 g ha^-1 of glyphosate at EARLY BOOT had a reduced plant height to the extended panicle compared with those treated with any rate at BOOT SPLIT. This supports the percent panicle emergence rating, indicating reduced panicle emergence which resulted in an overall reduction in height to the tip of the extended panicle. Percent germination of rice seed collected was 80% when rice was treated with 53 g ha^-1, and the rice treated with 160 and 210 g ha^-1 at the EARLY BOOT timing had reduced seed germination of 42 and 37%, respectively.

A glyphosate rate main effect occurred for overall canopy height and rice yield. Overall canopy height was slightly reduced in rice treated with 210 g ha^-1 of glyphosate compared with the nontreated and rice treated with 53 g ha^-1 of glyphosate. Averaged across timings, rice treated with higher rates of glyphosate had reduced yield compared with the nontreated and the 53 g ha^-1 rate. Yield of rice treated with 210 g ha^-1 of glyphosate was reduced 70% compared with rice treated with 53 g ha^-1. Rice treated with 105 g ha^-1 of glyphosate had a higher yield than rice treated with either 160 and 210 g ha^-1.

 This research indicates that 160 to 210 g ha^-1 of glyphosate applied to rice in the EARLY BOOT stage would help prevent rice from maturing. These rates reduced panicle emergence, resulted in little to no reduction in canopy height, little to no crop injury, rice yield was less than 20% of the nontreated, and visual observation indicated the rice remained in the vegetative stage. Though there was minimal effect on canopy height, the reduced height to extended panicle indicates that glyphosate application inhibits rice maturation. This delay in maturity would provide crawfish with an extended period of available forage and reduce the cost to producers by reducing the need for supplemental feed.

A study was established to evaluate the interaction of halosulfuron plus thifensulfuron-methyl, sold under the trade name Permit Plus, or halosulfuron, sold under the trade name Permit, when applied 24 hours after a malathion application to rice in the late boot growth stage.  The study was conducted on a producer location near Lake Charles, Louisiana planted with Clearfield medium grain ‘CL 261’ rice.  Halosulfuron has been used for several years as a salvage treatment in rice production to manage late emerging yellow nutsedge (Cyperus esculentus L.), rice flatsedge (Cyperus iria L.), hemp sesbania [Sesbania herbacea (P.Mill.) McVaugh], and Indian jointvetch (Aeschynomene indica L.).  Halosulfuron applied as a salvage treatment may not control the target weeds, but the herbicide has been successful at reducing seed production.

 The study was established as a strip trial on a producer location near Lake Charles, Louisiana planted with Clearfield medium grain ‘CL 261’ rice.  Each strip was approximately 180 m long by 3 m wide; individual strips were separate treatments.  Each strip was equally divided into four sections to be treated as replications.  Treatments were entered as a factorial.  Factor A consisted of malathion at 1.12 kg ai/ha and no malathion.  Factor B consisted of halosulfuron at 53 and 105 g ai/ha, halosulfuron plus thifensulfuron at 39 and 78 g ai/ha, and no halosulfuron or halosulfuron plus thifensulfuron. The initial application, factor A, of malathion was applied to rice in the late boot stage on July 18, 2011 and the halosulfuron plus thifensulfuron and halosulfuron were applied 24 hours later, on July 19, 2011.  Panicle emergence was evaluated at 14 and 28 days after treatment (DAT).  Height from the soil surface to the tip of the extended panicle at 21 DAT and at physiological maturity, rough rice yield, and harvest moisture was determined.  Yield was adjusted to 12% moisture.

 At 14 DAT, panicle emergence was 60% with the nontreated rice.  Panicle emergence was 40 to 50% with halosulfuron and halosulfuron plus thifensulfuron regardless of rate evaluated; however, following a malathion application panicle emergence was reduced to approximately 30% when rice was treated with halosulfuron and 10% with halosulfuron plus thifensulfuron.  At physiological maturity rice treated with halosulfuron with or without malathion, halosulfuron plus thifensulfuron with no malathion, and the nontreated, had panicle emergence of 98 to 100% compared with 62 and 63% panicle emergence with rice treated with halosulfuron plus thifensulfuron at 39 and 78 g/ha following a malathion application. 

The nontreated rice had a yield of 6920 kg/ha with a harvest moisture of 17.8%.  All rice treated with halosulfuron with or without malathion, or halosulfuron plus thifensulfuron without malathion, had harvest moistures of 17.2 to 17.5% and yields similar to the nontreated rice.  However, halosulfuron plus thifensulfuron at 39 to 78 g/ha following malathion had harvest moisture of 18.9 and 19%, respectively, and reduced rice yield compared with the nontreated.  This research indicates caution should be taken when applying halosulfuron plus thifensulfuron as a salvage treatment, and halosulfuron plus thifensulfuron in combination with a malathion application should be avoided.

Fertility and Cropping System Effects on Spring Annual Weeds in Eastern Washington Dryland Organic Systems. M. R. Manuchehri*, K. A. Borrelli, E. P. Fuerst, D. L. Pittmann, R. T. Koenig, I. C. Burke; Washington State University, Pullman, WA

Limited cultural weed control strategies presents many challenges for organic dryland growers in Eastern Washington. In an attempt to identify competitive and profitable cropping rotations, a dryland organic conservation tillage study was initiated in 2003 near Pullman, WA. Nine different systems were studied in the experiment over a twelve year period with the first three years representing a transition period from conventional to organic management. Systems included three different five-year alfalfa-wheat-barley rotations (systems 1, 2, and 3), four two-year rotations of various winter pea, triticale, barley, and wheat alternations (systems 4, 5, 6, and 7), and a three-year wheat emphasized rotation consisting of two different systems (systems 8 and 9). During year eight and nine of the study, crop and weed biomass and yield were monitored in order to evaluate the competitiveness of the cropping systems against spring annual weeds. The most common spring annual weeds at the site were downy brome (Bromus tectorum), jointed goatgrass (Aegilops cylindrica), wild oat (Avena fatua), Italian ryegrass (Lolium multiflorum), panicle willowweed (Epilobium brachycarpum), common lambsquarters (Chenopodium album), and prickly lettuce (Lactuca Serriola). In 2010, winter pea hay (system 4), alfalfa (system 1), and winter triticale (system 5) suppressed the most weeds while winter and spring wheat treated with manure had the greatest amount of weed biomass. System 4, planted to triticale, continued to have the least amount of weed biomass in 2011 as well as the greatest amount of crop biomass followed by winter wheat (system 1 and 6). Grain yields in 2010 and 2011 were highest for plots planted to winter triticale followed by winter wheat and spring wheat. Despite high amounts of weed biomass, winter wheat plots treated with manure in 2010 yielded more than winter wheat plots that were not treated. Additionally, winter wheat yields in 2011 for system 1 yielded more than winter wheat from system 6, suggesting that a previous planting of a competitive crop such as alfalfa may increase grain yields for the subsequent season.

Of the 50 species of Echinochloa worldwide, barnyardgrass [Echinochloa crus-galli (L.) Beauv.] and junglerice [Echinochloa colona (L.) Link.], are considered to be the most troublesome Echinochloa weeds in the southern Unites States.  The taxonomy of Echinochloa has been controversial and common names have been used loosely for the species.  To address this issue, more than 240 seed samples were collected during 2008-2010 from Alabama, Arkansas, Kentucky, Louisiana, Mississippi, and Tennessee to determine the morphological diversity, distribution, and frequency of Echinochloa species.  Junglerice was the most common species in row crop production and along field margins.  Rough barnyardgrass [Echinochloa muricata (Beauv.) Fern.] was the second most common followed by barnyardgrass and a variety of gulf cockspur [Echinochloa crus-pavonis (Kunth) Schultes var. macera (Wiegand) Gould].  Coast cockspur [Echinochloa walteri (Pursh) Heller] was least frequently found.  Junglerice was the most uniform morphologically when compared to all other Echinocloa species; however, our surveys indicated junglerice plants are variable with green and purple tinged inflorescences and with and without purple stripes on leaves.  With the increased reports of Echinochloa becoming late-season weed problem in row crops and the potential for developing herbicide resistance, it is important to determine if frequency, distribution, and inter- and intra-specific morphological differences.

Field studies were conducted at two sites in Ohio from the fall of 2009 through summer of 2010 to determine the residual control of horseweed from fall herbicide treatments. These treatments were again put out in the fall of 2010 through the summer of 2011, this time at South Charleston only.  Herbicides were applied in November and horseweed population density was measured from mid-April through early June of the following year.  The horseweed population at Mt. Orab was resistant to glyphosate and ALS inhibiting herbicides, and the population at South Charleston was resistant to glyphosate.  The herbicides in this study included the following:  flumioxazin, cloransulam + sulfentrazone, glyphosate, imazaquin, dicamba, pyrosulfatole, saflufenacil, metrubzin + sulfentrazone, metribuzin, and combinations of chlorimuron and tribenuron, metribuzin, flumioxazin or sulfentrazone.   Herbicides were applied with 1.1 kg/ha of 2,4-D ester and 0.84 kg/ha of glyphosate to ensure control of emerged horseweed and other weeds.  The treatment of glyphosate and 2,4-D alone was considered to be the non-residual control by which to assess the residual control from other treatments.  At South Charleston, glyphosate was applied on June 9 followed by a final assessment of control one month later.

Horseweed population densities in the spring of 2010 at Mt. Orab were not affected by herbicide treatment, and were extremely variable across the site.  The population density among treatments ranged from 133 to 1583 and 150 to 767 plants/m² on April 16 and June 7, respectively.  The horseweed population density at South Charleston ranged from 0 to 2333 and 50 to 1383 plants/m² on April 16 and June 8, respectively.  The combination of chlorimuron and flumioxazin (29 and 84 g/ha) resulted in 0 to 50 plants/m2 among sampling dates.  This treatment was not significantly different than lower rates of the same herbicide combination, or several other chlorimuron-containing treatments, which resulted in 250 to 716 plants/m² on June 6.  However, for the high rate of chlorimuron and flumioxazin, horseweed control was completely controlled one month following an early June glyphosate application, whereas control ranged from 50 to 73% for other residual herbicides.  

 Fall-applied chlorimuron-containing herbicides reduced the spring populations but did completely control ALS-sensitive horseweed into June, and had no effect on spring populations of ALS-resistant horseweed.  Based on these results, soybeans growers increase their risk of horseweed control failures where they rely on the combination of fall residual herbicide and in-season postemergence herbicide treatments.

Plantbacks of various rotational crops the following year after herbicide application to winter wheat were conducted over three years at different locations in the Palouse region of eastern Washington and northern Idaho.  Mesosulfuron-methyl  is an ALS inhibitor which has been registered since 2004 primarily for the control of grassy weeds in the U.S.  It has a short plantback to most rotational crops.  Iodosulfuron is an ALS inhibitor which has grass and broadleaf activity that is used in combination with mesosulfuron in many parts of the world.  The persistence of iodosulfuron varies relative to herbicide rate, soil characteristics, and precipitation.   A combination of mesosulfuron plus low rates of iodosulfuron was evaluated in comparison to the new ALS inhibitor pyroxsulam for carryover onto lentil, pea, canola, or mustard.  Results indicated greater rotational impact on lentil and chickpea from pyroxsulam than either mesosulfuron or mesosulfuron plus iodosulfuron the following year after application.  Other crops did not exhibit consistent rotational differences among the comparison herbicides.  The low soil pH common to this area plus the lack of tillage in these tests were the key variables in observing differences between plantback sensitivity of these herbicides.   

Perennial grasses that produce lignocellulosic biomass are generating much interest as sources of biomass for energy production. Elephantgrass, also called nappiergrass has been proposed as an appropriate bioenergy feedstock for lignocellulosic ethanol or direct combustion in south Florida. However, elephantgrass has been reported as having a high invasive potential in Florida where it is listed as a noxious weed. To limit future invasion of elephantgrass escapes in sugarcane and vegetables in south Florida, currently labeled POST grass herbicides were evaluated for its management. The response of elephantgrass to glyphosate (used for spot treatments), clethodim and sethoxydim (used in vegetables), and asulam and trifloxysulfuron (used in sugarcane) were determined using dose response curves. Herbicides were applied at rates ranging from 52.5 to 3360 g ha^-1 glyphosate, 17.5 to 1120 g ha^-1 clethodim, 19.7 to 1260 g ha^-1 sethoxydim, 230 to 14800 g ha^-1 asulam, and 1 and 64 g ha^-1 trifloxysulfuron. Log-logistic models were used to determine the herbicide dose required to produce 90% control (ED₉₀). The ED₉₀ values for elephantgrass control based on visual estimation were 448, 127, 489, 19050, and 91 g ha^-1 of glyphosate, clethodim, sethoxydim, asulam, and trifloxysulfuron, respectively at 21 d after treatment (DAT). The doses required to provide 90% shoot growth reduction (GR₉₀) at 21 DAT were 477, 262, 381, 12330, and 94 g ha^-1 of glyphosate, clethodim, sethoxydim, asulam, and trifloxysulfuron, respectively. The probability of elephantgrass resprouting 35 d following herbicide application decreased with increasing rates of glyphosate, clethodim, sethoxydim, asulam, and trifloxysulfuron. The GR₉₀ values for root dry weight were 570, 257, 432, 16919, and 183 g ha^-1 of glyphosate, clethodim, sethoxydim, asulam, and trifloxysulfuron, respectively. These results suggest that glyphosate, clethodim, and sethoxydim will provide acceptable control of newly established elephantgrass at currently labeled use rates.   However, elephantgrass was tolerant to asulam and trifloxysulfuron at currently labeled use rates implying that control of escaped elephantgrass will be difficult. 

Roundup Ready^® crops, which allow growers to use the broad-spectrum herbicide glyphosate, represent one of the most rapidly adopted weed management technologies in recent history, currently accounting for most of the acreage in soybean, cotton, and maize in the U.S. However, intensive selection pressure has led to the evolution of glyphosate-resistant weeds, which brings the need to incorporate herbicides with alternative modes of action as a strategy for weed resistance management.  Dicamba, a synthetic auxin herbicide that controls broad-leaf weeds, has been identified as an alternative mode of action that can be used in combination with glyphosate. Thus, the addition of dicamba tolerance to the Roundup Ready^® cropping system will allow growers to use dicamba and glyphosate tank-mixes for effective and flexible weed control management, especially where glyphosate-resistant weeds are present. Herbicide tank-mixtures can result in additive or synergistic interactions providing increased weed control, whereas antagonistic interactions would result in less weed control than predicted. Inhibitors of the enzyme acetyl-CoA carboxylase (ACCase) are post-emergence, systemic herbicides used to control narrow-leaf weeds. Here, we investigated the interactions between ACCase inhibiting herbicides and dicamba when combined in tank-mixtures to control weeds. 

In 2011, the University of Kentucky evaluated dicamba, at increasing rates, applied alone and with glyphosate to giant ragweed (Ambrosia trifida), smooth pigweed (Amaranthus hybridus) and morning glory (Ipomoea sp.).  Plots were established using a soil finisher to create an optimum uniform surface for weeds to germinate.  Once weed populations reached heights of 7.6 cm, 15.2 cm and 30.5 cm, dicamba was applied at 280 g ae ha^-1, 420 g ae ha^-1 560 g ae ha^-1 alone and in mixed with glyphosate at 841 g ae ha^-1.  Visual ratings were taken seven and 21 days after treatment.  Dicamba alone achieved ≥60 percent control of all species observed while dicamba mixed with glyphosate achieve ≥93 percent control at the 7.6 cm. application. Similarly, dicamba alone resulted in ≥77 % whereas with glyphosate, the control increased to ≥90% when applied to 15.2 cm weeds.  When applied to 30.5 cm weeds, control using dicmba only resulted in ≥80 % while the addition of glyphosate increased control to ≥85%.  The addition of glyphosate, regardless of the dicamba rate, increased control for all weed species at each application.

Kochia (Kochia scoparia), Palmer amaranth (Amaranthus palmeri), waterhemp (Amaranthus rudis) and redroot pigweed (Amaranthus retroflexus) are among the most common and problematic weeds in corn, soybean, wheat and sugarbeet production systems in Nebraska. Each species (except redroot pigweed) has had populations documented or suspected to be resistant to ALS and/or photosystem-II inhibiting herbicides. Soybean genetically modified to be resistant to dicamba and 2,4-D are being developed to provide an additional herbicide mechanism-of-action for postemergence weed control. The objective of this study was to observe the variation in response to a single dose of dicamba or 2,4-D among kochia, waterhemp, Palmer amaranth and redroot pigweed populations collected from Nebraska during Fall 2010. Seven replications of 67 kochia populations were treated with 420 g ae ha^-1 of dicamba. Seven replications of 41 waterhemp, 34 Palmer amaranth and 11 redroot pigweed populations were treated with a single dose of dicamba (420 g ae ha^-1) or a single dose of 2,4-D at (280 g ae ha^-1). Visual injury estimates were made 21 days after treatment (DAT) on a scale of 0 (no injury) to 100 (dead plants). Plant stems were then cut at the base and dried for two days in a forced air dryer at 65 C, and dry weight biomass was measured. Among kochia populations, the visual injury estimates 21 DAT with dicamba ranged from 23% for the least susceptible population to 78% for the most susceptible population. Among waterhemp populations treated with dicamba, visual injury estimates ranged from 53% to 77%, and for waterhemp treated with 2,4-D, visual injury estimates ranged from 46% to 61%. Among Palmer amaranth populations treated with dicamba, visual injury estimates ranged from 67% to 93%, and for populations treated with 2,4-D, visual injury estimates ranged from 53% to 80%. Among redroot pigweed populations treated with dicamba, visual injury estimates ranged from 93% to 100%, and for populations treated with 2,4-D, visual injury estimates ranged from 77% to 100%. Among the Amaranthus species, redroot pigweed was the most susceptible to both dicamba and 2,4-D, and waterhemp was the least susceptible. The within species variation across populations was similar among Amaranthus species, but was much greater for kochia.

Experiments were established in the greenhouse to evaluate the site of uptake for pyroxasulfone in both monocot and dicot species. Experiments were conducted in an Olney fine sandy loam soil with 0.81% organic matter. This soil type was selected in order to maximize the amount of plant available herbicide, and to minimize soil binding. The study consisted of three replications in a complete random design. The objectives of this study were to a) evaluate whether pyroxasulfone is adsorbed predominately through root or shoot tissue, and b) whether monocots or dicots differ in terms of their site of herbicide up-take. Individual pots per species measured 7.5cm² wide by 9cm deep. Root and shoot exposures were evaluated by separating treated from untreated soil with a layer of activated charcoal. For root uptake around 100ml of soil was sprayed with 300g ai/ha and then incorporated with ~ 12mm of simulated rainfall. Then a small layer of soil was placed above the treated soil followed by a layer of activated charcoal. Then a thin layer of soil was used to separate the charcoal and seed. Three to six seeds of a single species were planted into a single pot depending on species. Then 100ml of untreated soil was placed above the seed. For shoot uptake procedure was repeated but this time the bottom layer was left untreated while the top layer was again treated at 300g ai/ha and incorporated with simulated rainfall with activated charcoal separating the treated and untreated soil, and untreated soil separating treated soil and seed from activated charcoal. Treatments were established with activated charcoal above and below the planted seeds without treated soil. Treatments with untreated soil and no activated charcoal were also grown to evaluate the influence of activated charcoal on the growth of all species. Once treated and incorporated, pots were sub-irrigated as needed and grown in the greenhouse for biomass collection.  Sunflower and corn were used for comparison between large seeded monocots and dicots, while canola and wheat were used to evaluate small seeded monocots and dicots. Preliminary greenhouse data suggest that root exposure to pyroxasulfone produced a greater reduction of plant growth for dicot species when compared to herbicide shoot exposure. For monocot species, shoot exposure to pyroxasulfone produced more of a plant response and reduction of growth when compared to root exposure to pyroxasulfone. Although root and shoot exposure provided better control for dicots and monocots respectively, data suggests that uptake for a certain species is not exclusively limited to root or shoot tissue even if one pathway is preferred by that species.  

Italian ryegrass is an often difficult to control and competitive weed that can result in significant yield and quality loss for wheat producers.  Over the past decade, Italian ryegrass has been an increasing problem for southeast Kansas wheat growers.  The objectives of this study were to document the occurrence of Italian ryegrass in southeast Kansas and evaluate herbicide resistance to pyroxsulam, mesosulfuron, and imazamox.  In 2010, 60 wheat fields were scouted at wheat heading for the presence of Italian ryegrass.  The survey found that 27 of the 60 wheat fields contained at least one Italian ryegrass plant.  In general, the occurrence of Italian ryegrass increased in the more southern regions of Kansas.  This is not surprising since it is likely entering Kansas from Oklahoma, where Italian ryegrass is more common.  Seed samples from the 27 fields were grown in the greenhouse.  Four replications of four plants per plot were treated with 18, 15, and 35 g ai ha^-1 pyroxsulam, mesosulfuron, and imazamox, respectively, and the study was repeated.  Italian ryegrass control was rated 35 days after treatment on a scale of 0% = no control and 100% = complete control.  Plants were considered resistant if less than 70% control was observed.  Results from the greenhouse herbicide treatments found that every field sampled included at least one plant with resistance an ALS-inhibiting herbicide.  The greatest number of resistant plants occurred in a sample from Labette County where 91, 88, and 88% of the plants were resistant to pyroxsulam, mesosulfuron, and imazamox, respectively.  The most prevalent ALS-resistance was to pyroxsulam where 13 of the 27 sites had 50% or greater of the plants with resistance.  Mesosulfuron and imazamox had six and seven of the 27 sites with 50% or greater herbicide resistant-plants, respectively. Unfortunately, herbicide history at all the sites are unknown. dshoup@ksu.edu

Like many other land-grant universities, Penn State had the opportunity to evaluate the effectiveness of KIH-485 on weed control starting in the early 2000s. Since then this experimental herbicide from Kumiai Chemical has had some transformations and adjustments as it is prepared for the marketplace. The following is a summary of our experiences with this herbicide and its potential fit in cropping systems. KIH-485 was first tested at Penn State in 2003, with continued evaluations through 2011 in corn and soybean. During this timeframe it was determined its mode of action is a seedling growth inhibitor and its chemical structure that within the isoxazoline family and was assigned the common name, pyroxasulfone. Initially, it was formulated as a liquid but was later reformulated to its current water dispersible granule form. Over the years, application rates have been evaluated PRE between 0.07 to 0.44 lb ai/A; but the typical rate will likely be 0.13 lb ai on a medium soil type with <3% organic matter. The use rates for pyroxasulfone are up to eight times lower than s-metolachlor with comparable weed control.  It has been tested in combination and against other commercially available PRE herbicides such as atrazine, pendimethalin, mesotrione, isoxaflutole, s-metolachlor, dimethenamid-P, saflufenacil, and others. Late season evaluations of up to seven studies revealed that pyroxasulfone herbicide alone (0.13 lb ai) provided 86 – 91% control of giant foxtail (Setaria faberi), common lambsquarters (Chenopodium album), velvetleaf (Abutilon theophrasti), common ragweed (Ambrosia artemisiifolia), and smooth pigweed (Amaranthus hybridus) when applied PRE.  However, when pyroxasulfone (0.13 lb) was applied in combination with atrazine (PRE, 1 – 1/5 lb ai) or glyphosate (POST, 0.75 lb ae), control of these same weed species improved to 89 – 95% and 94 – 96%, respectively. Compared to PRE-grass herbicides such as s-metolachlor, in general, pyroxasulfone provides similar annual grass control but has better annual broadleaf activity. Overall, Penn State has evaluated pyroxasulfone for the past several years in corn and soybean and has noted good weed control performance and crop safety. Kumiai Chemical has agreements with BASF, Valent, and FMC allowing these companies to sell pyroxasulfone-containing products. Once registered, it appears BASF will initially sell Zidua® (pyroxasulfone), Valent will sell Fierce® (pyroxasulfone plus flumioxazin) and FMC will introduce Anthem® (pyroxasulfone plus fluthiacet) and Anthem ATZ® which contains atrazine. Depending on the product, these could be used in corn, soybean, and/or wheat.  EPA approval is expected for pyroxasulfone during 2012 or later.

Benchmark Study: Assessing the Economic Viability of Herbicide Resistance Management Programs. B. Edwards, D. R. Shaw, J. W. Weirich, M. D. K. Owen, P. M. Dixon, B. G. Young, R. G. Wilson, D. L. Jordan, S. C. Weller; Mississippi State University, Mississippi State, MS, University of Missouri, Portageville, MO, Iowa State University, IA, Southern Illinois University, Carbondale, IL, University of Nebraska, Scotts Bluff, NE, North Carolina State University, Raleigh, NC, Purdue University, West Lafayette, IN.

On-farm research was conducted from 2006-2010 to determine the economic viability of herbicide resistance management programs. Over 150 producers were selected to participate in the study, which were from six diverse states- Iowa, Illinois, Indiana, Mississippi, North Carolina, and Nebraska. The production systems utilized were continuous glyphosate-resistant (GR) crops, GR crops rotated with another GR crop, and GR crops rotated with a non-GR crop. Each field was split into two treatments, one of which remained as the producer’s glyphosate-based weed management program and the other followed intense best management practices (BMPs) set forth by the university. All input costs were recorded throughout the year, and variable input costs were analyzed. An economic analysis of herbicide costs, crop yield, and net return were used to assess the differences between the various production systems used and by the producer’s glyphosate-based management program compared to the university recommendation.

As expected, herbicide costs were higher for the intense BMPs set forth by the university when compared to the producer’s management program. However, there was no significant difference in net returns due to a slight increase in yield from the BMPs used. Thus, by implementing an herbicide resistance management program there is no economic disadvantage in the short-term and can delay the development of herbicide-resistant weeds in the long-term.

Farmer-advisor relationships may play a significant role in how farmers perceive and manage weeds. As part of a larger project assessing Michigan farmer’s perceptions of changes in soil quality due to management practices in Michigan, we noticed marked differences in the way organic and non-organic farmers perceived weeds and who they sought for management advice. To explore these observations, we conducted 22 in-depth interviews with nine organic (O), ten non-organic (NO) and three no-till (NT) growers each farming between 400 and 4,695 acres ( mean = 1,700 acres) in Michigan’s Thumb Region. Interview questions included, what are your problematic weeds? And, who do you rely upon to learn about pests and pest management? Participants grew a variety of row crops including sugar beets, soybeans, corn, wheat, and dry beans. We used emergent thematic content analysis to identify common themes across all transcribed interviews. Results of the analysis indicated that both NO and O farmers identified lambsquarters (Chenopodium album L.) and redroot pigweed (Amaranthus retroflexus L.) as the two “most problematic” weeds on their farms. The third most problematic weed differed for each weed management strategy: NO identified common ragweed (Ambrosia artemisiifolia L.), O farmers included foxtail (Setaria spp.) and NT farmers identified both foxtail and velvetleaf (Abutilon theophrasti Medik.). When describing their management of these weeds, NO farmers focused on herbicide effectiveness and efficacy; whereas, O farmers emphasized timing and frequency of mechanical weed management. The notion of weeds as soil health indicators was constant throughout the O interviews. This was present in the NT interviews, but nearly absent in the NO interviews. Organic farmers identified experience-based advisors (e.g. other farmers) as their primary source for management advice; whereas, NO and NT farmers never mentioned other farmers as advisors. Non-organic and NT farmers relied primarily on expert-based advisors (e.g. private consultants). Expert-advisors typically advised farmers to manage weeds with residual herbicides; while experience-based advisors suggested diversified crop rotations and adjustments in soil fertility to manage weeds. Results of this study suggest a shared agricultural philosophy between farmers and their advisors that reinforces the farmers’ perceptions of weeds and the weed management strategies they employ. Non-organic and NT farmers appear to be missing opportunities for alternative weed management approaches by excluding other farmers from their advisory committees.

As farmers are aware, certain weeds are much more difficult to manage than others.  Difficult-to-control weeds can be designated as being most troublesome to the producer.  We conducted a survey of the most troublesome weeds in grain and silage corn, soybeans, and winter wheat in the fourteen states represented by the Northeastern Weed Science Society.  An electronic invitation to participate in a five question online survey was directly sent to 517 agricultural professionals and researchers and indirectly received by approximately 150 others through posts on targeted list-serves and forums.  This distribution method generated 485 submissions from 256 respondents, which constituted a 49.5% direct response rate and a 38.4% indirect response rate.  Respondents were asked to designate the top ten most troublesome weeds by crop, conventional or organic management and tillage system within National Oceanic and Atmospheric Administration (NOAA)-defined climatic regions.  Participants could designate a weed as troublesome if suspected of being herbicide resistant.  State lists of the 10 most troublesome species in each crop were generated using a rank-sum method in which sums were compared against the highest scoring, and therefore most troublesome weed.  These lists revealed that several species are most problematic only in certain geographic locations and suggest that herbicide resistance may have an influence on whether or not a species is considered troublesome.  For example, quackgrass (Elymus repens (L.) Gould) and field bindweed (Convolvulus arvensis L.) are the 2^nd and 3^rd most troublesome species, respectively in New England corn cropping systems.  These two species rank 7^th and 2^nd in NY State corn cropping systems, but fail to rank in the top 10 in any state south of Maryland.  Similarly, annual morningglories (Ipomoea spp.), which are absent from much of New England, are of major concern in mid-Atlantic and southern corn cropping systems.  Annual morningglories were ranked as the worst weed in NC, VA, and DE, and 6^th in MD and NJ.  Reports of highly troublesome annual morningglories in PA and NY raise concerns that these species are undergoing a northward range expansion, possibly linked to global climate change.  Weeds with primarily southern troublesome ranges include Palmer amaranth (Amaranthus palmeri S. Wats) and Johnsongrass (Sorghum halepense (L.) Pers.), which ranked in the top ten most troublesome weeds in DE, MD, VA and NC and WV, VA, and NC, respectively.  Palmer amaranth was designated resistant to herbicides in 82% of all reports.  The confinement of troublesome ranges to specific geographic locations independent of management practices and the designation of certain species as troublesome within a portion of their known ranges suggest the presence of troublesome-range bioclimatic niches.  On-going work is focused on analyzing climatic data to determine bioclimatic envelope parameters.  Factors that may be especially important include frost-free period, temperature extremes, and precipitation.  Candidate species for analysis include burcucumber (Sicyos angulatus L.), which was reported to be the most troublesome species in PA corn cropping systems, but was much less troublesome elsewhere.  Once completed, bioclimatic information will be paired with climate change models to generate range-expansion predictions.  Such predictions will serve as advanced warning for researchers, industry professionals and growers and will facilitate proactive development and deployment of management strategies in regions projected to experience increased deleterious impacts from troublesome weed species.

Herbicide registrations in minor crops have been stagnant in recent years for several reasons, including the adoption of herbicide-resistant agronomic crops and subsequent lack of new product development, increasing pesticide registration cost and liability associated with use on high-value crops.  With this context in mind, a multi-species herbicide screen was conducted in 2010 to determine vegetable crop tolerance to several existing herbicides applied pre- or post-emergent.  Herbicide active ingredients included: cloransulam-methyl, ethalfluralin, flumioxazin, fomesafen, imazosulfuron, KIH 485, linuron, mesotrione, oxyfluorfen, pyroxsulam, rimsulfuron, saflufenacil, sulfentrazone and topramezone.  Crops included: carrot, cucumber, onion, pea, potato, pumpkin, radish, red beet, snap bean, spinach, sweet potato and transplanted pepper.  In the multi-species screen, 72 crop-herbicide combinations exhibited sufficient crop safety to warrant further evaluation.  In 2011, several potential herbicide-crop combinations identified in the multi-species screen were evaluated in replicated studies. Crop safety and yield were similar to the hand-weeded or industry standard treatments where cloransulam-methyl, KIH 485, mesotrione or saflufenacil were applied individually in potato, where oxyfluorfen was applied in transplanted pepper, where imazosulfuron or sulfentrazone were applied in cucumber and where fomesafen, linuron, saflufenacil or sulfentrazone were applied in onion.  While the multi-species screening methodology used in this research is not novel and some of the results not unprecedented, this project demonstrates that the bottleneck in minor crop herbicide registrations is not necessarily due to a lack of existing viable products, but likely more so related to the above-mentioned economic and registration hurdles.  Given the withdrawal of several herbicides in vegetables and resistant weed development, the future of minor crop weed control is reliant on a creative solution, such as the creation of federal support programs that could act as a third-party registrant.

There has been an increase in the number of experimental and registered organic herbicides in the past few years.  The objective of this research was to evaluate weed control with a Biolink (fatty acid),  Weed Pharm (20% v/v acetic acid), Green Match (55% v/v d-limonene), Matratec (50% v/v clove oil), and Weed Zap (45% v/v clove oil + 45% v/v cinnamon oil).   Greenhouse experiments evaluated control of Brassica nigra, Amaranthus retroflexus, and Echinochloa colona with organic herbicides at either 327 or 655 l/ha spray volumes.   Results indicated that 655 l/ha spray volumes were more effective than 327 l/ha, and that E. colona was more difficult to control than broadleaf weeds.   Field experiments examined control of Plantago lanceolata in January or May, 2011 with Biolink at 3% or 6% v/v, Green Match at 7.5% or15% v/v, Matratec at 7.5% or 15% v/v, Weed Zap at 7.5% or15% v/v, and Weed Pharm at 50% or 100% v/v.  The spray volumne for all treatments was 655 l/ha and an organic adjuvant was added to each to improve coverage.   Weed Pharm, Biolink and Weed Zap, at the highest concentrations provided the best control at 9 days after treatment following the January application.  Similar results were seen following the May application, however, the average level of control from all treatments was improved.   

A field trial was established at Harrow, ON from 2007 to 2010 to evaluate the effectiveness of compost and compost plus newspaper as a weed control barrier in organic vegetables. The trial was a fully phased 4-year rotation that included processing tomatoes, pumpkins, red clover, and oats under-seeded with red clover. The compost was obtained from the municipality and contained lawn clippings, leaves, and wood chips. The newspaper was sourced as roll-ends from the local newspaper printing press and contained no ink. Compost was either applied at a 5cm thickness alone or on top of 2 layers of newspaper. Treatments included application to row middles only, crop row only, or to the entire plot. The most effective treatment in all crops was when the combination of compost and newspaper was applied to the entire plot providing >95% control of weeds 56 days after application (DAT). The least effective treatment was the application of compost alone either in the row middle or crop row which provided <50% weed control by 56 DAT. Tomato yields were 3-fold higher when compost plus newspaper was applied to the entire plot versus compost alone. Differences among treatments for pumpkin yields were less pronounced.

In 2003, an organic vegetables production system was initiated at the WSU Puyallup Research and Experiment Station.  The experiment compares 12 organic management systems, including three cover cropping systems, 2 tillage treatments, and 2 amendment types, arranged in a split-split plot design. Treatments were chosen based on input from local farmers through workshops, farm visits, surveys, and focus groups.  Single crops were grown the first three years of the experiment, including snap bean (2003), fall spinach following summer cover (2004), and winter squash (2005). Beginning in 2006, four crop rotations were grown within each plot each year, including snap bean, winter squash, and spring broccoli followed by fall spinach.  Treatments included three cover crops (1.) Fall planted cereal-legume mix, 2.) Summer planted relay legume, and 3.) Fall planted grass-legume mix managed as pasture in year 1 then incorporated [livestock raised in pasture years]), two tillage systems (A.) Conventional [moldboard plow], B.) Reduced Tillage [Spader]), and two organic amendments (i.) Broiler litter [low C:N ratio], ii.)On-farm compost [medium C:N ratio).  Weed populations were monitored through in-season counts and through seedbank analysis (2010-2011 only).  Analysis to date of in-season weed counts suggests that the impact of different cover cropping strategies and tillage implements have on weed densities varies year to year.  We did not observed differences in weed densities or seedbank levels between low/medium carbon nutrient sources.        

The desire to minimize the use of agri-chemicals in crop production to safeguard environmental and human health has stimulated interest in organic crop production systems. This has created a growing interest in the consumption of organically-produced food.  There is a need for more effective natural-product weed management tools since control of weeds remains the most significant problem in the production of organic crops. The objective of these studies was to provide enhanced weed management in organic fruit and vegetable production. Studies were conducted to evaluate several biological or low- risk herbicides for crop safety and efficacy in controlling weeds, common in the organic production of peaches, tomato, sweet corn and pepper.  In vegetable crops, Green Match EX, Matratec Ag and Weed Zap (all received one cultivation), gave the best overall weed control with an initial rating of 80% broadleaf weed control and about 60% grass control, depending on the weed species involved. While level of control varied with weed species, the standard treatment of 30% acetic acid and Weedphyter initially gave 89% and 93% broadleaf weed control, respectively, however grass weed control with these products  at final rating was 5% or less. Manuka Oil and Organo-Sol gave the poorest control, ranging from 0 to 10%, averaged over ratings from July 15 to August 22. Green Match EX plus one cultivation gave the highest yields across all crops. Yields from this treatment were in some cases equivalent to yields from the weeded control. Matratec Ag plus one cultivation gave excellent tomato and sweet corn yields. Weed Zap plus one cultivation gave yields that were lower, despite providing adequate early weed control. Yields were significantly lower for all other treatments. This was likely due to poor early control. There was no effect from any treatment on peach tree diameter, tree height or injury. Green Match (20%) and Matratec Ag gave the best weed control with a final broad leaf weed control rating of 80%. Green Match (14%) gave control of 54% while Acetic Acid (30%) gave control of 43%. The addition of Nu-film P at 1 or 2% increased control to 55 and 49%, respectively. Grass control followed a similar pattern.  Inter-row cultivation combined with an organic herbicide enhanced weed control.  Inter-row cultivation has potential for controlling late flushes of weeds. However, integration with organic herbicides is required for satisfactory results.  This research on novel uses of bioactive natural products will lead to improved weed control options that organic growers could potentially use and provide society with environmentally and economically sustainable alternatives to synthetic chemical herbicides.  

Meadowfoam (Limnanthus alba Hartw. ex Benth.) seed meal, a by-product of meadowfoam oil extraction, has glucosinolate degradation compounds that are similar to those from Brassicaceae species. The glucosinolate degradation compounds are reported to be herbicidal. A greenhouse study confirmed that the herbicidal affect of soil amended with 3% activated meadowfoam seed meal (1% fresh seed and 99% seed meal) lasted 6 days after seed meal incorporation and provided 94% suppression of lettuce emergence and growth compared to the control. Two field studies were conducted to evaluate the use of meadowfoam seed meal for weed control in lettuce. Three seed meal concentrations: 3%, 5%, and 7%, and two different forms of meadowfoam seed meal, nonactivated and activated, were used. The 7% activated seed meal provided the best control of monocot (barnyardgrass) and dicots (nightshade, sharppoint fluvellin, and wild carrot) compared to other treatments while there was a more pronounced fertilizer effect of treatments in the second experiment. Lettuce aboveground biomass was 4 to 6 times greater in meal-amended treatments than in the control treatment. Nitrate in lettuce tissues of meal-amended treatments also was greater. More lettuce biomass was produced in the first experiment (early summer) as compared to the second experiment (late summer). The difference in growth was most likely a result of the difference in environmental conditions between two studies. In the second experiment, the diversity indices including species richness, diversity index, and evenness confirmed that weed diversity varied with seed meal concentrations. The highest rate of seed meal produced the smallest increases in weed species richness, diversity, and evenness compared to other treatments. Both fertilizer and bioherbicide effects were observed with the use of meadowfoam seed meal as a soil amendment.

Organic squash (Cucurbita pepo L.) producers need appropriate herbicides that can effectively provide season- long weed control.  Research was conducted in southeast Oklahoma (Atoka County, Lane, OK) to determine the impact of potential organic herbicides on weed control efficacy, crop injury, and yields.  The experiment included AXXE® (65% pelargonic acid) and Scythe® (57% pelargonic acid) applied post-directed at 1.5, 3, 5, and 10% v/v application rates, plus an untreated weedy-check and an untreated weed-free check with 4 replications.  Yellow squash, cv. ‘Enterprise’, was direct-seeded on June 27, 2011 into raised 91-cm centered beds.  The primary weeds included smooth crabgrass (Digitaria ischaemum  (Schreb.) Schreb. ex Muhl.), cutleaf groundcherry  (Physalis angulata L.), and spiny amaranth (Amaranthus spinosus  L.).  Axxe® and Scythe® were post-directed applied on July 14 and then the 1.5, 3, and 5% v/v treatments were reapplied 11 days later (July 25).  Weed control (total, broadleaf, and grass) increased as the application rates increased, producing a minimum of 99% control 1 (days after initial treatment) DAIT for the 10% v/v rate for each herbicide. The single application of each herbicide at 10% v/v performed similarly across weed control rates (12 to 41 DAIT) to the sequential application of 5% v/v. Squash injury increased as the application rates increased.  The 10% v/v application rates produced the greatest squash injury at 1 DAIT with the 5% v/v producing the greatest injury at 12 DAIT following the sequential application.  Squash yields (fruit/acre and t/acre) increased as the herbicide rates increased, peaking at the 5% v/v rates and dropping off with 10% v/v.  The decrease in yields for the 10% v/v rates indicate that the greater initial injury produced season-long yield reductions compare to the two 5% v/v sequential applications.  In general, all the herbicide applications produced as good or greater yields than the weedy-check.  The 5% v/v sequential applications provide additional flexibility in the timing of the weed control treatments.  Additional research should focus on fine-tuning the herbicide application to control specific weeds at various maturity levels and sizes.

Strip-tillage (ST) can reduce input costs by accomplishing primary and secondary tillage with one pass while protecting and improving soils relative to full-width conventional tillage (CT).  However weed management under ST can be challenging, especially for vegetable crops with limited herbicide options. Field trials were conducted on sandy soils in SW Michigan to assess the interactive effects of tillage (ST or CT), cover crops [none, rye (Secale cereale) or rye-vetch (Vicia villosa)], and weed management intensity (low or high) on weeds and snap beans (Phaseolus vulgaris).  Tillage and cover crop treatments were imposed on the same plots for two years in a sweet corn-snap bean rotation in two separate fields.  In snap beans, the entire experimental area received S-metolachlor PRE at 0.95 lb ai/A, and clethodim at 0.10 lb ai/A 35 days after planting (DAP).  Low intensity weed management (LWM) treatments received no other herbicides, while high intensity weed management (HWM) treatments received an additional application of bentazon at 0.75 lb ai/A 27-29 DAP.  Weed emergence and dry weight by species as well as snap bean quality and yield were evaluated.  In addition, the germinable weed seedbank density following snap beans was estimated based on greenhouse emergence from composite soil samples taken from one of the experimental sites in May 2011. Tillage did not affect emergence or final density of broadleaf weeds in either year, but in 2011 both emergence and final density of large crabgrass (Digitaria sanguinalis) were higher under ST.  When winter rye was used in combination with ST, emergence and final density of weeds was either unaffected or reduced compared to ST without rye.  The addition of bentazon in HWM treatments improved control of broadleaf weeds in 2011, but also caused temporary stunting of snap beans.  No effects of tillage, cover crops, or weed management intensity on snap bean yield or quality were detected in either year.  Tillage had no effect on the germinable seedbank density of summer annual broadleaf weeds or winter annual weeds.  However, the density of large crabgrass in the germinable seedbank was 2-fold higher following ST compared to CT.  In both tillage systems, cover crops reduced the seedbank density of winter annual weeds—including henbit (Lamium amplexicaule) and chickweed (Stellaria media)—relative to bare soil treatments, but had no effect on summer annual weed seedbanks.  Our results demonstrate that 1) ST can produce comparable snap bean yields to CT with fewer tractor passes; 2) winter cover crops in combination with ST can enhance weed suppression; but that 3) control of weeds such as large crabgrass can be more challenging under ST.  Although weeds did not have any detectable effect on snap bean yields, additional complementary weed management practices aimed at improving large crabgrass control in ST snap beans may be necessary to avoid reductions in harvester efficiency or increases in seedbank densities of this problematic weed.

Some organic weed management practices for San Joaquin Valley (SJV) vineyards are costly, others may be inadvertently discouraged due to air quality (dust and smoke) regulations, and data to document relative cost and efficacy of different options are lacking.  Thus, science-based information is needed to help growers select the most economically and environmentally sustainable organic weed control practices for their vineyards.  On-farm studies were conducted in 2010 and 2011 in organic raisin and winegrape vineyards in the SJV.  Weed management treatments included steam, French plow (raisin vineyard only), Bezzerides cultivator, and an organic herbicide (Greenmatch®).  These treatments were followed by a second treatment of steam, organic herbicide, or hand weeding.  Non-weeded controls were also included.  Data on weed control, grapevine growth, crop yield, and fruit composition were collected.  Time needed to hand weed each plot was recorded.  The mechanical treatments (French plow and Bezzerides cultivator) provided the best weed control.  However, generally, no treatments affected vine growth or crop yield or quality, suggesting that established vineyards may have high weed thresholds.  Nevertheless, growers should manage weeds to reduce their potential interference with cultural practices, and to prevent them from serving as alternate hosts to other pests and diseases, reducing irrigation efficiency, adding seeds to the soil seedbank, and lowering the aesthetic quality of a vineyard.   The French plow and the Bezzerides cultivator were the most economical in the raisin and winegrape vineyard, respectively.  The costs for these treatments were $235 and $158 ha^-1, respectively.  The steam treatment cost was approximately $475 and $ 865 ha^-1 and the herbicide treatment cost was $1140 and $ 775 ha^-1, in the raisin and winegrape vineyard, respectively.  These costs are for weed management twice during the growing season where the main treatment (steam, mechanical, or herbicide) was followed by hand weeding.

Glyphosate should be applied before bud break in vineyards to minimize potential crop injury. Glyphosate is is typically tank-mixed with soil-active herbicides to provide soil residual control. In some cases however, application of soil-active herbicides later in the spring (following glyphosate alone) may improve weed control and possibly extend efficacy into the subsequent winter. The objective of this study was to compare the efficacy of soil-active herbicides in vineyards when applied as a tankmix with glyphosate before bud break (GBB) or when applied one to two months following the glyphosate application (FG). Experiments were conducted in 2010 and 2011 at the Oregon State University Woodhall Vineyard near Alpine, OR. Herbicides were applied at 187 L/ha in a 1.5 m wide band under the vine row. Weed control efficacy was evaluated in mid-summer, at harvest, and mid-winter (2011 only), and crop yield was estimated by harvesting fruit from plots.

Efficacy of most treatments in 2010 was unaffected by length of time between the glyphosate and soil active herbicide applications, but there were exceptions. Control of northern willow herb (Epilobium ciliatum) dropped when flazasulfuron and flumioxazin were applied on May 24 (FG) rather than April 22 (GBB), but control increased when oxyfluorfen, oryzalin, and rimsulfuron were applied on May 24 (FG) rather than April 22 (GBB). The composite rating of broadleaf and grass weed control on July 5 was less when oryzalin was applied on May 22 (FG) than when applied on April 22 (GBB). A very late spring in 2011 with cold and wet conditions through mid-June delayed bud break. Simazine and oryzalin treatments had slightly greater densities of northern willow herb midsummer than other treatments when averaged over the three application dates. Oryzalin and mesotrione (GBB) had poorer efficacy mid-summer than when applied with glyphosate on April 9. Mesotrione, flumioxazin, and rimsulfuron provided better broadleaf control in mid-January when applied on May 20 (FG) than when applied April 9 (GBB) and May-4 (FG). Indaziflam efficacy was not affected by application timing of soil-active herbicide.

Indaziflam was granted EPA registration with a trade name of Alion in April, 2011.   This group 29 herbicide provides preemergent control of monocot and dicot weeds in perennial crops.   Alion has been demonstrated in numerous trials from 2009 through 2011 with various external cooperators across the U.S.  In these studies, Alion was applied at 73  g ai/ha (5 oz/A) in combination with appropriate burndown herbicides and compared to local standards on a wide variety of tree and vine crops.  Weed control at 1-2 and 2-4 months after application was similar between Alion and local standards for both monocot and dicot weeds.  At 4-6 months after treatment, dicot and especially monocot efficacy was greater with Alion than current standard herbicide programs.   Trials that were continued to 6-9 months after application further indicated that Alion provided longer residual weed control.   The use of indaziflam, a cellulose biosynthesis inhibitor, is a new option for long lasting preemergent weed control with excellent crop safety in tree, nut, and vine crops. 

Broad spectrum weed control with tank mix of saflufenacil and glufosinate in Florida citrus. Megh Singh*,
Analiza H.M. Ramirez and Amit J. Jhala, Citrus Research and Education Center, IFAS, University
of Florida, 700 Experiment Station Road, Lake Alfred, FL 33850-2299.
*Corresponding author’s E-mail: msingh@ufl.edu.

Abstract

Citrus (Citrus spp.) is one of the most important crops in Florida agriculture. Weed control is a major component in citrus production and it is heavily dependent on use of herbicides. Saflufenacil (Treevix), an inhibitor of protoporphyrinogen oxidase (PPO) is a new post-emergence herbicide registered for broadleaf weed control in citrus. Glufosinate (Rely 280) is a non-selective, post-emergence herbicide for control of grasses and broadleaf weeds. Glufosinate is not registered for weed control in citrus, but
it is expected that it will be registered in future. Saflufenacil has no grass activity; therefore, it should be tank mixed with other herbicide(s) for broad spectrum weed control in citrus. Field experiments were conducted in citrus groves in Polk and Orange Country, FL in 2011 to determine the efficacy of saflufenacil applied alone or in a tank mix with glufosinate and indaziflam (Alion)
for broad spectrum weed control. The results suggested that saflufenacil applied alone was usually effective for early season broadleaf weed control; however, weed control efficacy reduced beyond 30 d after treatment (DAT) compared to a tank mix of saflufenacil and glufosinate. Addition of indaziflam as a tank mix partner resulted in excellent residual control of grass and
broadleaf weeds compared to tank mix of saflufenacil plus glufosinate. There was no injury to citrus trees in any of the herbicide treatments. It is concluded that with its novel mode of action, saflufenacil tank mixed with glufosinate
and indaziflam would provide citrus growers with another chemical tool to control broadleaf and grass weeds.

In Mid-Atlantic, commercial watermelons are grown with plastic mulch and require residual weed control for the area between the rows of plastic. If not controlled broadleaf and grass weed species will reduce yield, interfere with harvest, interfere with plastic removal, as well as produce significant seeds contributing to weed problems in subsequent years.   Most growers use hooded sprayers to apply a non-selective herbicide tank mixed with residual herbicides for weed control between the rows.  The objective of the study was to evaluate the effect of flumioxazin safety with watermelon and its weed control efficacy.

This study was conducted between 2010 and 2011 at two locations on Delmarva Peninsula. The study locations were University of Maryland’s Lower Eastern Shore Research and Education Center, Salisbury Facility and University of Delaware’s Research and Education Center near Georgetown, DE. Watermelon variety at both locations was ‘Millionaire’. All treatments were replicated three times and arranged in a randomized complete block arrangement.  Residual herbicides were applied in combination with paraquat.  Residual products included flumioxazin and fomesafen applied at two rates in combination with ethalfluralin, flumioxazin plus pyroxosulfone, ethalfluralin plus clomazone, ethalfluralin plus clomazone plus halosulfuron, as well as paraquat alone.

Large crabgrass and pigweed species were present at all sites.  Large crabgrass control was similar for all treatments containing a residual herbicide. Control of pigweed species did not differ among treatments indicating limited emergence after the treatments were applied. 

Crop injury differed between the locations. Initial leaf burn, rated within 7 days of application, was higher at UM-LESREC in 2011, averaging 13% compared to UM-LESREC 2010 and UD-REC 2010 which averaged 8%.  Injury, a combination of stunting and leaf burn, differed by site at 1 and 4 weeks after treatment, but did not differ by treatment.  However, at 2 weeks after treatment, treatments containing flumioxazin had higher watermelon injury than paraquat plus ethalfularin plus clomazone or paraquat
alone. 

Differences in yield were observed between sites, but there were no treatment differences.  Early-season injury did not impact earliness of harvest, total number of marketable fruit, or total yield.

Hooded applications of paraquat and residual herbicides are applied shortly after transplanting.  The injury from these herbicides treatments is before a rapid growth phase of the watermelon and prior to flower development.  Watermelons are able to overcome the early-season injury observed with the herbicide combinations used in this trial.  However, growers need to be cautioned that injury can occur with flumioxazin treatments.

Response of citron melon (citrullus lanatus var citroides) to preemergence herbicides. A..H.M. Ramirez, A.J. Jhala* and M. Singh. University of Florida, Citrus Research and Education Center, Lake Alfred, FL. Corresponding author’s email:ahmramirez@ufl.edu

ABSTRACT

Citron melon (Citrullus lanatus var citroides) is a monoecious, hairy annual
vine commonly found in citrus, cotton and peanut. There is limited information
on citron melon control with new preemergence herbicides such as indazifalm. A
greenhouse study was conducted in 2011 to evaluate the response of citron melon
to new and commonly used preeemergence herbicides. Treatments consist of
indaziflam at three rates (0.045, 0.073 and 0.095 kg ai/ha), recommended label
rates of diuron, bromacil, bromacil+diuron, flumioxazin, norflurazon,
pendimethalin, simazine, oryzalin, dichlosulam and flazasulfuron at 0.04 kg
ai/ha. Results suggested that percent cumulative emergence of citron melon at 14
days after treatment (DAT) varied by herbicide treatments. Indaziflam at all
rates greatly reduced emergence to 13 to 47% at 7 DAT compared to other
herbicides that resulted in 75-100 % emergence. Control at 7 DAT was <70% except
for indaziflam at 0.095 kg ai ha^-1 which gave the highest control at
83%. At 14 DAT control of citron melon increased in all treatment and was
excellently controlled with indaziflam at 0.095 kg ai ha^-1 (96%),
indaziflam at 0.073 kg ai ha^-1 (83%), flumioxazin (83%) and
norflurazon (82%). At 21 DAT citron melon control with indaziflam at 0.073 and
0.095 kg ai ha^-1, bromacil, bromacil + diuron, flumioxazin,
norflurazon and simazine was >90%.  There was inadequate control of citron melon
using diuron, oryzalin and flazasulfuron. These results indicated that citron
melon can be adequately controlled by the majority of available preemergence
herbicides.

Field experiments were conducted to identify the effect of low temperatures associated with herbicide treatment on Canada thistle  (Cirsium arvense L. ) control in wheat-potato and potato-wheat sequence with two environments in each crop sequence. Fields were selected with a natural infestation of Canada thistle at North Dakota State University’s agricultural research field in Fargo. Treatments were arranged in a randomized complete block design with a three by six factorial arrangements and application timing and herbicides as treatments.  Glyphosate and dicamba plus diflufenzopyr were applied to Canada thistle after harvest regrowth and one of three temperature regimes. In the wheat–potato sequence, before freeze and after a single freezing temperature, influenced Canada thistle control 12 MAT. Plant densities following potato harvest were much lower when herbicides were applied compared to the wheat field due to harvest operations and physiological characteristics of regrowth. These low initial plant densities in the potato-wheat sequence field resulted in increased Canada thistle populations at the second environment 12 MAT.  Average initial thistle populations in the wheat-potatosequence differed between years with 5 and 15 plants/m² and were decreased to 1 and 4 plants/m², respectively 12 months after the treatment.  Canada thistle densities were reduced from the initial densities by 79% and 71% at the two environments, while densities in the untreated control increased in 2002-2003 by 3% and reduced 78% during 2003-2004.

Potato virus Y (PVY) is a common problem in Idaho potato production. It is primarily spread by green peach aphid (Myzus persicae Sulzer) which feeds on the potato plant but also, often preferentially, feeds on hairy nightshade (Solanum sarrachoides
Sendtner).  Hairy nightshade (SOLSA) also acts as a host to PVY. GPA then spread PVY from the weed to potato plants. The objective of these studies was to determine if hairy nightshade density or growth stage when green peach aphids (GPA) and PVY-infected potato plants are present affects PVY spread in a field. This poster provides information about the materials and methodology used to conduct the studies.  In 2011, Russet Norkotah was planted in 3-row plots, 6 plants per row, 18 potato plants total per plot. A PVY-infected tuber was planted in the center of the middle row for an inoculums source. In Trial I, greenhouse-grown SOLSA were transplanted when 1- to 2-leaf at either a high or low density at potato emergence between rows 1 and 2 and rows 2 and 3. In Trial II, greenhouse-grown SOLSA were transplanted similar to Trial I at potato emergence or 20 days after emergence in order to have different height weeds at aphid placement time. A SOLSA-free control treatment
was included in each trial. Before the natural GPA flight period at the end of June, each plot was covered entirely with a cage built with mesh and PVC pipe so that no undesirable aphids could bring in PVY from outside the trial area. The first week of July, non-infected GPA were placed on the center infected potato plant. Infection had been previously confirmed with ELISA. Cages were replaced immediately after aphid placement. Approximately three weeks after placement, leaf samples were collected from all 18 potato plants and all SOLSA in each plot then analyzed with ELISA to determine whether or not SOLSA density or height at aphid placement time aided in the spread of PVY throughout the plot.  First year indications are that PVY spreads further when SOLSA greater than 8 inches tall are present than when smaller SOLSA or none are present. In the density trial, results were inconclusive most likely because all SOLSA were taller than 8 inches since they had been transplanted at potato emergence. The study will be repeated in 2012 and SOLSA in the density trial will be transplanted at 20 days after potato emergence rather than at potato emergence.

Evaluation of Risk Factors in Utilizing PPO Inhibitor Herbicides in Potato Production.  D.J. Heider^*1, J.B. Colquhoun², R.A. Rittmeyer³, ^1,2,3University of Wisconsin, Madison, WI.

Potato production has relied upon a very limited set of herbicide modes of action for decades.  In fact, metribuzin (a site of action group 5 Inhibitor of photosynthesis at phostosytem II herbicide) has been and remains the backbone of potato production in the U.S. and abroad.  In recent years, several site of action group 14 (protoporphyrinogen oxidase or PPO inhibitors) have been granted tolerances for use on potato by EPA and marketed by registrants in some production areas.  The addition of the PPO inhibitor mode of action provides potato growers with an option that is rarely utilized in crops rotated with potato, making it an excellent resistance management tool.  Unfortunately, some PPO inhibitor active ingredients are restricted from use in a number of potato production areas due to long aerobic soil half-life.  Other PPO inhibitor active ingredients have at times exhibited a propensity for unacceptable potato crop injury.  This research focused on evaluating risk factors involved in PPO inhibitor-induced injury in potato.

Potato cultivar can play a major role in herbicide tolerance.  In 2008 and 2009, 6 potato cultivars (‘Russet Burbank’, ‘Superior’, ‘Russet Norkotah’, ‘Goldrush’, ‘Shepody’ and ‘Russet Silverton’) were evaluated.  Depth to seed-piece has also been shown to play a role in PPO inhibitor potato injury.  All potato cultivars were evaluated at three depths (5.08 cm-shallow, 10.16 cm-standard, and 15.24 cm-deep) to account for variability that can occur at planting.  Six weed management treatments were evaluated pre-emergence (hand-weeded, s-metolachlor 1.064 kg ai ha^-1 + metribuzin 0.56 kg ai ha^-1, flumioxazin 0.036 kg ai ha^-1, flumioxazin 0.055 kg ai ha^-1, sulfentrazone 0.071 kg ai ha^-1, sulfentrazone 0.105 kg ai ha^-1) to all potato cultivars and seeding depths.  Immediately after application an excessive irrigation of between 7.6 and 10.2 cm was applied to simulate a worst case large rainfall event capable of leaching herbicide to the seed-piece or emerging shoot.  Each potato cultivar by seed-piece depth by weed management treatment was replicated 3 times.    

Data collection included percent injury, potato crop height, tuber set and potato yield and grade.  Few significant differences were noted in average potato height or percent injury within a potato cultivar.  In general, as expected, shallow planting increased the level of injury observed, however injury did not exceed 10 percent and persisted for only 1 to 2 weeks.  Deep planting did provide protection from herbicide injury for all treatments, but had a negative effect on tuber set and yield.  Of the six potato cultivars, ‘Superior’ was not injured in any depth or herbicide combination.  The remaining cultivars experienced minor short lived injury that increased with PPO inhibitor herbicide rate.  Injury was relatively consistent between flumioxazin and sulfentrazone across the low and high rates.  Interestingly, injury from the chemical standard of s-metolachlor + metribuzin often equaled or exceeded that observed from PPO inhibitors.  djheider@wisc.edu

Glyphosate can translocate from potato foliage to developing tubers being grown for seed and affect emergence, growth, and yield of plants growing from those daughter tubers the following year. A study using Ranger Russet was conducted in Idaho, Oregon, and Washington in 2008-09. In 2008, glyphosate was applied at 0, 8.5, 54, 107, 215, or 423 g ae/ha when potatoes were 10 to 15 cm tall, or at stolon hooking, tuber initiation, or tuber mid-bulking stages. Visible foliar injury was rated periodically after applications and the greatest injury was caused by applications at hooking or tuber initiation. No injury was visible after the mid-bulking application timing. Tubers were harvested and graded according to USDA standards then stored until planting spring 2009. U.S. No 1 and total tuber yield in 2008 was less and malformed cull yields were greater in plots which had glyphosate applied at hooking or tuber initiation compared with yields from the 10 to 15 cm, mid-bulking, or control treatments. Averaged across application times, U.S. No 1 and total tuber yields decreased in a quadratic manner as glyphosate rate increased. In 2009, twenty tubers per plots were planted, 10 of which had symptoms such as folds at the end or rough, elephant hiding, and 10 which had no symptoms. Emergence from these daughter tubers was assessed and plant symptoms ated during the season after which tubers were harvested and graded. No underground multiple, candelabra type sprouting was observed. Averaged across rates, tuber emergence was lowest when glyphosate was applied to the mother plants in 2008 at mid-bulking even though no foliar injury was observed on those mother plants. Emerged plants in these plots were chlorotic and stunted. As expected, as glyphosate rate increased, emergence decreased. The 2009, yields were affected by emergence and subsequent plant injury displayed during the season. Implications are that even though glyphosate drift or miss-application occurring during mid- to late-bulking times may not be noticed on the mother crop, the daughter tubers could be affected and seed growers would incur monetary and reputation losses.  

The IR-4 Project is a publicly funded effort to support the registration of pest control products on specialty crops.  The IR-4 Project continues to meet specialty-crop grower’s needs for weed control options despite the challenges of a mature market for herbicides and the selectivity of specialty crops to many of the more-recently-introduced herbicides.  The Pesticide Registration Improvement Act continues to effect IR-4 submissions and EPA reviews of packages. IR-4 submitted herbicide petitions to the EPA from October 2010 to December, 2011 for: EPTC on Watermelon, Citrus Fruit, group 10-10, Sunflower subgroup 20 B, Quinclorac on Rhubarb and Berry, low growing, except strawberry, subgroup 13-07H.From October 2010 through December, 2011, EPA has published Notices of Filing in the Federal Register for: Clopyralid on apple, Brassica leafy greens, subgroup 5B, Rapeseed subgroup 20A, except gold of pleasure, Paraquat on Perennial Tropical and Sub-tropical Fruit Trees; Pendimethalin on leaf lettuce, Brassica, leafy greens, subgroup 5B, turnip greens, Melon subgroup 9A, Soybean, vegetable, succulent, Fruit, small vine climbing, except grape, subgroup 13-07E; Quizalofop-p-ethyl on sorghum (grain), and Rapeseed subgroup 20A, Rimsulfuron on Caneberry subgroup 13-07A and Bushberry subgroup 13-07B; Rimsulfuron + thifensulfuron-methyl on chicory; S-metolachlor on cilantro and garden beet leaves; Sulfentrazone use on turnip, rhubarb, Wheat (PNW only), Sunflower subgroup 20B.EPA established tolerances from October 2010 to December 2011for:Dicamba +2,4-D on teff;Fomesafen on pepper (bell and non-bell), potato, and tomato; Sulfentrazone on Vegetable, tuberous and corm, subgroup 1C, Brassica, head and stem, subgroup 5A, Brassica leafy greens, subgroup 5B, vegetable, fruiting,group 8-10, melon subgroup 9A, pea succulent, Strawberry, and flax, and Triflusulfuron-methyl on garden beet.

Comparisons of Management Strategies for Poa annua on Bentgrass Putting Greens

Annual bluegrass (Poa annua L.) is an aggressive weed in managed turf. In particular, annual bluegrass reduces the aesthetics, surface quality, uniformity, and the functionality of golf course putting greens. Current practices to manage this weed in bentgrass (Agrostis stolonifera L.) putting greens rely upon plant growth regulators. However, herbicides for this use are also under development. To compare these approaches, a field experiment was conducted with various herbicide and plant growth regulator (PGR) application regimens for annual bluegrass control in a soil-based bentgrass nursery maintained at putting green height with the cultivar “L-93.” The study was initiated in April 2009 at the University Club of Kentucky, in Lexington, using a randomized complete block design of the following treatments: bispyribac-sodium (12.5 g a.i./ha), bispyribac-sodium (25 g a.i./ha), HM9930 (cumyluron) (1.2 kg a.i./ha), paclobutrazol (140 g a.i./ha or 280 g a.i./ha), flurprimidol (91 g a.i./ha or 182 g a.i./ha), flurprimidol (96 g a.i/ha) plus trinexapac-ethyl (36 g a.i./ha), and trinexapac-ethyl (96 g a.i./ha). One year after study initiation, all treatments, with the exception of flurprimidol plus trinexapac-ethyl and paclobutrazol, reduced annual bluegrass populations from the non-treated control. However, by June 2010, there were no differences in annual bluegrass populations between treated and non-treated plots. HM9930 treatments discolored bentgrass in both 2009 and 2010. Bispyribac-sodium treatments discolored the bentgrass in 2010 but not 2009. Color effects of both HM9930 and bispyribac-sodium were transitory. Trinexapac-ethyl improved bentgrass quality in 2010. The annual bluegrass population in the non-treated control increased between 2009 and 2010. In May 2011, plots treated with HM9930 in 2010 had less annual bluegrass than those treated in 2010 with flurprimidol plus trinexapac-ethyl, trinexapac-ethyl, or flurprimidol. All treatments were repeated in 2011 with the exception of HM9930. No treatments in 2011 affected creeping bentgrass color. Over the three-year study, bispyribac-sodium (12.5 g a.i./ha), HM9930, and paclobutrazol provided the best control of annual bluegrass with minimal effect on bentgrass.

Amicarbazone is a photosystem II inhibiting herbicide similar in mode of action to the triazine herbicides atrazine and simazine.  Amicarbazone has potential use in turfgrass for control of Poa annua.  However, triazine-resistant Poa annua populations have been previously identified.  Preexisting resistance to amicarbazone could potentially complicate its future use.  Research was conducted to evaluate previously identified triazine-resistant Poa annua populations to amicarbazone.  Two triazine-resistant (MS-01, MS-02) and –susceptible (AL-01, COM-01) Poa annua populations were treated with amicarbazone, atrazine, and simazine at 0.26, 1.7, and 1.7 kg ai ha^-1, respectively. Quantum yield (Φ_PSII) of Poa annua bluegrass was measured 0 to 72 hours after application (HAA) to determine the photochemical effects of amicarbazone compared to other PSII inhibitors. Neither triazine-resistant Poa annua population was controlled with amicarbazone. Quantum yield data of triazine-susceptible populations suggest amicarbazone efficiently inhibits PSII immediately following treatment. Amicarbazone inhibited PSII of susceptible populations significantly greater than atrazine and simazine 1-16 and 1-72 HAA, respectively. Amicarbazone did not reduce Φ_PSII of the MS-01 population. Amicarbazone slightly reduced Φ_PSII of the MS-02 population during several measurement timings; however, these reductions were not dramatic and were not further investigated. Sequencing of the psbA gene revealed a Ser to Gly substitution at amino acid position 264 known to confer resistance to triazine herbicides. These data indicate amicarbazone efficiently inhibited PSII of susceptible Poa annua populations; however, triazine-resistant annual bluegrass populations with Ser₂₆₄ to Gly mutations are cross-resistance to amicarbazone.

A preliminary study on a new method for the selective control of noxious creeping perennials in urban vegetation

 Misako Ito: Institute for Urban Weed Science

Kanji Ito: MicroForest Research Co. Ltd

Ao Min: Shirasaki Corporation Co. ltd

 Creeping perennials are very noxious weeds that are naturally vigorous. With the recent climate changes, these perennials have particularly increased in urban vegetation such as turfs, ornamentals in parks and gardens, and in necessary grass covers on the embankments of roads, railways, rivers, etc. They are difficult to control because of their well-developed subterranean organs, which easily reproduce new shoots. Our new idea for effectively controlling them was to inject chemicals before their emergence in winter so that bud sprouting could be prevented through the following growing season. In the preliminary study, the distributions of the subterranean reproductive organs of 8 species and the positions of sprouting thereon, and their responses to 5 chemicals were determined. The weeds tested were the following 6 rhizomatous species—Solidago altissima, Artemisia princeps, Polygonum cuspidatum, Calystegia japonica, Imperata cylindrica, and Equisetum arvense—and the following 2 species with creeping roots: Solanum carolinense and Cayratia japonica. The maximum shoot-sprouting depth was found to be approximately 40 cm in I. cylindrica, E. arvense, and S. carolinense and 20 cm in the other 5 species, assuming that most of the control targets are located in the region, wherein injected chemicals could reach, although whole subterranean organs extended to lower than 60 cm in some species. The efficacies of trifluralin, chlorpropham, dichlobenil, triclopyr, and flurprimidol for the suppression of sprouting from the subterranean reproductive organs were determined. The chemicals at 1/2, 1, and 2 times the common doses diluted with 1000 ml/m² of water were applied across the upper 15-cm layer of the potted soil, in which the segments of the rhizome or the creeping root were laid at a depth of 5 cm. Three of the 5 chemicals completely suppressed the growth of each species. The results suggested that winter injection of these chemicals would be a promising method for the selective control of creeping perennials in mixed vegetation.

One of the largest issues facing the turfgrass industry when traditional herbicides are restricted is establishing turfgrass from seed.  One of the more promising active ingredients for controlling broadleaf weeds under pesticide restrictions, in mature turfgrass, is chelated iron although it results in a severe darkening of the turfgrass and stunted growth.  The purpose of this research was to determine the safety and efficacy of a chelated iron product on newly seeded Kentucky bluegrass, perennial ryegrass and a fine fescue mix.  The chelated iron negatively affected turfgrass growth when applied 1 and 2 weeks after germination (WAG).  Perennial ryegrass was not negatively affected by the same applications.  A significant rate affect was observed with regard to weed control with the highest rates providing the best control.  Weed numbers were lowest in plots treated 2 and 3 WAG and higher in plots treated at 1 and 4 WAG for fine fescue and Kentucky bluegrass turfgrasses.  In perennial ryegrass earlier treatment resulted in lower weed numbers.  All rates and application timings had fewer weeds than the untreated control.  The results of this study show that chelated iron applied 2 or 3 WAG can significantly reduce weeds in establishing turf without severely inhibiting turfgrass growth.

Revegetation of areas where cheatgrass and leafy spurge co-occur requires control of both invaders. Imazapic is one of our most effective chemical tools for control of leafy spurge and invasive annual species, including cheatgrass. However, application rates to achieve desired weed control without damage to native species varies with site soil properties, climate, time of application, and plant community composition. We examined the efficacy of  imazapic fall applications (0 to 10 oz / acre) with low concentrations of glyphosate (6 oz / acre) for dual control of cheatgrass and leafy spurge. Native forbs and grasses were broadcast seeded across replicate treatments to fill niches vacated by weeds. Six sites that varied in soils, climate, and native and invasive plant community composition were examined.

Herbicide treatment efficacy differed between sites. Cheatgrass control decreased with canopy cover and/or surface litter. Imazapic applied at the highest rate (10 oz /acre) decreased cheatgrass and leafy spurge cover without significantly reducing native species abundance or diversity. Although native species increased in some plots, overall response to decreased weed competition was small. Seedling establishment rates were low and limited to specific sites. Our results suggest that imazapic provided effective short-term control of both species, but that seeded species recruitment or repeated imazapic treatments may be required to achieve long-term management goals.    

Yellow toadflax (Linaria vulgaris P. Mill.) has spread over hundreds of acres of rangeland in western North Dakota that were previously infested with leafy spurge.  Leafy spurge was controlled 10-20 years ago through biological and chemical means.  Given less competition, yellow toadflax has now replaced one yellow-flowered noxious weed with another.  The objective of this study was to evaluate DPX-MAT28 (aminocyclopyrachlor) for yellow toadflax control in rangeland compared to picloram.  DPX-MAT28 is an experimental herbicide being developed by DuPont for weed control in rangeland, pasture, and non-cropland areas.  Treatments were applied to 10 by 30 ft plots with a hand boom using standard small plot procedures.  Treatments were applied at the vegetative stage (Jul 25), flowering stage (Sep 11), and in late fall (Oct 16) of 2008. No other treatments have been applied.  The treatments were evaluated for percent visual control in 2009, 2010, and 2011.  Weed density was recorded prior to application in 2008 and again in 2009, 2010, and 2011.  Picloram (2 pt/A) provided 23-60% yellow toadflax visual control in 2009, but decreased to 0-10% in 2011.  Picloram reduced toadflax density 6-55% in 2009, but density gradually increased in 2010 and 2011.  DPX-MAT28 at 1.5 oz ai/A provided 90-95% yellow toadflax visual control in 2009, but decreased to 27-43% in 2011. Toadflax density was reduced 84-98% in 2009; however, density increased from 0.2-1.0 plants/ft² in 2009 to 3.1-4.9 plants/ft² in 2011.  DPX-MAT28 at 3 oz ai/A provided 98-100% visual control and reduced density 100% in 2009 and 2010.  Plants are just beginning to appear again in 2011 with 0-0.3 plants/ft².  DPX-MAT28 at 2 oz ai/A tank mixed with chlorsulfuron at 0.75 oz ai/A provided 99-100% yellow toadflax visual control in 2009, but decreased to 76-89% in 2011. Toadflax density was reduced 99% in 2009; however, density increased from 0-0.1 plants/ft² in 2009 to 0.9-1.3 plants/ft² in 2011.  Grass injury from all treatments was 6% or less in 2009, but no visual injury was observed in 2010 or 2011. 

Aminocyclopyrachlor is an auxin-mimic herbicide that was developed for invasive weed control.  Initial studies found that aminocyclopyrachlor effectively controlled several noxious weeds in North Dakota including Canada thistle [Circium arvense (L.) Scop.] and leafy spurge (Euphorbia esula L.).  The purpose of this research was to further evaluate aminocyclopyrachlor on three troublesome weeds: absinth wormwood (Artemisia absinthium L.), houndstongue (Cynoglossum officinale L.), and yellow toadflax (Linaria vulgaris Mill.).  In separate studies, aminocyclopyrachlor was applied alone or with either 2,4-D, chlorsulfuron, or metsulfuron in the spring, summer, or fall.  Visual evaluations were recorded and weed density was measured at approximately 0, 15, 30, 60, 90, 270, and 365 d after treatment.  Aminocyclopyrachlor applied in the spring at 70 or 210 g ai ha^-1 provided 24 and 95% absinth wormwood control, respectively, 12 mo after treatment (MAT).  When the same treatments were applied in the fall, absinth wormwood control averaged 98% 12 MAT.  Houndstongue control was greatest when aminocyclopyrachlor plus chlorsulfuron was applied at 70 + 28 g ai ha^-1 in the fall and averaged 96% control 12 MAT.  Yellow toadflax control with aminocyclopyrachlor varied by application date.  Aminocyclopyrachlor applied in July at 105 to 210 g ha^-1 provided 71 to 93% control, while treatments applied in September only averaged 48 to 78% control, 12 MAT.  Aminocyclopyrachlor controlled absinth wormwood, houndstongue, and yellow toadflax, however, time of application may be an important factor to achieve maximum control.  Aminocyclopyrachlor applied alone in the spring or fall provided excellent absinth wormwood control, but was best applied to yellow toadflax in the summer when plants were flowering.  The combination of aminocyclopyrachlor and chlorsulfuron applied in the fall provided excellent control of houndstongue.

Nonindigenous invasive cost the US an estimated $137 billion a year from environmental damage and losses.  Proximity to the major ports of New Orleans and Mobile, as well as, a temperate climate puts Mississippi at a high risk for the introduction of nonindigenous invasive plants.  It is estimated that nearly 20% of the species in the state are nonindigenous.

Cogongrass (Imperata cylindrica (L.) Beauv.) is a highly invasive, warm-season, perennial grass species from the Poaceae family.  It effectively chokes out other species forming dense, monotypic stands.  In Mississippi, cogongrass replaces native grasses in longleaf pine savannas, which also decreases the habitat for endangered species.

In the fall of 2010, the Environmental Protection Agency approved the registration of several herbicide products containing aminocyclopyrachlor.  Developed by DuPont Crop Protection they are marketed to combat invasive weeds at low application rates.  There are currently four products on the market, Perspective, Streamline, Viewpoint, and Imprelis.  The mode of action has recently been determined to be auxin mimic.

Field trials were established in Forrest County, Mississippi in 2010 to evaluate the effectiveness of these products in the treatment of cogongrass.  Plot size for the cogongrass was 3 by 6 meters, with subplots sized 3 by 3 m.  Two weeks prior to the initiation of the trail, the subplots were mowed to 12.7 cm.  A backpack sprayer was used to apply the herbicides to the split-plots previously determined to receive early-summer applications.  Herbicides applied were 120 + 40 g ai/ha aminocyclopyrachlor + metsulfuron methyl (Streamline) and 1% v/v MSO , 87 + 35 g ai/ha aminocyclopyrachlor + chlorsulfuron (Perspective) and 1% v/v MSO, 101 + 73 + 26 g ai/ha imazapyr + aminocyclopyrachlor + metsulfuron methyl (Viewpoint) and 1% v/v MSO, 315 g ai/ha aminocyclopyrachlor as a liquid and 1% v/v MSO, 315 g ai/ha aminocyclopyrachlor as a soluble granule and 1% v/v MSO, 140 + 1064 g ai or ae/ha aminocyclopyrachlor + 2,4-D amine and 1% v/v MSO, 140 + 280 g ai or ae/ha aminocyclopyrachlor + triclopyr ester and 1% v/v MSO, 840 g ai/ha imazapyr as a liquid and 1% v/v MSO, and 1120 g ae/ha potassium salt of glyphosate.  A 0.5 liter shaker was used to distribute 840 g ai/ha imazapyr as a granule with calibration blanks to aid in even distribution.

Evaluation of the plots began 1 month after treatment (MAT) and continued until 4 MAT.  Each plot was evaluated monthly for control.  Culm density and shoot height were evaluated at the time of application and at 4 MAT.  In the unmowed subplots, imazapyr liquid showed the significantly greatest visual control and the significantly greatest reduction in density of culms.  For the mowed subplots, there was imazapyr granule, glyphosate, and Viewpoint (imazapyr, aminocyclopyrachlor, and metsulfuron) all showed significant visual control of cogongrass.  Glyphosate and the imazapyr, aminocyclopyrachlor, and metsulfuron combination provided the significantly greatest reduction of culm density in the mowed subplots.

The results show that aminocyclopyrachlor, when paired with imazapyr and mowing, can provide an acceptable level of control for cogongrass when applied in early summer.  This will provide landowners with additional mean of combating this highly invasive plant.

Medusahead (Taeniatherum caput-medusae) is an annual grassy weed capable of invading established stands of bunchgrasses, reducing forage, and increasing the risk of fire and soil erosion. Plots were established in the fall of 2007 north of Madras, Oregon in rangeland highly infested with medusahead. Six species of bunchgrasses were planted following treatment with imazapic or imazapic + glyphosate. Grass stand establishment improved as a result of close to normal average precipitation during the 2009-2011 period.  In 2011, the most vigorous grass stands were observed in crested wheatgrass, intermediate wheatgrass, Sherman big bluegrass, and bluebunch wheatgrass, while Sandberg’s bluegrass and particularly smooth brome were unsuccessful in establishment.

Medusahead (Taeniatherum caput-medusae) is an annual grassy weed that degrades range and wildlands of the Pacific Northwest. Trials were established in 2008 near Madras, Oregon in highly infested stands of medusahead. Treatments consisted of imazapic, imazapic + glyphosate, rimsulfuron, and sulfometuron + chlorsulfuron applied in the fall of 2008. Herbicide treatments provided 99 percent control of medusahead the spring of 2009, with suppression near 50 percent during the spring of 2010. Grass injury was observed in the sulfometuron + chlorsulfuron treated plots 213 days after treatment with height reductions of 17 percent. The effects of reducing medusahead competition were still visible on crested wheatgrass in the spring of 2011. The average grass height was greater for herbicide applications with the exception of sulfometuron + chlorsulfuron.

It is generally thought that the optimalherbicide application times for Canada thistle (Cirsium arvense) control occurs at the bud to early flowering growth stage and in the fall after a light frost but prior to a desiccating frost.  These recommendations are partially based on research that indicates these are the times when carbohydrate mobilization from the Canada thistle shoots to the roots is greatest.  The objective of this research was to evaluate Canada thistle control associated with several different application times to determine which application time is most effective.  Seven studies were established at four locations in South Dakotagrasslands and pastures from 2007 to 2011.  Herbicides included aminopyralid (88 – 123 g ae/ha), aminocyclopyrachlor (123 g ae/ha), clopyralid (315 g ae/ha), and picloram (420 g ae/ha).  Application times varied among some studies, but studies generally included treatments applied in May, June, July, August, September or August, September, October, November.  In South Dakota, Canada thistle usually flowers in late June, the first light frost often occurs in mid-September, and complete desiccation from frost usually occurs around mid-October.  The magnitude of thistle control varied among herbicides, locations, and years, but trends regarding the effect of application time appeared consistent.  The optimal herbicide application time for Canada thistle control was June to August.  Although September appeared to be the best time for fall applications, control from a September application was either equal to or less than control associated with an August application.  Therefore, results from this research contradicts some previous Canada thistle herbicide recommendations as several herbicides may be most effective if applied any time from June to the end of August while control may decline prior to or after this period.  Darrell.Deneke@sdstate.edu.

Managing vegetation that competes directly for light, nutrients, and soil moisture with newly planted Douglas-fir (Pseudotsuga menziesii) seedlings is a key management concern for landowners whose goal is to maximize timber production in the Coast Range of western Oregon.  Many woody broadleaf species can compete with Douglas-fir and forest managers have expressed difficulties with effective and economical long-term management of Pacific rhododendron (Rhododendron macrophyllum) in southwest OR.  Anecdotal evaluations by industry foresters have indicated that acceptable control of Pacific rhododendron could be achieved with spring-applied applications of foliar-applied triclopyr in combination with COC or MSO compared to standard basal bark or hack and squirt applications.  Therefore, the objective of this research was to evaluate a range of foliar-applied triclopyr rates and adjuvant types to determine which combinations would provide cost-effective, foliar-applied Pacific rhododendron control.  The study site was located on privately owned timberland in Coos County, OR, that had been previously harvested using clearcut methods.  The average elevation of this location is 879 m, average slope 15%, and average precipitation more than 200 cm per year.  The experimental design was completely random with 7 treatments assigned to individual Pacific rhododendron plants.  Each treatment was replicated ten times.  Replications were permanently marked.  Treatments included triclopyr (Garlon 4™) foliar applications applied at the following concentrations:  0, 2.5, 5 and 10% solutions in combination with either NIS (Agridex Induce™) at 0.5% v:v or MSO (Premium™) at 3% v:v.  Pacific rhodendron plants were treated at the site on May 25, 2007, using a backpack sprayer.  Spray coverage was thorough enough to wet all leaves, stems and root collars of the Pacific rhododendron plants.  Visual estimates of percent plant injury were conducted monthly for the first 6 months, and then at 1 year after treatment, 1.5 years after treatment, and 2 years after treatment, with 100% representing plant death and 0% representing no identifiable control.  In addition, the height and width of living foliage was measured for each plant prior to treatment and at the subsequent evaluation dates to develop an estimate of a live to dead shoot ratio for each plant.  This ratio was used as a standard measure of control for plants which varied somewhat in size and shape. Before and after-treatment digital photos were taken of each plant so that a visual comparison could be made between treatments.  Photos of each plant were used to document any regrowth of the treated plants.  All triclopyr treatments resulted in similar results one year after the treatments were applied.  Most of the rhododendron plants experienced 100% mortality, regardless of triclopyr concentration.  The triclopyr treatments applied with NIS exhibited greater variation compared to those applied with MSO, but control was acceptable with either triclopyr and adjuvant combination.  In summary, Pacific rhododendron plants were controlled with the lowest rate of triclopyr evaluated, a 2.5% solution, applied in the spring and performance differences between the two adjuvants were not evident. 

Bamboo is a species that can escape cultivation and invade lawns, landscapes, and other areas.  Limited information is available on ways to control bamboo.  In previous field experiments by Czarnota and Derr, it was shown that bamboo could be controlled with herbicides containing the active ingredient glyphosate or imazapyr.  These experiments showed at 58 weeks after treatment (WAT), a single postemergence applications of either glyphosate or imazapyr provided 76% and 98% control, respectively.  Since then, several researchers have indicated that difficult perennial weeds could be controlled with stem injections of select herbicides.  To test this theory on an aggressive bamboo species, a stem injection experiment was designed.  A two acre thicket of Golden Bamboo (Phyllostachy aurea Carrière ex A. et C. Rivière) was chosen for the experiment.  The average cane height of Phyllostachy aurea was 40 feet and the average cane diameter was 2 inches.  On June 15, 2011 an area of the bamboo was prepared for experimental treatment.  The footprint of the experiment was 96 feet (ft.) long and 6 ft. wide.  Each plot was 6 ft. x 6ft. with a 2 ft. wide ally in between each plot and replication.  Treatments were applied on June 29, 2011.  Only two herbicides, glyphosate and imazapyr, were used in the experiment.  Treatments consisted of injecting 5 milliliters of concentrated herbicide into a ¼ inch hole that was predrilled into the top of the first long node.  Only canes over 1.5 inches were treated, and each treated stem was painted for future identifications.  After treatments were completed, ¼ inch holes were sealed with silicone.  The experiment was arranged as a randomized complete block with 4 replications.  At the 12 WAT rating, canes injected with imazapyr were dead.  Bamboo canes injected with glyphosate, at 12 WAT, were only exhibiting minor foliar damage.  Ratings are planned for 24 and 48 WAT, and it is hoped that translocation of these herbicides will be seen in canes connected to treated canes. 

Due to the strong effect white-tailed deer (Odocoileus virginianus) often have on understory vegetation, selective and heavy herbivory by deer might result in plant communities that are more susceptible to exotic plant invasion. Mid-Atlantic region study sites where deer had access or were excluded from forest plots revealed that deer presence influenced plant species abundance unevenly, with some invasive plants increasing in abundance with deer and others decreasing. We hypothesized that differential palatability could contribute to this plant species-specific response. Because deer preferences for weedy and invasive plants have not been directly tested, we conducted 16, 1-day deer preference trials using eight captive deer to test the palatability of eight exotic and seven native plant species that commonly occur in northeastern deciduous forests. Based on literature reviews and analysis of field plot data collected across the Mid-Atlantic region, we hypothesized that half of the native and half of the exotic species would be palatable to deer. We determined relative preference for the plant species according to the percentage of plant biomass consumed during the multiple-choice preference trials in late summer and fall 2011. Additionally, we used videography to record key behaviors of the deer, including sniffing and biting. Deer consumed over 80% of Celastrus orbiculatus (Oriental bittersweet), Lonicera morrowii (morrow’s honeysuckle), and Ligustrum obtusifolium (European privet) biomass, indicating high deer preference for these species. Consumption of these invasive exotic shrubs was comparable to the consumption of the highly preferred native species, Acer rubrum (red maple) and Parthenocissus quinquefolia (Virginia creeper). In contrast, very little Alliaria petiolata (garlic mustard)(16%), Microstegium vimineum (Japanese stiltgrass)(13%), and Berberis thunbergii (Japanese barberry)(7%) biomass was consumed. Videography-based behavioral data supported biomass results, with more browsing observed on preferred species. Deer likely facilitate the spread of the preferred invasive exotic shrubs in this study because they bear fleshy fruits, which were highly palatable to deer in the preference trials. Limited herbivory of the unpalatable species could explain their large spatial distribution and high abundance in the study region, where deer are thought to be overabundant. Apparent competition might be a mechanism of success for such unpalatable species. In conclusion, the preference patterns observed in this study corroborate the regional field plot data analysis, suggesting that the influence of deer on plant invasion acts at the level of plant species or plant functional group. 

    Phragmites australis, common reed, is an invasive plant that reproduces poorly by seed but regenerates vigorously by rhizomes. Because P. australis propagates well through rhizome growth, invasion often occurs from transported rhizome tissue. We investigated the amount of biomass needed to produce a plant capable of photosynthesis. We also assessed the season in which P. australis shown the highest probability of growth. Rhizomes were collected along roadside ditches near Green Bay, Wisconsin during the autumns of 2009 and 2010 and summers of 2010 and 2011. Autumn and summer were chosen because the plants were either dormant or actively growing, respectively. Rhizomes were cut so lengths that ranged between 0.5 and 25 centimeters. The fragments were grown in a greenhouse for 60 days in vermiculite with no added nutrients. Rhizomes with low biomass had the fewest emergent stems and lowest survival rate, while large rhizomes highest emergence and survival. Small fragments—as short as 4.0 cm and 3.03 g—were able to produce plants capable of photosynthesis. Rhizomes collected in the fall also had a significantly higher survival rate (71.07%); however, there were no seasonal differences in the subsequent biomass produced by the surviving plants. There were no differences in stomatal conductance between the seasons or any correlations with initial rhizome size. Large rhizomes produced taller plants with more biomass. This study shows that, under optimal greenhouse conditions, a rhizome fragment with a length ≥4 cm is capable of producing a stem and that both size and season affect the ability of rhizomes to regenerate. By understanding the reproductive biology of P. australis, land managers can develop an integrated weed management program to control this weed and will have a greater awareness of the viability of rhizome fragments and their establishment risks.

Invasion and partial homogenization of Central Texas grasslands by the C₄ grass KR Bluestem (Bothriochloa ischaemum) has resulted in negative ecological impacts in both managed and natural grasslands.  Reduced native species diversity of these grasslands has been primarily attributed to selective grazing by cattle, which reduce abundances of high forage value native species relative to KR Bluestem.  In previous studies, however, we found evidence to suggest that other animals may feed preferentially on indigenous grass foliage and seeds.  This study is designed to assess the role of herbivory and granivory as potential determinants of the competitive dynamics between KR and native grasses and subsequent homogenization of central Texas grasslands.  Hadrotettix trifsciatus (Three-banded grasshopper) and Aramdillium vulgare (common pill bug) were selected as our focal invertebrates.  These species were assumed to be likely candidates as they are found in great abundance in local grasslands and are known to be large consumers of grass foliage and/or seed. Various experimental feeding trials were performed both in the field and lab to assess preference and extent of feeding of these two invertebrates.  The trials also served in the development of our experimental protocols.  Neither H. trifsciatus nor A. vulgare readily consumed grass seeds of any species under either field or lab conditions.  Nonetheless, H. trifsciatus exhibited intense herbivory on live grass plugs of both invasive and native species and lower rates of herbivory on clipped foliage, suggesting that future studies should be conducted on live forage. A field study was also conducted testing the effects of partial and complete exclusion of small grassland consumers on the plant species establishment and distribution patterns of a KR dominated grassland. Results suggest that a higher exclusion level of small consumers promotes increased forb plant success, while lower levels of exclusion may increase KR success and lower forb presence. The overall results of these studies suggest that granivory from H. trifsciatus and A. vulgare do not affect competition between KR Bluestem and native grasses. The seasonal timing of the consumption preferences in both the field and lab studies may be another determining factor, especially when assessing granivorous feeding, as most central Texas grasses flower and fruit in the fall.  Future research will utilize research protocols developed here under fall field condition to determine the role of these invertebrate consumers in central Texas grassland ecosystems.

Yellowflag iris (Iris pseudacorus L.), native to Europe, is a rhizomatous emergent invasive found in pond margins, ditches, and other wetland sites in much of the United States. In water depths up to ~50 cm, it forms dense stands which displace native sedges and rushes, reducing waterfowl habitat and water flow. In a pond with a shallow depth gradient, yellowflag iris may form a perimeter band 6 to 12 m wide. Yellowflag iris reproduces both by seeds, which disseminate by floating, and vegetatively through rhizome fragmentation. The rhizomes, which can reach 6 m in lateral spread, make it very difficult to eradicate yellowflag iris by mechanical methods. Accessing a yellowflag iris infestation for making boom herbicide applications is often difficult due to its height and density, and because it grows in shallow water and mud. In addition, aerial applications would be impractical or harmful in many natural and ornamental settings. Drizzle application is a technique developed at the University of Hawaii for directed treatment of hard-to-reach invasive plants along forest trails. In this technique, low volumes (2 to 5 gpa) of concentrated herbicide solution are applied using a spray gun with a fine orifice disk. The spray gun puts out a thin stream of solution with an effective range of 6 m. Advantages of this technique include reduced drift due to larger droplet size, easier access to difficult-to-reach treatment sites, and low application volumes which require fewer tank refills, resulting in significant savings in labor costs. Because the drizzle technique allows treatment from a distance, it shows potential for treatment of emergent pond weeds. However, this technique is usually used as a directed treatment on individual plants. Yellowflag iris grows in dense stands, necessitating a broadcast type application. In this study, we evaluated whether drizzle applications could provide sufficient coverage for control of yellowflag iris. In fall 2008, we tested three herbicides in a yellowflag iris infestation in a pond at the University of California, Davis. We used a conventional boom on an extended wand to make broadcast treatments and compared these with two drizzle treatments. Broadcast and drizzle treatments included Competitor surfactant at 1% and 30% v/v, respectively. Plots were 3 m wide (along the shore) and extended from the water’s edge to the deepwater limit of the infestation (<6 m). In evaluations in spring 2009, we found that a drizzle treatment using imazapyr (Habitat, 20%, 5.5 gpa) reduced yellowflag iris cover from 92% to 0.7%. This was as effective as 100 gpa boom treatments with imazapyr (1% to 3%) and was faster and easier to apply, particularly at the deepwater edge of the stand. Boom treatments with glyphosate (Rodeo, 2% to 4%) or triclopyr (Garlon 3A, 4%) were less effective, as was a drizzle treatment with glyphosate. In fall 2010, we established similar plots in an adjacent pond.  In this second trial we compared drizzle applications of glyphosate and imazapyr at several rates and volumes. Imazapyr (Habitat, 10% to 20%, 2.5 to 10 gpa) consistently reduced yellowflag iris cover by 98% to 99%, with little to no effect on native cattails. Glyphosate (Rodeo, 20%, 5 and 10 gpa) reduced cover by 96%. The low end of rates for each chemical was within the maximum permissible rate per acre. Results from this study demonstrate that drizzle application is a practical application method for control of yellowflag iris. In addition, imazapyr was shown to be the most effective control option for this species. These results suggest that drizzle application may be an efficient option in other large patch situations where broadcast treatment with a conventional boom sprayer is problematic.

Natalgrass (Melinis repens (Willd.) Zizka) is an annual grass species native to Africa that is invasive in Florida and many tropical and sub-tropical regions throughout the world.  Management of natalgrass is a growing concern for land managers and interest in restoration of native plant communities increases.  Little research is available about the chemical control of this species, so a greenhouse study was initiated to address this need.  Herbicides were tested in the greenhouse to determine potential for control of natalgrass pre- or post-emergence.  Herbicides were applied to pots of field soil with natalgrass seeds scattered on the surface (pre-emergence study) or to mature natalgrass plants (post-emergence study).  Herbicides were applied with a backpack sprayer at 0.0625, 0.125, 0.25, 0.5, 1, 2 and 4x rates and included imazapic, imazapyr, imazamox, hexazinone, sulfometuron, metsulfuron, metolachlor (pre- only), pendimethalin (pre-only), fluazifop (post- only), and glyphosate (post- only).  For the pre-emergence study, above-ground biomass was harvested 10 weeks after treatment (WAT) and compared to the control.  For the post-emergence study, plants were harvested 5 cm above the soil surface 2 WAT, and again at 10 WAT.  The latter biomass harvested was compared to the regrowth harvested from the control.  Nonlinear regression was used to develop dose-response curves for each herbicide, and I₅₀ and I₉₀ values were calculated to determine the herbicide rates necessary to reduce natalgrass biomass by 50 percent and 90 percent, respectively.  Metsulfuron does not appear to be a viable option for natalgrass control; the rate required to reduce natalgrass biomass by 50% is much greater than the maximum labeled rate.  Hexazinone offered inconsistent control.  Imazapyr, imazapic and imazamox did not provide the highest levels of control observed, but did appear to severely stunt emerging seedlings.  Many native grass species in Florida are tolerant of these compounds, suggesting that these herbicides might be an option for land managers in that area.  Sulfometuron provides moderate control at labeled rates, but required greater than the maximum labeled rate to provide 90% control.  Metolachlor and pendimethalin both provided excellent control of natalgrass within labeled use rates.  Glyphosate also provided good control of natalgrass plants, but is non-selective and might give natalgrass seedlings emerging after treatment a competitive advantage by eliminating competing native plants.

The WeedOlympics was the first national weed science contest engaging student members of the NorthEastern Weed Science Society (NEWSS), the North Central Weed Science Society (NCWSS), the Southern Weed Science Society (SWSS), and the Western Society of Weed Science (WSWS).  A total of 137 graduate and undergraduate students from across the United States and Canada participated in this event hosted at the University of Tennessee (Knoxville, TN) on July 26th - 27th, 2011.  This national competition involved a series of events in which students were challenged in weed identification, herbicide identification, sprayer calibration and field problem solving.  At the national level, the top graduate team was from Purdue University; members were Jared Roskamp, Ryan Terry, Chad Barbham, and Paul Marquardt. The top undergraduate team at the national level was the University of Guelph Team; team members included Thomas Judd, Adam Parker, Michael Vanhie, and Jessica Gal. The overall national winners in the individual graduate and undergraduate competition were Jason Parrish from The Ohio State University and Dan Tekiela from Virginia Polytechnic Institute, respectively.   Distinguished WSSA members Garry Schnappinger (NEWSS), Cal Messersmith (NCWSS), Jim Bone (SWSS), and Robert Norris (WSWS) spoke at the awards banquet on the history of each regional weed science society and their respective student contests.  The current president of each regional society presented winning students with awards at the regional level.  Thank you to all the student contestants, coaches, and volunteers who made the first WeedOlympics possible.

Migrating extension education materials to dynamic web-based platforms is important to engage traditional and new audiences.  The Guide for Weed Management in Nebraska, publication EC130, is a successful annual print publication produced by the weed science faculty at the University of Nebraska-Lincoln.  Through a grant from the North Central IPM Center, a dynamic online platform was created to display content from the Guide for Weed Management in Nebraska.  The goal of the project was to create sortable herbicide efficacy ratings for many common weeds along with use recommendations, weed photos and biological information and label links.  The application provides information for corn, soybeans, wheat, sorghum, and alfalfa grown in Nebraska.  Herbicide efficacy ratings and use recommendations are stored in a MSSQL database.  Users access the information through a Flash interface which uses Adobe ColdFusion to dynamically populate the tables with database information.  The application allows users to 1) drag the weed columns in any order by clicking, holding, and dragging the column header left or right to the desired location, 2) click once on the weed column header to re-order the herbicide list from highest to lowest efficacy, 3) click on the herbicide name to view detailed information with use recommendations and a direct link to the label at CDMS.net, and 4) click on the camera icon in the weed column header to view identification photos and additional information about each weed species.  The application may be accessed at http://weedscience.unl.edu/WeedTables/index.html.

Have you ever spent time looking for a photograph of a weed that you know you took but cannot remember where the file is?  If the answer is ‘yes’ you should consider the advantages of using a photographic database manager.  Most programs for looking at photographs on a computer are file viewers, not database managers. This means that the user has to know where the files are located that you want to look at.  Once you have more than a few hundred files this can be time consuming.  Many professional photographers now use a program called ‘Lightroom^®‘ to keep track of their files. It provides a useful way to organize, and locate, weed (any plant actually) photographs quickly and flexibly without having to know where the file is actually stored. Once the database has been set up using a system of ‘collections’ and ‘tags’ it is possible to retrieve a specific plant photo in a few seconds from a database of many thousands of files (mine is currently at nearly 40,000 files).  It is easy to locate all photographs within a family, a genus, or of a single species.  If the necessary tagging has been entered all that is required is to type the common or Latin name of the plant in the search engine, and within a second or two the photographs of the selected species are displayed. Photographs can also be retrieved by parameters such as date, location, habitat, or altitude. All of this ability depends on entering the photograph files into the database, along with adding the necessary ‘tags’; this can be time consuming for existing photographs, but is relatively quick for new photographs as they are added to the database.  The tagging codes that I have developed for organizing plant photographs are presented and discussed.

Dow AgroSciences is committed to stewardship of the Enlist™ Weed Control System.  Enlist Duo™ featuring Colex-D Technology™ will be a new herbicide solution with reduced potential for drift and low volatility of 2,4-D.  The types of nozzles used in an application will also greatly impact the potential for drift.  Dow AgroSciences will provide comprehensive stewardship guidance for deploying this technology system along with recommendations for the types of nozzles to use that reduce potential for drift. 

In 2011, field research trials were conducted under two separate protocols to evaluate crop tolerance and weed efficacy results using XR TeeJet^©, TurboTeeJet^©, AIXR TeeJet^© and TurboTeeJet^© Induction spray nozzles delivering spray droplet sizes ranging from fine to ultra coarse.  In the crop response study, these nozzles were used to apply the high- end 2X use rate of the lead premix formulation of new 2,4-D choline + glyphosate, plus or minus  2.5% v/v AMS at 7.5 and 15 gallons per acre spray volume over-top Enlist™ corn stacked with SmartStax^® and Enlist soybean stacked with glyphosate tolerance.  Likewise, these nozzle types at 10 gallons per acre spray volume, were used to apply multiple, sub 1X to low- end 1X use rates of the new 2,4-D choline+glyphosate premix, to evaluate the effect of drift reducing nozzles on weed control over-top Roundup Ready^® 2 Corn.  Results from these trials support previous technical assumptions that nozzle tip selection criteria for reduced drift can be obtained without effect on crop tolerance or weed control. 

 ™ Enlist, Enlist Duo and Colex-D are trademarks of Dow AgroSciences LLC.  Components of the Enlist Weed Control System have not yet received regulatory approvals; approvals are pending. Enlist Duo herbicide is not registered for sale or use. The information provided here is not an offer for sale. Always read and follow label directions.^©2012 Dow AgroSciences LLC

 ^© XR TeeJet, TurboTeeJet, AIXR TeeJet and TurboTeeJet Induction are trademarks of Spraying System Co.

SmartStax^® multi-event technology developed by Monsanto and Dow AgroSciences LLC.

Roundup Ready^® Corn 2,  SmartStax and the SmartStax logo are trademarks of Monsanto Technology, LLC

Dow AgroSciences is committed to stewardship of the Enlist™ Weed Control System.  Enlist Duo^TM herbicide featuring Colex-D^TM technology will be a new herbicide solution with reduced potential for drift, ultra low volatility and reduced odor.  A key component of Colex-D Technology is new 2,4-D choline.  Qualitative and quantitative laboratory studies have been reported that clearly show lower volatility of 2,4-D choline compared to 2,4-D ester and 2,4-D dimethylamine formulations (DMA).  Large 0.5-5.5 acre field studies using both quantitative and qualitative methods have validated the laboratory studies.  For demonstration and training of sales representatives, growers, dealers and applicators, it is desirable to develop reproducible small plot methodology for comparing performance of various formulations.

Previous work at Dow AgroSciences has shown that the use of plastic row covers, referred to as low tunnel structures, will trap volatile emissions from treated surfaces, concentrate the vapors close to the row crop canopy and demonstrate the volatility effects of different formulations on susceptible plant species.   Moveable low tunnel structures were constructed with ½” metal electrical conduit and 1 inch by 4 inch by 12 ft sideboards.   A 5 ft long conduit was bent at 90 angles to result in 18 inch tall by 24 inch wide “u-shape”.  The bottoms of five conduit u-shapes spaced 3 ft apart were connected to the inside of two boards.  Clear, 1 mm plastic was stretched over the structure and attached to the conduit with ½ copper tubing hangers.  Flats (10.5 x 21 x 2.5 inch) filled with sand were treated with herbicide at a location at least 1000 ft from the cotton field to avoid any potential physical drift.  Applications were made with a back pack CO2 sprayer with three TT11002 nozzles spaced at 20 inches delivering 15 GPA. 

A series of experiments were conducted in 2011 to evaluate various factors in the experimental design to optimize results.  The first experiment evaluated crop injury resulting from 2,4-D DMA applied at 1120, 2240 and 4480 g ae/ha.  After application, three treated flats were placed in the center of a 24 ft by 30 inch low tunnel structure in two reps.  After 48 hours the low tunnels and flats were removed.  A second experiment evaluated the impact of the length of exposure (24 vs 48 hours) on crop injury for 2,4-D DMA at 2240 and 4480 g ae/ha.   A third experiment evaluated the effect of area treated by comparing 3 flats treated with 2,4-D DMA at 2240 g ae/ha to 1.5 flats treated with 2,4-D DMA at 4480 g ae/ha and 3 flats treated with 2,4-D DMA at 4480 g ae/ha.  A fourth experiment evaluated the effect of soil type (silty clay loam vs sand) on volatility injury from 2,4-D DMA.  In the fourth experiment, plots were 2.5 x 12 ft with a single treated flat placed in the middle of the plot.  Results from these experiments show that 2,4-D DMA rate has minimum impact on level of injury under these conditions and that most of the injury results from volatility that occurred in the first 24 hours.   The treated area can be minimized as long as the total amount of product applied is the same as that applied to larger area.   Injury to cotton from volatility of 2,4-D DMA was not significantly impacted by the soil type.  Results from these experiments validate the use of low tunnel structures to assess 2,4-D volatility on susceptible crops.

^™ Enlist, Enlist Duo and Colex-D are trademarks of Dow AgroSciences LLC.  Components of the Enlist Weed Control System have not yet received regulatory approvals; approvals are pending.   The information provided here is not an offer for sale. ©2012 Dow AgroSciences LLC.

The US EPA will soon implement a new Drift Reduction Technology (DRT) program which would allow farmers and applicators to reduce the size of buffer zones required on some herbicide labels. DRT will need to be certified through the use of spray particle analysis or field trials proving a reduction in driftable fine droplets. Winfield Solutions has a history of expertise and efforts in training growers and applicators on spray application. In 2011, Winfield Solutions trained over 10,000 growers and 600 custom applicators. The impending DRT program will require an expanded need for the use of high and low speed wind tunnels with the ability to do laser particle analysis. Today, only the University of Nebraska has plans to fulfill those needs. In 2011 Winfield Solutions completed the construction of a state of the art low speed wind tunnel utilizing a Sympatec laser diffraction particle analyzer. This unit will be able to test a variety of herbicide active ingredients, adjuvants, nozzles and combinations of these to evaluate potential off-target movement. This poster will display pictures, uses and some results from this new system.

The use of herbicide tank mixtures by growers and applicators has greatly increased recently. Tank mixtures are being used to save time and improve efficiency, convenience, yields and profitability. High crop prices and weed resistance are also contributing factors. The tank mixtures that growers and applicators are attempting to use have increased in complexity.  Herbicides are commonly mixed with additional herbicides, insecticides, fungicides, adjuvants, NPK fertilizers, micronutrient fertilizers, plant growth regulators, growth enhancers and other products.  Adjuvants include non-ionic surfactants, ammonium sulfate, water conditioners, drift reduction aids, petroleum based oils, vegetable oils, pH adjusters and other types.  Many new herbicides are updated formulations such as soluble concentrates or encapsulated. There have been many instances where tank mixtures were tried with undesirable results. Problems can include physical or chemical incompatibility, antagonism of the herbicide by other herbicides, fungicides, or micronutrients.  There can also be antagonism of the micronutrient by the herbicide.  Tank mix partners may change the pH and reduce the activity of the herbicide. Winfield Solutions has evaluated the physical and chemical compatibility of hundreds of herbicide mixtures with other herbicides and various insecticides, fungicides, micronutrients and adjuvants.  Many tank mixtures were compatible and many were not.  

Formulation of the herbicide can be critical to the successful use of a tank mixture. Choosing the right formulation of 2,4-D when mixing with other herbicides or fertilizers is critical to ensure compatibility and the ability to apply the mixture. Several different formulations of 2,4-D herbicide were tested for compatibility and performance with various herbicides, fertilizers and other tank-mix products. The formulations tested included 2,4-D butoxyethyl ester, 2,4-D 2-ethylhexyl ester, 2,4-D dimethyl amine salt, and AGH 09008, a novel 2,4-D acid. AGH 09008 will be marketed by Winfield Solutions, LLC as Rugged™ herbicide. AGH 09008 contains 3.49 pounds of 2,4-D acid per gallon.  The 2,4-D formulations were tested for compatibility with several glyphosate formulations. AGH 09008 and the 2,4-D ester formulations were compatible with all glyphosate formulations including the K-salt and dimethyl amine salt. Precipitates formed when 2,4-D dimethyl amine was mixed with K-salt glyphosate. The various 2,4-D formulations were also tested with 28% and 32% UAN solutions as the spray carrier. The UAN solution temperature was -1º C at the time of mixing. Precipitates formed immediately when the 2,4-D dimethyl amine formulation was poured into the 28% and 32% UAN.  The precipitate formed into a thick layer that could not be dissolved with agitation. The AGH 09008 and the 2,4-D ester formulations did not form any precipitates when mixed with 28% or 32% UAN.  The AGH 09008 and 2,4-D ester UAN mixtures did not have any separation 4 hours and 24 hours after mixing. The AGH 09008 plus UAN mixtures had a few crystals in the mixtures when evaluated after seven days. The 2,4-D ester formulations in UAN mixtures had a dark layer on the top of the mixtures when evaluated after seven days. The 2,4-D UAN mixtures were agitated after seven days. The 2,4-D plus UAN mixtures that contained AGH 09008 or the 2,4-D ester formulations were capable of being applied with a sprayer. The 2,4-D dimethyl amine plus UAN mixtures were not capable of being sprayed due to the precipitate that had formed. AGH 09008 and certain 2,4-D ester formulations provide greater benefit to the user than dimethyl amine formulations when glyphosate and UAN compatibility are required.

The demand for increasingly complex tank mixtures will continue to increase.  Manufacturers of pesticides, adjuvants, and other tank mix partners should consider tank mixtures when designing, testing and developing products.  Growers and applicators will need to make tank mixtures with greater care.  Communication of information about tank mixtures needs to improve.

The timing of herbicide application and nitrogen fertilization often coincide for winter wheat in the spring.  Applying herbicides with 28% urea ammonium nitrate (UAN) as the spray carrier can save time and money.  However, 28% UAN combinations with certain herbicides have been shown to cause injury to wheat and there are concerns that this injury may result in lower wheat yields.  Therefore, the objectives of this study were to determine the effects of combinations of 28% UAN at 50 or 100% spray carrier with different herbicides on crop injury and yield.  This study was conducted for three seasons, fall 2007- summer 2010.  The herbicides: 1) 2,4-D amine (0.56 kg ha^-1) 2) 2,4-D ester (0.56 kg ha^-1), 3) thifensulfuron (13 g ha^-1) & tribenuron (13 g ha^-1) (Affinity BroadSpec) + surfactant (0.25% v/v), and 4) pyrasulfotole (30 g ha^-1) & bromoxynil (170 g ha^-1) (Huskie) + surfactant (0.25% v/v) + 28% UAN (0.28 L ha^-1) were applied in the spring when winter wheat was at Feeke’s stage 4 to 5 with three different spray carriers. The spray carriers were water, a 50:50 ratio of water and 28% UAN (30 kg actual N ha^-1), and 100% 28% UAN (60 kg actual N ha^-1).  All plots received the same fertility program of 110 kg actual N per ha, between urea applications in mid-March and the remainder of N applied as 28% UAN, within 3 days of the herbicide applications. Thifensulfuron & tribenuron was the only herbicide treatment that showed any signs of injury (<5%) when water was the carrier, 1 week after treatment (WAT). Using 28% UAN (100%) as the spray carrier for the thifensulfuron & tribenuron and pyrasulfotole & bromoxynil treatments resulted in the greatest damage (~20%) to wheat, 1 WAT. Reducing the 28% UAN spray carrier amount to a 50:50 water:28% UAN mixture resulted in less injury from both of these herbicides, but it was still significantly higher than when they were applied with water as the carrier. Nitrogen (28% UAN) as a spray carrier had very little effect on wheat injury from 2,4-D amine or ester applications. For all herbicides, spray carrier composition had no effect on wheat injury, 2 WAT. However, there were some differences among the herbicides at this timing. Thifensulfuron & tribenuron was the only herbicide treatment that still had some signs of injury (5%). With some treatments, early-season wheat injury was not the best predictor of wheat yield. At the 0.05 significance level, there were not any differences in wheat yield with any of the herbicide-spray carrier combinations. However, at a 0.10 significance level, the thifensulfuron & tribenuron and pyrasulfotole & bromoxynil treatments resulted in yields that were significantly lower than the highest yielding treatment. These treatments were also the treatments where we observed the greatest injury. The use of the full rates of surfactant may have contributed to the lower yields of the thifensulfuron & tribenuron and pyrasulfotole & bromoxynil treatments when applied with 100% 28% UAN. Lowering the surfactant rate with these treatments may help alleviate some of these concerns.

Dow AgroSciences is committed to stewardship of the Enlist™ Weed Control System.  Enlist Duo^TM herbicide featuring Colex-D^TM technology will be a new herbicide solution with reduced drift potential, volatility, and odor.  A key component of Colex-D Technology is a new 2,4-D choline + glyphosate formulation with patent-pending technology designed to reduce off-target particle movement under typical application conditions.  In laboratory studies, the amount of spray particles <141 µm generated from an application of GF-2726 was reduced by 45% compared to the tank-mix combination of 2,4-D dimethylamine (DMA) + glyphosate DMA using broadcast nozzle tips producing a medium droplet size, based on the American Society of Agricultural and Biological Engineers (ASAEB) S572.1 standard.  In a wind tunnel study, the treatment with the same formulation and nozzle tip set up created a 57% reduction in amount of spray solution airborne at 2 m from the spray solution release location.  Reduction in airborne spray of GF-2726 was 73% less than the 2,4-D DMA + glyphosate DMA treatment when using nozzle tips that produce coarse/very coarse droplet in this wind tunnel study.  A large-scale field study, using standards established by the International Organization for Standards (ISO) and ASAEB, was conducted in Nebraska using commercial application equipment (John Deere 4730).  Three different droplet sizes were evaluated using a 140 L/ha spray delivery volume. The greatest reduction in off-target drift resulted from application of GF-2726 through coarse droplet nozzle tips.  Drift reduction was > 90% compared to drift of 2,4-D amine DMA + glyphosate DMA applied with medium droplet nozzle tips.  Laboratory, wind tunnel and field research results consistently supported superior reduction in the particle drift achieved with the new 2,4-D choline + glyphosate formulation.

 ™Enlist, Enlist Duo, and Colex-D Technology are trademarks of Dow AgroSciences LLC. Components of the Enlist Weed Control System have not yet received regulatory approvals; approvals are pending.  The information presented is not an offer for sale.  Enlist Duo is not yet registered for sale or use as part of the Enlist Weed Control System. Always read and follow label directions. ©2012 Dow AgroSciences LLC

Soil moisture is one of the main environmental factors affecting germination and survival of seedlings. In this study, effects of excessive soil moisture condition on seedling emergence of summer annual weeds (four wetland and eight dryland weeds) were evaluated to test@the hypothesis that seedling emergence of wetland weeds is increased but that of dryland weeds is reduced by an excessive soil moisture condition.

Seeds were buried in plastic boxes 123cm wide, 75cm long and 55cm deep, and the boxes were placed in two locations of varying soil water levels: the moist location, where groundwater level of the boxes was 10 cm below the soil surface, and the control location, where the boxes were placed upland. Experiments were conducted in the course of two years, one in 2010 and the other in 2011, and the seedling emergence was observed from April to November of both the years.  

In the 2010 experiment, moist treatment increased seedling emergence of four wetland and three dryland weeds. In contrast, in the 2011 experiment, increased seedling emergence was not observed, except for one wetland weed. Moist treatment actually reduced seedling emergence of one wetland and four dryland weeds. In general, this study did not support the hypothesis. However it is speculated that effects of excessive soil moisture condition on seedling emergence would depend on the degree of dormancy. The level of dormancy of seeds in the 2010 experiment were lower than that in the 2011 experiment because the 2010 experiment had seeds that were collected in 2006, 2007 or 2008 from a field and stored at 5°C, and the 2011 experiment had seeds collected only in 2010.

Seeds developing at different heights within the parent plant canopy may experience different   environmental conditions during maturation.  This can lead to variations in the germinability of seeds after they enter the seedbank.  In field and laboratory experiments, we investigated the possible effects of varying light microenvironment on seed germination using jimsonweed (Datura stramonium L.) and common cocklebur (Xanthium strumarium L.) grown in mixture with corn.  Following canopy closure of corn at 80 days after planting, light intensity and the red to far-red [R: FR] ratio were measured in the canopy at 15-day intervals.  Three canopy layers were sampled for jimsonweed (90-130, 131-180,181+ cm) and four layers sampled for common cocklebur (0-110, 111-150, 151-180 and 181+ cm) based on height of the first capsule or bur produced and maximum potential height of each species.  Jimsonweed capsules and common cocklebur burs were collected at physiological maturity of corn in all treatment plots.  Seeds from the different treatments were then placed in Petri dishes (25 seeds of jimsonweed) and (20 seeds of common cocklebur) and moved to a growth chamber set at 32/26 C (light/dark) for 2 weeks under a16/8 h photoperiod.  There were three replicates of each treatment combination.  Germination of seeds was recorded every other day.  For jimsonweed, the highest germination (74% ± 7) was recorded for seeds collected from the lowest canopy layer (90-130 cm) which received the least photosynthetically active radiation (PAR). Germination levels for this species decreased (63% ± 2) with increasing height of the canopy layer (131-180 cm), but increased again (66% ± 1) for the highest canopy layer (181+ cm).  Given that jimsonweed seeds exhibit physical dormancy because of a hard seed coat, it is possible that seeds produced under lower light availabilities within the lower canopy resulted in seeds with thinner seed coats that were more likely to germinate.  However, the indeterminate growth pattern of this species at the highest canopy level may have resulted in seeds with more permeable seed coats which would have facilitated germination.  A different trend was observed for common cocklebur seeds as germination was lower for seeds harvested from the two lower canopy layers (0-110 and 111-150 cm) where PAR was substantially lower than the two upper canopy layers.  As with jimsonweed, common cocklebur seeds produced under more light limiting conditions within the lowest canopy layer, may have produced seeds with thinner seed coats thus increasing their ability to  germinate (3% ± 0.5) compared with seeds from the second canopy layer (2% ± 0.3).  However, germination was highest (10% ± 2) for seeds collected from the third canopy layer (151-180 cm).  Seeds produced at the highest canopy layer of 181+ cm had lower germinability (2% ± 1.2) than seeds from the third canopy layer largely because seeds may have been immature and/or had thicker seed coats from the higher PAR levels available. These findings are consistent with the seed biology of common cocklebur in which fruits (burs) of this species typically contain two seeds of differing size and exhibit both physical and physiological dormancy (light sensitivity).  The smaller seed is strongly dormant and very light sensitive germinating well under the high R: FR light experienced within the third canopy layer (151-180 cm) in this experiment.  The larger seed is relatively light insensitive but has a hard seed coat that may prevent germination.  Understanding differences in the germinability of seeds produced at different canopy heights as determined in this study can more effectively guide the proper timing of weed management strategies such as cultivation and herbicide application.fk226@cornell.edu.

Compost can increase the sustainability and productivity of cropping systems by building soil organic matter and improving soil quality. However, organic amendments such as compost may influence weed growth, seed production, and seed mortality. A field experiment established in 2010 in Lakeview, MI investigated the effect of compost on weed seed production and seed survival in a potato cropping system. Cured dairy compost was applied at 0, 4, or 8 t C ha-1 in April and incorporated to a 10-cm depth. Hairy nightshade (SOLSA), giant foxtail (SETFA), and common lambsquarters (CHEAL) were transplanted in June into the potato field and competition of individual weed species was evaluated across compost rates. Weeds, including seeds, were harvested in September prior to senescence, cleaned, and air dried, and seed production per g of weed biomass calculated. One hundred seeds of each weed species from each of the composted field plots (maternal environment) were buried in 7 x 7 nylon bags at a 5-cm depth in the weed-free plots that received 0, 4, or 8 t C ha-1 of compost in April. Soil enzyme activity was measured monthly, and seed bags were removed 9 months after burial to determine seed retention, mortality, and dormancy. The experiment was a split-plot completely random design, with burial environment as the whole plot and maternal environment and species as sub-plot effects. Data was subjected to analysis of variance with p<0.05 indicating significance. The maternal environment (compost rate) did not affect seed production, initial seed viability, or innate dormancy of any weed species. Initial viability was 89, 98, and 94% for CHEAL, SETFA, and SOLSA, respectively; innate dormancy was 99, 59, and 98% for CHEAL, SETFA, and SOLSA, respectively. Cellulose degrading enzyme activity, important for seed coat destruction, was greatest in plots amended with compost. However, chitin degrading enzyme activity was greater in composted plots which may have reduced fungal populations and decreased seed decay. Conversely, lignin and phenol degrading enzymes, which can destroy seed defense mechanisms, were least active in composted plots. These differences may have resulted in no relationship of soil enzyme activity to weed seed mortality. The number of seeds retained in the seed bags following nine months of burial did not differ due to the maternal or burial environment; retention of CHEAL, SETFA, SOLSA seeds in berries, and SOLSA seeds alone was 88, 72, 99, and 71%, respectively. As the compost rate in the maternal environment increased, SOLSA seed mortality decreased. Conversely, SETFA seed mortality increased as compost rate increased; CHEAL seed mortality was not influenced by maternal environment. SOLSA seed dormancy was unchanged after burial, CHEAL dormancy slightly decreased (5%), and SETFA dormancy increased by 30%. This suggests that a number of SETFA seeds fatally germinated during the burial period, which resulted in a greater percentage of dormant seeds remaining. Seed mortality and dormancy within a species was not affected by burial environment. Compost did not affect weed seed production, viability, or innate dormancy; however, the maternal environment influenced seed mortality to a greater extent than the burial environment. Maternal effects on weed seed fate varied by species, suggesting that soil amendments may influence weed seed persistence in farm fields.

Common ragweed (Ambrosia artemisiifolia) is a common weed throughout South Dakota.  A glyphosate resistant biotype was identified in South Dakota in 2008 in a no-till field and is now suspected in several other fields.  When glyphosate resistant weed populations increase in no-till fields, some people switch to tillage to better manage the weeds.  The objective of this study was to determine how common ragweed seed placement in the soil affects the seed bank longevity.  Common ragweed seed burial studies were established in Brookings (eastern SD) and Highmore (central SD) in October, 2008 and seedling emergence was measured in 2009, 2010, and 2011.  In 2008, approximately 1,000 common ragweed seeds (73% viability based on a tetrazolium test) were placed with field soil in a 10 cm diameter PVC pipe 5 cm deep.  Treatments included 5 pipe segments placed on the soil surface with the common ragweed seed placed on the soil surface within each pipe (to replicate no-till), 5 pipe segments placed on the soil surface with common ragweed seed mixed in the soil within each pipe (to replicate chisel plowing), and 25 pipe segments buried approximately 30 cm below the soil surface with common ragweed seed mixed in the soil within each pipe (to replicate moldboard plowing).  To keep the seed and soil mixture within the pipe segments, 0.6 cm wire mesh was attached to the bottom of the pipe segments that were placed on the soil surface or to the top and bottom of the pipe segments that were buried below the soil surface.  The surface pipe segments and five buried pipe segments from the Brookings and Highmore locations were transported to Brookings, SD in April of 2009, 2010, and 2011 to facilitate periodic weed emergence counts.  The pipe segments were returned to their original locations in the soil in November of each year.  Each year, five additional buried pipe segments were exhumed for annual weed emergence monitoring to determine how the duration of seed burial affects germination.  Results were generally consistent between the two locations except seed losses associated with the seeds placed on the soil surface were greater at the Brookings location than the Highmore location.  Only about 2% of the viable seeds placed on the soil surface at Brookings emerged whereas approximately 14 - 23% emerged over the same period for the other treatments and location, including seeds on the soil surface at Highmore.  Therefore, total germination on the third year after seed deposit did not vary greatly among the placements in the soil, but the rate of depletion seemed slowest for the seeds mixed in soil within 5 cm of the soil surface.  In this treatment, emergence at Brookings was 7, 9, and 7% and at Highmore it was 8, 4, and 4% for 2009, 2010, and 2011, respectively.  Emergence on the third year in the surface or buried treatments ranged for 0.2 – 3% at Brookings and Highmore.  When buried seeds were unearthed each year, 7 – 8 % emerged after one year of burial, 12 – 13% emerged after two years of continuous burial, and 3 – 5% emerged after three years of continuous burial.  This response suggests common ragweed seed viability may begin to decline if left in the soil for at least two years.  In conclusion, preliminary results indicate that common ragweed seed banks may be depleted most rapidly if either left on the soil surface, where they may be exposed to predators, or buried in the soil where they may be exposed to microbes and anaerobic conditions.  Common ragweed germination will continue to be observed in these treatments for approximately two more years.  Michael.Moechnig@sdstate.edu

Kochia (Kochia scoparia) is becoming much more difficult to manage in central South Dakota as biotypes resistant to glyphosate and ALS-inhibiting herbicides are becoming more common.  However, previous research has indicated kochia seed lacks dormancy mechanisms which could enable seed bank depletion if kochia populations are managed aggressively.  Consequently, the objective of this study was to quantify the effects of different crop canopies on kochia seed production in order to develop integrated weed management recommendations that account for crop competition.  In 2010 and 2011, corn, soybeans, field peas, wheat and fallow field plots (each 6 m by 15 m) were established in Brookings SD and replicated four times.  Two kochia cohorts, each consisting of 100 seeds in 0.3 by 0.3 m subplots, were planted at the time of crop planting and approximately 28 days after crop planting.  In addition, three single kochia plants, evenly spaced (50 cm), were established from seed in each plot.  Kochia germination and survival were quantified from the cohorts.  Biomass and seed production were quantified for each of the single-kochia plants at crop harvest. After the seed was counted, it was returned to the same spot from where it was harvested in the field.  Seedling germination counts were done in the subsequent spring. Kochia germination and survival counts were similar (P >0.05) among the treatments with an average of 78% and 60% per square foot respectively for the first cohort. In the second cohort germination and survival counts averaged 10%. For the first kochia planting, seed counts averaged 26000, 312, 134, 104 and 46 in fallow, soybeans, wheat, corn and field peas respectively. In the second planting, the single kochia plants did not grow enough to produce seed with an average height of 5mm. Relative to the fallow treatment, all crop canopies reduced (P<0.05) kochia biomass and seed production by more than 95%. Kochia biomass production was positively correlated with seed count per plant (Kochia seed count = [510.08 x kochia biomass] – 458.93 with R² = 0.98).  The magnitude of kochia shoot and seed reduction was similar among the different crop canopies.    Therefore, results from this study indicated that corn, soybeans, wheat, and field peas competed similarly with kochia as they greatly reduced kochia seed production.  Additional research is needed to determine if the combined effects of crop competition and aggressive kochia management could deplete kochia seed banks.  Rutendo.Nyamusamba@sdstate.edu.

Seed fate plays a central role in the population dynamics of annual weeds. Persistent seeds remain in the seedbank and create future weed infestations; non-persistent seeds are lost from the seedbank through mortality due to aging, seed decay by soil microorganisms, and germination that is either fatal or results in weed emergence. Little is known about the mortality of winter annual weed seeds, which are becoming more prevalent as conservation tillage practices increase and the climate changes. The objective of this research was to determine seed mortality (i.e. decay plus fatal germination) at various burial depths over a 12 month period. A three-way factorial experiment was set up at the Michigan State University Agronomy Farm examining four winter annual weed species (shepherd’s-purse, henbit, common chickweed, and field pennycress), three burial depths (0, 2.5, and 10 cm), and four burial times (3, 6, 9, and 12 months) with four replications. Seeds were buried in June of both 2009 and 2010 with 50 g of sterilized field soil in polyester mesh bags which were protected from predation in cages. Upon retrieval of the bags, intact seeds were retrieved and viability was accessed through a combination of germination and tetrazolium chloride testing. Overall seed mortality was very high and duration of burial did not have a consistent effect. Three months after burial seed mortality averaged 96, 82, 84, and 88% for shepherd’s-purse, henbit, c. chickweed, and field pennycress, respectively. Common chickweed mortality was not impacted by the burial depths studied. In 2009, more shepherd’s-purse and henbit seeds survived on the soil surface compared to those buried. Conversely, in 2010, more seeds survived when seeds were buried for shepherd’s-purse (2.5 cm), henbit (10 cm), and field pennycress (2.5 and 10 cm). This difference among years may be explained by the precipitation total for the three month storage period, which in 2009 (29 cm) was more than double that in 2010 (13 cm). Increased soil moisture may have lead to higher incidence of disease of the buried seeds in 2009. Due to the high rate of seed mortality observed, future work should examine seed mortality during the first three months following winter annual seed dispersal.

Cover crops can be important components of diversified cropping systems; however, little is known about how particular cover crop species or mixtures of cover crops may affect weed population and community dynamics.  Given that ecological theory suggests that diverse plant communities should be more resistant to weed invasion, and that competition between plant species should be strongest when species are closely related and/or have similar traits for resource acquisition and utilization, we assessed the ability of five spring-sown cover crops (grown in monoculture and mixture) to suppress weeds emerging from an ambient and “surrogate” weed seed bank.  Specifically, we tested the following hypotheses: (1) cover crop mixtures are more weed suppressive than cover crop monocultures, and (2) individual cover crops more strongly suppress weed species that are ecologically similar to the cover crop.  The cover crop treatments included monocultures of buckwheat, mustard, cereal rye, sorghum-sudangrass, and hairy vetch, and two mixtures containing all five cover crop species sown at full rate (Mix1X) or at 20 percent of the full rate (Mix20).  The “surrogate weeds” were crop species in the same (spring wheat, sorrel, canola, and field pea) or different (sunflower) family as the cover crops.  Cover crop treatments were established in early June 2011, surrogate weeds were sown three days later, and weed and cover crop biomass were sampled in late July.  The Mix1X and buckwheat monoculture treatments both reduced surrogate and ambient weed biomass by more than 50 percent compared to the no cover crop control (fallow); however, weed biomass in the Mix20 treatment did not differ from the control.  Surrogate weed species were not more strongly suppressed by cover crops that belonged to the same family as the “weed”.  These data suggest that in regards to the five spring-sown cover crop species assessed in this study, (1) buckwheat is the most weed suppressive, (2) mixtures containing all five species are not more weed suppressive than the most suppressive monoculture (i.e., buckwheat), and (3) weed suppressive ability is not well linked to the relatedness of the “weed” to the cover crop, at the family level.

Winter annual weed infestations have increased in the Midwest U.S. because of increased adoption of conservation tillage practices, milder winters, and a reduction in residual herbicide use in glyphosate-resistant crops.  Managing winter annual weeds requires tillage or burndown herbicide applications prior to planting. Using growing degree days (GDD) to determining the time of emergence and seed rain of winter annual weeds could improve the timing of management practices to prevent seed development and dispersal, thereby improving winter annual weed control. A field experiment was designed to measure cumulative emergence and seed rain of four winter annual weed species at the Michigan State University Agronomy Farm. To examine emergence, 500 seeds of each weed species were planted in June of 2009 and 2010 (a timing corresponding to the end of seed rain) in a 1 m² cage with buried sides to protect from predation and lateral seed movement. Germinated seedlings were recorded and removed on a biweekly basis and recording times were converted to GDD (base 0 C) accumulated from the time of planting. Seed rain was collected weekly from naturally occurring populations within 1 m² plots using cups placed on a grid. Collection days were converted to GDD (base 0 C) accumulated from January 1^st. Both cumulative emergence and seed rain were fit to the Gompertz equation. Emergence of all winter annuals commenced at 170 GDD in 2009 and 190 GDD in 2010, with the exception of common chickweed which emerged at 250 GDD in 2010.The rate of henbit and common chickweed emergence were similar in both years; the rates of field pennycress and shepherd's-purse emergence were similar each year.  Shepherd’s-purse seed rain began at 600 GDD and ended by 1500 GDD in both years studied. Henbit seed rain began at 450 GDD in three of four years; and at 650 GDD in 2008. By 1200 GDD, seed rain was complete in all study years. Common chickweed seed rain began at 420 GDD in three of four years, and at 650 GGD in 2008. By 1500 GDD, seed rain was complete in three of four years; in 2008 seed rain continued through 2000 GDD.  Seed rain of field pennycress was later and of a more limited duration, commencing at around 1200 GDD each year and complete by 2600 GDD.

Successful control of wild oat (Avena fatua L.) in cereal crops requires an accurate prediction of the developmental stages of wild oat plants emerged over the growing season. The  objective of this research was to evaluate wild oat growth and to predict the phyllochron of wild oat plants emerged at different times in the Red River Valley region of Minnesota and North Dakota. Field experiments were conducted in 2002 and 2003 in Crookston, MN and Fargo, ND. Four emergence cohorts were established in four successive weeks. Research plots were arranged in randomized complete blocks with six replications. From the naturally emerged wild oat population, ten randomly selected plants per plot were evaluated for plant height, leaves on main stem, tillers plant^-1, total leaves plant^-1, days to flag leaf emergence and to heading, biomass plant^-1, and seeds plant^-1. The Haun scale was regressed on days after emergence (DAE), day length (DL), growing degree-days (GDD), or photothermal units (PTU). Wild oats that emerged first required more time for flag leaf emergence and heading, and were taller, and had more biomass, leaves, tillers, and seed production compared to wild oat plants that emerged later. Wild oat phyllochron intervals were 5.3 days, 94 GDD, or 1468 PTU, regardless of emergence timing. These data suggest that wild oat phyllochron is primarily driven by air temperature and is relatively stable over the extended emergence period; and that later emerging wild oat plants, though not as competitive as earlier emerging ones, still have the potential to contribute to the seed bank if left uncontrolled.

When considering the likelihood of coexistence
between two competitors, niche difference (ND) and relative fitness difference
(RFD) influence competitive dynamics. In order to quantify these measures, Carroll et al. (2011) use
MacArthur’s resource-based model to define ND and RFD as a function of
sensitivity, or the proportional reduction in growth rate due to interspecific
competition. We aimed to use the Carroll et al. model to assess the competitive
dynamics between KR Bluestem (Bothriochloa
ischaemum) and Sideoats grama (Bouteloua
curtipendula) in a 3-way factorial greenhouse experiment involving
seedlings of the two focal species.  The
three factors controlled were nitrogen level (ranging from 0 g/pot to 0.0769 g/pot), presence or
absence of mycorrhizal fungi, and pot composition (monoculture or 50:50
competition). 
Seedlings were grown in small pots (7 x 24.5 cm) filled with sand and 2
cm of Jiffy Organic Seedling Mix , and harvested weekly over the course of 4 weeks, beginning once the target densities (16 plants/pot)
had been achieved.  MacArthur’s
equation requires multiple (2 or more) competitors as well as multiple
resources for proper analysis.  Since our experiment manipulated only one resource (N), it therefore became necessary
to modify MacArthur’s model by adding a parameter that takes into account direct
interspecific competition and then reduce the number of parameters involved to
increase the accuracy of the non-linear regression analysis. Calculation of
niche difference and relative fitness difference and analysis of the stability
of coexistence equilibrium points generated by the model allow the prediction
of the species’ competitive dynamics.

Vegetation is a significant safety and management responsibility for departments of transportation.  Still, it is not well understood.  In recent years early detection and rapid response of invasive species has become increasingly important.  Only about 20 percent of departments of transportation have taken statewide inventories of invasive species and far less have took surveys of all species that occur on state roadsides.  A better understanding of weed occurrences and their ecology could greatly assist with management efforts.  The purpose of this study was to conduct a species survey on roadsides managed by the Mississippi Department of Transportation during 2011.  Survey locations were broke down into ten physiographic regions in which 10 cross-section transects were established.  Species data was collected in eight plots along each transect.  For each plot (800 plots total), all species and their percent cover was recorded.  Over 360 plant species were identified during the study, including both native and exotic species.  Exotic species accounted for about 24 percent of the species.  Tishomingo hills had the highest while the Mississippi delta had the lowest species diversity.  In addition, species diversity was highest along roadside margins as opposed to plots closer to pavement.  Bermudagrass (Cynodon dactylon) and bahiagrass (Paspalum notatum) had the highest mean cover statewide at 16.1 and 13.1 percent, respectively.  As expected, most species correlations were negative.  However, there appears to be positive correlations between at least one exotic, legume (Fabaceae) species and non-legume species that are more common near pavement.  Given the magnitude of this study, this presentation only covers an overview of the data and implications regarding weed management are still being investigated.

Red rice is a serious threat to the rice industry because of its deleterious effect on rice yield and quality. This weed is widespread in the southern U.S. rice-producing states and continues to be a major constraint to production wherever it occurs. Among its weedy traits, dormancy is of major importance to its persistence. Red rice exhibits different levels of dormancy allowing them to escape weed management tactics increasing the potential for flowering synchronization, and therefore gene flow between weedy and cultivated rice. Additionally, red rice populations are phenologically and morphologically diverse and genetic introgression and several agroecological factors contribute to their diversification and persistence. The objective of this study is to determine the phenotypic and genotypic diversity of red rice using 18 simple sequence repeat (SSR) markers linked to dormancy, and 20 sequence tagged site (STS) loci primers used for rice population genetic studies. Four populations, dormant blackhull, dormant strawhull, non-dormant blackhull, and non-dormant strawhull, were fingerprinted using SSR markers; and, 17 blackhull red rice accessions, representing different maturity periods and plant heights, were genotyped using STS markers.

SSR fingerprinting results show that the overall Nei’s genetic diversity (GD) of these dormancy-linked loci was high (GD= 0.66). High GD was observed among populations within each of the four groups. The blackhull group of populations, BH-D and BH-ND, showed the highest GD of 0.55 and 0.58, respectively. Genetic diversity between strawhull and blackhull red rice was higher than the GD among strawhull or blackhull ecotypes. The SH-ND group was most distant from BH-D (0.63) and BH-ND (0.60) group. These data reveal the evolutionary divergence of red rice populations with respect to dormancy. Markers associated with the dormant accessions maybe unique, and can be used for study of dormancy gene expression. STS genotyping experiment identified a total of 40 single nucleotide polymorphisms (SNPs) across the 20 loci for the seventeen accessions of blackhull red rice used in this study. Ten out of 20 loci  are polymorphic  and the average pairwise nucleotide sequence diversity (π) and polymorphism (θ) estimates are highest between the “early” and “intermediate” maturing group (0.00180 and 0.00173); “tall” and “short” height group (0.00169 and 0.00162); and from “central” and “northeast” zones (0.00130 and 0.00135). The highest sequence divergence estimates (K) were observed between the “late” and “intermediate” maturing group (0.00150), “short” and “intermediate” height group (0.00197), and the “northeast” and “southeast” zone group (0.00148).  Overall, the comparison of these nucleotide sequence diversity estimates in blackhull red rice accessions from Arkansas is higher versus sequence variation in these same loci within strawhull red rice accessions from Arkansas. Further in-depth analyses of divergence population genetics in red rice biotypes are in progress that will utilize 28 additional STS loci and will entail population structure and phylogeographic model-fitting by incorporating genus-wide sampling of the same loci.

Knowledge of environmental factors influencing demography of weed species will improve understanding of current and future weed invasions. The objective of this study was to quantify regional-scale variation in vital rates of giant ragweed (Ambrosia trifida) and common sunflower (Helianthus annuus). To accomplish this objective, a common field experiment was conducted across seven sites between 2006 and 2008 throughout the north central US maize (Zea mays L.) belt. Demographic parameters of both weed species were measured in intra- and interspecific competitive environments and environmental data were collected within site-years. Site was the strongest predictor of belowground vital rates, indicating sensitivity to local abiotic conditions. However, biotic factors influenced aboveground vital rates. Partial least squares regression (PLSR) indicated that demography of both species was most strongly influenced by thermal time and precipitation. The first PLSR components, both characterized by thermal time, explained 63.2% and 77.0% of variation in the demography of giant ragweed and common sunflower, respectively; the second PLSR components, both characterized by precipitation, explained 18.3% and 8.5% of variation, respectively. The influence of temperature and precipitation is important in understanding the population dynamics and potential distribution of these species in response to climate change.

Kochia (Kochia scoparia) emergence profiles across the Central Great Plains. J. Anita Dille*¹, Phillip W. Stahlman², Patrick W. Geier², J.D. Riffel¹, Randal S. Currie³, Robert G. Wilson⁴, Gustavo M. Sbatella⁴, Philip Westra⁵, Andrew R. Kniss⁶, Mike J. Moechnig⁷, Richard M. Cole⁸. ¹Kansas State University, Manhattan, KS, ²Kansas State University, Hays, KS, ³Kansas State University, Garden City, KS, ⁴University of Nebraska-Lincoln, Scottsbluff, NE, ⁵Colorado State University, Fort Collins, CO, ⁶University of Wyoming, Laramie, WY, ⁷South Dakota State University, Brookings, SD, ⁸Monsanto Co., St. Louis, MO.

The timing and duration of weed emergence influence the ability to implement timely and effective control practices.  Emergence patterns of kochia populations in cropland and non-cropland were monitored in 2010 and again in 2011 at sites in Colorado {Fort Collins (irrigated and dryland cropland)}, Kansas {Garden City (cropland), Hays (cropland, non-cropland), Manhattan (non-cropland), Ness City (non-cropland), and Stockton (non-cropland)}, Nebraska {Mitchell (non-cropland) and Scottsbluff (cropland)}, Wyoming {Lingle (non-cropland)}, and South Dakota (cropland). Quadrats (0.25 to 1-m²) were marked in which weekly observations of emergence were documented and emerged seedlings removed by hand or sprayed with glyphosate.  Observations were initiated as early as March 15 and continued through July 30 or until no new emergence was seen on consecutive observation dates.  Total season population densities varied among locations and ranged from as few as 10 to almost 332,000 seedlings/m².  Earliest observed emergence was in Kansas soon after March 15, while first observations in Wyoming and Nebraska occurred around April 8.  Even though the calendar dates shift from march to April as location moves from south to north, the growing degree days (GDD) for 10% cumulative kochia emergence based on air temperatures since January 1 revealed that fewer GDD were needed before seedling emergence occurred when moving from south to north.  This may indicate a lower critical temperature for kochia in more northern latitudes.  In general, rate of kochia emergence was slowed in cropland compared to non-cropland environments.   Between 70 and 95% of the kochia seedlings had emerged between the first two observation dates across all locations.  The combination of high seedling emergence occurring very early in the season emphasizes the need for early weed control.  However, the high number of seedlings that appear in the second flush (between 5 and 30% of the total population) emphasizes the need for extended periods of early-season kochia management. 

dieleman@k-state.edu

Weedy rice (Oryza sativa L.) infestation has been reported at several areas where direct seeding rice cultivation had been conducted in Japan. There are weedy rice accessions with white pericarp in a particular area of western Japan in spite of the majority of Japanese weedy rice accessions have red pericarp. The white weedy rice accessions have been found in the rice fields where common varieties “Akebono”, “Kibinohana” or “Omachi” have been cultivated. The morpho-physiological characteristics of these white weedy accessions are analogous to those of these common rice varieties. We compared genetic backgrounds between the white weedy rice and the common rice variety by a set of 15 STS (sequence-tagged site) primers for Japanese rice variety identification. A dendrogram from UPGMA (unweighted pair group method of arithmetric average) cluster analysis based on their DNA band-patterns data revealed that the genetic backgrounds of the white weedy rice and the common rice variety were very similar.

Strong seed-shattering habit is a morpho-physiological characteristic that the white weedy rice is different from the common rice variety, i.e., the white weedy rice shatters most seeds at harvest time though the common rice variety does not drop seeds at the same time. We histologically examined pedicel structures which affect the difference of seed-shattering habit of the white weedy rice and the common rice variety using a paraffin section method. The results cleared that the forms of abscission layers between them were different. The abscission layers of the white weedy rice were completely formed and the cells were cracked, while the abscission layers of common rice variety were incomplete and the cells were un-cracked. Gene analysis, however, indicated no significant differences in sequences of major rice seed-shattering genes, qSH1 and sh4, which related a formation of abscission layers between the white weedy rice and the common rice variety.

We concluded that the white weedy rice in Japan originated from the common rice variety which accompanied by functions of unidentified shattering-related gene(s).

Vincetoxicum nigrum (L.) Moench [Cynanchum louiseae Kartesz & Gandhi] (black swallow-wort) and V. rossicum (Kleopow) Barbar. [Cynanchum rossicum (Kleopow) Borhidi] (pale swallow-wort) are herbaceous perennial vines in the Apocynaceae native to Europe. Both species are considered invasive in their introduced ranges in the northeastern U.S. and southeastern Canada, where they form dense stands, especially in high light environments such as old fields and field-woodland ecotones. These Vincetoxicum species were introduced into North America in the late 1800s, likely as ornamentals, but soon after escaped cultivation. Numerous rare and sensitive plant and animal species have been negatively impacted by their introduction. During the last decade, more than 40 refereed publications have focused on one or both of these species substantially enhancing our knowledge of their taxonomy, biology, ecology, and management. This is particularly true for V. nigrum, the least understood of the two species. New chemical and molecular information has clarified taxonomic inconsistencies such that the genus Vincetoxicum is now considered more closely related to the genus Tylophora than Cynanchum as previously thought. Moreover, the genus Vincetoxicum is now included in the Apocynaceae rather than the Asclepiadaceae, as the three subfamilies of this latter family, including the Asclepiadoideae, were transferred intact into the Apocynaceae. New information from European and North American populations confirms the diploid and tetraploid nature of V. rossicum and V. nigrum plants respectively, suggesting that hybridization is unlikely in regions where their ranges overlap. Preliminary bioclimatic modeling indicates that expansion of the two species south and west of their current range is likely. New data have provided a better understanding of factors that allow for successful establishment and spread of the two vines including seedling survival, vegetative expansion, and effects of allelochemicals and intra- and inter-specific competition. Additional morphological, physiological and life history differences between the two species have been elucidated. Management options using herbicidal, cultural, and/or biological tactics have also been intensively studied during the last decade. The herbicides triclopyr, glyphosate, and imazapyr have shown most promise. Mowing may be effective in reducing populations in sub-optimal habitats such as forest understories, but is generally not recommended in high density habitats like old fields. Substantive advances have been made in the search for biological control agents to suppress Vincetoxicum populations in their introduced range. Promising non-native insect candidates include defoliating moths in the genera Abrostola and Hypena. Root-feeding beetles in the genus Chrysochus appear to present a risk to native milkweeds. Other insect species continue to be screened. The pathogenic fungi Colletotrichum lineola and Sclerotium rolfsii have recently been isolated from diseased plants and may hold promise. The increased knowledge and research attention afforded these two Vincetoxicum species in the last decade has resulted in their classification as ‘noxious weeds’ in some U.S. and Canadian jurisdictions including several New England States.

The C₄ grass King Ranch
Bluestem (Bothriochloa ischaemum) was
originally planted throughout much of Texas to restore degraded rangeland;
however the species has since become an invasive pest.  Invasion theory suggests that species
coexistence is enhanced through niche partitioning and that species with
overlapping use for limiting resources (such as nitrogen) will be in
competition.  These competitive effects
may, however, be mediated by mutualist symbionts, such as mycorrhizal fungi,
that increase a species’ ability to acquire resources.  Here we use niche theory to assess the
mechanism of competition between a native and non-indigenous grass at the
seedling stage and the potential for restoration of native plant species as
biocontrol to reduce KR Bluestem establishment and spread.  We employ a three-way factorial greenhouse
experiment with species composition (3 levels), nitrogen (5 levels), and
mycorrhizal fungi (with and without) as factors.  King Ranch bluestem (KR) and sideoats grama (Bouteloua curtipendula), a common native
grass used widely in rangeland restoration, were grown from seed in either 100:0,
50:50 or 0:100 ratios. Small pots (7 x 24.5 cm) were filled with sand to 3 cm
below the top.  The top 2 cm of each pot
was filled with Jiffy Organic Seedling mix. Each pot was seeded with
approximately 50 seeds of each species. 
Once germinated and established the seedlings were thinned to the
assigned species ratios with 16 individuals per pot. Using Hoagland’s solution,
nitrogen was manipulated to create a nitrogen gradient ranging from 0 to 0.0769
g nitrogen per pot in 0.0192 gram intervals. Weekly
harvests were conducted over the course of four weeks.  KR Bluestem grew more vigorously than sideoats
grama both alone and in competition, a trend that was reinforced by addition of
nitrogen.  Addition of mycorrhizal fungi
served to mediate the interaction between the species, increasing the fitness
of sideoats grama in competition with KR. The positive effect of the addition
of mycorrhizal fungi was more significant at lower levels of nitrogen.

Maize dwarf mosaic (MDM) stunts corn growth, delays development, and is the most prevalent viral disease of sweet corn.  Although weeds evade control in most sweet corn fields, the extent to which MDM influences the crop’s weed suppressive ability is unknown.  Field studies were conducted over a three-year period to characterize the influence of variable MDM incidence in sweet corn on growth, fecundity, and germinability of wild-proso millet, a common weed in the crop.  Treatments included five levels of MDM incidence (0, 25, 50, 75, and 100% of plants infected) in two MDM-susceptible hybrids differing in weed suppressive ability.  Wild-proso millet biomass and fecundity depended in part on the hybrid in which the weed was growing.  For instance, wild-proso millet growing in Sugar Buns weighed 45 to 117% more than wild-proso millet in Legacy.  Under high weed population densities, incidence of MDM in sweet corn affected wild-proso millet biomass and fecundity.  When wild-proso millet was observed at 122 plants m^-2, weed biomass increased nine g m^-2 for each additional 10% incidence of MDM of sweet corn.  The competitive hybrid (i.e. Legacy) was influenced to the same extent by MDM as the poorly competitive hybrid (i.e. Sugar Buns).  Coupled with the fact that two-thirds of commercial sweet corn hybrids have no resistance to MDM, the disease is an additional factor perpetuating weed growth and fecundity in sweet corn, particularly in fields with high weed population densities.

Soybean cyst nematode (SCN) is the most yield limiting disease of soybeans in the United States. Henbit is a prevalent winter annual weed species in no-till fields and is reported to be an alternative host of SCN. A greenhouse study was conducted to evaluate how the development of SCN on henbit roots was affected by herbicide application timing and herbicide active ingredient.  Henbit seeds were germinated and then transplanted to individual watertight pots filled with 750 ml of sterilized sand soil. Pots were placed in a water bath bench that kept soil temperature constant during the study (27 ± 1 C). Ten days after transplanting, pots were inoculated with approximately 1,000 SCN eggs. At 7, 14, or 21 days after inoculation (DAI), henbit plants were sprayed with either glyphosate (870 g ae ha^-1) + AMS (2,860 g ha^-1) or 2,4-D (1,070 g ae ha^-1) + NIS (350 ml ha^-1) + AMS (2,860 g ha^-1). The control treatment was inoculated plants not treated with either herbicide. The experiment was arranged in a randomized complete block design with 5 replications per treatment, and was repeated (two runs). At 28 DAI, experimental units were processed and the total number of cysts, number of eggs, and plant shoot and root dry weights per pot were determined. SCN cyst number and the number of eggs per cyst were influenced by both the herbicide application timing and the herbicide active ingredient. The number of SCN cysts per plant increased as the herbicide application was delayed from 7 to 21 DAI. Plants treated at 7 and 14 DAI with glyphosate resulted in fewer cysts per pot than plants treated with 2,4-D, and plants treated with glyphosate resulted in fewer eggs per cyst than plants treated with 2,4-D at all three application timings. Henbit shoot and root biomass also increased as the time of herbicide application was delayed, but there was no effect of herbicide active ingredient on shoot or root biomass.  These results suggest that controlling henbit plants while they are small may play an important role to prevent SCN reproduction on henbit in SCN infested fields.   

Protection from Lepidopteran Feeding is Unlikely to Significantly Alter the Weediness Potential of Glycine soja.  M. Horak*¹, H. Goto², A. Ahmad¹, B. Baltazar¹, H. Shimada², D. Stojšin¹, S. Nakai², A. Arii², S. Yamane²,  ¹Monsanto Company, St. Louis, MO, ²Monsanto Company, Tokyo, Japan.

Glycine soja is considered the likely progenitor species from which cultivated soybean (Glycine max) originated.  G. soja is an annual, self pollinating species that grows wild in Japan, Korea, China, Taiwan, and parts of Russia.  It is known to cross with G. max at very low frequencies and significant barriers to outcrossing and introgression between these two species exist. G. soja occurs as a ruderal, early successional species and as such is typically non-dominant in established plant communities and is not invasive.  The major factor thought to constrain G. soja populations is competition from other plant populations in the communities where it occurs. It is known that some herbivores, including insects, feed on G. soja, however limited information has been reported on potential interactions of G. soja with herbivores, or on the effects of defoliation on G. soja seed production. 

Environmental risk assessment of a genetically modified (GM) crop is an integral part of the process to gain approval for the import or cultivation of these crops.  One specific aspect of an environmental risk assessment for GM soybean is an assessment of the potential for increased weediness of G. soja if it crossed with soybean with a GM trait. To provide information and data for a potential weediness assessment of G. soja should it cross with soybean with a lepidopteran protection trait, two studies were conducted: 1) a survey of natural G. soja populations to determine what herbivores fed upon G. soja and what level of defoliation they caused, and 2) an experiment to assess the impact of defoliation on G. soja seed production.

Survey of natural G. soja populations: G. soja populations were surveyed seven times from June through September 2011 in the Ibaraki (20-23 locations) and Saga (15-17 locations) prefectures in Japan.  At each observation time, percent damage and defoliation to G. soja caused by different herbivores was evaluated and was assigned to various herbivores based on feeding symptomology. Results of the population survey indicated that many different herbivores are feeding on G. soja.  When assessed across all populations within each prefecture, the highest levels of defoliation were caused by Orthopteran and Coleopteran species (e.g. Figure 1).  In contrast, while lepidopteran species were responsible for some defoliation the levels were always very low at all observation times, locations, and prefectures and in almost all cases were lower than defoliation by Orthopteran and Coleopteran species.

Impact of defoliation on G. soja seed production: A randomized complete block experiment (12 replications, 5 treatments) was initiated in which G. soja was grown in pots in a growth chamber.  At the flowering stage (R1 – R2), defoliation treatments (0%, 10%, 25%, 50% and 100% defoliation) were administered.  Pod and seed number per plant were collected at plant maturity.  Results of the defoliation study indicated that compared to the undefoliated control, no significant reduction in G. soja pod or seed number was observed when up to 50% of the leaves were removed at the flowering stage (e.g. Figure 2) . In contrast, significant reduction in both G. soja pod number or seed number was observed when 100% leaves were removed.

The results of these studies were used to assess the potential impact of trait transfer to G. soja.  First, defoliation from lepidopterans was very low (averaging less than 2% across locations) and many different organisms were feeding upon G. soja.  When considered in the context of total plant damage the lepidopteran contribution to the total overall defoliation was low at the 35 – 40 total locations across the Ibaraki and Saga prefectures.  Secondly, in the growth chamber experiment, G. soja plants were able to maintain high pod and seed production despite defoliation of up to 50%.  Since the defoliation by lepidopteran observed at Ibaraki and Saga is very low compared to that caused by other taxa, and defoliation levels were low relative to those that would likely cause reductions in pod and seed production, it is reasonable to conclude that there would likely be little to no impact to the reproductive ability of G. soja should outcrossing to G. soja with a lepidopteran protection trait occur.  Thus, acquiring the lepidopteran trait alone would likely have little impact on G. soja weediness potential.  Considering these results and the very low level of outcrossing between G. max and G. soja, it is highly unlikely that introgression of a GM trait conferring lepidopteran tolerance into G. soja  would impact its weediness potential. michael.j.horak@monsanto.com

Figure 1.        Overall G. soja plant damage at Ibaraki during 7 observation times

Figure 2. Number of seed per plant of G. soja as affected by different defoliation treatments at the flowering stage.

Hound’s-tongue, a rangeland weed of British Columbia, hosts several phytophagous insects. Little information on effects of environmental stressors on its interaction with these insects is available. We studied the effect of soil moisture stress (SMS) during hound’s-tongue growth on the feeding preference and growth of 5^th instar grasshoppers (Melanoplus sanguinipes). Hound’s-tongue plants were grown under four SMS levels [100, 80, 60, and 40% field capacity (FC)] in a glasshouse. In one study, grasshoppers were released on intact plants grown under 40 or 100% FC in an enclosed system. The insects displayed no leaf age preference for plants grown under 100% FC, but consumed more mid-aged leaves from plants at 40% FC. Three bioassays comparing feeding preference for discs excised from young (Expt. 1) or old (Expt. 2) leaves developed at 100% FC versus 40, 60 or 80% FC as well as from young and old leaves from plants at the same SMS level (Expt. 3) were conducted. In bioassays employing discs from young leaves, grasshoppers chose discs from plants grown under 40% FC over those under 100% FC. Grasshoppers showed no statistically significant preference for old leaves in individual bioassays, but when pooled results of three experiments were analyzed they preferred discs from old leaves of 40 and 60% FC treatments compared to 100% FC. In bioassays involving young versus old leaves from plants at the same SMS, the insects preferred young over old leaves for 40% FC. In a separate study, grasshoppers feeding on discs from young leaves of plants at 40% FC had higher fresh weights compared to those feeding on discs from old leaves developed at the same SMS, or on discs from the young or old leaves developed at 100% FC. A greater preference for, as well as better grasshopper growth, on young leaves from stressed (40% FC) hound’s-tongue plants could have significant implications for grasshopper herbivory when this weed is distributed on microsites with varying SMS.  

Leafy spurge is a model for studying well-defined phases of dormancy in underground adventitious buds (UABs) of herbaceous perennial weeds. A 12-week ramp down in both temperature (27°C → 10°C) and photoperiod (16 h → 8 h light) induces a transition from para- to endo-dormancy in UABs of leafy spurge; whereas, a ramp down in either temperature or photoperiod alone does not. A conceptual model for seasonal dormancy transitions, based on previous genomics studies, highlighted a central role for AP2/ERF transcription factors (TFs) i.e., DREBs. To refine our model and evaluate the effects of photoperiod and temperature on molecular networks and AP2/ERF TFs associated with endodormancy induction, we compared transcripts obtained from UABs of leafy spurge exposed to a ramp down in both temperature and photoperiod (RD_tp) vs. a ramp down in temperature (RD_t) alone. In this study, DREB1A/CBF3, DREB1B/CBF1, and DREB2A were specifically identified as hubs of up-regulated genes in endodormant buds. Further analysis of 27 leafy spurge AP2/ERF TFs by qRT-PCR indicated that they respond similarly to RD_tp and RD_t treatments; indicating that temperature is the main factor affecting their expression. Since an RD_tp treatment is required to achieve endodormancy, these results suggest that expression of these TFs alone is not the primary mechanism driving endodormancy. Interestingly, pathways involved in winter survival, such as carbohydrate metabolism, were among over-represented genes up-regulated in endodormant buds. Since several reports have provided evidence for a link between carbohydrate metabolism pathways and DREBs, we propose that DREBs identified as hubs of molecular networks may be playing a critical role in survival of buds during endodormancy.

Abiotic stress-tolerant genetically modified (GM) crops are expected to be next-generation crops that will bring future stable yields against population growth and climate changes due to global warming. Research and development of the GM crops are advancing all over the world, and now the stage of commercialization is coming near in the U.S. and some countries. However, no assessment methods of an environmental impact of such GM crops on biodiversity have been established in Japan. Therefore, we tried to quantify the persistence of the feral population escaped from a field using the transition matrix model to establish the method. First, we created a scenario in which wheat escaped from a field and established as a feral population. Next, we determined crucial stages along the life cycle by the scenario, and then we applied survival rates after a transition from a stage to the next and seed productions to the transition matrix by reference to literatures and field experiments. Finally, we calculated the λ which is the eigen values of the matrix, and this enabled us quantifying the persistence of the population. As a factor, feeding damage by bird influenced the population persistence significantly; in the absence of bird damage, a fair percentage of seeds were left and once the birds find the seeds, most seeds were eaten. Therefore, we simulated the dynamic state of population using encounter frequencies of the bird damage. The simulations showed that with only a 10% encounter rate, the wheat population would become extinct after the 23rd generation at a probability of 50% and after the 50th generation at a probability of 90%. Even low encounter rate that occurred in several consecutive years dwindled the population quickly. Although we used non-GM wheat as a material in this study, we can also assess the persistence of GM wheat population by a partially modification of the survival rate, giving consideration to their features. Additionally, this assessment method can be applied to other crops as a pattern for quantitative assessment of the competitive superiority as the meaning of “competitiveness” defined in the Cartagena Protocol domestic law enforced in Japan.

The spread of herbicide-resistant weeds into cropping areas that previously lacked resistant populations is problematic.  While the spread of resistant populations is facilitated by seed dispersal methods, the rapid infestation of numerous acres suggests that pollen transfer is a contributing factor.  Johnsongrass (Sorghum halepense) is a perennial weed that also produces much seed; there are no known herbicide-resistant biotypes in Missouri.  The objectives of this trial were to determine the frequency and distance for transmission of herbicide resistance in johnsongrass through pollen.  A biotype (R91F) with resistance to ACCase inhibiting herbicides has previously been shown to: (i) be 388-fold more resistant to fluazifop-P than the susceptible biotype; and (ii) express resistance through a single dominant gene.  Forty-five R91F plants were placed in a four meter diameter circle in the center of a soybean field.  Six concentric circles of susceptible plants, containing 12 to 42 plants per circle, were placed at distances of 2, 4, 8 16, 32, and 64 meters from the resistant plants.  All plants were established in 30 cm pots containing a modified soil mix.  Plants were allowed to reproduce under natural field conditions and F₁ seeds were harvested from each pot over the course of the growing season.  Seedlings from each pot were later established in 25 by 50 cm polypropylene flats in the greenhouse.  As plants reached 12 cm in height, a maximum of 25 plants per flat were treated with fluazifop-P at a rate of 0.525 kg ai ha^-1 (5-fold greater than the labeled rate).  Three weeks after treatment, individual plants were visually rated for percent injury (0-100%) and harvested to determine dry weight biomass (g).  Visually, injury for each plant was characterized as resistant (0-30%), intermediate (31-89%), or susceptible (90-100%).  To date, 257 (2 m distance), 174 (4 m), 163 (8 m), 336 (16 m), 692 (32 m), and 544 (64 m) plants have been evaluated.  While a minimum of 95% of the progeny from susceptible plants are susceptible to fluazifop-P, 10 to 43 resistant and 2 to 7 intermediate offspring were identified from all distances.  Concerning plant biomass, susceptible johnsongrass plants averaged 0.45 g plant^-1 while the mean of intermediate and resistant plant biomass was 1.19 and 1.17 g plant^-1, respectively.  The frequency of resistance transfer was 16.7, 7.5, 12.3, 4.5, 2.2, and 1.8% at 2, 4, 8, 16, 32, and 64 m, respectively.  Results indicate that herbicide resistance can be spread through pollen of johnsongrass across significant distances.  Transfer of resistance through pollen likely facilitates the spread of resistant populations across roads and other barriers between fields.

Imazethapyr is a valuable herbicide for control of weeds in winter wheat – spring pulse rotations. Crop injury due to residual herbicide persistence continues to be a problem to growers in the inland pacific northwest. In 2008, field trials were conducted in Moscow, ID, Pullman, WA, and Pendleton, OR, to determine the soil persistence and resulting yield loss caused by increasing rates of imazethapyr. The study was repeated in 2009 in Moscow and Pullman. Soils from Moscow and Pullman are considered Palouse silt loam while Pendleton soil is Walla Walla silt loam. Imazethapyr was applied preplant and incorporated to activate herbicide prior to planting wheat. After application, wheat varieties ‘Tubbs06’, and ‘ORCF-102’ were conventionally planted into the study areas. Plots received either 52 or 26 g/ha imazethapyr and soil samples were taken at intervals 0, 1, 2, 3, and 4 wks after treatment. Cores were then collected on a monthly basis. Four cores were taken from each plot and combined. To extract the imazethapyr residue, composite samples were dried, ground and thoroughly mixed before extraction. A sub-sample (10 g) was removed for analysis. Each sub-sample was first extracted with 0.5 N NaOH. The extract was acidified and particulate removed using a combination of Celite 545 stirring for 30 min followed by vacuum filtration. The filtrate was extracted with 3 x 50 mL of dichloromethane (DCM) and the extract was dried by addition of a small amount of anhydrous sodium sulfate (Na2SO4) to remove residual water. The DCM was removed using a rotoevaporator and the residue was re-eluted in acetone for transfer to a screw-cap vial. Derivatization was carried out in the screw-cap vial containing the extract in acetone by adding 160 µL of tetrabutylammonium hydroxide solution (1.0 M in methanol) and 320 µL of iodomethane to the acetone solution. The reaction mixture was heated for 1.5 h at 40°C. Methylated imazethapyr was extracted with 3 x 30mL ether/hexane solution (1:2 v/v). The extraction solvent was removed and the extract residue was re-eluted in 1mL acetone/hexane (9/1 v/v) prior to analysis by GC-MS. A half-life of 50 d was observed in a Palouse silt loam soil collected from Pullman averaged over 2 site-years. Palouse silt loam soil near Moscow had a half-life of 245 d when averaged over 2 site-years. Walla Walla silt loam soil had a calculated half-life of 165 d. The rate of imazethapyr degradation was likely affected by cold soil temperatures over the winter and moisture availability during the sampling period. Yield loss in non-Clearfield winter wheat occurred when a rate of 2.6 g/ha or above imazethapyr was applied at planting. Based on the degradation rate for a fall application, a single application of imazethapyr at the labeled rate is sufficiently persistent to cause injury or yield loss when applied 307 d or less before winter wheat is planted in Pullman Palouse silt loam soils, 1058 d in Moscow Palouse silt loam soils, and 713 d in Walla Walla silt loam soils. Imazethapyr is degraded primarily by soil microbial activity and is not strongly adsorbed to soil. Sorption increases as organic matter and clay content increase and, more importantly, as pH and moisture content decrease. The inland Pacific Northwest production region is a Mediterranean environment with cool wet winters and hot dry summers. The lack of moisture to keep imazethapyr in the soil water solution during the summer months when microbial activity is highest could be contributing to increased imazethapyr soil persistence and reduced yields in winter wheat.

Water foxtail is one of the most troublesome annual grass weeds of wheat and oilseed rape crops in China. The objective of this study was to confirm and characterize the resistance to fenoxaprop-P-ethyl and cross-resistance to clodinafop-propargyl in water foxtail biotypes and to investigate the basis of resistance to these herbicides. Two resistant water foxtail biotypes R1 and R2 were collected from wheat fields in different areas in Anhui province of China where fenoxaprop had been continuously used over 5 yr and control failure was evident in these fields. A susceptible water foxtail biotype S was collected from wheat field in Jiangsu province to use as standard biotype. Whole-plant dose-response experiments revealed that the resistant water foxtail biotypes R1 and R2 were 52- and 45-fold resistant to fenoxaprop and were 27- and 22-fold resistant to clodinafop, respectively compared with the S biotype. These results indicate that the resistant water foxtail biotypes exhibited more resistance to fenoxaprop than clodinafop. The R1 biotype exhibited more resistant to both of herbicides than the R2 biotype. The molecular basis of resistance indicated that the Ile₁₇₈₁ to Leu mutation in the R1 biotype and the Trp₂₀₂₇ to Cys mutation in the R2 biotype were identified in their ACCase gene to confer the resistance to fenoxaprop and cross-resistance to clodinafop in water foxtail. The resistance pattern in these water foxtail biotypes is resulted from the presence of altered target site to fenoxaprop and clodinafop.

Fenoxaprop-P-ethyl was the most important herbicide, which was widely used to control wild oat in wheat field in China. Because of lack of herbicide rotation, farmers have complained that fenoxaprop were not effective. Twelve wild oat populations respectively collected from six provinces in 2004, 2008 and 2009 were evaluated resistance to fenoxaprop. All experiments were carried out at the recommended field rate of 62.1 g/ha in greenhouse. Eleven wild oat populations collected were tested fenoxaprop resistance, whereas the Inner Mongolia population showed no resistance. The fenoxaprop-resistance frequency of the five wild oat populations ranged from 4.8% for the Qinghai population to 14.3% for the Anhui population. Four-five years later, our survey of six populations collected in 2008 and 2009 from the same region revealed more resistant to fenoxaprop than the 2004 collections. For example, for population collected in Anhui province, the fenoxaprop-resistant frequency was 14.3% for 2004, 18.0% for 2008, and 17.9% for 2009. For the Henan population, resistance frequency increased with fenoxaprop from 8.8% in 2004 to 15.7% in 2008 and 16.1% in 2009. This indicates that exposure of wild oat populations to fenoxaprop over 4-5 yr has resulted in an increase in the proportion of resistance. Allele-specific PCR was performed to examine point mutation in all collected populations. The results indicated that only one type of mutant allele, Asp- 2,078-Gly, was detected in all fenoxaprop-resistant samples from large geographical scales and different years. The herbicide-resistance result screened by greenhouse whole plant was comparable to the status by AS-PCR assay.

Horseweed (Conyza canadensis) and hairy fleabane (C. bonariensis) are two common weeds of increasing prevalence in the perennial cropping systems and non-crop areas of Central California. Further, glyphosate-resistant (GR) populations of these two species were recently documented.  In this region, these species can emerge in fall and overwinter as a rosette or emerge in late winter/early spring and set seed in late summer. However, the difference in growth and phenological development of the plants emerging at these two times of the year has not been studied.  Also, it is not known if emergence characteristics or phenological differences contribute to glyphosate susceptibility in GR and GS biotypes of these two species. Therefore, a study was conducted in 2010/2011 to compare the growth and development of fall and spring planted GR and GS horseweed and hairy fleabane. The time taken to reach various phenological stages was recorded in growing degree days (GDDs) and final dry mass of the plants was recorded.  Time of planting affected the GDDs required to reach various phenological stages only in hairy fleabane but biotypes did not differ.  In contrast, GR horseweed plants required fewer GDDs to reach the various phenological stages than the GS plants.  Planting date had no effect on final aboveground hairy fleabane biomass but fall-planted horseweed amassed more dry matter than the spring-planted individuals.  The study is being repeated to confirm these findings.    

Aphthona spp. flea beetles were released in the Little Missouri National Grasslands in western North Dakota in 1999 to control leafy spurge.  The change in soil seedbank composition and leafy spurge density were evaluated 5 and 10 yr after Aphthona release to monitor the effectiveness of the biological control agents and resulting weed control on associated plant communities.  A total of 480 soil cores were excavated from loamy overflow and loamy ecological sites and evaluated in the greenhouse.  Leafy spurge populations dramatically declined 5 and 10 yr after Aphthona release.  Leafy spurge stem density decreased from 94 stems/m² in 1999 to 8 and 5 stems/m² in 2004 and 2009, respectively.  Leafy spurge was reduced approximately 97% in the loamy overflow ecological sites and nearly 79% in the loamy ecological sites.  Leafy spurge was the dominant species in the soil seedbank in 1999 and constituted nearly 70% of the seeds, but 10 yr after Aphthona release, leafy spurge seed total was less than 10% of the seedbank.  High seral forbs increased from less than 5% of the seedbank in 1999 to 25% by 2004.  However, both high seral grasses and forbs were being replaced by Kentucky bluegrass (Poa pratensis L.) in 2009.  Kentucky bluegrass was the most prevalent plant species in the loamy overflow sites by 2009 and increased over 200% from 1999.  Additionally, 10 yr after Aphthona release, there was a slight increase in native plant species diversity, but a decrease in germination numbers.  High-seral forbs that appeared in the loamy overflow seedbank in 2009 but were absent in 1999 and 2004 included wild onion (Allium textile A. Nelson & J. F. Macbr.), shy wallflower [Erysimum inconspicuum (S. Watson) MacMill.], locoweed (Oxytropis spp. DC.), and prairie groundsel [Senecio plattensis (Nutt.) Weber & A. Love].  High-seral forb species also increased in the loamy seedbank during the 10 yr study, and constituted 21% in 2009 compared to 5% in 1999.  High-seral grass species that commonly appeared in both the loamy overflow and loamy seedbanks throughout the study included green needlegrass [Nassella viridula (Trin.) Barkworth], little bluestem [Schizachyrium scoparium (Michx.) Nash], and sand dropseed [Sporobolus cryptandrus (Torr.) A. Gray] which maintained a similar percentage of the total seedbank over time.  The recovery rate of native vegetation has been slow; however, the increase in native plant species diversity and the successful long-term control of leafy spurge suggests the soil seedbank is gradually moving towards the recovery and reestablishment of native species in the Little Missouri National Grasslands. 

Organic amendments have been shown to reduce weed emergence and growth and can serve as an invaluable tool for building soil health within organic cropping systems. While the weed suppressive effects of cover crops have been studied extensively, far less attention has been paid to the weed suppression potential of another commonly used organic amendment: compost. Although compost has been shown to suppress emergence of certain weed species, little is known about the mechanisms responsible for this suppression. The central objectives of this research were to evaluate 1) the impact of different rates and placement of compost on weed emergence and growth, and 2) the effects of chemical components of compost on weed seed germination.  A field trial was conducted in fall 2011 to evaluate the effects of mature dairy compost placement (broadcast full-width or banded in-row) and rate (0, 5 or 15 wet T/a) on broccoli yield as well as on emergence and growth of common lambsquarters (Chenopodium album) and giant foxtail (Setaria faberi) sown in microplots either in the broccoli row (IR) or between rows (BR).  Greenhouse studies were performed to test effects of different rates (0 , 5, 10, 20, 50, and 100%) and placement of compost (incorporated vs surface) on emergence of four weed species (C. album, Amaranthus powellii, S. faberi, and Abutilon theophrastii).  In addition, leachate from greenhouse compost treatments was analyzed for pH, electrical conductivity, and available nutrients and evaluated for suppressive effects on weed seed germination in petri dishes.  In the field, C. album emergence IR was stimulated by full-width compost applications (IR rate of 5 T/a), but not at concentrated compost placement in the crop row (IR rate of 15 T/a).  Compost rate and placement had no effect on emergence of S. faberi or on broccoli yields.  In greenhouse studies, compost and compost leachate had differential effects on weeds depending on species and rate.  For A. powellii and A. theophrastii, cumulative emergence declined at higher rates of compost.  In contrast, compost had no effect on cumulative emergence of S. faberi and produced mixed results for C. album- with cumulative emergence declining at low rates of compost, but slightly increasing at high rates of compost compared to the no compost control.  Higher rates of compost produced leachates with progressively higher pH, EC, and nutrients including N, K, Ca, and Mg.  Interestingly, effects of leachate on seed germination did not parallel effects of compost on weed emergence.  Leachates from higher compost treatments suppressed both C. album, S. faberi, and A. theophrastii germination, but had no detectable effect on A. powellii.   Our results demonstrate that 1) compost rate and placement can influence weed emergence; 2) the nature of those effects vary with weed species; and 3) the mechanism of compost suppression or stimulation of weed emergence is not easily explained by the effects of chemical constituents of compost leachate on seed germination.  

Perennial pepperweed is a mustard (Brassicaceae) native to Eurasia, and was unintentionally introduced to North America in the early 1900s.  It has since spread over millions of acres, and is an aggressive invader of wetlands, meadows, roadsides, and agricultural fields where the soil is slightly alkaline or saline.  Control of this weed is problematic; physical control (mechanical removal, prescribed burning, and inundation) and chemical control are generally not effective and have other adverse consequences.  In North America the occurrence of several native Lepidium species, as well as brassicaceous crops, makes biological control a challenge.  However, foreign exploration in regions where perennial pepperweed co-occurs with other Lepidium species may nevertheless yield promising candidate agents.  The natural enemy complex of perennial pepperweed in its introduced range is poorly understood.  This information would be useful in future control efforts because it would help evaluate whether existing natural enemies could be enhanced, as well as determine the potential for interference, or perhaps synergistic effects, between candidate agents for introduction and natural enemies that are already present.  Results of a 3-year study in Nevada and California showed that perennial pepperweed is attacked by several above-ground natural enemies, including weevils, flea beetles, leafhoppers, and white rust.  Root attack was rare.  Site-specific differences in natural enemy attack were observed; for example, there was a paucity of natural enemies at sites west of the Sierra Nevada mountains.  Our results will provide baseline information that will aid foreign exploration and guide biocontrol agent selection.

A conventional practice for tropical soda apple (TSA; Solanum viarum) control in pastures is mowing, although it may be necessary to mow up to three times in order to kill TSA roots and prevent regrowth.  Application of an herbicide to cut plant surfaces while mowing with a “wet-blade” mower might eliminate the need for repeated mowing.  Tobacco mild green mosaic tobamovirus (TMGMV), a common naturally occurring plant virus has been formulated into a bioherbicide (SolviNix LC).  Cutting TSA stems with hand-held pruning shears dipped in SolviNix was shown to prevent regrowth. This wet-blade simulation made it feasible to test the application of SolviNix using a wet-blade mower under field conditions.  SolviNix concentrations at 10 and 50 ug/ml were applied 9.4 and 18.8 L/ha; application rates on a per hectare basis were 0.24 g and 1.2 g for the 10 and 50 ug/ml concentrations applied at 9.4 L/ha and 0.47 and 2.3 g for the 10 and 50 ug/ml concentrations applied at 18.8 L/ha. Other treatments included aminopyralid at 88 g/ha and aminocyclopyrachlor at 561 g/ha applied at both 9.4 and 18.8 L/ha. Water was applied as the untreated control for both application volumes.  The experiment was arranged in a randomized complete block design and was repeated at two locations in central and south Florida. Treatments were evaluated by counting plants in each 3 m by 60 m plot at 50 days after the wet-blade application.  Control of TSA ranged from 57 to 59% with water alone at 9.4 and 18.8 L/ha, respectively.  Aminopyralid resulted in 80% TSA control when applied at 9.4 L/ha, but increased to 92% when applied at 18.8 L/ha.  Control of TSA with aminocyclopyrachlor was >95% regardless of application volume.  SolviNix did not result in greater control than water alone at any application rate, suggesting that either the application volume or an increased concentration may be required to obtain similar results as those with synthetic herbicides.  Since excellent control with SolviNix has previously been demonstrated with a simulated wet-blade application, future testing should examine the use of increased application volumes or increased solution concentrations of the bioherbicide using wet-blade equipment. 

The influence of ground cover plants on the ecosystem service of weed seed predation by crickets was evaluated on paddy field levees in Japan in 2010 and 2011. We compared the activity density of crickets and invertebrate seed predation on Lolium multiflorum, a non-native grass weed, among 5 vegetation types grown on paddy levees: the ground covers Eremochloa ophiuroides, Phyla canescens, Phlox subulata, and Zoysia japonica and weedy vegetation dominated by Digitaria ciliaris. Simultaneously, the activity density of crickets and invertebrate seed predation were quantified in a paddy field interior to determine whether crickets penetrate into paddy fields and consume weed seeds after irrigation is stopped and the water recedes. Camera recordings showed that crickets were the predominant invertebrate seed predators on the paddy levees and in the paddy field interior. The activity density of crickets tended to be higher on the levees with E. ophiuroides, P. canescens, and P. subulata [5.8–7.2 individuals (2010) and 5.4–7.6 individuals (2011)/trap/day] than on those with Z. japonica and weedy vegetation [1.0–2.2 individuals (2010) and 2.2–3.2 individuals (2011)/trap/day]. In particular, on the levees with P. canescens and P. subulata, seed predation was also consistently high in both years. In the paddy field interior, the activity density of crickets and invertebrate seed predation were similar to those on the paddy levee. These results indicate that P. canescens and P. subulata can increase the number of crickets and stably enhance seed predation on paddy field levees. Furthermore, crickets may penetrate into the paddy fields from the levees after irrigation water recedes and contribute to weed suppression in the field interiors.

Johnsongrass is one of the ten most noxious weed in the world causing great yield losses to crops through interference.  An alternative weed management is through biological control. A study with three Fusarium oxysporum strain (S1, S2 and S3) at three conidia concentration was performed to evaluate the effect over johnsongrass sprouting. Rhizomes of johnsongrass were trimmed to pieces with one node each, weighting from 0.5 to 1.0 grams. These pieces were washed-free of soil, then soaked in a solution with 10^-4, 10^-5 and 10^-6 conidia(.cm^-3) concentration. Rhizomes were layered in trays filled with sand and held in growth chamber up to experiments were established. Temperature and relative humidity were 25°C and 65 %, respectively.

For the highest concentration there was no weed emergence at any of the strain of fungi. In the intermediate concentration, there was no sprouting in the S2 strain with respect to control. The S1 and S3 produced a emergence decline of 70 % and 50 % respectively.

At the lowest concentration, the sprouting reduction was 75 %, 50% and 70 % for S1, S2 and S3, respectively.

The three strains of Fusarium oxysporum are appearing as interesting biocontrol agents of Johnsongrass vegetative propagation.

Parasitic broomrapes (Orobanche spp.) are major uncontrolled weeds causing major losses to vegetable, grain legume and sunflower crops. Many broomrape control strategies have been tested over the years. In this investigation isolates of Fusarium solani were recovered from diseased broomrape collected from fields in Southern Khorasan. The pathogenicity of isolates on broomrape was evaluated on orobanch stem and seed. F. solani damaged all of the developmental stages of broomrape and prevented the damage that broomrape causes to tomato plants .The germination of inoculated seed was significantly reduced, germ tubes of microconidia penetrated all parts of the thick, complex seed testa, and seed contents were completely destroyed. Thus, the inoculation of soils with F. solani may be used to reduce the Orobanche seed bank.

Due to the absorption and remittance of ambient sunlight through leaf tissue, the ratio of red to far-red light has been cited as a major factor influencing the ability of a plant to detect neighbors.  This study examined corn and soybean responses to soil covered with red or black tarps and compared these responses to weed-free and weedy treatments.  Corn and soybean were grown in the field, where tarps covered the soil.  In the field, tarps and weeds were removed at V-2, V-4, V-6, and V-8 corn growth stages and V-1, V-3, and V-5 soybean growth stages with sampling occurring at each stage.  In addition, corn was grown under greenhouse conditions, where tarp strips were hung to surround the plants and sampled at V-2 and V-4. The red tarp treatment reduced the red/far red light ratio by about 15% compared with the weed-free control. For corn, unlike weed interference which reduced most measured parameters by V-2, red and black tarps did not influence plant biomass, chlorophyll, or height compared with the weed-free control.  However, leaf area per plant was increased over both the black tarp and weed-free treatments when red tarp remained until V-6 or V-8 and plants were sampled at V-8.  At harvest, corn grown with weed competition beyond V-4 had reduced corn stover and grain yields.  Red and black tarp treatments had yields similar to the weed-free control.  At V-1, soybeans grown under the influence of the red tarp had increased leaf area compared to soybean grown with black tarp, weeds, or weed-free control but were shorter than the weed-free control and grass treated plants.  At V-3, soybeans grown with red tarp until either V-1 or V-3 had greater leaf area than the control or plants grown with weeds.   At V-5, when treatments remained until V5, soybean leaf areas were similar between the red tarp and weed-free control treatments but much greater than if weeds or black tarp were present.  In the greenhouse, corn grown with grass weed interference had reductions in plant height, leaf area, and biomass at V-2 and V-4 growth stages, compared with weed-free control plants.  At V4, the classic shade avoidance response may have been observed as corn height and leaf area increased by about 30% compared with weed-free control, although biomasses between these treatments were similar. These data show differences between weed competition and red tarp treatments and may indicate that far red light response may not account for the majority of weed interference effects in the field.              

Drought and weed pressure are two variables that can negatively affect crop yield. The impacts of drought and weed pressure on a plant are not limited to the visual and physiological indicators readily observed by the eye or by chemical measurements (such as protein, weight, density, starch, etc.).  Biotic and abiotic stresses on a plant are met by reactions and adjustments in gene regulation. Drought is a more simply defined stressor (lack of adequate available water) than weed stress which may affect crop growth and yield by competing for water, nutrients, and/or light, or change light quality. If weeds affect yield primarily by competing for water, then plant responses to drought and weed stress would consist of somewhat similar gene expressions. 

Results from two studies compare the similarities and differences of drought and weed stresses on gene expression in corn. In the drought study, corn was sampled at V-12 stage of plant growth in summit (low soil water) and toeslope (adequate soil water) field positions. Weed-stressed corn was sampled at the V-8 stage with weeds removed at V2, V4, V6, or V8 and growth and gene expression were compared to weed-free corn.  Gene expression was analyzed using transciptome analysis with microarray chips and qRT-PCR for both studies.

Drought stressed corn displayed leaf curling, and had 15% less biomass and plant height than non-stressed corn.  Genes up-regulated in water-limited plants were associated with tolerance to cold, salt, and drying. However, down-regulated gene expression in water limited plants included those involved with nutrient uptake, wound recovery, pest and fungal disease resistance, and photosynthetic capacity.  Circadian rhythm (clock genes and red/far red signaling pathway) were impacted, which potentially has a profound effect on flowering, growth, and nutrient uptake. Transcriptome analysis was crucial to demonstrate water-stress at a landscape position can greatly diminish ability to uptake nutrients and withstand and recover from pest attacks.

Weed-stressed corn had reductions in biomass ranging from 0% (V-2 removal) to 60% (V-8 removal) and up to 52% leaf area loss (V-8 removal). Weed-stressed corn displayed gene expression patterns indicating photosynthetic processes were down regulated when weeds were present. Examples of the genes that were preferentially down-regulated as early as V2 were Rubisco, and Pepc. These photosynthetic gene expressions remained down-regulated even if weeds were removed after the critical weed free period. Genes associated with circadian rhythm, nutrient uptake, and changes to cold, salt, and drying tolerance showed slight or no impact when weeds were present.  The comparison of these data indicates that corn growth under weed competition may not be primarily influenced by water stress early in the crop season.

In an environment under water deficit and competition, weed species may show inefficient water use. In order to determine the strategy of water consumption of Zea mays and Sorghum halepense under two soil water availability conditions, soil (Y_s) and leaf water potential (Y_l) , relative water content (RWC) and leaf gas exchange parameters were measured during the critical period of crop competition in pot experiments where these species where grown alone (one plant per pot) or in competition (one plant of each species per pot).

In addition, , relative yield total and aggressivity index of both components were calculated. S.halepense showed continuous absorption of water, reaching a lower Y_l than  Z.mays hybrids. S.halepense maintained a RWC above 90%, and decreased to 70% only in competition under low water availability. In Z.mays, RWC declined to values of 70% for both water levels studied. S.halepense showed an active leaf gas exchange. Z.mays hybrids showed lower competitive ability than S.halepense for both competition levels due to a conservative strategy for water use.

Sustained water use by the weed could be the cause of the increased aggressivity of S.halepense under water deficit conditions.

The glyphosate is a broad spectrum herbicide, non-selective, and the site of action is the inhibition of the enzyme 5-enolpyruvylshikimate 3-phosphate synthase (EPSPs). The inhibition of the enzyme results in a reduction in the synthesis of aromatic amino acids (phenylalanine, tyrosine and tryptophan), and secondary compounds. The glyphosate block of the shikimic acid pathway and causes the accumulation of some compounds like shikimic acid and quinic acid, and other metabolic and physiological effects in plants. The objective of this study was to evaluate the metabolic and physiological effects in corn plants after application of glyphosate and phosphite. The experiment was carried out in greenhouse in the Faculty of Agronomic Sciences at São Paulo State University. It was used the corn Pioneer 30F53, planted in vases containing 5 liters of substrate. The treatments were: glyphosate (72 g a.e. ha^-1), glyphosate (720 g a.e. ha^-1), glyphosate (72 g a.e. ha^-1) + phosphite (3 L ha^-1), glyphosate (720 g a.e. ha^-1) + phosphite (3 L ha^-1), phosphite (3 L ha ^-1) and an untreated control. Two experiments were carried out with the same treatments but with different evaluations. At first, it were realized five samples of all corn plant leaves at 2, 4, 6, 10 and 15 days after application (DAA). The second experiment was performed the evaluation of the electron transport rate (ETR) in young and mature leaves, visual evaluations of intoxication, height and weight of the plants. The leaves collected were dried, grated and used to quantify the compounds: shikimic acid, quinic acid, 3-dehydroshikimic acid, aminomethylphosphonic acid (AMPA), glyphosate, phenylalanine, tyrosine and tryptophan. Extraction tests of compounds were conducted to choose the most appropriate and were development of analytical methods in LC-MS/MS. The extraction of the compounds that proved most appropriate was using the dry mass of samples. Glyphosate and AMPA were detected only at the highest dose applied, with or without the phosphite, and these treatments were observed the higher concentrations of shikimic acid, quinic acid and 3-dehydroshikimic acid. The effect of glyphosate on aromatic amino acids levels was only transient. The association of potassium phosphite with the lower dose of glyphosate increased the toxicity of corn in comparison to the control and the glyphosate isolated. The corn plants had a decrease in the electron transport rate (ETR) after application of the highest dose of glyphosate associated or not with potassium phosphite.

Ryegrass (Lolium sp.) is a common weed problem in wheat and barley crops in the South region of Buenos Aires province (Argentina). Glyphosate is frequently used to control weeds on  field prior to crop sowing or emergence. The herbicide triggers the inhibition of the target enzyme pone el nombre completo (EPSP sinthetase). Also, The initial effect in photosynthesis is an immediate decline of ribulose-1,5-biphosohate levels (the primary acceptor of CO₂ in the Calvin cycle), followed by decreased levels of other intermediates in carbon fixation. In the last years, several Lolium spp. populations were characterized as glyphosate-resistant weeds.

The aim of this work was to assess the glyphosate effects on the net photosynthetic rate (An)  of two Lolium perenne L. populations with differential herbicide-sensitivity. Plants of resistant and susceptible populations were grown in a greenhouse and treated with 1,020 g ae.ha^-1 of glyphosate.   The last fully expanded leaf was used to determine the An with a portable infrared gas analyzer with a photon flux density 1,000 µmol photons.m^-2.s^-1, 360ppm CO₂ at 25°C. The recordings were repeated periodically until 10 days post-application (DPA).

At 2 DPA, the An decreased 23% in the susceptible population sprayed with glyphosate. From that moment, the glyphosate promoted a gradually inhibition in the An that reached 80% of inhibition at 10 DPA. In contrast, An in the resistant population did not decrease significantly until 5 DPA when the reduction was 22%. This difference remained stable up to 10 DPA.

The current results contribute to the physiological characterization of glyphosate-resistant perennial ryegrass population.

Plant responses to biotic and abiotic stress could be determined through optical remote sensing. However there is no information about differences in reflections spectra obtained by remote sensing that different biotypes of same species can shown. In this work by using spectral signatures in the range 350-900nm (at 1nm resolution), we studied the spectral response of Lolium perenne biotypes, obtained from crosses between resistant and susceptible to glyphosate. No substantive differences in the visible spectral range (400-950 nm) where observed for the different genotypes. This spectral response is determined by pigments. Moreover, spectral differences were detected in the far red (770 nm) and near infrared (800-900 nm) range. Here, the leaves reflectance is due to the internal structure of the leaf that affects the refractive index. These results suggest that is possible to determine by means of remote sensing the resistance degrees of perennial ryegrass biotypes to glyphosate.

A tall waterhemp [Amaranthus tuberculatus (Moq.) Sauer] population selected from a glyphosate-resistant soybean field in Mississippi was confirmed to be resistant to glyphosate in 2010. Studies were initiated to determine the mechanism of glyphosate resistance in this population. A glyphosate-susceptible population was included for comparison. The absorption pattern of ¹⁴C-glyphosate between the resistant and susceptible populations was similar up to 24 h after treatment (HAT). Thereafter, the susceptible population absorbed more glyphosate (55 and 49% of absorbed) compared to the resistant population (41 and 40% of absorbed) by 48 and 72 HAT. Treating a single leaf with glyphosate solution at the field use rate (0.84 kg ha^-1) as ten 1-µl droplets provided greater control (85%) and shoot fresh weight reduction (73% of nontreated control) of the susceptible plants compared to the resistant plants (29% control and shoot fresh weight reduction of 34% of nontreated control), indicating a reduced movement of glyphosate from the treated leaf to other plant parts in the resistant compared to the susceptible population. Sequence analysis of 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), the target site of glyphosate, transcript from resistant and susceptible plants identified a consistent single nucleotide polymorphism (T/C) between resistant/susceptible plants, resulting in a proline to serine amino acid substitution in the resistant population. Genomic estimation of EPSPS gene copy number relative to acetolactate synthase (ALS) using quantitative PCR showed that the resistant population contained a single copy of the EPSPS gene as with the susceptible population. Quantitative RT-PCR on cDNA revealed that the single copy of EPSPS gene was equally expressed in resistant and susceptible populations. Further investigations on the role of glyphosate translocation and EPSPS gene sequence in the mechanism of glyphosate resistance are underway. vijay.nandula@ars.usda.gov

Historically, acetolactate synthase (ALS) –inhibiting herbicides have effectively controlled rice flatsedge, a troublesome weed of rice in the Midsouth.  In 2010, halosulfuron, an ALS-inhibiting herbicide, failed to control rice flatsedge in some rice fields of Arkansas.  Greenhouse studies were conducted with halosulfuron-resistant and –susceptible biotypes to confirm cross resistance to other ALS-inhibiting herbicides, characterize resistance to halosulfuron, evaluate alternative rice herbicides for the control of halosulfuron-resistant rice flatsedge, and evaluate if altered target site or increased halosulfuron metabolism by cytochrome P450 monooxygenase is the mechanism of resistance to halosulfuron.  Dose response studies revealed that the resistant biotype was more than 488-times resistant to halosulfuron compared to a susceptible biotype.  Field rate applications of ALS-inhibiting herbicides [belonging to different chemical families including, imidazolinone (imazamox or imazethapyr at 35 and 70 g ai ha^-1, respectively), pyrimidinylthio-benzoate (bispyribac-sodium at 35 g ai ha^-1), sulfonylurea (halosulfuron or orthosulfamuron at 53 and 22 g ai ha^-1, respectively), and triazolopyrimidine (penoxsulam at 49 g ai ha^-1)] controlled the susceptible biotype 77 to 100%, whereas, control of the resistant biotype was 0%.  Control of resistant and susceptible rice flatsedge biotypes with bentazon at 840 g ai ha^-1, propanil at 4487 g ai ha^-1, and propanil at 2522 g ha^-1 plus thiobencarb at 2522 g ai ha^-1 was >93%; however, control of both biotypes with quinclorac at 560 g ai ha^-1 and thiobencarb at 4484 g ai ha^-1 was less than 39%.

Cytochrome P450 monooxygenase metabolizes various herbicides, and in turn imparts herbicide resistance to several weed species.  Addition of malathion (cytochrome P450 monooxygenase inhibitor) at 1000 g ai ha^-1 to halosulfuron at 53 g ha^-1 did not increase control of the resistant biotype compared to halosulfuron at 53 g ha^-1 applied alone, revealing that increased halosulfuron metabolism by cytochrome P450 monooxygenase is not the mechanism of resistance in rice flatsedge.  Partial ALS gene sequences of resistant and susceptible biotypes were aligned together to find if mutation in ALS gene is imparting resistance to halosulfuron.  No mutation compared to the susceptible biotype was detected in the sequenced conserved region of ALS gene of resistant biotype.  However, high level of resistance to halosulfuron, and cross resistance to ALS-inhibiting herbicides of all chemical families point towards altered target site resistance.  Further studies with regards to ALS gene expression and copy number can shed more light on the resistance mechanism.

Grass weeds are ubiquitous in common bean (Phaseolus vulgaris L.) crop production in Brazil. The objectives of this work were to investigate the correlation of all dependent variables from an herbicide efficacy experiment; and to evaluate the impact of weed leaf angle on the herbicide efficacy. A field experiment has used a factorial arrangement of treatments with five fluazifop rates and five time of the day of herbicide application. The dependent variables assessed at the time of herbicide application included environmental (relative humidity, air temperature, and photossintetically active radiation) and morphological (weed  leaf angle) ones. Herbicide efficacy variables included grass weed mass, density, and visual ratings.  A greenhouse experiment, with Avena sativa L. as the model plant, has investigated the impact of four leaf angle (0, 45, 67, and 90^o in relation to the vertical) on fluazifop efficacy. There was a high correlation for the combination of each two of all the variables evaluated at the time of the herbicide application. Individually, all dependent variable assessed at the time of the herbicide application correlated with the herbicide efficacy variables. From the field experiment, the weed leaf angle was the variable with the highest correlation with each herbicide efficacy variable.  The greenhouse experiment confirmed the hypotheses the plant leaf angle has a major impact of the efficacy of the herbicide. High spray droplet deposition and high droplet duration has been determined when the grass plant had leaves positioned on the horizontal. This work indicates the correct time of the day the herbicide application can reduce the rate of the herbicide and maintain the compound efficacy.

Several USDA conservation programs are promoting the conversion of cropland to non-agricultural use.  These areas are often planted with native species to attract wildlife and / or to provide a barrier to inhibit runoff from adjacent cropland.  During transition periods, other plant species may also emerge or become dominant.  In Beasley Lake Watershed, Sunflower County, Mississippi, areas along the edge of cropland were converted to quail buffer (planted with a mixture of native plants) or cottonwood trees in Fall 2007.  Succession of plant species was monitored by a sequential time study of species occurrence within twenty-seven 2m x 2m plots, with three replicate plots located in each of three different management areas (row crop, quail buffer, and cottonwood trees) in three different sub-drainage areas.  Species occurrence was measured as presence of at least one live plant within the plot area, recorded during late winter, late spring, and late summer each year from 2008 through 2011.  A visual estimate of surface coverage by living plant material was also recorded.  At least 90 different species were observed during the study period.  Overall, the five most commonly encountered species were Solidago spp. (goldenrod), Lamium amplexicaule L. (henbit deadnettle), Echinochloa crus-galli (L.) P. Beauv. (barnyard grass), Conyza canadensis (L.) Cronquist (Canadian horseweed), and Urochloa ramose (L.) Nguyen (signalgrass).  Average number of species encountered per year was lowest in the row crop area (5 species), somewhat greater in the quail buffer (11 species), and highest in the cottonwood tree areas (15 species), a pattern seen consistently in each of the four years of the project.  Average number of grass species were 1, 4, and 4 for the row crop, buffer, and tree areas, respectively.  Average number of species encountered in plots of all areas were very similar during Fall and Winter periods (9 and 8, respectively), but higher during Spring (12 species).  Average number of species observed varied from year to year, but no trends were observed over the study period.

Understanding nutrient cycling in agro-ecosystems is essential for maximizing corn grain yield while minimizing environmental impact.  Weeds assimilate large quantities of N, which generally increases with N application rate, and net mineralization occurs at C:N ratios less than 30, but little is understood about the fate of weed residues subsequent to postemergence weed control.  Our objectives were to compare N mineralization of three weed species (common lambsquarters, common ragweed, and giant foxtail) at two sizes (10 and 20 cm) over a twelve week period.  Weeds were collected from a field study conducted in 2011 in East Lansing, MI.  Weeds were collected from plots where 0, 67, 134, or 202 kg N ha^-1 was applied.  Total C and N content of the weed residues was determined by the Dumas method.  Weed residues were placed in specimen cups containing 20 g dry weight equivalent field soil at a rate of 60 mg N kg^-1 soil.  Specimen cups were incubated at room temperature and soil NO₃-N and NH₄-N was destructively measured 0, 1, 2, 4, 8, and 12 weeks after incubation.  Control (soil only) NO₃-N and NH₄-N was measured at each incubation time to correct for N mineralization from soil organic matter.  Nitrogen mineralization was considered to be the total inorganic N content of the soil after subtracting N mineralization from the control.  Nitrogen mineralization was analyzed using ANOVA in Proc Mixed and modeled over the twelve week period.  Nitrogen mineralization from weed residue was rapid during the first 2 wk of incubation.  Approximately 50% of the N was released from common lambsquarters and common ragweed residue when weeds were grown at 67 to 202 kg N ha^-1.  Approximately 20% of the N was released from giant foxtail residue when grown at 67 to 202 kg N ha^-1.  When no N was applied, rate of N release was slower and N was immobilized from residue of giant foxtail that was 20 cm tall and grown with no N.  Results of this laboratory study indicate that weeds can significantly impact N cycling and mineralization is dependent on weed species, N application, and weed size.

The herbicides dynamics in the environment and soil cultivated with sugarcane, can be very affected by the crop production system adopted in relation to the presence or absence of straw on the ground. The herbicide interception by straw may promote the herbicide retention and exposition to favorable conditions for the photodegradation and volatilization until it is taken to the soil, where it can suffer processes of sorption, leaching and/or degradation by physical, chemical and biological effects, and be absorbed by weeds and crops. In the sugarcane culture these processes are very important, because they determine the product amount that will be available in the soil solution, in enough quantities to promote the weed control, the herbicide selectivity and environment safety. The objectives of this study were to evaluate the amicarbazone leaching and availability in the soil, when applied in the different sugarcane production systems in relation to the presence of the straw on the ground and to establish a correlation between the amicarbazone levels in different systems and the control of the most important weeds of the sugarcane. Soil samples were collected in the depths from 0 to 10, 10 to 20 and 20 to 40 cm, in five experiments and application timings in the locations of São Paulo State – Brazil, with the applications on June 27^th, August 31^st, October 3^rd and 20^th and November 23^rd. Two treatments without the application of the herbicide (with and without the mulch) were also set up to referee the efficacy evaluations. An evaluation was done for the control to the Ipomoea grandifolia, Ipomoea nil, Ipomoea quamoclit, Merremia cissoides, Euphorbia heterophylla, Bidens pilosa, Brachiaria decumbens, Panicum maximum and Digitaria spp and 80 soil samples were collected at each depth in each treatment at different periods. A method for extraction of soil solution by cartridges centrifuging containing 7 g of soil and a method in liquid chromatography and mass spectrometry to quantify the amicarbazone in the samples were developed. After determining the amicarbazone concentrations in soil, a study was conducted comparing the results of the amicarbazone amount in the soil in a surface layer (up to 10 cm) and the percentages of weed control. In all areas and times of the application the amicarbazone was found in all depths evaluated, demonstrating a high mobility in soil. In periods of higher water restriction were observed at all depths, higher amicarbazone levels in the treatments without straw and with the harvester application (under the straw). In the clay soil with high organic material levels, low amicarbazone concentrations at different depths and periods were observed. In the periods of high water availability in sandy soils of medium texture, high concentrations were observed for the application with the harvester or on the straw. The most sensitive species in descending order to amicarbazone are B. pilosa, I. quamoclit, M. cissoides, E. heterophylla, I. nil, I. grandifolia, B. decumbens and P. maximum and their critical concentrations (from which there was control over 95%) were 2, 3, 7, 10, 13, 27, 30 and 30 µg kg of soil^-1.

Pyroxasulfone is a highly active, soil-applied herbicide that controls many grasses and small-seeded broadleaf weeds.  This herbicide is being developed for use in wheat, corn, soybeans and sunflowers.  In Australia pyroxasulfone is ofen applied to dry soils prior to the beginning of winter rainfall, which may occur several weeks after applicaiton.  A study was conducted comparing the rate of dissipation of pyroxasulfone with dimethenamid and metolachlor on six Australian soils.  The soils ranged from loamy sand to clay.  All three herbicides bound weakly to the soils tested.  the average binding constant across all six soils was 0.7, 1.2 and 2.1 for pyroxasulfone, dimethenamid and metolachlor, respectively.  The bioavailability of the three herbicides declined over the 28 d of the experiment.  The average half life of the three herbicides averaged over the six soils was 26.6, 10.9 and 15.8 for pyroxasulfone, dimethenamid and metoalchlor, respectivley.  These resuls indicate the pyroxasulfone binds less tightly and dissipates more slower in these six Australian soils compared to dimethenamid and metolchlor.  Furthermore, the bioavailability of these herbicides decreases over time.

Indaziflam, a new alkylazine herbicide that inhibits cellulose biosynthesis, is under current development for soil
applications in perennial crops and nonagricultural areas. Sorption and desorption of indaziflam in six soils from Brazil and three
soils from the United States, with different physical chemical properties, were investigated using the batch equilibration method.
Sorption kinetics demonstrated that soil-
solution equilibrium was attained in <24 h. The Freundlich equation described the
sorption behavior of the herbicide for all soils (R2 > 0.99). Kf values of the Brazilian oxisols ranged from 4.66 to 29.3, and 1/n values
were ≥0.95. Sorption was positively correlated to %OC and clay contents. U.S. mollisol Kf values ranged from 6.62 to 14.3; 1/n
values for sorption were ≥0.92. Kf values from mollisols were also positively correlated with %OC. These results suggest that
indaziflam potential mobility, based solely on its sorption coefficients, would range from moderate to low in soil. Desorption was
hysteretic on all soils, further decreasing its potential mobility for offsite transport.

Imidazolinone herbicides may persistent in soil and may carryover to non-tolerant crops such as non-tolerant rice. As an alternative to minimize the herbicide carryover, it can be used plants to reduce the herbicide concentration in soil in a process called phytoremediation. For this reason, greenhouse experiments were carried out with the objective of evaluate the efficiency plant species to remediate paddy soil contaminated with the herbicide mixture of imazethapyr and imazapic, using the non-tolerant rice cultivar IRGA 417 as herbicide indicator. It was carried out four experiments, two of them to grow the species in the contaminated soil (summer and winter) and two to check the carryover effect to non-tolerant. The experiments were in a randomized blocks design in a split plot arrangements with four replications. Factor A consisted of plant species: in the winter experiment the species were: Avena strigosa, Brassica sp., Lolium multiflorum, Lotus corniculatus, Raphanus sativus, Secale cereale, Trifolium pratense, Trifolium repens, Trifolium vesiculosum, Triticum aestivum, Vicia sativa, and a uncultivated plot; in the summer experiment the species were: Canavalia ensiformis, Crotalaria juncea, Glycine max, Stizolobium aterrimum, and an uncultivated plot. Factor B, included nine initial rates of the herbicide mixture of imazethapyr + imazapic (75 + 25 g ai L^-1) in soil: zero, 50, 100, 200, 300, 400, 500, 1000 and 4000 mL ha^-1. After the cultivation of the species, they were harvested and non-tolerant rice was drilled to evaluate the remediation effect (Carryover). It was evaluated rice injury at 7, 14, 21 and 28 days after emergence (DAE), and rice shoot biomass at 28 DAE. The winter species Brassica napus, Lolium multiflorum, Vicia sativa, Raphanus sativus, Trifolium pratense, Trifolium vesiculosum, Triticum aestivum and the summer species Crotalaria juncea, Canavalia ensiformis, Glycine max and Stizolobium aterrimum were effective in reducing the effect of the herbicide on non-tolerant rice plants grown in succession.

Weed control in irrigated organic potato production relies on the effectiveness of cultivation, harrowing, and weed suppressing varieties.  A potential alternative that maximizes early season weed suppression is the use of cover crops.  When potato is planted into a killed cover crop residue, the residue acts to minimize safe sites for weed seed germination.  Two studies were conducted to determine if cover crop treatments including no cover crop, triticale, rye, hairy vetch, turnip/radish, rye/canola, or rye/hairy were more effective than current weed control in organic potato.  Cover crop residue was sufficient and reached an average high of 5,892 kg/ha with the rye/canola combination.  Triticale and rye cover crops accumulated far less biomass in 2011 than in 2010.  Cover crops were killed chemically with glyphosate or mechanically with disk-till or roto-till prior to planting the two potato cultivars ‘Russet Norkotah’ and ‘Yukon Gold’.  Weed counts, weights, and visual evaluations within a 0.09 m² quadrat were taken three times throughout the growing season at approximately two, four, and six weeks after potato planting.  Treatments that included a cover crop had similar weed control to treatments with no cover crop.  Differences were seen between the three cover crop kill methods, though the best kill treatment varied between years.  The three cover crop kill methods and subsequent potato planting presented mechanical difficulties, as potatoes are typically planted into well worked soil, as opposed to no-till or high residue soil.  Potato yields were lower than expected in conventional or standard organic practice, but still deemed acceptable.  The use of cover crops to control weeds in organic potato production shows promise as an alternative method for producers looking for alternate weed control methods. 

Weed management in organic cropping systems is challenging and often heavily reliant upon tillage.  Organic production emphasizes building soil quality and increasing soil organic matter, both of which are negatively impacted by frequent, intense tillage.  Obtaining adequate weed control while reducing tillage frequency is desirable in organic systems because of the potential for improving soil structure and reducing costs associated with field operations.  The Reduced-tillage Organic Systems Experiment (ROSE) was initiated in 2010 at three locations in the Mid-Atlantic region of the United States to test different combinations of weed control tactics in a cover crop-based, rotational no-till organic grain rotation.  ROSE is being conducted at the University of Delaware Carvel Research and Education Center in southern Delaware, the USDA-ARS research facility in Beltsville, Maryland, and at the Penn State Russell E. Larson Agricultural Research Farm in central Pennsylvania.  In ROSE, a roller-crimper terminated cover crop acts as a weed-suppressive mulch in two of three years and replaces early-season weed control techniques such as tine weeding, rotary hoeing, and shovel cultivation.  Corn and soybean cash crops are no-till planted into the cover crop mulch which results in a reduction of soil disturbance events by about half compared to full-tillage organic systems in which cover crops are terminated with a moldboard plow and the seed bed is prepared for cash crop planting with subsequent disking and harrowing.  The first of three field seasons was completed in 2011 and weed, insect pest, crop yield, and soil data were collected.  First year data are still being processed so preliminary results are presented.  Hairy vetch-triticale and rye cover crop biomass increased with later planting dates at the Delaware site; at the Pennsylvania site, rye biomass increased as planting was delayed while hairy vetch-triticale biomass did not differ across planting dates.  In Pennsylvania, regrowth of hairy vetch-triticale and rye cover crop biomass after rolling was strongly influenced by planting date with later planting dates exhibiting less regrowth.  Total biomass of three weed species, common ragweed (Ambrosia artemisiifolia), smooth pigweed (Amaranthus hybridus), and giant foxtail (Setaria faberi), was reduced by high-residue cultivation in corn at the Delaware site and in both corn and soybean in Pennsylvania.  This study will be repeated in 2012 and 2013 with both corn and soybean entries present in all years.  At completion, guidelines for managing grain crops in reduced tillage organic systems will be developed to help Northeast farmers improve the sustainability of their cropping systems.

Cotton in California’s San Joaquin Valley (SJV) has traditionally been grown with soil- disturbing tillage systems that are irrigated by flood, furrow, or sprinkler, and have limited crop rotation options.  In recent years, water supplies have been diminishing, soil quality is deteriorating, and air quality regulations are increasing in the SJV. These issues have challenged growers to look for new cropping systems to continue farming economically.  Overhead and subsurface drip irrigation systems are two water conservation techniques being tested in the SJV.  These techniques are being combined with reduced tillage and strategic crop rotations.  However, the weed population dynamics in these new cropping systems has not been documented.  Therefore, the goal of this study was to compare the weed population dynamics and crop yields in the overhead, subsurface drip, and furrow irrigation, in standard and no-tillage systems in a corn-silage wheat-cotton rotation.  The rotation was initiated in 2008.  Crop rotation can be difficult in traditional cotton cropping systems because it requires reformation of raised beds.  However, the use of overhead or subsurface drip irrigation allowed planting of cotton without beds and made crop rotation feasible.  Results have shown that the overhead system had more (P<0.05) weed densities than the furrow or drip system.  In one season there were more (P<0.05) weeds in the no tillage than in the standard tillage plots.  Strategic use of Roundup Ready (RR) corn – silage wheat – RR cotton rotation and reduced-tillage system has reduced weed population to almost zero in some plots in 2011.  Wheat has been planted in Fall 2011 after cotton and it will be harvested as silage.  The study will rotate to cotton in Spring 2012.  Weed seedbanks in the different treatments will be monitored.  Crop growth parameters, crop yield, soil moisture, and data on other pests are also being collected.

We examined the feasibility of applying low input systems to mature 20+ yr-old conservation tillage plots. The objective of this study was to assess the relative efficacy of weed control across cropping systems by comparing POST to PRE weed control weed communities. The experiment was conducted at La Pocatière, QC (47E 21' N, 70E 02' W), on a Kamouraska clay (fine, mixed, frigid Typic Humaquept). The strip spilt plot design included tillage and cropping systems as factors, and four replicates (plot size: 5 x 13 m). Tillage treatments, initiated in autumn 1987, were: moldboard plow (MP), chisel plow (CP), and no‑till (NT). Cropping systems included: an organic (ORG) system relying on organic fertilizers and mechanical weed control; an herbicide-free (HF) system using mineral fertilizers and mechanical weed control; a system using transgenic herbicide resistant crops (GM); and a conventional (CONV) system using mineral fertilizers and various herbicides. In 2009, plots were seeded to corn on 26 May in 76 cm rows. Glyphosate + MCPA was applied to CONV plots on 8 June, whereas glyphosate was applied to GM plots on 8 and 24 June. On 18 June, MP-HF and MP-ORG plots were harrowed, whereas CP-ORG, CP-HF, and exceptionally NT-ORG and NT-HF plots were cultivated (Hiniker^TM), this being the first tillage operation in these NT plots in 22 years. In 2010, glyphosate was applied on 1 May to all cropping systems except OR. A stale seedbed was prepared in tilled plots (MP, CP) with a rigid tooth harrow on 18 May and 27 May. Soybean was seeded on 28 May in 18 cm rows. HF and ORG plots with MP and CP tillage were harrowed on 30 June. Fomesafen + fluazifop-butyl was applied to CONV plots and glyphosate to GM plots on 2 July. The HF and ORG plots were harrowed on 30 June. Weed communities sampled PRE (June) and POST (July) weed control in two quadrats (2009: 50x76 cm; 2010: 50x50 cm) per plot. Plant density was estimated for each weed species. Variables were analyzed with PROC GLIMMIX, with cropping system, tillage, crop and sampling time (PRE, POST) as fixed effects, and replicate as random effect, and a negative binomial error distribution with log-link function. POST weed density was similar or greater than PRE in CONV and GM, despite a reduction in species richness. POST weed density was greater than PRE in HF and ORG, despite no change in species richness, except for HF-corn. Heavy POST infestations were observed for dandelion (Taraxacum officinale) in ORG-corn; yellow foxtail (Setaria pumila) in HF-corn and CONV, HF and ORG soybean; and lambsquarters (Chenopodium album) in HF-soybean. In both crops, POST density in NT was greater than PRE, in spite of weed species richness being similar, and was due to heavy POST yellow foxtail infestations. In soybean, POST densities were greater than PRE in MP and CP, in spite of fewer species. Redroot pigweed (Amaranthus retroflexus), lambsquarters, and cleavers (Galium aparine) had large POST populations in CP-soybean; dandelion and yellow foxtail in MP-soybean. Herbicide-based (CONV and GM) and mechanical (HF) weed control in corn provided marginal efficacy; weed control was inadequate in ORG and NT. Herbicide-based and mechanical weed control in soybean was generally inadequate (marginal in GM). These mature tillage systems each came with their own weed problems, independent of cropping systems. Herbicide-based systems, particularly CONV in soybean, did not perform as expected. The poor performance of mechanical weed control in HF and ORG suggested that weed management could be further optimized across all tillage treatments. email: anne.legere@agr.gc.ca

There is currently a high demand for bread wheat grown under sustainable practices. Bread wheat quality and yield can be affected by Fusarium head blight (FHB), a serious disease mainly caused by Fusarium graminearum. This fungus can produce a mycotoxin called deoxynivalenol (DON). The purpose of this study was to determine the effect of three 24-year old tillage treatments (MP: moldboard plow, CP: chisel plow and NT: no-till) and two cropping systems (high-input: herbicide and mineral fertilizer, low-input: mechanical weed control and organic fertilizer) on grain yield, DON content and F. graminearum inoculum production, and weed populations in hard red spring wheat (‘AC Brio’). Trials were conducted in 2009 and 2010 at La Pocatière, QC, Canada, according to a split-block design with tillage treatment as main plot and cropping system as sub-plot, with four replicates (experimental unit: 5 x 30 m). In 2009, low-input CP and NT wheat yields were 13% and 31% lower, respectively, than low-input MP yield which was comparable to all high-input treatment yields (average: 3557 kg ha^-1). Mid-season weed biomass in low-input CP and NT (average: 157 g m^-2) was greater than in other treatments (average: 44 g m^-2). DON content was lower in low-input (3.9 ppm) than in high-input systems (5.5 ppm), regardless of tillage. Fusarium graminearum inoculum from crop residues, isolated at ear base as colony-forming units (CFU), was similar across tillage treatments in the high-input system (average of 12.0 CFU), whereas in the low-input system, the F. graminearum inoculum was lower in NT (6.8 CFU) than in MP (17.0 CFU). The greater weed biomass in reduced tillage in the low-input system may have acted as a physical barrier, preventing spores produced on crop residues to reach wheat ears, thus partially explaining the lower DON content in these treatments in 2009. In 2010, wheat yields were 23% lower in CP and NT compared with MP (3002 kg ha^-1), and 32% lower in low-input than in high-input systems (3028 kg ha^-1). Weed biomass was greater in CP and NT (average: 148 g m^-2) than in MP (65 g m^-2) and was greater in low-input (204 g m^-2) than in high-input systems (53 g m^-2). Tillage and cropping system treatments had no effect on DON content, which averaged 0.4 ppm. On average, F. graminearum inoculum from crop residues in 2010 was less than half that measured in 2009, but in contrast to 2009, F. graminearum inoculum was higher in CP and NT (average:  6.1 CFU) than in MP (3.2 CFU). The presence of wheat crop residues and possibly the greater weed biomass in CP and NT may have created a more favorable environment for inoculum production than in the MP treatment during this relatively hot dry year. It would appear that the potential physical barrier effect provided by weeds, as observed in 2009, was cancelled out in 2010, likely because of environmental conditions. Ultimately, an economic analysis of the data would be needed to determine whether the potential disease protection benefits occasionally provided by weeds could outweigh crop yield loss, particularly in low-input CP systems. email: helene.munger.1@ulaval.ca

Research was conducted to evaluate herbicides for weed control efficacy on perennial grasses, grown for biofuel. The response of four perennial grass crops to PRE and POST herbicides, representing a broad range of herbicide groups, was evaluated. Weed control, especially annual grass control is essential for successful crop establishment. Herbicides with activity on grass weed species that do not injure the crop or reduce biomass yield are required. The objective of these studies was to identify suitable candidate herbicides for registration and labeling to manage weeds in switchgrass, big bluestem, prairie cordgrass and miscanthus.  Saflufenacil and saflufenacil/dimethenamid PRE gave good broadleaf weed control across all crops, however, there was significant injury, especially on switchgrass. Quinclorac PRE gave grass control with no injury while indaziflam gave excellent broad spectrum weed control with no injury. Mesosulfuron-methyl EPOST gave good broadleaf weed control but resulted in significant injury on big bluestem and miscanthus. Several herbicides POST gave good control of broadleaf weeds without crop injury. These include dichlorprop-P/2, 4-D, bromoxynil/MCPA and quinclorac plus dichlorprop-P/2,4-D.  As expected, it was much more difficult to achieve acceptable grass weed control.  Only indaziflam gave excellent grass control with no injury. Quinclorac gave about 50% grass control with no injury. The density of weeds present in the non-weeded control plots compared with treated plots confirmed the need for weed control to ensure successful crop establishment. Herbicides identified that can be used safely to provide acceptable levels of broadleaf and grass weed control include indaziflam and potentially a combination of indaziflam  plus quinclorac. This will lead to improved weed control options that growers could use when establishing these bioenergy crops.

Seedbanks contribute to the persistence of weeds in arable fields and understanding seedbank dynamics is important for predicting future weed problems and for devising suitable seedbank management strategies. Field experiments were conducted in Fayetteville (silt loam soil) and Keiser (clay soil), AR, from autumn 2010 to autumn 2011, to understand the loss in seedbank as a result of seed decay and germination for key arable weeds, including barnyardgrass, johnsongrass, pitted morningglory, Palmer amaranth, and red rice. Two hundred seeds of each species were mixed with soil collected from the experimental site and filled in polyethylene mesh bags. Seed bags were buried during early November at two depths, surface and 5 cm, in three replications. Bags were retrieved at 0.5 (spring 2011) and 1 year (autumn 2011) of burial. Seeds were recovered by washing the soil from each bag; germination and viability (using 1% tetrazolium chrolide solution) tests were subsequently carried out on the recovered seeds. The rate of seedbank loss was greater from spring to autumn compared with that of autumn to spring. Seedbank loss was generally greater in Keiser compared with Fayetteville; the clay soil in Keiser could have facilitated moisture retention and favored microbial infestation of weed seeds. The depth of burial, however, had little effect on seedbank loss for all the weed species investigated, suggesting that production practices that result in a shallow burial of weed seeds (such as disking) may not be sufficient to cause seed loss. In general, most of the retrieved seeds exhibited dormancy, with <5% germination. Among the weed species investigated in this study, johnsongrass was the most persistent species at the end of 1 year (about 55% viable seeds, averaged over locations and burial depths), followed by pitted morningglory (about 29%), Palmer amaranth (about 21%), barnyardgrass (about 8%), and red rice (about 4 %). It is likely that germination could also have contributed to the seed loss observed from spring to autumn, but the environmental conditions were not conducive for futile germination from autumn to spring. The knowledge gained from this study is valuable for parameterizing population dynamic models for these weed species.

Waterhemp has been a sporadic weed in Kentucky soybean production since the 1970’s.  However, it was not a major weed problem because metribuzin and linuron were widely used and waterhemp was controlled effectively with these herbicides.  The introduction of imazaquin and imazethapyr in the late 1980’s and their widespread adoption in the 1990’s by Kentucky farmers resulted in ALS-resistant waterhemp in some Kentucky areas.  Since the introduction to glyphosate resistant soybeans in 1996, herbicides with the glyphosate active ingredient have increased steadily due to its efficacy in weed control and low input costs.  In the past few years, waterhemp populations resistant to glyphosate have occurred in soybeans.  The majority of Kentucky soybeans are produced in some type of conservation tillage.  Most Kentucky growers do not desire to return to tillage for soybean production and wish to use glyphosate to control other weeds besides waterhemp.   Waterhemp is known to be resistant to several different mechanisms of action, including EPSPS, ALS, PPO, Triazine, and HPPD.  Kentucky farmers have not used preemergence herbicides for many years and have not used postemergence herbicides that require treating small weeds.  All of these factors have resulted in waterhemp being difficult to control in soybeans that rely exclusively on glyphosate.  For these reasons, waterhemp control research trials were conducted in Union and Hancock Counties in western Kentucky in an attempt to find herbicide combinations to provide season-long control. 

A field in Union Co. in 2010 revealed a waterhemp population not controlled by glyphosate.  ALS herbicides including chlorimuron and imazethapyr controlled an average of 15% of the waterhemp, while PPO herbicides, fomesafen and acifluorfen controlled an average of 46 and 31% of the waterhemp. These herbicides were applied to waterhemp that were between .5 and 1 meter in height.  Seeds from surviving plants were collected at the end of the growing season.  Seeds were scarified and planted; plants were treated with chlorimuron, glyphosate, or fomesafen at 1, 4, and 8 times the labeled rate.  Waterhemp survival decreased as herbicide rate increased.  Percent survival for glyphosate was 47% at 1x, 21% at 4x, and 5% at 8x respectively.  Percent survival for chlorimuron was 68% at 1x, 27% at 4x, and 29% at 8x.  Only one plant survived the fomesafen at the labeled rate, with no survivors at the 4 and 8x rates. 

A field study was established in 2011 in Hancock County.  Herbicides evaluated as pre-emergence treatments were fomesafen plus metolachlor, metribuzin plus metolachlor, sulfentrazone, saflufenacil, and sulfentrazone plus metribuzin.  These same treatments plus fomesafen and glyphosate applied at V3 were also evaluated.  The trial consisted of three replications of plots 3 by 12 meters.  Paraquat was applied to the entire area to control existing weeds. Soybeans were planted on June 1^st and pre-emergence treatments applied on June 3^rd.  Preemergence treatments provided an average of 74.5% control compared to the untreated check.  Preemergence treatments followed by a postemergence treatment provided an average of 97% control 67 days after application of pre-emergence treatments.  Among the treatments applied preemergence, fomesafen plus metolachlor, sulfentrazone plus metribuzin, metribuzin plus metolachlor, and sulfentrazone provided waterhemp control of 91%, 80%, 78%, and 50%, respectively.   Another study in the same field compared flumioxazin plus chlorimuron, sulfentrazone plus chlorimuron, sulfentrazone plus cloransulam, and flumioxazin plus pyroxasulfone followed by glyphosate, glyphosate plus fomesafen, or glyphosate plus fomesafen plus acetochlor.  All treatments provided 90 to 99% waterhemp control.

Pre-emergence treatments provide a longer duration for foliar treatments.  Waterhemp in this study never exceeded 15 centimeters in height which allowed for excellent post application waterhemp control.

Increased use of the herbicide glyphosate for broad spectrum weed control in glyphosate-resistant crops has contributed to the evolution of glyphosate-resistant weeds. The mechanism of resistance in many glyphosate-resistant weeds is poorly understood. In part, this is due to a poor understanding of how exactly glyphosate kills a plant. Previous research conducted on non-weed plant species observed that plants grown in sterile media suffer much less injury following a glyphosate application than those grown in field soils. Glyphosate inhibits aromatic amino acid production, which are precursors to a suite of plant defense responses. Therefore, the pathogen defense system of a glyphosate treated plant is impaired, predisposing plants to disease infection. Previous research has indicated that glyphosate efficacy is strongly influenced by root invading soil-borne microorganism. This poses a possible problem when conducting greenhouse dose-response screenings in soil microbe free potting media; as this is the standard method used to identify glyphosate resistance in weeds. Therefore, the objective of this study was to determine the effect of soil microorganisms on the response of glyphosate-susceptible and -resistant/tolerant giant ragweed (Ambrosia trifida), horseweed (Conzya canadensis), and common lambsquarters (Chenopodium album) biotypes to glyphosate. A greenhouse dose-response study was conducted on each of the three weed species and respective biotypes grown in sterile and unsterile field soil, treated with a range of glyphosate rates, and dry weight response was measured. Each weed species used in this study responded differently to glyphosate when grown in the sterile and unsterile soil. Giant ragweed biotypes had a greater amount of shoot dry weight across all glyphosate rates when grown in sterile soil. The presence and absence of soil microbes did not affect glyphosate efficacy on horseweed, while glyphosate-susceptible common lambsquarters biotype was more tolerant to glyphosate when grown in sterile soil. The differential response of the three weed species to glyphosate in the presence and absence of soil microbes demonstrates that rhizosphere interactions are fundamental to the mode of action of glyphosate. These finding suggest that the range of tolerance to glyphosate observed in weeds, and the evolution of resistance in weed biotypes may also be influenced by rhizosphere interactions. Therefore, the soil media used in dose-response screenings to identify susceptible and resistant weed biotypes is very important and unsterile field soil should be incorporated into growth media when conducting dose-response screenings.

Generally plant response measured in a bioassay is not specific to one source. The lack of specificy may be desirable because the presence of all herbicide residues that detrimentally affect the same plant parameter are detected. However, other soil applied chemicals apart from herbicides may also alter the parameter measured in a bioassay. Typically, ALS-inhibiting herbicides are detected in soil using root inhibition of susceptible plant species. Oriental mustard root length bioassay was found suitable for detection of thiencarbazone in soil; root response is sensitive and correlates well with thiencarbazone concentration. However root length of oriental mustard plants is also reduced by ammonium nitrate; therefore mustard root inhibition due to ammonium containing or producing fertilizers may be misinterpreted as root reduction due to thiencarbazone. Canaryseed root length inhibition due to thiencarbazone is very small but the canaryseed response to ammonium nitrate is similar to the response of mustard plants; therefore canaryseed root length bioassay can be helpful in identifying inhibition caused by N-fertilizer. Use of oriental mustard root and canaryseed root bioassays together can aid in interpreting bioassay results for detection of thiencarbazone residues.

Organic soybean producers in the mid-Atlantic region of the USA are interested in weed management programs that reduce their tillage frequency and labor requirements. A cover crop-based system for suppressing weeds is one approach to accomplish these goals.  A cereal rye cover crop mulch suppresses weeds by modifying soil surface conditions including light quantity and quality, soil temperatures and moisture content, nutrient availability, and adding phytotoxic allelochemicals.  While previous work suggested cereal rye biomass levels would not adequately suppress weeds, manipulation of seeding rates, planting and termination dates, and fertility has resulted in biomass levels necessary for weed suppression. As a result, technology adapted for high residue systems are required for adequate crop establishment. However, inability to consistently control annual weeds where annual weed seedbank densities are high and/or perennial weeds are present has required supplementary control tactics (high residue cultivators) and evaluation of multi-tactic weed management practice combination. The success and consistency of a cover crop-based system for suppressing weeds in reduced-tillage organic soybean production requires: 1) a multi-tactical approach that synergizes weed management tactics; 2) periods of rapid decline in annual weed seedbanks and perennial weed propagules; and 3) decision support tools that enable cover crop management flexibility.

The challenges associated with the adoption of conservation tillage and/or low-input cropping systems, whether organic or herbicide-free, across Canada are shaped by sheer scale, environment and local practices. Québec (QC) and Saskatchewan (SK) exemplify the range of contrasting agricultural realities in which this needs to occur. Although these provinces have a similar number of farms (approx. 1000), the average size of farms in SK is at least five times that QC (587 vs. 113 ha). Conservation tillage is practiced on 75% [approx. 50% no-till (NT)] of cultivated land in SK but only on 40% in QC (10% NT). The Certified Organic Acreage in 2009 was approx. 400,000 ha in SK (57% of Canadian total) compared to 41,000 ha in QC. However, in spite of these dissimilarities, the challenges can be similar. When surveyed in 2008, Canadian organic farmers identified comparable research needs for cropping systems, e.g., increased knowledge on the effects of crop rotations on biodiversity and weed management, and the use of reduced tillage/no-till in systems with cover crops. A study conducted at La Pocatière, QC, captured the challenges of introducing low-input cropping systems in mature (20+ years) tillage treatments in a 4-yr barley/red clover/corn/soybean rotation. Each mature tillage system came with its own weed problems but this did not affect crops like barley and red clover which produced similar yields, even in low input systems. However, for both corn and soybean, some form of primary tillage was needed to achieve adequate weed control and yield in organic (ORG) and herbicide-free (HF) systems. The HF and ORG systems with NT failed to produce a corn crop. Including a forage crop prior to corn did not provide expected benefits in ORG-NT, partly because of poor red clover establishment. Mechanical weed control operations (one pass Hiniker cultivator / one pass Hatzdenbichler harrow) failed to control weeds in these systems. In contrast with corn, the HF and ORG systems with chisel plow and NT actually produced a soybean crop but yields were half or less than those in other treatments. The successful combination of conservation tillage practices and low input systems in eastern Canada would thus appear to be crop specific, being much easier to achieve in competitive crops. In western Canadian organic agriculture, current tillage practices are relatively low disturbance as plowing is rarely used and most tillage is accomplished with chisel plows. However, green manure crops (summer lay crops) are often terminated with tandem discs. Roller crimpers and mowing can both successfully kill annual green manure crops such as field pea and rye and usually result in reduced weed growth following termination. However, the lack of tillage can result in lower crop yields in wheat following green manure terminated by roller crimping compared to tillage. This probably occurs because of the reduced mineralization in the NT termination compared to tillage. Current experiments are assessing alternative green manure termination machinery including low disturbance wide blade cultivators (“Noble blades”). Although organic with NT will remain an elusive goal in Canada, targeted reductions in soil disturbance are attainable. However, the effect of this tillage reduction on soil fertility and weed populations will determine if it can be commercially viable. Email: anne.legere@agr.gc.ca

With growing agricultural demands from both conventional and organic vegetable production systems comes the need for sustainable practices to ensure long-term productivity.  Implementation of reduced- or no-till practices offers a number of environmental benefits for agricultural land and maintains adequate yield for current and future production.  Concerns over satisfactory pest control options, weed control in particular, have contributed to the slow adoption conservation practices in many areas.  To identify effective, alternative weed management options for use in conservation systems, research in the Southeast U.S. has continued to evaluate the use of cover crops in conjunction with reduced tillage practices.  Recent investigations have examined a number of cover crop species and associated allelopathic properties that may aid weed suppression including cereal grains, legumes, and Brassicaceae species.  Many recent research projects in the Midsouth and Southeast U.S. have assessed the success of cover crops in reduced-tillage row crop settings with promising outcomes in some systems. Research conducted to date has shown that no single non-chemical tactic will provide effective season-long weed control; however, integration of cover crops into current vegetable production systems does aid early-season weed control, which is especially important in organic systems that rely heavily on handweeding.  Continued research is necessary to identify appropriate cover crop and tillage systems for use in a variety of agricultural settings such as vegetable and organic systems. 

In Northern vegetable cropping systems, attempts at no-till (NT) production have generally failed due to poor crop establishment and delayed crop maturity. Strip tillage (ST) minimizes these problems by targeting tillage to the zone where crops are planted while maintaining untilled zones between crop rows that foster improvements in soil quality.  Strip tillage has been shown to maintain crop yields while reducing energy use and protecting soils in vegetable crops including sweet corn, winter squash, snap beans, carrots and cole crops.  Despite potential benefits of ST, weed management remains an important obstacle to widespread adoption.  Successful weed management under ST without increased reliance on herbicides requires integration of multiple cultural, biological and mechanical approaches targeting weak points in weed life cycles.  In some respects, weeds in the tilled zone under ST behave like those under CT, while weeds in the un-tilled zone behave like those under NT.  However, weed population dynamics under ST is more complex than just the sum of its CT and NT components because weed propagules—as well as factors influencing them—can move readily between adjacent zones.   For example, untilled zones in ST may provide a refuge for seed predators that contribute to greater seed mortality in adjacent tilled zones than would be expected under CT.  Similarly, creeping perennial weed species which are preserved in untilled zones may readily recolonize tilled zones, resulting in greater prevalence of these species than would be expected under CT.  Greater understanding of such interactions between zones in ST systems is important for predicting weed community shifts, and identifying management practices to suppress weeds in ST.  Technological advances including precision tractor guidance systems; real-time weed recognition systems; in-row cultivators and flame weeders; slow release N fertilizers; and precision cover cropping hold promise for improving weed management under ST. However, a concerted research effort focused on understanding and manipulating weed populations as well as testing and refining new weed management technologies will be necessary before ST is likely to be widely adopted in many vegetable crops.

Non-inversion tillage with tine or disc based
cultivations prior to crop establishment is the most common way of reducing
tillage for arable cropping systems with small grain cereals, oilseed rape (canola)
and maize (corn) in Europe. However, new regulations on pesticide use may hinder
further expansion of reduced tillage systems. European agriculture is asked to
become less dependent on pesticide use and promote crop protection programmes
based on integrated pest management (IPM) principles. Non-inversion tillage systems
rely entirely on the availability of glyphosate products and herbicide
consumption appears to be slightly higher as compared to plough based cropping systems.
Annual grass weeds and stickywilly often constitute the principal weed problems
when the soil is not inverted because crop rotations concurrently have very
high proportions of winter cereals. There is a need to redesign cropping systems
to allow for more diversification of the crop rotations to combat these weed
problems with less herbicide input. Cover crops, stubble management strategies
and tactics that strengthen crop growth relative to weed growth are also seen
as important components in future IPM systems but their impact in non-inversion
tillage systems needs validation. Direct mechanical weed control methods based
on rolling weeding devices such as rotary hoes may become useful in reduced
tillage systems where more crop residues and less workable soils are more
prevalent but further development is needed for effective application. Owing to
the frequent use of glyphosate in reduced tillage systems, perennial weeds are
not particularly problematic. However, results from organic cropping systems clearly
reveal that desisting from glyphosate use inevitably leads to more problems
with perennials, which need to be addressed in future research.      

Keywords: Non-inversion
tillage, preventive control, cultural control, grass weeds, stickywilly, cover
crops, non-chemical control

Rice-wheat rotation is the major production systems in the Indo-Gangetic Plains (IGP) of South Asia covering 13.5 million ha and is crucial for food security in the region. Continuous rice-wheat rotation involving intensive tillage particularly the wet tillage (puddling) and straw burning has resulted in deterioration of soil health, and decline in factor productivity and farm profitability. Moreover, the region is facing problem of rising scarcity of labor and water. Conservation agriculture based practices such as zero-tillage (ZT) [ZT direct seeded (ZT-DSR) or transplanted rice (ZT-TPR) and ZT drill-seeded wheat) is being promoted in the region to overcome these problems. Despite many benefits of ZT, weed control is a serious challenge in ZT rice-wheat systems because of more complex and high weed pressure and shift in weed flora, resulting into more dependence on herbicides for weed control. Risks of evolution of herbicide resistance, and environmental and human health concerns associated with herbicide use warrants to identify alternative non-chemical weed control methods which are based on the foundation of good knowledge of weed biology and ecology. Littleseed canarygrass (Phalaris minor Ritz.), a single most important weed of wheat, has already evolved multiple herbicide resistance which further warrants to evolve effective non-chemical weed control strategies to reduce the dependence on herbicides.  Stale seedbed practice can reduce the weed emergence by 45-85% and biomass by 60-85% in ZT-DSR. Similarly, residue mulch was found effective in suppressing weeds in both rice and wheat with 22-76% lower weed density and about 70% lower biomass in ZT-DSR with 5 t/ha wheat residue mulch than no mulch. In ZT wheat, rice residue mulch reduced the weed emergence in the range of 45-100% depending on species and mulch amount. Early planting (last week of October) of wheat also reduces 68 and 80% emergence of littleseed canarygrass compared to normal and late planting, respectively as temperature is not optimum at that time for its emergence. The ZT-TPR with machine transplanting can also create the competition in favour of rice as compared to ZT-DSR. ZT with residues enhanced the seed predation from 13% and 29% (under conventional tillage) to 39% and 71% of Caesulia axillaris and barnyardgrass (Echinochloa crus-galli), respectively and of littleseed canarygrass from 10% to > 50%. In Eastern IGP where perennials like purple nutsedge (Cyperus rotundus) and barmudagrass (Cynodon dactylon) are carried over in rice or wheat, crop management practices like hybrids or competitive varieties and nitrogen management are important components for creating the competition in favour of crop. Therefore integration of (1) stale seed bed practice, (2) tillage (e.g. ZT), (3) residue retention, (4) planting time adjustment, (5) cultivars with weed suppressive ability, (6) appropriate agronomic practices including appropriate seed rate and crop geometry, water and nutrient management to give more advantage to crop than to weeds, (7) practices which enhances weed seed predation and seed mortality such as zero-tillage and residue retention to reduce weed seedbank, (8) appropriate crop rotation, (9) manual weeding to prevent seed production from the escaped weeds, and (10) prevention of entry of weeds through seed contamination, irrigation water, use of manures/compost, and machinery etc. is crucial for achieving effective weed control in conservation till rice-wheat systems.

In Nepal, the largest numbers of rural poor are concentrated in the mid-hills physiographic region in the central and western parts of the country.  Rainfed maize is the principal food staple in this region and yields are both low and variable, principally because of poor crop management practices coupled with uneven seasonal rainfall patterns and soil degradation. At the same time, out-migration is accelerating at a rapid pace and labor scarcity is negatively affecting crop yields and profitability.  In such environments, conservation agriculture (CA = minimum tillage + crop residue retention) can offer a pathway towards sustainable intensification that addresses the major production challenges that keep investments in productivity and maize yields low.  Despite its promise, transitions to CA-based cropping systems management in a given region are contingent on a host of enabling factors including the availability of scale-appropriate machinery and sound options for managing weeds without tillage.  To establish the context and scope for CA in the mid-hills of Nepal, this study has initiated a linked set of farmer surveys, on-farm studies and on-going cropping system trials conducted under controlled conditions. The survey was conducted on 77 farm households in three districts typical of the mid-hills of Nepal during 2010. In addition, we conducted on-farm studies of crop yield response to weed interference in 10 farmer fields in two of the surveyed districts, Parbat and Baglung. Smaller land holdings, soil erosion and declining soil fertility, severe weed infestations and interference with crop yields, inadequate manure and fertilizer application and poor crop establishment were identified as serious problems for the area. The small-holders surveyed appeared to be caught in a vicious cycle of declining crop yields leading to more off-farm labor, which in turn further lowered crop yields due to inadequate time spent on crop husbandry.  In on-farm studies, 10 major weed species were observed, with mean populations of 688 plants m^-2 in Parbat and 1244 plants m^-2 in Baglung. Compared to weed-free subplots, in which maize yields averaged 2.6 Mg ha^-1, weed infestations under typical farmer management practices reduced maize grain yield by 0.8 Mg ha^-1 in Parbat (33% yield loss) and 1.0 Mg ha^-1 in Baglung (37% yield loss). Weed-free fingermillet yields averaged 1.3 Mg ha^-1, and weed interference caused yield losses of 500 kg ha^-1 in Parbat (29% yield loss) and 700 kg ha^-1 in Baglung (38% yield loss). Maize population density under farmer management was 36,800, compared to 52,200 plants ha^-1 in the best management practices (BMP) treatment. Maize in the BMP treatment yielded 3.7 Mg ha^-1, outyielding the FP treatment by 2.24 Mg ha^-1 (164% yield increase) and indicating population-level sink limitation at lower plant population densities.  Results of the on-station trials revealed complex interactions between crop establishment, residue retention, fertilizer levels, and maize yields.  At higher fertilizer levels and no residue retention, yields were on par with no-till and conventional tillage (ca. 6.3 Mg ha^-1) under partially-irrigated conditions.   Independent of fertilizer practice and residue retention, weed biomass was consistently lower under no-tillage.  Efforts are underway to verify and interpret these outcomes.  Transitioning to more stable food production systems for the mid-hills of Nepal will require addressing a complex mix of factors, including biophysical limitations, labor constraints, agronomic performance and appropriate technologies.

Field trials were conducted in 2010 and 2011 near Columbia, Missouri to determine the effects of postemergence (POST) applications of pyroxasulfone and acetochlor on soybean (Glycine max) injury and yield reduction. Pyroxasulfone (59 and 118 g/ha) and acetochlor (1,300 g/ha) applications were made to soybeans at the V2, V4, V6, and R1 stages of growth.  An overlap application of each herbicide and rate was also evaluated by applying each treatment twice across each plot.  Both trials were maintained free of weeds and conducted in a randomized complete block design with six replications.  Soybean height and visual injury ratings were conducted at regular intervals following treatment.  Soybean yields were taken from the center two rows in each plot.  In both years, less than 8% visual injury was observed following any POST application of pyroxasulfone or acetochlor.  Overlap applications of acetochlor or pyroxasulfone at 118 g/ha resulted in the greatest soybean height reductions, regardless of application timing.  In 2010, only the V6 overlap applications of acetochlor and pyroxasulfone at 118 g/ha reduced soybean yields compared to the weed-free, non-treated control.  In 2011, soybean yields were reduced by V6 and R1 applications of acetochlor, and by the R1 overlap application of pyroxasulfone at 59 g/ha.  When averaged across all treatments, soybean yields were reduced with herbicide applications made to soybeans at the V6 and R1 stages of growth in 2010, and at the R1 stage of growth in 2011.  Overall, results from these trials indicate that soybean injury, height, and yield reductions can occur with overlapped applications of acetochlor and pyroxasulfone when applied at the V6 or R1 stage of growth, but not with standard applications of these herbicides at an earlier timing. 

paper withdrawn by author.

Development of Next Generation Herbicide Tolerant Traits to Enable Enhanced Weed Management.

Syngenta and Bayer CropScience are co-developing HPPD-inhibitor tolerant soybeans (HPPD soybeans), a novel herbicide tolerance trait for soybeans.  The event consists of a molecular stack of a gene conferring tolerance to HPPD-inhibiting herbicides as well as a gene for glufosinate tolerance.  This multiple herbicide tolerance trait will enable the use of herbicides such as mesotrione and isoxaflutole pre- and post-emergence in soybean in addition to glufosinate post-emergence.

HPPD inhibitors are the leading selective herbicide chemistry in corn and provide growers with:  1) unprecedented broadleaf and grass weed control including ALS-, triazine-, PPO-, and glyphosate-resistant weeds, 2) proven residual control, 3) application flexibility, and 4) weed resistance management.  HPPD soybeans will provide growers with a valuable tool to improve weed management options in soybeans.  Herbicide programs can be built around HPPD soybeans to offer an increased range of chemistry and superior residual control for sustainable weed management.

Weed resistance management is an important consideration for all new weed management technologies.  Syngenta and Bayer CropScience are committed to maintaining the effectiveness and longevity of current and future herbicides and weed management tools.  Therefore, a comprehensive resistance management strategy will accompany the development of HPPD soybeans.

A lead event has been selected for commercial development based on agronomic parameters, tolerance to mesotrione, isoxaflutole and glufosinate, and yield performance with and without herbicide treatments.  The lead event has shown consistent results in numerous environments across five field seasons in North and South America.  Studies to support regulatory approvals and commercialization are on-going with target for commercial launch post mid-decade. brett.miller@syngenta.com

M.S. Technologies and Bayer CropScience are developing a new soybean event that is tolerant to both glyphosate and p-hydroxyphenyl pyruvate dioxygenase (HPPD) inhibitor herbicides.

M.S. Technologies and Bayer CropScience are developing a new soybean event that is tolerant to both glyphosate and p-hydroxyphenyl pyruvate dioxygenase (HPPD) inhibitor herbicides. Tolerance to glyphosate is equal to commercially available soybean lines. There is differential tolerance to HPPD inhibiting herbicides in this new event. This event is tolerant to preemergence applications of isoxaflutole and mesotrione. There are varying levels of tolerance to postemergence applied HPPD inhibitors. This event exhibits the best postemergence tolerance to isoxaflutole. There is reduced tolerance to mesotrione, topramezone and tembotrione in this soybean event.

paper withdrawn by author.

The Enlist™ Weed Control system, developed by Dow AgroSciences,will introduce an innovative combination of herbicides and herbicide-tolerant traits in elite germplasm to meet the weed control challenges facing farmers around the world.   Components of the Enlist system have not yet received regulatory approvals, but approvals are pending.  Weed control programs that utilize preemergence (PRE)-applied foundation treatments followed by postemergence (POST) applications of multiple modes of action provide consistent, highly effective control and help prevent the onset of herbicide-resistant weeds.

Studies were conducted in 2011 across 10 locations in the U.S. to evaluate the weed control delivered by a systems approach composed of a PRE followed by POST herbicide applications. Preemergence foundation treatments consisted of cloransulam + sulfentrazone, S-metolachlor + metribuzin  or S-metolachlor + fomesafen  herbicides.  Postemergence treatments were  GF-2726 (2,4-D choline + glyphosate DMA) applied at 1092, 1640, and 2185 g ae/ha at approximately 30 days after planting.  Separate studies were conducted at 5 locations in the U.S. to evaluate a total POST weed control program of GF-2726 alone or in combination with micro-encapsulated acetochlor, fomesafen or S-metolachlor + fomesafen.  Treatments were applied either to V3 growth stage soybean or V3 followed by a second application 17 to 21 days later. 

Results indicate that the formulation, GF-2726, provided greater than 95% control of several important broadleaf weed species, including Amaranthus palmeri S.WATS. (AMAPA), Amaranthus tamariscinus NUTT. (AMATA).   Abutilon theophrasti MEDIK. (ABUTH), Ambrosia artemisiifolia L. (AMBEL), Ambrosia trifida L. (AMBTR), Chenopodium album L. (CHEAL), and Sida spinosa L. (SIDSP), This Enlist Weed Control System herbicide product is a new tool that offers broad spectrum broadleaf weed control including control of many glyphosate-resistant weeds.

 ^™Enlist is a trademark of Dow AgroSciences LLC. Components of the Enlist Weed Control System have not yet received regulatory approvals; approvals are pending.  The information presented is not an offer for sale. ©2012 Dow AgroSciences LLC

Effect of Saflufenacil Application Timing on Soybean and its Role in Managing Glyphosate-Resistant Horseweed (Conyza canadensis L.). J.Ikley^*, R. Ritter, University of Maryland, College Park, MD. 

     The commercial release of the herbicide saflufenacil (trade name Sharpen) in 2010 has provided a new tool to help farmers manage the growing population of glyphosate-resistant horseweed. The original labels for saflufenacil and the prepackaged mix of saflufenacil + imazethapyr (trade name Op-Till) restricted applications to 30 days preplant (DPP) for soybeans [Glycine max (L.) Merr.] planted on coarse-type soils with less than 2% organic matter.  In 2011, a supplemental label allowed up to 37.5 g ai ha^-1 of saflufenacil on coarse-type soils with a 44 day interval from application to planting.  Much of the farmland on the Delmarva Peninsula is categorized as coarse or coarse-type soils.  Up to 50% of horseweed plants in Maryland do not germinate until the spring, leaving growers with a small window between using a burndown herbicide application and planting their soybean crop.  Sensitive and non-sensitive soybean varieties have been identified when saflufenacil is applied within 30 DPP on coarse-type soils.

     Field studies were conducted in the summers of 2010 and 2011 at the Wye Research and Education Center (WREC) located in Queenstown, MD, and the Central Maryland Research and Education Center (CMREC) located in Beltsville, MD, on the effect of saflufenacil on full-season no-till soybeans. The WREC site was selected for its medium-type soils, while the CMREC site was selected for its coarse-type soils.  Studies included one saflufenacil-susceptible soybean variety, and one saflufenacil-tolerant soybean variety at each location.  Treatment combinations consisted of the following:  potassium salt of glyphosate at 874 g ae ha^-1, saflufenacil at 25 g ai ha^-1 + glyphosate at 874 g ha^-1, saflufenacil at 50 g ai ha^-1 + glyphosate at 874 g ha^-1, and the prepackaged mix of saflufenacil + imazethapyr at 95 g ai ha^-1 + glyphosate at 874 g ha^-1.  Ammonium sulfate (AMS) and a methylated seed oil (MSO) were added to all saflufenacil treatments. These treatments were repeated at 0, 15, and 30 DPP on separate plots.  All treatments received a subsequent postemergence application of glyphosate at 874 g ha^-1. Stand counts and height measurements were taken at 4, 7, and 10 weeks after planting (WAP).  In 2010, crop injury and reduced yields were observed for the treatments containing saflufenacil at 25 and 50 g ha^-1 at 0 DPP in the sensitive soybean variety at CMREC. In 2011, reduced yields were observed for the same treatments despite no observed crop injury in the sensitive variety at CMREC. No significant differences were noted in the other studies. 

     Greenhouse studies were conducted in 2011 on the efficacy of saflufenacil on both glyphosate-resistant and glyphosate-susceptible horseweed.  Treatment combinations consisted of the following: glyphosate at 874 g ha^-1, saflufenacil at 25 g ha^-1, saflufenacil at 25 g ha^-1 + glyphosate at 874 g ha^-1, and the prepackaged mix of saflufenacil + imazethapyr at 95 g ha^-1.  As in the field studies, AMS and MSO were added to all saflufenacil treatments.  Treatments were applied to horseweed rosettes that were 1.90, 4.45, and 8.25 cm tall for both biotypes.  Visual assessments were made on treatment efficacy at 1, 2, and 4 weeks after treatment (WAT).  At 4 WAT, fresh and dry weights of the plants were taken.  The combination of glyphosate + saflufenacil provided significantly better control than other treatments for the resistant-biotype. Both the glyphosate and the glyphosate + saflufenacil treatments provided the most effective control for the susceptible-biotype.

^*jikley@umd.edu

Soybean production has increased steadily both in the United States and New York State in the last 20 years.  As new soybean growers enter production, agronomic factors such as optimal row spacing to be used become increasingly important.  Soybeans are currently planted in 19 cm rows using a grain drill or in 38 cm and 76 cm rows using a corn planter.  Recent studies show that planting soybeans in narrow rows lead to a yield advantage over soybeans planted in wider rows in northern latitudes.  One of the goals of this 2-year field study was to determine the impact of soybean row spacing and weed management program on weed abundance, soybean yield and farm profitability. This research was initiated on two collaborator farms in the major soybean production regions of New York.  At both locations, soybeans were seeded at approximate populations of 309,000 and 420,000 plants/ha at three row spacings (19, 38, and 76 cm widths). There were three replicates of each row spacing treatment at each location.  One of the sites was chisel plowed, disc harrowed and received a pre-emergence application of Enlite (premix of flumioxazin, chlorimuron- ethyl and thifensulfuron-methyl at 0.204 liters /ha), which resulted in very low weed densities during both growing seasons.  The other site was planted under no-till conditions in both years.  In 2010 the site received and early pre-plant burndown application of glyphosate, 2-4 D and tribenuron.  In 2011 due to weather a pre-emergence application glyphosate was applied as a burndown two days after planting.  These were followed by post emergent applications of glyphosate 4-5 weeks after planting.  Weed densities were determined before post-emergent herbicide application and at five weeks after post-emergent herbicide application in both years. A total of 2.0 meters was sampled in each row spacing treatment using a 1 m X 0.5 m quadrat.  Dry weed biomass within each row spacing treatment was determined at harvest.  Soybeans plots planted in narrow rows (19 and 38 cm) had substantially lower weed densities compared to soybeans planted at 76 cm row spacing after herbicide application at both populations.  The narrow row soybeans also had lower weed biomass at harvest compared with the wider row spacing.  Soybean planted in 19 cm rows at 420,000 seeds/ ha yielded significantly more (~3 %) than all other row spacing x seeding rate combinations at the farm that practiced conventional tillage.  No yield differences were seen among row spacings or seeding rates at the no-till farm.  Economic analysis showed that planting soybeans at 19 cm rows increased net farm profitability under both tillage systems.  

A field study was conducted to contrast levels of weed control (i.e. untreated, low, medium, and high) in glyphosate-resistant soybeans (Glycine max), ‘Allen’, with a near genetically identical variety of conventional soybeans, ‘5601T’.  In correlation with the soybean variety comparison, different herbicide treatments were applied in order to determine overall economic benefit.  Weed control methods included herbicide applications of only glyphosate herbicide on the Allen soybeans and a regimen of pendimethalin, imazaquin, clethodim, and imazethapyr on the 5601T soybeans.  High level weed control plots in both Allen and 5601T soybeans were also hand weeded.  Both Allen and 5601T varieties had comparable yield data within all levels of weed control, regardless of herbicide treatment. 

Herbicide resistant weeds are becoming a greater concern within field crops and specifically soybeans.  Currently, one of
the greatest weed problems in states such as North Carolina is Palmer amaranth (Amaranthus palmeri).  Resistant to both
ALS inhibiting herbicides as well as glyphosate was observed in North Carolina in 1995 and 2005, respectively.  Resistance in the state is currently shown as 98.5% glyphosate resistant and the study of the level of ALS resistance is underway and estimated to be approximately 75%.  With these numbers, it is evident that other methods of control must be utilized and rotated in order to delay or prevent further resistance.  For this reason, LibertyLink soybeans are of interest as well as herbicides that may work well with this system.  Herbicide treatments in this study included, S-metalochlor + Sodium Salt of Fomesafen, Sulfentrazone + Chloransulam-methyl, Flumioxazin, Flumioxazin + Chlorimuron-ethyl, Sulfentrazone + Metribuzin, S-Metalochlor + Sodium Salt of Fomesafen, Glufosinate-ammonium, Glufosinate-ammonium + S-metalochlor +Sodium Salt of Fomesafen, Glufosinate-ammonium + Pyroxasulfone.  LibertyLink soybeans were rated for the percentage of chlorosis, stunting and injury as well as the percentage of control for large crabgrass (Digitaria sanguinalis), redroot pigweed (Amaranthus retroflexus), prickly sida (Sida spinosa), and ivyleaf morningglory (Ipomoea hederacea) after PRE herbicide application, and five weeds after an early POST herbicide treatment.  In this study, all POST treatments resulted in injury which was greater than that observed following any PRE-treatments. However, injury was transient and no injury was observed at the time of the final rating.  Large crabgrass control was greater than 90% with all treatments.  Redroot pigweed control was 80% or greater with the Ignite + Dual II Magnum treatment having the least control at 80%.  Prickly sida control was greater than 90% with all treatments. Ivyleaf morningglory control was greater than 90% for all treatments except Prefix and Valor which both provided 88% control.  Although soybean yields were not shown to have significant differences, several treatments clearly showed greater yield due to improved weed control when compared to other treatments.

Field experiments were conducted in 2011 to evaluate preemergence (PRE), postemergence (POST) activity, and phytotoxicity of different herbicide programs on glyphosate-resistant (GR) Palmer amaranth (Amaranthus palmeri). Trials included potential the new herbicides encapsulated acetochlor and flumioxazin+pyroxasulfone. ‘AG5605’ soybean was planted on May 31, 2011 on a cooperator farm near Pinetops, NC. PRE applied treatments included flumioxazin at 71 g a.i. ha^-1, acetochlor at 1260 g a.i. ha^-1, flumioxazin + acetochlor, sulfentrazone at 140 g a.i. ha^-1 + metribuzin at 210 g a.i. ha^-1,  metribuzin at 420 g a.i. ha^-1, flumioxazin + pyroxasulfone, and glyphosate at 840 g a.e. ha^-1. These PRE treatments were followed by POST application of either glyphosate at 840 g a.e. ha^-1 + fomesafen 330 g a.i. ha^-1, glyphosate  + acetochlor at 1260 g a.i. ha^-1, or glyphosate + fomesafen + acetochlor. Parameter measurements included Palmer Amaranth control and soybean phytotoxicity at 14, 28, and 48 days after PRE treatment (DAPRE). Results showed that a PRE application of sulfentrazone + metribuzin, metribuzin, flumioxazin + acetochlor, flumioxazin, and flumioxazin + pyroxasulfone provided greater than 90% control of GR Palmer amaranth at 14 DAPRE. In a predominantly GR population of Palmer amaranth, glyphosate efficacy was less than or equal to 10%.  Following the POST application, observations at 28 and 48 DAT showed the need of a tank-mix partner with POST activity as glyphosate applied with acetochlor resulted in less than or equal to 72% control of Palmer amaranth. Additionally, where fomesafen was applied with glyphosate, late season control of Palmer amaranth was greater than or equal to 98%. This field trial demonstrates the importance of multiple herbicide options to control Palmer amaranth as early as possible. Any POST applications should include an herbicide with POST activity where the PRE application failed to control at least 90% of Palmer amaranth.

Field trials were conducted in 2011 in Monroe County, MO to evaluate herbicide programs for the management of glyphosate-resistant (GR) giant ragweed in glyphosate- and glufosinate-resistant soybeans.  In both trials, glyphosate was applied alone or in combination with 2,4-D ester, dicamba, saflufenacil, 2,4-D ester plus flumioxazin, 2,4-D ester plus flumioxazin plus chlorimuron, and 2,4-D ester plus sulfentrazone plus cloransulam 2 weeks prior to planting when GR giant ragweed was less than 4-cm in height.  In the glyphosate-resistant soybean trial, all PRE glyphosate combinations were followed with an in-crop application of glyphosate plus fomesafen.   For comparison, several PRE treatments of glyphosate plus 2,4-D ester plus flumioxazin were followed with an in-crop application of glyphosate plus cloransulam, glyphosate plus chlorimuron plus thifensulfuron, or glyphosate only.  In the glufosinate-resistant soybean trial, PRE glyphosate combinations were followed with an in-crop application of glufosinate. For comparison, several PRE treatments of- glyphosate plus 2,4-D ester plus flumioxazin were followed by postemergence (POST) applications of glufosinate alone, glufosinate plus fomesafen, or glufosinate plus cloransulam.  In both trials, visual soybean injury and percent GR giant ragweed control were evaluated at regular intervals following treatment.  Counts of GR giant ragweed plants that survived PRE and POST herbicide treatments in comparison to the non-treated control were also conducted at canopy closure.  In both glyphosate- and glufosinate-resistant soybeans, control of GR giant ragweed 35 days after PRE herbicide applications was at least 93% or greater with all treatments except glyphosate alone which provided less than 28% control of GR giant ragweed.  In glyphosate-resistant soybeans, 33% of the GR giant ragweed had survived a PRE application of glyphosate followed by a POST application of glyphosate plus fomesafen by the time of canopy closure.  All other PRE followed by POST herbicide programs resulted in less than 1% GR giant ragweed survival by the time of canopy closure.  In glufosinate-resistant soybeans, less than 1% of the GR giant ragweed survived all PRE followed by POST herbicide programs by the time of canopy closure.  Results from this research indicate that GR giant ragweed can be effectively controlled with the use of herbicides that have an alternative mode of action in the PRE burndown application.  Also, this research indicates that any GR giant ragweed plants that survive the PRE treatment should be treated with an effective POST glyphosate tank-mix partner in glyphosate-resistant soybeans, or with glufosinate in glufosinate-resistant soybeans.

Field trials were conducted in 2010 and 2011 to evaluate soybean yield response to increasing levels of pest management.  A total of 25 trials were summarized from 2010 (10) and 2011 (15).  Twenty trials were conducted by university weed scientists and 5 trials were conducted by BASF (internal or contractor).  A randomized complete block design was utilized at all locations.  Typical plot size was 15’ wide (10’ treated; 5’ harvested) by 50’ long; each treatment was replicated 6 times.  Yield data were taken at season end.  Most trials were conducted under a no-till production system.  A base program of glyphosate + 2,4-D preplant followed by glyphosate postemergence (conventional till locations did not apply the preplant treatment) was the first treatment.  Each subsequent treatment added a level of management with the replacement of 2,4-D with a BASF burndown/residual program in the second treatment, the addition of a fungicide treatment applied at R3 stage of soybean in the third treatment, and the addition of an insecticide to the fungicide application in the fourth treatment.  Compared to the base program, the BASF residual program replacement, the addition of the fungicide application, and the addition of the insecticide resulted in a 2.3, 5.6, and 6.8 bu/A increase in yield, respectively.   The return on investment (ROI) for the most intensive management program vs. the base program was $3.47 for each dollar spent in 2010.  An ROI could not be calculated for the 2011 due to lack of pricing for unregistered products used in 2011.  These results demonstrate increased yield potential and positive ROI for intensively managed soybeans.

dan.westberg@basf.com

Historically the cost of seed was a relatively minor expense to soybean production. The seeding rate needed to maximize yield and economic return is an important decision.  Seeding rates in the Midwest have typically ranged from 150 to 200% of the number of plants needed to maximize yield at harvest. High seeding rates provide ‘insurance’ against unfavorable conditions that could cause reduced emergence. Moreover, high soybean plant densities and reduced row widths lead to quicker canopy closure, and therefore reduced weed competition.  The practice of dramatically over-seeding was therefore a good decision from both an agronomic and economic point-of-view. However, soybean seed costs are five-fold higher today than 15 years ago due to new genetics and herbicide tolerant traits. Soybeans regulate growth and yield components in response to changes in plant population and competition.  There is a lack of reports evaluating how interplant competition affects plant size variability, or how different sized plants respond to different plant density environments, or competition relief at various developmental growth stages.  A field experiment was conducted in 2009 and 2010 at Urbana, Illinois. The hypothesis was that plant growth and yield variability will increase as soybean densities increase and as interplant competition relief is delayed, and small cohorts will not recover plant growth or seed yield as well as large cohorts from similar environments and growth stages.  Two soybean cultivars (AG3803 and AG3205) were compared at four initial seeding densities of 15, 30, 45 and 60 plants m^-2.  Both large and small cohorts were selected at four growth stages (V3, V6, R2, and R4) to be relieved of competition (-) (i.e. thinned) to 5.3 plants m^-2, while similar sized (large or small) cohorts remained in the level of competition of the initial seeding density all season.  Plant heights, growth stages, and node counts were recorded at each respective thinning time for, both, cohorts relieved of competition, and cohorts that remained in competition.  At maturity, yield component (pod count, seed count, seed mass) data were collected and analyzed as differences between levels of competition.  Dry weights of the stems at R8 was also collected and Harvest Index (HI) of a Stem:Grain ratio was calculated. Plants recovered yield by increasing total seed yield plant^-1 for all timings and initial population densities when densities were thinned (interplant competition relieved). Earlier timings compensated seed yield by increasing pods plant^-1 while seed mass contributed to yield compensation when plants were removed at R4. HI remained relatively constant between 52 and 55% across all planting densities when competition was not relieved suggesting small plants in high density environments contribute to yield at equal biomass to grain ratios. However, there were differences in HI among cohorts when competition was relieved at different timings suggesting plants have a different ability to compensate yield if interplant competition changes.

Liberty Link soybean, that carries the tolerance trait for the active ingredient glufosinate-ammonium found in Ignite herbicide, has been introduced and is gaining acceptance by a greater number of soybean growers.  With the increased presence of Liberty Link soybean in a market dominated by soybean tolerant to the use of glyphosate, there is a practical risk of cross contamination of herbicide applications on soybean not tolerant to one of the specific non-selective herbicides.  Various levels of contamination of Ignite or glyphosate were included in the intended herbicide application to soybean.  Visual effects were scored. Both herbicides were damaging to soybean varieties without specific tolerance in 2010 and 2011.  Yields in both years were less affected than anticipated based on foliar symptoms observed, but a clear yield decline trend existed with increasing levels of glyphosate contamination.

Separate field trials were conducted in 2011 near Mokane and Mt. Airy, Missouri to evaluate herbicide programs for the management of glyphosate-resistant (GR) giant ragweed (Ambrosia trifida L.) and GR waterhemp (Amaranthus rudis Sauer) in dicamba-resistant soybeans.   In the GR giant ragweed trial, a variety of preplant (PREPLT) treatments containing either 2,4-D or dicamba were followed with postemergence (POST) applications of either glyphosate alone, or glyphosate plus dicamba, fomesafen, or cloransulam in a no-till system.  In the GR waterhemp trial, a variety of pre-emergence (PRE) herbicide treatments were followed with POST applications of glyphosate alone, or glyphosate plus fomesafen, dicamba, or dicamba plus acetochlor in a conventionally-tilled system.  Two-pass POST programs that contained glyphosate plus dicamba were also included for comparison.  Visual evaluations of GR giant ragweed and GR waterhemp control were conducted at weekly intervals following treatment.  In the GR giant ragweed trial, all PREPLT followed by POST herbicide programs provided greater than 93% GR giant ragweed control 21 days after treatment (DAT).  PREPLT treatments that contained dicamba generally provided as good or better control of GR giant ragweed than the other PREPLT combinations evaluated.  In the GR waterhemp trial, PRE followed by POST herbicide programs generally provided slightly higher levels of GR waterhemp control than two-pass POST programs.  Similar levels of GR waterhemp control were achieved with two-pass POST programs that contained glyphosate plus dicamba, fomesafen, or dicamba plus acetochlor, but all two-pass POST programs that contained these tank-mix combinations provided much higher levels of GR waterhemp control than sequential applications of glyphosate alone.  Overall, results from these experiments indicate that effective control of GR giant ragweed and GR waterhemp can be achieved in dicamba-resistant soybeans through the use of effective PRE or PREPLT herbicide treatments and timely POST applications of herbicides with an alternate mode of action other than glyphosate.

Indaziflam is the active ingredient in the new herbicide Alion from Bayer CropScience.  In April 2011 the EPA granted federal registration of Alion for weed control use in many perennial fruit and tree nut crops.  It has been previously shown that indaziflam generally provides little activity on weeds that have already emerged from the soil at the time of application.  Similar to other soil residual herbicides, moisture is necessary for incorporating indaziflam into the soil where it is active on weeds.  Trials conducted during the development of Alion have demonstrated that the timing of application and an activating rain or irrigation are important for the performance of indaziflam.  Application timing will vary by region and grower preferences and is flexible as long as activating moisture occurs in a timely manner.

Photosystem II inhibitors have been the primary herbicides for long-term residual weed control in tree, vine, and other perennial crops.  Herbicides registered recently for perennial crops include flumioxazin, mesotrione, pendimethalin, saflufenacil, rimsulfuron, halosulfuron, and indaziflam.  Flazasulfuron and isoxaben will be labeled soon for tree fruit crops during production.

Experiments were conducted in 2010 and 2011 to evaluate residual herbicides for weed control in apple, cherry, blueberry, and grape.  Herbicides were applied in late fall or early spring before new weed growth emerged.  Foliar-active herbicides were included in tank mixes to kill emerged weeds.  Standard herbicides were included as controls. None of the herbicides caused crop injury in any of the experiments. 

Indaziflam applied at 0.073 kg/ha plus glufosinate at 1.12 kg/ha in the fall did not suppress perennial ryegrass in the spring, which expanded from the alleys into the crop area.    Indaziflam plus glufosinate applied in the fall controlled horseweed completely until mid-year.  Indaziflam plus glyphosate applied in the spring gave fair to good horseweed control.  Indaziflam in combination with glufosinate or glyphosate applied in fall or spring did not provide sufficient dandelion or wild carrot control.  

Rimsulfuron was weak against dandelion, perennial ryegrass, white clover, and common mallow.  Rimsulfuron plus halosulfuron did not control large crabgrass or fall panicum.  The combination gave fair control of horseweed.  Flazasulfuron controlled most annual and perennial weeds but did not control field bindweed.  It gave fair control of horseweed and prostrate knotweed.  

Flumioxazin did not control horseweed when applied alone in the fall.  If combined with glyphosate in the fall, it controlled horseweed through the following July.  Flumioxazin applied with or without glyphosate in the spring did not provide sufficient horseweed control. It also was weak against dandelion and wild carrot.

Registration of several new residual herbicides should improve annual and perennial weed control in perennial crops.

An experiment was conducted in 2008 through 2011 to evaluate the impact of sprout year applications of herbicides and 15-37-4 fertilizer (0 versus 337 kg ha^-1) on weed and blueberry cover, density, and diversity.  Tree removal occurred five years prior to project initiation and the field had been mowed once.  Sprout year herbicide treatments included: (i) no herbicide input, (ii) industry standard (hexazinone), (iii) attempt to remove all weeds (tank mix of hexazinone, terbacil, and diuron, followed by tribenuron methyl), and (iv) removal of weeds above the blueberry canopy (wiping with glyphosate).  All herbicides were applied using the recommended label rate.  Blueberry stem density varied across years (p=0.045) and with herbicide treatment (p<0.001).  Hexazinone or the herbicide combination treatment had significantly more blueberry stems than the control or wiping treatment.  There was a significant year by herbicide interaction (p=0.007) on blueberry cover with blueberry cover increasing with time and remaining significantly higher where hexazinone or the herbicide combination was applied.  Blueberry cover remained relatively constant in the control plots.  Fertilizer applications did not impact blueberry density or ground cover but did tend to increase floral bud numbers in plots where weeds were controlled.  Our results suggest that biannual hexazinone applications without fertilizer inputs is the most economical way to promote wild blueberry clonal spread in early establishment fields.

    Primocane management in red raspberry using herbicides to increase berry production has been practiced for more than forty years in the Pacific Northwest. Given the changes in cultivars, herbicides, and machine harvesters since its development during the 1970s, a study was initiated in 2010 to determine whether caneburning of current Pacific Northwest raspberry cultivars still is a useful practice. The first trial was conducted on commercial fields using red raspberry cultivars ‘Meeker’, ‘Coho’ and ‘Cascade Bounty’, while the second trial was conducted on a research field at the Washington State University Northwestern Washington Research and Extension Center near Mount Vernon, WA using ‘Meeker’ and ‘Cascade Bounty’. Caneburning with oxyfluorfen and carfentrazone was evaluated in both trials, while terbacil with and without caneburning was evaluated in the first trial.

     All caneburning treatments successfully eliminated the first flush of primocanes and suppressed primocane regrowth of all cultivars in the early season. Oxyfluorfen suppressed ‘Meeker’ primocane regrowth about 14 days longer than did carfentrzone in both trials. Oxyfluorfen also suppressed ‘Cascade Bounty’ primocane regrowth 14 days longer than did carfentrzone in the first year in both trials and 46 days longer in the second year in the second trial. Most caneburned raspberry growth rates were similar to non-caneburned raspberry by about 80 days after treatment in both trials, except ‘Cascade Bounty’ growth rate was suppressed by caneburning until about 119 days after treatment on the second trial. Two-year average yield of ‘Meeker’ was increased 27 to 31% by caneburning in the first trial and 33 to 40% in the second year of the second trial. ‘Coho’ yield was not increased by caneburning and ‘Cascade Bounty’ yield was not increased by caneburning in either trial. Caneburning reduced time spent on dormant-season training of ‘Meeker’ by about 45 hr/ha/person in the first year, but no difference was observed in the second year in either cultivar. Weed control provided by caneburning herbicide alone ranged from 73 to 88% until early Jun. when weed pressure was high, while weed control exceeded 96% in late Aug. when weed pressure was low. Terbacil with or without caneburning herbicides provided over 89% weed control in late Aug. regardless of weed pressure.

Tulip, daffodil, and iris are grown in northwestern Washington for bulb and cut-flower production.  Due to the high value of the crop and limited acreage, few herbicides are registered for use in field production of these flower crops.  In typical production, bulbs are transplanted from September to October and soil is allowed to settle around the bulbs through mid to late October.  Fields are then treated with preemergence herbicides, often mixed with glyphosate or paraquat to remove emerged weed seedlings.  The crop is grown through early spring flowering, at which time some of the blooms are collected for floral markets.  After foliar dieback in mid-summer, bulbs are harvested, sized, and marketed.  Herbicide trials in ornamental bulbs from 2009 through 2011 have identified several products that provide excellent weed control with little crop injury.  Weed control through mid April of both years ranged from 91 to 100%.  By May of 2010, only oryzalin alone and various combination treatments were still providing >90% weed control.  Four of the five combination treatments providing the best weed control included oryzalin mixed with mesotrione, napropamide, s-metolachlor, or with a combination of napropamide plus s-metolahlcor; the fifth combination with >90% weed control was mesotrione plus napropamide.  By mid-June of 2011, treatments providing acceptable weed control included dithiopyr alone or in tank mixture, mesotrione plus either napropamide or oryzalin, and oryzalin plus s-metolachlor.  Bulb foliage was not visually injured by any treatment either year.  Flower height and number for a given species also did not differ by treatment, and bulb yield was also similar within a species for total bulb yield, total bulb number, and average bulb weight.  These results indicate that these ornamental bulb species were tolerant to the herbicide combinations tested.

In fresh market systems, tomatoes are typically transplanted into wide rows and weeds are controlled during a critical period to protect yields.  Weeds that emerge after this period produce seed which can increase the soil seed bank and lead to increased weed problems in subsequent years.  Four treatments were examined under field conditions in 2010 and 2011: 1) tomatoes transplanted into plastic beds (ORG); 2) tomatoes transplanted into plastic beds plus clover sown between crop rows after the critical period (CLOVER); 3) tomatoes transplanted in no-till roller-crimped rye beds (RYE); 4) tomatoes transplanted in no-till roller-crimped rye beds plus clover sown between crop rows (MIX).  Weed biomass in the CLOVER treatment was less than half of the biomass in the other treatments in both years.  Seed dry weight was lower in the CLOVER treatment than in the ORG and MIX treatment in 2011 but no differences in seed dry weight were detected between CLOVER and ORG in 2011.  Tomato yields were approximately 16% lower for the CLOVER treatment than for the ORG treatment.  Intercropping clover between crop rows may therefore reduce tomato yields.  The RYE and MIX treatments provided very poor weed control and tomato yields.  Replacing plastic mulch with roller-crimped rye resulted in substantially higher weed biomass and lower tomato yields.  Although the use of a living mulch grown between tomato rows has potential for reducing weed seed banks, additional research is needed to better understand how a living mulch like clover affects tomato yields. 

Crop rotation is an important element of effective weed management.  Crop rotation benefits for weed management may be attributable to factors such as variations of temporal disruption associated with crop establishment, alterations of weed management tactics associated with different crops, and competiveness or cultural needs of different crops.  Vegetable producers seek rotations that are compatible with their herbicide programs and that effectively reduce weed populations in the long-term while maintaining profits.  A five-year study was initiated to evaluate the effectiveness of four different vegetable crop rotations combined with three different levels of weed management intensity in North Central New York (Freeville, NY).  Crop rotations included different combinations of five commonly grown processing vegetable crops: sweet corn (SC); snap beans (SB), red beet (RB), cabbage (CB) and potatoes (PO).  Plots were setup in a split-plot design with crop rotation sequence as the main plot factor and weed management intensity as the sub-plot factor.  Five crop rotations were examined, each culminating in snap beans (SB) in the final year: 1.) continuous sweet corn (SC), 2.) alternating sweet corn and red beet (SC-RB), 3.) a diverse rotation (DR1) including SC-RB-CB-SB, and 4.) a second diverse rotation (DR2) including SC-SB-RB-PO.   Three levels of weed management intensity were examined in subplots: 1) No herbicides + cultivation (0X); B.) Banded herbicides + inter-row cultivation only (1/3X); and C.) broadcast herbicides with no-cultivation (1X).  Weed populations were monitored through in-season counts and biomass assessments and through seedbank monitoring using both elutriation and soil greenhouse germination methods.  Galinsoga ciliata (13-78%), Amaranthus retroflexus (0-39%), and Chenopodium album (0-16%) were the dominant species in all rotations across all years.  Crop rotation had a relatively small effect on weed seedbank composition, weed emergence, or yield of snap beans in the final year.  The crop rotation effect on weed seedbank density were only significant at the 1/3X and 1X weed management intensity levels.  In both cases rotation 2 and 4 had the lowest weed seedbank densities.  We speculate that a reduction in the seedbank in rotation 2 was the result of effective control of G. ciliata by beet herbicides used in the 1/3X and 1X weed management treatments.  In rotation 4 there was a potential cleaning effect with the inclusion of potato (2005) in the rotation that reduced seed production.   In contrast to crop rotation, the cumulative effects of weed management intensity were large.  For example, weed management at 1/3X and 1X resulted in significantly lower seedbank densities than 0X under diverse rotations (D1 and D2).  Weed seedbank densities after 4-years was significantly different (p<0.0001) between weed management programs with 148.55 (0X), 71.75 (1/3X), and 46.13 (1X) viable seeds/kg of soil. 

With the loss of methyl bromide, there will be an increase in importance of cultural practices in commercial tomato production in Florida.  Implementing additional cultural practices can help maintain the sustainability of methyl bromide alternatives by keeping problematic weed pests to minimal levels.  A trial was conducted at the Gulf Coast Research and Education Center to determine the best combination of glyphosate and cultivation for fallow season management of yellow and purple nutsedge.  Eight cultivation/glyphosate combinations were tested in combination with two fumigant treatments (1,3-dichloropropene plus chloropicrin, 40:60 1,3D:Pic, at 280 kg ha¹ and dimethyl disulfide plus chloropicrin, 79:21 DMDS:Pic, at 123.5 gal ha¹) and a non-fumigated control.  Prior to trial initiation the average nutsedge shoot emergence was 460 shoots per m².  The cultivation (C)and glyphosate (G) combinations consisted of C, C+C, G, G+G, C+G, G+C, G+C+G, and a non-treated control and were applied to main plots 22.5m long and 7.5m wide.  Cultivation and herbicide treatments were applied over a 4 month period prior to fumigation treatments.  Fumigation treatments consisted on a single bed of tomato 22.5m long with nutsedge shoot emergence counts taken from 6m of this length. 

Initial nutsedge counts provide the best separation of treatments.  At 7 and 14 days after fumigant application (DAA) DMDS:Pic provided almost complete control of all nutsedge present in the field.  PicClor 60 provided 84.1% control of nutsedge, averaged over all cultivation treatments. 

Cultivation-only treatments and a single glyphosate application provided no benefit compared to the no cultural treatment plots.  The addition of a second glyphosate treatment reduced the number of nutsedge sprouts by 59.7% for 14 DAA counts, compared to the single glyphosate treatment.  The most intensive treatment of glyphosate followed by (fb) cultivation fb glyphosate provided the greatest reduction in nutsedge populations.  Compared to the no cultural treatment plots, this would be equal to 77.2% control of nutsedge at 14 DAA. 

Reduced use rates of two fumigant chemistries (iodomethane and dimethyl disulfide) were used in combination with totally impermeable film (TIF) mulch and compared to standard use rates with virtually impermeable film (VIF) mulch for the control of soil-borne pests and weeds.  Fumigant retention under both films was measured to determine the effect of mulch type on the expected plant back period.  Yellow nutsedge (Cyperus esculentus) was the primary weed species present during these experiments.  Nutsedge management was excellent with both fumigants.  When combined with TIF, fumigant use rates could be reduced by 30-40% while maintaining similar nutsedge control compared to standard use rates under VIF mulch.  Plant back period was extended by using TIF mulch in combination with dimethyl disulfide, but not with iodomethane.  TIF in combination with reduced fumigant use rates could have several benefits including reduced input costs, decreased buffer zones, and decreased fumigant odor perception. 

Studies were conducted to study the effect drip applied sulfonylurea herbicides to pepper (Capsicum anuum L.) tolerance and yellow nutsedge (Cyperus esculentus L.) control.  Yellow nutsedge studies were conducted at the Cunningham Research Station, Kinston, NC and Horticultural Crops Research Station in Clinton, NC in 2010.  The pepper trials were conducted in 2009 and 2010 at Mountain Horticultural Crops Research Station, Mills River, NC.  All studies included drip applied and foliar treatments (POST-directed in pepper and POST-over the top in yellow nutsedge studies).  Drip applied treatments included halosulfuron at 13, 25, and 53 g/ha; imazosulfuron at 112, 224, and 336 g/ha; trifloxysulfuron 5, 11, and 16 g/ha.  Foliar treatments included halosulfuron at 24 g/ha, imazosulfuron at 224 g/ha, and trifloxysulfuron at 11 g/ha.  In yellow nutsedge studies, yellow nutsedge plants were counted the day of application and 56 days after application to establish percent increase in yellow nutsedge density [(final count – initial count) / initial count].  At both locations, herbicide rate were not different and all rates were combined.  Increase in yellow nutsedge density was greatest in the nontreated control plots compared to the halosulfuron and imazosulfuron treatments.   In Clinton, yellow nutsedge density was similar drip applied and foliar application were similar among all herbicides.  In Kinston, drip applied halosulfuron and imazosulfuron decreased nutsedge density expansion compared to the nontreated.  In the pepper studies, no visual injury was observed.  Pepper plant height (39 to 47 cm) and total yield (31301 to 40690 kg/ha) was similar among treatments.  Applying halosulfuron and imazosulfuron through the drip irrigation may be a viable method of yellow nutsedge control in bell pepper.  But a foliar application may still need to be integrated into the spray program.

Greenhouse trials were conducted during the winter of 2010-2011 at the Gulf Coast Research and Education Center to determine relative plant injury with increasing rates of clopyralid.  The four varieties used in these trials were ‘Festival’, ‘Radiance’, ‘Treasure’, and ‘Winter Dawn’.  Bare root transplants of the mentioned varieties were planted into 6 inch pots using Fafard #2 potting media.  All plants received overhead irrigation until the time of application, when afterwards the water was directed at the base.  This was done to reduce the possibility of any washing off of the applied clopyralid and ensure maximum foliar uptake of clopyralid by the strawberry plants.  For the greenhouse trials there was only one application timing, that being made during fruiting.  This timing would essentially coincide with growers making an application of clopyralid to actively growing and fruiting strawberry plants.  Clopyralid applications were made at the rate of 0, 213, 426, 628, and 841 g ai ha^-1, equivalent to 0.0, 0.5, 1, 1.5, and 2 pt A^-1 respectively.  Herbicide treatments were made with a CO₂ pressurized backpack sprayer calibrated to deliver 280 L/ha at 213 kPa. 

A rate relationship was observed for new leaf formation for all four varieties.  The non-treated control for treasure was observed to form 9 new leaves while the 841 g ai ha^-1 rate had only 5.5 new leaves.  Festival and Radiance varieties observed almost a 4 leaf reduction in new formation while Winter Dawn observed only a 3 leaf reduction. 

The number of malformed leaves was recorded and converted to a percentage for comparison.  Treasure and Radiance strawberry had almost no leaves malformed by clopyralid at 213 g ai ha^-1 but this increased to 26% at 841 g ai ha^-1.  Festival had 9% leaf malformation at the lowest of the rates tested which increased to 45% at the 841 g ai ha^-1 rate.  Winter Dawn had the greatest tolerance to clopyralid with the 841 g ai ha^-1 rate causing only 6.5% leaf malformation. 

This malformation of the new leaves causes concern for the future fruiting capability of the strawberry plant.  Futhur field testing is necessary to determine the extent the malformed leaves have on future fruiting potential.  

Pyroxasulfone, a new broad-spectrum seedling growth-inhibiting herbicide has been evaluated as a low-use-rate herbicide to provide residual weed control in several crops. However, there is limited information about the efficacy of pyroxasulfone in high organic matter soils of the Everglades Agricultural Area (EAA) in south Florida. Therefore, dose-response field experiments were conducted in 2011 in Belle Glade, Florida to evaluate the response of sweet corn and weed control to pyroxasulfone. Pyroxasulfone was applied preemergence at 31.25, 62.5, 125, 250, 500, 1000, and 2000 g ha^-1 on a Dania muck soil with 78% organic matter. Dose response curves based on a three parameter log-logistic model were used to determine pyroxasulfone rate required to provide 90% control (ED₉₀) of common lambsquarters, common purslane, and spiny amaranth. The ED₉₀ values for common lambsquarters, common purslane, and spiny amaranth control were 269, 188, and 205 g ha^-1 of pyroxasulfone, respectively at 21 d after treatment (DAT). At 42 DAT, the ED₉₀ values for common lambsquarters, common purslane, and spiny amaranth control were 273, 230, and 347 g ha^-1 of pyroxasulfone, respectively. Sweet corn yield increased with increasing rates of pyroxasulfone. An estimated 249 g ha^-1 of pyroxasulfone was required to maintain sweet corn yield at 95% level of the weed-free yield. In addition, pyroxasulfone did not result in sweet corn injury. These results indicate that pyroxasulfone will provide acceptable residual weed control in sweet corn in high organic matter soils of the EAA. Additional field studies will be conducted to corroborate these results.

Pigweed populations resistant to linuron have become a significant threat to carrot producers. Alternative herbicides were evaluated for control of linuron resistant redroot pigweed and crop tolerance in carrots grown on muck soil. PRE treatments of pendimethalin (ME formulation), thiobencarb, pyroxasulfone, and flufenacet, were applied at:  3000, 1680, 89, and 450 g ai ha^-1, respectively.  Pyroxasulfone and flufenacet gave >75% control at 3 WAT (weeks after treatment).  Control at 6 WAT was poor with all treatments. Carrots exhibited excellent tolerance to 2X of the proposed label rates of pendimethalin, thiobencarb, and flufenacet.  Pyroxasulfone reduced canopy growth but not yield. In a separate trial, ethofumesate applied PRE at rates of 2160 to 8640 g ai ha^-1 gave >80%  control of redroot pigweed at 3 WAT but later control was maintained only with 8640 g ai ha^-1. Sequential treatments of ethofumesate at 2160 and 4320 g ai ha^-1 applied PRE and POST at the 2-3 leaf stage of carrots gave  >80% control. Carrots exhibited excellent tolerance to ethofumesate applied PRE at rates up to 8640 g ai ha^-1 but injury resulted with POST treatments. Below label treatments of oxyfluorfen (SC and EC formulations), acifluorfen, sulfentrazone, fluthiacet-methyl, and fomesafen, at doses of 70, 60, 18.75, 15, 1.5, and 3.75 g ai ha^-1, respectively, applied POST demonstrated potential for the control of redroot pigweed. Carrot tolerance to 2X rates of these herbicides applied when carrots were at the 2-3 and 4-5 leaf stage was commercially acceptable.  The EC formulation of oxyfluorfen, and sulfentrazone applied POST resulted in yield loss. 

Field studies were conducted in 2011 at the Malheur Experiment Station, Ontario, OR and Prosser, WA to evaluate the effect of simulated glyphosate drift on direct-seeded dry bulb onion. Glyphosate was applied at 8.6, 25.8, 86, 290, 434, and 860 g ae ha^-1 when plants were at the flag-, 2-, 4-, and 6-leaf stages. Foliar injury to onion was directly related to glyphosate dose and varied by the application timing. Foliar injury at 7 DAT ranged from 0 to 12% for glyphosate ≤ 25.8 g ha^-1. Foliar injury increased sharply at 21 DAT when glyphosate was applied ≥ 25.8 g ha^-1 to plants at the flag- and 4-leaf stage, and ranged from 24 to 99%. The I₅₀ glyphosate dose at 21 DAT was lowest when onions were treated at the 4-leaf and flag stages and was estimated to be 76.8 and 81 g ha^-1, respectively. Onion injury severity increased when glyphosate was applied at ≥ 86 g ha^-1 and eventually resulted in plant death at 860 g ha^-1. The relationships between foliar injury and U.S. no. 1 onion yield and plant height at 35 DAT and U.S. no. 1 onion yield were strongly correlated. Onions displayed severe sensitivity to very low glyphosate doses especially at the 4-leaf stage. Shikimic acid accumulation was negatively correlated with onion yield. Extreme care should be exercised when spraying glyphosate on field edges or to glyphosate tolerant crops in order to avoid injury to onion in surrounding fields.

Eight field trials were conducted in Ridgetown, Ontario from 2008 to 2010 to identify the possibility of cumulative herbicide stress caused by a simulated glyphosate spray drift application followed by an in-crop metribuzin application 3 to 5 days later, in processing tomato.  The simulated drift rates examined were 22.5, 45, 90, and 180 g a.e. ha^-1 of glyphosate both alone and followed by 250 g a.i. ha^-1 metribuzin.   Visual crop injury increased with increasing glyphosate drift rates at all rating dates.  Despite the lack of a significant decrease in plant dry weight at 14 days after metribuzin application (DAT-B) and visual injury at 28 DAT-B between the untreated check and the 22.5 g a.e. ha^-1 application of glyphosate, a 23% yield reduction of mature tomatoes was observed.  This yield reduction was significant and resulted from a simulated spray drift rate of just 2.5% the recommended Ontario glyphosate field dose.  Similar to the injury ratings, mature tomato yield reductions increased with increasing simulated spray drift rates and ranged from 22 to 88% of the untreated check.  Total tomato yields (red and green tomatoes combined) were not significantly different from the untreated check in the 22.5 g a.e. ha^-1 treatment, but were reduced in the 45, 90, and 180 g a.e. ha^-1 treatments.  Similar total yields to the untreated check but reduced mature tomato yields at 22.5 g a.e. ha^-1 glyphosate suggest that the low simulated drift rate delays tomato maturity but does not decrease tomato number.  Across most ratings the herbicide interaction between a simulated glyphosate spray drift rate followed by metribuzin was additive using Colby’s equation.

Two trials were conducted inside a greenhouse in order to determine at what rate carfentrazone reduces plant growth and causes injury in tomato. The tomato seedlings were placed in 3.8 L pots that contained a Myakka fine sand field soil and fertilized throughout the trial as needed.  The first study consisted of carfentrazone being applied as a direct drench to the pots at four weeks after transplanting.  Carfentrazone was applied at 8x, 4x, 2x, 1x, 0.5x, 0.25x, 0.125x, 0.0625x, and 0.03125x of the field rate of 14.2 g ai ha^-1 that would be applied to an area of 0.360 m².  The second study consisted of carfentrazone treatments being applied as a subsurface irrigation to the tomato plants.  The potted tomato plants were placed in containers and 2L of solution containing the carfentrazone was placed into the containers allowing for adsorption through the soil to the roots of the plants.  Carfentrazone was applied at 16x, 8x, 4x, 2x, 1x, 0.5x, 0.25x, 0.125x and 0.0625x of the field rate of 14.2 g ai ha^-1 that would be applied to an area of 0.360 m².  For each study the 1x rate equaled 0.0013 g ai of carfentrazone per plant. 

In the drench trial, there was a relationship of increased injury as the rate of carfentrazone increased.  Using curve fitting, the estimated level of 10, 20, and 50% visual injury to the tomato would be observed with 0.89, 2.1, and 7.9 g ai ha^-1 of carfentrazone, respectively.  The injury observed resulted in a reduction in tomato growth and dry tissue weight.  The growth rate of the tomato was estimated to be reduced 10, 20, and 50%, compared to the non-treated control with rates of carfentrazone at 0.082, 0.180 and 0,71 g ai ha^-1, respectively.  Dry tissue weight was estimated to be reduced 10, 20, and 50%, compared to the non-treated control, with carfentrazone applied at 0.47, 1.06, and 4.53 g ai ha^-1, respectively. 

In the subsurface irrigation trial, there was a relationship of increased injury as the rate of carfentrazone increased. Using curve fitting the estimated level of 10, 20, and 50% visual injury to the tomato would be observed with 5.0, 11.1, and 40.5 g ai ha^-1 of carfentrazone.  The injury observed resulted in a reduction in tomato growth and dry tissue weight.  The growth rate of the tomato was reduced 10, 20, and 50%, compared to the non-treated control with rates of carfentrazone at 1.6, 2.8, 9.6 g ai ha^-1, respectively.  Dry tissue weight was estimated to be reduced 10, 20, and 50%, compared to the non-treated control, with carfentrazone applied at 5.3, 13.3 and 62.5 g ai ha^-1, respectively. 

In our research we have shown that severe injury can occur with root uptake of carfentrazone on tomato.  However, from field experience, very specific conditions must occur before injury is observed.  An application must be made to dry soil and followed within the next several weeks with heavy rainfall of at least 2.5 cm falling within a single hour.  Tomato injury levels are usually low (10% or less) and spotty when observed in the field but may cause a delay in harvest due to the reduction in growth and dry weight observed in these trials. 

Two trials were conducted inside a greenhouse in order to determine at what rate soil applied paraquat would cause visual injury and reduce tomato plant growth.  Tomato seedlings were placed in 3.8 L pots that contained a Myakka fine sand field soil and fertilizer sufficient for the growth of the tomato throughout the trial.  Treatments were applied by mixing the herbicide with 400mL of water and the soil in the pots being drenched with the solution.  Paraquat treatments consisted of 8x, 4x, 2x, 1x, 0.5x, 0.25x, 0.125x, 0.0625x, and 0.03125x of the maximum field rate of 812 g ai ha^-1.  The 1x rate equaled 0.32 g of paraquat per tomato plant which is based on the amount of paraquat applied to 0.360 m² of soil.  This area equals the total size of the row middles on each side of a commercial tomato field in Florida. 

Paraquat reduced the growth of tomato with the 1x and greater rates.  Growth was reduced 76% with the 1x rate and 92% or greater with the 2, 4, and 8x rates.  Paraquat at 0.5x or less reduced growth 7% or less.  This can be related to the death of the tomato plants.  The 2, 4, and 8x rates of paraquat caused 90% or greater death of the tested tomato plants.  The 1x rate caused 60% of the plants to die while the remaining treatments caused death 7.5% or less.  For dry tissue weight, only the 0.0625, 0.03125, 0.125, and 0.25x rates were similar to the non-treated control.  The 0.5x rate reduced dry tissue weight 16% while the 1x rate caused a 54% reduction.  The 2x rate or higher reduced dry tissue weight 65% or greater. 

Our research has shown the possibility of paraquat to cause injury to tomato via root uptake.  In the field this has been an extremely rare occurrence, with only one possible case in the last four years with greater than 60,000 hectares of tomatoes being planted in Florida during that period. 

Pampas Grass (Cortaderia jubata & C. selloana):  Challenges & Results of Control Efforts on Maui, Hawaii, 2006 – 2011.  B. Mahnken*, T. Penniman, S. Miller, M. Ade, Maui Invasive Species Committee, Makawao, HI

Cortaderia jubata and C. selloana, two species of South American pampas grass, have long been valued as ornamentals but are now internationally recognized as serious pests of natural areas, particularly in California and New Zealand. Of the two, C. jubata, an apomictic species with a demonstrated ability to self-seed, has invaded a diverse range of habitats and forest types on the island of Maui, including dry (500 mm annual rainfall) to very wet (up to 5000 mm annual rainfall) areas, dryland, mesic, and wet koa-ohia forests, and subalpine shrublands.  Large areas of Maui’s watersheds are comprised of open-canopy forests, allowing pampas grass to establish a strong foothold, where it threatens to exclude native understory flora and impair watershed integrity. Coordinated efforts of the Maui Invasive Species Committee (MISC) to control pampas grass began in 1998, but were initially limited to surveys of residential properties and open country sweeps.  Subsequent operations included extensive helicopter reconnaissance and aerial control in otherwise inaccessible, backcountry areas, but were not consistently successful at interrupting the reproductive cycle.  Employing an adaptive management strategy, MISC began using helicopters to drop ground crews into these remote, infested areas of the watershed.  The combination of aerial and ground efforts in the most densely infested area on East Maui has proven successful, reducing the average number of mature plants found per acre from >5 in 2008 to 0.1 in 2011.  Other locations on Maui face different challenges to successful control, including sociological (landowner reluctance to permit control in residential areas), topographical (extreme terrain), and climatological (inclement weather).  Despite an intensive focus on aerial operations, the number of mature plants controlled on the steep walls of the West Maui mountains has increased annually; inhospitable terrain has limited the ability to stage ground crews in the area to find and control plants before they reproduce.. More effective aerial treatment methods are currently being evaluated. GIS is used as a tool to highlight strategies, progress, and challenges associated with controlling pampas grass populations throughout Maui.

Miconia
(Miconia calvescens) is a highly
invasive tree native to Central and South America that threatens native
tropical forested areas throughout the Pacific Islands.  Miconia displaces complex native communities
and jeopardizes biodiversity and watershed integrity by forming monotypic
stands of shallowly-rooted individuals.  Miconia
is self-fertile, reaches sexual maturity in 3 to 5 years, and seed-bank viability
is thought to be at least 20 years.  Dispersal
is largely facilitated through frugivorous activity with a dispersal range that
can exceed 1 km. Thus, a single mature plant can potentially impact over 700
ac.  Other vector pathways include both
intentional and unintentional human transport, feral ungulates, and water
runoff.  Introduced to Tahiti in 1937,
miconia had displaced over 70% of its functioning forest ecosystems by the
1990’s, resulting in notable loss of topsoil and native vegetation.  Miconia was first discovered as an escaped
ornamental on the Island of Maui, Hawaii in 1988. Surveillance and control
efforts on eastern Maui were slow to mobilize across the 120,000 ac of
available habitat, delaying comprehensive problem definition and scoping for a
decade.  In 2012, following 10 years of
concerted effort to survey and treat miconia, the prognosis for containment is
mixed but with some clear progress.  An
interagency partnership developed an advanced aerial and ground-based control
program involving extensive use of helicopters and ground crews for
surveillance and treatment of individual targets.  The goal of the partnership is to achieve a
state of zero-fruiting trees.  Most treatment
work involves surgical application of herbicide to isolated individual plants
on steep terrain, making for a labor-intensive but low herbicide-volume project.  An integrated GPS/GIS program records tabular
and spatial data for all field work.  Despite
an eight-fold increase in available resources in 2003 over previous years, the
program is still plagued by inadequate capacity to treat recruitment across all
infestations in a timely manner.  All
known infestations have received some type of management action with outlier areas
receiving priority over more dense core populations.  An estimated 39,000 ac on Maui are
potentially contaminated with seed, thus delimiting the known infestation, or
footprint, of miconia.  However, in
excess of 77,000 ac have been surveyed since 1999, to adequately refine the
scope of infestation and to ensure that miconia has not progressed beyond
current containment areas.  The entire suspect
area requires periodic aerial reconnaissance to track potential recruitment and
locate previously-undetected individuals. 
Approximately 2,500 ac of the suspected contaminated area are heavily infested,
meaning that control crews are likely to encounter multiple mature miconia
during an operation.  Another 15,000 ac
are lightly to moderately infested, meaning few mature individuals should be
encountered, although seedlings will be expected.  Evidence of successful control within a
defined management unit occurs when repeat entries result in reduced densities
of mature plants.  Successful control has
mostly been achieved for isolated infestations that initially had low plant densities.  More developed core populations are less
encouraging, with recent evidence in some areas of increasing densities of
mature plants.  Maintaining control of
core infestations was aggravated by a seven-fold decrease in survey acres
during the 2011 operational year due to budget restrictions.  Efforts to increase efficiency and
effectiveness are ongoing, with notable recent innovations showing potential
for further development, including improvements in the delivery and application
of herbicide.  Successful control of
outlier populations indicates that the combined aerial and ground strategy is a
functional approach. A need for more concerted effort or modified strategy is
apparent in high-density areas, but ultimately, sustainability and a consistent
resource base are the most significant challenges to ensuring long-term containment
of miconia on Maui.

Miconia (Miconia calvescens) is a tropical shrub from South and Central America that is a highly invasive colonizer of intact forested watersheds in Hawaii.  Elimination of incipient satellite populations is critical to an effective containment strategy, but extreme landscape topography limits access to remote populations via helicopter operations.   Herbicide Ballistic Technology (HBT) is a novel weed targeting platform designed to pneumatically deliver herbicide-filled, gelatin projectiles (17.27 mm dia.)  with unique capabilities to target weed satellites within an effective range of 30 meters at sub-meter accuracy. Triclopyr in small doses is known to be lethal to all size classes of miconia.  Preliminary tests confirmed lethality of the experimental batch HBT-TCP200 (199.4 mg triclopyr ae/projectile) in 5-unit increments targeting stem axial points of the leaf canopy.  Experimental
calibrations were conducted with the HBT platform on a Hughes 500 model 369D helicopter from November 2010 through October 2011 on the islands of Maui and Kauai (n=13) for calculating efficiencies in surveillance and target reduction operations. Surveillance rate (min/ha; R²=0.933, P<0.000) and target acquisition rate (targets/hr; R²=0.926; P<0.000) displayed positive linear and logarithmic trends, respectively, with target density.  The linear equation was further deciphered to estimate the acquisition time at 25.1 sec/target and a minimum surveillance rate of 67.8 sec/ha when no targets are detected.  The maximum target acquisition rate of the HBT platform is estimated at 143 targets/hr.  A mean mortality factor of 0.525 was derived from the product of target detection (0.54) and treatment lethality (0.97), in areas with repeated operations.  With the surgically direct method of application and the strategic targeting of low-density satellite populations, herbicide use patterns on average were calculated  to be less than 100 g ae/ha. Effective containment of miconia is achieved when a detectable population approaches extinction within a 314.16 ha management unit (1 km radius).  A feasibility model and cost analyses, based
on the empirical calibrations and a miconia matrix model adopted from Australian research, can project potential management strategies targeting incipient populations using the HBT platform where current conventional methods are not effective.

Early detection and rapid response (EDRR) seeks to control or eradicate new invasions to prevent their spread, but effective EDRR remains elusive due to financial and managerial constraints.  As part of the Great Lakes Early Detection Network, we asked stakeholders to indicate their needs for an effective EDRR communication tool.  Our results led to the development of a website with five primary features: 1) the ability of casual observers to report a sighting; 2) a network of professionals to verify new sightings; 3) email alerts of new sightings across data providers; 4) maps of species distributions across data providers; and 5) easy communication channels among stakeholders.  Using these results, we provide a cost-effective framework for online EDRR networks that integrate data and develop social capital through a virtual community.  This framework seeks to provide real-time data on current species distributions and improve across jurisdictional collaboration with limited oversight. 

Despite monitoring and control efforts invasive plants continue to spread. In addition, budgets for monitoring and control are limited. One way to make efficient use of budgets is to prioritize sites for monitoring. Creating models that predict which habitats are prone to invasion is one approach to prioritization. We tested the accuracy of habitat suitability models in predicting the invasion of two invasive plants along roadsides in Wisconsin.  In addition we evaluated the ability of sampling model targeted areas to improve the efficiency of sampling as compared to a random approach We expected the targeted sampling to have a more favorable ratio of species presences to effort expended. We used MAXENT version 3.3.3a to develop habitat suitability models scaled to 30 m raster cells covering the entire state of Wisconsin for two invasive species. These two species were chosen due to the differing number of initial data points that we collected for each species from statewide database consolidation efforts (spotted knapweed = 1200, wild parsnip =700). Four probability classes were created for each model using a quantiles classification in ArcMap 10. Quantiles place an equal number of raster cells in each class. This project focused on the highest and lowest probability classes. At least 150 sites were sampled for each species from an initial pool of 1200 sites. All sites were along roadsides as this is the main corridor for the spread of these species and accessible to field crews. An equal percentage of identified sites were sampled north and south of the Wisconsin Tension Zone to address differences in habitats invaded and direction of spread of specific species. After sampling, each site was categorized as true if the classification agreed with the observation and false if it did not agree. Poison hemlock was removed from the analysis due to a lack of location data in the model. This was because the points used to build the original model did not represent many of the environmental conditions found in Wisconsin. In the low probability category the model accurately predicted the absence of the species >90% of the time. For the high probability category the model accurately predicted presence 59% of the time for spotted knapweed and 35% of the time for wild parsnip. Lower success of prediction in the high probability category is likely influenced by areas not being exposed to propagules from these invasive species, and may not reflect inaccuracy of the model. This would explain why our model for spotted knapweed, which is a plant with a wider distribution in Wisconsin than wild parsnip and, one would assume, higher propagule pressure, was more accurate.  Results confirm that this model is a useful tool for prioritizing areas for monitoring. While successful prediction was lower in the high probability category, the low probability category was highly accurate and will allow for prioritization of monitoring. This prioritization will allow for limited resources to be targeted to areas of greatest need. To accomplish our second goal, we compared targeted sampling to random sampling carried out by the Department of Agriculture, Trade and Consumer Protection (DATCP). A targeted survey found new presence points on 60% of their site visits while the random approach found new presences on 20% of their site visits. This emphasizes the value to the targeted sampling in improving detection of invasive species. These results taken together show that targeted sampling based on habitat suitability models can make monitoring efforts more efficient and less resource intensive.

The history of invasive plant introduction because of hasty decision making has caused the United States billions of dollars in plant eradication efforts. The prevention of another “Kudzu” is important to protect our natural ecosystems and our economy. Cellulosic bioenergy crops such as members of the Saccharine family are being selected for potentially weedy characteristics which could result in the introduction of new invasive plant species. The Department of Energy timeline for the production of cellulosic bioenergy crops does not allow for complete examination of the potential invasiveness of all of the bioenergy grass species prior to their establishment in field.  Due to this issue, producing an eradication plan for potential escapes of these crops, as well as management of abandoned and transitioning fields, is an important part of protecting our environment while maintaining a profitable bioenergy future. Complete removal of these crops will also become important for producers who want to rotate their fields into other crop production systems after anywhere from 10-30+ years of production. Removal of these plants should be timely in order for producers to prevent spread of material and also to increase profitability.

The presentation will examine the current literature and where more research is needed. It will also discuss the various eradication procedures currently being trialed and comparisons will be made between the efficacy of current invasive plant management procedures and the relationship between species ecology, potential invasivity, and ease of eradication. 

Falcataria moluccana is a large, fast-growing tree planted widely in Pacific Islands over the past century. In Hawaii it trasforms invaded ecosystems by dramatically increasing inputs of nitrogen, facilitating invasion by other weeds while suppressing native species. Individuals rapidly reach heights of 40 m and their weak wood breaks easily in storms or with age. This species is easy to kill by mechanical and chemical means and these are being used with some success to control incipient infestations. The benefits of a combined chemical and biological control for F. moluccana would likely extend to tropical islands througout the Pacific. Futher loss of native forests and biodiversity in the Pacific can be expected from F. moluccana invasion if chemical and biological control work is not initiated. Successful containment of F. moluccana by self perpetuating bio-control agents along with chemical control measures also would result in savings of many millions of dollars throughout the Pacific by avoiding damage and maintenance costs associated with these trees growing near utilities, roads, homes, and workplaces.

Exotic earthworms and plants are invading eastern hardwood forests in the United States and have the potential to disrupt native plant communities.  We sampled earthworm densities and understory plant species cover in transects located in paired old and second growth forests in Indiana to investigate the relative importance of stand age and distance from edge in determining invader colonization rates. Exotic earthworms and plants were found in both edge and interior transects regardless of stand age. The number of native plant species decreased linearly with increasing densities of the exotic earthworms Lumbricus rubellus and L. terrestris.  Densities of Lumbricus adults and Rosa multiflora, an invasive plant species, explained 43% of the variation in the number of native plant species found in transects across the state.  Multivariate analyses suggest that L. rubellus and total earthworm densities affected the species composition of Indiana understory plant communities. Exotic earthworms and plants are ubiquitous in Indiana hardwood forests and appear to affect plant species richness and the species composition of understory plant communities.     

Chinese privet (Ligustrum sinense Lour.) is one of the most prevalent invasive shrubs in the southeastern United States. In many bottomland hardwood forests, older privet infestations are composed of treelike shrubs six to nine meters in height that may be single or multi-stemmed clumps. These situations are well suited for basal bark treatment with triclopyr. However, there is little published research on this method for Chinese privet control. Our objective was to compare label and reduced rates of triclopyr for Chinese privet control using the basal bark treatment method. We established two research sites near Auburn and Opelika, AL where Chinese privet dominated the forest midstory and understory. Treatments included triclopyr ester applied at 0.1, 0.05, and 0.025 kg/l in an oil carrier. One additional treatment was a “ready to use” triclopyr ester formulation (0.09 kg/l). Treatment timings included early winter (January) and early spring (March). Each treatment was applied to forty or fifty individual privet clumps with a 1.5 liter single nozzle sprayer. Prior to treatment, root collar diameter was measured for each privet clump to account for potential treatment variation by privet size. Treatments were applied to the bottom 30 cm of the entire circumference of each stem. Data was collected at six, twelve, and eighteen months after treatment. In general, triclopyr at the commercial rate of 0.1 kg/l was very effective for controlling Chinese privet at both timings. However, reduced triclopyr rates provided inconsistent control across locations. A significant treatment by timing interaction also indicated the two lowest rates of triclopyr reduced canopy defoliation less than the commercial rate with March treatments but not January treatments. These studies indicate that triclopyr ester basal bark treatment can be a very effective method for Chinese privet control but care should be taken when attempting to use reduced rates.

Beach vitex (Vitex rotundifolia) is a salt tolerant, perennial, invasive shrub that has naturalized in coastal areas of the southeastern United States. Since its introduction in the 1980’s, this Pacific Rim native has invaded many fragile beach dune ecosystems along the Mid-Atlantic, Southern Atlantic, and Gulf of Mexico. Large-scale monocultures of beach vitex supplant native species through rapid vegetative reproduction and seed production. Fruits are capable of water-based dispersal, allowing for potential rapid range expansion in coastal areas. Ecosystem damage resulting from exclusion of native plant species by beach vitex and fears associated with potential negative impacts on sea turtle nesting have served to promote the control and survey efforts presently underway in coastal areas of the Carolinas, Virginia, and Maryland. Much of its invasive potential may be the result of intense substrate hydrophobicity underneath established stands, which is believed to prohibit seedling establishment by other plants including native plant species. Our findings indicated that sand under BV cover was significantly hydrophobic,that cuticular alkanes from leaves and fruits were responsible for this hydrophobicity, and that extreme substrate hydrophobicity persisted for >3 years following BV removal. Fruit characterization studies of drupe lots from three consecutive years found that the average drupe weighed 50 mg, had a diameter of 6.5 mm, and contained 1.29-1.54 seeds in 2003-2005. An average of 75-80% of drupes contained viable seeds. Germination percentages were highest when drupes were subjected to stratification at 10 ºC for 8 weeks. Because any amount of stratification caused germination, the majority of seeds should meet their dormancy requirements in the dunes of the Carolinas. An observational case study on a beach dune site indicated that beach vitex regrowth occurred 3 years after initial cut stem glyphosate treatments and directed development of greenhouse and field studies. Imazapyr solution applied to recently cut stems or stumps effectively controlled beach vitex in both greenhouse and field studies. Foliar applications of imazapyr also effectively controlled beach vitex.

Buffelgrass (Pennisetum ciliare) is a perennial bunchgrass from Africa that is spreading across
southern Arizona. It threatens the Sonoran Desert ecosystem including the region’s
signature saguaro forests by increasing the frequency and intensity of fires in
an ecosystem where fire has been rare and localized. Current control practices
include hand pulling and individual plant treatment (IPT) with glyphosate; strategies
that require lots of labor and are difficult to execute on steep rocky terrain.
The extent and size of buffelgrass populations in remote areas and on rough terrain
suggests that aerial herbicide applications may be needed to manage this
invasive species. Experiments were initiated to investigate using broadcast
herbicide applications to control buffelgrass such as those made by helicopter
or fixed wing aircraft. In addition to investigating rates of glyphosate per
unit area needed for control, the graminicides clethodim, fluazifop and
sethoxydim were also investigated in the hope that tank mixtures could be used to
reduce the collateral damage caused by the non-specific herbicide glyphosate. Seed
was collected from Saguaro National Park, aged at room temperature for several
months to overcome dormancy and planted in pots in a greenhouse. Plants were
grown until they had 8 to 10 tillers, were clipped about 3 to 5 cm above the
soil, allowed to regrow and were sprayed when they had 11 to 12 tillers and
were about 60 to 70 cm in height. About 3 to 4 weeks after spraying, the above
ground biomass was harvested (fresh and dry weights were measured) and the pots
were returned to the greenhouse. About 3 weeks after the first biomass harvest,
shoot regrowth, if any, was harvested and fresh and dry weights were measured. Herbicides
were applied using a CO₂ pressurized backpack sprayer with a 3
nozzle boom and XR8001 nozzles typically calibrated to deliver about 93 L/ha
(about 10 GPA). In one typical experiment, glyphosate (Aquamaster) was applied
with a non-ionic surfactant (0.5% v/v) and ammonium sulfate (1% w/w) at 0.0
(untreated control), 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.86, 1.12, 1.4, 1.68, and
1.96 kg/ha. Even low rates of glyphosate were sufficient to stop the growth of
these greenhouse plants and there were no significant differences in fresh or
dry weights between any of the herbicide rates except that the untreated plants
had much larger weights per plant than plants sprayed with glyphosate. We found
it extremely difficult to visually estimate injury symptoms and this was
compounded by the different symptoms caused by different herbicide modes-of-action.
The only reliable indicator of phytotoxicity was regrowth after spraying and biomass
harvest. In the above glyphosate experiment, shoot regrowth (dry weight) was
5.9, 5.3, 6.5, 1.2, 1.6, 3.4, 0.5, 0.4, 0.4, 0, 0, 0, and 0 g/plant,
respectively. In a typical graminicide experiment, clethodim (Select 2EC) was
applied with 1% v/v methylated seed oil (MSO) at 0.0 (untreated control), 0.07,
0.14, 0.2, 0.27, 0.34, 0.41, 0.48, 0.54, 0.61, 0.68, 0.75, and 0.82 kg/ha.
Similar to glyphosate, all rates substantially suppressed growth and there were
only small differences in dry weight at the first biomass harvest; 56, 24, 17, 19,
15, 12, 17, 12, 15, 14, 15, 15 and 17 g/plant, respectively. At the second
regrowth harvest, the dry weights were 3.9, 1.5, 1.0, 0, 0, 0, 0, 0, 0, 0, 0,
0, and 0 g/plant indicating that most of the clethodim rates killed the plants.
As expected, the greenhouse plants were much more susceptible to the herbicides
than mature perennial plants in the wild. However, the greenhouse experiments
will allow us to determine if tank mixtures of graminicides with glyphosate
will be synergistic and useful in field applications.

Novel chemicals contribute to the Invasion success of Ageratina adenophora

Devika Bajpai* and Inderjit

Abstract

Ageratina adenophora, a native of Mexico is an aggressive perennial invader in Asia. Exotic plants like A. adenophora bring novel chemicals to introduced ranges, which then provide them with competitive advantage over native residents. It has been shown that A. adenophora suppresses species richness in the invaded regions and has no effects in its native range. In addition to this biogeographic difference in emission of volatiles was found. Here we will present our data on the effect of A. adenophora on species richness, demographically and volatiles emitted from it that might contribute to its invasion success.

A waterhemp population from a native-grass seed production field in Nebraska was reported to no longer being effectively controlled by 2,4-D. Thus, dose-response studies were conducted to determine if this population was herbicide resistant.  In the greenhouse, plants from the putative resistant and a susceptible waterhemp population were treated with 0, 18, 35, 70, 140, 280, 560, 1120, or 2240  g ae ha^-1 2,4-D.  Visual injury estimates (I) were made 28 DAT, and plants were harvested and dry weights (GR) measured.  The putative resistant population was approximately 10-fold less sensitive to 2,4-D (R:S ratio) than the susceptible population based on both I₅₀ (50% visual injury) and GR₅₀ (50% reduction in dry weight).  The R:S ratio increased to 19 and 111 as the data were extrapolated to I₉₀ and GR₉₀ estimates, respectively.  GR₅₀ doses of 995 g ha^-1 for the resistant and 109 g ha^-1 for the susceptible populations were estimated. Plants from the resistant and susceptible populations were also treated with 0, 9, 18, 35, 70, 140, 280, 560, or 1120 g ae ha^-1 dicamba. The resistant population was 3-fold less sensitive to dicamba based on I₅₀ estimates, but less than 2-fold less sensitive based on GR₅₀ estimates.  A field dose-response study was conducted at the affected site with 2,4-D doses of 0, 140, 280, 560, 1120, 2240, 4480, 8960, 17920, and 35840 g ha^-1.  At 28 DAT, visual injury estimates were 44% in plots treated with 35840 g ha^-1.  Plants treated with the highest rate recovered and produced seed.  The synthetic auxins are the sixth mechanism-of-action herbicide group to which waterhemp has evolved resistance.

Italian ryegrass is one of the most difficult to control weeds in wheat, clover, and perennial grasses grown for seed in the Willamette Valley of Oregon.  Depending on the population, resistance occurs to some ALS inhibitors and to most and in some cases all of the ACCase inhibitors. Flufenacet plus metribuzin (Axiom) was introduced into the cropping systems the late 1990s for Italian ryegrass control in winter wheat and perennial ryegrass grown for seed. Pyroxasulfone (Zidua) has provided excellent Italian ryegrass control in our studies and will potentially to be labeled for use in winter wheat for the 2013 growing season.  Pyroxasulfone is reported to have the same mechanism of action as flufenacet and will be included in Group 15.  Therefore, there are concerns that there would be increased selection pressure for Group 15 resistant Italian ryegrass.  Control of Italian ryegrass with flufenacet plus metribuzin was excellent in winter wheat until 2010-2011 when there were several reports that the herbicide was no longer effective.  In field trials, we have observed a reduction of Italian ryegrass control with flufenacet plus metribuzin but not with pyroxasulfone. Seeds from four Italian ryegrass populations were collected and greenhouse dose response studies conducted to determine if the populations were resistant to flufenacet (Define) and pyroxasulfone.  Metribuzin was not included in the flufenacet treatments so that results would not be confounded with an additional herbicide. The four populations were resistant to flufenacet but not to pyroxasulfone.  Plants emerged only in the pyroxasulfone treatment of 7.5 g ai/ha (0.0625X rate) so it was not included in further dose response studies.  Two populations were selected for further testing.  These populations were collected from different cropping systems that were 64 km apart.  The populations were still segregating for resistant and susceptible plants, but some plants in both resistant populations emerged in the flufenacet treatments of 2300 g ai/ha (6.0X rate).  We have not explored the mechanism of resistance nor characterized the multiple-resistance patterns of these two populations, but have determined that they are resistant to clethodim.  It is particularly interesting that the populations are not resistant to both of the Group 15 herbicides.

Glyphosate-susceptible and -resistant/tolerant biotypes of giant ragweed (Ambrosia trifida), horseweed (Conzya canadensis), and common lambsquarters (Chenopodium album) responded very differently to glyphosate when grown in sterile and unsterile field soil. Thus, the presence or absence of soil microorganisms appeared to play a vital role in glyphosate efficacy. Johal and Rahe (1988) demonstrated that when the fungal pathogens Pythium sp. and Fusarium sp. were added to sterile soil, injury due to glyphosate was greater on bean seedlings. These studies suggest that plant death due to glyphosate involves an interaction with soil microbes, and glyphosate efficacy is strongly influenced by root invading soil-borne plant pathogens. Therefore, the objective of this study was to investigate the relationship between soil microbial root colonization in three weed species upon a glyphosate application. A greenhouse study was conducted with glyphosate-susceptible and -resistant/tolerant biotypes of common lambsquarters, giant ragweed, and horseweed grown in sterile and unsterile field soil. Glyphosate was applied at the average GR₁₀ and GR₅₀ for each of the three weed species tested, determined in a previous study. Three days after the glyphosate application roots of each treatment were plated onto fungi specific media and Oomycete (e.g. Pythium and Phytophthora species) selective media. Microbial colonization data was collected and microbial types were identified. At 21 DAT dry weight response to glyphosate was collected. The identity and number of microbes isolated from each of the three weed species were vastly different. A greater diversity of microbe colonies were isolated from giant ragweed roots, compared to horseweed. The soil-borne plant pathogens Pythium sp. and Fusarium sp. were isolated frequently from both giant ragweed and common lambsquarters. Within all three weed species the biotype grown in the unsterile soil and treated with glyphosate had the greatest amount of microbial infection. Also, biotypes that were resistant or tolerant to glyphosate were colonized by fewer microbes. Therefore, the ability of these three weed species to resist glyphosate may involve differences in the response to soil microbes. Preliminary results from this study indicate that differing microbial diversity between the three weed species and glyphosate-susceptible and -resistant/tolerant biotypes may play a role in the response to glyphosate when grown in sterile and unsterile soil.

A glyphosate-resistant (GR) biotype of hairy fleabane was first documented in the San Joaquin Valley of California in 2007 in the same area where GR horseweed (Conyza canadensis) was reported in 2005.  Previous studies found differences in the growth and development of the GR and GS horseweed biotypes as the GR horseweed reached different phenological stages earlier than the GS horseweed.  However, similar phenological comparisons have not been made for hairy fleabane.  Therefore, the objective of this research was to evaluate growth and development of several GR and GS hairy fleabane populations.  Seeds of hairy fleabane were collected from more than 100 locations representing a wide geographical region in central California.  Each population was tested for glyphosate-resistance using an in vivo shikimate enzyme assay.  Of these, five populations confirmed as GR and five populations confirmed as GS using the assay were selected for further study.  The ten populations represent a widespread geographical distribution and crop and non-crop systems in the state.  Plants were grown outdoors in pots filled with a potting media in the summer of 2010 and 2011.  The time taken by the plants to reach various phenological stages was determined and modeled based on growing degree days (GDDs).  Unlike horseweed, no differences (P>0.05) were observed in the phenological development rate of the GR and GS hairy fleabane.  Regardless of biotype, the plants developed a rosette and produced seeds at approximately 375 and 1530 GDDs, respectively. Therefore, it may be possible to develop a common GDD model for spring-emerging hairy fleabane populations of central California which can serve as a guideline for application of POST herbicides.

Glyphosate-resistant (GR) horseweed is a common, persistent problem in no-till cropping systems with the GR crop trait.  Currently, no study has found a fitness cost in GR horseweed.  Therefore, resistant plants may survive and reproduce in unmanaged, disturbed environments, such as field margins, becoming a source for future invasion.  The purpose of our study was to examine the relationship between the occurrence of GR horseweed in field margins and environmental variables collected as part of an ongoing larger study, the Benchmark study, which seeks to determine the future sustainability of GR cropping system technology.  Horseweed seed was collected from the margins of Benchmark fields in the fall of 2008, and occurrence of resistance was analyzed for association with environmental variables from 2006 to 2008.  We tested for associations between the occurrence of GR horseweed in field margins and geography, field management practices, herbicide selection pressure, in-field weed community diversity, in-field changes in horseweed populations (λ), and in-field presence of perceived difficult-to-control horseweed plants.  Seed accessions came from 17 sites in Illinois, Indiana, and Nebraska, representing USDA Plant Hardiness Zones 4, 5, and 6.  A discriminating spray test was conducted in the greenhouse on germinated and established plants.  Visual ratings and dry weights were analyzed using Principle Components Analysis (PCA) to determine a resistance “score” per field site and also analyzed using Discriminant Analysis (DA), which allowed plants in the margin of each field to be classified as resistant or susceptible.  The clearest relationship in these data was between occurrence of resistance (PCA score and DA percent resistance) in the margin and geography; there were low levels of resistance north of 40°N latitude and west of 95°W, with greater and more variable occurrence of resistance to the south and east .  There was no indication that horseweed was perceived as difficult-to-control in any of the field sites; however, in 2007, the year prior to our seed collection, sites with the greatest occurrence of resistance in field margins used tillage and more applications of herbicides with alternative modes of action to glyphosate than fields with less occurrence of resistance.  Other management practices (crop rotation, rotation of GR crop trait, crop type) and measures of herbicide selection pressure (number of glyphosate applications, total number of herbicide applications within the growing season) did not show a significant relationship to the occurrence of resistance in the field margin.  Occurrence of resistance was positively correlated with measures of in-field weed community richness and diversity, possibly a confounding result of a larger latitudinal diversity gradient.   There was a negative correlation between 2006 to2007 λ and occurrence of resistance, indicating little or no increase in horseweed populations within fields with the greatest occurrence of resistance in field margins, suggesting in-field management was successful in minimizing field presence of horseweed.  These findings suggest that in order to minimize future infestations of fields with a history of GR horseweed, field margins may need to be managed to reduce niche space for horseweed establishment.

Emergence and development of red sorrel (Rumex acetosella L.) and wild blueberry (Vaccinium angustifolium Ait.) ramets in Nova Scotia, Canada. S.N. White*¹, N.S. Boyd², R.C. Van Acker¹, C.J. Swanton¹, and S. Newmaster¹. ¹University of Guelph, Guelph, Ontario; ²Nova Scotia Agricultural College, Truro, Nova Scotia. 

An experiment was established to monitor the emergence and development of red sorrel and wild blueberry ramet populations in non-bearing and bearing year wild blueberry fields in Nova Scotia, Canada. Emergence and development was monitored in four
0.09m² quadrats in multiple non-bearing and bearing year blueberry fields, and red sorrel emergence was monitored in four additional 0.09m² quadrats established in bare soil patches between blueberry clones at each site. Blueberry ramets emerged between 250 and 280 growing degree-days (GDD; T_base=0^oC) and reached 90% emergence by 600 to 800 GDD. Emergence was best explained by a four-parameter Weibull function fit to blueberry ramet emergence as a function of GDD (R²>0.95), and analysis to calibrate and validate the model is in progress. Red sorrel ramets emerged continuously from late April until monitoring stopped in late November or early December, and cumulative emergence tended to follow a linear pattern as a function of GDD (T_base=0^oC). Total net gain to red sorrel ramet populations at sprout year sites was higher in blueberry clones (70% survival rate) than in bare soil patches (24% survival rate), but survival in both environments was low in crop year fields (about 39%). Bolting and flowering of red sorrel was primarily limited to ramets that over-wintered or emerged before 250 GDD, indicating specific temperature and photoperiodic requirements for flower induction. Greenhouse and growth chamber experiments indicate that flowering might be induced by vernalization, but results are preliminary and experiments are ongoing. However, autumn and spring paraquat applications at two field sites reduced over-wintering ramet populations by 92 and 87%, respectively, and significantly reduced the density of flowering ramets. Timing of spring herbicide applications to reduce or
eliminate flowering ramets can be improved through use of the proposed thermal model for wild blueberry emergence. swhite09@uoguelph.ca

Overwintering Survival of Canada fleabane (Conyza canadensis) in a Changing Climate.

Eric Tozzi and Rene Van Acker, Department of Plant Agriculture, University of Guelph, Guelph, ON

The facultative nature of some winter annuals has a large effect on the fitness or success of that organism in an area. Understanding the recruitment nature and survival of facultative winter annuals can provide insight into the mechanisms of their success and, in some cases, their invasiveness. This may be particularly relevant in the context of accelerating climate change.

 Conyza canadensis (Canada fleabane) is a facultative winter annual native to North America that has since spread to several different continents, with prominence in the U.S.A, Canada, Europe, Brazil, and China. Canada fleabane flowers and sets seed in late summer, with some seed germinating and forming a rosette over winter, and other seed persisting and germinating in the spring of the following year.

  Winter hardiness of both the rosette and seed is an important area of study when determining spring emergence mechanisms.  Low temperatures keep Canada fleabane seed from germinating and the rosette from bolting throughout the winter period.  Warm spells or winter breaks may affect winter survival and spring emergence. The frequency and severity of warm spells in Southern Ontario are expected to increase as global climate change progresses (Shabbar and Bonsal 2003).  Shorter warm spells (1 or 2 days) are even more frequent and may still affect the winter survival of Canada fleabane. Experiments on the effect of winter breaks on winter survival, fecundity, and aboveground biomass will provide data to further explore these hypotheses.

  Canada Fleabane rosettes will be planted in small containers and placed within the ground over the winter.  The containers will be removed, placed in warming chambers for 3 days, and returned outside for the remainder of the season. Information gained on the survival, fecundity, and aboveground biomass of Canada fleabane after exposure to warming spells will help shed light on the effect of climate change will have on the pervasiveness of this species in the future. 

Weedy red rice is the most difficult-to-control weed in rice production. Seed dormancy is of major importance to its persistence. Understanding the genetic controls of dormancy could help find means to circumvent this weedy trait for better red rice management. This study aimed to determine the population variation in red rice seed dormancy at different incubation temperatures and after-ripening time, and to evaluate the genetic diversity of dormancy-linked loci among and within selected Arkansas red rice populations. The germination behavior of red rice was evaluated at incubation temperatures of 1, 15, and 35°C and after-ripening periods of 0, 30, 60, and 90 d in two independent experiments. Overall, blackhull red rice populations were more dormant than the strawhull populations and in many cases dormancy differed within populations. The blackhull populations showed higher inter- and intrapopulation variation in dormancy than the strawhull populations. To evaluate the genetic diversity of dormancy loci, 18 simple sequence repeat (SSR) markers, distributed across 4 chromosomes were used. Four populations were included: dormant blackhull (BH-D), dormant strawhull (SH-D), non-dormant blackhull (BH-ND), and non-dormant strawhull (SH-ND). A total of 90 alleles with a mean value of 6.9 alleles per locus were detected. The overall Nei’s genetic diversity (GD) of these dormancy-linked loci was high (GD= 0.66). High GD was observed among populations within each of the four groups. The blackhull group of populations, BH-D and BH-ND, showed the highest GD of 0.55 and 0.58, respectively. Genetic diversity between strawhull and blackhull red rice was higher than the GD among strawhull or blackhull ecotypes. The SH-ND group was most distant from BH-D (0.63) and BH-ND (0.60) group. Red rice populations differ greatly in their potential to persist. Seed dormancy expression in red rice populations is affected differently by germination temperature, after-ripening period and genotype. Deep dormancy in several populations indicates longer persistence in the soil seed bank and longer rotation periods out of rice for effective management.

To quantify the proportion of seeds from natural shattercane populations that will pollinate in syncrony with grain sorghum, field experiments were conducted at two locations (Lincoln NE and Clay Center NE). Seeds from shattercane populations were collected from four locations in Nebraska and two locations in Kansas.   Seeds from the six populations were broadcast in 0.5m bands in the fall following soybean harvest.  Half of each replicate was tilled prior to seed dispersal and half was left untilled. The populations were separated by 2m to prevent cross contamination.  The following spring sorghum was planted in rows perpendicular to the shattercane bands.  Three sorghum hybrids were used, an early maturing, an average maturating, and a later maturing hybrid. Each of the three lines was planted on three separate planting dates (Approximately May 20^th, June 1^st and June 10^th) and any shattercane emerged prior to that planting was removed.  A control without sorghum was also included. Shattercane were marked as they emerged and were tracked by emergence cohort.    Flowering was recorded for both shattercane and sorghum by estimating the proportion of the panicle that that had visible anthers.  Both the start and end of flowering as well as the peak flowering were estimated using this data.  Day of peak flowering for the shattercane populations at the Lincoln site ranged from day 211 (July 20^th) to day 216 for the tilled treatment and day 212 to day 221 for the no till.  At Clay Center day of peak flowering ranged from day 212 to 222 for the tilled treatment and day 220 to 228 for the no till.  Peak flowering for the sorghum at Havelock ranged from day 205 (early maturing hybrid, early planting date) to day 225 (late maturing, late planting) for the tilled and from day 205 to 226 for the no till.  Peak flowering at Clay Center ranged from 209 to day 233 in both the till and no till treatments.  Data suggests that later planting dates for sorghum resulted in less total panicles synchronously flowering with shattercane. 

After introduction as a horticulture plant, Japanese knotweed (Fallopia japonica) has invaded throughout North America. Japanese knotweed can form monospecific stands in disturbed areas, riparian ecosystems, and wetlands and impact native invertebrate and plant communities. Introduction often occurs because disturbance creates rhizome and shoot fragments that can easily root at the nodes. Once established spread is mainly through rhizome growth, although seed production occurs occasionally. Despite the importance of Japanese knotweed belowground spread, there are few mechanistic data on development of the rhizomes. Predicting the production and spread of Japanese knotweed rhizomes can provide insight on the establishment of an initial infestation and improve timing of management options to target growth and/or spread.

Two new Japanese knotweed infestations (5.22 m² and 5.72 m²) in western Oregon were monitored starting in autumn 2009. Following aboveground senescence in autumn 2011, soils were excavated to expose the underground rhizome network to a depth of 12 cm. Based on emergence data of connected ramets, rhizomes were determined to be produced in 2009 or 2010, assuming shoots emerged 1 year after bud formation on the newly produced rhizome. Surprisingly, many of the 55 emerged shoots were not connected via rhizomes at this depth and we were unable to determine if the shoots emerged from deeper rhizomes or a new plant fragment.

In 2009, 7 rhizome segments were produced with average length 30.9 cm (SE=2.25). In 2010, 6 rhizome segments were produced with average length 38.6 cm (SE=5.91). Average rhizome growth rates were 2.84 cm (SE=0.55) and 3.55 cm (SE=1.33) per week, assuming a constant growth rate from initiation of July 1^st through cessation of growth on September 15^th. Two rhizomes were monitored bimonthly in an exploratory study in Michigan in summer 2011. Rhizomes elongation peaked at 3.5 cm per week and total lengths reached 46.5 and 26.0 cm, similar to Oregon sites. Maximum rhizome elongation occurred during periods of zero shoot emergence, zero shoot growth, and following flowering time. Ramets produce buds at regular intervals, but these buds do not form new shoots until the following spring.

A non-spatial, two-class ramet matrix model of old and new ramets shows that the Oregon Japanese knotweed populations are increasing at a per capita (ramet) growth rate of 1.82 and 1.44 per year. Projection matrices will inform targeted weed management strategies by identifying weaknesses in the Japanese knotweed life cycle. As the USA tests biological control agents for Japanese knotweed, it is critical to understand Japanese knotweed growth patterns, especially during the establishment phase, to correctly biological control agents that will have the greatest per capita effect.

In the past, mountain systems have been claimed to be relatively unthreatened by non-native plant invasions.  However, several studies have shown that non-native plants are indeed present within mountainous areas of the world, and increased human use of mountain areas and global climate change both have the potential to exacerbate this problem.  It is therefore imperative that studies of individual non-native species be initiated in order to better understand any potential factors which may either limit or increase the potential of non-native plant species to spread in mountain systems.  A study was initiated in 2008 to investigate the phenomenon of non-native plant invasions along three mountain roads in the Absaroka-Beartooth Mountain Range (MT and WY) and the Northern Range of Yellowstone National Park (WY), using Dalmation toadflax (Linaria dalmatica) as the focus species.  The roads commenced at approximately 1700 m elevation and in all cases the upper elevation extents of the road were higher than the highest known Dalmation toadflax populations in the area.   Analyses suggest that while elevation significantly affects the presence of Dalmation toadflax along the studied elevation gradients, it has little direct effect on the local abundance of this species.  Instead, local habitat factors appear to have much more direct influence on the cover of this species.  This suggests that climate may influence the processes of establishment or extinction for this species along elevation gradients, but that characteristics of the plant community have much more influence on the local abundance of Dalmation toadflax.

Cultivance^® Soybean Production System - A New Tool for Soybean Weed Control in South America.    D.R. Carlson¹, L. Louzano², B. Luzzi¹, A. Ulbrich², D. Contri², M. Ismael², F. Mariscal³, R. Sandhu³, M. Scott¹, J. Stevenson-Paulik¹, E. Rech⁴, F.J. Aragão⁴, C.  Arrabal⁵.  ¹BASF Plant Science LP, Research Triangle Park, NC; ³BASF Corporation, Research Triangle Park, North Carolina; ²BASF South America, São Paulo, Brazil; ⁴Embrapa, Brasilia, Brazil;  ⁵Embrapa, Londrina, Brazil.  

The Cultivance weed control system combines broad spectrum imidazolinone herbicides with high-yielding herbicide tolerant soybeans that offer the South American grower a new tool for crop management.  Cultivance^® is a new brand that represents transgenic imidazolinone tolerant crops.  Cultivance soybeans were created by a joint collaboration with Embrapa scientists and will be launched in Brazil pending key global regulatory approvals of the transgenic event.  Cultivance soybeans were developed by the introduction of a mutant Arabidopsis AHAS gene into ‘Conquista’ soybeans.  Embrapa breeders are developing Cultivance soybean varieties for launch in the major soybean producing states in Brazil.  Soyvance^® and Soyvance Pre^® herbicides (imazapyr +imazapic in different formulated ratios) will be introduced into the marketplace sequentially to provide season-long residual weed management in Cultivance soybeans.   Field trials with post-emergent applications of Soyvance herbicide at 0.070 kg ai ha^-1 plus crop oil concentrate (1.0% v/v) or pre-emergent applications of Soyvance Pre at 0.105 kg ai ha^-1 have resulted in > 95% control of broadleaf weeds such as morning glory (Ipomoea grandifolia),  smallflower (Galinsoga parviflora L.), wild radish (Raphanus raphanistrum L.), wild pointsettia (Euphorbia heterophylla L.), horseweed and hairy fleabane (Conyza canadensis L. and bonariensis L.).   A similar level of control is observed with post-emergent applications of Soyvance at 0.070 kg ai ha^-1 plus crop oil concentrate (1.0% v/v) to such problem grasses as alexandergrass (Brachiaria  plantaginea L.), guineagrass (Urochloa maxima L.), southern crabgrass [Digitaria ciliaris (Retz) Koel] and southern sandbur (Cenchrus echinatus L.).   There has been no impact on yield when Cultivance soybeans were treated with post-emergent applications of 2x the proposed label rate of Soyvance (0.140 kg ai ha^-1 imazapyr + imazapic) from trials conducted over several years across Brazil.  The Cultivance weed control system will provide an effective new herbicide tolerant crop system in South America that can also be used to manage the development of weed resistance.   BASF will publish stewardship recommendations describing appropriate grower management of this new tool in order to sustain maximum system efficacy and longevity.     

Separate field trials were conducted in 2011 near Mokane and Mt. Airy, Missouri to determine the effects of the timing of sequential dicamba applications on the control of glyphosate-resistant (GR) giant ragweed (Ambrosia trifida L.) and GR waterhemp (Amaranthus rudis Sauer).  Initial applications of 0.28 kg/ha dicamba or 0.28 kg/ha dicamba plus 0.86 kg/ha glyphosate were made to GR waterhemp or GR giant ragweed that averaged either 7.5- or 23-cm in height.  Sequential applications of 0.56 kg/ha dicamba or 0.56 kg/ha dicamba plus 0.86 kg/ha glyphosate were made 4, 7, and 14 days after the initial application (DAA).  Single applications of 0.28 and 0.56 kg/ha dicamba, and 0.28 kg/ha dicamba plus 0.86 kg/ha glyphosate were included for comparison to the sequential treatments.  A non-treated control was also included for comparison.  Visual control of GR giant ragweed and GR waterhemp was determined 21 days after the 0, 4, 7, and 14 day sequential application (DAA).  When applied to 7.5-cm plants, all sequential applications of dicamba resulted in 100% control of GR giant ragweed 21 DAA, regardless of whether or not glyphosate was included as a tank-mix partner.  GR giant ragweed control was reduced when the initial dicamba applications were made to 23-cm tall plants.  When applied without any sequential dicamba application, the initial application of dicamba alone at either 0.28 or 0.56 kg/ha provided from 95 to 96% control of 7.5-cm GR giant ragweed, but only 62 to 84% control of 23-cm GR giant ragweed.  As with GR giant ragweed, control of GR waterhemp was higher when initial applications were made to 7.5- compared to 23-cm plants.  The addition of glyphosate increased control of GR waterhemp at either the 7.5- or 23-cm application timing.  When applied to 7.5-cm plants, sequential applications of dicamba plus glyphosate provided from 86 to 92% control of GR waterhemp, while sequential applications of dicamba alone provided from 33 to 49% control of GR waterhemp.  Single applications of dicamba or dicamba plus glyphosate provided from 18 to 67% control of 7.5-cm GR waterhemp, but only 11 to 21% control of 23-cm GR waterhemp plants.  Overall, results from these experiments revealed that early application timings and sequential applications of dicamba combined with glyphosate resulted in the highest levels of GR giant ragweed and GR waterhemp control 21 DAA.  There was not a significant difference in the level of GR giant ragweed or waterhemp control observed with sequential dicamba applications at 4, 7, or 14 DAA.  Results also indicate that GR giant ragweed is much more sensitive to applications of dicamba than GR waterhemp.

Field trials were conducted in 2010 and 2011 to evaluate corn yield response to increasing levels of pest management.  A total of 19 trials were summarized from 2010 (6) and 2011 (13).  Thirteen trials were conducted by university weed scientists and 6 trials were conducted by BASF (internal or contractor).  A randomized complete block design was utilized at all locations.  Typical plot size was 15’ wide (10’ treated; 5’ harvested) by 60’ long; each treatment was replicated 6 times.  Yield data were taken at season end.  Most trials were conducted under a conventional till production system.  A base program of glyphosate applied postemergence was the first treatment.  Each subsequent treatment added a level of management with the addition of a dimethenamid-p (DMTA-p) + atrazine premix applied preemergence in the second treatment, the replacement of the DMTA-p + atrazine premix with a DMTA-p + saflufenacil premix in third treatment, and the addition of a fungicide treatment applied at VT stage of corn in the fourth treatment.  Compared to the base program, the addition of the DMTA-p + atrazine, the DMTA-p + saflufenacil replacement, and the addition of the fungicide application resulted in a 17.2, 19.5, and 28.9 bu/A increase in yield, respectively.   The return on investment (ROI) for the most intensive management program vs. the base program was $3.51 for each dollar spent.  The ROI for the most intensive management program vs. the DMTA-p + atrazine premerge followed by glyphosate program was $2.73 for each dollar spent.  These results demonstrate increased yield potential and positive ROI for intensively managed corn.

dan.westberg@basf.com

Control of early emerging weeds is essential in order to protect the yield potential of maize.  A better understanding of the physiological changes that occur as a result of weed interference caused by a delay in weed control is required in order to address variability in yield loss across sites and years. A field trial was conducted at the University of Guelph (UG), the Ohio State University (OSU) and Colorado State University (CSU) during 2009 and 2010 in order to document changes in biomass partitioning and yield components as weed control was delayed.  There were six treatments (season-long weedy and weed-free, and weed control at the 1^st, 3^rd, 5^th and 10^th leaf tip stages of maize development) and twenty individual plants per plot were harvested at maturity.  We tested the hypothesis that, as weed control was delayed, weed interference in the early stages of maize development would increase plant-to-plant variability in plant dry matter accumulation which would result in a reduction of grain yield at maturity.  The onset of the critical period for weed control (CPWC) was reached on average between the 3^rd and 5^th leaf tip stages of development (i.e., V1-V3, 121 and 182 GDD, respectively).  The rate of loss following the onset of the CPWC ranged from 0.05 MG ha^-1 d^-1at UG 2009 to 0.22 MG ha^-1 d^-1 at CSU 2010 (i.e., 0.5 and 1.6% d^-1, respectively).  On average, reductions in kernel number per plant accounted for approximately 70% of the decline in grain yield as weed control was delayed.  Biomass partitioning to the grain was stable through early weed removal treatments, increased and peaked at the 10^th leaf tip time of control and decreased in the season–long weedy treatment.  Plant-to-plant variability in dry matter at maturity and incidence of bareness increased as weed control was delayed. However, the contribution of plant-to-plant variability to the overall yield losses was small relative to the decline of the mean plant dry matter at maturity as a result of weed interference.

The Enlist^TM trait in field corn has been extensively evaluated in research trials since 2006.  Enlist corn has demonstrated excellent tolerance to 2,4-D in single and sequential treatments applied preemergence and postemergence at rates up to 4480 g ae/ha per application.  The Enlist trait has been stacked with SmartStax® traits to confer both 2,4-D and glyphosate tolerance.  Enlist Duo™ herbicide is a novel premix containing the active ingredients 2,4-D choline and glyphosate dimethylamine (DMA) under development by Dow AgroSciences for use on Enlist crops.  Dow AgroSciences will be recommending the use of soil residual herbicides as a part of the Enlist Weed Control System to provide early season weed control for crop yield protection and weed resistance management by providing additional modes of action. 

 Field research trials were conducted in 2011 to evaluate a system approach involving GF-2726, the lead formulation of Enlist Duo, in conjunction with SureStart^® herbicide (acetochlor + clopyralid + flumetsulam).  Crop tolerance studies included GF-2726 plus SureStart at 1X and 2X recommended rates applied at spike stage or 10-11 inch corn.  Additionally, sequential applications of SureStart at 1X and 2X rates applied PRE followed by a POST application of GF-2726 at 1X and 2X rates to 10-11 inch corn were evaluated.  Applications of SureStart plus GF-2726 at spike stage resulted in <1% visual injury 14 days after application.  Applications to 10-11” corn of GF-2726 following or tank mixed with SureStart resulted in <10% injury 14 days after application. 

 Weed control studies were conducted utilizing weed management systems consisting of SureStart PRE followed by POST application of GF-2726 to V4-V5 corn, SureStart plus GF-2726 applied early POST to V2 corn, or SureStart plus GF-2726 applied POST to V4-V5 corn.  SureStart was applied at the full recommended rate for the respective soil type.  The rate of GF-2726 was 1640 g ae/ha. Weed control ratings were taken at 0, 14 and 28 days after the V4-V5 application.  PRE followed by POST, early POST only, or POST only treatments provided >90% control of ABUTH, AMARE, AMATA, AMBEL, AMBTR, CHEAL, IPOSS, SIDSP, and XANST species.

 These studies demonstrate the utility of residual herbicides followed by post applications of 2,4-D choline + glyphosate DMA as part of the Enlist Weed Control system in Enlist corn.  Residual herbicides provide an effective means to prevent yield loss due to early season weed competition and bring additional modes of action to the weed control system for weed resistance management best practices.

 ^™Enlist, Enlist Duo, and SureStart are trademarks of Dow AgroSciences LLC. ®SmartStax is a registered trademark of Monsanto Technology LLC. .  Components of the Enlist Weed Control System have not yet received regulatory approvals; approvals are pending.   The information provided here is not an offer for sale. ©2012 Dow AgroSciences LLC.

Enlist^TM corn contains the aad-1 gene which provides tolerance to 2,4-D.  Previously reported results with Enlist corn have validated tolerance to pre-emeregence and postemergence applications of 2,4-D at 1120 to 4480 g ae/ha.  The Enlist trait has been stacked with the SmartStax^® traits enabling applications of 2,4-D plus glyphosate from planting through the V8 growth stage.  Results from 2010 demonstrated excellent tolerance to 1X and 2X rates of 2,4-D dimethylamine plus glyphosate dimethylamine applied at V4 and/or V7 growth stages.  In 2011, additional research trials were conducted  across the Midwest to evaluate crop tolerance and yield with a new pre-mix product containing 2,4-D choline salt and glyphosate dimethylamine.  Plots were 4 rows wide by 40 ft long.  Applications were made with standard small plot sprayers at 15 gallons per acre spray volume.  Visual crop injury ratings were taken at 7 and 14 days after each postemergence application.  Braceroot injury ratings were taken late in the season after emergence.  Yields were taken on the two center rows of the plot and converted to percentage of the paired untreated plot immediately behind the treated plot.  Results of these trials confirmed earlier findings and continue to demonstrate excellent plant and brace root tolerance to both 2,4-D alone and 2,4-D + glyphosate combinations.  2011 yield results validated 2010 data where no negative effects on crop yield were observed in Enlist corn.  The Enlist Weed Control System in corn includes Enlist corn and Enlist Duo™ herbicide featuring Colex-D Technology^TM.  The Enlist Weed Control System will offer excellent crop tolerance and weed management flexibility in field corn, including efficacy on many glyphosate resistant or difficult-to-control broadleaf weed species.

 ^™Enlist, Enlist Duo and Colex-D are trademarks of Dow AgroSciences LLC. Components of the Enlist Weed Control System are pending regulatory approvals.    The information provided here is not an offer for sale.

^©2012 Dow AgroSciences LLC

SmartStax® multi-event technology developed by Monsanto and  Dow AgroSciences LLC.  SmartStax® and the SmartStax logo are trademarks of Monsanto Technology, LLC.

Glyphosate resistant (GR) Canada fleabane (Conyza canadensis) was first confirmed in Ontario, Canada from seed collections in the fall of 2010. It is now confirmed that there are 8 fields in Essex County in southwestern Ontario with GR Canada fleabane. Field studies were conducted during summer of 2011 to determine a) the biologically effective rate of glyphosate, b) the efficacy of herbicides tankmixes applied preplant, c) the efficacy of herbicides applied preemergence for full season residual weed control, and d) the efficacy of postemergence herbicide tankmixes in soybean for the control of GR Canada fleabane in soybean. GR Canada fleabane survived glyphosate rates as high as 21,600 g ai/ha which is 24 times the manufacturer’s recommended rate. Among the preplant herbicide tankmixes evaluated, saflufenacil (98%), saflufenacil/dimethenamid-p (96%) and amitrol (93%) provided the best control while chlorimuron (87%), cloransulam-methyl (87%) and 2,4-D ester (86%) were also effective in controlling GR Canada fleabane. Glyphosate alone or tankmixed with carfentrazone, glufosinate, paraquat, flumioxazin and chlorimuron+flumioxazin provided poor/inconsistent control of GR Canada fleabane in soybean. Among the preemergence residual herbicide treatments evaluated, metribuzin (100%), flumetsulam (98%) and cloransulam-methyl (95%) provided the best control. Glyphosate alone or in combination with chlorimuron, linuron, imazethapyr, clomazone, flumioxazin, flumioxazin+chlorimuron or pyroxasulfone+flumioxazin provided poor/inconsistent control of GR Canada fleabane in soybean. Among postemergence herbicide tankmixes evaluated, cloransulam-methyl (64%) and chlorimuron (51%) provided marginal control of GR Canada fleabane in soybean. Glyphosate alone or in combination with acifluorfen, fomesafen, bentazon, thifensulfuron, imazethapyr, imazethapyr+bentazon or glyphosate/fomesafen applied POST provided poor/inconsistent control of GR Canada fleabane in soybean. In dicamba tolerant soybean, dicamba provided fair to excellent control of GR Canada fleabane depending on timing.

GLYPHOSATE-RESISTANT GOOSEGRASS CONFIRMED IN TENNESSEE:  POTENTIAL IMPLICATIONS AND CONTROL OPTIONS FOR SOYBEAN.  Kelly A. Barnett¹*, Thomas C. Mueller², James T. Brosnan², and Lawrence E. Steckel¹, ¹Univ. of Tennessee, Jackson, TN, ²Univ. of Tennessee, Knoxville, TN.

Glyphosate-resistant (GR) weeds are a major issue for Tennessee cotton growers.  Until 2011, GR horseweed, GR Palmer amaranth, and GR giant ragweed were the only three GR weeds that could be found in Tennessee.  In 2010, a grower complained
he was unable to control his goosegrass with repeated glyphosate applications.  Greenhouse tests were initiated in 2011 to compare glyphosate control of the suspected GR goosegrass population to a known susceptible population.  These greenhouse tests did confirm that this suspected GR goosegrass population was resistant to glyphosate.  At 21 days after application, the X rate (0.86 kg ae/ha) only provided 45% control of the GR goosegrass population while the X rate provided 98% control of the susceptible at this same rate.  An 8X rate (6.72 kg ae/ha) of glyphosate was required to achieve that same level of control for the GR goosegrass population.  Based on these results, a field study was initiated in 2011 to confirm the field level of glyphosate resistance in this population and to determine postemergence control options for goosegrass.  Treatments consisted of the following:  glyphosate at 0.86 kg ae/ha (1X rate), glyphosate at 1.72 kg ae/ha (2X rate) plus non-ionic surfactant at 0.25% v/v,
glyphosate at 3.44 kg ae/ha (4X rate) plus non-ionic surfactant at 0.25% v/v, glyphosate at 6.88 kg ae/ha (8X rate) plus non-ionic surfactant, glyphosate at 0.86 kg ae/ha plus clethodim at 0.085 kg ai/ha, clethodim at 0.085 kg ai/ha plus non-ionic surfactant at 0.25% v/v, fluazifop at 0.210 kg ai/ha plus non-ionic surfactant at 0.25% v/v, fomesafen at 0.263 kg ai/ha plus non-ionic surfactant at 0.25% v/v, glufosinate at 0.594 kg ai/ha, glufosinate at 0.594 kg ai/ha plus fomesafen at 0.263 kg ai/ha, clethodim at 0.085 kg ai/ha plus fluazifop at 0.210 kg ai/ha plus non-ionic surfactant at 0.25% v/v, and fluazifop at 0.210 kg ai/ha plus fomesafen at 0.263 kg ai/ha plus non-ionic surfactant at 0.25% v/v.  The objective of this study was to determine the level of glyphosate resistance observed in the field and to determine control options for goosegrass in soybean.  The experiment was a randomized complete block design with three replications.  An analysis of variance was performed to separate differences between treatments at p<.05.  The level of glyphosate resistance was higher than that observed in the greenhouse with a 1X
rate of glyphosate providing 35% control of goosegrass 21 days after application.  A 2X rate of glyphosate provided 57% control and a 4X rate of glyphosate provided 70% control.  An 8X rate of glyphosate provided 91% control and was not significantly different from clethodim alone, fluazifop alone, clethodim plus fomesafen, or fluazifop plus fomesafen.  These treatments provided 78% to 92% control of goosegrass 21 days after application.  Fomesafen alone provided very little control (10%) but did increase control when combined with clethodim (83%) or fluazifop (92%).  Glufosinate alone or in combination with fomesafen did not provide adequate control of goosegrass (40-43%).  Field studies validated previous greenhouse studies and indicated that an 8X rate of glyphosate would be required to provide adequate control of GR goosegrass.  Clethodim or fluazifop alone or in combination with fomesafen are treatments that can be used to control GR goosegrass.  However, these herbicides needed to be applied to goosegrass that is 3 tillers or less in height to provide adequate control of GR goosegrass.

kbarnet7@utk.edu 

Research trials were conducted from 2010 to 2011 in the greenhouse and the field in Henry County, IA to determine the response of tall waterhemp, Amaranthus tuberculatus (Moq.) Sauer, biotypes to foliar and soil-applied HPPD inhibiting herbicides.  The biotypes were initially identified in the field in either 2009 or 2010.  Greenhouse research demonstrated that the biotype identified in 2009 (IA1) was 8X, 10X, and 28X less responsive to mesotrione, atrazine, and thifensulfuron.  Under field conditions, the IA1 biotype was not controlled by twice label rates of  mesotrione, tembotrione, and topramezone applied under field conditions in 2010.  In 2011 field trials, the IA1 biotype was less sensitivie to soil-applied isoxaflutole and mesotrione and foliar-applied tembotrione than the biotype identified in 2010 (IA2).  Label use rates of soil-applied isoxaflutole or mesotrione did not give commercially acceptable control by the 2 week after emergence rating for the IA1 biotype.  Control of the IA2 biotype was not commercially acceptable at the label rate by the 4 week after emergence rating.  Tall waterhemp control increased when either metribuzin or atrazine were applied with either isoxaflutole or mesotrione applied to the soil.

A survey of soybean fields containing late-season waterhemp (Amaranthus rudis Sauer) infestations was conducted just prior to harvest in 2008 and 2009 to determine the frequency and distribution of glyphosate-resistant waterhemp in Missouri.  In this survey, seed from 144 separate waterhemp populations were collected for characterization of glyphosate resistance in greenhouse experiments.  All waterhemp populations were sprayed once plants reached 15-cm in height with 1.7 kg glyphosate ae/ha, or twice the recommended use rate (2X) of this herbicide.  Waterhemp populations were classified as resistant if 60% or more of the plants treated with the 2X rate of glyphosate survived and were clearly capable of reproduction three weeks after treatment.  The tillage type, row spacing, previous crop, type and density of other weeds present, degree of waterhemp infestation, and whether the waterhemp population showed obvious signs of surviving herbicide treatment were recorded at each sampling site. In addition, crop rotation and herbicide use history up to five years prior to waterhemp sampling was also obtained through a phone-based landowner survey.  Glyphosate resistance was confirmed in 99 out of 144, or 69% of the total waterhemp populations sampled.  These resistant populations occurred across 41 counties of Missouri. An analysis of the factors recorded at each sampling site was conducted with PROC GLIMMIX in SAS using a logit link function and a binomial distribution of the data. This procedure determined the probability of each factor having a significant effect on glyphosate resistance or susceptibility in a given waterhemp population.  Based on the data collected from each sampling site, soybean fields confirmed with glyphosate-resistant waterhemp were more likely to be free of other weed species, were more likely to occur where soybeans were continuously cropped, were more likely to occur where glyphosate was the only herbicide applied for several seasons consecutively, and were more likely to show obvious signs of surviving herbicide treatment than fields where susceptible waterhemp occurred.  Therefore we suggest that these four factors, and certain combinations of these factors, can serve as “indicators” of glyphosate-resistance in future waterhemp populations that remain until harvest in soybean fields in Missouri.

Glyphosate-resistant (GR) Italian ryegrass (Lolium perenne ssp. multiflorum) was first documented in the United States in Oregon in 2003.  Regionally, two populations of GR Italian ryegrass exhibiting a three-fold resistance were identified in field crops in Washington County, Mississippi, in 2005.  Glyphosate-resistant Italian ryegrass is now present in 13 counties in Mississippi.  Research to address management of GR Italian ryegrass was initiated at the Delta Research and Extension Center in Stoneville, Mississippi, in 2005.  The major conclusions of research from 2005 through 2008 were (1) postemergence (POST) options in the spring are extremely limited and require at least two herbicide applications to approach complete control and (2) residual herbicides applied in the fall offer the best opportunity for controlling GR Italian ryegrass.  More recently, the research emphases have transitioned to focus on programs for managing GR Italian ryegrass with control tactics utilized in the fall and spring.  

 Research was conducted in 2010-11 near the Mississippi State University Delta Research and Extension Center in Stoneville to develop GR Italian ryegrass management programs that integrate fall residual and spring POST herbicides.  Treatments were arranged as a three-factor factorial in a randomized complete block design with four replications, and the study was repeated in space.  Factor A was fall application and included no fall treatment, tillage, or application of a mixture of S-metolachlor (1.4 kg ai/ha) plus paraquat (0.84 kg ai/ha).  Fall applications were made November 1, 2010.  Factor B was winter application and included no winter treatment or clethodim (0.1kgb ai/ha) applied February 4, 2011.  Factor C was spring application and included no spring treatment or paraquat (1.12 kg ai/ha) applied February 23, 2011.  Data collected included visual estimates of GR Italian ryegrass control at different intervals following each application and GR Italian ryegrass density following fall applications.  Data were subjected to ANOVA and estimates of the least square means were used for mean separation. 

 S-metolachlor controlled GR Italian ryegrass 90% prior to winter application.  However, control from tillage treatment was only 42% at the same evaluation.  One-pass programs controlled GR Italian ryegrass ≤83% by late-March.  Programs utilizing only winter and/or spring applications controlled GR Italian ryegrass ≤85% by late-March.  Efficacy of one-pass POST programs was improved when these applications were preceded by fall tillage.  Fall tillage followed by clethodim followed by paraquat controlled GR Italian ryegrass similar to programs containing S-metolachlor followed by one POST application. 

 Following fall tillage, both clethodim and paraquat were required as POST treatments.  Following S-metolachlor application, control of GR Italian ryegrass was optimized with a single POST treatment.  GR Italian ryegrass control was reduced in programs that did not include a fall treatment.  A minimum of two herbicide applications were required for >90% control of GR Italian ryegrass.

 teubank@drec.msstate.edu

Pyroxsulam herbicide, a member of the triazolopyrimidine sulfonanilide chemical family, is a postemergence grass and broadleaf herbicide developed by Dow AgroSciences for use in spring and winter wheat.  This acetolactate synthase (ALS)-inhibiting herbicide can be applied postemergence (fall or spring) to actively growing winter wheat from 3 leaf to tiller stage, for control of  grass weeds from 2 leaf to 2 tiller stage and broadleaf weeds up to 2 inches tall or 2 inches in diameter.  The current U.S. formulation, PowerFlex^®, is selective in winter wheat, spring wheat (including durum), rye and triticale, but is not selective in barley, oats, rice, maize or broadleaf crops.

Dow AgroSciences has conducted over 300 internal and external field research trials in winter wheat with PowerFlex^® over the last six years (2006-11).  An in-depth evaluation was conducted on the effect of application timing, compared to key commercial standards, on the efficacy of major weeds and the resulting impact on wheat yields in those trials.  Herbicide applications were made either fall or spring at the appropriate timeframe for each geography. The key grass and broadleaf weeds evaluated included cheatgrass (Bromus secalinus), downy brome (Bromus tectorum), henbit (Laminum amplexicaule) and Italian ryegrass (Lolium perenne ssp. multiflorium). 

The experimental design in all trials was a randomized complete block with 3 or 4 replications.  Most plot sizes ranged from approximately 5 to 20 ft wide by 20 to 40 ft. in length.  Treatments were applied with either a CO₂ backpack or small plot tractor sprayer calibrated to deliver 10 to 15 GPA.

Data from these trials indicate that PowerFlex^® herbicide at 18.4 g ai/ha (0.016 lbs ai/A) provides control of cheatgrass, downy brome, non ALS-resistant Italian Ryegrass and henbit with either a fall or spring application, comparable to or superior to other commercial standards.  Winter wheat yields were increased with either a fall or spring application of PowerFlex^® vs. the non-treated weedy check for the key grass and broadleaf weeds listed above.  PowerFlex^®  caused minimal wheat injury (not presented).

^® Trademark of Dow AgroSciences LLC

PowerFlex^®  is not registered for sale or use in all states.  Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state.  Always read and follow label directions.

In the United States, downy brome (Bromus tectorum) and Japanese brome (Bromus japonicus) are becoming two of the most troublesome and difficult to control weeds in winter wheat (Triticum aestivum).  Increased no-tillage production practices, warmer winters, and limited herbicide choices have facilitated the increase in Bromus species populations.  The herbicide propoxycarbazone is labeled for postemergence (POST) applications in winter wheat for the control of Bromus species. Propoxycarbazone can be applied at 30-45 g ai/ha in the fall or spring.  Sequential treatments of 30-45 g ai/ha applied in the fall may be followed by an additional 15-30 g ai/ha in the spring.  The maximum use rate of propoxycarbazone in a 365 day period is 60 g ai/ha.  Herbicidal activity in weeds is due to root and foliar absorbtion of the active ingredient and propoxycarbazone offers both contact and residual control.  Prior to 2011, propoxycarbazone could only be applied to wheat from crop emergence up to but before jointing.  From 2009 through 2011, research trials were conducted to determine the efficacy of propoxycarbazone applied preemergence (PRE) or postplant preemergence (PPRE) alone or with glyphosate in winter wheat for the control of Bromus species.  Propoxycarbazone rates ranged from 15-30 g ai/ha applied either PRE or PPRE alone in the fall.  Sequential treatments of propoxycarbazone at 30 g ai/ha applied in fall followed by 30 g ai/ha in the spring were also evaluated. Propoxycarbazone treatments were compared to 14.7 g ai/ha of flucarbazone applied PRE or PPRE in the fall. On average, the maximum winter wheat injury from any treatment utilizing propoxycarbazone applied either PRE or PPRE did not exceed 6%. Average downy brome control achieved with 15 g ai/ha of propoxycarbazone applied in the fall was 57%, compared to 43% control provided by 14.7 g ai/ha of flucarbazone at the same timing. Downy brome control increased to 68% when propoxycarbazone was applied at 30 g ai/ha in the fall.  Propoxycarbazone at 30 g ai/ha applied sequentially in the fall and spring resulted in 87% downy brome control across 14 trials. This new use pattern for propoxycarbazone has been added to the Olympus^® label and was implemented commercially during the fall of 2011.

Herbicide Programs for Control of Italian Ryegrass (Lolium multiflorum Lam.) in Winter Wheat.  M.W. Marshall*¹, ¹Clemson University, Blackville, SC.

Italian ryegrass remains one of the most troublesome weeds in small grain production in South Carolina and southeastern United
States.  Given the prevalence of ACCase-resistance in Italian ryegrass in wheat producing areas of South Carolina, ALS-inhibitors, including mesosulfuron and pyroxsulam, are commonly used to control ACCase-resistant Italian ryegrass.  Mature ryegrass seed samples were collected from several wheat producing counties in South Carolina and subsequent greenhouse studies indicated that several of these biotypes were ACCase- and ALS-resistant in 2009.  Therefore, the objectives of this study were to examine soil residual combined with postemergence herbicides to control Italian ryegrass in winter wheat.  Field studies were initiated in winter of 2009 and continued in winter of 2010 at the Clemson University Edisto Research and Education Center.  Preemergence (PRE) treatments included pendimethalin at 1.1 kg/ha, flumioxazin at 0.072 kg/ha, premix of flufenacet plus metribuzin at 0.38 kg/ha.  Postemergence (POST) treatments included mesosulfuron at 0.20 kg/ha, pyroxsulam at 0.025 kg/ha, pinoxaden at 0.06
kg/ha.  Preemergence treatments were applied at the spike stage of wheat.  Postemergence treatments were applied at the 2 to 3 tiller stage of Italian ryegrass.  An untreated check was included for comparison. Studies were arranged as a randomized complete block design with 3 replications.  In study one, pendimethalin and flufenacet plus metribuzin PRE provided 97 and 98% Italian ryegrass control, respectively, at 4 weeks after treatment (WAT).  Similarly, flumioxazin PRE provided 100% Italian
ryegrass control across 4, 8 and 12 WAT. The POST treatments mesosulfuron, pyroxsulam, and pinoxaden provided excellent control of any Italian ryegrass that emerged later in the spring (susceptible population).  Very little wheat injury was observed with the PRE and POST treatments.  In study two, flufenacet plus metribuzin PRE followed by mesosulfuron or pinoxaden also provided excellent control (>95%) of Italian ryegrass treatments at 4 WAT.  In study 3, flufenacet plus metribuzin PRE alone and followed by mesosufluron or pyroxsulam provided 100% Italian ryegrass control.  In summary, soil residual herbicides play an
important role in controlling Italian ryegrass, especially in areas where ACCase and ALS-resistance in observed.  Future research will examine flumioxazin and pendimethalin PRE followed by either mesosulfuron or pyroxsulam POST.  Email address for author is marsha3@clemson.edu

                There are a limited number of preemergence herbicides for spring wheat (Triticum aestivum L.) that do not require incorporation. Preemergence herbicides can increase the number of modes-of-action used during a growing season and provide timing flexibility for post emergence herbicide applications. Pyroxasulfone and saflufenacil are preemergence herbicides that do not require incorporation. The purpose of this research was to evaluate the usefulness of pyroxasulfone and saflufenacil as preemergence herbicides in spring wheat by determining crop safety and weed control. Pyroxasulfone and saflufenacil were evaluated in separate experiments, each conducted in three environments. All treatments were applied within six days after planting with a backpack sprayer that delivered 80 L ha^-1 through Turbo Teejet 11001 nozzles. The rates of pyroxasulfone were 63 to 420 g ai ha^-1 and of saflufenacil were 18 to 196 g ai ha^-1. Visual evaluations for pyroxasulfone studies were conducted 4-6 weeks after treatment and evaluations for saflufenacil studies were conducted 6-8 weeks after treatment. Visible crop injury was not observed for any of the pyroxasulfone or saflufenacil rates used in these studies. Pyroxasulfone at 196 g ha^-1 provided 90% control of yellow foxtail (Setaria pumila (Poir.) Roemer & J.A. Schultes) and 95% control of redroot pigweed (Amaranthus retroflexus L.), but only 49% control of wild mustard (Sinapis arvensis L.). The greatest wild mustard control obtained with pyroxasulfone was 67%. Pyroxasulfone should be considered for a preemergence herbicide in spring wheat because of excellent crop safety and control of certain small seeded weeds. The current maximum rate of saflufenacil in spring wheat is 50 g ha^-1. When the rate of saflufenacil was increased from 50 g ha^-1 to 77 g ha^-1 broadleaf weed control increased as much as 33%. A maximum saflufenacil rate of 77 g ha^-1 in spring wheat should be considered because of excellent crop safety and increased weed control.

Historically, the foundation for success of the University of Georgia (UGA) Cooperative Extension program has been the county delivery system including crop production or grower meetings.  UGA Extension weed specialists receive requests from local county agents to make educational presentations at 35-40 grower meetings per year across the state of Georgia.  Declining budgets, increasing fuel costs, and the need to improve efficiency have challenged extension specialists to develop alternative methods of information delivery withour sacrificing impact.   Recent advances in internet technologies and hardware/software computer programs have made web-based delivery methods more attractive.  In February 2010 (Thomas County) and January 2011 (Walker County), weed science updates were delivered live over the internet from the UGA – Tifton Campus using various software programs (Google Chat, Horizon-Wimba, Microsoft^® PowerPoint^®, and Skype™) and a Logitech^® Webcam Pro 9000 camera. Topics discussed included herbicide resistance, Palmer amaranth (Amaranthus palmeri), Bengal dayflower (Commelina benghalensis), and emerging technologies in field corn/soybean.  Program evaluations indicated that 100% of the attendees liked the format of the internet meeting and would attend similar educational programs in the future.  Because of this success, internet delivery programs in the discipline of weed science are being offered to additional counties.   

Information delivery methods utilized by University Extension Service personnel as well as others in agriculture have changed substantially over the past several years.  Historically, Extension Service publications were produced, published in hard copy format, and delivered to clientele through county extension service offices as well as through Extension Service educational programs.  However, delivering information in this manner made communication of timely information on events currently occurring extremely difficult.  As technology has become more ubiquitous, personnel with the Mississippi State University Extension Service developed an electronic newsletter that dealt with entomological issues in cotton production.  The Mississippi Crop Situation Newsletter was delivered to clientele both electronically as well as through hard copy mail outs.  As time progressed this newsletter was expanded to address entomological issues in numerous cropping systems.  In order to meet the needs of an ever diversifying clientele, the Mississippi Crop Situation newsletter was further expanded to a multi-crop, multi-disciplinary newsletter.  Although producing a newsletter in this format was successful, it became apparent the further changes were needed in order to remain a valued source of information.  Information is available from numerous sources through smartphones and tablet devices such as IPad’s among others.  As a result the Mississippi Crop Situation Blog was developed and implemented in 2011. 

After implementation of the Mississippi Crop Situation Blog, the next task was determining the impact of this blog.  Numerous software tracking packages exist; however, the two utilized for tracking impact of this blog are Wordpress™ and Sitemeter™.  Each of these software packages offer the user numerous ways to determine distribution of content contained within the Mississippi Crop Situation blog.  Usage statistics can be viewed by day, week, month, or year.  In addition, the location that users are utilizing information from can be viewed as well as numerous other parameters such as screen resolution the content was viewed on, search terms used to get to content within the blog, and where the user was referred to the blog from.  Examining this information can aid those who maintain a blog understand how users are utilizing their blog and can help tailor content and delivery methods in order to maximize use of the blog.  Utilizing information from those who use your blog can help shape the direction the blog goes and ultimately increase the impact that a blog has. 

Controlling nuisance trees with persistent, soil-active herbicides is a commonly accepted form of weed control in many non-crop situations. Unfortunately, certain herbicides are occasionally used for this purpose in a malicious manner. These situations often involve property owners who are trying to quietly eliminate trees growing on neighboring properties. However, on the rare occasion, the target is an iconic tree or trees much in the public interest such as Treaty Oak that was poisoned in 1989 in Austin, Texas. In January 2011, a caller to a national radio talk show claimed he had poisoned Auburn University’s iconic Toomer’s oaks with the herbicide Spike 80DF. Toomer’s oaks are two live oak (Quercus virginiana) trees estimated to be over 70 years old that are located at the city center of Auburn, Alabama where the University and downtown meet. The trees are a cultural landmark in Auburn where alumni and fans gather to celebrate and “roll the trees with toilet paper” following football and other athletic victories. Very soon after the radio broadcast, University officials sampled the soil beneath the trees and laboratory analysis detected up to 51 ppm of the herbicide active ingredient tebuthiuron in the soil surrounding the two oak trees. A task force composed of faculty and industry representatives was rapidly assembled to attempt to save the trees. Remediation measures included applications of liquid activated carbon to the soil under the tree canopies, applications of an anti-transpirant to the foliage, and both dry and wet soil excavation methods to remove as much contaminated soil as possible.  While the fate of the trees is still unclear, the outlook is currently very bleak as the trees have manifest significant signs of tebuthiuron poisoning and have lost approximately ninety percent of their foliage during the 2011 growing season.  This presentation will highlight the lessons learned from this malicious poisoning including proper emergency preparedness, available remediation options for poisoned trees, and best approaches for communicating via public and media outlets.  

In the 1970’s and early 1980’s triazine-resistant weeds caused the most economic damage of any herbicide-resistant weeds.  The mid 1980’s and 1990’s saw the rise of ALS and ACCase inhibitor resistant weeds, superseding the economic impact of triazine-resistant weeds.  Glyphosate-resistant weeds have become the dominant issue of herbicide-resistance research in the last decade, however at present still have not surpassed the economic damage caused by ALS and ACCase inhibitor resistant weeds globally.  Glyphosate-resistant weeds have been found in Argentina, Australia, Brazil, Canada, Chile, China, Colombia, Czech Republic, France, Greece, Israel, Italy, Malaysia, Paraguay, Portugal, South Africa, Spain, USA.  However glyphosate-resistant weeds have not caused widespread economic damage in most of these countries.  Researchers entering data into the International Survey of Herbicide Resistant Weeds (www.weedscience.com) are asked to estimate the area infested for each case.  Whilst these estimates have a wide margin of error they do give a general indication of the area infested.  The area infested with glyphosate-resistant weeds in Roundup Ready cropping systems in the United States account for more than 93% of the global total.  The only other countries to have been impacted significantly by glyphosate-resistant weeds are Brazil, Australia, Argentina, and Paraquay.  Conyza canadensis  and Amaranthus palmeri from the mid-western and southern states of the USA account for 87% of the area (48% and 39% respectively) infested with glyphosate-resistant weeds globally.  Even though glyphosate resistant Conyza canadensis is the most widespread, it is Amaranhus palmeri that has the greatest economic impact because it is more difficult and expensive to control with alternative herbicides than Conyza canadensis.  Digitaria insularis from Brazil and Paraquay accounts for 6% of the global acres infested with glyphosate-resistant weeds and is rapidly increasing.  Amaranthus tuberculatus is next with 5% and is likely to increase significantly over the next few years, having the potential to become the worst glyphosate-resistant weed globally because it is a primary weed of the 170 million acres of corn/soybean production in the mid-west.  Ambrosia trifida, Sorghum halpense, Lolium rigidum, Ambrosia artemisiifolia, and Kochia scoparia have a small but economically significant impact on agriculture and most of the other glyphosate-resistant weeds have little or no economic impact.  Glyphosate-resistant Sorghum halepense (primarily in Argentina but also in the USA) and Kochia scoparia (USA and Canada) are both likely to increase rapidly in area and economic significance over the next 5 years.  While only 11 of the 21 species have evolved glyphosate-resistance in Roundup Ready cropping systems these 11 species account for more than 97% of the total estimated area infested with glyphosate-resistant weeds.

Herbicide resistance education and training have been identified as critical paths toward advancing the adoption of proactive best management practices to delay and mitigate the evolution of herbicide-resistant weeds. In September 2011, the Weed Science Society of America (WSSA) introduced a training program designed to educate certified crop advisors, agronomists, pesticide retailers and applicators, growers, students, and other interested parties on the topic of herbicide resistance in weeds. A peer reviewed, five-lesson curriculum is currently available at the Society’s web page via web-based training and PowerPoint slides. Topics include: (1) An introduction to herbicide resistance in weeds (2) How do herbicides work? (3) What is herbicide resistance? (4) How do I scout for and identify herbicide resistance in weeds? and (5) How do I manage resistance? The lessons are unique among herbicide resistance training materials in that, for the first time, the WSSA presents a unified message on the causes of herbicide resistance and offers several strategies for identifying and mitigating herbicide resistance in weeds. The lessons contain the most up-to-date definitions for use in the field, including those for low- and high-level resistance, a video on how to scout for herbicide-resistant weeds, and an emphasis on proactive management. The lessons utilize animations to showcase these important points. A Spanish-language version has been also produced.  As of January 11, 2012, the English lessons have been downloaded greater than 526 times since they were made available the end of September and the Spanish lessons have been downloaded 4 times since they were made available about five weeks ago.

While herbicide resistant weeds have been a factor in agriculture since the 1970’s, the impact that herbicide resistance has now is unprecedented and becoming increasing problematic from several fronts. The occurrence of wide-spread resistance to atrazine was addressed by better management and the inclusion of other herbicides.  When the ALS- inhibitor herbicides predominated and the rapid evolution of resistance to this important group of herbicides occurred, agriculture did not miss a beat as genetically-engineered resistance to glyphosate in the major crops was available.  However, with the adoption of glyphosate as the most important and often sole tactic for weed control, weed management went by the wayside.  This technology changed not only how agriculture viewed weeds but also the very economic fabric of agriculture.  Simple and convenient were the Sirens song that lead growers to increase the size of their farming enterprise based largely on the time saving from conservation tillage and weed
control practices which the glyphosate-based technology supported.  Predictably weeds evolved resistance to glyphosate and still growers were reticent to change weed control tactics.  Now, with a number of very well adapted weeds that have also evolved resistance to glyphosate, growers are beginning to understand the errors made.  The weed science community is also culpable from the perspectives that many of us were more concerned about tweeking the system rather than educating growers of the
actual nature of the problem and were also reluctant to address the issue head on with the industry.  As a result, discussion about “proactive” weed management tactics to preserve the technology are no longer valid and we must now look to make major changes in the crop production system in order to provide opportunities for growers to management the glyphosate-resistant, and often times weeds with multiple resistances.  While growers will not receive this message well, it is important that it be delivered.  Unless, major changes in how weeds are managed are accepted, growers may have problems that cannot be effectively resolved.  While there is a need for new herbicides to help resolve the problems for which the system has selected, unless we dramatically change the system and how the herbicides are used, we are destined to reinforce the mistakes that have historically occurred.  Diversity in weed management must be established.  Mechanical and cultural strategies must be included in a crop production system to sustain the economic, ecological, and environmental success of the system.

Weed management strategies implemented by growers in glyphosate-resistant (GR) corn, cotton, and soybean in the U.S. are currently in a state of flux in response to infestations of GR weeds.  A full range in grower awareness and infestation levels of GR weeds exists across these major crop regions which can effect what weed management strategies are recommended by academic weed specialists in each state.  Furthermore, the specific weed species that pose the greatest challenge in the different cropping system may further influence the specific tactics that are promoted for proactive and reactive approaches for managing herbicide resistance.  The objective of this research was to identify the most problematic weeds considered in weed management recommendations and to characterize the most common parameters being recommended in proactive and reactive strategies in GR corn, cotton, and soybean compared with a non-GR system.  A survey was sent to academic weed specialists in the major states for production of GR corn, cotton, and soybean in July 2011.  The survey responses comprise 22 academic weed specialists from 19 states.

The least amount of herbicide diversity in terms of the number of herbicide ai’s (x=3.6 ai’s) and sites of action (x=3.3 SOA) was found in the proactive GR soybean recommendations in conventional tillage compared with any other recommendation in either corn or cotton.  This highlights both the diversity of herbicides commercially available in corn and cotton and the challenges in providing greater diversity in soybean, whether limited by the availability of effective herbicides for the most problematic weeds or the reluctance of soybean growers adopt a diverse weed management strategy that rivals those used in corn or cotton.  Minor differences were evident in the diversity of herbicides between the proactive and reactive recommendations in GR corn.  However, reactive recommendations for GR weeds in cotton and soybean typically include an additional herbicide ai or SOA compared with proactive strategies.  One of the core aspects of herbicide resistance management is the integration of herbicide diversity such as the aforementioned parameters on herbicide ai’s and SOA.  However, the use of the most effective herbicides at the optimal time and use rate are part of the overall comprehensive management plan was evident in the academic recommendations, especially in the reactive recommendations where glyphosate-resistant weeds are present.  Working within the confines of modern crop production systems is another limiting factor as less than 10% of the recommendations included in-season row cultivation as a weed management tool.

From 2006 to 2010 a total of 155 commercial fields in Illinois, Indiana, Iowa, Nebraska, North Carolina, and Mississippi were monitored to compare the weed management tactics used in grower practices versus academic recommendations for use in glyphosate-resistant corn, cotton, and soybean production systems.  The academic recommendations were based on best management practices to deter the shift to weed species more difficult to control with glyphosate or glyphosate-resistant weed biotypes.  Each field was divided into two sections with half managed with grower practices and the other half using the academic recommendations.  Fields were categorized into three cropping systems:  1) a single continuous glyphosate-resistant (GR) crop, 2) a rotation of two GR crops, and 3) a GR crop rotated with a non-GR crop. 

The use of tillage in the cropping system by growers was the lowest in continuous GR soybean (30%) which was in direct opposition with the greatest frequency of tillage in continuous GR corn (70%).  Over the course of the research from 2006 to 2010 grower adoption of residual herbicides applied either preplant or postemergence in continuous GR soybean increased over 3X and were similar for both tilled and no-tillage sites.  A concomitant reduction in the reliance on glyphosate alone in this cropping system was also realized starting from approximately 60% of the sites in 2006 using glyphosate as their sole herbicide for weed management to no field sites in 2010.  The frequency of growers utilizing residual herbicides in GR soybean was up to 1X greater in no-tillage systems versus tilled sites when soybeans were rotated with another crop.  Thus, a significantly greater proportion of the field sites in GR soybean rotated with corn relied solely on glyphosate for chemical weed management.  In GR corn the frequency of residual herbicides was near 40% of the field sites whether in a continuous corn or corn/soybean rotation.  However, the use of residual herbicides was twice as common in no-tillage versus tilled GR corn rotated with GR soybean.  Furthermore, growers using tillage in corn production used glyphosate alone twice as frequently as no-tillage field sites.  The need for a preplant burndown herbicide application in no-tillage provided a greater opportunity for the inclusion of a residual herbicide compared with the more common system in corn with tillage performed at planting.  Common theory would suggest that the risk for the evolution of glyphosate-resistant weeds would be greater in no-tillage fields since mechanical weed control isn’t a component of a diverse weed management system.  However, if no-tillage systems are twice as likely to include residual herbicides at some point in the cropping season compared with fields which are tilled, then the heightened risk for summer annual weed species evolving resistance to glyphosate in no-tillage is arguable.

Dicamba has been a highly effective weed management tool for nearly 50 years.  It is the fifth most widely used herbicide in the United States with more than 25 million acres of crops including corn, wheat, pasture, and turf treated annually.  Dicamba was discovered in 1958 and first registered as Banvel^® herbicide for broadleaf control in turf.  Registration of dicamba products for use in corn, sorghum, small grains, and pasture soon followed in 1964 through 1966.  Since then dicamba chemistry has evolved over time with the development of formulations such as Marksman^®, Clarity^®, Distinct^®, and Status^® herbicides.  These dicamba formulations effectively control or suppress over 190 broadleaf weeds including many problematic weed species such as ragweed (Ambrosia spp.), common cocklebur (Xanthium strumarium), common lambsquarters (Chenopodium album), morningglory (Ipomoea  spp.), pigweed (Amaranthus spp.), and horseweed (Conyza canadensis).  Currently, a next generation dicamba formulation is in development that reduces potential volatility more than the improvement achieved with Clarity^® over Banvel^®.  The next generation of dicamba (EXP; not a registered product) demonstrates similar efficacy as past generations of dicamba when applied postemergence and preemergence.  Field trial results show that the EXP formulation and Clarity^® provide similar control of broadleaf weeds including glyphosate-resistant common waterhemp and Palmer amaranth when applied postemergence in corn. Research results also show that the combination of dicamba with residual herbicides improves broadleaf weed control compared to residual herbicides alone.  The dicamba EXP formulation exhibits a wide-spectrum of broadleaf weed control similar to Clarity^® with the additional benefit of even lower volatility.  Dicamba will be an important component for integrated weed management systems that include herbicides with additional mechanisms of action, residual herbicides, and agronomic practices that favor early season weed control and crop competition.

New weed control options are needed to manage a growing weed resistance problem that is limiting control tactics and in some areas cropping options.  Glyphosate is an important herbicide in many cropping systems, but problematic weeds like Palmer amaranth (Amaranthus palmeri), waterhemp (Amaranthus tuberculatus), giant ragweed (Ambrosia trifida), and horseweed (Conyza canadensis) have been confirmed resistant to it in at least 24 states.  And many of these populations are also resistant to more than one herbicide mode of action.  Given the limited herbicide options in many cropping systems, these weeds present significant management problems for producers.  The dicamba tolerant cropping system will offer growers a new weed management option in cotton (Gossypium hirsutum) and soybean (Glycine max).  Dicamba complements the weed control spectrum of glyphosate and controls many broadleaf weeds that have been reported to be resistant to glyphosate.  However, proper implementation of the dicamba tolerant cropping system is required to ensure its long term sustainability.  As part of an integrated strategy, one should consider several stewardship tactics to address weed resistance management and on-target deposition.  Weed management programs should consider an integrated system using multiple herbicide modes of action, residual herbicides, effective rates and timings, and site monitoring as well as mechanical weed control when necessary.  Maximizing on-target deposition can be addressed with formulation and application techniques including nozzle selection, boom height, and spray pressure.  Environmental conditions such as wind and inversions also have significant influence on the level of on-target deposition and need to be considered before application.  The goal of such a stewardship program is to allow growers to maintain flexibility and control of their farming operation.  A training and education program can assist growers in achieving this goal.  An improved formulation, optimized application techniques, and integration of other effective weed control tactics like alternate modes of action, tillage, and crop rotation will ultimately provide the most sustainable production system.

Organic growers need additional tools for weed control. A new technique using abrasive grit propelled by compressed air was tested in field plots for corn in 2009 and 2010 and soybean in 2011. Grit derived from corn cobs was directed at seedlings of summer annual weeds growing at the bases of crop plants when the crop was at differing early stages of leaf development. Season-long, in-row, weed control exceeded 90% when two or three abrasion events were coupled with between-row cultivation. Timing of weed abrasion was critical, with highest levels of control corresponding to the 1- and 5-leaf stages or the 1-, 3-, and 5-leaf stages of corn development. Corn yields associated with these treatments were equivalent to those of hand-weeded controls in which no abrasive grit was applied. Thus, air-propelled abrasive grit applications at the 1-, 3-, and 5-leaf stages of corn controlled weeds sufficiently to prevent weed-induced reductions in corn grain. Additionally, these applications were not harmful to corn plants. For soybean, one application or two sequential applications of grit at any stage of development between emergence and the first trifoliate had no effect on soybean yield. However, three sequential grit applications at emergence, cotyledon, and unifoliate stages damaged soybean and reduced yield by 28%, but three similar sequential applications at cotyledon, unifoliate, and first trifoliate stages had no effect. Thus, young soybean plants are relatively unresponsive to damage by grit. This new concept for weed control may be of interest to growers who manage row crops of corn and soybean organically.

Mikania micrantha, known as “mile-a-minute”, “Chinese creeper”, or “American rope” is a perennial creeping vine in the Asteraceae capable of both rapid growth and rapid geographic spread through seed dispersal and vegetative propagation. It readily colonizes a wide variety of agricultural and natural habitats with high levels of fertility, organic matter, soil moisture and humidity. It can severely impact growth of other plants through shading and/or smothering. M. micrantha is native to Central and South America where it seldom causes economic or ecological problems. It reached Asia in about 1910 and subsequently it has been introduced throughout the Indo-Pacific region and has been identified as a serious problem in many countries, including India, Bangladesh, Sri Lanka, Mauritius, Nepal, Vietnam, Cambodia, Laos, Thailand, China, Myanmar, the Philippines, Malaysia, Indonesia, Australia, and Papua New Guinea, as well as a number of other Pacific Islands. In Nepal it covers large areas of Chitwan National Park, threatening endangered populations of one-horned rhinoceros and other rare species. Mile-a-minute is rapidly spreading in Yunnan Province, China, increasing the level of infestation of many cropland and natural areas on an annual basis. This rapid spread follows the same pattern seen in other Chinese provinces such as Guangdong Province. Out of this Chinese experience, expertise for managing this weed is growing, along with funding, although control via herbicides and/or mechanical means is costly and time consuming, and not always effective. Some alternative control measures such as biological control are also being explored. Perhaps the most hopeful sign is that governments throughout the region are starting to join forces in order to put together comprehensive strategies, share resources, and draw from international expertise in weed management. This presentation will particularly highlight the efforts of a team at the Yunnan Academy of Agricultural Sciences lead by Fudou Zhang, in coordination with experts in nearby countries such as Vietnam, Cambodia, Laos, Thailand, and Myanmar as well as experts from Japan, Australia, the U.S. and Canada.

*clements@twu.ca

Large and small crabgrass (Digitaria sanguinalis L. and Digitaria ischaemum (Schreb.) ex Muhl.., respectively) are problem weeds within turfgrass, particularly in the absence of synthetic herbicides.  Due to the increasing commonality of cosmetic pesticide bans, it is important to assess the recruitment biology and ecology of crabgrass species, as well as their response to cultural management techniques.  This project focuses on determining the emergence timing of natural populations of large and small crabgrass in turfgrass, as well as the effects of fertilization on their recruitment.  Controlled chamber experiments confirmed that KNO₃ increased the germination level of freshly harvested seed of both species in comparison to a water control.  The same effect did not occur with aged seed suggesting that KNO₃  affects seed dormancy and not germination per se.  Experiments under controlled conditions with a model turfgrass system showed similar results where recruitment levels increased with increasing fertilizer rate for both species although there was greater variation for large crabgrass dependent upon turfgrass type.  However, under outdoor conditions the effects of fertilization on recruitment were not significant.  Disturbance (raking) also had no effect on crabgrass recruitment. The results of this study suggest that typical home owner turf management (raking and fertilizer application) will not necessarily have a direct impact on crabgrass recruitment.  Crabgrass emerged later than the typical establishment period of cool season turfgrass.  This suggests that while turf vigour may affect the survival of crabgrass throughout the season through competition, it does not control the initial recruitment of crabgrass to an acceptable level.

Eriochloa villosa (Thunb.) Kunth is an annual C₄ grass of East Asian origin that is now present in North America, particularly in the U.S. Corn Belt. The species was discovered in Canada for the first time in 2001 in southern Québec. New populations have been found every year since 2007 and the species became a nationally regulated and quarantined weed in 2011. In order to evaluate the species potential weediness in Canada, the emergence pattern and fitness of a population was evaluated in unmanaged as well as alfalfa and clover plots. Moreover, the phenology of plants from one Canadian population (near Bedford, 45° 07' N, 72° 59' W Quebec) was compared to that of plants originating from north-eastern China (near Nenjiang, 49° 13' N, 125° 14' E Heilongjiang) in a greenhouse study. In Canada (Bedford), in 2009, 2010 and 2011, woolly cupgrass started to emerge early (between April 29 and May 5) and continued to do so during a 42 (2011) to 76 (2010) day period. In the forage plots, per area seed inputs from woolly cupgrass increased every year, despite the control of the initial spring cohort in 2009 (using a grass herbicide: sethoxydim) and standard crop mowing. In the greenhouse, the Chinese population started booting 23 days before the Canadian population. Woolly cupgrass shows no signs of limited fitness in Canada and could potentially adapt to more northern latitudes.

The native range of Taeniatherum caput-medusae includes much of Eurasia, where three distinct subspecies have been recognized, but only T. caput medusae ssp. asperum (hereafter referred to as medusahead) is believed to occur in the United States (U.S.). Medusahead, a primarily self-pollinating annual grass, was introduced into western U.S. in the late 1800s. The results of an earlier allozyme analysis were consistent with the genetic signature associated with multiple introductions, although this finding can only be confirmed with the analysis of native populations. In the current study we compared allozyme diversity in native and invasive populations of medusahead to: identify the geographic origin(s) for the U.S. invasion, test the multiple introduction hypothesis, and determine the genetic consequences of these events. Five of the seven homozygous multilocus genotypes previously observed in the western U.S. have been detected in native populations.  The geographic origins for these introductions appear to have been drawn from France, Sardinia, Greece and Turkey, although additional analyses are ongoing. These findings provide support for the multiple introduction hypothesis. Across native populations, 17 of 23 loci were polymorphic and a total of 48 alleles were detected, while only five polymorphic loci and 28 alleles were found among invasive populations. On average, invasive populations possess reduced within-population genetic diversity, compared with those from the native range. While U.S. populations have experienced founder effects, 38% (17 of 45) these populations appear to be genetic admixtures (consisting of two or more native genotypes). Results of this study have implications for the biological control of medusahead: i) the search for effective and specific biological control agents will have to occur broadly across the species’ native range, ii) multiple agents may be required to control invasive populations that are admixtures, and iii) because invasive population are genetically depauperate, highly adapted biocontrol agents are likely to be quite effective.

Email:  snovak@boisestate.edu

Prickly lettuce is a troublesome broadleaf weed that conversely has potentially useful characteristics. Prickly lettuce contains high molecular weight polyisoprene that could be used as an alternative source of natural rubber. To better understand prickly lettuce biology, two distinct eastern Washington biotypes (P1 6-9/13, P2 4-10/6) were crossed to generate an F2 segregating population. In 2010 a field plot of 248 F2 plants was planted in Pullman, WA. Phenotypic characteristics including leaf area, leaf perimeter, latex components and quality, bolt number, and growth habit were collected. Too phenotype leaf differences, four fully expanded leaves from each plant were collected and scanned on a flatbed scanner. Leaf area and perimeter were calculated using ImageJ. Leaves were also scored as lobed or non-lobed. The lobed phenotype is dominant and appears to be controlled by a single gene (3:1 ratio). Leaf area and perimeter had a normal distribution indicating multiple interacting genes control these traits. For latex component analysis, latex was tapped from stems of each F2 plant into a tared tube. Tapped latex was dried under vacuum for 48 hrs. at 35ºC and solvent extracted to yield percent latex components by weight. The average F2 latex components consisted of water (58.0%), insolubles (26.6%), acetone soluble resin (14.2%), and Hex/THF soluble rubber material (4.9%). Extractable rubber material ranged from 2.2% to 12.3% by weight in the population. The rubber fraction was further analyzed by gel permeation chromatography (GPC) HPLC, with refractive index detector to evaluate rubber (polyisoprene) polymer chain length. GPC software was used in conjunction with polystyrene standards to give an estimation of weighted average molecular weight (Mw). Average Mw was 9.2x10⁵ g/mol and ranged from 1.4x10³ to 2.9x10⁶ g/mol. Polyisoprene molecular weight had a normal distribution that was heavily weighted toward low molecular weight polymers. The number of bolts was counted on each plant to reveal a normal distribution suggesting bolt number is a quantitative trait. Growth habit varied between parents with P1 having a more erect bolting pattern with a single dominate bolt and P2 a prostrate bolt growth pattern. Growth habit was scored 1-5, 1 resembling P1 and 5, P2. Growth habit also had a normal distribution over the population. To understand the genetic control of these traits, 460 EST-SSRs have been mined from the Compositae Genome Project database. All mined markers were screened on the crossed parents and 150 polymorphic markers have been selected to generate a genetic map. Phenotypic and genetic information will reveal markers that are linked to prickly lettuce traits of interest, allowing for future screening and selection of these traits.

Red rice in southern U.S. rice fields remains a widespread, economically challenging problem despite nearly a decade of rice production systems that include true-breeding rice cultivars and indica-derived hybrid rice with resistance to imazethapyr.  Both of these herbicide-resistant rice systems have provided good control of red rice, but outcrossing between red rice and rice, which has been investigated previously, has reduced the effectiveness of these approaches in some instances.  True-breeding indica rice lines and cultivars are being used increasingly as a source of high yield and pest tolerance in U.S. rice breeding programs as well as in low-input production systems, however their levels of outcrossing with red rice have not been investigated.  Thus, the objectives of this study were to determine the rates of red rice outcrossing with four indica cultivars from China in comparison to a tropical japonica, southern US long grain, commercial standard.  The red rice type and rice cultivars were selected based on previous field trials in which the red rice exhibited significant overlap in flowering dates with the rice cultivars.  Indicas were Teqing, Rondo, 4484, and 4593 (PI 536047, PI 657830, PI 615022, PI 615031, respectively).  Kaybonnet served as the tropical japonica standard.  Outcrossing plots, consisting of drill strips of a single row of red rice (TX4, awned blackhull type; PI 653424) flanked by four rows of the rice cultivar on each side, were established at Stuttgart, AR in 2008 and 2009.  Subsamples of seed collected from panicles of these rice and red rice plants were planted subsequently in observation field plots for screening purposes in 2009 and 2010, respectively.   Putative F₁ hybrid plants were identified based on expected phenotypic traits.  Green leaves of these putative hybrids were sampled and extracted for DNA.  True F₁ hybrids were confirmed to be heterozygous at five selected loci using genetic markers (Rid12, RM5, RM232, RM234, and RM253).  Outcrossing rates were calculated as:  100 x (number of true F₁ hybrids in screening plot) / (number of seedlings in screening plot).  With rice serving as the female, all indicas had similar outcrossing rates, which averaged 0.0088%.  Among all cultivars, outcrossing was greatest for Kaybonnet (0.0326%).  The greater outcrossing rate for Kaybonnet appeared to be due in part to its close synchronization in flowering with red rice.  Outcrossing rates were positively correlated with flowering synchronization among all rice entries.  With red rice as female, outcrossing with indicas was usually undetectable.  This follows the trend typically observed for tropical japonica cultivars in similar tests, that outcrossing rates are substantially lower with red rice as female than with rice as female.  These studies show that late maturing indica cultivars have outcrossing rates similar to or less than that of the tropical japonica cultivar Kaybonnet, and that flowering synchronization can play an important role in determining outcrossing rates between red rice and rice. (email address: david.gealy@ars.usda.gov)         

Values of weeds will be discussed in this review paper. Apart from being notorious to native biodiversity, invasive plants and weeds may have positive roles in distinct ways such as its use as compost and plant-based fertilizer; its relationship with arthropod in maintaining diversity within agroecosystems; its medicinal uses; its potential to provide food source for the growing world’s population; and its genetic diversity as source for coping with environmental fluctuations. Many weeds are relatives of crop lines, it is essential to preserve such unique genetic sources in its wild relatives for coping with future climatic variations. For instance, previous research has shown that wild (red) rice responds to elevated CO₂ more than crop rice in terms of seed yield (Ziska & McClung 2008), therefore providing an opportunity of increasing seed yield under other environmental conditions different from the current. Some weeds e.g. Canadian thistle (Cirsium arvense) are under genetic and population research to understand mechanisms of their adaptation strategies.

Japanese stiltgrass (Microstegium vimineum) is a shade-tolerant annual C₄ grass that is invasive in eastern North American hardwood forests where it can negatively impact native species diversity. The most common treatment for Japanese stiltgrass management is 2% glyphosate applied in a spray to wet application, which often has negative non-target impacts. However, in the understory environment where Japanese stiltgrass thrives, it is nearly impossible to eradicate.  Additionally, little information exists on the long-term efficacy, cost, and non-target effects of large-scale Japanese stiltgrass eradication efforts.  The objective of this work is to compare the cost, efficacy, and non-target impacts of long-term Japanese stiltgrass management options.

A study was initiated in Newport, Virginia August 16, 2011.  The experiment is a split-plot design with four replicates to assess the efficacy of one application per season compared to multiple “as-needed” applications in the same season.  Spot treatments included 2% glyphosate (GlyPro), reduced rate glyphosate (0.045kg ai ha^-1), 1.5% sethoxydim (Poast), a preemergence treatment of pendimethalin (Pendulum Aquacap), and selective mechanical removal with a string trimmer. Due to fall initiation in the first year, pendimathalin preemergence treatments were not applied (they will begin spring 2012), and will not be discussed here.

To examine non-target species effects, we collected plant community data before and after treatment application.  To assess economic costs for each treatment we recorded fuel, herbicide, and labor costs.  Herbicide costs was based on the current market price for each product. Fuel costs were calculated at $3.26 gallon^-1 and labor was assessed at $75 hr^-1.Initial Japanese stiltgrass cover averaged 51% (±18.6%).  Sethoxydim, 2% glyphosate, and reduced rate glyphosate controlled Japanese stiltgrass 98 to 100% with a single application. All treatments except sethoxydim reduced tree seedling cover 14-27%, while shrub cover was minimally affected (< 14%), and forb cover was most affected by 2% glyphosate which reduced cover by 32%.  Low rate glyphosate by comparison only reduced forb cover by 10%.  Overall, non-target species effects were greatest for 2% glyphosate applications and lowest in sethoxydim plots with 32% and 4% total cover reductions, respectively.

Labor was >95% of total cost for all treatments, and herbicide costs were not significantly different from one another (P > 0.05).  Single season herbicide treatments including labor costs averaged $258 ha^-1 and multiple as-needed treatment programs averaged $357 ha^-1.  Due to increased time requirements for proper application the mechanical treatment averaged $661 ha^-1, significantly more than all targeted herbicide treatments. Mechanical treatments are not feasible in this environment, are cost prohibitive, and cause tremendous non-target impacts.  One-time applications of glyphosate or sethoxydim controlled Japanese stiltgrass in a single season and had minimal non-target effects.

            Most experienced organic farmers consider weeds to be the worst pest problem they face. This problem can be exacerbated by fertility management that does not take weed ecology into account. Increased weed growth and competition has been observed in response to many inorganic fertilizers. The purpose of this research project has been to partition out the effects on weeds and crops of nitrogen (N), phosphorous (P), and potassium (K) from organic nutrient amendments. The long-term goal of this project is to contribute to integrated weed and fertility management by providing growers with information that will help them supply crops with necessary nutrients while minimizing weed pressure.

            Field and greenhouse experiments were carried out over two years, using blood meal for an organic source of N, bone char for P, and potassium sulfate for K.  Bone char did not supply plant-available phosphorous in either site year, at either high pH (7.7) or low pH (5.5) limed up to pH 6.0.  Three crops were studied: field corn (Zea mays), lettuce (Lactuca sativa cultivar ‘New Red Fire’), and kale (Brassica oleracea cultivar ‘Lacinato’).  Four weeds were studied: Powell amaranth or pigweed (Amaranthus powellii), common lambsquarters (Chenopodium album), giant foxtail (Setaria faberi), and velvetleaf (Abutilon theophrasti). 

            One of the main conclusions of this project is that certain weed species, Powell amaranth in particular, benefit from high compost amendments much more than certain crops, particularly field corn.  Lettuce may benefit somewhat from high compost amendment levels, but good weed management would be crucial to maintain that benefit.  The only species which responded to increasing organic N amendment (as blood meal) was velvetleaf.  For all other species that strongly responded to increasing compost amendment, that response was not explained by N or K. 

Invasive species are novel to a region, thus their timely and accurate identification is a critical first step in recognizing and managing the threats that they may present in their new habitats.  Accurate identification of an introduced species in its new range can prove difficult however for a species that displays taxonomic complexity in its native range, i.e. consists of multiple, morphologically similar subspecies. 

Across its native range, Taeniatherum caput-medusae (medusahead) exhibits taxonomic complexity. Three subspecies have been recognized: T. caput-medusae ssp. caput-medusae, T. caput-medusae ssp. asperum, and T. caput-medusae ssp. crinitum. While subspecies caput-medusae is found in the western Mediterranean and subspecies crinitum occurs from eastern Europe to Central Asia, subspecies asperum is distributed across the geographic distribution of the species. Only subspecies asperum is believe to occur in the United States, where it is now invasive in portions of California, Idaho, Nevada, Oregon, Utah and Washington. As part of our ongoing research to better understand and manage this invasion, we are conducting genetic analyses of both native and invasive populations of medusahead.  An important prerequisite to these analyses is the proper identification of the three subspecies.  In the current study, plants from each native population were grown in a greenhouse common garden, harvested at maturity, and measured using previously described morphological characters.  After Bonferroni correction, three characters, glume length, glume angle and palea length, were found to be statistically significant.  Thus, these three characters were quite useful in assigning plants to each of the three subspecies.  We found that two other characters, lemma hairs and conical cells, were less informative.  Differentiation among native populations of medusahead was further assessed using a molecular genetic marker. The results of a UPGMA cluster diagram based on allozyme data, indicates that subspecies crinitum is genetically differentiated from the other two, some populations of subspecies caput-medusae and asperum co-occur within different clusters, and subspecies asperum is the most variable. Results of the analysis of multilocus genotypes are generally consistent with the UPGMA diagram (e.g., subspecies caput-medusae and asperum share six multilocus genotypes).

Our findings confirm the need of such studies to disentangle the taxonomic complexity that can be found in the native range of invasive species.

Email: snovak@boisestate.edu

Evidence from small-scale experimental investigations suggests that species diversity and introduced species success are negatively correlated and that resident species identity can determine the strength of this interaction.  In this study, we assess the applicability of the diversity-invasion hypothesis to restoration.  We hypothesize that, following management efforts, richness of restored plots will be a determinant of invasive species re-establishment and, furthermore, that some restored species and species combinations will be more effective than others.  Attempts are also made to apply the overlapping-resource-use hypothesis to explain our findings.  We employed a two-way factorial experiment in a randomized complete block design where richness and native species composition were manipulated in 1 x 1 m plots.  Richness levels include 1, 2, 3, and 4 species.  At richness levels 2 and 3, all possible species combinations were established.  This resulted in 20 treatment combinations per block and each block was replicated four times.  Restored species were plug planted in January 2010 following removal of the target invasive (Bothiochloa ischaemum or KR Bluestem; hereafter referred to as KR) using a prescribed burn in fall 2009.  Restored species were native, perennial grasses available commercially and widely used in restoration projects in Central Texas.  They include: big bluestem (Andropogon gerardii), indian grass (Sorghastrum nutans), sideoats grama (Bouteloua curtipendula), and little bluestem (Schizachyrium scoparium).  Response variables measured to date include cover of KR, resident, and restored species; ellipsoid area of all individuals of restored species; KR and restored species phenologies; and soil available nutrients (KCl extractions). Restored species established at an overall rate of 60%.  Nonetheless, rates of establishment varied greatly among species.  Re-establishment of KR was found to be a negative function of restored species cover and establishment success as well as the average and total restored species ellipsoid plug area.  We also found significant differences among species as determinants of KR re-establishment; however, this effect was confounded by species identity.  We found no significant relationship between assigned or actual richness and KR re-establishment.  KR establishment was negatively correlated with plot over-yielding, suggesting that species combinations that perform better than the highest performing species grown in monoculture were effective in invasion control.  We aim to utilize this study to inform local land management efforts in restoration regarding the suppressive effects of native species combinations.   

Our objective was to determine the impact of integrating a biological control agent (Hadroplontus litura Fabricius, a stem-mining weevil) and a native annual cover crop (Helianthus annuus L., common sunflower) on Canada thistle height, basal stem diameter, reproductive output, leaf number, side shoot number, final root biomass, and shoot biomass. Previous research has found that H. litura acting alone is a mildly effective control agent; however integrating multiple control tactics may provide enhanced control of Canada thistle. During the summers of 2010 and 2011, outdoor microcosms (19-L containers of field soil) were established with full factorial combinations of weevil and cover presence/absence and high vs. low soil nutrient levels. Thistle morphological characteristics were measured weekly and final above and below ground biomass was harvested at the end of the growing season. During the first third of the sampling period during both years, no treatments affected thistle morphological characteristics. In 2010, cover presence was associated with reduced thistle height and basal stem diameter. Weevil presence was associated with reduced thistle height and basal stem diameter, however this effect was transient. Weevil presence, cover presence, and low soil nutrients reduced overall leaf number and reproductive output. Cover presence and low soil nutrients reduced side shoot production. Cover presence reduced both final root and shoot biomass. Increased soil nutrients increased final shoot, but not root, biomass. In 2011, weevil presence was associated with reduced thistle height and this effect was persistent throughout the growing season. Cover presence reduced overall thistle height and leaf number, but only in low soil nutrient environments. High soil nutrients were associated with greater thistle height and leaf number regardless of cover. Cover presence and low soil nutrients reduced overall reproductive output, shoot production, and basal stem diameter.  Cover presence was associated with reduced final shoot biomass in high soil nutrient treatments. Increased soil nutrients were associated with greater final shoot biomass compared to the low soil nutrient treatment, regardless of cover presence or absence. Cover presence and low soil nutrients reduced final root biomass. Inconsistencies between 2010 and 2011 could be due to environmental differences, such as colder early season temperatures in 2011. In general, weevil effects on thistle morphology were transient, whereas the effects of soil nutrition and cover were more persistent throughout the duration of the experiment. Research results also suggest that effects of weevils and cover were additive rather than synergistic, but that integrating plant competition with biological control could provide enhanced Canada thistle control.     

Along with downy brome and giant reed, Taeniatherum caput-medusae ssp. asperum

(Poaceae), medusahead, is considered one of the worst invasive grasses in North

America. Medusahead is widely distributed across Eurasia, and was first collected in

the United States (U.S.) in Roseburg, OR, in 1887. It has now invaded millions of

hectares of semi-arid rangeland in the western U.S. Many management strategies

have been investigated over the last three decades without achieving substantial

success, and the species is still expanding its range in the western U.S. Land

managers, stakeholders and researchers still hope to find a way to slow down the

spread of this species at local and regional scales; biological control thus appears to

be the last option. Starting in 2001, field surveys were conducted across Eurasia to

identify and observe native natural enemies of medusahead. Preliminary impact

studies with plant pathogens were conducted in Turkey in 2003 and were initially

encouraging, but subsequent studies in the U.S. indicate that these pathogens are

not appropriate biocontrol agents. Financially supported by the Bureau of Land

Management, additional surveys in the native range were initiated in 2011/12, and

squamosus (Col.: Curculionidae) and Dicraeus sp. (Dipt.: Chloropidae). A preliminary

experiment was set up in Turkey in 2011 to examine the feeding impact of the Dicraeus

fly in a no-choice test with medusahead and barley. In 2012/13, additional 

 funding was obtained for determining the host specificity of new pathogenic strains of

plant species consisting of crop plants and North American natives will be inoculated

and evaluated. This study is currently underway in Greece. In addition, data obtained

from our ongoing phylogeographic study of medusahead using allozymes has

identified an area in northeastern Greece, plus bordering territories in Turkey, which

contain populations that match genotypes previously detected in the western U.S.

This region may have served as the geographic origin for the invasion of

medusahead in the Great Basin.

By combining genetic studies with biocontrol surveying and testing we hope to

determine, in a 2-year time frame, whether control of medusahead with natural

enemies at a local and regional scale is feasible and should be pursued further.

Biocontrol may be the last option open to land managers and stakeholders for

reducing the ecological and economic impacts of medusahead within western U.S.

rangelands.

the smut fungi Ustilago phrygica, collected from Spain and Kazakhstan. More than 30

two insect species were found feeding on medusahead: Pachytychius hordei

The Agricultural Research Service of the United States Department of Agriculture

has maintained a long term effort in classical biological control of exotic Eurasian

insect pests and weeds invasive in the U.S. The overall goal of research at EBCL is

to develop biological control technologies, which can be used to suppress invading

weeds and insect pests. This is done through exploration to find natural enemies

(phytophagous, parasitoid or predator species of insects and mites, and pathogens).

These are characterized by careful experimentation in quarantine facilities and

eventually developed as biological control agents. Besides insect projects, a number

of weed targets invasive in the western United States are studied. Three grasses are

Taeniatherum caput-medusae (medusahead). Against giant reed, 4 insect

candidates collected from Eurasia were intensively studied due to their severe impact

on young shoots of giant reed. Over the last 2 years, two species of wasp and scale

insect were released in Texas and have reduced giant reed shoots by 92% in

laboratory conditions, and two additional species are still under evaluation.

Guineagrass invades the Southern U.S. states, including California. Exploration in

West Africa led to ca. 80 insect species collected from Guineagrass. The selection of

potential candidates is still ongoing. Starting in 2001, field surveys were conducted

across Eurasia to identify and observe native natural enemies of medusahead.

Several smut fungi and insects were identified and are being evaluated in open field

tests. The results will be presented in detail. At the EBCL station in Greece, several

Colletotrichum gloeosporioides, Canada thistle (Cirsium arvense) with field testing of

Puccinia punctiformis, and silverleaf nightshade (Solanum elaeagnifolium). All above

programs are combined with genetic studies that help to understand insect/plant

genetics has helped to identify insects that cannot be distinguished by morphological

characters. Preliminary results showed the evidence of distinct genetic lineages

thistle. In addition to classical biocontrol studies, EBCL conducts ecological tests to

understand feeding behavior, flight activity, and host preference using plant models

such as tamarisk and swallow-worts, to improve the knowledge of bio-ecology of

candidate insect agents.

The use of natural enemies to control non-native pests can be an effective tool in managing invasive plants. In recent times, major invasive plant species on Guam were identified (Reddy 2011). The best option for managing these plant species may require more work on the possibility of using biological control agents. A biological control program on Coccinia grandis has been effective in Guam and Saipan following the success achieved in Hawaii by introducing the natural enemies Melittia oedipus (Lepidoptera: Sesiidae), Acythopeus burkhartorum (Coleoptera: Curculionidae) and Acythopeus cocciniae (Coleoptera: Curculionidae). Similarly, control of Chromolaena odorata was achieved using the Pareuchaetes pseudoinsulata (Lepidoptera: Arctiidae) and Cecidochares connexa (Diptera: Tephritidae) in Micronesia. At this moment biological control programs are started for the control of Mikania micrantha and Mimosa diplotricha on Guam. If successful, these programs will be extended to other neighboring islands.

Impact of soil pH on Bahiagrass:Smutgrass Competition. N. Rana¹, B. A. Sellers¹, J. A. Ferrell² and G. E. MacDonald², ¹University of Florida Range Cattle REC, Ona, FL; University of Florida, Gainesville², FL.

Smutgrass (Sporobolus sp.) is an invasive perennial bunch-type grass native to tropical Asia. The two varieties of smutgrass found in Florida are small smutgrass (Sporobolus indicus var. indicus) and giant smutgrass (Sporobolus indicus var. pyramidalis). Forage losses due to lack of smutgrass control is a major problem in bahiagrass (Paspalum notatun) pastures. Information on pH affecting bahiagrass-smutgrass competitive interactions might aid in developing improved weed management programs for smutgrass control in bahiagrass pastures. Replacement series experiments were conducted in a controlled environment in 2010 and 2011 to compare the competitive ability of bahiagrass with each of the two varieties of smutgrass at three levels of soil pH (4.5, 5.5 and 6.5), two densities; 4 (low) and 8 (high) plants pot^–1, and at five planting ratios of 100:0, 75:25, 50:50, 25:75, and 0:100. Bahiagrass and each smutgrass variety was planted at ratios of 4:0, 3:1, 2:2, 1:3 and 4:0 for 4 plants pot^–1, and planting ratios of 8:0, 6:2, 4:4, 2:6 and 0:8 for 8 plants pot^–1 at the three levels of soil pH. The experiment was a completely randomized design with three replications. Relative competitive ability and aggressivity of giant smutgrass were higher than bahiagrass across all pH levels and densities, whereas relative competitive ability and aggressivity of bahiagrass was greater than small smutgrass in all pH levels and densities, except at pH 6.5. At pH 5.5 and pH 6.5, biomass accumulation of giant smutgrass was at least 73 and 67%, respectively, higher than bahiagrass at both density levels, at the 50:50 planting ratio. Giant smutgrass biomass was not different from bahiagrass at pH 4.5. In general, small smutgrass responded differently than giant smutgrass. At pH 4.5, small smutgrass biomass was 80% lower than bahiagrass at the low density level and 50:50 planting ratio. At pH 5.5, small smutgrass biomass was at least 46% lower than bahiagrass at both density levels at the 50:50 planting ratio. At pH 6.5, small smutgrass was 42% higher than bahiagrass at low density level at the 50:50 planting ratio. Small smutgrass biomass was not different than bahiagrass at the high density levels of pH 4.5 and 6.5.  The results obtained from this study indicate the differential response of soil pH on bahiagrass competitive ability with small and giant smutgrass. Amending soil pH is not a likely option to increase the growth and competitive ability of bahiagrass over giant smutgrass. However, for small smutgrass, it is likely to increase the aggressivity of bahiagrass in bahiagrass vs. small smutgrass mixture, unless the soil pH is raised above 5.5. 

Strip tillage (ST) offers many potential benefits to vegetable growers, especially those in cooler climates.  However, weed management in ST systems remains a challenge and a better understanding is needed of how various factors that differ in ST compared to full-width conventional tillage (CT) affect weed dynamics.  This research seeks to understand how Powell amaranth (Amaranthus powellii) emergence varies in ST cabbage (Brassica oleracea var. capitata) with and without cover crops.  Fully-factorial field trials were established in 2010 and 2011 with tillage (ST vs. CT), cover crop (oat (Avena sativa) or none) and crop competition (cabbage or no cabbage).  To measure emergence, quadrats of Powell amaranth seeds were established both in the crop row (IR) and between rows (BR) immediately following tillage and again 9-13 days after tillage (DAT) at the time of cabbage transplanting; only BR data is presented here.  In an attempt to elucidate the mechanisms responsible for tillage and cover crop effects on weed emergence, we added the following treated microplots within each main plot in 2011:  two rates of additional N, two moisture levels (supplemental irrigation or plastic tent exclosures), and fungicide-coated seeds.  Emerged seedlings were counted and pulled daily.  Soil temperature and moisture were assessed in both years.  Powell amaranth emergence was affected by tillage, cover crop, and their interaction; emergence at 9-13 DAT was also affected by crop.  Emergence of Powell amaranth was suppressed by 80-92% in ST-oats when seeds were sown 0 DAT.  However, when seeds were sown 9-13 DAT, plots with oats had either equivalent or higher emergence relative to those without oats: without cabbage, ST-oats had the highest emergence but when cabbage was present, emergence in both ST-oats and CT-oats was higher than those without oats.  In 2011, fungicide and water addition treatments had significant interactive effects on Powell amaranth emergence, but N additions did not.  For seeds sown in oat treatments 0 DAT, fungicide coating resulted in 48% higher emergence than uncoated seeds.  Interestingly, fungicide had no effect on seeds sown 13 DAT, suggesting that fungi play an important but fleeting role in oat-mediated suppression of Powell amaranth emergence.  Soil moisture was low in all plots (averaged 5% gravimetric soil moisture) from 0-12 DAT in 2011, but was significantly higher in the ST oat plots compared to the others (including the CT oat plot).  Adding water to plots with oats (both ST and CT) did not affect emergence.  When water was added to plots without oats sown 0 DAT, BR emergence was double that in the unirrigated plots, suggesting that water was limiting in the latter.  At 13 DAT, water did not play a significant role in determining emergence; soil moisture during this time did not differ between treatments and was also higher than during the first trial (average 12.7% gravimetric soil moisture).  In sum, our results suggest that 1) weed emergence is influenced by tillage, cover crops and their interactions; 2) the impact of cover crop surface residue in ST systems on weed emergence can shift from suppression to stimulation over a relatively short period of time; 3) weed suppressive effects of cover crop mulch under ST may be explained in part by promotion of fungal pathogens which reduce weed emergence; and 4) stimulatory effects of surface mulch on weed emergence may be explained in part by their capacity to conserve soil moisture in dry conditions.

Pyroxasulfone is a selective soil applied herbicide under development for residual control of grass and small seeded broadleaf weeds. Kumiai Chemical Industry Co., Ltd. and Ihara Chemical Industry Co., Ltd. have granted BASF the exclusive right to develop and commercialize solo herbicide products with pyroxasulfone for corn, soybeans, wheat and sunflower in the United States and Canada.

A series of experiments were conducted  in 2010 and 2011 to evaluate the performance of pyroxasulfone as a component of weed control systems in corn and soybean.  Pyroxasulfone was evaluated at a rate range of 119 – 179 g ai/ha and at various application timings including preplant, preemergence and early postemergence.   Studies indicate that pyroxasulfone will provide an effective solution for many problematic weeds including Setaria spp. and glyphosate-resistant Amaranthus spp.  Negligible corn and soybean injury has been observed from pyroxasulfone, regardless of application timing. Field trials indicate pyroxasulfone can provide a flexible weed management tool that consistently controls numerous grasses and small-seeded broadleaf weeds.

Biochar, a carbon rich product formed by the incomplete combustion of biomass, has the ability to increase crop yields but has yet to be used in prairie restoration. A replacement series experiment was conducted under greenhouse conditions to evaluate the effect of biochar on competition between a native perennial grass, Androgopon gerardii (big bluestem), and a non-native herbaceous perennial, Lespedeza cuneata (sericea). Main treatments were biochar rates (0 and 20 t/ha), nitrogen rates (0 and 10 g/m²) and the following big bluestem to sericea ratios: 6:0, 4:2, 3:3, 2:4 and 0:6. The effect of biochar on soil characteristics was also evaluated. After 180 days, big bluestem height and biomass were significantly greater in biochar amended soils than in unamended soils. However, sericea height and biomass were unaffected by biochar amendments and the addition of biochar did not alter competitive outcomes. Competition between big bluestem and sericea was asymmetrical; sericea reduced the growth of big bluestem but big bluestem had relatively little effect on the growth of sericea. The addition of biochar increased percent organic matter by 30%, cation exchange capacity by 8% and available potassium, phosphorus, magnesium and calcium were increased by 147%, 31%, 35%, and 4%, respectively. This research suggests that although biochar did not alter competitive outcomes between the native and invasive species, it could be used to increase big bluestem growth and improve soil nutrient availability during the first year, which is a critical period in prairie restoration.

Scientific Advances Improve Stewardship Practices and Methods Used in Environmental Assessments of Herbicides Janis McFarland, Paul Hendley, JiSu Bang and Ron Williams, Syngenta Crop Protection LLC. 

Technology advancements in high resolution soil mapping, geospatial analyses and modeling have improved assessments of the environmental fate of herbicides. Increased data access in combination with new technology allows modeling of rainfall, land use (cropping), soil characteristics and slope, application timing, crop growth rates and vulnerability for agrochemical, sediment or nutrient transport via surface water runoff and soil erosion at the watershed and field scale.  LIDAR (Light Detecting and Ranging) data can also provide quantitative metrics on topography, hydrology and natural vegetation at the field level.  High resolution aerial photography combined with LIDAR data enable the identification of engineered features at the field level including terracing, overhead irrigation and intakes for tile drainage systems. Proximity analyses on distances between fields, streams, and other types of habitat can be used to refine potential exposure estimates for endangered species via runoff or drift.  These new approaches for comprehensive environmental characterization at the field scale level provide a novel tool for improving watershed management, conservation planning and to determine priority areas for implementation of best management practices and stewardship.

Field studies were conducted to examine the dissipation of fomesafen for bare‑soil compared to soil under low density polyethylene (LDPE) mulch in field studies while laboratory experiments evaluated dissipation over time at 10 and 30 C.  Studies indicated that fomesafen dissipation was more rapid for bare-soil than soil under LDPE mulch.  T_1/2 for fomesafen at 30 C was 120 d, in contrast to 10 C at 220 d.  Data from these experiments indicate that fomesafen dissipation can be extended at colder soil temperatures and when covered with LDPE.  A bioassay was also conducted infield where fomesafen was applied either to bare soil or under LDPE mulch.  After the spring crop was removed, a fall cabbage crop was planted and there was significant fomesafen carryover for the soil under the LDPE mulch, but little to no injury for the bare soil applications.  These data indicate that fomesafen applied to soil under LDPE could carryover in vegetable rotations.

Distribution coefficient (K_d) values had been estimated for decades to study pesticide adsorption. K_d values must be calculated prior to pesticide registration and are extensively used to understand environmental processes and biological activity. However, the accurate comparison of adsorption results published by the scientific community remains unattainable as K_d values are potentially affected by the methodology used. The objective of this research was to investigate 1) the use of reference compounds (minimum and maximum K_d values) during the determination of pesticide adsorption with different soil to solution ratios, 2) the impact of calcium chloride (CaCl₂) on adsorption values measured using mass spectrometry, and 3) the potential for comparing adsorption of multiple compounds across methodologies. Ten soils, five herbicides (2,4-D, atrazine, clomazone, S-metolachlor and saflufenacil) and three soil to solution ratios (1:3, 1:5 and 1:10) were selected to conduct the study. Samples of each soil were weighed (1 g) and were placed in a round bottom centrifuge tube. Estimated field application rates of the herbicides in µg g soil^-1 were added into the samples with the aqueous aliquot. Herbicides were equilibrated with soil samples for a period of 24 hours in a side-to-side shaker (125 cycles min^-1) at room temperature (24.5 C ±0.5). Ultrapure water without CaCl₂ was used to perform the batch equilibrium. Furthermore, aqueous solution containing 0.01 M of CaCl₂ was used to perform an additional comparison study for all soils using the 1:5 soil to solution ratio. Methodology was developed allowing the quantification and estimation of adsorption coefficients for all five herbicides in a single sample. The analyses were performed using a Waters ACQUITY^® TQD integrating an ultra performance liquid chromatography (UPLC) with tandem quadrupole mass spectrometry detection (MS/MS). Results from this study indicated that 0.01 M of CaCl₂ affected adsorption results of saflufenacil, 2,4-D, clomazone and S-metolachlor. Atrazine adsorption was not altered in any of the soil samples by adding the CaCl₂ salt. Effects of soil to solution ratios were particularly noticeable for soil with higher organic carbon content. The use of reference compounds during the estimation of K_d values allowed for calculation of a conceptual adsorption window (AW). Furthermore, AW was used to calculate the adsorption relativity coefficient (ARC), which indicated the relative K_d value of a particular compound within the AW range. For most of soils with AW > 1.0 mL g^-1, the ARC corrected for the variation of individual K_d values encountered at the different soil to solution ratio used in the batch equilibrium.

Leaching of indaziflam in Florida citrus soils collected from different horizons. Amit J. Jhala*, Analiza H. M.
Ramirez and Megh Singh; Citrus Research and Education Center, IFAS, University of Florida, 700 Experiment Station Road, Lake Alfred, FL 33850-2299. *Corresponding author’s E-mail: amit@ufl.edu

Abstract

Groundwater contamination with soil-applied herbicides such as bromacil has been reported in citrus growing areas in Florida. Indaziflam {N-[(1R,2S)-2,3-dihydro-2,6-dimethyl-1H-inden-1-yl]-6-[(1RS)-1fluoroethyl]-1,3,5-triazine-2,4-diamine} is a new pre-emergence herbicide recently registered for broad spectrum weed control in several perennial crops including citrus. There is no information available on leaching behavior of indaziflam (Alion) in sandy soil. Experiments were conducted to evaluate leaching of indaziflam applied at 73 and 145 g ai ha^-1 in Florida Candler soil under simulated rainfall of 5, 10, and 15 cm ha^-1. Herbicide movement down the soil columns was measured by evaluating visible injury and biomass of a bioassay species ryegrass (Lolium perenne L.) seeded into the soil columns split longitudinally. The results suggested that indaziflam leached the least (12.6 ± 0.6 cm) when applied at 73 g ai ha^-1 under 5 cm ha^-1 rainfall and maximum leaching was observed (30.2 ± 0.9 cm) when applied at 145 g ai ha^-1 under 15 cm ha^-1 rainfall. The visual injury symptoms of ryegrass was 87% and 97% at 10 and 15 cm ha^-1 rainfall, respectively when indaziflam applied at 145 g ai ha^-1 in the 0 to 30 cm horizon indicating the maximum movement and activity of indaziflam in this horizon. There was no mortality of ryegrass plants beyond the 30 cm and the biomass of ryegrass was comparable with untreated control. Experiments were also conducted to compare leaching of indaziflam with five residual herbicides commonly used in Florida citrus. Averaged across rainfall, herbicide ranking from high to low mobility was: bromacil > norflurazon > indaziflam > simazine > pendimethalin > diuron.

Directed genome modification of plants by genetic engineering techniques started in the early 1980s. In 1983 several labs simultaneously reported the first successful transfer of a foreign gene into the plant genome. Because the introduction of a single gene was sufficient, resistance of crop plants against specific herbicides was one of the first traits which could be realized by genetic engineering methods. Resistance could be obtained against different herbicides, but only resistant crops against glyphosate or glufosinate gained significant market share in the 1990s. Glyphosate resistant crops were developed by Monsanto and glufosinate resistant crops were developed by Bayer CropScience and its predecessors. Both companies used different routes to reach their goals and both routes were successful. Obtaining glyphosate resistance by overexpression of a special EPSP synthase gene was a fairly arduous approach, whereas resistance against glufosinate by detoxifying the herbicide in the plant could be more easily achieved. When the first herbicide resistant crops reached the market in the mid 1990s, glyphosate was already a well-known and well-established product in non-row crop markets, whereas glufosinate was just finding its place in the market. Whereas Monsanto’s strategy was to earn money by selling both the herbicide and transgenic herbicide resistant seeds, Bayer CropScience wanted to license the technology to seed companies and make money by selling more glufosinate. Eventually the Monsanto approach was more successful and glyphosate resistant crops conquered the agricultural world in the Americas. As a consequence companies reduced their efforts to find new herbicides. Due to an almost exclusive reliance on glyphosate for weed control in soybeans and its use for burndown before seeding, weed shifts occurred and glyphosate resistant weeds developed in this row-crop and subsequently in others.  Consequently the race for new herbicides and herbicide resistant crops has begun all over again.
peter.eckes@bayer.com

Since the first introduction of a glyphosate resistant (GR) crop, Roundup Ready® soybeans in the U.S. in 1996, the number of crops and acres planted to GR crops has increased significantly.  To date, glyphosate resistant varieties or hybrids of soybeans, corn, cotton, canola, sugar beets and alfalfa have been commercialized around the world. In 2010, it was estimated that glyphosate resistance crops have been planted on over 120 million hectares worldwide.  In most countries, farmer adoption of the technology has been rapid. In the U.S. within 5 years after introduction, GR soybeans and GR cotton were planted on approximately 70% and 60% of total planted acres, respectively.  Today, approximately 95% of soybeans and 90% of cotton planted are glyphosate resistant varieties in the U.S. Adoption of GR corn in the U.S. was slower relative to GR soybeans and cotton, due in part to delays in obtaining export approvals in key countries. However, by 2010, approximately 90% of the planted corn acres were glyphosate resistant. Rapid adoption has also occurred in other countries, i.e. GR soybeans in Argentina and GR corn in Philippines. 

The speed and extent to which glyphosate resistant crops have been adopted by farmers has been attributed to both pecuniary (financial) and non-pecuniary (non-financial) benefits related primarily to the use of glyphosate for in-crop weed management. Greater net returns have been demonstrated due to lower herbicide plus seed costs, higher yields, and/or lower planting and machinery costs.  Lower planting and machinery costs are associated with the transition to conservation tillage production practices as promoted by the adoption of this technology. Flexibility, simplicity, and consistency of the glyphosate based weed management systems are among the non-pecuniary benefits often attributed to the use of glyphosate in GR crops and valued by farmers. Some farmers place a significant value on the non-pecuniary benefits. Market research with farmers has shown evidence that the non-pecuniary benefits can result in farmers being more reluctant to switch from a GR crop to conventional varieties even in the face of issues such as glyphosate resistance.

The widespread planting of GR crops has been associated with significant changes in crop production practices. One change has been the impact of GR crops on tillage practices.  In the U.S. and Argentina a clear correlation has been demonstrated between increased plantings of GR crops and increased adoption of no-till and conservation tillage practices.  This increase in conservation tillage has resulted in cost savings (i.e. savings in time and fuel consumption) and environmental benefits (i.e. reduced soil erosion, improved aquatic habitats, reduction in CO2 emissions).  In addition, the adoption of GR crops in many cases has been correlated with reductions in total volume of herbicides and number of herbicides used for weed management. This is due to the broad spectrum control of grasses and broadleaves provided by glyphosate thus reducing or eliminating the need for multiple herbicides with different spectrums of activity.  The reduction in the use of other herbicides and decreased use of mechanical tillage has generally led to an overall reduction in the diversity of weed management practices used by farmers in GR crops.   In some situations glyphosate has been used as the sole method of weed control for many years.  This reduction in diversity has been associated with an increase in weed species and populations with resistance to glyphosate. In order to reduce the evolution and spread of glyphosate resistant populations, broad based stewardship programs have been implemented to encourage farmers to implement diversified programs that include the use of glyphosate in combination with other herbicides and/or weed management methods for both proactive (retard evolution and spread of resistance) and reactive (managing a resistant population after it has become established) weed management programs.  These stewardship programs include farmer and farm advisor focused educational and training programs and company sponsored marketing programs. Tracking studies designed to measure the success of these programs indicate that significant progress is being made in farmer adoption of more diversified weed management programs in their GR crops.

The Evolution of Glyphosate-Resistant Weeds. T. A. Gaines*; University of Western Australia, Crawley, WA, Australia.

Evolution of resistance to glyphosate, the world’s most widely used herbicide, is a significant problem facing world agriculture.  Glyphosate-resistant crops have been rapidly adopted since their introduction and provide many economic and agronomic benefits.  Some growers using these crops have essentially replaced all other weed control tactics with glyphosate alone.  This extensive reliance on a single weed control tactic has resulted in intense selection pressure for any traits enabling survival.  Glyphosate resistance has also evolved in weeds found in perennial crops such as vineyards and orchards, fence lines, and no-tillage fallow, highlighting that glyphosate resistance can evolve in any situation where glyphosate is used as the sole weed control tactic.  Glyphosate resistance now has been reported in 21 species globally.  Resistance mechanisms reported to date include target site mutations in the EPSPS gene, amplification of the EPSPS gene, and reduced glyphosate translocation.  Glyphosate metabolism has recently been reported in Digitaria from Brazil.  EPSPS gene amplification has now been reported in three species.  Reduced translocation has been shown in several species to be due to sequestration of glyphosate in the vacuole.  The resistance mechanism in giant ragweed is currently unknown and involves a rapid necrosis response in resistant individuals.  Clearly, multiple mechanisms confer resistance to glyphosate, and these mechanisms can combine via cross-pollination so that a single individual carries multiple mechanisms.  High selection pressure occurs with intensive glyphosate use, meaning that any individuals carrying traits that confer greater survival and reproduction will produce more offspring and result in the continued evolution of glyphosate resistance.  This process occurs through both the combination of known mechanisms and selection for any additional unknown mechanisms that are capable of conferring higher survival.  Greater diversity in weed control tactics is necessary, and practices that permit reliance on a single weed control tactic must be avoided, in order to disrupt the evolutionary processes that result in evolution of glyphosate resistant weeds.  Future weed management programs in herbicide resistant crops must include diverse tactics such as pre-plant burndown treatments (knockdowns) with a different mode of action, pre-emergent herbicides, mixtures of different modes of action within a crop, removal and/or destruction of seeds produced on surviving plants, and rotation to different herbicide modes of action and crops from year to year.  New innovations with novel modes of action are also urgently needed.  These actions will improve the sustainability of future herbicide resistant crops and help address the current problem of glyphosate resistance.

E-mail: todd.gaines@uwa.edu.au

The evolution of resistance in a weed population to a single herbicide or herbicide site-of-action (SOA) group generally is a manageable problem, in that alternative herbicides are available for effective control (at least in most major crops). A more serious situation for weed management, however, is the increasing occurrence of weed populations that have evolved resistances to herbicides from multiple SOA groups. In the extreme case, this could result in no effective herbicide options for control of a weed population in a given cropping system. Multiple herbicide resistances often evolve in a weed population through sequential selection by different herbicides, in which multiple herbicide-resistance genes accumulate within the population. Even more problematic is when the resistance genes accumulate within individual plants, which occurs most commonly in weed species that are highly outcrossed. Resistance to herbicides from different SOA groups also can occur as a result of cross resistance when the resistance mechanism is not target-site based. For example, metabolism-based resistance in rigid ryegrass (Lolium rigidum) and blackgrass (Alopecurus myosuroides) selected by a herbicide from one SOA group often results in unpredictable cross resistance to herbicides from one or more different SOA groups. In the US, waterhemp (Amaranthus tuberculatus) currently is the most notorious weed for evolving multiple resistances. A population from Illinois was identified with resistances to glyphosate, ALS inhibitors, PPO inhibitors, and triazines. Over the past few years, we have utilized DNA-based tests for herbicide resistances to document the extent of multiple resistances in Illinois waterhemp populations. In about one-third of all cases, glyphosate-resistant waterhemp populations were found to also have resistances to ALS inhibitors and PPO inhibitors. We contend that the current situation of multiple herbicide resistances in waterhemp populations is not fully appreciated by farmers and weed management practitioners, and will result in many weed control failures.

Best management practices (BMPs) that mitigate the risks of herbicide-resistant weeds evolving in cotton and soybean are generally no different than those recommended for other crops.  Best management practices that should be emphasized in these and other crops include: 1) an understanding of the biology of the weeds present, 2) start with clean fields at planting, overlaying residual herbicides, 3) scout fields routinely, 4) use multiple herbicide modes of action that are effective against the most troublesome or resistant-prone weeds, 5) apply a full labeled herbicide rate at the recommended weed size, 6) emphasize cultural and mechanical practices, 7) prevent weed seed production, 8) prevent field-to-field and within-field movement of weedy propagules, 8) prevent an influx of weeds from field borders, 9) manage weed seed at harvest or post-harvest, 10) use a diversified approach focused on reducing the soil seedbank.  Diversity of management practices, which has been lacking in most U.S. cotton and soybean production systems, is the key to having a long-term successful weed management program.  No doubt, these BMPs will increase weed management costs; however, they are essential to ensuring sustainable weed management and crop production, particularly low soil seedbank densities.  Unfortunately, many of these BMPs were not used by producers of glyphosate-resistant crops in the Midsouth until herbicide-resistant weeds became present.  Reactive adoption of these BMPs is occurring in the Midsouth as a result of wide-spread glyphosate resistance in Palmer amaranth.  Hopefully, lessons learned as a result of glyphosate resistance in this region can be employed to preserve the effectiveness of glyphosate in other regions.    

While herbicide-resistant weeds have become of greater importance within the last five years, evolved resistance to herbicides has been a long-term problem in maize production and predates herbicide-resistant maize hybrids by 40 years.   The occurrence of wide-spread resistance to atrazine was followed by wide-spread ALS- inhibitor herbicide resistance.  Agriculture did not learn from history and ignored the obvious shortcomings of past management practices when genetically-engineered corn hybrids became available.  While there are (currently) two herbicides that have genetically-engineered resistance in maize, glyphosate and glufosinate, glyphosate has the significant acreage compared to glufosinate.  The adoption of glyphosate-resistant maize
resulted in a further reduction in diversity in practices for weed management. Predictably weeds evolved resistance to glyphosate and still growers were reticent to change weed control tactics.  Consider that in the Corn Belt, glyphosate-resistant crops are the predominate cultivars grown and glyphosate represents the primary weed control tactic.  There are a number of recognized best
management practices that can and should be included in a maize production system.  However, given the existing crop production system, one of the important practices, crop rotation, is not particularly robust; from the weed management perspective, corn/soybean or corn/cotton rotations, regardless of genetically-engineered trait, do not represent crop rotation programs that effectively help combat the evolution of herbicide-resistant weeds.  Similarly, while herbicide mechanism of action rotations and/or the inclusion of multiple herbicide mechanisms of action are useful practices, these best management practices do not serve as a solution to the evolution of herbicide resistance but rather serve to delay the inevitable evolution of herbicide resistance.  Furthermore, a discussion about “proactive” best management practices should be considered of limited utility given the widespread existence of herbicide-resistant weed biotypes.  In most instances, when triazine, ALS, PPO, HPPD and glyphosate
resistant weed biotypes and the number of weed species that have evolved resistance to one or more of these herbicide mechanisms of action are considered, growers should be developing reactive best management practices.  Unfortunately, growers typically look only as far as the next herbicide and this strategy is supported by the herbicide industry and academics, in general.  It should be clear to anyone who objectively reviews the current weed management programs that they are not sustainable.  The evolution of herbicide-resistant weed biotypes is increasing at an increasing rate.   Agriculture must make major changes in the crop production systems in order to provide opportunities for sustained crop production and the management of herbicide-resistant weeds.  Simply adding herbicides will, at best, delay herbicide resistance evolution.  Even
when systems are modified to include other genetically-engineered crops and the concomitant use of the herbicide, evolved resistance will still be a concern if the alternate technology is used (better said misused) like the glyphosate-based systems.  While there is a need for new herbicides, unless the systems become truly diversified, the new herbicides may help resolve the problems for only a short period.  It appears at this time agriculture is destined to reinforce the mistakes that have historically occurred.  The emphasis on herbicides must be reduced.  Simple and convenient are not working.  Diversity beyond herbicides for weed management must be established.  Mechanical and cultural strategies must be included in systems to sustain the economic, ecological, and environmental success of weed management.

Aminocyclopyrachlor is a new herbicide candidate under development by DuPont Crop Protection.  Aminocyclopyrachlor has a potential fit in many markets including rangeland and pasture.  Field testing of aminocyclopyrachlor began in 2004 and   registration was received in early 2011 for use in noncrop markets in premixtures and sold under the trade names Perspective, Streamline, and Viewpoint.    Aminocyclopyrachlor has both contact and systemic activity on a broad spectrum of brush weed species commonly found in the United States.  Aminocyclopyrachlor is taken up by leaves, stems and roots.  Premixtures with other herbicides are being investigated for control of invasive brush species in pasture and rangeland.

       Aminocyclopyrachlor is a new herbicide candidate under development by DuPont Crop Protection.  Aminocyclopyrachlor has a potential fit in many markets including rangeland and pasture.  Field testing of aminocyclopyrachlor began in 2004 and   registration was received in early 2011 for use in noncrop markets in premixtures and sold under several trade names.    Aminocyclopyrachlor  has both foliar and residual activity on a broad spectrum of broadleaf weeds.  Aminocyclopyrachlor is taken up by leaves, stems and roots.  Effects can be seen in hours to a few days however death may require weeks or months.  Premixtures with other herbicides including sulfonylureas are being investigated for broadleaf weed control in pastures.  The mixtures increase the spectrum of species controlled and will be beneficial in controlling or delaying the onset of ALS resistant species.    

Experiments in pasture weed control were conducted in 2011 with combinations of aminocyclopyrachlor and other herbicides.  In Experiments 1 and 2, the herbicide treatments in product/ha included 105 or 175 g/ha AMCP+MET {DPX-RDQ98 WP (44.5% aminocyclopyrachlor + 6.67% metsulfuron-methyl)}, 0.59 or 0.89 L/ha AMCP+TRI {DPX-RRW96 SL (7.3% aminocyclopyrachlor + 14.6% triclopyr)}, 2.2 L/ha AM+2,4-D {Grazon Next EC ( 3.4% aminopyralid + 27.2% 2,4-D)},  105 g/ha NIC+MET {Pastora WG (56.2% nicosulfuron + 15% metsulfuron-methyl)} and an untreated control.  Experiment 3 consisted of tank-mixes of 105 + 39, 208 + 55, or 263 + 70 g/ha AMCP+CHL {DPX-MAT 28 SG (50% aminocyclopyrachlor) + Telar WG (75% chlorsulfuron)} or 140 + 140, 210 + 210, or 280 + 280 g/ha AMCP+RIM {DPX-MAT 28 SG (50% aminocyclopyrachlor) + Matrix WG (25% rimsulfuron)} and these were compared to a tank-mix of 56 + 20 g/ha AM+2,4-D {Milestone EC  (21.1% aminopyralid + Escort WG (60% metsulfuron-methyl)} or an untreated control.  All treatments were applied with a CO2 backpack sprayer with a total spray volume of 236 L/ha. Plots which were replicated 4 times averaged 3 by 10 m and the application dates were as follows: Experiment 1-June 13, 2011, Experiment 2-June 28, 2011, and Experiment 3-July 14, 2011.  In addition all treatments were applied with 0.25% V/V non-ionic surfactant.  In Experiment 1, control of woolly croton (Croton capitatus Michx.) with all treatments was 95% or greater by 28 days after treatment (DAT).  At 51 or 72 DAT, control was 90% or greater with all treatments.  In Experiment 2, either rate of AMCP+MET, AM+MET, or NIC+MET controlled spiny amaranth (Amaranthus spinosus L.) 93 to 100% at 35 DAT while 0.59 L/ha AMCP+TRI provided 38% control and 0.89 L/ha AMCP+TRI provided 65% control.  By 73 DAT, either rate of AMCP+MET, AM+MET, or NIC+MET controlled spiny amaranth 95 to 100% while 0.59 L/ha AMCP+TRI provided 53% control and 0.89 L/ha AMCP+TRI provided 80% control.  Also in Experiment 2, woolly croton was controlled better by AMCP+MET or AM+2,4-D compared to AMCP+TRI or NIC+MET at 35 DAT with the AMCP+TRI or NIC+MET providing 85 to 88% control and AMCP+MET or AM+2,4-D providing 95 to 100% control.  By 73 DAT control was equivalent with all treatments with 90 to 100% control.  No injury to common bermudagrass was observed from any treatment at 14 or 35 DAT.  In Experiment 3,  common ragweed (Ambrosia artemisiifolia L.) was easily controlled by all treatments with 90 and 100% control observed at 33 and 64 DAT, respectively.  Arrowleaf sida (Sida rhombifolia L.) control did have some differences at 64 DAT but the results did not indicate a clear rate response.  The best control was the low rate of AMCP+RIM with 78% control.  The mid and higher rate of AMCP+RIM had 40 and 65% control respectively.  The high rate of AMCP+CHL had 63% control and the low and mid rate had 45 and 40% control, respectively.  AM+MET provided 18% control of arrowleaf sida.  Injury to bahiagrass was only observed at 33 DAT with no injury observed from any treatment at 64 DAT.  The AM+MET treatment caused the highest injury of 35% which can be expected since the treatment contained metsulfuron-methyl.  The other treatments resulted in 10 to 23% injury to bahiagrass.  The results form these trials indicated that combinations of aminocyclopyrachlor plus other herbicides have the potential to provided weed control of common pasture weeds in warm-season forage grasses.          

Performance of Aminocyclopyrachlor for Pernicious Weed and Brush Management in Texas Pastures and Rangeland.  P.A. Baumann^1, T.W. Janak¹, M.E. Matocha¹ and E.P. Castner², Texas AgriLife Extension¹, College Station, TX, and DuPont Crop Protection², Weatherford, TX.

In 2009 and 2010, three studies were initated to evaluate the effrectiveness of aminocyclopyrachlor alone or in combination with metsulfuron for control of bitter sneezeweed (Helenium amarum), dogfennel (Eupatorium capillifolium) and silverleaf nightshade (Solanum eleagnifolium).  Rates of aminocyclopyrachlor evaluated in the bitter sneezeweed and dogfennel experiments ranged from 0.5 to 3.0 oz a.i./A and 0.5 to 2.0 oz a.i./A in the silverleaf nightshade experiment. Metsulfuron was combined with some of the aminocyclopyrachlor treatments at rates of 0.1 and 0.2 oz a.i./A.  Aminocyclopyrachlor was highly effective for controlling bitter sneezeweed in a study conducted on a mixed stand of native range grasses during 2009.  Rates of 1.0 to 3.0 oz a.i./A provided 100% control of this species 6 WAT.  When this herbicide was applied at 0.5 oz a.i./A, control was 82% at this rating date. The addition of metsulfuron at 0.2 oz a.i./A to 1.0 oz a.i./A of aminocyclopyrachlor provided equal control. When evaluated 3 MAT, dogfennel control was greater than 90% from aminocyclopyrachlor rates ranging from 1.0 to 3.0 oz a.i./A. This control was maintained into the following year, 12 MAT.  Aminocyclopyrachlor at 0.5 oz a.i./A did not achieve control greater than 77%, 12 MAT.  The addition of metsulfuron at 0.2 oz a.i. to 1.0 oz a.i. of aminocyclopyrachlor did not significantly improve control of this species at the native rangeland site.  In the silverleaf nightshade study, conducted on a mixed stand of bermudagrass and native range grasses, aminocyclopyrachlor rates ranging from 0.5 to 2.0 oz a.i./A resulted in 100% control when evaluated 2, 3 and 4 MAT.  However, when evaluated 12 MAT, the 0.5, 1.0, 1.5 and 2.0 oz a.i./A rates were providing only 45, 65, 77 and 87 % control, respectively.  A study was initiated in 2010 to examine control of Chinese tallow (Sapium sebiferum) from aminocyclopyrachor rates ranging from 1.0 to 4.0 oz a.i./A.  Combinations of 1.33 oz a.i./A of this herbicide and either 0.2 or 0.367 oz a.i./A of metsulfuron were also evaluated.  Initial defoliation caused by all treatments, 3 MAT, exceeded 90%.  However, this same level of control was only achieved by the 4.0 oz a.i./A rate, when evaluated 13 MAT.  The 1.0 and 2.0 oz a.i./A rates of aminocyclopyrachlor provided 80% control at this rating date.  When either 0.2 or 0.367 oz a.i./A of metsulfuron were added to 1.33 oz a.i./A of aminocyclopryachlor, control was 60% or less, suggesting a possible antagonism from this combination.  The same apparent antagonism was noted when 1.0 oz a.i./A of aminocyclopyrachlor was combined with 2.0 oz a.i./A of triclopyr.

Seasonal management of cool season grasses in rights-of-way includes mowing and herbicide applications to meet safety and aesthetic requirements. Application of plant growth regulators (PGRs) to suppress seedhead development and growth can reduce the number of time consuming and costly mowings. Some herbicides also have seedhead suppression effects, depending on the rate and timing of application. However, these products can injure the turf causing discoloration, which is undesirable but in many cases is temporary.  These products are normally applied in the spring, before seedhead emergence.  Can fall applications also result in seedhead suppression the following spring?

A trial was established at Spindletop Research Farm in Lexington KY with 21 treatments and 3 replications arranged in a randomized complete block design.  Plots were 3 m by 9 m with running unsprayed checks between each of the plots. The treatment list included 10 products or tank mixes applied in the fall (November 12, 2010) and the same 10 treatments applied in the spring (April 21, 2011) plus an unsprayed control.  All applications were at 187 L/ha and included a non-ionic surfactant at 0.25% v/v.  They included new and existing products and tank mixes using one or more of the following active ingredients:  aminocyclopyrachlor, aminopyralid, chlorsulfuron, glyphosate, imazapic, imazapyr, imazethapyr, mefluidide, metsulfuron methyl, and 2,4-D.  The tall fescue was 6 inches tall at the fall application and 11 inches at the spring application. 

 Visual percent seedhead suppression was assessed by comparison to the running check strips 17 (5/8/2011), 34 (5/25/2011), 52 (6/12/2011), 74 (7/4/2011) and 113 (8/12/2011) days after spring application (DASA). Tall fescue color was assessed by comparison to the running check strips 17, 34, 52, and 74 DASA. The color rating ranges from 0 (dead) to 9 (full green). The color of the check strips was set at 8.  Canopy and seedhead heights were measured 17, 34, 52, 74, and 113 DASA.  Data were analyzed using ARM software and treatment means were compared using Fisher’s LSD at p = 0.05.

The spring applications resulted in greater seedhead suppression than the fall applications.  Fall application of the GF-2703 (Dow AgroSciences) + aminopyralid treatment reduced seedheads by 50% while spring application had 100% seedhead suppression at all assessment dates.  The other spring applied treatment with 100% seedhead suppression was imazapic + 2,4-D. Green color of these two spring applied treatments was less than the check strips 17 and 34 DASA while they were greener than control 52 and 74 DASA.

Impact of pasture herbicides on seedling growth response of
three tall fescue varieties.  W. Witt, P.
Moraes, and T. Phillips. University of Kentucky, Lexington KY

The tall fescue cultivar ‘KY 31’is a dominant forage grass
for beef animals in Kentucky and surrounding states and frequently contains the
natural race of the endophytic fungus Neotyphodium coenophialum.  Body temperature of beef animals consuming
tall fescue with the fungus is frequently elevated.  The development of tall fescue varieties
without N. coenophialum or
containing other endophytic fungi is of interest for improving animal
performance.  The tall fescue varieties
KYFA 9821 and KYFA 9301 were developed at the University of Kentucky and were
evaluated with and without the endophytic fungus AR584.  The response of these fescue varieties to
herbicides used for pasture weed control were of interest.  Seeds of the tall fescues KY31 containing N. coenophialum, KYFA 9821 with and without AR584, and
KYFA9301 with and without AR584, were planted into a sand/soil mixture and
grown in a greenhouse.  Herbicides were
applied to about 5 cm grasses. 
Herbicides evaluated were 2,4-D, aminopyralid,  aminopyralid plus metsulfuron, metsulfuron,
2,4-D plus dicamba, and aminocyclopyrachlor. 
Herbicide rates evaluated were those normally used for pasture weed
control in Kentucky.  Visual injury,
height, and number of tillers were determined 7, 14, 21, and 28 days after
treatment and grass biomass 28 days after treatment.  All varieties exhibited injury (5 to 20%)
from all treatments 7 DAT; however, 28 DAT only metsulfuron containing
treatments exhibited injury.  The height
of KY31 was not reduced by any treatment 28 DAT while the height of all other
varieties was reduced by metsulfuron containing treatments.  Dry matter 28 DAT was reduced by metsulfuron
containing treatments for all varieties. 
The number of tillers per plant among the varieties was variable but, in
general, tiller number was reduced in all varieties by metsulfuron containing
treatments 28 DAT.  The presence or
absence of the endophyte AR584 did not alter the response of UKFA 9821 or KYFA
9301 to the herbicides evaluated.

Ventenata (Ventenata dubia) is an aggressive annual grassy weed that is rapidly degrading range and wild lands of the Pacific Northwest.   A compromised forage base for livestock and wildlife, increased risk for wildfire, erosion, and displacement of perennial grasses are some of the consequences of this introduced species.

Plot trials for ventenata control were established in central Oregon at Warm Springs in a rangeland area where ventenata was one of the dominant annual grasses, and few to no bunchgrasses remained.  The site is clay-dominated and stays saturated in early spring, at a moderate elevation.  Four different herbicides were applied, followed by seeding six different perennial grass species in order to assess potential range restoration efforts.  Herbicides were applied in single strips of 20 ft. by 288 ft. within a larger plot of 80 ft. by 288 ft.   Seeding occurred across the larger plot in 20 ft. wide treatments, replicated three times.  Both herbicide efficacy and seeding establishment success were evaluated after initial application and seeding efforts. 

Imazapic , imazapic /glyphosate were applied in the fall of 2008 immediately  followed by seeding.  Rimsulfuron, and sulfometuron/chlorsulfuron were also applied in the fall of 2008, but seeding was postponed for a year for crop safety reasons.  Seeded bunchgrasses included squirreltail (Elymus elymoides), intermediate wheatgrass (Agropyron intermedium), bluebunch wheatgrass (Pseudoroegneria spicata), sandberg’s bluegrass (Poa sandbergii), sherman big bluegrass (Poa secunda), and smooth brome (Bromus inermis).

All four herbicides provided 100 percent control of Ventenata in the first year.  Within the 2008 seeded plots, sherman big bluegrass achieved the best stand establishment, followed by sandberg’s bluegrass, intermediate wheatgrass, and smooth brome. There was poor stand establishment with bluebunch wheatgrass and essentially no squirreltail plants.  Residual efficacy for the four herbicides on ventenata the second season following application ranged from 95 percent for sulfometuron/chlorsulfuron and 90 percent for rimsulfuron, to 60 percent for imazapic and imazapic/glyphosate.  Stand establishment following the 2009 fall planting of the rimsulfuron and sulfometuron/chlorsulfuron plots was highest for sandberg’s bluegrass followed by sherman big bluegrass, smooth brome, and intermediate wheatgrass. Very few bluebunch wheatgrass or squirreltail plants were observed.  The plot was retreated in 2011 with imazapic due to the dominant presence of ventenata once again.  Evaluation of the plots will continue to monitor seeded bunchgrass establishment.

Privet (Ligustrum sp.) Control Field Trials and Results in Georgia

E. David Dickens and David J. Moorhead; The University of Georgia – WSF&NR, Andy Ezell; Department of Forestry - Mississippi State University, and Chip Bates – Georgia Forestry Commission

Abstract:  Privet (Ligustrum sp.) is the second most prolific invasive species in the Southeastern United States occupying approximately 23 million acres. This abstract will discuss two replicated trials installed in Bulloch County, Georgia from 2006 through 2011 to control privet. The main objectives were to determine herbicide and type of privet plant coverage efficacy using hand pump Solo diaphragm backpack sprayers applied in the fall or winter (late October and early February). Herbicide control estimates used were as follows: Excellent; greater than 90% control, Good; 80-90% control, Fair; 60-80% control, and Poor <60% control using visual observations and looking at the cambium color from broken privet stems (brown=dead, green=living) as well a control consistency across the plots. The first replicated trial was installed using the following treatments: (1) Garlon 4 (61.6% triclopyr) @ 25% solution + a basal bark penetrant oil @ 75% applied to the first 18 vertical inches of each stem 360 degrees around each stem, (2) Pasturegard (25% triclopyr + 8.6% fluroxypyr) @ 37% solution + a basal bark penetrant oil @ 63% applied as Garlon 4, (3) Razor Pro (41% glyphosate + surfactant) @ 5% solution + water applied as a foliar spray (100% coverage to full wetting), and (4) Razor Pro @ 5% solution + 5% crop oil applied as a foliar spray. Two replications in 75 feet by 5 feet plots of each treatment were applied to 10 to 15 feet tall thick, small diameter (primarily < 1 inch at groundline) Chinese privet hedge-rows in Bulloch County on 31 October 2006. Six, 12, and 18 month post treatment evaluations were performed. The 18 month results were as follows: the basal bark treatments of Garlon 4 and Pasturegard + penetrant oil gave inconsistent control with an overall rating of fair to poor for these two treatments while the foliar application of Razor Pro and Razor Pro + crop oil control was more consistent and with an overall rating of good to excellent for these two treatments. The second trial was initiated using the following herbicides provided by Dow Agrosciences: (1) Accord XRT (53.6% glyphosate) @ 2% + water (white flags) as a foliar spray, (2) Accord XRT @ 4% + water (red flags) as a foliar spray, (3) Garlon Ultra (60.5% trichlopyr) @ 20% solution + 80% UAP basal oil (yellow flags) as a basal bark treatment, and (4) Garlon 4 Ultra @ 20% solution + Milestone VM (21.1% aminopyralid) @ 2% solution + balance UAP basal oil (orange flags) as a basal bark treatment with three replications in thick, small diameter (<1 inch at groundline) stands. A set of untreated plots; controls were installed as well (pink flags) in this study. All treatments were applied in 20 feet long by 15 feet deep plots on 6 February 2009. Chinese privet control evaluations were performed on this second site six, 12, 18, and 24 months post treatment. Twelve months after treatment results were as follows: Accord XRT @ 4%; excellent and consistent control, Accord XRT @ 2%; good control and less consistent control than the 4% Accord XRT treatment, Garlon 4 Ultra @ 20% solution; good to excellent control, but somewhat variable control, and Garlon 4 Ultra + Milestone VM; poor to fair control and rather variable control. Results after 24 months were as follows: Accord XRT @ 4% solution; good to excellent control and consistent control, Accord XRT @ 2% solution; good control but not quite as consistent control as the 4% treatment, Garlon 4 Ultra; fair to good control and relatively inconsistent control with some resprouting, Garlon 4 Ultra + Milestone VM; fair to good control and relatively inconsistent with some resprouting. Based on these two trials in thick, small diameter stands of privet, the foliar application of glyphosate with a surfactant @ 4% (using 53.6% glyphosate) or 5% (using 41% glyphosate) gave the best control results and the most consistent results when compared to the basal bark trichlopyr (with and without aminopyralid or fluroxypyr) treatments when applied in late October or early February. There was no collateral damage to adjacent mature loblolly pine, sweetgum, water oak, or sycamore trees at both sites during the evaluation periods. The glyphosate treatments were also the most cost-effective as 4 gallons/acre Accord XRT were used at the 4% rate (10.25 oz Accord XRT used per 0.02 acre) compared to 10 gallons Garlon 4 Ultra at the 20% rate (25.6 oz used per 0.02 are) used for the basal bark treatment. In another set of privet control (unreplicated) trials in Bulloch County on larger diameter (1-2 inch groundline diameters) less dense stands, the Garlon 4 basal bark treatment was very effective.  

In Alaska Conservation Reserve Program (CRP) lands, succession of fields planted with grass and clover to shrubs and small trees is resulting in program compliance problems related to ease of re-conversion to crop lands.  Standard practice for slowing this succession is mowing every 2 to 3 yr, which does not kill the woody vegetation.  A field study was conducted at 5 sites over 3 years to determine if 2,4-D (2.2 kg ae ha^-1 2-ethylhexyl ester) or triclopyr (2.2 kg ae ha^-1 butoxyethyl ester) applied broadcast or with a Diamond Wetblade™ mower (DWB) (2.2 kg ae ha^-1 2,4-D dimethylamine salt and 1.7 kg ae ha^-1 triclopyr triethylamine salt, respectively) would result in improved shrub control compared to mowing.  Mowing was conducted at both 15 and 45 cm above ground level and herbicides were applied with the DWB at three rates in three fields.  Measurements from 2 yr after treatment (YAT) confirmed that both herbicides reduced shrub cover about 50% compared to controls.  At 2 of 3 sites reduced rates of the herbicides used with the DWB did not result in decreased shrub control.  Mowing alone resulted in intermediate shrub cover compared to herbicides and controls.  Grass cover was greatest where herbicides were used (47%) followed by mowing alone (29%) then controls (17%).  Generally, mower cutting height did not alter treatment effects.  Treatments typically had little impact on forb cover and composition 2 YAT, with the exception of fireweed (Chamerion angustifolium), which was generally reduced where herbicides were applied.  Application of 2,4-D and triclopyr should reduce the frequency of mowing and decrease compliance problems in CRP lands in Alaska.

The purpose of this study was to screen Streamline and imazapyr combinations as an individual tree treatment for general brush control.  DuPont produces Streamline, a pre-mixed blend of aminocyclopyrachlor and metsulfuron-methyl.  Because small batches were needed in this study, separate active ingredients were measured and  mixed for each treatment.  All herbicide treatments contained .5% NIS all rates are reported in gms/gal of product.  Test treatments are:  1) MAT28+Escort XP 4.7+1.2, 2) MAT28+Escort XP 8.5+2.3,  3) MAT28+Escort XP 15.3+4.1, 4) MAT28+Imazapyr+Escort XP 3.3+3+0.9, 5)  MAT28+Imazapyr+ Escort XP 6.5+6+1.8, 6) MAT28+Imazapyr+ Escort XP 13.1+12+3.5, 7) Garlon 25% v/v, and 8) Untreated check.  MAT28 is formulated as a 50% soluable granule, Escort XP as a 60% water-dispersed granule, imazapyr as a 75% water-dispersed granule, and Garlon as a 4 pound, soluble liquid.

The test site was near Timpson (Shelby County), TX, clearcut in 2005, and dominated by unwanted yaupon and sweetgum.  Four rootstocks in each of the 1-, 2-, and 3-inch ground line diameter classes were selected per species and treatment.  All stems in a clump were treated.  In September 4, 2010, initial height and ground line diameter were recorded for each rootstock.  On September 30, 2010 foliage was sprayed until wet but without drip.  Brownout was visually evaluated 30 days after treatment (DAT) on October 29, 2010 and total height measured again on January 4, 2011.  Percent control was computed as the ((initial pre-treatment height - height January 4, 2011)/initial pre-treatment height)*100.

Sweetgum brownout by Garlon at 30 DAT was numerically greatest.  Least browning was observed on rootstocks treated with MAT28+Imazapyr+Escort XP (13.1+12+3.5).  After one growing season, control was greatest and similar for Garlon and imazapyr containing mixtures.  MAT28+Escort XP mixtures without imazapyr provided lowest herbicidal control with the untreated check significantly less and least.  In conclusion, Streamline control of sweetgum control was significantly enhanced with the addition of imazapyr.  High rates of Streamline alone or with imazapyr were needed for moderate control of yaupon.  An extreme drought during most of 2011 probably impacted control.

Yaupon brownout by Garlon at 30 DAT was significantly greater than other herbicides.  MAT28+ Escort XP (15.3+4.1,  8.5+2.3) and MAT28+Imazapyr+Escort XP (13.1+12+3.5) were intermediate in brownout.  MAT28+Escort (1.24+.32), MAT28+Imazapyr+Escort (6.5+6+1.8, 3.3+3+0.9) provided lowest herbicidal brownout but significantly more brownout than untreated checks.  Yaupon control, one growing season after treatment, was greatest for Garlon, intermediate with MAT28+ Escort XP (15.3+4.1) and MAT28+Imazapyr+Escort XP (13.1+12+3.5) and lowest for remaining herbicide and check treatments.  jyeiser@sfasu.edu.

Herbaceous weed control is considered essential during the first growing season in the establishment of loblolly pine plantations in the southern U.S. Over the past 30 years, a number of herbicides have been tested for this application, and some have proved more effective than others. Flazasulfuron has not been tested for such an application. Thus, the crop tolerance of loblolly pine was unknown and the efficacy of treatments was also unproven. A total of 13 treatments which contained flazasulfuron applied alone or in tank mixtures were applied on a total of four sites in Mississippi and Texas. All applications were completed on areas of recently planted loblolly pine. Plots were evaluated on a 30-day interval starting at 30 DAT and continuing until 180 DAT. Pine seedlings were evaluated at each timing for any symptoms of phytotoxicity. A drought of historic proportions impacted the response for all treatments  on the Texas sites, but growing conditions were excellent on the Mississippi sites and evaluations on those sites produced very a good test of the herbicide.  Results of herbaceous weed control and crop tolerance will be presented.

Herbaceous weed control is generally recognized as essential for the successful establishment of hardwoods on retired agricultural areas in the South. Survival and growth can both be enhanced by cotrolling the intense competition on these sites for the first growing season. However, information regarding the response to multiple years of herbaceous wed control in these plantings is lacking. A total of 4,320 oak (Quercus) seedlings representing three species were planted in the study utilizing three planting sites. Half the seedlings received herbaceous weed control for one growing season and half received the treatment for two growing seasons. In each application, two ounces of Oust XP were applied per sprayed acre. Initial height and groundline diameter were recorded soon after planting and these parameters were remeasured at the  end of the first and second growing seasons. Data were analyzed for differences in growth between treatments and in consideration of different sites, species, and mechanical site preparation treatments. Results will be presented for each of the analyses.

Dicamba has been a highly effective weed management tool for nearly 50 years.  It is the fifth most widely used herbicide in the United States with more than 25 million acres of crops including corn, wheat, pasture, and turf treated annually.  Dicamba was discovered in 1958 and first registered as Banvel^® herbicide for broadleaf control in turf.  Registration of dicamba products for use in corn, sorghum, small grains, and pasture soon followed in 1964 through 1966.  Since then dicamba chemistry has evolved over time with the development of formulations such as Marksman^®, Clarity^®, Distinct^® and Status^® herbicides. A key difference in the formulations is the use of different bases as counter ions to neutralize the carboxylic acid moiety of dicamba. The respective salts differ in their physical properties, notably in their water solubility and tendency to volatilize. Volatilization is, besides spray drift, a concern for off-target movement of dicamba.  Although volatilization contributes 2 to 3 orders of magnitude less than spray drift, it is a concern that can be addressed by formulation innovation.

The presentation introduces a new experimental dicamba formulation innovation based on a proprietary dicamba-BAPMA salt, which is currently under development. The formulation possesses good stability, mixing and handling properties, and is optimized to further reduce the field volatilization potential of dicamba.  BAPMA (N, N-Bis-(aminopropyl) methylamine) is a tridentate amine, that provides strong and effective binding of dicamba spray residues, thus suppressing potential volatilization of the herbicide. Since volatilization is a kinetic process, it cannot be easily addressed by thermodynamic material constants like vapor pressure. Vapor pressure defines the equilibrium condition of pure compounds between a deposit and a saturated atmosphere in a closed system.  For agrochemical applications the atmosphere is an open system so vapor phase saturation is not reached.  The volatilization kinetic is further influenced by external factors such as wind, relative humidity, temperature and contact substrate.  In addition, vapor pressure measurements of less than < 1.0 kPa are subject to systemic errors.  In conclusion, the thermodynamically static conditions, such as vapor pressure, are not directly relevant under dynamic agronomic conditions.

However, real life kinetic data like field sampling results are difficult to measure and are notoriously sensitive to a number of unwanted external factors. Therefore, methods were sought to measure and compare volatilization of candidates in screening but also under field conditions with different requirements regarding throughput and sensitivity. Five methods will be presented that can be used to compare and measure dicamba volatilization under lab and field conditions. These include TGA (thermo gravimetric analysis), non-equilibrium evaporation, humidome bioassay and ¹⁴C contained system laboratory studies, and field air sampling studies.

In an effort to help address concerns about spray drift of dicamba applications in field crops, The Ohio State University has collaborated with The Andersons in the development of a new Wetted Granule application system and Foliar Granule formulations for dicamba.

Foliar Granules represent new technology which is based on dry granules that are distributed by a pneumatic applicator, modified to wet the granules and the crop with water spray as the application takes place. The granules disperse in a few seconds due to contact with water, and this provides for foliar adhesion and herbicide release on the weed. The particle size and formulation of the foliar granules has been developed so as to provide efficacy with practically no potential for windblown drift of herbicide due to the spray containing no herbicide and the granules being larger than 200 microns in size.

Field studies were conducted in the spring and summer of 2011 to determine the relative effectiveness of several experimental dicamba Foliar Granule formulations.  These were also compared to a standard liquid formulation of dicamba applied in 15 gpa of water.  The dicamba rate was 0.56 kg ai/ha for all treatments.     The spring study was conducted in a no-till fallow area.  Weeds were 1 to 8 cm tall at the time of application on April 13, and included bushy wallflower, common chickweed, henbit, pennycress, purple deadnettle, and shepherds-purse.  The summer study was conducted in a fallow area that was tilled earlier in the spring.  Weeds were up to 28 cm tall at the time of application on July 6, and included common lambsquarters, giant ragweed, redroot pigweed, and velvetleaf.  Control with the liquid dicamba formulation was low in both studies, ranging from only 10 to 55% in the spring study, and 15 to 100% in the summer study.  In the spring study, most of the experimental formulations provided control similar to the liquid dicamba formulation.  Several formulations were somewhat more effective on field pennycress and bushy wallflower than the liquid dicamba, but not to the point of commercially acceptable control.  In the summer study, several experimental formulations provided 94 to 100% control of giant ragweed, compared with 100% for the liquid dicamba.  Control of velvetleaf and common lambsquarters was only 15 and 30% for the liquid dicamba, respectively, while several experimental formulations provided up to 45 and 85% control of these weeds.

AGH 09008 is a novel 2,4-D acid type herbicide formulation. AGH 09008 will be marketed by Winfield Solutions, LLC. as Rugged™ herbicide. AGH 09008 contains 3.49 pounds of 2,4-D acid per gallon. Typical use rates are 0.5 to 2 pints per acre. Broadleaf weed control with AGH 09008 was more similar to that from 2,4-D esters than that from 2,4-D dimethyl amine. Generally, 2,4-D esters provided similar or greater weed control than AGH 09008 and AGH 09008 provided greater weed control than 2,4-D dimethyl amine. The compatibility and performance of AGH 09008 with K-salt glyphosate herbicides was similar to that of 2,4-D esters and better than 2,4-D dimethyl amine. AGH 09008 performed well when UAN was the spray carrier. AGH 09008 was more compatible than 2,4-D dimethyl amine in mixtures with other herbicides, fertilizers and other tank mix products. AGH 09008 caused no injury to soybeans when applied seven or more days prior to planting. Tomatoes showed significant growth regulator type injury when placed in volatility testing chambers with 2,4-D ester formulations. The appearance of tomatoes tested with AGH 09008 and 2,4-D amine were similar to tomatoes that were in not exposed to 2,4-D.

The transport of the widely-used auxinic herbicide 2,4-D in the vapor phase has been implicated in non-target plant damage issues for many years.  Previous generations of 2,4-D-containing formulations have included a variety of ester or salt forms of the herbicide.  An innovative new form of the herbicide is a recently-developed 2,4-D choline salt, specifically designed for reduced volatility in the Enlist^TM Weed Control System.  A working hypothesis for the chemical basis of the volatility reduction will be discussed.  Laboratory and semi-field research examining the relative amount of vapor phase movement of the new form in comparison to existing amine and ester forms of the herbicide showed a consistent level of reduced volatility.  Large-scale field flux studies, carried out in 2010 and 2011, showed an up to 13-fold reduction in mass loss versus the 2,4-D dimethyl amine and low-volatile ester forms.  These flux results can be extrapolated to meet risk assessment and product stewardship needs by employing environmental models.

^™Enlist is a trademark of Dow AgroSciences LLC. Components of the Enlist Weed Control System have not yet received regulatory approvals; approvals are pending.  The information presented is not an offer for sale. ©2012 Dow AgroSciences LLC

Glyphosate-resistant Palmer amaranth is the greatest pest management threat to Georgia cotton production.  To combat this pest, growers are using more tillage and more herbicides.  Herbicide input costs have more than doubled with growers’ currently spending $62.50 per acre.  Ninety-two percent of these growers’ are also hand weeding 52% of the crop at a cost of $23.70 per hand weeded acre.  Cotton producers desperately need more economically effective tools to manage glyphosate-resistant Palmer amaranth.  Enlist Cotton^[TM] [Dow AgroScience Trademark] would provide cotton tolerant to topical applications of glyphosate, glufosinate, and/or 2,4-D.  Weed management programs using mixtures of 2,4-D and glufosinate can effectively control glyphosate-resistant Palmer amaranth and reduce current herbicide costs.  However, the concern for potential 2,4-D volatility damaging sensitive crops nearby could limit adoption.  Therefore, research was conducted to compare volatility of 2,4-D when formulated as an Ester, Amine, or Choline salt. 

 The experiment was conducted at the Sunbelt Agriculture Expo in Moultrie, GA during September 9-11, 2010 and August 30-September 2, 2011.  Each formulation of 2,4-D at 2 lb ae/A plus glyphosate at 2 lb ae/A was applied on a 90 foot by 90 foot block with treated blocks being at least 800 feet apart.  Treatments were applied to an 88% sand soil with 10 to 20% of the soil covered with plant debris.  Maximum soil temperatures ranged from 99 to 113 F and the entire study area was irrigated the day prior to experiment initiation.  Immediately after application, cotton plants grown off site in 8-inch diameter cotton pots were placed along transects oriented in 8 directions (S, SW, W, NW, N, NE, E, SE) at distances of 5, 10, 20, 40, 80, and 160 feet from each treated block.  Four cotton plants (5 to 7-lf) were placed at each direction-by-distance location and allowed to remain in-field for 48 hours before being removed.  Four additional plants were placed at each location and were allowed to remain on-site for the first 24 hours after application.  A third set of four plants were placed at each direction-by-distance from 24 hours after application through 48 hours after application.  Additionally, two 40-inch tall by 48-inch wide by 12-feet long tunnels covered with plastic were placed over part of the treated areas for each 2,4-D formulation.  For each tunnel, 10 cotton plants were present for the following: full 48 hours, the first 24 hours, or the second 24 hours.  Once various time intervals expired, plants were removed from the experimental area and transported 35 miles to TyTy, Georgia where they were placed under irrigation and allowed to grow.  Visual injury, cotton heights, and nodes were measured; however, visual injury 21 to 27 day after treatment is reported. 

When plants remained at the experimental site for the entire 48 hours and data was pooled over years and direction, the Ester formulation injured cotton 63, 57, 48, 29, 13, and 2% at distances of 5, 10, 20, 40, 80 and 160 feet, respectfully.  Less than 2% visual injury was detected with the Amine formulation and only at the distances of 5 and 10 feet from the treated area.  No visual injury was detected with the Choline formulation at any distance.  For plants present during the first 24 hours after application only, the Ester formulation injured cotton 58, 55, 44, 24, 8, and 2% at distances of 5, 10, 20, 40, 80, and 160 feet, respectively.  For plants brought into the experimental area 24 hours after initiation and allowed to remain at the site for the following 24 hours, the Ester formulation injured cotton 23, 18, 14, 7, 2, and 0% at distances of 5, 10, 20, 40, 80, and 160 feet, respectively.  No visual injury was observed with the Amine or Choline formulation when plants remained at the site for only a single 24 hour period. Direction influenced injury observed by the Ester formulation each year.  As expected, the amount of visual injury observed was greatest along transects in which the majority of winds were blowing for each day (range of 0 to11 mph each day and year). Maximum soil temperatures ranged from 125 to 135 F under tunnels each year.  Averaged over years and tunnels, the Ester, Amine, and Choline formulations injured cotton plants remaining under the tunnels for 48 hours 76, 13, and 5%, respectfully.  Plants present for the first 24 hours were injured 71, 4, and 2% by the Ester, Amine, and Choline formulations, respectively, while 47, 1, and 0% injury was observed for plants present during the second 24 hour period.

Dicamba is a synthetic auxin herbicide shown to be efficacious on numerous annual and perennial dicotyledonous weeds, including glyphosate-resistant weeds such as pigweed spp. (Amaranthus spp.), horseweed (Conyza canadensis), and common ragweed (Ambrosia artemisiifolia). Recently, Monsanto announced development of dicamba-resistant cotton and soybean genetics with intentions to stack the genes for dicamba, glufosinate, and glyphosate tolerance. Utilizing a tank-mix of dicamba and glyphosate has been shown to lead to antagonism of the activity of glyphosate on grasses. A prior field study indicated possible herbicide antagonism between glyphosate and dicamba with barnyardgrass (Echinochloa crus-galli). In that experiment, grass control was not significantly different between dicamba formulations; however, rate of dicamba did affect glyphosate efficacy.

Thus, a greenhouse study was implemented to determine absorption and uptake of glyphosate in response to the presence of dicamba, and to determine the ability to overcome possible antagonism by increasing rates of glyphosate.

Treatments included 0.28, 0.56, and 0.84 kg ae/ha of glyphosate as well as, a set of similar glyphosate rates that included the addition of 0.56 kg ai/ha diglycoamine dicamba. A radio labeled C¹⁴_-glyphosate was utilized in and added to a small portion of the prepared spray solution. Plants were treated with the radio labeled spray solution on the 2^nd leaf from the top midway between the leaf tip and collar on the adaxial surface. At 24 hours after treatment, the treated area was washed with water and chloroform. The plants were then excised and partitioned.

The majority of the C14 recovered from the leaf washes was found in the aqueous fraction.  When applied alone, the highest rate of glyphosate resulted in the greatest absorption of glyphosate.  The addition of dicamba to the treatment solution resulted in decreased glyphosate absorption for some treatments.

Pest control is greatly affected by the quality of the application. Hence, the effort in this area. Pesticide Application Technology is taught at many programs, the most intensive being our three day Custom Application Training.

            In late February of each year since 1990 a Custom Applicator Intensive Training Seminar has been conducted at Hastings Community College in Hasting, NE. Following the two-day seminar is a one day Pesticide Certification for Custom Application.The Pesticide Certification consists of training in the general standards and ag plant categories. Personnel from the Nebraska Department of Agriculture are present and do the testing in both areas.

            The custom applicator training starts with a class survey using “clickers” to determine their years of experience, job knowledge, and performance levels. Other information which includes acres sprayed, types of equipment, custom rates and problems encountered. Professional application which includes attitudes, getting to the right field, how to spray a field, mixing, and customer relations is included in the next session. A workshop is held on liquid calibration and calculations. This includes calculating speed, nozzle output and nozzle spacing along with information on different nozzle types and uses, mixing, drift control nozzle, spacing and boom height, how nozzles are rated, how spray solutions affect nozzle output, pressure changes, nozzle overlap, and how to best set up both high capacity and low capacity ground sprayers.

            Sessions concerning dry fertilizer application and markers (spraying a field, treating spots in a field, what to do when your marking systems or Auto-Steer breaks down along with the plus and minus of each kind of system) are included in the training. Monitors, rate controllers, and new developments in application technology are discussed in a session which also includes direct injection, spatially variable applicators, and the global positioning and information system. The first day is concluded with training on tank cleaning which includes disposal of rinsate, left over materials, reducing leftovers, tank contamination, pressure and triple rinsing and an optional work study that evening on calibration and calculations.

            The second day begins with training on compatibility and mixing order. This is followed by the applicators divided into four groups: maintenance and operations, spray/liquid, group problem solving and weed identification for hands on training. Each of these one-hour and 15 minute sessions are concluded with testing in that category which includes both days of training. The groups are rotated through all four areas. The training is completed with a session on doing a professional job and the awarding of certificates to those who passed the tests. From comments, interest and the survey filled out by the participants at the end of the training the seminar has been especially valuable.

            Materials used at the Custom Applicator Training and other training meetings include nozzle kits, spray nozzle catalogs, spray tables, sprayers, NebGuides, Weed Management Guides, and PowerPoints which includes the use of clickers,.

Spray droplet size has been closely correlated to drift. Many studies have been conducted to show that as droplet size decreases, drift potential increases. In order to reduce drift, the easy recommendation is to increase droplet size; however, there are herbicides that loose performance when droplet size increases to larger spray qualities. A spray quality trial was conducted at four locations in Nebraska to determine the effects of droplet size on weed control for different herbicides.  The four sites were Bancroft, Clay Center, Cortland, and Elba, NE.  There were five different nozzles tested.  Each nozzle was used to spray cloransulam, glyphosate, clethodim, dicamba, and fomesafen. All plots consisted of two rows of planted non-traited corn, non-traited soybean, grain amaranth, velevetleaf, and flax and a naturally emerging foxtail population.  All plots were 1.7 m wide and spanned the planted rows of crops and weeds.  The nozzles used for the study were XR11003 (Fine/Medium spray quality), XR11002 (Fine), TT11002 (Medium), AIXR11002 (Coarse), and AI11002 (Extra Coarse) based on the TeeJet Catelog 51.  Treatments were arranged in a randomized complete block design and were replicated 4 times at each site.  Treatments were sprayed at 94 L/ha and all herbicides were used at 50% of the recommended rate. (Note – While it is not recommended that herbicides be used at 50% of the recommended rate for weed control, greater separation between nozzles is observable when herbicide rates are reduced.)  Plots were rated using visual estimations of injury on a 0-100% scale where 0 is no observable injury and 100 represents all plants of a particular species were dead in the plot. 

While we were not able to get all species well established in all locations, a general trend was clearly observed between the chemical compounds used. Efficacy was not compromised when using nozzles that produce large droplets for chemical compounds with systemic activity while contact herbicides generally had better performance using nozzles that did not produce Coarse or Extra Coarse spray qualities. The ideal spray quality depended on the herbicide being used and the species being targeted. The 280 g ae/ha rate of glyphosate was too effective to separate out differences between the spray qualities. However, work done in the past suggests that this translocated herbicide performs as well or better with Coarse and Extra Coarse spray qualities as it does with smaller spray qualities. Dicamba was similar with no difference between spray qualities. Clethodim and fomesafen had as much as 30% decrease in efficacy when spray quality was Coarse or Extra Coarse. The results for cloransulam varied greatly between species. Droplet size is important as tank-mixtures of herbicides are used to manage resistant weeds.

The objective of this field research was to develop small-scale (backpack and hand boom) methodology for studying actual particle spray drift, rather than “simulated” drift that is commonly used in weed science research.  Particle drift was evaluated by applying a tank mixture of dicamba (560 g ae/ha, Clarity® herbicide) plus glyphosate (840 g ae/ha or 1120 g ae/ha, Roundup WeatherMAX® herbicide) using four different #2 nozzles, providing spray droplets in the desired spray quality categories (based upon the ASABE standard 572.1, March, 2009): fine  droplets were attained using the XR TeeJet® nozzle (XR); medium to coarse droplets were attained with the Turbo TeeJet® nozzle (TT); very coarse to extra coarse droplets were achieved with the Air Induction TeeJet® nozzle (AIXR); and ultra coarse droplets were achieved using the Turbo TeeJet® Induction nozzle (TTI).  Plots were established by planting long strips (>350 m) of Roundup Ready® corn (8 rows), flanked on each side by 35 to 70 meter wide fields of Genuity® Roundup Ready® soybean.  Care was taken to plant the corn perpendicular to the normal prevailing winds during the summer months.  The herbicide treatments were applied POST to corn, when the soybeans were between the V3 and V6 stage.  Plot sizes varied by site, ranging from 2 to 3 m wide and 9 to 31 m long.  Buffer area equal to plot length were included between the plots to prevent accidental cross contamination of the drift field.  Treatments were installed on days when wind speed was relatively steady and as close to perpendicular to the direction of the corn rows as possible.  Wind speed and wind direction was continuously monitored and spray start and stop times recorded for each plot so drift from individual plots could be correlated with associated wind conditions.  Each of the different nozzle types was calibrated for the desired output (94 to 188 L/ha) and ground speed (3 to 4.8 km/hr).  The criteria used to assess drift distance of the dicamba plus glyphosate tank mixture was to record the maximum distance into the soybean field where 5% visual crop malformation was observed; 5% malformation is defined as the newest expanding trifoliate showing leaf cupping along the margins of all three leaflets.  Distances were recorded for 3 to 5 transects from the edge of the treated plot. 

Monsanto researchers completed two different studies during the 2010 field season.  There were 28 locations for the first study where drift distance was evaluated and six locations for the second study where drift distance, plant height and yields were also evaluated.  The distance to which drift was observed was associated with the percent fine spray droplets (<150 microns) produced by the nozzles in both studies.  The drift field was the greatest with the XR nozzle, and the lowest for the TTI nozzle in both studies.  Drift distances for the TT and AIXR nozzles were intermediate between the TTI and the XR nozzles.  Higher wind speeds resulted in greater drift distances.  In a second drift study the same nozzles and the same methods were used as in the first study but evaluations of visual soybean malformation, plant height and soybean yield was made starting from the edge of the treated plot.  The greatest drift was observed with the XR and TT nozzles, and the least drift with the TTI nozzle, with the AIXR being intermediate.  Soybean yields were not affected past 3 m from the edge of the treated plot and when the visual crop response was less than 45%.  When a drift reduction agent (InterLock® from Winfield Solutions™) was included at 46 ml/ha in the tank-mix of dicamba and glyphosate in the second study, statistical differences between nozzles, in regard to drift distances, were not observed.   In laboratory tests, InterLock reduced the percentage of fine spray droplets for the XR (-17%) and AIXR (-30%) nozzles, but not the TT or TTI nozzles. 

The results of this field research shows that nozzle selection and wind speed are important criteria in drift potential of spray applications.  The results also show that the methodology used is a viable method quantifying drift control strategies for dicamba herbicide.

Roundup®, Genuity® and Roundup Ready® are registered trademarks of Monsanto Company.

Clarity®is a registered trademark of BASF Corp.

TeeJet® is a registered trademark of Spraying Systems Company.

InterLock® is a registered trademark of Winfield Solutions™

The U.S. Environmental Protection Agency is expected to establish a drift reduction technology (DRT) program to minimize spray drift onto non-target areas and organisms.  Drift reducing adjuvants will be used as DRT in agricultural spray applications. Field studies and Laser Particle Size Analysis were conducted to determine the effect of four oil emulsion drift reduction and deposition adjuvants on glyphosate performance. Some adjuvants increased efficacy, while others reduced efficacy of glyphosate. Additional herbicides including clethodim, saflufenacil, florasulam + pyroxsulam + fluroxpyr and 2,4-D were tested with AG 02013 adjuvant. The additional herbicides tested in the field showed equal or greater performance when AG 02013 was used. Laser particle analysis was done using a Sympatec laser diffraction particle size analyzer in a low speed wind tunnel. The proportion of fine droplets (< 105 μm) was decreased with several of the adjuvants, without a substantial increase of ineffective large droplets. It is likely that the decrease in fine droplets as a result of using AG 02013 results in less spray volume lost to drift and thus increased herbicide efficacy in the field. This oil emulsion drift and deposition adjuvant can be an effective tool for achieving drift reduction and optimizing herbicide performance.

The occurrence of herbicide resistant rigid ryegrass in cereal farming systems across four states in southern Australia is currently a significant issue. Random weed surveys across south eastern Australia have revealed high levels of resistance to ACCase- and ALS-inhibiting herbicides. In addition, trifluralin-resistant rigid ryegrass has been confirmed in several regions in South Australia and Victoria.  In situations where rigid ryegrass possesses multiple resistance to trifluralin, ACCase- and ALS-inhibiting herbicides, there are limited in-crop selective herbicide options available.

Since 2005, extensive research has occurred to identify herbicides that control multiple resistant rigid ryegrass in cereal crops. As an outcome of this research, two pre-emergence herbicide products, pyroxasulfone (Sakura^® ; Bayer-Kumiai) and prosulfocarb + S-metolachlor (Boxer Gold^® ; Syngenta) have been registered in Australia.  Both herbicides control multiple-resistant rigid ryegrass that is not controlled by trifluralin and can be used in wheat sown with low disturbance seeding systems. Pyroxasulfone has the added advantage of extended weed activity of up to three months whereas the effective activity period of prosulfocarb + S-metolachlor is approximately 3-4 weeks. In addition, studies have shown that pyroxasulfone is safe to use in zero disturbance disc systems in wheat, although this use is not included in the current registration. Prosulfocarb + S-metolachlor is also registered for use in barley and has shown promising early-post emergent activity on rigid ryegrass. The option of having alternative mode of action herbicides to the ACCase-inhibitors, ALS-inhibitors and dinitroanilines that are effective on multi-resistant rigid ryegrass is of significant importance to Australia cereal growers.

Grain producers in southern Australia have shifted to lower disturbance seeding systems resulting in almost 80% of growers adopting no-till seeding practices.  The dominant form of no-till seeding is a knife-point system where 17 mm points cut a slot in the soil into which the crop seed is placed.  At the same time, resistance to post-emergent herbicides in the major grass weed, rigid ryegrass, occurs on more than 75% of cropped fields. Without post-emergent herbicides to control weeds, other practices need to be used. The herbicide trifluralin has been widely adopted in no-till farming for rigid ryegrass control, despite the risks of crop damage.  Crop damage is managed by spraying in front of the seeder where the knife points throw the herbicide treated soil out of the crop furrow and onto the inter-row.  In recent years, resistance to trifluralin in rigid ryegrass has started to increase and it is now found on more than 25% of fields in some parts of Victoria and South Australia.  At the same time there is increased interest in disc seeding systems that are not compatible with trifluralin use. 

This research was conducted to examine the utility of alternative pre-emergent herbicides for rigid ryegrass control in cereal cropping using different seeding equipment.  Of the herbicides examined, trifluralin, triallate, prosulfocarb + metolachlor and pyroxasulfone were safe to use in wheat when the knife-point and press-wheel seeding system and provided effective control of trifluralin susceptible annual ryegrass.  Dimethenamid-P controlled rigid ryegrass, but was less safe on wheat.  With disc seeding equipment, herbicide damage depended on the amount of disturbance created in the crop row.  High disturbance disc seeding equipment increased safety of trifluralin, dimethenamid-P and prosulfocarb + metolachlor.  With low disturbance seeding equipment, pyroxasulfone was the only safe herbicide with all other herbicides increasing crop damage. Dry crop residue increased the safety of trifluralin and dimethenamid-P to wheat, but tended to decrease the safety of prosulfocarb + metolachlor.  Activity of trifluralin and triallate on rigid ryegrass control was lower in low disturbance disc seeding systems, because these herbicides require incorporation to reduce volatilisation losses.  This research has shown that new pre-emergent herbicides, particularly pyroxasulfone, have the potential to successfully control multiple resistant rigid ryegrass in disc seeding systems.

Spring Wheat Seed Size and Cultivar Effects on Yield and Wild Oat, Avena fatua, Interference. R.N. Stougaard¹, Q. Xue², ¹Northwestern Agricultural Research Center, Kalispell, MT, ²Texas Agrilife Research and Extension Center, Amarillo, TX. 

We previously reported that, within a single cultivar, spring wheat plants grown from large seeds had significant benefits in reducing yield loss and suppressing wild oat as compared to similar plants derived from small seeds. The question remains as to whether or not the effect of seed size on wheat competitive ability is consistently expressed among different wheat cultivars.  The objective of this study was to investigate the association between seed size and competitive plant traits among genetically diverse spring wheat cultivars. The factorial treatment arrangement consisted of two wild oat densities (0 and 175 plants m^-2) and 8 spring wheat cultivars that varied in seed size. Seed size, expressed on a thousand kernel weight (TKW) basis, ranged from 52 to 27g. The experimental design was a split-plot, randomized complete block with four replications. Wild oat densities and spring wheat cultivars comprised the whole- and sub-plot treatment effects, respectively. Spring wheat competitive ability increased with seed size, significantly reducing wild oat biomass and seed production.  Spring wheat plants derived from the largest seed reduced wild oat biomass and seed production by 42 percent compared with plants grown from the smallest seed.  Concurrently, spring wheat biomass and yield increased with seed size both in the presence and absence of wild oat competition. Among the traits evaluated, spring wheat biomass and grain filling period were most strongly correlated to seed size, while percent ground cover and maximum emergence rate were most strongly correlated with reductions in wild oat biomass.

In recent Canadian Prairie field surveys, volunteer canola was detected in 10% of 3806 fields and ranked as the 14^th weed species in terms of relative abundance. Substantial combine-harvest seed losses continually supplement volunteer canola seedbanks. Canola biology allows seed to persist for several years in farm fields. Research to assess on-farm harvest losses of canola and their causes is currently being conducted across western Canada in Alberta, Saskatchewan and Manitoba.  In approximately 100 fields each year in 2010 and 2011, canola harvest losses averaged over 3,000 seeds m^-2 (> 2 bu ac^-1).  These losses are not only important from a weed management point of view, but also from a revenue loss standpoint.  Given the fact that favourable canola prices are leading farmers to grow canola more frequently than ever before (canola acreage surpassed wheat acreage in many areas of the Prairies); we expect that volunteer canola will continue to increase in abundance and provide management challenges for crop producers. Other factors that may impact canola harvest losses such as canola variety and combine type, speed and settings are also being studied.

Glyphosate Resistant Conyza bonariensis Is Now Managed Effectively Using IWM in Sub-Tropical Cropping Systems of Australia.

Steven Walker*¹, Michael Widderick², Anthony Cook³, ¹The University of Queensland, Toowoomba, Australia, ²Department of Employment, Economic Development and Innovation, Toowoomba, Australia, ³Department of Primary Industries, Tamworth, Australia

The sub-tropical cropping region of Australia consists of diverse rotations of winter crops, such as wheat, barley and chickpea, and summer crops, such as sorghum, sunflower, mungbean and cotton. These are interspersed with a 6-12 month fallow to conserve soil moisture for the following crop. In the last decade Conyza bonariensis, known as flaxleaf fleabane in Australia, has become widespread and is one of the most difficult-to-control weed of this region, particularly in the glyphosate-based, zero-tilled fallows.

We developed an effective IWM package based on a series of 18 greenhouse and field experiments, which investigated the extent of glyphosate resistance, chemical and non-chemical tactics for fallow and in-crop weed control, as well as the impact of weed size and soil moisture stress on herbicide efficacy. The IWM package focused on key parts of the C. bonariensis life cycle, incorporating a variety of tactics aimed at the depleting the seed-bank, controlling seedlings, and preventing seed-set on sprayed survivors.

The majority (57%) of the tested populations from this cropping region had 2 to 5 fold resistance to glyphosate. Susceptible populations were controlled effectively with glyphosate irrespective of weed size and moisture stress, but control of most glyphosate-resistant populations decreased significantly with increasing weed size and/or moisture stress.

In the field, ten phenoxy and pyridine herbicides gave 77-98% control of small rosettes (<10cm diameter), but efficacy decreased by an average of 39% when 10-15cm rosettes were treated. In the greenhouse, increasing weed age, but not changes in soil moisture, significantly decreased efficacy of these herbicides from 96 to 65%.

The residual herbicides atrazine, diuron, chlorsulfuron and isoxaflutole gave 94-100% control of new emergences for three months in fallows preceding and in early growth of sorghum, cotton, wheat and chickpea respectively.

Decreasing wheat rows from 50 to 25 cm was substantially more effective than doubling wheat density from 50 to 100 plants per m² in suppressing fleabane biomass and seed production.

In fallows, a range of knockdown herbicides and glyphosate mixes provided 62-100% control of young seedlings (≤1 month old). However efficacy decreased significantly with increasing weed age. The consistently most effective treatment for large rosettes was the double-knock (sequential) tactic of glyphosate + (2,4-D + picloram) followed seven days later with paraquat, providing 92-100% control. When this double-knock tactic included atrazine or diuron in the second knock, 100% control of pre-bolting weeds and subsequent emergences was achieved.

The strategy of using a residual and double knock in the fallow followed with sowing a competitive crop and applying a post-emergence phenoxy or pyridine herbicide to young C. bonariensis will greatly reduce the impact of this weed on crop productivity, minimise replenishment of the seed-bank and markedly lower the risk of further evolution of glyphosate resistance.

s.walker11@uq.edu.au

Effective Herbicide Options for Control of Glyphosate Resistant Echinochloa colona.

M. J. Widderick^*1, S. R. Walker², L. R. Boucher³

¹Department of Employment Economic Development and Innovation, Toowoomba, Australia, ²The University of Queensland, Toowoomba, Australia

The sub-tropical grain region of Australia stretches from northern New South Wales to central Queensland, where both summer and winter crops are grown.  Between crops it is common to include a 6-12 month fallow (non-crop period) to conserve soil moisture for the following crop.  Zero-tilled, chemical fallows are common and glyphosate is commonly relied upon for weed management. 

Echinochloa colona (called awnless barnyard grass in Australia) is a common weed of summer fallows and crops in this region. As a result of an over-reliance on glyphosate, populations of awnless barnyard grass have developed glyphosate resistance, with the first case confirmed in 2007. Since this time, 19 more resistant populations have been identified in this region, all in glyphosate-based chemical fallows. Glyphosate-based fallows continue to be relied upon and there is a great risk for more awnless barnyard grass populations to become glyphosate resistant.

Effective herbicide strategies were identified for fallow management of glyphosate-susceptible and resistant awnless barnyard grass using results from three field (glyphosate-susceptible populations) and two greenhouse experiments (with both glyphosate-susceptible and -resistant populations).  

Alternative knockdown herbicides were evaluated either alone or in mixture, or as part of a double-knock.  Double-knock refers to the sequential application of two different weed control tactics applied in such a way that the second tactic controls survivors of the first tactic. In this study double knock refers to the sequential application of glyphosate either alone or in mixture followed by an application of paraquat alone or in mixture with a residual herbicide. Timing of herbicide application was also evaluated with a delay of 7-14 days between treatments.

Double-knock treatments achieved high levels of knockdown control (>95%) in the field, and in the pot trials double knock treatments were consistently highly effective in controlling both glyphosate-susceptible and -resistant plants, providing 100% control.

The inclusion of residual herbicide significantly reduced the emergence of barnyard grass. When comparing against the standard double knock without residual treatment (glyphosate 720 g ai/ha followed by paraquat 400 g ai/ha), the treatments that gave the greatest reduction in emergence were metolachlor and metolachlor + atrazine with 95 and 87% reduction respectively.

Paraquat alone at either a low (250 g ai/ha) or high (500 g ai/ha) rate provided 100% control of both glyphosate-susceptible and -resistant populations. A low rate of paraquat applied late provided only 78.5% biomass reduction.

Resistance status had a significant impact on the level weed control with glyphosate. In general glyphosate treatments applied to resistant plants provided less reduction of biomass than achieved for susceptible plants at the same rate. For example, glyphosate at 158 and 315 g ai/ha applied to glyphosate-resistant plants provided an average 52 and 49% less reduction in biomass when compared with biomass reduction of glyphosate-susceptible plants.

Prevention and management of glyphosate-resistance should be possible with the introduction of a wide range of management options aimed at 100% seed set control in summer fallow. The introduction of non-glyphosate knockdown herbicides will be essential and these should be combined with residual herbicides. To obtain near 100% control in fallow, the double-knock tactic needs to be used.

michael.widderick@deedi.qld.gov.au

Adoption of no-tillage agriculture holds a number of benefits including soil and water conservation, potential improvements in soil quality, reduced energy costs, and implications for carbon sequestration.  At the same time, no-tillage systems rely greatly on herbicides for weed management increasing some environmental risks and the evolution of herbicide resistant weeds.  Diversifying the crop rotation is thought to help alleviate many pest problems including weeds and is probably even more important for breaking pest lifecycles in continuous no-till systems.   In no-till systems, herbicides substitute for tillage for control of any emerged vegetation at the time of crop establishment.  Nonselective burndown herbicide options include glyphosate, paraquat, and perhaps glufosinate, with glyphosate being the dominant herbicide choice in many no-till systems.  A number of selective herbicides may also be included depending on the crop and application timing.  However, for a number of reasons, glyphosate is often applied without tank-mix partners with reliance on this single mode of action for control of all emerged species.  This is a particular concern for the evolution of herbicide resistant weeds and a key problem with minor use crops and crops that have few herbicide alternatives.   The inclusion of other nonresidual could help broaden the weed control spectrum and reduce the selection pressure for herbicide resistant weeds.   The herbicide 2,4-D is relatively short lived and could be especially useful for broadleaf weed control.   Although this plant growth regulator herbicide is frequently used with glyphosate in no-till corn and soybean, labeling restrictions and concerns about crop injury limit its utility in many other crops.

To test the potential utility of 2,4-D in no-till establishment of some minor use crops, an experiment was conducted in early and then in late summer at the Rock Springs Agronomy Research farm.   The ester formulation of 2,4-D was applied at 0.28, 0.56, 1.12, and 2.24 kg ae/ha to soybean or wheat stubble.  The amine formulation of 2,4-D and dicamba were also included at 0.56 kg ae/ha each.  Alfalfa, red clover, and hairy vetch, were seeded the same day of herbicide application (0 day), and 7, 14, and 21 days after herbicide application.  In addition to these three legumes, crimson clover, canola, and forage radish were included in the late summer experiment.  About one month after seeding, crops were evaluated visually for injury and crops in selected treatments were harvested for biomass about 8 weeks after seeding.

In the late summer seeding on the day of herbicide application, 2,4-D LVE injury increased with rate and  ranged from 32 to 85% for alfalfa, 27 to 80% for red clover, 20 to 72% for crimson clover, 27 to 70% for hairy vetch, 21 to 81% for canola, and 16 to 76% for forage radish.   By 7 days after application, alfalfa injury did not exceed 19%, red clover 17%, crimson clover 11%, hairy vetch 14%, canola 29%, and forage radish 12%.  By 14 days after application, crop injury was mostly undetected even at the 2.0 lb rate.  Crop injury from the amine formulation was similar to the ester.  Dicamba crop injury was observed on all species at up to 7 days after application, but had also mostly dissipated by 14 days.  Rainfall during this time exceeded the average and may have helped increase the rate of dissipation.  The results from this trial suggest that 2,4-D tank mixtures may have greater utility for burndown application in minor use cash crops as well as some cover crops.

Structure of Weed Communities in Winter Wheat Field Due to Long-Term Fertilization. L. L. Tang^{1, 2}, K. Y. Wan¹, C. P. Cheng¹, R. H. Li³, J. F. Pan¹, Y. Tao¹, F. Chen¹, ¹ Key Laboratory of Aquatic Botany and Watershed Ecology, Wuhan Botanical Garden, Chinese Academy of Sciences, Wuhan, ² Graduate University of Chinese Academic of Sciences, Beijing, ³ Institute of Plant Protection and Soil Science, Hubei Academy of Agriculture Sciences, Wuhan. 

    Abstract: Manipulation of crop fertilization was considered to be an important component for integrated weed management systems. A long-term fertilization experiment (15 years) was conducted to evaluate the effect of fertilization on the floristic composition and diversity of weed communities and the effect of fertilization and weeds on the growth of winter wheat. Fertilization treatments consisted of six combinations of different rates of N, P and K fertilizers including the control (no fertilizer). Weed surveys were conducted during 2009 and 2011. Effects on weed communities were characterized in terms of growth and species diversity. Nutrient contents of plant biomass were also measured. Tender catchweed bedstraw (Galium aparine L. var. tenerum Rcbb.), common vetch (Vicia sativa L.), geminate speedwell (Veronica didyma Tenore.), common cirsium (Cirsium segetum Bge.), and carolina geranium (Geranium carolinianum L.) accounted for 90.8%, 93.8% and 80.1% of the total weed species in 2009-2011. Weed density and species richness were influenced both by fertilization and environment conditions (year). Balanced fertilization tended to greatly suppress the growth of weed, which could be explained by the greater and less nutrient accumulation in winter wheat and weed plants. Soil nutrient in the manipulation of weed community composition and construction in the study was in the P>N>K sequence. Regression linear analysis indicated wheat biomass had a significantly negative correlation with N (R²= - 0.455, P=0.0001) and K (R²= - 0.194, P=0.0005) content of weed. This work contributes to aid development of fertilization strategies as components of more comprehensive integrated weed management programs. [E-mail: tll20022003@yahoo.com.cn (L. L. Tang)]

Dodder is an obligate parasitic plant that is a serious pest in many crops including carrots, tomato, alfalfa, and cranberry and is also problematic in landscape and ornamentals.  Dodder is a prodigious seed producer and the seeds can persist for decades.  An infected cranberry vine is depleted of nutrients and photosynthates, reducing its ability to produce commercial yields and compromising the production of buds that will produce the following year’s crop.  There is not a single herbicide or control tactic in cranberry that manages dodder to desired levels.  An integrated approach must be taken but growers struggle to define an appropriate program that will consistently work on their farm. 

Based on grower-reporting forms submitted to Massachusetts, we estimate that more than 800 ha are seriously impacted by dodder in any given year and another 800 ha are at least moderately affected (about 30% of the industry).  Management options available to growers of annual crops (e.g., crop rotation, resistant varieties) are not possible in cranberry since it is a perennial crop.  The inability to manage dodder would seriously jeopardize the economic profitability of MA cranberry farms.  Consistent management of dodder is hampered by the lack of knowledge about the biology and taxonomy of the parasite, variable control of herbicides (perhaps related to application method), and more recently, the politics of trade negotiations.

The species found on MA cranberry bogs has been assumed to be swamp dodder, Cuscuta gonovii.  We have seen variations in stem color, stem thickness, and temporally distinct flowering times and speculated that some of these variations in phenotype may actually be variations in genotype. Concurrently, growers and researchers alike have experienced and reported variable results and/or failures when managing dodder with herbicides.  In particular, the use of quinclorac (3,7-dichloro-8-quinolinecarboxylic acid) in Wisconsin has given excellent and consistent control of dodder while MA farms treated with quinclorac have yielded inconsistent results.  A 2011 survey of MA growers who used quinclorac indicated that one-third reported good to excellent control, while half reported fair control and 20% reported poor control.  Research trials to date have not been able to tease out these efficacy differences.

We considered that differences in dodder species or ecotypes may play a role in the inconsistent management of dodder on some farms.  During the 2011 season, we collected dodder samples from 41 sites.  Dodder samples were sent to a DNA laboratory where polymerase chain reaction (PCR) was used to identify species.  Preliminary results from 23 bogs indicate that at least three different species are present in Southeastern Massachusetts.  Evaluation of species response to various control strategies are planned for 2012.

Quinclorac is a promising chemical for dodder control that has recently become available to cranberry growers. The use of this product by the majority of cranberry growers (primarily those in the Ocean Spray Cooperative) is restricted due to foreign market maximum residue level (MRL) issues.  Ocean Spray and other handlers are in the process of developing policies and procedures that will enable them to segregate and distributed quinclorac-treated fruit in the domestic market.  In 2011, some growers had to use less effective herbicides for dodder management due to procedural hurdles.  Until politics can resolve the foreign MRL issue, the domestic market is the only outlet for cranberry fruit treated with quinclorac.  The combination of these varied issues makes the management of dodder for the cranberry industry very difficult.

Plant community restructuring successfully ousted invasive weed mile-a-minute (Mikania micrantha). M. Li^*1, Q. Zan², P. Wei¹, Q. Guo³, ¹Sun Yat-sen Univ, Guangzhou, China, ²Shenzhen Wild Animal Rescue Center, Shenzhen, China, ³ Shenzhen Wildlife Protecting Administration, Shenzhen, China.

Mile-a-minute is a perennial herbaceous to semi-woody vine of Asteraceae. It is an economical and ecological nuisance in wide areas of the old world as well as in southern China. The fast growing photophilic vine readily climbs up, overtops small trees and shrubs and forms a thick covering that smothers plants underneath. A wide area field investigation conducted in south China in 2000-2001 inspired hope that restructuring vegetation invaded area into an environment unsuitable for mile-a-minute to live was highly possible.

Two 10 hm² survey plots in invaded areas within a closed off area intended for natural forest recovery were set up in 2001. The then vegetation of invaded areas was disturbed forests, abandoned orchids and other economic plants. Mile-a-minute spread fast and heavily covered the vegetation in 1990s, killing trees and shrubs, and forming many large flat mono layer patches completely covered by mile-a-minute after covered trees die and then fell down.

Idealized criteria for a plant species as community restructuring agents were set up for species selection. Several important preset criteria were: fast growing, dense canopy, broad crown and able to grow >6M. Eighteen local tree species were selected based on their closeness to the criteria. Their saplings as community restructured agents were planted within those large patches completely covered by mile-a-minute in the two survey plots in 2001 and 2002. All fostering was terminated in December 2002. Two hundred and fifty-five trees were tagged and monitored in certain interval periods.

Results indicated that, among eighteen species used, the saplings of Macaranga tanarius and Heteropanax fragrans grew particularly well under mile-a-minute stress. In 2006, they formed continuos close canopy and never were completely covered by mile-a-minute although without any human intervention. Some other species, such as Liquidambar formosa and Schima superba, could hardly survive in the same condition. Ten years after the restructuring, no vine could ever climb to the canopy.

In conclusion, selection of proper species that would continue to grow in the present of mile-a-minute was crucial so that fostering would be minimized, and restructured community did ousted mile-a-minute permanently. This simple but effective mesure could be used elsewhere.

LSSLMG@mail.sysu.edu.cn

Experiments were conducted in Fayetteville and Keiser, AR, to investigate the level of post-dispersal herbivory in barnyardgrass, johnsongrass, pitted morningglory, Palmer amaranth, and red rice, some of the important arable weeds in the Midsouth cropping region. Specifically, we attempted to understand the proportion of seeds that enter the active faction of the seedbank after loss through post-dispersal herbivory. The study represented late-season seed production by weed escapes; therefore, study sites (1 m² area) were over-seeded with respective weed seed to achieve a density level equivalent to 50% of the seed production capacity by an individual escape. A soil-filled plastic tray (area: 113 cm²) placed in the middle of the site and leveled to the ground served as a sampling unit. The bottom of the tray was replaced with a fine polyeythylene mesh screen capable of draining rain water, whereas the rim of the tray was sufficient to prevent seed escape through rain splash. The study was conducted in a factorial (two factor) randomized complete block design with three replications.  The first factor (weed species) consisted of five levels and the second factor (residue cover) was comprised of three levels, namely low, medium, and high residue. The experimental site was a freshly harvested soybean field where the soybean stubble served as a low residue cover, winter-annual weeds as medium cover, and a no-till fall rye as high residue cover. The study also consisted of control plots under each residue treatment where the trays were excluded from herbivory by covering with polyethylene mesh cloth. The experiment was initiated during early November and the samples (trays) were retrieved during early April, just before field operations began in this region. In each sample, the number of seeds lying on the soil surface was documented, and the soil was subsequently washed out to estimate the level of seed burial. Initial results suggest that the ability of the seeds to become buried within the top soil layer is an important factor affecting herbivory, irrespective of the residue cover. Seed herbivory was greater for red rice and pitted morningglory compared with the other species.

Choosing a competitive crop variety is often advocated as part of an integrated weed management. Ideally, a crop variety should be able to have a high yield under weedy and weed free conditions as well as be able to suppress weeds. However, very few cultivars are evaluated for weed competition and there only a few plant breeding programs that actively select for competitive crop cultivars. The objective of this talk is to discuss the costs and benefits associated with advocating competitive crop varieties in an integrated  weed management system. To do this we will present summary of IWM trials conducted by our lab in western Canada.  In peas, competitiveness is usually associated with vine length and the leafy characteristic. However, competitive with long vines leafy peas are highly susceptible to lodging and are usually avoided by all growers.  A separate experiment evaluated heritage, low input and modern high yielding varieties under organic production. Of all crops evaluated except wheat,   modern cultivars had the highest yield. In oat crosses were made between a competitive forage type oat and a high yielding semi-dwarf. Selections were made based on visual competitiveness and seed quality. None of the resulting genotypes suppressed wild oat better than the parent nor was there and significant difference e in yield.   We conclude that the expense, timeliness and unpredictability of elevating and breeding crops for weed competition make it a poor choice for an IWM. Frequently, the short life-span of crop varieties does not allow time for testing before they are replaced. In addition, the multiple quality traits that plant breeders select for make selecting for the polygenetic trait of competitiveness quite difficult. There are other tools in IWM that can give better and more consistent return for farmers. 

Using multiple cultural weed management practices as part of a whole-system approach is a guiding principle of ecologically based weed management. Cultural practices that may be weakly effective can provide acceptable weed suppression when they are used in combination, but determining which practices to combine is not entirely clear. Combining some practices can result in antagonistic effects, whereas others can interact synergistically. Although there is a rich body of literature on testing for synergism and antagonism between herbicides, relatively little attention has been given to developing systematic tests of synergism between multiple cultural, physical, and/or biological weed management practices. In addition to management practices whose effects act simultaneously, interactions between practices applied sequentially also have important implications for ecologically based weed management. Because some weed management practices can be density dependent (i.e., efficacy is greater at lower densities), previously applied practices can affect the efficacy of subsequent practices. Although not necessarily a synergistic interaction, such interactions between density dependent practices are important and deserve recognition. Harnessing synergistic interactions between practices applied simultaneously and strategic sequences of practices that result in effective non-chemical weed control is a promising solution to weed management challenges associated with herbicide resistance and organic cropping systems. Future research should aim to develop methods and approaches to testing the weed-crop competition, population, and community level effects of interactions between cultural, physical, and biological management practices. 

Cover crops can provide many benefits in agroecosystems, including the opportunity for improved weed control. However, the weed suppressive potential of cover crops may depend on the species (or mixture of species) selected and the method of cover crop termination and residue management. The objective of this study was to determine the effects of cover crop species diversity and termination method on weed biomass, density, community composition, and relative grain yield in an organic cropping system. A field experiment was conducted between 2009 and 2011 near Mead, NE where spring-sown mixtures of 2, 4, 6, and 8 cover crop species were included in a sunflower – soybean – corn crop rotation. Cover crops were planted in late-March, terminated in late-May using a field disk or sweep plow undercutter and main crops were planted within one week. Terminating cover crops with the undercutter consistently reduced early-season grass weed biomass and late-season broadleaf weed cover, whereas termination with the field disk typically stimulated grass weed biomass and total weed cover. The effects of cover crop mixture were not evident in 2009, but the combination of the undercutter and the most diverse mixture reduced early-season weed biomass by 48% relative to the no cover crop control (NC) in 2010. Cover crops provided less weed control in 2011, where only the combination of the undercutter and the two-species mixture reduced weed biomass (by 31%) relative to the NC. Weed community composition and species diversity were not influenced by cover crop mixture. However, termination with the undercutter reduced abundance of later-emerging summer annual weeds (velvetleaf [Abutilon theophrasti] and Amaranthus spp.) and promoted the presence of common lambsquarters (Chenopodium album) – an earlier-emerging summer annual weed. Termination with the undercutter resulted in relative yield increases of 16.6 and 22.7% in corn and soybean, respectively. In contrast, termination with the field disk resulted in relative yield reductions of 13.6 and 8.0% in soybean and sunflower, respectively. The strong influence of termination method highlights the importance of appropriate cover crop residue management in maximizing potential agronomic benefits associated with cover crops.

Integration of Cultural and Mechanical Weed Control Strategies Enhances Weed Control in Organic Cropping Systems. D. I. Benaragama and S. J. Shirtliffe, University of Saskatchewan, Saskatoon, SK.

ABSTRACT

Effective weed management strategies are limited in organic cropping systems as herbicide use is prohibited. Enhancing crop competitive ability by integrating both cultural and mechanical weed control methods is a key strategy in managing weeds in such instances. Yet, the relative efficacy of different cultural and mechanical strategies, their interactions, and additive effects when combined is not well known. The main objective of this study was to develop a competitive organic cereal cropping system integrating both cultural and mechanical weed control strategies. A study was carried out in two organically managed oat cropping systems in Saskatoon, Sk, Canada in 2008 and 2009. Three cultural practices; crop genotypes, (competitive) and (less competitive), planting densities (250 plants m^-2-standard, 500 plants m^-2-high), row spacings (11.5cm-narrow, 23 cm-standard), and post-emergence weed harrowing were factorialy applied in a randomised block design. Increasing the seeding rate increased the grain yield by 10.7 % and reduced weed biomass by 52 %. Competitive genotype reduced weed biomass by 22 % than non-competitive genotype. Post-emergence harrowing increased the grain yield by 13 % compared to the non-harrowed control. Moreover, harrowing reduced the weed density on three of the four site years tested. Despite individual effects, combining high crop density with post-emergence harrowing increased the grain yield up to 25 %. Furthermore, combined effect of high density, competitive genotype, and post-emergence harrowing decreased weed biomass by 71 % compared to the standard practices. The outcome of this study highlights that integrating both cultural and mechanical weed management practices is superior over the use of individual practices to manage weeds in organic cropping systems. steve.shirtliffe@usask.ca.

Key words- weed control, organic cropping systems, competitive ability, integration.

Canada thistle (Cirsium arvense) is a relatively common perennial weed that is difficult to control in organically managed cropping systems. A split plot experiment was conducted to evaluate the response of weeds and Canada thistle to different crops and weed management practices. Main plots were soybean, fresh market tomato, and a spring vegetable (radish) followed by buckwheat. Subplots were cultivated three times during the critical period in soybeans and tomatoes and then weeds were (1) controlled all season (no –seed threshold), (2) allowed to emerge and produce seed, or (3) mowed periodically. Weeds and Canada thistle densities were recorded every two weeks and biomass collected at the end of the growing season. In general, Canada thistle densities and biomass were lower in treatments where multiple tillage passes were possible. Thus Canada thistle was greatest in the radish-buckwheat treatment and lowest in the tomato treatment. No differences in Canada thistle biomass were found between the mowing and critical period treatments in soybean or in the radish-buckwheat treatment. Canada thistle biomass was greater in mowed plots than in the critical period plots in tomato. Weed densities differed among treatments in soybean and tomato, but yields were affected by the subplot treatments on tomato only. The results from the first year of this two year project suggest the importance of maintaining tillage options throughout the growing season to minimize Canada thistle growth.

Controlling johnsongrass (Sorghum halepense) in sugarcane is vital to achieve economically acceptable yields and to maintain ratoons.  Seedling johnsongrass can be controlled through application of preemergence herbicides and inter-row cultivation.  However, once rhizome johnsongrass becomes established within the sugarcane drill, the number of control options become limited.  Research was conducted at the USDA-ARS Sugarcane Research Unit in Houma, LA, to evaluate the effects of crop management practices on johnsongrass control and sugarcane production over a four-year sugarcane production cycle. The locations tested had a  history of johnsongrass infestation.  Tillage frequency was compared at three levels: conventional tillage (four inter-row tillage treatments each spring), reduced tillage (two inter-row tillage treatments), and no-till.  Three herbicide practices were compared: broadcast application of pendimethalin plus metribuzin (2.8 kg ha^-1 plus 1.1 kg ha^-1), banded application to sugarcane drill (90 cm band on a 180 cm row), and no herbicide application.  Three post-harvest residue management practices were compared: complete removal through burning, partial removal through brushing residue from the row top into the wheel furrow, and no removal.  Treatments were arranged in a split-plot design with tillage treatments as the whole plot and herbicide and residue treatments as sub-plots.  In the first-ratoon crop (second year), johnsongrass density was greatest when no herbicide was applied (13 tillers m^-1 row) and least with conventional tillage and broadcast herbicide application (1.7 tillers m^-1 row).  When post-harvest residue was not removed, johnsongrass density was less (4.2 tillers m^-1 row) than complete removal by burning (6.0 tillers m^-1 row), with partial removal being intermediate (5.1 tillers m^-1 row).  Johnsongrass density increased with all treatments, reaching a maximum of 22 tillers m^-1 row in the third ratoon (fourth year) when no herbicide was applied and no-till was practiced compared to 9.7 tiller m^-1 row under conventional tillage and broadcast herbicide application.  Not removing harvest residue suppressed johnsongrass (14 tillers m^-1 row) compared with removal by burning (20 tillers m^-1 row) and partial removal (16 tillers m^-1 row).  In plant cane (first year), no-till reduced cane yields by 3 to 4% compared to reduced and conventional tillage.  This increased to 10 to 28% yield losses in first ratoon, 24 to 45 % losses in second ratoon, and 52 to 76% losses in third ratoon, depending on herbicide usage.  When conventional tillage was used, banding herbicides resulted in similar yields to broadcast application in all four years.  When either no-till or reduced tillage was used, sugarcane yields were less when herbicides were band-applied compared with broadcast in the second- and third-ratoon crops.  Yields were always least in all three ratoon crops when no herbicide was used.  Results of this study showed that in sugarcane fields with history of johnsongrass infestation, the number of tillage applications can be reduced without sacrificing yield so long as herbicides are broadcast applied.  However, a no-till approach is not advised as yields were always reduced regardless of herbicide application.

EPA’s Office of Pesticide Programs is responsible for balancing the benefits that pesticides can provide with the potential risks, including those from pesticide spray drift, that may result from their use. Pesticide labeling is the means by which EPA implements the risk mitigation measures indentified through its risk assessment, and ensures that the measures meet statutory standards under actual use circumstances and commonly accepted practices. In 2009 EPA published for public comment draft documents for the purpose of providing guidance to pesticide manufacturers on labeling statements concerning pesticide drift, and to inform the public of EPA’s policies with regard to the prevention of pesticide drift (www.regulations.gov). The agency, believes the use of these statements and formats on labels will provide users consistent, understandable, and enforceable directions and therefore improved communication of drift management requirements to pesticide applicators, and as a result will improve protection of people and other non-target organisms and sites from potential adverse effects that may be caused by off-target pesticide drift. EPA plans to finalize its guidance in 2012 after completion of its consideration of the public comments. Associated with this initiative is the agency’s Drift Reduction Technology (DRT) program also scheduled for 2012. This is a voluntary program with the intention of encouraging industry’s development, testing, and marketing, and applicators’ use of technologies with the potential to significantly reduce spray drift, as verified by EPA’s test protocol (http://www.epa.gov/etv/este.html#pdrt) or another suitable method. EPA will encourage pesticide registrants to reference the use of verified technologies in pesticide product label use directions, thereby enabling the agency to credit the drift reduction potential in its risk assessments and registration decisions and providing applicators with greater flexibility in managing spray drift. ellenberger.jay@epa.gov

With the ongoing development of a number of different herbicide products for use with herbicide-tolerant crops, there is heightened concern for off-target movement and the potential for damage to sensitive crops. The term “off-target movement” comprises two distinct and independent modes of movement: spray droplet drift during application, and volatilization (vapor drift) of the herbicidal active ingredient following application. Each of these mechanisms requires its own unique solution to limit its contribution to off-target movement. To reduce spray droplet drift, the number of small droplets (driftable fines) needs to be minimized; to prevent vapor drift the herbicide needs to be utilized (formulated) in a form that has inherently low volatility.  As an integral part of the Enlist™ Weed Control System under development by Dow AgroSciences, a novel 2,4-D  + glyphosate pre-mix formulation, Enlist Duo™ herbicide, was developed which contains built-in attributes to address both modes of off-target movement. The 2,4-D contained in the formulation is present as its choline salt. Past work has shown that the choline salt of 2,4-D has significantly lower volatility than all other commercially available forms of 2,4-D. Laboratory volatility studies will be presented showing significantly lower levels of herbicide vapor transmission for Enlist Duo™ herbicide relative to appropriate 2,4-D + glyphosate and dicamba + glyphosate tank mix controls. Additionally, Enlist Duo™ herbicide has been formulated to significantly reduce the formation of fine spray droplets. Laboratory and wind tunnel results will be presented demonstrating the reduction in drift obtained for Enlist Duo™ herbicide relative to a 2, 4-D + glyphosate commercial tank mix control both with a conventional flat fan nozzle, as well as, with a low drift (air induction) nozzle design.

 *Corresponding author. Email: slwilson2@dow.com

 ^™Enlist and Enlist Duo are trademarks of Dow AgroSciences LLC. Components of the Enlist Weed Control System have not yet received regulatory approvals; approvals are pending.  The information presented is not an offer for sale.  Enlist Duo is not yet registered for sale or use as part of the Enlist Weed Control System. Always read and follow label directions.©2012 Dow AgroSciences LLC

There are many things to consider in developing an adjuvant for field application.  You must think about compatibility with the active ingredient(s) it will be positioned with.  The class of adjuvants will need to be selected.  All adjuvants are not equal.  There are differences between adjuvants within an adjuvant class.  The designed functionality desired to enhance the product(s) it is mixed with is important.  Efficacy of the selected actives needs to be improved in some fashion and never reduced.  There are numerous testing methods that should be investigated to measure the robustness of an adjuvant.  Every adjuvant should be evaluated as to its DRT rating by using atomization data.  This is primarily accomplished by using laser diffraction instrumentation to determine the Dv0.1, Dv0.5 (Volume Median Diameter), Dv0.9, and the percent volume (fines) less than 100 microns that are generated.  Relative span can also aid in determining the uniformity of the droplet spectrum.  The use of an appropriate air speed for data collection for ground application scenarios is paramount.  As labels are evaluated by EPA, generally spray quality, VMD, total volume per acre to be applied with different equipment types and buffer zone (non-spray area) language is being added.  Field trials applied at appropriate spray quality will be needed to determine efficacy.  Evaluation timing and frequency are important.  Data will also need to be collected on the influence of total volume per acre applied.  Plot size, weed species present and plant populations are important to populate a good data base library.  Selection of the appropriate nozzle type can have an influence on performance data.

No abstract to be submitted

Herbicide Efficacy with Coarser Spray Quality. K. A. Howatt*¹, J. R. Lukach², ¹North Dakota State Univ., Fargo and ²North Dakota State Univ., Langdon Research Extension Center, Langdon.

Reducing drift is one focus of current EPA scrutiny. One method to achieve this is the encouragement or mandate of certain language on herbicide labels related to drift reduction technologies (DRT). Increasing spray droplet size, or spray quality, is one DRT method used to reduce drift, but the implications of larger droplets for herbicide efficacy often is overlooked. Control of several species with paraquat at 4 oz ai/A or 2,4-D at 8 oz ae/A was evaluated in non-crop areas under four spray qualities: fine, medium, coarse, and very coarse. Paraquat efficacy with very coarse droplets generally was less than 55% control, while control with smaller droplet sizes was 75 to 98%. 2,4-D efficacy also decreased as droplet range increased.  For example, control of canola (Brassica napus L.) with 2,4-D was 92 to 96% with fine spray compared with 70 to 77% control when spray quality was very coarse. Likewise, buckwheat (Fagopyrum esculentum L.) control was 67 to 78% when equipment was set to deliver fine droplet sizes but only 23 to 47% with very coarse droplets.  Herbicide applied in fine and medium spray qualities often provided similar control that tended to be greater than control with coarse spray quality, and much greater than control with very coarse spray quality. Formulation of 2,4-D affected the magnitude of spray quality effect, with amine formulation resulting in amaranth (Amaranthus cruentus L.) control as much as 25 percentage points lower with coarse compared with medium spray. Additional control through wheat competition was not achieved even when full rates of fenoxaprop plus clopyralid and fluroxypyr were used. Control of wild oat (Avena fatua L.) was 97% compared with 87% and of wild mustard (Sinapis arvensis L.) was 97% compared with 42% for medium and very coarse spray patterns, respectively.  kirk.howatt@ndsu.edu

To determine the ability of a vegetable grower to co-exist with the potential for herbicide drift, one must 1) understand the benefits of the technology posing a drift risk, 2) determine the influence of spatial and temporal separation of target and sensitive crops, 3) develop estimates of crop biological sensitivity, 4) calculate the value of non-target crops and determine the potential impact of drift onto these crops, 5) be knowledgeable of residue tolerances established for sensitive crops, and 6) understand how research and new application technology can reduce drift.

In Georgia, the benefits of new technology that would aid in management of glyphosate-resistant Palmer amaranth in cotton and other crops would be monumental.  Currently, cotton growers are adopting more tillage and greatly increasing herbicide use.  The average grower invested $62.50 per acre in herbicides in 2011.  Additionally, 92% of these growers hand-weeded 52% of their crop at a cost of $23.70 per hand weeded acre.  New technology, such as auxin-resistant cotton, could reduce herbicide and hand weeding costs at least 40% and would greatly reduce the potential for herbicide injury to cotton.

Where target crops can be spatially or temporally separated, drift can be avoided.  In Georgia, this management approach is not effective as vegetables are grown on over 200,000 acres of land ($1.2 billion farm gate value) year around and cotton is grown on over 1.3 million acres of land ($1.1 billion farm gate value) in the same areas.  Many cotton producers also grow numerous vegetables. 

 When drift occurs, understanding the biological sensitivity of the off-target crop is critical.  Vegetable crops are often extremely sensitive to herbicides such as glyphosate or auxins.  2,4-D (X = 0.75 lb ae) at 1/50, 1/100, 1/200, and 1/400 X rate reduced pepper yield 58, 50, 20, and 11%, respectively.  Potential impact from yield loss is greatly magnified by crop value.  Production of watermelon, pepper, and tomato, with variable costs of $3200, $8865, and $11,500/A, respectfully, and potential net returns of $1500, $4500, and $10,500/A, respectfully, requires high certainty that nothing will influence yield or maturity. For non-target crops where a residue tolerance is not established for a specific herbicide, drift from that product often requires total crop destruction.   

 Vegetable producers and herbicide drift, that could impact maturity or yield, will not co-exist simply due to economics. Therefore, research to better understand factors causing drift and to develop new technology for drift reduction is critically needed.  Once factors reducing drift and potential impact to non-target crops are understood, an intelligent analysis of drift potential can be calculated allowing greater use of needed new technologies without posing significant risks to vegetables or other sensitive crops.  Inevitability, such an analysis will determine that regardless of drift reduction technology there will be certain areas where vegetable production cannot co-exist with use of auxin herbicides on cotton or other crops.   

More than 200 million acres are sprayed annually with crop protection products.  Many herbicides can cause non-target plant effects at very low concentrations associated with spray drift. Managing off target movement is essential for the continued success and expanded use of these products in conventional and tolerant crop systems. While spray drift cannot be completely eliminated, there are practices that can minimize off field movement.  Regulators have been revising label language to included spray drift protections away from just threatened and endangered species habitat to protecting all non-target areas.  This presentation outlines a process for determining buffer distances using non-target species study NOEC’s, EC₂₅’s or EC₅₀’s endpoints.  Product losses can be broadly fit into three categories: Drift and airborne loss (Most significant and controllable process), volatility losses, and evaporative loss (can be controlled with formulation advancements).  Herbicide losses to non-target areas can be greatly minimized by following application “BMP’s” as outlined in the presentation.  

Commensurate with the decreasing cost of database deployment, increasing ease of application development and increasing availability of geospatial data layers, many tools are emerging that can aid in managing pesticide product applications.  Such tools will make critical information easily accessible and can aid the applicator in making decisions that help mitigate the potential for off-target movement and increase the accuracy of product deposition.  Support for development and deployment of the applications and tools can come from a variety of sources including : 1) retailer-developed applications that optimize field application volumes and equipment utilized in custom applications services; 2) farm management and retail services software that integrate back office work processes with currently-offered database services; 3)scientific applications that advance the analysis of data to support product development; and 4) applications developed by product manufacturers offering recommendations to optimize product performance.

This presentation focuses on the development and deployment of geospatial applications that increase user access to information and allow the applicator to plan equipment and application parameters appropriate for the local field environment.  The adoption of these tools will often depend upon how easily they integrate into current user practices as well as the confidence of the user in operating their equipment in alignment with the output of the application or tool. 

Understanding the potential for offsite transport is a critical factor in environmental stewardship and ultimately the sustainable use of crop protection products.  Particle drift and vapor-phase movement can be important mechanisms for pesticide movement, motivating the use of carefully-designed research programs to quantify the transport.  Base physico-chemical properties of pesticides are typically indicative of only the relative potential for movement, necessitating research at sequentially larger length scales and under more realistic environmental conditions to obtain quantitative estimates of transport properties.  Small field and lab scale studies are often most useful for relative comparisons or range-finding unless proper scaling procedures are used.  Experiments to evaluate transport at the semi-commercial or larger scale are the most desirable, but are often only available in small numbers due to resource considerations.  Thus, efficient study designs are needed, such as aerodynamic method or back-calculation studies for volatility and ISO-standard studies for spray drift evaluation.  With careful execution of such studies, results can be extrapolated to local and regional scales to give refined estimates of a pesticide’s potential exposure to non-target organisms.

Spray drift exposure from ground spray applications with hydraulic booms can be modeled using several different approaches. This paper discusses and reviews those approaches. Modeling is usually based on either fully predictive approaches using physics-based calculations of particle transport, evaporation and deposition, or on curve-fitting a drift deposition curve. The latter approach is currently the most commonly-used for risk assessment by regulatory bodies although many agree that the former approach is a more appropriate medium- to long-term goal because it offers the user a wide range of options for inputting the factors that are considered most important in affecting spray drift: droplet size spectrum from the nozzle/ tank mix combination applied during spraying; release height of the nozzles on the spray boom; and meteorological conditions, especially the wind speed and direction. Fully-predictive models such as AGDISP can also calculate the effect of other parameters on spray drift – for example the wake effect of the sprayer on transport, the evaporation rate of the droplets and increasingly the impact of the canopy and vegetation on spray deposition.

Despite several current efforts to develop fully-predictive models for drift from ground sprayers, including a dynamic ground model within AGDISP, most regulatory bodies still use field data for their risk assessments. There are two main data sets for such use: the Spray Drift Task Force ground field study data contained within AgDRIFT and the German government data from several sets of studies under the BBA, now JKI. Other data sets also exist in the UK, Netherlands, Belgium and other countries.

The author of the current paper proposes a hybrid approach that uses both field study data and fully predictive modeling to assess off-target deposition rates from ground spray applications. The approach which is planned to be included in a ground drift model called AgDRT is “hybrid” in that it requires library data for its initial running and the processes those data through AGDISP. The library data can be collected by measuring initial airborne spray flux and droplet size in wind tunnels (e.g. for nozzles and adjuvants) and in field studies (e.g. for entire sprayers or sprayer modifications) at a suitable sampling distance downwind of the spray release (e.g. 2 m in wind tunnels and 5 m in the field), following standard measurement and sampling techniques. A wind tunnel model called WTDISP takes this approach for wind tunnel data and when linked with a proposed field model that can include drift reduction technologies (DRTs) could offer a powerful approach to modeling airborne spray drift and subsequent deposition downwind of the application. In essence, whenever a new sprayer or spraying technique is developed, data would be collected for the airborne spray which does not deposit on the canopy (for tree and vine crop scenarios for example) or on the ground (for row crop and broadacre scenarios) and then added to the libraries for running through AGDISP.  Field data will also be used to validate this modeling approach.

Anthem is new proprietary herbicide premix than contains pyroxasulfone and fluthiacet-methyl that provides growers a convenient and flexible product for pre-emergence and early post emergence grass and broadleaf weed control. Anthem is formulated as a 2.15 pound per gallon suspoemulsion liquid. Anthem will be labeled for both corn and soybean uses. Anthem ATZ is new three way herbicide premix than contains pyroxasulfone, atrazine and fluthiacet-methyl that provide growers a convenient and flexible product for pre-emergence and early post emergence grass and broadleaf weed control. Anthem ATZ is formulated as a 4.5 pound per gallon suspoemulsion liquid. Anthem ATZ will be labeled for corn uses only. Both Anthem and Anthem ATZ offers growers several modes of action for control of weeds, including weeds resistant to glyphosate and many difficult to control species. Both products provide excellent crop safety when used at the recommended pre-emergence rates for the particular soil type or in post applications. Anthem uses rates will vary from 6-13 fluid ounces per acre and Anthem ATZ uses rates will vary from 1.5 to 4 pints per acre. Research trials conducted by FMC and University researchers has shown excellent grass and broadleaf weed control with both Anthem and Anthem ATZ.

A field trial was established during the summer of 2011 in Northern Colorado to evaluate the crop response of multiple species over time by planting crops into a range of pyroxasulfone rates five times over a five month period. The objectives of the study were to a) evaluate crop tolerance of multiple species to increasing rates of soil-applied pyroxasulfone, b) Evaluate crop response of species planted into dissipating levels of pyroxasulfone over time, and c) evaluate control of indigenous weed species. Plots were established at the Colorado State University Horticultural Research Station located just North of Fort Collins Colorado. The soil type was a Nunn clay loam with 2.2% organic matter. Based on previous soil sorption research, this soil type had a sorption coefficient of .838 L/kg which ranked 17^th out of 25 soils (ranking 1=most binding). Previous dissipation studies at this field site resulted in an average dissipation half-life of 30.8 days for the two years in which dissipation was evaluated. Plots were sprayed with a CO₂ pressurized backpack sprayer at 187 L/ha on May 27^th 2011. Pyroxasulfone was soil-applied at rate of 300, 150, 75, 37.5 g ai/ha and set up in a randomized design along with an untreated check. Herbicide treatments were three meters wide by 45 meters long and oriented from north to south. Thirteen different species were planted on a monthly bases for a total of 5 planting from 5-27 to 10-27. Crop species were planted east to west across herbicide treatments in a block for each time point. For each time point, crops were seeded with a ribbed-belt push seeder in rows spaced 30cm apart. Plots were irrigated with an over-head linear on a consistent basis to maintain plant available water. Species that grew included sunflowers (Helianthus annuus), corn (Zea mays), sorghum (Sorghum bicolor), dry beans (Phaseolus vulgaris) and soy beans (Glycine max).  Individual plantings were harvested approximately seventy days after planting and data was collected for stand counts, heights and fresh weights in order to compare species tolerance to increasing rates of pyroxasulfone both initially and over time. Preliminary results indicate that for the first three plantings where adequate biomass was produced for analysis, corn (Zea mays), sunflowers (Helianthus annuss) and soy beans (Glycine max) were the three most tolerant species, while dry beans (Phaseolus vulgaris) were classified as moderate, and sorghum (Sorghum bicolor) appeared to be the most sensitive of the species tested. Preliminary data also suggests that crop injury was the most significant in the early plantings, and tended to decrease overtime as residual levels of pyroxasulfone decreased in the soil.

Palmer amaranth has become a driving force in weed management decisions in North Carolina due to widespread glyphosate and ALS-inhibitor resistance in the state. Growers are continually looking for options in primary crops as well as rotation options that allow for greater control. The pending introduction of pyroxasulfone for use as a preemergence herbicide in North Carolina corn production has led to interest in its ability to control Palmer amaranth. Studies were initiated to investigate the effectiveness of pyroxasulfone on various weeds at the Central Crops Research Station near Clayton, NC and the Upper Coastal Plains Research Station near Rocky Mount, NC. These locations were selected to provide a range of environmental conditions, weed species, and corn yield potential. Weed control varied by location with generally greater control on the sandier soils at Clayton. Greater weed control was observed as pyroxasulfone rates increased. Additionally, improved control of large seeded broadleaf weeds was observed when tank-mixes with atrazine or saflufenacil were applied.

New Fierce Herbicide is a pre-mix of flumioxazin and pyroxasulfone being developed by Valent USA Corporation for use in soybean and minimum tillage field corn.  Fierce Herbicide is formulated as a 76% WDG at a ratio of flumioxazin and pyroxasulfone at 1:1.27.  Fierce Herbicide provides pre-emerge control of a variety of broadleaf and annual grass weeds with excellent crop safety.  Use rates vary depending on soil type with the suggested use rate for Roundup Ready soybeans ranging from 3 to 3.75 oz/A.  Data from 2009 - 2011 demonstrated excellent control of amaranthus species including Palmer amaranth and common waterhemp at 56 days after treatment (DAT).  Other weeds controlled included hemp sesbania, broadleaf signalgrass, barnyardgrass and foxtail species.  Common cocklebur was not controlled.  Fierce herbicide also provided excellent control of winter annual weeds such as horseweed and Italian ryegrass when applied in the fall.  Fierce Herbicide has 2 non-ALS modes of action (Group 14 and Group 15).  This, combined with excellent control of resistant weed species such as pigweed and horseweed, will make Fierce an excellent resistance management tool.  Valent anticipates registration of Fierce Herbicide during the 2nd quarter of 2012.

Field experiments were conducted at the Southern Agricultural Research Center in Huntley, MT, in 2011, to evaluate herbicide programs for volunteer glyphosate-resistant canola control in glyphosate-resistant sugar beet.  Glyphosate-resistant canola was broadcast in the field just prior to planting sugar beet to obtain a uniform density of 5 to 7 canola plants m^-2.  Glyphosate-resistant sugar beet variety “BTS 36RR50 Pro 200” was planted on April 20 at a seeding rate of 119,500 seeds ha^-1 in 61-cm wide rows.  Treatments were arranged in a randomized complete block design with four replications.  Herbicides were applied as a single POST application at the 2-leaf stage of sugar beet or a sequential POST application at the 2-leaf followed by (fb) 6-leaf stage of sugar beet (10-14 days after the 2-leaf application), with or without PRE.  Single POST treatments included triflusulfuron methyl (Upbeet®) applied alone at 17.5 g ai ha^-1 (half rate) or at 35 g ai ha^-1 (full rate).  Sequential POST treatments included triflusulfuron methyl at half or full rate applied alone, in combination with ethofumesate (Nortron SC®) at 140 g ai ha^-1, or in combination with phenmedipham + desmedipham + ethofumesate (Progress®) at 44.73 g ai ha^-1.  Additional treatments included ethofumesate applied as PRE at 4200 g ai ha^-1 fb the sequential POST treatment of triflusulfuron methyl at half or full rate, and ethofumesate applied alone at 140 g ai ha^-1 as a sequential POST.  A non-treated check and a hand-weeded control were also included for comparison, with a total of 13 treatments.  All triflusulfuron treatments included methylated seed oil (MSO) at 1.5 % v/v.  The test site was kept free from all other weeds by spraying glyphosate at 840 g ae ha^-1 with 2% w/w of ammonium sulfate (AMS).  Herbicides were applied with a hand-held boom calibrated to deliver 94 L ha^-1 at 276 kPa.  Sugar beet injury and canola control were visually rated at 7, 14 and 21 days after each application on a scale of 0 (no injury or control) to100 (complete control or plant death).  Weed control data at 21 d after the last application (DAA) were used for analysis.  Sugar beet root and sucrose yields were recorded at harvest.  Data were subjected to ANOVA using PROC MIXED in SAS.  Means were separated using Fisher’s protected LSD test at α = 0.05.  None of the herbicides caused any injury to sugar beet.  The most effective herbicide program for glyphosate-resistant canola control in glyphosate-resistant sugar beet was ethofumesate (4200 g ai ha^-1) applied PRE fb a sequential POST treatment of triflusulfuron methyl at 35 g ai ha^-1, with a control of 91% at 21 DAA, which was equivalent to the hand-weeded treatment.  Canola control did not differ between half and full rates of triflusulfuron methyl.  Irrespective of rates, the single POST application of triflusulfuron provided lower canola control than the sequential POST treatment of triflusulfuron.  There was no additional advantage of tank-mixing ethofumesate or phenmedipham + desmedipham + ethofumesate with triflusulfuron.  Ethofumesate alone at the 2-leaf fb 6-leaf application did not provide any control of glyphosate-resistant canola.  Consequently, canola biomass was greater in ethofumesate alone treatment than all other herbicide treatments.  Canola biomass in sequential POST treatments containing triflusulfuron averaged 80% lower than single POST treatments of triflusulfuron at high and low rates.  Furthermore, canola survivors in the single POST treatments produced seeds.  Sugar beet root and sucrose yields with all triflusulfuron-based herbicide programs were similar to the hand-weeded plots, except for the single POST treatment of triflusulfuron at the reduced rate (17.5 g ai ha^-1), which yielded less than the hand-weeded control.  Sugar beet root and sucrose yields were least in the ethofumesate (POST) alone treatment, and were comparable to the nontreated check, averaging 40,320 kg ha^-1 of root and 4,480 kg ha^-1 of sucrose yields, which were almost two-fold less than the yields obtained in hand-weeded plots.  In conclusion, POST applications of triflusulfuron methyl at rates ≥ 17.5 g ai ha^-1 at 2-leaf fb 6-leaf stage of sugar beet was needed to prevent volunteer glyphosate-resistant canola interference and yield reductions in glyphosate-resistant sugar beet.   

Waterhemp is becoming more prevalent in sugarbeet production in Minnesota and North Dakota.  Two major reasons for the increase in waterhemp include excessive rainfall causing movement of seeds from one area to another area and the increased frequency of glyphosate-resistant waterhemp populations. 

   Small-plot field research was conducted in 2011 at two locations having glyphosate-resistant waterhemp near Holloway, MN to determine the most effective herbicide combinations in glyphosate-resistant sugarbeet.  A three factor factorial study was established with four replications on May 4 and May 16, 2011.  Site one had a lighter textured soil compared to site two.  The first factor included the presence or absence of clycloate applied at 4.5 kg ai/ha.  The second factor included glyphosate applied alone at 1.3 kg ae/ha to 2-leaf sugarbeet followed by glyphosate at 0.84 kg/ha 10 and 20 days later, glyphosate in combination with desmedipham at 0.13 kg ai/ha to 2-leaf sugarbeet followed by 0.18 kg/ha 10 days later, followed by 0.27 kg/ha 20 days later, or glyphosate in combination with desmedipham plus phenmedipham (1:1) at 0.13 kg ai/ha to 2-leaf sugarbeet followed by 0.18 kg/ha 10 days later, and followed by 0.27 kg/ha 20 days later.  Ethofumesate was added at 0.14 kg ai/ha to desmedipham plus phenmedipham for each postemergence application.  Each treatment contained AMS at 3.8 kg/378 L of spray mixture and Destiny HC at 1.75 L/ha.  The third factor included the addition of S-metolachlor at 1.6 kg ai/ha to 2-leaf sugarbeet followed by 1.1 kg/ha 10 days later, dimethenamid-P at 0.74 kg ai/ha to 2-leaf sugarbeet followed by 0.53 kg/ha 10 days later, acetochlor (Warrant) at 1.3 kg ai/ha to 2-leaf sugarbeet followed by 0.84 kg/ha 10 days later, or no layby herbicide.  The waterhemp were less than 2 cm at the time of the first postemergence application.

   Sugarbeet injury and waterhemp control was visually evaluated at various times of the season.  Sugarbeet were harvested September 7^th and root yield calculated and sugar quality and content analyzed.  Sugarbeet injury averaged 22% at the time of the first postemergence application at site one.  At site one applying cycloate, including desmedipham and desmedipham plus phenmedipham plus ethofumesate, and adding S-metolachlor or dimethenamid-P usually caused the greatest injury.  At site two, the addition of acetochlor or dimethenamid-P usually increased sugarbeet injury compared to glyphosate alone.  Glyphosate applied three times alone controlled 51% and 66% of waterhemp at site one and two, respectively, indicating the presence of glyphosate-resistant waterhemp at each site.  The use of cycloate, combining desmedipham and desmedipham plus phenmedipham plus ethofumesate to glyphosate and combining a layby herbicide improved waterhemp control compared to glyphosate alone at harvest.  Cycloate plus desmedipham plus glyphosate plus dimethenamid-P controlled the most waterhemp at site one.  Several herbicide combinations maximized waterhemp control at site 2 due to the reduced waterhemp density.  Cycloate increased root yield and extractable sucrose at site two with no other factor influencing these variables.  No treatments influenced root yield or extractable sucrose at site one due to variability in waterhemp density, frequency of resistance, soil type, and Cercospora outbreak.  Glyphosate-resistant waterhemp can be managed in glyphosate-resistant sugarbeet, however timely applications of several herbicides will be necessary and input costs will substantially increase.

Kochia and biennial wormwood are two weeds commonly found in Manitoba sunflower fields.  Between 2009 and 2011, field experiments were conducted across southern Manitoba with the objective of measuring the yield loss caused by kochia and biennial wormwood interference with sunflowers.  The experiments were a split-block, randomized complete block design.  The main plots were the time of weed emergence relative to the sunflower crop, either at the same time as the sunflowers, or when the sunflowers were at about the 4 leaf stage.  The sub-plots were six weed densities.  Each weed species was treated as a separate experiment.  Seven site-years of data were collected for kochia and five site-years for biennial wormwood.  Kochia and biennial wormwood seedling recruitment was variable among years.  Significant yield loss was observed at five site-years for the kochia experiments and at three site years for biennial wormwood experiments.  The level of yield loss depended on actual weed recruitment densities and the time of weed emergence.

Growth and Development of Spring Crops in Response to Oat Competition. M. R. Manuchehri*, E. P. Fuerst, I. C. Burke, D. L. Pittmann; Washington State University, Pullman, WA

Weed control in organically managed grain production in Eastern Washington presents many challenges. Spring crops, in particular, are weak competitors against weeds and often fail due to weed pressure. Organic spring crop trials were established near Pullman, WA in May of 2010 and 2011. The studies addressed the relative competitiveness of spring barley, wheat, pea, lentil, and chickpea against oat (Avena sativa). The experiment was a randomized complete block with a split-split plot design with four replications. Main plots included each crop planted at two different seeding rates (a recommended and a doubled rate) and subplots were two oat density treatments (22 kg ha^-1 and 88 kg ha^-1) and a weed free control. The growth and development of crops and weeds were assessed by measurements of stand establishment, plant height, leaf area index, biomass, and yield. Stand establishment increased with increasing seeding rate and decreasing oat density. Plant height varied among all five crops with barley being the tallest crop followed by wheat, pea, lentil, and chickpea. Leaf area index readings increased with increasing planting rate and were greatest for barley compared to all other crops. Crop biomass decreased as oat density increased while oat biomass was most suppressed in barley plots. Grain yield decreased as oat density increased, but was not affected by an increase in crop planting rate. Broadleaf crop yields were low and did not increase when planting rates were doubled. Overall, spring grain crops were more competitive than broadleaf crops, however, all yields decreased at oat pressure increased and yields were not responsive to increases in planting rates.

Dose-response, ammonia accumulation, enzyme activity and DNA sequencing studies were conducted to elucidate the basis for glufosinate resistance in an Italian ryegrass population. The glufosinate rates required to reduce the growth by 50% (GR₅₀) were less for the control populations C1 and C2, than for the resistant population MG. The GR₅₀ was 0.15 and 0.18 for C1 and C2 respectively, and 0.45 for MG, resulting in a resistance/susceptible index of 2.8.  Ammonia accumulation after glufosinate treatment for the resistant population MG was on average 1.5 times less than for the susceptible populations C1 and C2. The glufosinate concentration required to reduce the glutamine synthetase enzyme activity by 50% (I₅₀) was greater for the MG population compared to the susceptible populations.  The I₅₀’s values were 4.3 and 3.7 for C1 and C2, respectively, whereas the resistant population had an I₅₀ of 10.7, resulting in a resistant ratio of 2.6-fold higher than the average of the control populations. Eighty three percent of the plastidic GS gene was cloned and sequenced. One amino acid substitution was identified that may be associated to the reduced enzyme sensitivity. This is the first report of glufosinate resistance conferred by an altered target site in a weed species.

Confirmed glyphosate resistance in multiple kochia (Kochia scoparia) populations in western Kansas prompted the need to investigate alternative (to glyphosate) practices for control of kochia.  Separate field trials comparing standardized preemergence or postemergence herbicide treatments were conducted at one or more locations in Colorado, Kansas, Montana, Nebraska, and Wyoming to evaluate kochia control effectiveness in spring fallow or prior to crop planting. Only one of the two trials (PRE or POST) was conducted at some locations.  Preemergence herbicides were applied in March or April 2011, depending on location, and postemergence treatments were applied along with appropriate adjuvants when the majority of kochia plants were 3-10 cm tall.  Timing of control assessments varied among locations making time comparisons difficult because of different numbers of trials with similar times of evaluation.  Control percentages between most treatments varied widely both within locations and especially between locations, likely because of differing environmental conditions between locations.  Preemergence-applied acetochlor at 1,680 g ha^-1, flumioxazin at 120 g ha^-1, and package-mixed acetochlor plus flumetsulam plus clopyralid at 1,054 + 107 + 34 g ha^-1 controlled kochia poorly (<40%, n = 4 trials) at 5-6 weeks after application (WAT).  Mean kochia control with saflufenacil plus demethenamid at 75 + 657 g ha^-1, isoxaflutole at 88 g ha^-1, acetochlor plus atrazine at 2,770 + 1,100 g ha^-1, and sulfentrazone at 210 g ha^-1 ranged from 60 to 80% in sequential order.  Tank mixtures of preemergence dicamba and 2,4-D low volatile ester at 280 + 280 g ha^-1 and 560 + 560 g ha^-1 provided the greatest and most consistent kochia control of 97 and 98%, respectively.  Postemergence-applied paraquat at 840 g ha^-1 plus atrazine at 560 g ha^-1 controlled kochia 96% at 3-4 WAT, averaged across eight trials.  No other treatment controlled kochia by as much as 90%.  Mixtures of tembotrione at 92 g ha^-1 or topramezone at 105 g ha^-1 in combination with atrazine at 280 g ha^-1 and saflufenacil at 37 g ha^-1 plus atrazine at 238 g ha^-1 controlled kochia 86-89%.  Kochia control with glyphosate at 1,277 g ha^-1 was less than 30% in each of four Kansas trials; 43% in one Colorado trial; 82% in one Montana trial; and 93 and 96% in one Nebraska and a second Colorado trial.

Kochia has developed resistance to several herbicide mechanisms of action and is a troublesome weed in the western Great Plains. Dicamba-resistant soybeans are being developed to provide an additional herbicide mechanism-of-action for postemergence weed control. The objective of this study was to evaluate the variation in response to dicamba of 67 kochia populations collected in 2010 from 53 counties across Nebraska. Seed was planted in potting mix in 0.9 L plastic pots. Plants were grown in the greenhouse and were treated with dicamba when they were approximately 10 cm tall. A single dicamba dose of 420 g ae ha^-1 was applied to seven replications of all 67 populations, and visual injury ratings were taken 21 days after treatment (DAT). Two populations among those that were most susceptible, and two populations that were among the least susceptible were selected for dose response experiments. Twelve dicamba rates (0, 35, 70, 140, 280, 560, 1120, 2240, 4480, 8960, 17920 and 35840 g ha^-1) were applied in spray chamber equipped with a single TP8001E nozzle. The carrier rate was 193 L ha^-1 and the spray pressure was 207 kpa. At 28 DAT visual injury estimates were made and 5 replications of plants were harvested and dried for 48 h to determine dry weights. Three replications of plants for each population and each dose were allowed to grow until 110 DAT. At 110 DAT, visual injury ratings were taken, plants were harvested and the total dry weight and number of seeds per plant was measured. Kochia response to dicamba was described using a four parameter log-logistic model fit to visual injury estimate (I) and dry weight (GR) data. At 28 DAT, there was an 18.4 fold difference in I₉₀ dose, and a 7.4 fold difference in GR₉₀ dose between the least (11) and most (7) susceptible populations. Population 11 is resistant to dicamba. A dicamba dose of 3,500 g ha^-1 was required to reduce dry weight 50% (GR₅₀), a dose 12.5 fold greater than typical dicamba use rates of 280 g ha^-1. At 110 DAT, one plant from population 11 survived a dicamba dose of 35,840 g ha^-1. At least one plant from each of the other three populations survived a dicamba dose of 1120 g ha^-1 at 110 DAT. We suspect that there may be a fitness penalty associated with the resistance expressed in population 11. Plant biomass and seed number in population 11 for the untreated control were 30 and 60% less than for the most susceptible population (7). The identification of one resistant population among 67 collected randomly, the variability in response to dicamba within and among populations, and the fact that dicamba doses greater than 560 g ha^-1 were required to achieve GR₈₀ for all populations screened suggest that repeated use of dicamba for weed control in fields where kochia is present may quickly result in the widespread evolution of dicamba-resistant kochia populations.

Field studies were conducted on waterhemp (A. tuberculatus, syn. rudis) which is resistant to post-emergence HPPD inhibiting herbicides. Pre-emergence application of mesotrione alone and in combination with s-metolachlor and atrazine provided effective control. Also, s-metolachlor in combination with metribuzin and fomesafen applied pre-emergence controlled the waterhemp. Post- emergence herbicides including glyphosate, glufosinate, fomesafen and synthetic auxins provided effective control.

Silvery threadmoss (Bryum argenteum) is one of the most prevalent weed problems for creeping bentgrass putting greens especially since the deregistration of mercury and other heavy metal based pesticide products.  Heavy metal based products were effective at controlling moss on putting greens.  Now as superintendants reduce mowing heights, increase passes of equipment over the greens and reduce fertility to meet golfer demands for faster playing surfaces moss is becoming more problematic.  These practices create optimal conditions for competitive displacement of creeping bentgrass by silvery threadmoss.  Currently few products are labeled for moss control on putting greens.  Only one herbicide, carfentrazone (Quicksilver) and two fungicides, chlorothalonil (Daconil) and mancozeb (Manzeb) are labeled.  The objective of this study was to quickly screen large numbers of crop protection chemicals for efficacy against silvery threadmoss in order to identify novel options for moss control on creeping bentgrass putting greens. 

Two trials were initiated, one in 2010 and one in 2011, to examine herbicide effectiveness on silvery threadmoss.   Studies were conducted as randomized complete block designs with ten replications.  Each had forty-nine herbicide treatments at one and two times the labeled use rates as well as a nontreated control.  Herbicides were applied in a spray chamber calibrated to apply 792 L ha^-1.  After treatment moss plots were randomized into 24-well cell culture plates.  Plates were then placed into growth chambers on a bed of sand and sub-irrigated.  Growth chambers were programmed to a 16/8 day/night cycle with a constant temperature of 77F.  Digital photos images were taken at 0, 3, 7, 10, 14, 21, and 28 days after treatment (DAT).  Each image was cropped in Adobe Photoshop 9 to include a single plot per image.  Sigma Scan Pro 5 was set to evaluate images for green pixels in a range from hue=38 to 100 and saturation =0 to100. All images were compared to Day zero pixel counts and % reduction in green pixels was calculated for each plot which equates to a measure of control.  Data were subject to ANOVA and means separated by fishers protected LSD (p=0.05).  By 10 DAT in 2010 five herbicides reduced green color more than 90% including flumioxazin, carfentrazone, fosamine, diquat, and sulfentrazone.  In 2011 nine treatments controlled moss greater than 80% by 10 DAT: carfentrazone, diquat, fenoxaprop, flumioxazin, fosamine, glufosinate, pelargonic acid, sulfentrazone, and an experimental.  Several rates of these treatments and select tank-mixtures will be examined in the field this growing season to evaluate their efficacy and safety for use on golf course putting greens.

Topramezone (BAS 670) is a relatively new herbicide being evaluated to selectively control weeds in cool-season turfgrasses.  Topramezone is an HPPD-inhibiting herbicide in the triketone family.  Previous research has shown that other HPPD inhibitors, such as mesotrione, can selectively suppress bermudagrass in cool-season turfgrass.  The objective of this study was to evaluate topramezone at various rates applied alone or mixed with triclopyr for selective bermudagrass control in tall fescue.  Two trials were initiated on turf-type tall fescue, one at the Virginia Tech Golf Course (VTGC), and one at the Turfgrass Research Center (TRC) in Blacksburg, Virginia. Sequential herbicide applications were applied July 20, August 11, and September 3, 2010 for both trials.  Topramezone was applied alone at 13 and 25 g ai ha^-1 and 13, 25, and 34 g ai ha^-1 + 1120 g ae ha^-1 triclopyr.  Comparison treatments included fenoxaprop at 101 g ai ha^-1 + 1120 g ae ha^-1 triclopyr, and 1120 g ae ha^-1 triclopyr alone.  A nontreated check was also included for comparison purposes.  All topramezone treatments included methylated seed oil adjuvant at 1% v/v, fenoxaprop plus triclopyr included nonionic surfactant at 0.25% v/v, and the triclopyr only treatment included crop oil concentrate at 1% v/v. 

At VTGC, bermudagrass cover at initiation ranged from 43 to 72%.  In fall 2010, two weeks after the last herbicide treatment, the front of each plot was overseeded with tall fescue, and subsequently evaluated separate from the back of the plot.  The following March, seedling tall fescue cover did not differ between treatments.  In May 2011, topramezone alone at either rate and topramezone at 13 g ha^-1 plus triclopyr did not control bermudagrass more than 33%.  Topramezone at 25 g ha^-1 or more plus triclopyr controlled bermudagrass 92 to 98%.  Fenoxaprop plus triclopyr and triclopyr alone controlled bermudagrass 85 and 37%, respectively, and less than better performing topramezone treatments.  Topramezone applied alone whitened bermudagrass foliage accounting for 5 to 35% discolored turf for eight weeks during the treatment season.  Whitening was eliminated when triclopyr was mixed with topramezone. 

At TRC, bermudagrass cover in late July ranged from 20 to 63%.  In May of the year following the treatment program, topramezone alone controlled bermudagrass 20 and 63% when applied at 13 and 25 g ha^-1, respectively.  All combinations of topramezone and triclopyr controlled bermudagrass 93 to 100%.  Triclopyr alone and fenoxaprop plus triclopyr controlled bermudagrass 3 and 60%, respectively and less than topramezone plus triclopyr.  Topramezone applied alone whitened bermudagrass foliage accounting for 17 to 50% discolored turf for six weeks during the treatment season.  Again, whitening was eliminated when triclopyr was mixed with topramezone.  Tall fescue was not significantly injured by any treatment at either location.  These data suggest topramezone plus triclopyr could be a market-leading herbicide combination for selective bermudagrass control in tall fescue turf. 

            Due to copious seedhead production and poor growth attributes under common summer climatic conditions throughout the southern United States, annual bluegrass (Poa annua L.; ABG) is considered the most problematic weed in creeping bentgrass (Agrostis stolonifera L.; CB) putting greens.  Currently, there are no registered postemergent herbicides in the United States for ABG control in CB putting greens.  Paclobutrazol, a plant growth regulator, is commonly used for ABG seedhead suppression and limited growth inhibition.  Recent research has shown amicarbazone, a photosystem-II inhibiting herbicide, has potential utility for ABG control in CB putting greens.  Field trials were conducted in 2010 and 2011 to evaluate various treatment regimes including paclobutrazol and amicarbazone for ABG control in CB putting greens. Treatments included amicarbazone (49, 65, or 92 g ai ha^-1) and paclobutrazol (70, 140, or 280 g ai ha^-1) applied individually, as a tank-mixture, or sequentially with one compound following another.  All amicarbazone treatments included a non-ionic surfactant (0.25 % v v^-1).  Broadcast spray treatments were applied to 2.1 x 1.1 m plots with a CO₂-pressurized sprayer comprised of three, 8002VS nozzles on 25 cm spacings, calibrated to deliver 304 L ha^-1.   Four replications of each treatment were arranged in a randomized complete block design.  Annual bluegrass control trials were initiated on ‘Penncross’ CB putting greens at three locations including: Prestonwood Country Club (Cary, NC), Occoneechee Golf Club (Hillsborough, NC), and the Sandhills Research Station (Jackson Springs, NC).  Creeping bentgrass tolerance trials were conducted on a contiguous putting green surface containing zones of ‘A1’, ‘A4’, ‘L-93’, and ‘Crenshaw’ varieties at the Lake Wheeler Turfgrass Field Laboratory (Raleigh, NC).  All trials were initiated March 8 – 10 in both years.  Annual bluegrass control was determined by converting weekly visual cover estimations on a 0 – 100 % scale as a percent of the nontreated within a respective block using the formula: (((nontreated plot cover – treated plot cover) / nontreated plot cover) x 100).  Creeping bentgrass quality was visually rated every week on a 1-9 scale (1 = complete turfgrass death; 9 = ideal turfgrass growth).  Five normalized difference vegetation index (NDVI) readings were captured monthly and averaged over a given CB plot.  These data were then converted to a 1-9 grass index to allow for comparisons with visual quality estimations.  In addition, percent CB coverage was evaluated monthly using digital image analysis (DIA).  Data for CB tolerance and AB control were subjected to analysis of variance (P = 0.05) and means were separated using Fisher’s protected LSD test (P < 0.05).  The addition of amicarbazone applied monthly at 65 g ai ha^-1 to paclobutrazol applied at 140 or 280 g ai ha^-1 provided superior ABG control compared to stand-alone paclobutrazol treatments 8 and 12 WAIT.  Pooled over CB variety, turf quality, NDVI, and turf coverage differences were not observed between the aforementioned amicarbazone treatments and nontreated plots.  CB quality 8 WAIT was negatively impacted by all treatment regimes including amicarbazone applied at 49 or 92 g ai ha^-1.  Further, CB regrowth from the most injurious treatment evaluated varied by variety 12 WAIT.  Turf coverage in ‘Crenshaw’ (77%) and ‘L-93’ (81%) plots differed significantly from ‘A4’ (94%) and ‘A1’ (95%) plots treated with amicarbazone applied at 92 g ai ha^-1.  These data indicate the addition of amicarbazone to spring paclobutrazol treatment regimes provides improved ABG control; however, CB tolerance is dependent on amicarbazone application rate and frequency, as well as CB variety.

Methiozolin is a new herbicide under development for annual bluegrass control on golf putting greens and other turfgrass sites.  Previous research suggest methiozolin more effectively controls annual bluegrass when applied in fall compared to spring applications.  Conventional approaches to annual bluegrass control with methiozolin include 1 or 2 applications at 500 to 1000 g ai/ha in spring and fall.  In most studies, annual bluegrass is not controlled until fall treatments have been applied.  Questions remain as to how many treatments and at what rates completely control annual bluegrass while maintaining high quality putting surfaces.  In efforts to determine appropriate annual use rates and number of annual applications, studies were conducted to evaluate 2000 or 4000 g ai/ha per year applied in 2, 4, or 6 applications split between spring and fall application times.

Studies were conducted on creeping bentgrass putting greens infested with annual bluegrass located at three golf courses in Blacksburg, Draper, and Harrisonburg, VA.  Methiozolin was applied in 280 L/ha with Teejet 11004 TTI nozzles.  Initial treatments were applied on March 4 for spring and September 30 for fall.  Bensulide at 9000 g ai/ha was applied spring and fall as a comparison.  Methiozolin was applied at two annual use rates of 2000 or 4000 g ai/ha.  These rate totals were divided in 2, 4, or 6 applications split between spring and fall.  For example, when 6 applications were applied to reach a total of 4000 g ai/ha per year, each application included 667 g ai/ha with three applications applied at three week intervals in spring and another three applications applied in fall.

In May 2011 one year after study initiation, methiozolin at 2000 g ai/ha/yr did not control annual bluegrass more than 53% regardless of number of applications applied the previous year.  Bensulide did not control annual bluegrass.  When applied at 4000 g ai/ha/yr, methiozolin controlled annual bluegrass 61, 87, and 93% when applied 2, 4, or 6 times per year, respectively.  Creeping bentgrass was not injured at any time.  These data suggest methiozolin controls annual bluegrass better when applied multiple times at lower rates compared to fewer high-rate treatments.  If complete annual bluegrass control is desired, methiozolin annual use rates should be higher than 2000 g ai/ha.

In the southwest United States low desert region, bermudagrass is dormant during the winter and takes on a blonde or straw color. Winter weed infestations can reduce the aesthetics of the turf and eventually the quality of the bermudagrass turf.  Annual bluegrass (Poa annua) is a major winter weed along with several winter broadleaved weeds.  Annual bluegrass generally emerges when high quantities of irrigation are applied during the fall overseeding period in October.  Typically, a preemergence application of prodiamine, pendimethalin, or dithiopyr provides very good annual bluegrass control until December when a sequential treatment may be needed.  Indaziflam and flumioxazin were evaluated in separate experiments to determine effective rates, timing of application, and safety on desirable turfgrasses.  Small plot field experiments were initiated during the fall seasons of 2009 and 2010 in bermudagrass turf on golf courses in the vicinity of Phoenix, AZ.  Initial rates of indaziflam at 35 to 75 g a.i. ha^-1 applied in early November 2009 demonstrated effective annual bluegrass control of better 90% in May 2010.  Weeds were emerged at the 1- to 2- leaf stage and prodiamine offered no control in comparison.  In the fall of 2010, indaziflam was effective at 26 to 52 g a.i. ha^-1 and timings of application in October and November were better than when applied later in December.  The applications in mid-November and mid-December caused delayed greenup of bermudagrass in the spring as it emerged from winter dormancy.  Flumioxazin at 425 g a.i ha^-1 was consistently more effective in controlling annual bluegrass than 280 g a.i. ha^-1.  The October application caused bermudagrass discoloration and injury compared to later fall and winter applications.  Spring transition of bermudagrass was not affected by flumioxazin applied in the fall or winter.  Optimum time of flumioxazin application was November for effective annual bluegrass control and minimizing injury on bermudagrass turf that was entering dormancy.

Doveweed (Murdannia nudiflora) is a problematic weed of golf course roughs, fairways, and tees. Previous research at Clemson University has shown that preemergence herbicides applied in the spring of the year are ineffective at providing season long control of Doveweed. The purpose of this study was to evaluate Specticle (indaziflam) with various postemergence herbicides at a postemergence timing for improved control of Doveweed. Treatments for the study included: Blindside 66WG at 0.394 lb ai/ac, Blindside followed by (FB) Blindside 4 weeds after initial treatment (4WAIT), Blindside FB Blindside + Specticle 20WP at 0.04 lb ai/ac, Blindside + Specticle FB Blindside, Manor 60WG at 0.04 lb ai/ac FB Manor, Manor FB Manor + Specticle, Manor + Specticle FB Manor, Speedzone 2.2L at 1.1 lb ai/ac FB Speedzone, Speedsone FB Speedzone + Specticle, Speedzone + Specticle FB Speedzone, Celsius 68WG at 0.16 lb ai/ac FB Celsius, Celsius FB Celsius + Specticle, Celsius + Specticle FB Celsius. All treatments received a non-ionic surfactant at 0.25% V/V. Initial treatments were applied on June 15, 2011 with sequential treatments occurring 4 weeks later on July 13, 2011. Applications were made using a CO2 powered backpack sprayer calibrated at 20 GPA. Plot size measured 1.5 X 2 meters with 3 replications. Visual control ratings were taken on a 0-100% scale where 0 represented no control and 100 represented complete control. Of the treatments not containing Specticle only the SpeedZone applied twice provided greater than 75% Doveweed Control 90 days after initial application. Greater than 90% Doveweed control was seen with: Blindside + Specticle FB Blindside, Manor + Specticle FB Manor, Speedzone + Specticle FB Speedzone, and Speedzone FB Speedzone + Specticle 90 days after initial application. No treatment combination or timing provided complete Doveweed control. Future research will be to continue to evaluate additional herbicides for preemergence and postemergence Doveweed control. Along with evaluating herbicide rate, timing, and combinations for improved Doveweed efficacy.

Abstract

The purpose of this study was to evaluate various pre-emergence and post-emergence herbicides for control of doveweed (Murdannia nudiflora), a problematic weed of golf course roughs, fairways and tees that germinates much later in spring than traditional summer annual grassy weeds such as crabgrass and goosegrass.

Several studies evaluated the efficacy of various herbicides for pre-emergence and post-emergence control.  Study 1 included Specticle (Indaziflam) 7 oz/ac applied March 18, April 28, or May 11, 2011.  All other treatments initiated on May 11, 2011 included Specticle 5 & 3.5 oz/ac, Specticle 3.5 oz/ac fb Specticle 3.5 oz/ac 12 WAIT, Specticle 5 oz/ac fb Specticle 2 oz/ac 12 WAIT, Specticle 3.5 oz/ac fb Specticle 3.5 oz/ac + Celsius (Thiencarbazone-methyl, Iodosulfuron-methyl-sodium, Dicamba) 4.9 oz/ac 12 WAIT, Tower (Dimethenamid) 32 oz/ac, Tower 32 oz/ac fb Tower 32 oz/ac 6 WAIT, Tower 32 oz/ac fb Tower 32 oz/ac + Celsius 4.9 oz/ac 6 WAIT, Tower 32 oz/ac fb Tower 32 oz/ac 6 WAIT fb Celsius 4.9 oz/ac 12 WAIT, Tower 32 oz/ac fb Specticle 3.5 oz/ac 6 WAIT, Ronstar (Oxadiazon) 3 lb ai/ac, Ronstar 3 lb ai/ac fb Specticle 3.5 oz/ac + Celsius 4.9 oz/ac 6 WAIT. 

Study 2 evaluated post-emergence herbicides for doveweed control and treatments included single applications of Celsius 4.9 oz/ac applied on June 15, July 13 and July 27 2011.  Other treatments initiated on June 15 included Celsius 3.7 oz/ac fb Celsius 3.7 oz/ac 30 DAIT, and Trimec Classic (2,4-D, MCPP, Dicamba) 4 pt/ac.  Remaining treatments initiated on July 27 included Celsius 4.9 oz/ac fb Celsius 4.9 oz/ac 30 DAIT, and Trimec Classic 4 pt/ac. 

Study 1 and Study 2 were conducted on irrigated golf course rough comprised of Tifway-419 bermudagrass.  Applications were made using a CO₂ powered sprayer calibrated at 20 GPA.  Three treatment replications were applied on 1.5 X 2 meter plots.  Visual ratings were based on a 0-100% scale, 0% indicating no control and 100% indicating complete control.  All applications received a non-ionic surfactant at 0.25% V/V.  ANOVA was evaluated with alpha at 0.05. 

In study 1, less than 40% control followed pre-emergence treatments applied during March or April regardless of rating date.  Specticle 3.5 oz/ac applied May 18 fb Specticle 3.5 oz/ac 12 WAIT and Specticle 3.5 oz/ac applied May 18 fb Specticle 3.5 oz/ac + Celsius 4.9 oz/ac 12 WAIT provided ~95% control 26 WAIT (September 9 2011). In study 2, Trimec Classic demonstrated >80% control 8 WAIT.  Celsius treatments applied on or after July 13 demonstrated statistically similar control regardless of rate 8 WAIT.  No treatments demonstrated significant control 13 WAIT. 

Currently, for preemergence Doveweed control, Specticle at 3.5 oz/ac and Ronstar at 3 lb ai/ac provide ~12 weeks control while Tower at 32 oz/ac provides ~ 6 weeks control.  Due to the later germination of Doveweed, treatments should not be initiated until early May in upstate SC.  Postemergence control is provided with repeat applications of 3-way type herbicides.  Another strategy is waiting until late June and applying a 3-way herbicide.  Repeat this in 7 to 10 days and combine one of the before mentioned preemergence herbicide for extended control.

Additional herbicides will continue to be evaluated for pre and post emergence doveweed control along with alternate application timings to target doveweed’s late germination period.  

Liverwort (Marchantia polymorpha L.)  grows best in cool, moist conditions.    In areas of frequent irrigation, such as in plant propagation or in the production of perennials, liverwort can develop into a troublesome weed.     Trials were conducted to evaluate chemicals for the control of this weed species. Liverwort was grown in 5.7 cm pots in a peat/vermiculite growing medium. Liverwort covered 50 to 75% of each pot, and was approximately 1 cm tall at treatment.   Shasta daisy [Leucanthemum x superbum (Bergmans ex J. W. Ingram) D. H. Kent] was 30 cm tall at application.   Oregano oil (1 and 2%) and pelargonic acid (5 and 10%) caused significant and rapid injury (80% or higher) to liverwort within 30 minutes of application.  Effects from most of the other treatments were apparent 1 day after treatment (DAT).  At 1 DAT, oregano oil, pelargonic acid, and acetic acid (10 and 20%) all provided 75% or greater control of liverwort.  By 21 DAT, however, only flumioxazin at 0.42 kg ai ha^-1 and dimethenamid  at 1.7 kg ai ha^-1 gave greater than 85% control as regrowth occurred in the other treatments, with pelargonic acid, acetic acid, and the higher rate of oregano oil providing 60% or greater control.  A second application of all treatments was made at 3 weeks after the initial treatment.  At 15 minutes after the second application, oregano oil, the higher rate of ammonium nanoanoate (10%), pelargonic acid, flumioxazin, dimethenamid, and acetic acid all gave 75% or greater liverwort control.  These treatments all provided 80% or greater control at 8 DAT2.  The lower rate of ammonium nanoanoate (5%) and both sodium carbonate peroxyhydrate treatments (366 kg ai/ha and 60 g ai/L) did not provide acceptable control of liverwort.  Thorough coverage of liverwort appears to be critical for all of these treatments since the action seems to be contact for each one.  Flumioxazin was the most injurious treatment to Shasta daisy, followed by acetic acid and pelargonic acid, with the injury being unacceptable for all 3 chemicals. Directed sprays would be needed to improve crop safety as overtop applications were used in thisstudy.   Less injury was seen with the other treatments.  More data on crop safety is needed for these chemicals.

Mesotrione (Tenacity) is an effective post-emergent herbicide that can be used on cool-season turf to control grass and broadleaf weed species.  To improve weed control and reduce white tissue symptoms, triclopyr (Turflon Ester) is often added to mesotrione.  The addition of triclopyr to mesotrione can broaden the spectrum of weed control, while lowering the number of applications needed.  Aminocyclopyrachlor (Imprelis) is a new synthetic auxin herbicide primarily used for post-emergent broadleaf control but has also exhibited pre-emergent crabgrass control.  Combinations of mesotrione plus triclopyr were compared to mixtures of mesotrione plus aminocyclopyrachlor and mesotrione plus prodiamine (Barricade) to determine which provided the best control of post-emergent grass and broadleaf weeds.
            
Two studies were conducted on perennial ryegrass and Kentucky bluegrass maintained at 1.5 cm and mown three times per week.  Mesotrione alone and mesotrione plus triclopyr at two rates was applied on June 26 and again on July 15, 2011 (3 week interval), and mesotrione plus aminocyclopyrachlor or prodiamine was applied once on June 26.  An untreated control was included for comparison.  Herbicide rates included mesotrione at 0.18 kg ai/ha, triclopyr at 0.56 and 1.12 kg ai/ha, aminocyclopyrachlor at 0.08 kg ai/ha, and prodiamine at 0.56 kg ai/ha.  Treatments were applied at 280 L/ha, using a CO2 pressured backpack sprayer.  Percent weed cover, turf cover, and control of smooth crabgrass (Digitaria ischaemum) and white clover (Trifolium repens) was assessed at 14, 28, and 56 DAT.
       
At 14 DAT, mesotrione plus triclopyr at both rates and mesotrione plus aminocyclopyrachlor controlled smooth crabgrass and white clover significantly greater than mesotrione alone and mesotrione plus prodiamine.  At 56 DAT, mesotrione plus prodiamine controlled smooth crabgrass and white clover significantly less than all other treatments.  Mesotrione plus triclopyr at both rates controlled smooth crabgrass and white clover 98 to 100%.  Mesotrione alone only controlled smooth crabgrass 70-90% and white clover 60 to 80%.  Mesotrione plus aminocyclopyrachlor controlled smooth crabgrass 93% and white clover 100%.  Mesotrione plus prodiamine controlled smooth crabgrass and white clover 30%.  Perennial ryegrass and Kentucky bluegrass were not injured at any time during the study.  These results suggest that triclopyr at .56 to 1.12 kg ai/ha is an excellent admixture with mesotrione for crabgrass and broadleaf weed control.

MSMA has been one of the most widely used and effective postemergence herbicides for weed control in warm-season turfgrass.  Due to environmental concerns, MSMA is no longer available for turfgrass use in Florida and continued registration in other warm-season turfgrass states is in jeopardy. Studies were conducted at the University of Florida, West Florida Research and Education Center near Jay, FL to evaluate potential replacements for MSMA. Weeds studied included nutsedge (Cyperus sp.), crabgrass (Digitaria ciliaris (Reutz.) Koel.), goosegrass (Eleusine indica (L.) Gaertn.), carpetgrass (Axonopus affinis Chase), and tropical signalgrass (Urochloa subquadripara (Trin) R.D. Webster).  Nutsedge control can be achieve with several effective herbicides including trifloxysulfuron, sulfosulfuron and flazasulfuron.  Quinclorac is effective for crabgrass control and foramsulfuron and diclofop provide postemergence control of goosegrass.  The three-way prepackaged mixture of thiencarbazone, iodosulfuron, and dicamba is the only effective alternative found for postemergence carpetgrass control and none of the herbicides tested provided acceptable postemergence control of tropical signalgrass.  Weed control in the absence of MSMA will require a higher level of management of the part of turfgrass managers, will rely more on the use of preemergence herbicides and will be more expensive than when MSMA was available.  

Greenhouse experiments were conducted to evaluate the effect of selective herbicide placement on sedge shoot number, shoot weight and root weight.  Evaluated sedge species included purple nutsedge, yellow nutsedge and false-green kyllinga.  Sulfentrazone, sulfosulfuron and trifloxysulfuron were applied to soil only, foliage only, or soil plus foliage.  Sulfentrazone provided greater yellow nutsedge and false green kyllinga growth reduction compared to purple nutsedge.  Soil- and soil plus foliar-applied sulfentrazone, sulfosulfuron and trifloxysulfuron provided greater shoot number, shoot weight and root weight reduction than foliar applications 60 DAT, averaged over sedge species.  Further, soil-applied sulfentrazone provided greater shoot number reduction than soil plus foliar applications.  Soil-applied sulfentrazone reduced shoot number 95% while soil plus foliar and foliar applications provided 66 and 5% shoot number reduction, respectively, relative to the nontreated.  Foliar-applied sulfentrazone provided minimal (< 15%) shoot and root weight reduction.  Sulfosulfuron reduced purple nutsedge and false green kyllinga shoot number, shoot weight and root weight greater than yellow nutsedge.  Purple nutsedge and false green kyllinga shoot number, shoot weight and root weight were reduced > 73% while yellow nutsedge was reduced < 55%.  Trifloxysulfuron reduced shoot number and shoot weight > 75%, regardless of species.  Further, trifloxysulfuron reduced purple nutsedge and false green kyllinga root weight > 79%.  These data indicate herbicide-soil contact is imperative for optimum sedge control hence; future research should evaluate techniques that optimize herbicide-soil contact.

Experiments were conducted to investigate the downward mobility of select herbicides in an established bermudagrass (Cynodon dactylon (L.) Pers.) fairway compared to bare ground.  Evaluated herbicides included atrazine, sulfentrazone and MSMA.  Field lysimetry techniques were utilized and summer and winter applications were compared.  Lysimeters remained in the field for 120 days prior to removing and analyzing for parent analyte.  Atrazine and sulfentrazone samples were extracted and analyzed with liquid chromatography coupled with tandem mass spectrometry according to published environmental chemistry methods.  Attempts to extract and analyze MSMA samples were unsuccessful; therefore, MSMA samples were analyzed for total arsenic (As) and background levels were subtracted to determine the increased As levels presumably due to MSMA applications.

Atrazine concentrations after summer applications were minimal (< 0.1% of initial concentration), regardless of system.  However, after winter applications, greater than twice as much atrazine was recovered in dormant turf compared to bare ground.  Of total atrazine recovered, 90% was recovered in the surface soil (0 - 4 cm) or above ground vegetation of dormant bermudagrass compared to < 50% in the surface soil of bare ground.  Atrazine was not reported in depths > 45 cm, regardless of system or season indicating atrazine leaching potential under similar soil and climatic conditions is limited.

Sulfentrazone was the only herbicide that the highest concentration was not reported in the shallowest depth.  After summer applications in bare ground, the highest sulfentrazone concentration, which was five-times greater than the surface soil concentration, was reported in the 8 - 15 cm depth.  In actively growing bermudagrass, sulfentrazone distributed uniformly from the surface through 30 cm.  Although sulfentrazone was mobile under evaluated conditions, downward mobility was reduced in an established bermudagrass system compared to bare ground.  Of recovered sulfentrazone, < 20% was present in the surface soil of bare ground compared to 45% in the surface soil or above ground vegetation of the actively growing bermudagrass.  After winter applications, 42% of recovered sulfentrazone was present in the surface soil of bare ground compared to > 85% in the surface soil or above ground vegetation of dormant bermudagrass. 

The highest elevated As concentrations were reported in above ground vegetation in established bermudagrass, regardless of season indicating bermudagrass may absorb and accumulate various forms of As.  Elevated As concentrations were not reported deeper than 45 cm, regardless of system or season.  After summer applications of MSMA in bare ground, elevated As concentrations were observed uniformly 0 - 8 cm while deeper concentrations were reduced.  In established bermudagrass, As concentrations deeper than 4 cm were reduced compared to shallower depths.  Of the soil-As presumably due to MSMA applications during summer, 35% was present in the surface soil of bare ground compared to 51% in actively growing bermudagrass.  After winter applications, 39% of the elevated-soil As was present in the surface soil of bare ground compared to > 80% in the surface soil under dormant bermudagrass.

Generally, evaluated herbicides remained in the surface soil (0 - 4 cm) or above ground vegetation of established bermudagrass while they distributed beyond the surface soil of bare ground.  Additionally, greater herbicide concentrations were reported after winter applications compared to summer indicating herbicides were more persistent after winter applications.  This is likely due to increased biotic and abiotic herbicide degradation after summer applications compared to winter.  These data also indicate the downward mobility of soil-mobile herbicides vary among systems and seasons and may be used to assist in devising integrated pest management principles.

With the increased usage of transgenic herbicide technology cropping systems, off-target deposition of herbicides to sensitive crops continues to be of concern. When transgenic crops are planted within short distances of crops that do not contain the same transgenic technology, there is an increased chance for crop injury due to off-target movement of the herbicide. Assessment of such an event is difficult due to the large areas which can be affected. The availability of remotely sensed data can allow for a more accurate assessment of off-target deposition. One problem with the acquisition of remotely sensed data is the cost associated with data collection. Aerial imagery is a popular method for collection of remotely sensed data; however, this method can become quite expensive based on the type of imagery being collected. Therefore, it could be beneficial to acquire a ground-based method for collecting such information.

Experiments were conducted at the Black Belt Branch Experiment Station in Brooksville, MS to evaluate the use of a ground-based spectral acquisition system to monitor instances of off-target herbicide deposition. Pioneer 31G97 corn seed was planted at 70,000 seeds per hectare in a field measuring 3.19 hectares in size. In order to simulate crop response to an off-target application incident, 6 treatments consisting of glufosinate rates of 0.59, 0.30, 0.15, 0.07, 0.04, and 0.02 kilograms of the active ingredient per hectare (kg ai/ha) were applied in addition to an untreated check to susceptible corn at the V6 growth stage. Applications were made in 7.7 by 30.5 meter plots using a tractor mounted boom with an application volume of 140 liters per hectare. Visual injury ratings were recorded 7, 14, and 28 days after application. Additional data collected included spectral signatures recorded using the Analytical Spectral Device’s (ASD™) Fieldspec Pro handheld spectroradiometer and the SpecTIR™ airborne hyperspectral imagery as well as crop yields. Handheld hyperspectral data were recorded over a 14 day period with collection timings of 1, 4, 8, and 14 days after herbicide application, depending on the weather. Handheld spectroradiometer data were collected in conjunction with a Topcon HiPer Lite Plus real time kinematic (RTK) global positioning system (GPS) to ensure that each data point would have a fixed spatial information description. This system was mounted on a tractor and set to automatically collect an average from 10 signature readings each second as the machine moved through the field. Due to the expense of the SpecTIR™ airborne hyperspectral imager, a single image was collected 4 days after the glufosinate applications. At harvest, machine harvested yields were collected from the 2 center rows of each plot. Spectral data were analyzed using a multi classifier decision fusion method to determine classification accuracies of the different rates of glufosinate.

Visual ratings showed significant crop injury for all rates of glufosinate applied to susceptible corn 7 days after application (DAA) with the exception of the lowest rate of 0.02 kg ai/ha, which corresponds to a 1/32X ratio of the labeled glufosinate rate. However, by 14 DAA, visual injury ratings showed that all rates were significantly greater than the untreated. The handheld spectral data collected from the ground-based spectral acquisition system provided an overall accuracy of 70.4% for correctly identifying spectral features associated with the 7 treatments in this study while data collected from the SpecTIR™ airborne hyperspectral imager provided an overall accuracy of 55%.  Harvest data showed significant yield reductions only for the 2 highest glufosinate rates (1X and 1/2X). Additional research is needed to verify that injury quantified using the hyperspectral acquisition system is not being contaminated with agronomic effects such as nutrient or drought stress. These data show potential for utilizing a ground-based spectral acquisition system to differentiate between certain levels of herbicide damage which may occur in an off-target deposition situation. This can be of benefit due to the fact that a ground-based spectral acquisition system is more economical and efficient in terms of collecting data in a timely manner.

Non-transgenic cotton varieties are extremely sensitive to auxinic herbicide drift. With current industry efforts to develop dicamba and 2,4-D resistant cotton, off target drift of these herbicides is of concern.  Dow AgroSciences is developing a new herbicide product featuring Colex-DTM Technology which combines a new 2,4-D choline product, the latest formulation science and a proprietary manufacturing process developed to deliver ultra-low volatility, minimized potential for physical drift and lower odor.  Thus, two studies were performed to assess new advances in this technology to combat drift.  In 2010, a study was performed to assess the effectiveness of a shielded sprayer to reduce 2,4-D drift, compared to a unshielded (open boom) sprayer.  Weedar 64 (2,4-D amine) was applied at 1.12 kg ae/ha and tank mixed with Durango® DMA (glyphosate) at 1.12 kg ae/ha.  Herbicides were applied to PhytoGen 485 WRF cotton with a WSW wind between 9.65 to 12.87 kmph.  Yield data were collected at harvest to assess the impact of the herbicides in the treated area as well in the drift plume of each treatment.  Highly injurious drift was detected 8 rows downwind from the shielded sprayer, and 16 rows away with the unshielded sprayer.  Auxinic symptomology was detected at a maximum of 24 rows away from the application area for the shielded boom, and 64 rows away for the unshielded sprayer.

In 2011, a study was performed to compare GF-2726 to 2,4-D amine tank-mixed with Durango at two different boom heights (45.72 and 91.44 cm above cotton) in a simulated drift environment with a west wind of ~ 9.65 kmph.  GF-2726 contains glyphosate and 2,4-D choline, a new salt formulation of 2,4-D.  The formulation has been reported to have a low volatility and a reduced drift potential compared to 2,4-D amine.  The study was repeated at two geographic sites (Brooksville, Mississippi and Milan, Tennessee).  Herbicides were applied at both sites in July to PhytoGen 375 WRF cotton at 130.53 l/ha and an application speed of ~ 9.65 kmph with either XR 11003 or XR 11004 tips in Tennessee and Mississippi, respectively.  In Tennessee, data were collected using aerial imagery, with visual data collected 3, 7, 14, 21 and 42 days after application (DAA) for visual injury for each row downwind of the applications.  Data were also collected 6 and 12 weeks after application (WAA) for visual % fruit loss.  Data were collected in Mississippi using aerial imagery prior to application, 4 DAA, and 77DAA with visual data collected 28 and 42 DAA for evidence (yes/no) of epinasty, fruit loss or both.  Yield data were also collected at harvest for both sites.  Both sites showed that the GF-2726 applications at 45.72 and 91.44 cm above the crop appeared to have the best potential for reducing drift, with the lower boom height dispersing less than all other treatments.  In Tennessee, visual observations concluded that at 42 DAA, epinasty and fruit loss was detected out to 4 or 5 rows away from the treated area for the 45.72 and 91.44 cm boom height applications of GF-2726, respectively.  Epinasty and fruit loss was detected out 8 or 9 rows away from the application site 42 DAA for the 2,4-D amine + glyphosate applications at the 45.72 and 91.44 cm heights.  In Mississippi, fruit loss was detectable 42 DAA up to 21 rows away from the site of application for both the 45.72 and 91.44 cm applications of GF-2726.   Fruit loss and epinasty were detected 29 rows away from the site of application for both applications of the 2,4-D amine formulation tank mixed with glyphosate. Yield data from both locations indicated little injury response for all applications beyond the treated area.  Affected areas were smaller where GF-2726 was applied when compared to 2,4-D amine + glyphosate at either boom height.  Yields in the drift plumes were not significantly affected in 2011

™Enlist and Colex-D are trademarks of Dow AgroSciences LLC. ®Durango is a trademark of Dow AgroSciences LLC. Components of the Enlist Weed Control System have not yet received regulatory approvals; approvals are pending.  The information presented is not an offer for sale. ©2011 Dow AgroSciences LLC

A simulation analysis of the use and benefits of chloro-s-triazine herbicides, in U.S. field corn, sweet corn and grain sorghum employed previously established methods with 2009 regionally-specific data on weed incidence by species, crop yield losses by weed species, herbicide efficacy by weed species and herbicide use data by active ingredient. USDA Farm Resource Regions (FRR), as established by USDA served as the aggregation basis. 

Across five FRRs and two apportionment scenarios, models predicted that without atrazine weed control costs for U.S. field corn farmers would rise in 7 out of 10 FRR by scenario analyses and that yield would decline in all 10.  Scenario 1 assumes that corn farmers would not have access to atrazine or simazine and that acres treated with these herbicides would shift to other herbicides, including glyphosate, causing glyphosate use to expand beyond 2009 levels. In this scenario, field corn yield declines ranged from 4.4 to 15.3 bushels per current atrazine-treated acre. Averaged across all acres in the FRRs, yield declines ranged from 1.8 to 9.2 bushels per planted acre.  Averaged across all U.S. field corn acres, the projected yield decline is 6.4 bushels per planted acre.

Scenario 2 assumes that corn farmers would not have access to atrazine or simazine and that the glyphosate market share would remain constant at 2009 levels (approximately 75% of corn acres). In this scenario, field corn yields decline even more, between 5.7 and 17.6 bushels per current atrazine-treated acre. Averaged across all acres in the FRRs, yield declines range from 2.9 to 13.6 bushels per planted acre.  Averaged across all U.S. field corn acres, the projected yield decline is 7.7 bushels per planted acre.  The difference between 6.4 and 7.7 bushels per planted acre predicts a 20% marginal yield loss due to maintaining the percent of field corn acres treated with glyphosate at 2009 levels, and thus causing the use of non-glyphosate and non-triazine alternatives.

Atrazine is equally important for grain sorghum farmers.  This analysis showed that if atrazine and propazine were not available to U.S. producers, grain sorghum yield would decline approximately 17 bushels per triazine treated acre, or 13 bushels per planted acre, nationwide. Sweet corn yields also would decline without atrazine or simazine in all FRRs. Yield declines would range from 25% to 33% per atrazine-treated acre and approximately 20% per planted acre.  The author’s email address is dbridges@abac.edu.

With the concurrence of the US Environmental Protection Agency’s (EPA) Office of Pesticide Programs (OPP), the Weed Science Society of America (WSSA) Board of Directors created the position of Academic Weed Science Subject Matter Expert (SME) in 2007. This position is designed as a partnership between WSSA and EPA-OPP’s Registration Division – Herbicide Branch.  The function of this position is to develop a technical relationship between weed scientists and the EPA and to provide information to the Agency that is useful for addressing terrestrial weed issues which impact stakeholders. The interaction allows the Agency better access to current information when dealing with the broad range of issues that arise as well as answering highly specific technical questions. The position was modeled after the aquatic weed SME assignment. These SMEs work collaboratively with others to represent the overall weed science discipline and to identify key weed scientists who can provide input on topics of mutual concern to the Agency and the weed management community. Key issues include: the National Pollution Discharge Elimination System (NPDES) permits for application of pesticides on, near, or over water under the Clean Water Act (CWA) and management of herbicide resistant weeds. A tour of herbicide resistance management issues in the central U.S. was hosted in August 2011 by Kevin Bradley, Missouri, Bryan Young, Illinois, and Jason Norsworthy, Arkansas.  Attendees included representatives of all divisions within OPP, USDA-Office of Pest Management Policy, and WSSA.  Tour objectives were to demonstrate the problem of herbicide-resistant weeds in corn, soybean and cotton production systems, to share the current state of knowledge about herbicide resistance management, and to demonstrate the diversity of crop production systems within the region.

Three types of APHIS pest program decision making use slightly different models: 1) the new pest advisory group (NPAG) assessment and decision process; 2)the “not authorized For importation pending pest risk assessment” evaluation factsheet; and 3) the pest risk assessment (or weed risk assessment) system. The NPAG assessment and decision process is divided into domains used by the National Incident Management System (NIMS) Response Continuum. The five domains are Awareness; Prevention; Preparedness; Response & Recovery. This process is usually used for pests in an early detection and rapid response situation, triggered when APHIS is notified of a new or imminent pest. A new process has been recently established by APHIS for propagative plants not currently known in the U.S. "Not Authorized for Importation Pending Pest Risk Assessment" (NAPPRA) uses a different but similar process. A third category is used for evaluation of pest plants for potential regulation using a recently revised assessment system.

The nursery industry has introduced thousands of ornamental plants, but only a small percentage (~1%) has escaped to become invasive and cause economic or ecological damage. Thus, a pre-screening of potential introductions would be expected to accept most species as possessing low invasive potential, and identify relatively few as having a high probability of becoming invasive. Currently, several Weed Risk Assessment (WRA) models have been developed, the most common of which was developed by Paul Pheloung and his colleagues in Australia. This model is currently used to evaluate new introductions in other parts of the world. The model consists of 49 questions which require a considerable time commitment to answer, but has proved to be 90% accurate when comparing known invasive and non-invasive ornamental plant species and is currently used to evaluate new introductions in other parts of the world. In addition to being time consuming to use, it’s major  limitation for use as a practical application tool in a potential third party certification program is that while it is highly accurate in predicting invasive species, it is far less accurate in predicting non-invasive plants. That is, the WRA classifies too many non-invasive plants as invasive or potentially invasive. In this study we evaluated the accuracy of an abbreviated version (27 questions) of the Pheloung model, called the Plant Right Model. In an independent study with three biologists we compared 174 species, equally represented by known invasive and non-invasive species, using both the Plant Right and the Pheloung models. While the Pheloung model accurately classified all the invasive plants, it was not nearly as consistent in categorizing the non-invasive ornamental species, with the three evaluators being 4, 24, and 88% accurate. In contrast, the Plant Right Model was 99% accurate in correctly classifying invasive plants and averaged over the three evaluator and 95% accurate in classifying known invasive species. In addition, the abbreviated model takes about 8% less time to complete compared to the Pheloung model. These levels of accuracy suggest that the Plant Right WRA model may be an acceptable tool in discussions with the nursery industry on a potential third party certification process to evaluation current inventories, as well as to ensure that new potentially invasive plants are not introduced through the industry.

As the bioenergy industry gains momentum, the invasion potential of
these new crops must be evaluated in the context of current regulatory
regimes for noxious and invasive plants.  Our analysis shows that most
current regulatory typologies are ineffective in legislating action
for non-agricultural invasive species in unmanaged systems.  We
recommend allocating authority for evaluating and listing regulated
species to formalized invasive plant councils (IPCs), which could
remove the political influence driving noxious weed lists, and would
empower those better tuned to impending threats.  We endorse
preventive measures suggested by the Invasive Species Advisory Council
to lower the risk of invasiveness in bioenergy crops, but we go
further to suggest that new crops should be required to undergo field
testing to evaluate escape and invasion potential prior to release,
and to be evaluated by standardized and improved Weed Risk Assessment
(WRA) protocols administered by authorized IPCs.  Recognizing that
preventive measures are not failsafe, we also recommend a negligence
liability scheme for anyone introducing new species or genotypes for
production.  Under this model, new products must be assessed for
potential invasiveness prior to introduction to avoid liability for
future impacts.  These recommendations, if adopted, would protect
ecosystems to a greater extent than achieved by current noxious weed
legislation, and could have strong implications for bioenergy
producers and others in plant industry.

Invasive species can spread rapidly and cause great harm to the environment, economy, and in some cases to human health. There is widespread agreement that invasive species are best prevented; where they cannot be prevented, their establishment and spread stopped.  In addition, invasive plant invasions often do not have the same urgency or attention as do insect, animal, or pathogen invasions.  Failure to take timely effective action can result in a loss of the last opportunity to halt the establishment of an additional invasive species.  The federal government alone spends over $1.5 billion on invasive species prevention and control each year. However, the bulk of the costs of controlling invasive species fall to states, tribes, local governments, and private land owners. Left unchecked invasive species can spread exponentially. Doing nothing is not an option.  Dollars must be found within already strapped budgets, often by taking away from other vital efforts. Invasive species cost us all. Rapid response grants have been called for repeatedly and enjoy wide support. They are seen as essential tools to halt the established and spread of invasive species. Yet, how to actually accomplish this remains a central challenge.

Mechanisms, such as rapid response grants, must be responsive enough to meet urgent needs and streamlined avoid undue bureaucratic obstacles. However, fairness and accountability must be maintained.  There will be budgetary limits. Funding a project that is too large could preclude all other projects. Supporting projects that are too small runs the risk of doing only the trivial. Criteria that match the scale of potential projects to available funds must be in place, but also flexible if funding levels change.  Although rapid response efforts are often urgent, they may not be short in duration. The geographic scale of work can expand. On-the-ground efforts are subject to local factors, such as weather, that cannot be predicted fully.  How long funding is provided, where it can be spent, and contingency planning must all be taken into account.  Balancing support among different species, locations, and  habitat types will require a combination of formulaic and risk-based funding. Additionally, funds may have specific allocation restrictions that limit what species, locations, and types of recipients can receive support. Perverse incentives and overreliance on the funding source must be avoided. Data must be collected to support the administration and coordination of the program as well as an on-going review and refinement of the process.  All this must be done while keeping overhead as low as possible. Ultimately, any such mechanism will have to maintain support for species and issues that have not and might never have become “big and bad” problems.  To do that, the focus must shift from the invasive species to the value and importance of the threatened resources. 

Through the 2007 Energy Independence and Security Act the federal government has mandated a 20% reduction in CO₂ emissions accompanied by the production of 36 billion gallons of transportation fuel, both of which need to be achieved through the use of alternative energy sources. The most promising crops for co-firing and bioethanol will likely include a selection of non-native plant species.  Economically and sustainably competitive energy crops will need to be high yielding, perennial species, which require minimal inputs despite their ability to grow on marginal land. These traits, which are highly desirable for successful cultivation, have caused concern for their potential to become invasive.  

The use of weed risk assessments has become a useful tool for predicting invasive potential in many parts of the world.  To evaluate several proposed biofuel crops we used the Australian Weed Risk Assessment (A-WRA) and the Animal and Plant Health Inspection Service PPQ weed risk assessment (PPQ-WRA), which will serve as the new U.S. standard for evaluation of potentially invasive species.  Our evaluation compared newly proposed biofuels: Arundo donax, Miscanthus sinensis, M. x giganteus, and Panicum virgatum against the known weedy species specifically introduced for agronomic purposes: Elymus repens and Dactylis glomerata as well as the non-weedy crops: Glycine max and Zea mays. The two risk assessment models can be used to predict the invasive potential of future bioenergy crops in this emerging industry, with the potential to assist in future policy and management decisions.  Both assessments suggest that many of the leading biofuel candidates have the potential to become weedy in specific ecoregions of the United States.  Differences in the screening process are evident in the percentage of plants rejected by the Australian model (82%) in contrast to those receiving a high risk rating by the APHIS model (72%). However it should be noted, despite the similar percentage of high risk recommendation by the assessments, the species receiving acceptable or low risk ratings was not identical between the two.  For example, the A-WRA recommends rejecting Panicum virgatum, while the PPQ-WRA suggests further evaluation. Conversely the PPQ-WRA rejects Sorghum bicolor (grain), but is scored acceptable by the A-WRA. While both models benefit from objectivity, the PPQ-WRA includes the ability to include uncertainty and leaves management decisions to policy makers. The PPQ-WRA also allows hypothetical iterations, which can be run for plants not yet in the U.S. or taking into consideration genotypic variability.  Based on the outcomes of these assessments we can be better prepared for widespread commercialization of these crops, while planning ahead for improved stewardship in those that are predicted to be of high risk. 

Goatsrue (Galega officinalis) is a federally-listed noxious weed that is both fatal to livestock and highly invasive in riparian areas. It has limited distribution nationwide. Goatsrue was discovered in Pennsylvania at six locations in 1998 as a result of the USDA-funded cooperative survey. Three of these locations were in McKean County and goatsrue was added to the Pennsylvania Department of Agriculture (PDA) Noxious Weed Control List in 2000. Additional surveys in 2009 identified more goatsrue populations emerging in McKean County in the vicinity of Smethport. PDA responded and began intensively surveying the county in the fall of 2009. Since its discovery, the PDA has assisted affected property owners with control measures to prevent the flowering and further spread of this noxious weed, and is targeting sites for eradication. As of 2011 populations have been detected in 5 PA counties. Less than 7,000 square feet of infested roadside ditches, meadows, and streams are known from 8 sites in Cameron, Potter and Montgomery Counties. Less than a ½ acre has been found in Elk County, along forest roads in the Alleghany National Forest and Elk State Forest. These counties are being targeted for eradication. In McKean County, however, approximately 43 acres of goatsrue has been discovered, surveyed and monitored as of the fall of 2011. The infestations can be found along roadside ditches, driveways, cropland meadows, and edges of waterways (streams, lakes, rivers) on 174 properties in 11 municipalities. Thirty-six sites are state-owned, 30 sites are municipality owned, 2 sites are federally-owned and 101 sites are privately-owned. The 2007 Ag Census Report for McKean County lists 313 farm operations and 41,466 acres of land dedicated to farming. The county is 982 sq. mi. of which 2.6 sq. mi. are waterways. PDA and partners are focused on preventing the poisonous plant from invading cropping and pasture systems and protecting the counties waterways while targeting individual populations for eradiation. Since 2009 at least 85% of the known locations in McKean County have been prevented from producing new seed. With the exception of areas that can only be mowed, pre- and post-emergence herbicides have been effective in killing 95% of existing plants and emerging seedbank.

Giant hogweed (Heracleum mantegazzianum) is a federally-listed noxious weed that is both poisonous to humans and highly invasive in riparian areas with limited nationwide distribution. Giant hogweed (GH) was discovered in Pennsylvania (PA) in 1985; two years after the USDA-APHIS declared the plant a federal noxious weed. As of 2011, GH had been found in 18 states and in Canada. It was added to the PA Noxious Weed Control List in 2000. PDA and USDA-APHIS launched the GH Hotline in 1998 and created a national giant hogweed campaign to promote awareness of this poisonous plant. Since the PA state program began, 453 sites have been found in 17 PA counties. The targeted eradication program has been very successful and 325 of these sites have been declared eradicated.  More than 55% of the PA populations are found in Erie County. Sites are still known in northwestern PA counties of Crawford, Mercer, McKean, Venango, and Warren. Isolated sites are also known from Elk, Potter, Butler, Blair, Huntingdon, Carbon, and Wayne counties. PDA detected 11 new populations of GH in 2011, however, they all relate to existing sites on an adjoining landowner’s property. In all only 74 (16%) of the 453 known sites in the state required treatments in 2011.

In Ohio, with the cooperation of the PDA and USDA-APHIS, several sites of GH have been treated in Ashtabula and Lake Counties. In 2011 a new site was found in Cuyahoga County. The Ohio Department of Agriculture will continue to monitor all known sites until GH is eradicated and relies heavily on local townships and municipalities for their help in reporting and controlling GH. Maine reports that GH is not prevalent with less than 25 known sites in the state, but new sites are being reported each year. In New York, the GH program is in its 3rd field season with more than 800 sites surveyed, monitored or controlled in 2010 by the NY Department of Environmental Conservation. More than 900 sites have been detected in 35 NY counties since the media began extensively reporting on the GH infestations.

Although foliar herbicide absorption has been studied intensively, there is currently no standardized method for data analysis when evaluating herbicide absorption over time. Most peer-reviewed journals require the treatment structure of data be incorporated in the analysis; however, many herbicide absorption studies published in the past 5 yr do not account for the time structure of the experiment. Herbicide absorption studies have been presented in a variety of ways, making it difficult to compare results among studies. Asymptotic regression and rectangular hyperbolic models with similar parameterizations are proposed, so that the maximum herbicide absorption and absorption rate may be adequately modeled and statistically compared among treatments. Adoption of these models for herbicide absorption analysis over time will provide a standardized method making comparison of results within and among studies more practical.

Plant cells possess a number of membrane bound organelles that play important roles in compartmentalizing a large number of biochemical pathways and physiological functions that have potentially harmful intermediates or by-products.  The plasma membrane is particularly important as it holds the entire cellular structure whole and is at the interface between the cell and its environment.  Consequently, breaches in the integrity of the lipid bilayer, often via reactive oxygen species (ROS)-induced stress membrane peroxidation, result in uncontrolled electrolyte leakage and in cell death.  A simple 3-step bioassay was developed to identify compounds that cause electrolyte leakage and to differentiate light-dependent mechanisms of action from those that work in darkness.  Herbicides representative of all known modes of action (as well as several natural phytotoxins) were selected to survey their effects on membrane integrity of cucumber cotyledon discs.  The most active compounds were those that are known to generate ROS such as the electron diverters and uncouplers (paraquat and dinoterb) and those that either were photodynamic (cercosporin) or caused the accumulation of photodynamic products (acifluorfen-methyl and sulfentrazone).  Other active compounds targeted lipids (diclofop-methyl, triclosan and pelargonic acid) or formed pores in the plasma membrane (syringomycin).  Herbicides that inhibit amino acid, protein, nucleotide, cell wall or microtubule synthesis did not have any effect.  Therefore, it was concluded that the plant plasma membrane is a good biomarker to help identify certain herbicide modes of action and their dependence on light for bioactivity.

Natural herbicides approved in organic agriculture are primarily non-selective burn-down essential oils applied POST.  Multiple applications are often required due to their low efficacy.  To address this problem, the in vivo herbicidal activity of manuka oil, the essential oil distilled from Leptospermum scoparium (J.R. et G. Forst), was tested on selected broadleaf and grass weeds.  While manuka oil exhibited good POST activity when applied in combination with a commercial lemongrass oil-based herbicide, it ultimately demonstrated interesting PRE activity, providing control of crabgrass seedlings at a rate of 3 L ha^-1.  Manuka oil and its main active ingredient, leptospermone, were stable in soil for up to 7 days and had half-lives of 18 and 15 days, respectively.  The systemic activity of manuka oil addresses many of the major limitations normally associated with natural herbicides.  Additionally, its soil persistence opens up a multitude of new possibilities for the use of manuka oil as a tool for weed management and may be a potential bridge between traditional and organic agriculture. 

Novel herbicidal compounds are highly valued as potential solutions to many of the difficulties present in weed management including but not limited to herbicide resistant weed biotypes. Finding novel, economically viable herbicide chemistry that targets a novel mode/site of action is not an easy task.  Therefore, it is imperative to study areas of new chemistry associated with modes of action that have few reported cases of resistant weed biotypes.  To that end, several companies have recently evaluated a new area of chemistry containing molecules with para–chlorophenyl substitutions that have activity consistent with auxin mimic herbicides. Several patents have been filed covering multiple variations of these para-chlorophenyl substitutions on chlorinated pyridine and pyrimidine carboxylic acids.  In general, the patent literature suggests that these compounds are highly active at rates below 100 g ai/ha on several broadleaf weeds with crop safety to multiple monocot crops including excellent activity on weeds in flooded rice.  Five novel analogues were synthesized and tested in greenhouse studies at the University of Tennessee in 2011. The compounds were applied preemergence and postemergence at rates between 50 to 2500 g ai/ha alongside the commercial auxin mimic herbicide standards clopyralid at 280 g ai/ha and quinclorac at 840 g ai/ha. Assay species treated included the broadleaf weeds redroot pigweed (Amaranthus retroflexus), field bindweed (Convolvulus arvensis), and velvetleaf (Abutilon theophrasti), as well as the monocot plants, corn (Zea mays), large crabgrass (Digitaria sanguinalis), barnyardgrass (Echinochloa crus-galli), and the sedge species yellow nutsedge (Cyperus esculentus). Synthesis strategies for these new analogues as well as structure activity relationships among this new class of chemistry will be discussed in this presentation.

The frequent occurrence of weeds with resistance to herbicides threatens the productivity of modern agricultural systems. Currently, there are over 200 resistant weed species worldwide. There is a need to improve our understanding of the patterns of resistance in order to develop and implement effective herbicide resistance management plans.  Historically, there has been a focus on the mechanism of resistance in those species that have developed resistance, without an examination of the broader view of why some weeds are more prone to developing resistance than others.  In this study, we have examined multiple botanical characters of 100 common weed species to determine if there are combinations of botanical characters that predispose a given weed to developing resistance. A principal components analysis was used to separate clusters of weeds that have developed herbicide resistant from species that have not using botanical characteristics .  The botanical factors of fecundity, seedbank longevity, outcrossing, climatic adaptation, geographic distribution, family, order, past cases of resistance were examined. From this analysis, a ranking can be assigned that can be used to delineate those weeds most apt to develop herbicide resistance.  This information can be integrated into a matrix to predict what weed-herbicide-weed management combinations have the greater chance of developing resistance problems.

Low rates of herbicides typically select for the large number of genes that confer a small modicum of resistance (usually those that increase the rate of herbicide degradation – as polygenes, gene amplifications, or allelic modifications of catabolism genes).  Target site mutations with a much greater level resistance are far more rare, and while on they can be selected for at high rates of a given herbicide, they are less likely to be found at the lower rates. Many had assumed that only those chemicals that directly affected DNA replication and repair were mutagens.  There are many ways to increase mutation rates indirectly by depleting the cell of material needed of DNA replication and repair (e.g. of ATP and NADPH) or increase DNA damage (e.g. oxidative stress) beyond the threshold capacity of DNA repair enzymes. Stress is a general enhancer of mutation rates, as the cell often requires ATP and/or NADPH to overcome the stress, or stress directly damages the DNA. 
At very low herbicide rates, a certain low proportion of weeds may receive a sub-lethal dose, yet survive despite being highly stressed by the herbicide. Thus, the survivors are likely to have more mutations due to the stress.  These would include mutations leading to herbicide resistance, both for multi-factorial (polygenic, gene amplification, sequential allelic mutations), as well as for major gene resistance.  The more such small mutations conferring a modicum of resistance occur, the quicker they can recombine or duplicate, conferring much higher levels of resistance.  Weed resistance management strategies should consider how to eliminate the sub-population of weeds with the high mutation rates, but the best strategy is probably to avoid too low application rates of herbicides from the onset. The mutagenicity of sub-lethal doses also has implications to herbicide discovery, as many excellent herbicide leads were dropped when found that they were mutagenic at low doses in a bacterial mutagenesis (Ames) test.  We now know that stressed bacteria mutate at higher rates than non-stressed bacteria. Many such compounds may have stressed the bacteria at the levels tested, but below regulatory residue threshold doses would not have stressed mammalian systems enough to increase the mutation rate.  If this had been considered good potential pesticides would not have been lost.  This must also be considered in re-registration of older compounds. Thus, it is important for many reasons that we must be cognizant of the potential of very low doses to increase the rate of resistance mutations via the stressing of target weeds.
References

Gressel, J.  and A. A. Levy (2010) Stress, mutators, mutations and stress resistance, in  Abiotic Stress Adaptation in Plants: Physiological, Molecular and Genomic Foundations, A. Pareek, S.K. Sopory, H. J. Bohnert, and Govindjee, eds., Springer, Dordrecht, pp. 471-483.
Gressel, J. (2011) Low pesticide rates may hasten the evolution of resistance by increasing mutation frequency. Pest Management Science 67:253-257.

jonathan.gressel@weizmann.ac.il

The adoption of no-till farming systems in Australia has increased reliance on herbicides for weed management. Both glyphosate and paraquat are used extensively in many farming systems including the pasture seed industry. The intensive use of paraquat for weed control in pasture seed production increases risks for the evolution of resistant weed species. Rigid ryegrass (Lolium rigidum Gaud.) is the most significant weed in Southern Australian agriculture and wide-spread resistance to glyphosate has been well documented in this species; however, paraquat resistance in this species had not previously appeared in Australia. Rigid ryegrass plants were collected from pasture seed fields reporting problems with control by paraquat in South Australia and tested for herbicide resistance. Multiple populations were identified as having varying degrees of resistance to paraquat. Dose response studies showed that one of these populations had resistance at 40 times the field rate of paraquat. Two populations collected were also found to have resistance to both glyphosate and paraquat.  Translocation studies on one paraquat resistant population showed reduced translocation of paraquat from the treated leaves in the resistant population compared with a known susceptible population.  Inheritance studies show resistance is partially dominant and inherited on the nuclear chromosome.  The appearance of rigid ryegrass populations resistant to paraquat and to both paraquat and glyphosate has implications for the sustainable use of these herbicides in weed management in this industry.

Waterhemp (Amaranthus tuberculatus) is a difficult-to-control weed in Illinois soybean and corn production.  This is in part due to the evolution of multiple herbicide resistances in waterhemp, which is facilitated by its dioecious biology and genetic diversity.  A population of waterhemp (designated MCR) from a seed corn field in McLean County, Illinois displays resistance to mesotrione and other 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitors, as well as to atrazine and certain ALS-inhibiting herbicides.  Growth chamber and laboratory experiments were conducted to determine if differential herbicide uptake or metabolism are the basis for mesotrione resistance in the MCR population.  Mesotrione-resistant (MCR) and mesotrione-sensitive (ACR and WCS) biotypes of waterhemp were treated with radiolabeled mesotrione for analyses of uptake and metabolism during time course experiments.  Absorption studies in intact plants revealed that mesotrione uptake was not significantly different among biotypes.  However, initial rates of mesotrione metabolism were faster in MCR than in ACR and WCS (using whole plants) and half-lives of mesotrione in MCR and corn were shorter than in ACR and WCS (using an excised leaf assay), which correlate with phenotypic responses to mesotrione applied postemergence in these waterhemp biotypes and in corn.  The cytochrome P450 inhibitors malathion and tetcyclacis significantly inhibited mesotrione metabolism in excised leaves of MCR and corn at 6 and 24 HAT, but had no effect in ACR leaves.  Our results indicate that enhanced metabolism in MCR may contribute significantly to mesotrione resistance, but further research is needed to determine if additional non-target site mechanisms may also contribute to mesotrione resistance in the MCR population.

Palmer amaranth, Amaranthus palmeri continues to be a serious weed problem in crop production fields in Kansas.  Seeds were gathered from Palmer amaranth plants in Stafford County that were treated postemergence with pyrasulfotole&bromoxynil 1:8 ratio at 245 g/ha and from plants in the same field not treated with a HPPD inhibiting herbicide.  Reports from evaluation of these populations in greenhouse and field dose response experiments indicated the populations were 7 to 11 times more resistant to pyrasulfotole&bromoxynil than a susceptible population.  The objective of this research was to determine the mechanism of inheritance, and to determine the level of resistance of this population to mesotrione, tembotrione, and topramezone.  Surviving ‘R’ plants were crossed with susceptible plants and progeny treated with pyrasulfotole&bromoxynil to determine if the resistant trait was passed through pollen.  Palmer amaranth is a true dioecious species.  Surviving progeny, assuming heterozygosity and that the trait was transferred via pollen, were crossed and 167 progeny were treated with a 2X rate (604 g) of pyrasulfotole&bromoxynil to evaluate segregation for the trait.  Visual evaluations 10 d after treatment suggest 33% of the plants were recovering from treatment and were rated 40% injured or less.  Thirty eight percent of the plants were killed from the treatment.  Initial crosses also were made with male and female plants surviving pyrasulfotole&bromoxynil treatment to develop homozygous resistant plants.  Progeny were treated and crosses from surviving plants were made.  Progeny of these crosses were used in greenhouse dose response experiments.  Dose response curves were developed using AMR 8.0 based on visual evaluations 3 weeks after treatment. The rates required to give 50% control of the resistant progeny were 5.4 g of mesotrione, 4.9 g of tembotrione, and 0.4 g of topramezone. The S population was very susceptible to these HPPD inhibitors resulting in resistance indexes of 54 for mesotrione, 55 for tembotrione, and 63 for topramezone.  The Palmer amaranth biotype evaluated in these experiments is resistant to several of the HPPD inhibiting including isoxaflutole, and to atrazine and is not controlled with thifensulfuron or  imazamox herbicides which will make control strategies of this population much more complex for crop producers.  Further work must be conducted to fully understand the inheritance of this HPPD resistant trait in Palmer amaranth.  cthompso@ksu.edu

Barnyardgrass biotypes from Arkansas (AR1 and AR2) and Mississippi (MS1) have evolved cross resistance to several acetolactate synthase (ALS) -inhibiting herbicides, including bispyribac-sodium, imazamox, imazethapyr, and penoxsulam.  Dose response studies revealed that AR1, AR2, and MS1 biotypes were >94-, >94-, and 3.3-times, respectively, more resistant to imazamox; >94-, 30-, and 9.4-times, respectively, more resistant to penoxsulam; and 15-, 0.9-, and 7.2-times, respectively, more resistant to bispyribac-sodium.  Studies were conducted to evaluate if increased herbicide metabolism by cytochrome P450 monooxygenase or mutation in ALS gene were the mechanism of resistance to various ALS-inhibiting herbicides in these biotypes.

Malathion inhibits the activity of cytochrome P450 monooxygenase, an enzyme known to metabolize various herbicides.  Addition of malathion at 1000 g ai ha^-1 to field application rate of penoxsulam (35 g ai ha^-1) in comparison to penoxsulam applied alone reduced dry weight of AR1, AR2, and MS1 biotypes by 40, 94, and 96%.  Addition of malathion to field application rate of imazethapyr (105 g ai ha^-1) did not affect dry weight of any resistant biotype, but increased mortality of MS1 biotype.  Addition of malathion to field application rate of bispyribac-sodium (30 g ai ha^-1) had no effect on dry weight, but increased mortality of AR1 and MS1 biotypes to 100% compared to 70 and 85% mortality of AR1 and MS1 biotypes, respectively, by bispyribac-sodium at 30 g ha^-1 applied alone. 

The ALS gene sequence alignment of AR1, AR2, MS1, and susceptible biotypes revealed that a mutation in the conserved region of ALS gene of AR1 and AR2 biotypes resulted in the substitution of alanine₁₂₂ to valine and threonine, respectively.  However, no mutation was detected in the MS1 biotype.  Mutation at alanine₁₂₂ is known to confer high level of resistance to imidazolinone herbicides, as was observed in AR1 and AR2 biotypes.  Low level of resistance to bispyribac-sodium in AR1 and MS1, and to imazamox and penoxsulam in MS1 is probably due to the increased metabolism of herbicides in resistant biotypes by cytochrome P450 monooxygenase.  These studies show that multiple mechanisms of resistance are involved in imparting cross resistance to ALS-inhibiting herbicides in these resistant barnyardgrass biotypes.

Glyphosate chelates metal cations. Claims have been made that glyphosate alters mineral nutrition of glyphosate-resistant (GR) crops, especially causing reductions in Mn, Fe, and Ni.  Others have not found such effects.  The purpose of this study was to determine the effects of glyphosate on mineral content of GR soybean leaf and seed  tissues after treatment with recommended rates of glyphosate.  Greenhouse and field studies were conducted.  In the field, glyphosate was applied to test plants at 0.86 kg ae/ha at both 3 and 6 weeks after planting (WAP). Young and old leaf tissues were sampled at both 9 and 12 WAP, and seeds were sampled at harvest.  Inductively coupled plasma mass spectroscopy was used to accurately determine the content of 14 minerals that will chelate glyphosate (K, Ca, Mg, Fe, Zn, Mn, Ba, Sr, Ni, Cu, Cd, Cr, Co, and Se).  In the field study, no effects were found on content of any minerals in young or old leaves at either time point or in seeds.  Similar results were obtained in greenhouse studies.  Our results support the view that recommended rates of glyphosate do not alter mineral nutrition of GR soybean in non-mineral deficient soils.

Sequence Analysis of EPSP Synthase in Mutagenized Spring Wheat. A. Aramrak*¹, I. C. Burke¹, C. M. Steber², A. H. Carter¹, K. Kidwell¹, ¹Washington State University, Pullman, WA, ²USDA-ARS, Pullman, WA.

ABSTRACT

Glyphosate is a broad spectrum herbicide that potently inhibits 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), an enzyme in shikimate pathway. Several weed populations have evolved glyphosate resistance through a point mutation of EPSPS at position 106 of proline to serine, threonine, alanine, or leucine (P106S/T/A/L). Glyphosate-resistant spring wheat cv. Louise (Triticum aestivum, AABBDD) was developed by mutagenesis using ethyl methanesulfonate (EMS), which induces base changes from GC to AT. To investigate whether the EMS-induced point mutation of EPSPS at position 106 confers glyphosate resistance in mutagenized spring wheat lines, epsps sequence and gene location were studied. Mutant spring wheat lines designated as ORI-Louise and Louise 33-6-1-4, wild-type spring wheat cv. Louise, wheat progenitors [T. turgidum (AABB), Aegilops tauchii (DD), T. monococcum (AA), and A. speltoides (BB)], and Nullitetras were used in this study. Specific primers for amplifying and for identifying the epsps gene location were designed based on epsps mRNA sequence of wheat cv. Chinese spring (EU977181) and based on sequenced EPSPS, respectively. Extracted RNA from individual plants were synthesized to cDNA by reverse transcriptase. Using cDNA as a template and proofreading Taq DNA polymerase in PCR amplification, PCR products were cloned into a pGEM-T vector. Twelve independent clones carrying a pGEM-hexaploid epsps and three independent clones carrying a pGEM-progenitor epsps were randomly selected to sequence. The partial ORF of epsps gene determined was 1190 bp in length and contained significant GC content - approximately 52% - and predicts for a polypeptide of 395 amino acid residues. The epsps sequence of hexaploid wheat can be divided into D and AB consensuses. Using Nullitetra DNA as templates in PCR amplification, epsps genes were located on chromosome 7A, 5B, and 7D. The alignment of EPSPS sequences indicated that P106 is conserved in both wild type and mutant lines. Four out of twelve clones of ORI-Louise contained the point mutation of nucleotide C715T that resulted in an amino acid substitution of L239F. No point mutation was found in the mutated Louise 33-6-1-4 line. Mutagenized spring wheat lines ORI-Louise and Louise 33-6-1-4 do not have the mutation at P106 in the target site as a mechanism for glyphosate resistance. 

Glyphosate is the most widely used herbicide for weed control in Australia, in both agricultural and non-agricultural situations. The first glyphosate resistant weed population in Australia was confirmed in 1996 in rigid ryegrass. Since then, resistance has been found in a growing number of other weed species including jungle rice, first document in 2007, liverseed grass in 2008, hairy fleabane and windmill grass in 2010 and most recently ripgut brome in 2011. Currently, there are 309 documented glyphosate-resistant populations of rigid ryegrass, 49 of hairy fleabane, 21 of jungle rice, 3 of liverseed grass, 2 of windmill grass and 1 of ripgut brome.

Altered translocation of glyphosate to the leaf tips has been found to be the most common mechanism of resistance in rigid ryegrass, however a few cases of target-site mutation based resistance have also been observed. In addition, two populations of rigid ryegrass containing both resistance mechanisms have been identified. Target-site mutations have been found in resistant jungle rice and liverseed grass. No target-site mutation has been identified in the resistant ripgut brome.

Glyphosate resistant populations of rigid ryegrass have been identified from a variety of different agricultural situations, such as winter grain crops, chemical fallows, orchards and vineyards, while resistance in the other weed species has occurred mainly in chemical fallows. Resistance has also begun to appear in a number of non-agricultural settings including fence lines, roadsides, railways and irrigations channels. In a recent survey of non-agricultural areas likely to be of high risk of glyphosate resistance conducted across Australia, more than 50% of 82 hairy fleabane samples, 53% of 188 rigid ryegrass samples and 2% of 151 windmill grass contained high numbers of glyphosate resistant individuals. As resistance in these non-crop areas has the potential to spread into other areas and cause management difficulties elsewhere, this large amount of resistance identified suggests the need for increased focus on management in these areas

Complaints of poor kochia (Kochia scoparia) control with glyphosate in western Kansas have increased in recent years. We collected eight suspected glyphosate-resistant kochia biotypes from western Kansas in 2010 and conducted greenhouse and laboratory experiments to confirm and quantify the level of glyphosate resistance in these biotypes. In whole plant bioassay, a series of glyphosate rates ranging from 0.04 to 5.4 kg ai ha^-1 were applied on 15-cm tall plants. A known glyphosate susceptible biotype from Hays, KS was used as a control and the experiment included 6 replications.  Mortality and growth reduction were determined 21d after glyphosate treatment. Based on the LD₅₀ (50% mortality) and GR₅₀ (50% growth reduction) values, the suspected kochia biotypes were four- to eight-times and three- to six-times more resistant to glyphosate, respectively, compared to the susceptible biotype.  An In-Vivo shikimate assay was performed by treating 4-mm leaf discs from fully expanded young leaves with 200µM glyphosate and incubating for 16 hours under continuous light. The assay included 8 plants from each population and was done in duplicate.  The susceptible biotype accumulated at least three times more shikimic acid than did the suspected resistant biotypes. This confirms the suspected wide-spread presence of glyphosate-resistant kochia throughout western Kansas and reinforces the need for increased awareness and implementation of alternative (to glyphosate) management practices to mediate the problem.

Eastern black nightshade (Solanum ptycanthum Dunal) is a problem in several crops on Virginia’s Eastern Shore including corn, soybean, and tomato.   Most growers on the Eastern Shore utilize no-till practices which rely heavily on herbicides for weed control.  ALS-inhibiting herbicides such as chlorimuron and thifensulfuron have been frequently relied upon to control weeds in these particular crops.  However, a lack of control using sulfonylurea herbicides has been reported in eastern black nightshade.  In the summer of 2010 a field trial was established in a corn field in Eastville, VA.  Plots were 2 m x 6 m and consisted of 4 replications per treatment.  This same trial was repeated in 2011 as a greenhouse study.   The following herbicides were applied POST before the V6 growth stage of corn: bromoxynil (21 g ai ha^-1), dicamba (561 g ai ha^-1)+ NIS (0.25%) + UAN (1.25% v/v), nicosulfuron (35 g ai ha^-1) + NIS (0.25%) + 30% N (0.25%) , nicosulfuron (26 g ai ha^-1) + rimsulfuron (14 g ai ha^-1) + COC (1% ) + 30% N (0.25%), rimsulfuron (16 g ai ha^-1) + thifensulfuron (4 g ai ha^-1) + isoxadifen-ethyl (8 g ai ha^-1) + NIS (0.25%)  + 30% N (0.25% ), acetochlor (1346 g ai ha^-1) , acetochlor (1346 g ai ha^-1) + glyphosate (841 g ai ha^-1) + NIS (0.25%), and glyphosate (841 g ai ha^-1).  The additional treatment of imazamox 44 g ai ha^-1 was added to the greenhouse study to screen for possible ALS resistance.  In 2010 plots were visually evaluated for percent control 1, 2, and 3 weeks after treatment (WAT).  In 2011 individual plants were evaluated for percent injury 1, 2, 3, and 4 weeks after treatment.  4 WAT plants were harvested and dry weights obtained.  There was no visible injury to the crop throughout the growing season. In both studies glyphosate alone provided greater than 85% injury/control but declined by the end of the study. The acetochlor + glyphosate showed a similar trend in both studies with plants recovering by 3 and 4 WAT.  Results of the bromoxynil and dicamba treatment varied between years, with bromoxynil providing less than 30% control and dicamba providing less than 70% control 3 WAT in 2010.  However, both herbicides showed greater than 99% injury 3 WAT in 2011.  Even though injury symptoms were observed with the sulfonylurea herbicides, all provided less than 25% injury/control of eastern black nightshade in both studies, whereas plants sprayed with imazamox in 2011 showed 95% injury 4 WAT.  This helps to confirm that eastern black nightshade on Virginia’s Eastern Shore is tolerant to the sulfonylurea family of ALS-inhibiting herbicides, but may still be susceptible to the imidazolinone family of ALS-inhibiting herbicides.  This study also shows that glyphosate may not be a viable means of providing seasonal control of eastern black nightshade.

This presenter did not attend the WSSA meeting, and did not notify the WSSA of his absence.

Annual bluegrass (Poa annua) invades newly-established and established grasses grown for seed in OR causing significant production, economic and seed quality challenges for grass seed growers.  In addition, annual bluegrass populations have evolved resistance to several commonly applied herbicides used to manage annual bluegrass in grasses grown for seed including diuron and ethofumesate.  Field experiments were conducted from 2007-2011 to determine the potential for using fall-applied applications of indaziflam and pyroxasulfone to control annual bluegrass in established perennial ryegrass and tall fescue grown for seed.  A range of application rates of these two herbicides were compared to current industry standards including applications of flufenacet+metribuzin.  Annual bluegrass control, crop injury and crop yield were evaluated each year.  Indaziflam applications at rates ranging from 12-50 g ai/ha resulted in excellent annual bluegrass control (greater than 90%), but injured the perennial ryegrass and tall fescue. However, the tall fescue was more tolerant to indaziflam than the perennial ryegrass.  Applications rates of 12-25 g ai/ha of indazaiflam applied once during the life of the grass seed stand may be appropriate to manage annual bluegrass.  Indaziflam applications over multiple years may reduce the life of the stand, particularly perennial ryegrass stands.  Pyroxasulfone applications also resulted in excellent annual bluegrass control (greater than 90 %) and were less injurious to both tall fescue and perennial ryegrass than indaziflam applications.  Application rates ranging from 50-100 g ai/ha resulted in little crop injury and no yield loss.  These studies suggest that the active ingredients indaziflam and pyroxasulfone appear to provide adequate annual bluegrass control as well as crop safety when applied to established perennial ryegrass and tall fescue.  Additional studies utilizing indaziflam and pyroxasulfone as replacements for diuron applied at significantly lower rates then those discussed above during the traditional carbon-seeding establishment phase of grasses grown for seed are ongoing.  Results from these studies indicate that both indaziflam and pyroxasulfone also have utility when used during this establishment phase of perennial ryegrass and tall fescue grown for seed.  Therefore, research trials are ongoing to build needed weed control efficacy and crop safety data sets with these compounds should industry choose to pursue labels and uses of these materials in grasses grown for seed.

Abstract.
Miscanthus giganteus is under consideration for biofuel production in the US, however there is little to no
information on the effects of herbicides for establishment and control of this species. Therefore,
greenhouse and field studies were conducted in summer 2011 at Tifton, GA with the objective of
screening potential PPI, PRE and POST emergence herbicides and herbicide combinations for M.
giganteus when establishing from vegetative rhizomes. For the POST treatments, M. giganteus was
established from rhizomes in 7.6 L containers using an organic medium amended with soil. Containers
were placed outdoor, received daily irrigation and proper fertilization. After establishment to
approximately 40 cm in height, M. giganteus was treated with POST applications of thifensulfuron,
metsulfuron, tribenuron, chlorimuron, nicosulfuron, primisulfuron, halosulfuron, rimsulfuron,
trifloxysulfuron, sulfometuron, imazamox, imazethapyr, imazaquin, imazopic, pyrithiobac, cloransulam,
sethoxydim, clodinafop, dichlofop, fluazifop, tembotrione, topramezone, betazon, metribuzin, pinoxaden,
carfentrazone and flumioxazin, to evaluate efficacy. Nicosulfuron, trifloxysulfuron, sulfometuron,
clodinafop, fluazifop, pyrithiobac caused significant injury, reducing height as well as dry weight as
compared to the non-treated control. Sethoxdim, dichlofop, imazamox, flumioxazin, imazapic and
imazethapyr caused either significant lower height or injury; these treatments also produced dry weights
lower than 80% of the non-treated control, but the differences were not significant. PPI and PRE
emergence herbicides included ethalfluralin, oryzalin, trifluralin, EPTC, EPTC plus atrazine, oxadiazon,
imazethapyr, flufenacet plus metribuzin, metribuzin, pronamide, atrazine plus pendimethalin, atrazine
plus acetochlor, atrazine plus metolachlor, atrazine plus mesotrione, atrazine plus imazethapyr,
mesotrione plus acetochlor, mesotrione plus pendimethalin, mesotrione plus metolachlor, mesotrione plus
imazethapyr, imazethapyr plus metolachlor and imazethapyr plus pendimethalin. Results of the PPI and
PRE emergence study in greenhouse using M. giganteus rhizomes indicated that most of the treatments
did not cause significant injury and growth stunt, except for EPTC at a 2x rate, which produced
significant lower height and dry weight than the non-treated control. Furthermore, oxadiazon and
combinations containing imazethapyr exhibited the tendency to generate more injury, lower height and
less biomass, which posed a concern if utilized under field condition where environmental variables could
be more complex. These data indicate that PPI, PRE, and POST emergence herbicides can be utilized for
establishment of M. giganteus from vegetative rhizomes. Further experiments are needed in field trials to
evaluate establishment success and weed control spectrum utilizing these herbicides.

Interest exists in establishing perennial crops such as switchgrass for biofuels in the Midwestern United States.   Establishment and resulting productivity of switchgrass can be reduced by weeds, but few studies have evaluated if weed management the year after establishment can improve productivity. Research was conducted on six fields in Wisconsin in 2008-10 to measure the effect of weed management methods in the second year of establishment on weed suppression, switchgrass cover and yield. Management methods included an application of glyphosate at 1.12 kg ae/ha, glyphosate at 0.14 kg/ha and 0.07 kg ae/ha of imazapic, a low intensity prescribed fire of residual material, and an untreated control. All methods were applied in early to mid-May after emergence of the common weed species (Setaria spp.).  Switchgrass percent cover was annually estimated in September and yield was collected after a killing frost in 2009 and 2010. No effect of second-year weed management treatments were observed on cover or yield in 2009 or 2010, and switchgrass establishment varied greatly among plots.  To account for this variability the percent switchgrass cover observed in the fall of the establishment year was used to classify all plots as high (>70%), medium (30-70%) or low (<30%) establishment to test whether the effect of second-year weed management depends on establishment success .  Differences were only observed within the medium establishment class in 2009.  In this class, glyphosate and prescribed fire treatments increased yield 1.0 or 1.8 Mg/ha relative to the control, respectively.  In contrast, glyphosate and imazapic resulted in similar productivity compared to all other treatments.  No differences in productivity of switchgrass were observed the following year within classes.  These data suggest that while gains in productivity may occur, it is only with moderately established switchgrass stands and the results do not persist into the following production year. 

Enlist^™ soybean contains the AAD-12 protein which conveys tolerance to preemergence and postemergence applications of 2,4-D.  Previous research has shown excellent tolerance to 1120, 2240 and 4480 g ae/ha of 2,4-D.  In 2011, research trials were conduct to evaluate preemergence applications of 2,4-D choline at 1120 and 2240 g ae/ha applied in combination with 1X and 2X recommended soil use rates of cloransulam + sulfentrazone, pendimethalin and chlorimuron + flumioxazin + thifensulfuron.    2,4-D choline at 1120 or 2240 g ae/ha resulted in <2% injury at 21 days after application (DAA).  Cloransulam + sulfentrazone at 1X and 2X recommended soil rate resulted in <4% visual injury.   Combinations of 2,4-D choline and cloransulam + sulfentrazone at all rates tested resulted in <4% injury.  Pendimethalin at 1X and 2X recommended soil rates caused 6 and 14% injury at 21 DAA and the addition of 2,4-D choline did not increase injury.   Chlorimuron + flumioxazin + thifensulfuron at 1X and 2X recommended soil rates caused 7 and 13% injury 21DAA and the addition of 2,4-D choline did not increase injury.   Enlist soybean tolerance to delayed PRE applications of GF-2726, a pre-mix of 2,4-D choline and glyphosate DMA, applied alone at 2185 and 4370 g ae/ha or tank mixed with soil residual herbicides; metolachlor at 1420 g ae/ha, chlorimuron at 8.76 g ae/ha, or pendimethalin at 1070 g ae/ha.  Maximum visual injury was observed at 14DAA with metolachlor, chlorimuron and pendamethalin alone resulting in 15, 2 and 9% visual injury, respectively.  GF-2726 alone at 4370 g ae/ha resulted in 4% injury. Tank mixing GF-2726 with metolachlor, chlorimuron or pendimethalin did not significantly increase injury compared to the soil residual herbicides alone.  Enlist soybean demonstrated excellent tolerance to preemergence or delayed preemergence applications of 2,4-D choline or GF-2726 with soil residual herbicides.

 ^™Enlist, Enlist Duo, and SureStart are trademarks of Dow AgroSciences LLC. ®SmartStax is a registered trademark of Monsanto Technology LLC. .  Components of the Enlist Weed Control System have not yet received regulatory approvals; approvals are pending.   The information provided here is not an offer for sale. ©2012 Dow AgroSciences LLC.

Volunteer corn expressing glyphosate herbicide resistance is a problematic weed across much of the area where Roundup Ready^® adoption has been high. This issue is partially due to the increasing prevalence of stacking both glyphosate and insect-resistant (mainly Bt) traits into the same genetically-modified plant. Previous research indicates that the Bt toxin concentrations in nitrogen deficient volunteer corn roots may be less than that of volunteer corn plants with sufficient nitrogen. Because all current Bt toxins are crystalline proteins, we hypothesized that in-field factors such as soil nutrient levels (nitrogen, sulfur, etc.) could affect the expression levels of these proteins by corn plants. Our objectives were to quantify the concentration of Bt expressed in volunteer and hybrid corn root tissue in various nitrogen fertility environments. We conducted two sets of experiments (field and greenhouse) to accomplish these objectives. Cry3Bb1 toxin levels in roots were determined using quantitative ELISA. In the field, we planted three corn varieties (DKC 61-19 VT3 Cry3Bb1-positive hybrid corn, DKC 61-22 Cry3Bb1-negative hybrid corn, and an F₂ of DKC 61-19 VT3 Cry3Bb1-positive volunteer corn), and applied 5 rates of nitrogen (0, 45, 90, 180, and ≈ 360 kg N ha^-1). Expression of Cry3Bb1 protein in root tissues from the field experiment was highly variable, but there was no difference in the overall concentration of Cry3Bb1 expressed in the root tissue between Cry3Bb1-positive volunteer corn (18.7 ± 2.70 ppm) and Cry3Bb1-positive hybrid corn (13.2 ± 2.93 ppm) at the V6 to V9 growth stage. Nitrogen rate did affect Cry3Bb1 expression in the field; lower rates of nitrogen resulted in decreased Cry3Bb1 expression. We also conducted a greenhouse trial to quantify Cry3Bb1 expression in hybrid and volunteer corn growing in 5 nitrogen fertility environments (0, 25, 50, 100, and 200 mg N L^-1). DKC 61-19 was used as the Cry3Bb1-positive hybrid corn and the F₂ of DKC 61-19 was used as the Cry3Bb1-positive volunteer corn. All plants were harvested at the V6 growth stage. Root and shoot biomass was quantified after drying, and root tissue samples were collected at harvest to quantify Bt expression. As with the field experiment, there was no difference in Cry protein expression between volunteer corn (6.94 ± 1.24 ppm) and hybrid corn (9.32 ± 1.23 ppm).  As in the field experiment, there was an effect of nitrogen on Cry3Bb1 expression. When nitrogen was not applied there was less Cry3Bb1 expressed in volunteer corn plants. Interestingly, this effect was not observed in hybrid corn. These data illustrate that reduced volunteer corn Cry toxin expression may be more typically observed in soybean fields where nitrogen is not applied, and volunteer corn plants would be nitrogen deficient. In addition to being a troublesome weed, volunteer corn may be problematic for insect resistance management plans by exposing the target insects to sublethal doses of the toxin. Recent data has illustrated that the acetyl-CoA carboxylase inhibitor, clethodim, (a commonly used herbicide for POST volunteer corn control in soybean) also has reduced efficacy on nitrogen deficient volunteer corn. Thus, in order to control Cry3Bb1-positive volunteer corn, and decrease the likelihood of insects feeding on sublethal doses of the toxin, it is advisable to control volunteer corn in soybean early in the season and follow recommended herbicide use rates.

Pendimethalin is commonly used in the nursery industry for preemergence weed control in container production.  The medium used in containers in Virginia and other southern states is primarily a pine bark-based substrate.  Herbicide movement in these soilless mixes may differ from that seen in field soil. Trials were established to determine herbicide persistence and leaching of two pendimethalin formulations in 100% pine bark.  These studies used both a large crabgrass bioassay and laboratory extraction of pendimethalin.  Pendimethalin EC at 2.24 kg ai ha^-1 reduced crabgrass stands 83%, while the ME formulation reduced stand only 55%.   The microencapsulate (ME) form of pendimethalin had lower persistence and greater leaching than the emulsifiable concentrate (EC) formulation in pine bark, which explains the lower weed control. The soil column study indicated the ME formulation had significant downward movement in pine bark through the 9- to 12-cm depth after applying 3.4 kg ai ha^-1 pendimethalin and 17.8 cm of irrigation water, while the EC formulation leached only down to the  3- to 6-cm depth. Pendimethalin extraction from pine bark using a solid phase extraction method found 0.91 µg ml-1 for the EC and 4.0 µg ml-1 for the ME formulation in the 3- to 6-cm depth below the surface.  No pendimethalin was detected below the 6 cm depth when the EC formulation was applied, while 0.5 ppm was detected for the ME formulation at this depth.  Trace amounts of pendimethalin was recovered in effluent water collected from the bottom of the leaching columns for the EC formulation while 0.003 ppm  in leachate was found for the ME formulation.  The greater leaching of the ME formulation may be due to irrigation water moving the capsules deeper into the growing medium prior to the release of pendimethalin.

Aminocyclopyrachlor (AMCP) is a previously registered synthetic auxin herbicide utilized for broadleaf weed control in turfgrass systems.  Classified as a pyrimidine carboxylic acid, AMCP has similar chemical structure and mode-of-action to the pyridine compounds aminopyralid and clopyralid.  The absorption, translocation, and metabolism of radiolabeled AMCP has been documented in susceptible broadleaf weed species but no research has characterized AMCP in tolerant turfgrass.  Due to off-target plant injury from synthetic auxin residues in turfgrass clippings, information regarding AMCP absorption, translocation, and metabolism in turfgrass could provide useful environmental fate insight.

Research was conducted in 2011 at North Carolina State University, Raleigh, NC to characterize the absorption, translocation, and metabolism of radiolabeled ¹⁴C-AMCP in tall fescue [Lolium arundinaceum (Schreb.) S.J. Darbyshire]. Experiments were arranged in a randomized complete block design with three replications and two experimental runs.  Following a foliar AMCP application (79 g ae ha^-1 plus 0.25% v/v NIS), five 1 µL droplets of ¹⁴C-AMCP plus 0.25% v/v NIS were applied on the adaxial surface of a protected tall fescue leaf for a total of 4.2 kBq per plant.  Plants were harvested 0-192 hours after treatment (HAT) and separated into treated leaf, treated leaf wash, remaining foliage, crown, roots, and root exudates.  Radioactivity in each respective plant part was quantified through liquid scintillation spectroscopy and metabolism was determined through high performance liquid chromatography. 

At all harvest intervals, recovery was ≥80% of total applied radioactivity.  In general, the majority of ¹⁴C-AMCP was recovered in the treated leaf wash at all harvest intervals.  Absorption into the treated leaf increased as harvest intervals increased, ranging from 15% 12 HAT to a maximum of 39% 96 HAT.  Translocation of absorbed ¹⁴C-AMCP from the treated leaf to other foliage was 44% 192 HAT.  Minimal translocation was found in the roots or root exudates, indicating ¹⁴C-AMCP either remained unabsorbed or in the aboveground tissue of tall fescue. No AMCP metabolism was detected in any tall fescue plant part at 192 HAT.

There is continued demand for alternatives to chemical weed control, especially among those interested in organic approaches.  One potential alternative is the use of microwave radiation for weed control, a particular form of indirect thermal weeding. This dielectric heating has been evaluated for control of weeds, insect pests, and soil-borne plant pathogens. Absorption of microwave radiation causes water molecules within the tissue to oscillate, thereby converting electromagnetic energy into heat. This technique is rapid, versatile and effective, as the electromagnetic waves heat the plant tissue and destroy cellular integrity. Being an indirect thermal method, heat is generated inside the plant tissue, so there is less chance of fire or of resistance development in weed species. Microwave radiation is not affected by wind, thus extending the application window compared to conventional spraying methods. Microwave radiation does not disturb the soil or leave any residues in soil or air. In spite of these advantages, however, the technology has not been adapted to the agriculture sector due to limited research, safety concerns, and the lack of acceptable prototypes. The objective of this research project is to explore the potential use of dielectric heating for weed management. Our studies showed that microwave radiation orientation impacts the injury level in weed species. Horizontal microwave radiations from a vertical magnetron caused comparatively more injury in weeds than those exposed to vertical radiations. Postemergence weed control using microwave radiation uses comparatively less energy compared to preemergence weed control. Radiations were able to control all sizes of weeds, although larger weeds were more likely to regrow after treatment. Radiation leakages detected during the experiments were far below United State federal standard limits (5mW/Cm²), suggesting this technology can be adapted for weed control in field situations.

There were 600 golf courses by the end of 2010 in China mainland. The statues of weed and weed control in golf turf was based on the investigation in 106 golf courses in three turfgrass climate zones of China from 2005 to 2011.

The three turf zones in China included warm season turf zone, cool season turf zone and transition turf zone. Two types of weed in golf turf in china were occurred. One was the weed shifted from crop/wild field of which mainly 26 kinds among total 427 kinds of weed found. Another was the weed shifted from cultivated golf turf, which included mainly 6 kinds among total 10 kinds of weed.

There was bermudagrass, Zoysia or seashore paspalum in warm season turf zone. The weed in bermudagrass or Zoysia in most golf courses controlled by one or two of the followings: bensulfuron(Londax), isoproturon(Arelon), diuron(Karmex), metolachlor(Dual), oxadiazon(Ronstar), oxyfluorfen(Goal) or pendimethalin(Stomp) with twice applications a year. Additional treatments were with flazasulfuron (SL-160), trifloxysulfuron(Monument), fluroxypyr(Starane), quinclorac(Facet), bentazone(Basagran) or dicamba(Banvel)+ MCPA. The weed control in seashore paspalum in most golf courses was with one or two of the followings: ethoxysulfuron(Sunrise), metolachlor, pendimethalin once or twice a year. Additional treatments were with fluroxypyr, quinclorac, bentazone, dicamba+MCPA or halosufuron (Permit). Some superintendents chose atrazine, simazine, metribuzin, 2,4-D or MSMA in Bermudagrass and Zoysia.In a few golf courses.

Most turfgrasses were perennial ryegrass, bentgrass or kentucky bluegrass in cool season turf zone. Recently, Zoysia was popular and developed in rough areas instead of tall fescue. The weed in rough areas was controlled with metolachlor, pendimethalin, pyrazosulfuron(Nc-311) in early spring or later spring. Additional treatments were with fluroxypyr, quinclorac, bentazone, dicamba+MCPA both in cool and warn season turf.

The weed control in both of warm and cool turf in transition turf zone was same as both of two zones respectively. The Additional pre-treatments were with metolachlor, pendimethalin, pyrazosulfuron at low rate 45 days after over-seeding in fairways. Pre-treatments with pendimethalin, prodiamine, pyrazosulfuron, bensulfuron were as second application in early spring. Third application could be considered both for weed control and ryegrass suppression with flazasulfuron, trifloxysulfuron. In a few golf courses, post-treatment with paraquat(Gramoxone) in dormant turf of rough areas was as a remedy.

Controlling the weed transformed from unwanted turf in golf turf was preliminary introduced.

ANALYSIS OF ALS HERBICIDE-RESISTANT ANNUAL BLUEGRASS (POA ANNUA L.).  R. B. Cross, B. McCarty, N. Tharayil, A. Estes, W. Bridges, T. Whitwell; Clemson University, Clemson, SC.

ABSTRACT

Annual bluegrass (Poa annua L.) is a problematic winter annual grass weed to control in turfgrasses.  Its light green color and prolific seedhead production disrupt the aesthetic quality of turf stands.  ALS-inhibiting herbicides are a large group of herbicides whose mode of action is inhibition of the acetolactate synthase (ALS) enzyme and show promise as a control mechanism for annual bluegrass.

Recently, reports of poor control using ALS-inhibiting herbicides on annual bluegrass have surfaced from turfgrass managers.  Therefore, a screening method for rapid diagnosis of ALS-inhibiting herbicide resistance in annual bluegrass would be beneficial.

A laboratory study was initiated in 2011 at Clemson University to develop a rapid screening method to determine annual bluegrass resistance to ALS-inhibiting herbicides.  The laboratory screening method quantifies resistance by analyzing acetolactate accumulations, an intermediate in the branched-chain amino acid biosynthetic pathway.

Annual bluegrass leaves were incubated in a solution for 16-20 hours in a growth chamber under a light intensity of 300 µmol m^-2 s^-1 at ambient atmospheric conditions.  The solution contained a nutrient media, L-alanine, nonionic surfactant, and cyclopropane dicarboxylic acid (CPCA), an inhibitor of ketol acid reductoisomerase (KARI).  Trifloxysulfuron, an ALS-inhibiting herbicide used for annual bluegrass control in turfgrass, was added at 0, 0.001, 0.01, 0.1, 1, 10, 100, or 1000 µM.  Acetolactate concentrations were measured by analyzing aceotin (via decarboxylation of acetolactate) using a spectrophotometer to determine absorbance at 530 nm.

Of five suspected resistant (R) biotypes, two had significantly greater acetolactate accumulations than two known susceptible (S) biotypes.  These R biotypes showed continued accumulation of acetolactate at the highest concentration of trifloxysulfuron, 1000 µM.  In addition, these two biotypes had AR₅₀ values approximately 10,000 times greater than the known S biotypes.

This laboratory screening method is a rapid and accurate method to determine the activity of annual bluegrass ALS in the presence of ALS-inhibiting herbicides, and thus is useful for the determination and quantification of ALS-inhibiting herbicide resistance. 

For homeowners and gardeners concerned with the
environmental impact of herbicides, the use of natural products for fertilization
and weed control are popular options. 
CGM is a natural weed control product that can be used for preemergence
control of crabgrass.  Research has shown
that CGM partially controls weeds when applied at 20lbs/1000 ft².  For some homeowners, partial weed control is
not sufficient and additional CGM is added, sometimes up to three applications
of 20lbs/1000ft² during the summer. 
Those three applications equate to approximately 5.4 lbs of nitrogen/1000ft²,
exceeding the recommended nitrogen requirements for turf.  Excessive nitrogen is often a precursor for
disease problems and can encourage weed growth where the turf stand is not
competitive.  To minimize risk of nitrogen
over-fertilization while improving weed control, CGM was impregnated with 0.25
and 0.5 times the label rates of pendimethalin, prodiamine, oxadiazon, and
dithiopyr and applied to tall fescue lawn-height turf.

CGM was applied at 10 lbs/1000 ft² once
in a single application or at 5 lbs/1000 ft² twice at a 1-month
interval.  These rates were chosen
because they represent no more than 1 lb nitrogen per thousand square feet and
do not exceed Cooperative Extension recommendations concerning nitrogen use in
cool-season lawns during spring.  CGM was
impregnated with 0.25 or 0.5 times normal rates of dithiopyr, pendimethalin,
prodiamine, or oxadiazon and applied as a granule in late April and May (for
the split application).  These herbicides
were mixed with CGM, which was applied once at 10 lbs/1000 ft² or
twice at 5 lbs/1000ft².  When
applied twice, herbicide rates were split such that no more than the specified
0.25 or 0.5 times the labeled rate was applied per season.  Herbicides were also applied alone using sand
as the granular carrier.  Weed ratings,
weed counts, and turf quality were collected during the season.  Weed counts were conducted with a 98 point
grid on each plot, and all smooth crabgrass seedlings found underneath a grid
point were counted.

 In 2010,
smooth crabgrass covered 44% of nontreated plots in August and CGM alone or
most herbicides alone did not significantly reduce coverage.  Prodiamine mixed with CGM most consistently
suppressed smooth crabgrass, but only when applied once.  Pendimethalin applied once at the 0.5x rate
using sand carrier and twice using CGM also suppressed smooth crabgrass.  Additionally, the use of dithiopyr at a 0.25x
rate, applied twice using CGM, reduced smooth crabgrass coverage.  In 2011, pendimethalin and dithiopyr applied
at the 0.25x rate with sand carrier reduced smooth crabgrass coverage.  In the split CGM treatment, only
pendimethalin at both rates reduced smooth crabgrass coverage.  Additionally, in the single CGM treatment,
only prodiamine at the 0.25x rate significantly reduced smooth crabgrass
coverage.  Pendimethalin, in three trials
over two years, is the only herbicide that has consistently reduced smooth
crabgrass coverage when used in conjunction with CGM.  These data suggest that several herbicides
can be mixed with CGM and improve crabgrass control, but additional research
will be necessary to confirm if any of these products can provide reliable weed
control.

In April 2009 the government of Ontario banned traditional pesticides it categorized as being cosmetic in nature, including applications to parks, home lawns and athletic fields.  As a result of this legislation many new exempted products and weed control methods have been proposed and researched.  The legislation has negatively impacted the lawn care industry as they report fewer professional lawn care operators.  It has also been claimed to cause reduced athletic field quality and has been cited as a reason for installing synthetic playing surfaces.  Efficacy requirements for control are also being changed to potentially allow for alternative products with reduced efficacy to labeled for weed control in Canada. The talk will summarize a number of research and educational efforts that resulted from this legislation. 

Molecular techniques are increasingly being applied to key
weed science research projects including determination of the mechanisms of
glyphosate resistance in multiple weed species. 
Once successful primers have been constructed for the EPSPS gene in a plant,
the gene can be removed, cleaned up, and sent off for sequencing.  This DNA sequencing is frequently used to
look for known mutations that confer modest glyphosate resistance such as the
Proline 106 mutation.  Once this amount
of molecular testing has been successful, Q-PCR can be used to determine gene
copy number.  If an increase in EPSPS
gene copy number is detected, additional molecular research is used to
determine if the amount of EPSPS enzyme protein produced correlates with the
gene copy number.  New generation deep
sequencing coupled with advanced bioinformatics can then be used to construct
DNA sequence surrounding amplified genes to begin to probe possible genetic
mobile elements that may facilitate gene amplification under the stress imposed
by glyphosate selection pressure.   In the specific case of kochia (Kochia scoparia), advanced molecular
research at Colorado State University on multiple accessions from KS, CO, NE,
SD, and ND where glyphosate resistance was suspected, no Proline 106 mutation
was detected in any of the lines. 
However, QPCR results showed that gene amplification occurs in all of
these “resistant” populations with the increased copy number generally in the
range of 4 to 9 fold.  This appears to be
enough to provide kochia survival at lethal field rates.  Some kochia plants survive glyphosate rates
as high as 6 lb/acre in the greenhouse. 
Using an EPSPS specific antibody shows that EPSPS protein level
correlates with increased gene copy number.

Two glyphosate-resistant Echinochloa colona populations were collected from orchard fields of the Northern Sacramento Valley, CA, and shown to carry mutations resulting in an amino acid change at position 106 of the EPSPS protein. Studies at the whole plant level revealed widely different levels of resistance between plants possessing the same mutation, suggesting that additional mechanisms may be contributing towards resistance in these populations. No differences in EPSPS gene copy number were found between plants from the two resistant populations and a susceptible standard. Using qRT-PCR, relative EPSPS and DAHPS transcript levels were analyzed.  Although glyphosate treatment increased EPSPS gene transcription levels in the two resistant populations, the levels of expression were lower than for the susceptible population. Basal expression levels of the DAHPS gene were not different among the three populations and there was an induction of expression in response to herbicide treatment in all three populations. Thus, it appears resistance in these populations is unrelated to either an increase in gene copy number or changes in expression levels of these shikimate pathway genes compared to susceptible plants. Studies to measure glyphosate uptake and translocation also revealed no differences between resistant and susceptible populations. Since E. colona is a hexaploid species, mutations in different homeologous copies of EPSPS could impact resistance to different extents. It is also possible that different homeologues are expressed to different levels and that certain populations may carry mutations in two or more homeologous genes. We are currently developing homoeologue-specific primers to sequence all three copies from resistant and sensitive populations to answer these questions in addition to studies on herbicide metabolism.

Classical mechanisms for weed resistance to herbicides are not the principal mechanisms for glyphosate resistance.  While target site mutations in EPSPS are known in several species, eg., Lolium and Eleusine,  they are fairly ineffectual accounting for only a small portion of the resistance magnitude.  Glyphosate metabolism is still rare and although now measured in a few species by Duke et al., none of the resistant species are noted as using metabolism.  Glyphosate resistant Conyza canadensis has now been shown to sequester glyphosate into the cell vacuole by ³¹P NMR and this sequestration mechanism also seems to operate in glyphosate resistant Lolium sp.  A number of weeds have now been examined by ³¹P NMR.  Observations of intracellular and extracellular glyphosate observed using in vitro NMR of live leaf tissue allow measurements on the kinetics of glyphosate uptake and sequestration.  Competitive studies using analogues of glyphosate and some natural metabolites are useful in characterizing the apparent ABC transporters on the plasmalemma and tonoplast membranes.  These will be summarized and a discussion on various types of exclusions mechanisms put into the context of glyphosate resistance.

The evolution of herbicide resistance in weeds is a growing problem in modern agriculture. In order to design sustained weed management strategies, it is important to understand the mechanisms and dynamics of herbicide resistance in weeds. In this respect, we have investigated the mechanism(s) of resistance to glyphosate in a Lolium rigidum population (DAG1) from South Africa in comparison with a standard sensitive population (STD1). Sequencing of the EPSPS gene has revealed the presence of at least three homologs in the L. rigidum genome and identified a novel proline 106 to leucine substitution (P106L) in 52% DAG1 plants. Whole plant dose response assays conducted on wild and mutant EPSPS 106 genotypes showed that the P106L mutation conferred a 1.7 fold increase in resistance to glyphosate. Additionally, a 3.1 fold resistance increase, not linked to metabolism or transport, was estimated between wild-type P106-DAG1 and P106-STDS sensitive plants. Point Accepted Mutation analysis suggested that other amino acid substitutions at EPSPS position 106 are likely to be found in nature besides the P106/S/A/T/L point mutations reported to date. This study highlights the importance of minor mechanisms acting additively to confer significant levels of resistance to commercial field rates of glyphosate in weed populations subjected to high selection pressure.

Determining the Mechanisms of Resistance to Glyphosate in Giant Ragweed (Ambrosia trifida L.) in Ontario. A.C. Green¹, P.H. Sikkema ²,  J.C. Hall¹, F.J. Tardif¹,  ¹Univ. of Guelph, Guelph, ON, Canada, ²Univ. of Guelph, Ridgetown Campus, Ridgetown, ON, Canada

Glyphosate resistant giant ragweed has been documented in Ontario since 2008.  The mechanism of resistance has yet to be determined. Resistant plants exhibit two different phenotypes after glyphosate treatment. One phenotype from Windsor exhibits an unusual rapid necrosis in mature leaves while the growing points escape injury. The other phenotype from Leamington exhibits similar symptomology to a susceptible plant but recovers and regrows after a week. An initial dose response experiment revealed the Windsor and Leamington populations to have a resistant index of 6.5 and 4, respectively for biomass reduction.  The objectives of the experiments are to investigate if possible mechanisms include target site resistance, altered translocation or decreased absorption. Target-site sensitivity was determined through a shikimate assay. Shikimate is the dephosphorylated substrate of the enzyme 5-enolpyruvylshikimate-3-phosphate synthase which is the target site of glyphosate. Leaf discs collected from young and mature tissue were placed in assay solutions of glyphosate in microtiter plates, incubated under light and shikimate was extracted and quantified. All populations had an accumulation of shikimate in the young tissue. In the old tissue the Windsor population had minimal accumulation and the Leamington population had similar accumulation to the susceptible population. [¹⁴C]- glyphosate was used to measure absorption and translocation. Absorption levels of resistant and susceptible populations were similar. A greater amount of [¹⁴C]- glyphosate was retained in the treated leaf, less translocated to the roots and a similar amount translocated in an upwards direction in the Windsor population compared to a susceptible population.

ftardif@uoguelph.ca

Glyphosate is considered by many as the most important herbicide ever developed. Repeated glyphosate applications causes selective genetic pressure toward evolution of resistant weeds. Glyphosate-resistant (R) Palmer amaranth populations (R1 and R2) were identified in Mississippi. The inheritance of glyphosate resistance was examined by reciprocally crossing R maternal parents with susceptible (S) paternal parents (R/S) and crossing S maternal parent with R paternal parents (S/R) to generate F₁. Individuals from the F₁ populations were submitted to glyphosate dose-response assays resulting in a range of phenotypes from R to S. The response to glyphosate was more similar to the R than S parent when the female parent was R. Conversely, when R was used as pollinator the response to glyphosate was more similar to the S parent. Thus, the level of resistance was strongly influenced by the direction of the cross.  This led us to three hypotheses: (1) maternal effect of the R trait, (2) facultative apomictic reproduction, and (3) differences in transmission rates between male and female gametes. Sequence comparisons of the predicted 5-Enolpyruvylshikimate-3-phosphate synthase (EPSPS) mature protein from R1, R2, and S did not identify a target site mutation known to confer resistance in R populations. EPSPS activity was lower in S and S/R plants than in R and R/S plants in the absence of glyphosate; all were equally inhibited by the presence of glyphosate. Genomic estimation of EPSPS gene copy number relative to acetolactate synthase (ALS) using quantitative PCR showed that R and R/S contain more copies of EPSPS than S and S/R. Western Blot analysis confirmed that increased EPSPS protein levels were correlated with EPSPS copy number. Quantitative RT-PCR on cDNA revealed that EPSPS was highly expressed in R1 and R/S, but was  poorly expressed in S, S/R, and R2. The apomixis involvement in glyphosate resistance inheritance was studied using 44 S, 36 R1 and 38 R2 reproductively isolated female individuals. In all cases seeds were produced, with the exception of one R1 plant. We found 60 to 100% (depending on the population) produced 1 to 1,000 seeds, but some individuals produced up to 6,000 seeds. These results strongly suggest that A. palmeri can produce seed both apomictically (facultative apomixis), and sexually, with apomixis the determinant of low copy number inheritance in S/R population. Moreover, facultative apomixis would guarantee the glyphosate resistant trait stability in R populations. dnr34@pss.msstate.edu

The sustained high adoption of glyphosate-resistant (GR) crops is exerting a tremendous selection pressure on weeds. The population structure of highly diverse outcrossing species is expected to evolve rapidly in response to the primary stressor. Palmer amaranth has demonstrated such ability; glyphosate-resistant populations started appearing within 10 years of commercializing GR crops. Glyphosate-resistant Palmer amaranth is now widespread in the southern US. This research aimed to: 1) determine the frequency and level of resistance in Palmer amaranth populations across Arkansas and relate this to cropping systems; 2) determine the population structure using microsatellite markers; and 3) evaluate the EPSPS genetic variation patterns relative to resistance level. Bioassays were conducted using 38 populations, representing different production zones and cropping systems. Each population was composed of 10-20 plants sampled separately from the field.  Offsprings (100) of each field-collected plant were sprayed with 840 g ae ha^-1 glyphosate. Each seedling was scored separately and categorized according to the level of injury. Plants with 0 - 10% injury were classified as highly resistant (HR); 11 - 70% as moderately resistant (MR); 71 – 90% as slightly resistant; and 91 – 100% injury as susceptible (S). Thirteen populations with >50% HR offsprings were from fields in cotton or soybean production system for over 5 years. Moderately resistant plants comprised 2-77% of each population. All but one population had resistant plants.  Dose response assays were conducted on 4 HR, 1 MR, and 1 S populations. The GR₅₀ for the Arkansas S population was 302 g ae ha^-1; the resistant populations showed a resistance factor of 9- to 23-fold. Nine Palmer amaranth populations (3 S, 2 MR, 4 HR) and one spiny amaranth population were used for the microsatellite marker and EPSPS gene sequence analysis. Ten microsatellite markers for Amaranthus were used to generate genomic DNA fingerprints of these populations. All 10 loci were polymorphic, with an average of 12 alleles per locus, and 120 total alleles observed. Six genotypic clusters were observed. All individuals from the HR population, Grady, and all spiny amaranth formed separate clusters 1 and 5, respectively. In 70% of populations, all their respective individuals belong to the same cluster. Except for one individual, all S populations from AR and SC formed one cluster. The populations are not delimited by agroecological zones or geography. Resistant populations are established by independent selection and gene flow. There is a higher level of variation in the amino acid sequence of the S population than the Grady population. The Grady population has lost all diversity in two regions of the EPSPS gene. Grady (HR) and CL86 (S) differed in EPSPS amino acid sequence in three regions. Strong selection at this target site has resulted in a highly purified population with adaptive trait to survive the selection pressure.

5-EnolPyruvyl Shikimate 3-Phosphate synthase (EPSPS) is the target enzyme for glyphosate an uncompetitive inhibitor of the enzyme.  Glyphosate competes with the second substrate PEP to bind the EPSPS-S3P binary complex to form a transition state analogue that very effectively and selectively inhibits the enzyme.  Natural target site resistance to glyphosate has not really been discovered as yet although mutations adjacent to the active site have been discovered, namely those involving Proline106. The Pro has been found to be substituted with Ser, Thr, Ala and Ile however these mutations afford scant change in the Ki for glyphosate.  To examine the level of resistance afforded by point mutations model resistant weeds have been made in Arabidopsis and the resistance offered by 1,2 and 4 copy plants studied.  These studies show that a linear increase in resistance can be expected with copy number indicating enzyme levels are an important factor in tolerance to glyphosate as demonstrated in resistant Palmer amaranth.  A qualitative survey of enzyme levels by Western antibody in a variety of species for comparison of native EPSPS levels.  A quantitative enzyme assay and its use in detecting mutant EPSPS’s contributing to resistance will be discussed. A discussion of sensitive and resistant EPSPS's will reveal a commonly overlooked key amino acid that allows classification of glyphosate sensitivity. Finally a new mutant found in Palmer amaranth has been engineered and studied for its contributions to resistance and a discussion why this mutation is so auspicious.