Interest in the cultivation of bioenergy feedstocks has increased the need for information in this rapidly developing sector of agriculture. Many of these fast growing, large stature grasses have been selected because of their competitive nature and ability to tolerate less than ideal growing conditions. However, weed pressure in the first year can be detrimental to crop establishment and yield.  Weed control is one of the most costly and resource intensive aspects of bioenergy crop establishment. Unfortunately, little information exists on practical weed management techniques for the majority of these new crops. Therefore, our objective was to determine a cost effective weed management program for bioenergy crop establishment.

We evaluated preemergent (PRE), and postemergent (POST) tolerance of the bioenergy crops switchgrass, big blue stem, reed canarygrass, sorghum, Arundo donax and Miscanthus sinensis and M. × giganteus to 23 herbicides in 8 herbicide families. Plants were greenhouse grown and evaluated for percent germination, visual injury, and height every two weeks for five or seven weeks for PRE and POST applications, respectively. At the end of the experiment, plants were harvested and aboveground biomass was measured. Many herbicides appear to be acceptable, causing little or no injury, for PRE-emergent use, although not for all species in our trial. PRE-emergent herbicide application of topramezone and bentazon, proved to be effective and safe for all species in our trial. Newly emerged plants from M. × giganteus rhizomes were in all cases more tolerant to PRE- and POST-emergent herbicide applications than those produced from seed of the same species.  Interestingly, there was variability in the tolerance of different M. sinensis and switchgrass cultivars to the single application of herbicide in several cases, suggesting that further screens should include a variety of cultivars to assess herbicide tolerance. With the information gained in this study we have a suite of herbicides that show promise, but should be tested on larger scale field trials over one or more growing seasons.

With the large number of herbicides and feedstocks screened in this study, we not only have gained information regarding herbicide tolerance, but a selection of herbicides that may be useful for management in the event that seedlings or vegetative propagules escape cultivation as several products were lethal to the grasses at labeled rates. 

      Production of organic canola (Brassica napus L.) as a winter crop in North Carolina allows organic producers to diversify rotations while filling market demand for non-transgenic canola. Narrow row spacing and increased seeding rates may serve as a mechanism to reduce weed competition in organic cropping systems. This study was conducted to evaluate the effects of row spacing and seeding rate on weed pressure and yield in organic canola production. Canola variety ‘Hornet’ was planted at five seeding rates (3.4, 6.7, 10.1, 13.4, 16.8 kg/ha) at three row spacing’s (17, 34, 68 cm) in Goldsboro, Kinston, and Salisbury, NC in 2011. Yield, fall stand counts, and spring stand counts were measured at all locations and weed coverage was measured at Goldsboro. Both row spacing and seeding rate had an effect on weed coverage, P=<0.001 and P=0.006, respectively. Weed coverage was lowest with the highest seeding rates at row spacing 17 and 34 cm. Yields were highest with 17 cm row spacing at seeding rates of 16.8 kg/ha. Fall and spring stand count results show that wider row spacing at higher seeding rates led to more plants per linear meter but despite these results lower yields were obtained with wider row spacing at the highest seeding rates. Increased disease pressure and intraspecific competition are possible causes. At each seeding rate, narrow rows had the highest number of plants/ha in both the fall and spring stand counts, showing that thinning of the wider rows occurred rapidly. Results indicate that narrow row spacing and increased seeding rates can effectively reduce weed competition and provide high yields in organic canola production. 

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 and 2012 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 year, nitrogen source, and weed removal height effects were observed for corn yield. Differences based on year are not surprising considering the differences in weather patterns between the two seasons.  Significance based on source could also have been predicted due to the different sources being used with an organic source, and two synthetic sources one of which was a time release fertilizer.  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 potential of many crops to suppress weeds is undervalued. We hypothesize that this potential can be utilized by increasing crop density and spatial uniformity. We test this hypothesis in maize, using three varieties (Novillero, Amarillo ICA V-305, Híbrido HR Oro-Amarillo), three densities (5, 7 and 10.5 seeds/m²) and two spatial patterns (grid pattern and rows) in a weed-infested field (sown with Brachiaria bizantha seeds). The experiment was sown in Cauca Province, Colombia, in 2012. We measured weed biomass at the “critical period” (one month after sowing) and at harvest, and yield at harvest. At the highest density in the grid pattern, weed biomass was reduced by 89.76% and yield was increased by 70.03%. Density, variety and pattern of sowing had important effects in both weed biomass and yield, and there was also a significant densityXvariety interaction, showing that there are genetic differences in the response to high uniform-density conditions. Varieties with lower variation in the angle of insertion of first leave performed better than varieties with higher variation in this character. This suggests that angle of insertion is an important character for weed suppression, and that reduced phenotypic plasticity is related to a better crop population performance. Increased crop density and spatial uniformity can make a valuable contribution to weed control and increase the sustainability of crop production.

Field experiments were conducted at the Southern Agricultural Research Center in Huntley, MT, in 2011 and 2012, 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: atrazine (Aatrex® 4 L) at 1.12 kg ai ha^-1, pyroxasulfone (Zidua®) at 0.149 and 0.298 kg ai ha^-1, dimethenamid (Outlook®) at 0.840 kg ai ha^-1, saflufenacil + dimethenamid-P (Verdict®) at 0.737 kg ai ha^-1, acetochlor (Harness®) at 1.960 kg ai ha^-1 alone or in combination with pendimethalin (Prowl H₂O®) 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 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.  Irrespective of addition of pendimethalin, atrazine and saflufenacil + dimethenamid-P were the best treatments for kochia control, which averaged 91% 30 DAA.  Kochia control with dimethenamid + pendimethalin and pyroxasulfone + pendimethalin averaged 78%, and was higher than the control from dimethenamid alone or pyroxasulfone alone at high or low rate.  Dimethenamid alone and acetochlor alone were the least effective treatments for kochia control, which averaged 47% 30 DAA.  Common lambsquarters control 30 DAA with atrazine and saflufenacil + dimethenamid-P applied alone or tank mix with pendimethalin ranged from 89 to 95%.  Addition of pendimethalin improved pyroxasulfone (low rate) and acetochlor activity on common lambsquarters.  Pendimethalin + pyroxasulfone provided 78% control of common lambsquarters.  For wild buckwheat control, atrazine with and without pendimethalin provided 93% average control, which was superior to all other treatments, except saflufenacil + dimethenamid-P + pendimethalin and acetochlor + pendimethalin.  Saflufenacil + dimethenamid-P and dimethenamid-P alone provided 80% wild buckwheat control 30 DAA.  Addition of pendimethalin did not improve wild buckwheat control by dimethenamid or pyroxasulfone.  Pyroxasulfone (low rate) alone and acetochlor alone were less effective on wild buckwheat and control averaged 65%.  Corn yield with pendimethalin- and atrazine-based herbicide programs were superior to all other programs, except pyroxasulfone at the high rate (0.298 kg ai ha^-1) and saflufenacil + dimethenamid-P.  In conclusion, these soil residual herbicides can be potentially utilized as a valuable tool for weed control in glyphosate-resistant corn, especially for management of glyphosate-resistant kochia.

Palmer amaranth (Amaranthus palmeri) is a serious problem throughout the Southern United States.  However, this species has only recently been reported on the Eastern Shore of Virginia and Maryland.  Glyphosate-resistant Palmer amaranth has already been confirmed in at least one county in mainland Virginia.  In 2012 field studies were conducted in King William, VA and Hebron, MD to confirm suspected glyphosate resistance and evaluate different herbicide modes-of-action alone or in tank mix combinations for Palmer amaranth control in a glyphosate-tolerant corn system. The study was conducted as a randomized complete block design with 3 (MD) or 4 (VA) replications. PRE treatments included isoxaflutole (0.05), isoxaflutole (0.05) + thiencarbazone-methyl (0.02), isoxaflutole (0.05) + atrazine (1.1), isoxaflutole (0.05) + thiencarbazone-methyl (0.02) + atrazine (1.1), s-metolachor (1.4), s-metolachor (0.9) + atrazine (1.1), + atrazine (2.2) kg ai ha^-1. Glyphosate (1.1) + ammonium sulfate (AMS) (2.2) kg ai ha^-1 was applied POST to all plots receiving a PRE treatment.  Topramezone (0.02), topramezone (0.02) + atrazine (0.6), tembotrione, and tembotrione (0.1) + atrazine (0.6) kg ai ha^-1 were applied with the addition of MSO (1.0 % v/v) and UAN (1.25% v/v) POST only.  Plots were visually rated for percent control 34 and 64 days after initial treatment (DAIT) (VA), and 29 and 41 DAIT (MD).  Data was analyzed using ANOVA and Fisher’s LSD (α=0.05). At the VA site all PRE herbicides provided less than 85% control 34 DAIT, and a subsequent application of glyphosate failed to control emerged Palmer amaranth by 64 DAIT.   At the MD site the majority of PRE herbicides provided greater than 90% control 29 DAIT.  However, 29 DAIT, s-metolachor and the isoxaflutole/thiencarbazone-methyl/atrazine combination provided only 85 and 54% control respectively, but 41 DAIT control improved for both treatments following the glyphosate application.  POST applications of topramezone and tembotrione with or without atrazine provided greater than 95% control at both sites.  The difference in herbicide effectiveness at both locations could be attributed to a difference in rainfall needed to activate PRE herbicides.  Due to the majority of PRE treatments at the MD site continuing to be effective at the time of glyphosate application, a proper assessment of glyphosate resistance could not be made. Glyphosate was unable to control Palmer that escaped PRE application at the VA site.  This helps to confirm that Palmer amaranth at the VA site is glyphosate resistant, but additional testing is needed to confirm resistance at the MD site. 

Digital weed mapping using proximal and remote sensing was developed in a cotton field, as part of an EU LIFE+ project (HydroSense, www.hydrosense.org). The reference site was situated in a rural area in plain of Thessaly (Central Greece). The main objectives of the research work were to spatially record and map weed densities by integrating information gathered from multispectral groundbased sensors, analyzing high resolution satellite images and digitally processing RGB photographs. A set of WorldView-2 (WV-2) multispectral (2m pixel size) and panchromatic (0.5m pixel size) satellite data in 8^th June 2011 was acquired. The distribution pattern of NDVI’s values produced by groundbased sensors is comparable to the one produced by the satellite image. Yield data was recorded via a yield monitor mounted on a cotton picker at the end of the growing period. Preliminary data analysis showed a correlation between field data and the estimated weed density values derived from NDVI maps. Development of accurate weed pressure zones in field crops could provide the background information needed for determining herbicide spraying zones aiming to site-specific weed management.

Field and greenhouse studies were established to evaluate the activity of an experimental herbicide, GWN-9796, on common weed species occurring in rice cropping systems in the Mid-South. GWN-9796, or benzobicyclon, is a carotenoid biosynthesis inhibiting herbicide developed and marketed for use in Japan. Typical herbicide symptomology in susceptible weed species is bleached, white plant tissue. The field study was conducted at the Louisiana State University AgCenter Rice Research Station near Crowley, Louisiana and the greenhouse study was conducted at the LSU campus in Baton Rouge, Louisiana. A burndown application of glyphosate at a rate of 1.12 kg ai/ha was applied to control existing weeds and establish a clean seedbed. In the field study, 91-cm diameter galvanized rings were placed in individual plots for treatment containment seven days after the burndown application. A 5-cm seeding flood was established and pre-germinated ‘CL 161’ rice was water-seeded into each plot. Twenty-four hours after seeding the flood was removed to allow for seedling establishment. When the rice seedlings had developed a root and reached the 1-leaf growth stage, a permanent flood was established and maintained in a pinpoint fashion. GWN-9796 was applied at three timings: preplant, two- to three-leaf rice and four- to five-leaf rice. GWN-9796 was applied at 600 g ai/ha and a nontreated was added for comparison. Visual ratings were collected for rice injury and weed control ratings of four species; ducksalad [Heteranthera limosa (Sw.) Willd.], yellow nutsedge (Cyperus esculentus L.), hemp sesbania [Sesbania exaltata (P. Mill.) McVaugh], and barnyardgrass [Echinichloa crus-galli (L.) Beauv.]. The preplant application timing 42 DAT controlled ducksalad, yellow nutsedge, hemp sesbania and barnyardgrass 98%, 96%, 50% and 98%, respectively. The two- to three-leaf timing of GWN-9796 controlled barnyardgrass 75% and yellow nutsedge 83% compared with 96 and 98% control observed from the preplant application. Symptoms were slow to develop in hemp sesbania and observed control was only 53%. In the greenhouse study, 38-liter containers designed to hold a flood depth of 0, 5, 10 and 15.2 centimeters served as individual plots. A single two- to three-leaf yellow nutsedge, three- to four-leaf hemp sesbania, two- to three-leaf barnyardgrass and three- to four-leaf Indian jointvetch (Aeschynomene indica L.) seedling was transplanted into each container. The various flood depths were established 7 days after planting and treatments were applied 24 hours later. Herbicide treatments consisted of two formulations of GWN-9796, a G and an SC formulation applied at 600 g/ha. The SC formulation was applied with COC at 1% v/v.  Control was evaluated at 7 and 14 days after application. At 14 DAT, Indian jointvetch control in containers holding a 5-cm flood was 35 and 48% for the G and SC formulations, respectively. In the 10 cm-flood, control was 20 and 73% for the G and SC formulations, respectively. Increasing the flood depth to 15.2-cm increased control to 68 and 98% with G and SC formulations, respectively. The greatest barnyardgrass control was 98% observed in the 15.2-cm flood with the SC formulation, compared with 63% control with the G formulation. Control was reduced from these values as flood depth decreased. Control observed with the SC formulation was 85 and 80% in the 10-cm and 5-cm flood, respectively. Yellow nutsedge control was 98% with both the G and SC formulation with a 15.2-cm flood; however, the G formulation controlled yellow nutsedge 68% with a 10-cm flood compared with 98% control with the SC. Data indicates weed control increased when GWN-9796 is applied in the SC formulation with deeper flood water.

Clearfield hybrid rice (Oryza sativa L.) was introduced in 2003, and is resistant to the imidazolinone family of herbicides.  Imazethapyr and imazamox are the two herbicides labeled for use on Clearfield rice in the United States.  Hybrid rice seed has a history of dormancy, and it can become a weedy plant if allowed to establish the following growing season as an F2.  Clearfield F2 plants can vary in phenotype and are often resistant to imazethapyr and imazomox.  These resistant F2 plants can become a tremendous weed problem when Clearfield hybrid rice is grown in consecutive years.  Another problem with the Clearfield rice technology is outcrossing potential of Clearfield rice with red rice (Oryza sativa L.).

A producer location was identified in 2008 near Esterwood, Louisiana with a history of 3 consecutive growing seasons of Clearfield hybrid rice production.  This location was determined to have both weedy hybrid and red rice outcrosses.  A long term study was established in 2009 through 2012 to evaluate four different rotations to better determine the best management practices for managing weedy rice plants.  The rotations used were: 1) Roundup Ready soybean followed by (fb) Clearfield hybrid rice fb Roundup Ready soybean fb Clearfield hybrid rice; 2) Roundup Ready soybean fb Roundup Ready soybean fb Roundup Ready soybean fb Clearfield hybrid rice; 3) fallow fb fallow fb Roundup Ready soybean fb Clearfield hybrid rice; 4) fallow fb Clearfield hybrid rice fb Roundup Ready soybean fb Clearfield hybrid rice.  The herbicide programs and cultural practices were consistent across a given rotation.

In 2009, the field was divided into two 0.4 ha blocks.  One 0.4 ha block was planted to Roundup Ready soybean and treated with glyphosate at 1.12 kg ai/ha plus dimethenamid at 1.12 kg ai/ha in the first trifoliate leaf stage.  A second application of glyphosate at 1.12 kg/ha was applied at 14 to 21 days later.  The area was maintained weed free.  A second 0.4 ha block remained fallow and was treated twice with glyphosate at 1.12 kg/ha and fb tillage 14 days after each glyphosate application.  Both 0.4 ha blocks were maintained weed-free in order to prevent added seed to the seed bank.

In 2010, each 0.4 ha block was further divided into 0.2 ha blocks following the previously described rotation scheme.  Clearfield rice was treated with 105 g ai/ha imazethapyr fb 105 g/ha imazethapyr 14 days later fb 44 g ai/ha imazomox at panicle differentiation.  Weedy rice plants were counted in each 0.2 ha block planted to rice.  The soybean/rice rotation had 2.5 weedy rice plants/m² and the fallow/rice rotation had 6.5/m².  This indicates that the use of the Roundup Ready soybean rotation helped reduce the weedy rice population.

In 2011, the area was planted to Roundup Ready soybean and treated as previously described.  At harvest there were no weedy rice plants observed.

In 2012, the entire area was planted to Clearfield hybrid rice and treated as previously described.  The total number of weedy rice plants was obtained and an average/m² was determined.  The rotation scheme of soybean/soybean/soybean/rice reduced the total number of weedy rice plants to 37 plants, or 0.018 plants/m².  The fallow/fallow/soybean/rice rotation reduced weed rice plants to 73 plants, or 0.036 plants/m², and the soybean/rice/soybean/ rice rotation resulted in 860 weedy rice plants, or 0.43 plants/m².  The highest population, 1840 plants, or 0.909 plants/m² was observed with the fallow/rice/soybean/rice rotation.  The most successful program employed a 3-year soybean program in 2009, 2010, and 2011 fb Clearfield rice in 2012.

Studies were established in 2011 and 2012 at the Louisiana State University Agricultural Center Rice Research Station (RRS) near Crowley, Louisiana and in 2012 at the Northeast Research Station near St. Joseph, LA to evaluate herbicides for the control of Indian jointvetch (Aeschynomene indica L.), hemp sesbania [Sesbania exaltata (Raf.) Cory], Texasweed [Caperonia palustris (L.) St. Hil.], alligatorweed [Alternanthera philoxeroides (Mart.) Griseb.], and yellow nutsedge (Cyperus esculentus L.).

Three studies with three site-years each evaluated the efficacy 15 herbicides in controlling Indian jointvetch, hemp sesbania, Texasweed, alligatorweed, and yellow nutsedge at two- to three-leaf rice or early-postemergence (EPOST), at three- to four-leaf rice or mid-postemergence (MPOST), and at four- to five-leaf rice or late-postemergence (LPOST).  Texasweed and alligatorweed were only evaluated in 2012 at the RRS.  The studies followed a randomized complete block design with four replications.  Clomazone at 0.34 kg ai ha^-1 was applied preemergence to each location.  The treatments were: propanil at 3.4 kg ai ha^-1, halosulfuron at 53 g ai ha^-1, halosulfuron at 35 g ai ha^-1 plus thifensulfuron at 4 g ai ha^-1, bensulfuron at 42 g ai ha^-1, orthosulfamuron at 70 g ai ha^-1, penoxsulam at 35 g ai ha^-1, quinclorac at 0.45 kg ai ha^-1, triclopyr at 0.28 kg ai ha^-1, carfentrazone at 18 g ai ha^-1, bispyribac at 28 g ai ha^-1, imazosulfuron at 0.16 kg ai ha^-1, saflufenacil at 50 g ai ha^-1, quinclorac at 0.42 kg ai ha^-1 plus carfentrazone at 25 g ai ha^-1, penoxsulam at 48 g ai ha^-1 plus triclopyr at 0.40 kg ai ha^-1, and orthosulfamuron at 62 g ai ha^-1 plus halosulfuron at 17 g ai ha^-1. A crop oil concentrate was added at 1% v/v to all herbicides except propanil.  A nontreated was added for comparison purposes. Visual ratings were recorded as percent control at 21 d after treatment (DAT) for the EPOST and the LPOST studies, and at 28 DAT for the MPOST study.  Data were analyzed using an analysis of variances, and LSD at α=0.05 was used to determine mean differences.

In the EPOST study, Indian jointvetch control was 97 and 98% with imazosulfuron, penoxsulam plus triclopyr, respectively, all other herbicides controlled Indian jointvetch less than 90%.  Hemp sesbania control was 90 to 96% with orthosulfamuron, imazosulfuron, carfentrazone plus quinclorac, and orthosulfamuron plus halosulfuron.  Texasweed control was 91 to 97% with imazosulfuron, saflufenacil, penoxsulam plus triclopyr, and orthosulfamuron plus halosulfuron.  Penoxsulam was the only herbicide that controlled alligatorweed above 90%.  Yellow nutsedge control was 93 to 98% with imazosulfuron and all halosulfuron containing herbicides.

In the MPOST study, Indian jointvetch control was 47 to 83% when treated with bensulfuron, quinclorac, triclopyr, and carfentrazone all other herbicides resulted in 90 to 98% control.  Hemp sesbania control was less than 70% when treated with triclopyr, carfentrazone, and penoxsulam plus triclopyr; however, all other herbicides resulted in 90 to 98% control.  Texasweed control was 90 to 98% with bispyribac, imazosulfuron, saflufenacil, penoxsulam plus triclopyr, and orthosulfamuron plus halosulfuron.  Penoxsulam, penoxsulam plus triclopyr, and bixpyrbac controlled alligatorweed 98, 98, and 87%, respectively; however, alligatorweed control was below 50% when treated with all other herbicides.  Halosulfuron containing herbicides controlled yellow nutsedge above 90%, with 97 to 100% control.

In the LPOST study, Indian jointvetch control was 42 to 70% when treated with propanil, bensulfuron, triclopyr, and carfentrazone all other herbicides controlled Indian jointvetch 84 to 98%.  Hemp sesbania control was 98% with all halosulfuron containing herbicides.  Texasweed control was 94 to 96% with bensulfuron, imazosulfuron, and saflufenacil.  Alligatorweed control was 90 to 98% with penoxsulam, quinclorac, triclopyr, and penoxsulam plus triclopyr.  Yellow nutsedge control was 91 to 98% with all halosulfuron containing herbicides and imazosulfuron.

Rice injury was only present when treated with saflufenacil.  This was primarily at the EPOST timing with 30% injury.  In 2012 at RRS, the MPOST timing had 20% injury.  In all cases, except for 2012 at RRS with saflufenacil EPOST, the rice recovered.

In conclusion, the MPOST was the most consistent timing for all weeds evaluated.  Imazosulfuron was the most consistent herbicide evaluated.  The LPOST timing is probably to late to obtain acceptable weed control; also, when control is achieved at a high level, rice yield is already reduced due to prolonged competition.  In many cases the EPOST study had weed emergence following the application.

Smallflower umbrella sedge (Cyperus difformis L.) is a major weed of California rice that is typically treated in postemergence with propanil due to resistance to acetolactate synthase (ALS) inhibitors. However, growers have recently experienced poor C. difformis control with any of the available propanil formulations, suggesting resistance to this PSII inhibiting herbicide may have evolved in some populations. Confirming the presence of resistance among populations from rice fields with a long history of treatment with propanil, quantifying its level, and exploring a metabolic basis for it were the objectives of the present work.

Four C. difformis populations were resistant to propanil, making it the first such case outside the Poaceae family and the first case of C. difformis resistance to mechanisms of action other than ALS inhibition. Carbaryl and malathion reduced the resistance level (ED₂₀) of the R population PP, suggesting a contribution of enhanced metabolism towards the mechanism of resistance.  The ED₂₀ was more reduced by the addition of carbaryl than by malathion, thus the stronger resistance mitigation by carbaryl suggests enhanced aryl acylamidase activity could be more relevant than P450 metabolism as a mechanism of resistance. Moreover, the S population (HR) had much lower ED₂₀ and ED₅₀ values than PP (R) in all cases. 

Viability and Emergence of Red Rice and Irrigated Rice (Oryza sativa L.) are Influenced by Temperature. G.M.S. Sartori¹, E. Marcehsan¹, G.M. Teló*^1,2, S.A. Senseman², C. Azevedo¹, L.L. Coelho¹, M.L. Oliveira¹; ¹Universidade Federal de Santa Maria, Santa Maria, RS-Brasil, ²Texas A&M University, College Station, TX.

Red rice is one of the main weeds in rice due to it’s adverse effects on rice productivity and quality. The objective was to evaluate the effect of temperature on germination of the rice genotype Puitá INTA CL and red rice biotypes. The study was conducted in 2012, in a growth chamber and phytotron at Universidade Federal de Santa Maria, Santa Maria-RS, Brazil. An entirely randomized design with two factors was used with four replicates. The first factor consisted of temperatures 13, 17, 21 and 25 °C and second factor was cultivar Puitá INTA CL and three red rice biotypes, with and without dormancy. The following were evaluated: seed germination (SG), speed of emergence (SE), emergence uniformity coefficient (EUC) and length of the shoot (LS). Occurred increases SG, SE, EUC and LS of red rice biotypes with increasing temperature from 13 to 25 °C. At the temperatures of 13 and 17 °C the Puita INTA CL germinates 64% more than the mean germination of biotypes that did not have dormancy broken.  However at   21 and 25 °C the germination was 11% only. Red rice biotypes showed 56% higher germination at temperatures of 21 to 25 °C, compared with 13 and 17 °C. At lower temperatures (13 and 17 °C) there was less red rice germination. As a control strategy for this weed, it is recommended to prioritize planting rice early when the temperatures are lower.

E-mail:gustavo.telo@yahoo.com.br

Producers commonly apply two or more herbicides in a single application to improve the weed control spectrum, reduce production costs, and/or prevent the development of herbicide resistance in weed populations. Studies were established at the Louisiana State University AgCenter Rice Research Station and the Mississippi State University Delta Research and Extension Center to evaluate several herbicide mixtures and their impact on several weed species. Previous research indicates a potential for synergism between a pre-packaged mix of propanil plus thiobencarb and imazethapyr when mixed for the control of red rice (Oryza sativa L.) and barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.].

Two studies were established to evaluate the interactions between the pre-packaged mix of propanil plus thiobencarb and the individual components when mixed with imazethapyr. The experimental design was a randomized complete block with four replications in a two-factor factorial arrangement of treatments. In the first study, factor A consisted of imazethapyr at 0 and 70 g ai/ha. Factor B consisted of no mixture herbicide, propanil plus thiobencarb at 1680 and 3360 g ai/ha, propanil at 840 and 1680 g ai/ha, and thiobencarb at 840 and 1680 g ai/ha. Propanil and thiobencarb rates are equivalent to those found in the pre-packaged mixture of propanil plus thiobencarb. In the second study imazamox at 0 and 44 g ai/ha was substituted for imazethapyr. A modified Colby’s equation using a non-linear mixed model analysis was used to determine if a synergistic, antagonistic, or additive response occurred.

Red rice control at 14 days after treatment (DAT) resulted in a synergistic response when imazethapyr was mixed with propanil plus thiobencarb at both rates evaluated and propanil at 1680 g/ha. An additive response was observed for red rice control when imazethapyr was mixed with propanil at 840 g/ha and both rates of thiobencarb. An additive response was also observed with all mixtures evaluated for barnyardgrass control.

At 21 DAT, imazethapyr mixed with both rates of propanil plus thiobencarb resulted in a synergistic response for red rice control, while all other mixtures evaluated resulted in an additive response. A mixture of imazethapyr with propanil plus thiobencarb increased barnyardgrass control and was also deemed synergistic. An additive response was shown with propanil at 840 and 1680 g/ha and thiobencarb at 840 and 1680 g/ha when mixed with imazethapyr for barnyardgrass.

At 35 DAT, imazethapyr mixed with propanil plus thiobencarb at 3360 g/ha increased control of red rice and resulted in a synergistic response. All other mixtures displayed an additive response.  Imazethapyr mixed with propanil plus thiobencarb at both 1680 and 3360 g/ha was shown to be synergistic for the control of barnyardgrass. An additive response was observed with imazethapyr mixed with propanil or thiobencarb.

In general, yield increased as herbicide rates increased. Rice treated with imazethapyr mixed with propanil plus thiobencarb resulted in a yield of 6850 kg/ha, which further supports the synergistic response observed for control of red rice and barnyardgrass.

In conclusion, imazethapyr with propanil plus thiobencarb was shown to be synergistic for control of red rice for all evaluations and barnyardgrass at 21 and 35 DAT. This increased weed control translated into higher yields. This mixture can also be beneficial by helping prevent or slow the development of imazethapyr resistant red rice and barnyardgrass.

Evaluation of preemergence herbicides for southern soybean.  Todd A. Baughman, Oklahoma State University, and Eric P. Prostko, The University of Georgia.

Herbicide-resistant weeds have been a problem for soybean producers both historically and presently.  A key component of preventing and managing herbicide resistance is through the use of herbicides with various modes of action.  The best way to accomplish this is to use a combination of both preemergence and postemergence herbicides with different modes of action.  Herbicide studies were conducted in 2012 in Oklahoma and Georgia to evaluate the effectiveness of various preemergence herbicides applied alone and in combination for weed control in soybean.  Typical small plot research techniques were employed in all trials.  Trials were conducted at the Wes Watkins Agricultural Research and Extension Center near Lane, OK, the University of Georgia-Ponder Farm near Ty Ty, GA, and the Attapulgus Research and Education Center near Attapulgus, GA.  Two trials were conducted in Oklahoma investigating preemergence programs alone.  While some early season crop injury was observed with several treatments, soybean injury was less than 5% with all treatments later in the season.  In the first trial, late season tumble pigweed (Amaranthus albus) control was greater than 95% with CHA-044, Dawn, Zidua alone or in combination with Sharpen or Outlook, Verdict + Outlook, and Optill alone or plus Outlook.  Tumble pigweed control was at least 98% with Valor SX, Fierce, Canopy, and Axiom in the second trial.  The third trial conducted in Oklahoma investigated Canopy, Enlite, or Envive applied in combination with postemergence applications of either Classic or Synchrony plus glyphosate.  Injury was less than 10% with all treatment combinations.  All treatment combinations provided 100% control of tumble pigweed.  Trials in Georgia investigated various preemergence herbicide treatments followed by glyphosate postemergence.  In the first trial, initial soybean injury was 10% or more with several treatments. Valor XLT at 5 oz/A resulted in 25% injury.  Soybean injury was less than 10% mid-season except with the Valor XLT treatment.  Annual grass control was at least 90% with all treatments except Canopy followed by glyphosate.  Palmer amaranth (Amaranthus palmeri) control was 99% control with all treatment combinations.  Soybean yield was greater than 40 bu/A with all treatments except Anthem at 7.0 oz/A PRE.  This treatment had resulted in early stand loss of 10%.  In the second trial, injury was greater than 10% with all treatments except Valor SX at 3.0 oz/A and Authority MTZ at 14.0 oz/A both applied preemergence.  Injury with Canopy plus Zidua PRE was over 50%.  The only PRE treatments resulting in at least 90% season long control of annual grass control were Prefix, Valor, and Zidua + Canopy.  Pigweed control (combination of Palmer and Slender, Amaranths viridis) was 99% with all treatments applied in combination with glyphosate.  The only treatment that controlled sicklepod at least 95% was Prefix followed by Roundup.

Weed Control and Soybean Response to Acetochlor

Amit J. Jhala^a*, Mayank S. Malik^b and Megh Singh^c

^aDepartment of Agronomy and Horticulture, University of Nebraska-Lincoln, Lincoln, NE 68583-0915; ^bMonsanto Company, 7551 Crystal Ct., Lincoln, NE 68506. Citrus Research and Education Center, IFAS, University of Florida, Lake Alfred, FL 33880. *Corresponding author’s E-mail: amit.jhala@unl.edu.

Abstract

Acetochlor, an acetamide herbicide has been used for many years for weed control in several crops including soybean. However, the encapsulated acetochlor has been registered recently for Pre-Plant and PRE application in soybean. Information is not available on sequential application of acetochlor for weed control and crop safety in soybean. Field experiments were conducted in Nebraska to evaluate weed control efficacy and crop safety of acetochlor applied Pre-Plant, PRE and POST in tank mix with glyphosate in glyphosate-resistant soybean. The results suggested that the plant height and plant counts were not affected by any treatment. Weed control was similar at 30 DAT in all treatments; however, later in the season, weed control was poor in treatments where acetochlor was applied only Pre-Plant and PRE compared with followed by POST applications. Weed density was usually < 1.0 weed m^-2 in plots treated with a sequential application of acetochlor compared with a single application. There was no difference for weed control, weed density, biomass and yield among two or three time sequential application of acetochlor in a season. Acetochlor applied once in a season at different rates (1680 or 3370 g ai ha^-1) or even in sequential applications (two or three times) did not injure soybean plants. It is concluded that acetochlor tank mixed with glyphosate would provide soybean growers more flexibility to control weeds at different time intervals.

Herbicide resistant weeds are becoming a greater concern within field crops and specifically soybeans. Currently, one of the greatest weed problems in North Carolina is Palmer amaranth (Amaranthus palmeri). Resistance to 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 but estimated at 75%.  These results stress the need for other method of control that should be used and rotated in order to delay or prevent further resistance. PRE herbicides included metribuzin at 280, 420 and 560 g ai.ha^-1 or flumioxazin at 70 g ai.ha^-1. POST treatments included acifluorfen at 280 and 420 g ai.ha^‑1and acifluorfen at 280 g ai.ha^-1+bentazon at 560 g ai.ha^-1 alone or associated with gluphosinate at 595 g ai.ha^-1 or glyphosate at 1060 g ai.ha^-1, lactofen at 175 g ai.ha^-1 and fomesafen at 395 g ai.ha^‑1 associated with gluphosinate at 595 g ai.ha^-1 or glyphosate at 1060 g ai.ha^-1.  LibertyLink  and Roundup Ready soybeans were rated for the percentage of chlorosis, stunting and injury as well as the percentage of control for large crabgrass (Digitaria sanguinalis), common ragweed (Ambrosia artemisiifolia), and ivyleaf morningglory (Ipomoea hederacea) five weeks after PRE herbicide application, and 3 weeks after POST herbicide treatments. In this study, LibertyLink soybeans presented a greater rate of stunting with metribuzin applied at 420 g ai.ha^-1 or 560 g ai.ha^-1 than at 280 g ai.ha^-1. POST applications of acifluorfen, acifuorfen+bentazon, and lactofen resulted immediately after treatment in injuries (up to 25%) primarily made up of chlorosis and necrosis. However, injuries were transient and no injury was observed at the time of the final rating. Common ragweed control was greater than 90% with all PRE treatments and greater than 95% with all POST applications. Large crabgrass control averaged 50 to 60% for PRE applications of metribuzin at 280 g ai.ha^-1 and 420 g ai.ha^-1 or flumioxazin but increased to 80% with metribuzin at 560 g ai.ha^-1. For POST applications, large crabgrass control was greater than 95% when glyphosate or gluphosinate were applied and lower than 15% when these herbicides were not applied. Ivyleaf morningglory control was greater than 90% for all treatments except for metribuzin applied PRE at 280 g ai.ha^-1 with 85% of control. No differences of yields between the treatments were observed for the Roundup Ready soybeans. The yields for LibertyLink soybeans presented higher results for the treatments associating PRE applications of metribuzin at 280 g ai.ha^-1 or flumioxazin with POST applications of gluphosinate whereas PRE applications of metribuzin at 420 g ai.ha^-1 and 520 g ai.ha^‑1 alone resulted in lower yields than the non-treated control.

tebesanc@ncsu.edu

In recent decades the Argentinean agriculture development was closely linked to the soybean culture expansion, as well as with direct sowing as cultural practice. Consolidation of this sowing system, the use of glyphosate herbicide virtually exclusive and scarce or null rotation with glyphosate-resistant soybean (RR), have resulted in diversity and abundance of many weeds species decreases. Those facts have meant a significant selection pressure over weeds that are not controlled by glyphosate. This pressure helped to the evolution of weed resistant biotypes, as example the Johnson grass (Sorghum halepense (L.)) (S. h). The S.h. is one of main important weeds in the world, that in Argentina. In this study, experiments were conducted to examine the use of spectral reflectance curves to discriminate between RR/S.h plants species.  S.h  and RR plants were grown in pots, and spectral reflectance data were obtained in various phenological stages of weed and crop.. The ability to discriminate between crop and weeds was not affected by the different phenological stages Spectral signatures curves provided an accurate classification among weeds and crop. This suggests that these data are potentially be used to discriminate crop and weed in field scenarios. This information can be helpful to apply site-specific herbicide application and consequently to vary active ingredient  to help delay the resistance onset.

The greatest weed management issue for Southeastern soybean producers is glyphosate-resistant Palmer amaranth. Monsanto is currently developing soybean tolerant to both dicamba and glyphosate, which will be a new tool to address this challenge. To investigate crop tolerance and efficacy, research was conducted in North Carolina and South Carolina in 2012. Fourteen treatments arranged in a factorial plus a commercial standard were evaluated at three locations in North Carolina and one in South Carolina. Factorial treatments consisted of dicamba at 1 lb a.e./A or flumioxazin at 0.0638 lb a.i./A applied PRE, a premix of dicamba plus glyphosate at 1.5 lb a.e./A, dicamba plus glyphosate plus acetochlor at 1.125 lb a.i./A, or dicamba plus glyphosate plus acetochlor plus fomesafen at 0.3 lb a.i./A applied early POST, and dicamba plus glyphosate applied 2 weeks after early POST. A standard treatment of flumioxazin PRE fb glyphosate at 1 lb a.e./A plus a premix of S-metolachlor plus fomesafen at 1.33 lb a.i./A applied POST. Excellent crop tolerance was observed for all treatments. Palmer amaranth control was greater than 95% for all sequential treatments. Results from this study confirm the importance of a diversified weed management program for Palmer amaranth that utilizes multiple mode of actions including dicamba.

Glyphosate-resistant Palmer amaranth is the greatest weed management issue for Southeastern soybean producers. Farmers in North Carolina often design their production plans with Palmer amaranth management in mind. Bayer CropScience is developing soybean tolerant to HPPD-inhibiting herbicides in order to provide alternative control options. Research was conducted in North Carolina in 2012 to investigate crop tolerance and efficacy in HPPD tolerant soybeans. Two studies were conducted in Clayton, NC to investigate tolerance of HPPD tolerant soybeans to PRE and POST applied HPPD inhibitors and to determine efficacy of weed management programs based on these herbicides. In the first trial, fifteen treatments consisting of PRE fb POST herbicide applications were compared, and in the second trial seventeen PRE fb POST or POST only treatments were evaluated. In both studies excellent crop tolerance was observed. Palmer amaranth control was greater than 95% for all sequential treatments, with residual HPPD-inhibiting herbicides providing an excellent foundation for subsequent POST applications. Results affirm the need for residual herbicides in a comprehensive weed management program for Palmer amaranth.

Volunteer glyphosate-resistant corn is one of the most common weed problems found in glyphosate-resistant sugarbeet grown in Michigan.  While there are several options available for control of volunteer corn, there has been little research examining what effect the time of volunteer corn removal has on sugarbeet yield and quality.  Therefore, field trials were conducted in 2012 at the Michigan State University Agronomy Farm in East Lansing and at the Saginaw Valley Research and Extension Center near Richville, Michigan.  The objectives of this research were to: 1) compare two different herbicide programs for control of volunteer glyphosate-resistant corn, and 2) evaluate the effect of application timing on volunteer corn control and sugarbeet yield and quality.  Glyphosate-resistant sugarbeet ‘HM 9173 RR’ was planted at 124,000 plants ha^-1 in 76-cm rows.  Immediately after planting, ‘F2’ glyphosate-resistant ‘DeKalb 46-61’ corn seed was planted approximately 13-cm off the sugarbeet row at a target population of 8,610 plants ha^-1 (0.9 plants m^-2).  Plots were kept weed-free throughout the season with glyphosate at 0.84 kg a.e. ha^-1.  The two herbicide programs examined were: 1) clethodim (105 g ha^-1) + glyphosate (0.84 kg a.e. ha^-1) + ammonium sulfate (2%) and 2) quizalofop (34 g ha^-1) + glyphosate (0.84 kg a.e. ha^-1) + non-ionic surfactant (0.125%) + ammonium sulfate (2%).  These treatments were applied at five different times when volunteer corn was between the V2 and V10 stages of development.  Clethodim and quizalofop rates were increased as the season progressed.  Volunteer corn control was evaluated throughout the season and the remaining volunteer corn biomass was harvested and weighed prior to sugarbeet harvest.  Sugarbeet were harvested for yield and sucrose content and quality.  Both locations experienced minimal rainfall throughout the growing season which contributed to differences in the development of volunteer corn between the two locations.  At East Lansing, volunteer corn was more robust and when it was not controlled caused a 35% reduction in sugarbeet yield.  At Richville, minimal rainfall early in the season contributed to poor growth of volunteer corn and very little competition with sugarbeet.  This research will be repeated in 2013.

Differential Response to Imazamox of Different Imidazolinone Tolerant Wheat Cultivars

ABSTRACT

Imidazolinone (IMI) resistant crops are insensitive to herbicides that inhibit the enzyme acetolactate synthase (ALS) through processes that involve the target site (enzyme mutation or overexpression) or processes not related to it (reduced herbicide penetration or translocation, or increased herbicide metabolism). The objective of this work was to evaluate the mechanism of resistance of different wheat cultivars to imazamox herbicide. IMI resistant wheat cultivars (Dollinco, Impulso, Invento, Bicentenario, Ikaro, and Pantera), commercialized in Chile, were compared to a sensitive cultivar (Pandora S) using several approaches, ranging from in vitro to field experiments. Variables evaluated included dose-response to the herbicide, ALS enzymatic activity, leaf retention of imazamox, plant photosynthetic activity and chlorophyll content. Imazamox dose (expressed as active ingredient in g ha^-1) that reduced 50% wheat dry mass (ED₅₀) ranged between 151 for Ikaro to 1.6 for Pandora S. According to the ED50, the level of resistance was: Ikaro > Impulso > Invento > Dollinco ≥ Bicentenario > Pandora S. The imazamox retention by the wheat leaves was not related to the level of herbicide resistance of the plants. Imazamox reduced the photosynthetic activity of all wheat cultivars when assessed up to 14 days after the herbicide treatment. However, IMI resistant wheat cultivars have recovered the photosynthetic activity, whereas the susceptible one did not. The chlorophyll content of the sensitive wheat cultivar has decreased sharply after the herbicide treatment, independent of the herbicide rate. The herbicide concentration that inhibit the ALS enzyme activity by 50% (I₅₀) have correlated to the (ED⁵⁰), suggesting that the resistance mechanism to imazamox herbicide could be due to a mutation in the ALS enzyme.

Organic growers have identified weed control as one of their most challenging management issues.  Intercropping and tillage are two approaches for reducing weed populations in organic cropping systems; however, these approaches may work antagonistically when combined. This experiment is aimed at determining how weed communities respond across a gradient of increasingly integrated tillage and intercropping, so as to identify the most useful combination of both approaches. Six different management treatments, each replicated four times in a randomized complete block design, were established in 2012 at the University of New Hampshire Organic Dairy Research Farm in Lee, NH. Two control treatments, a pasture control (an established mixture of alfalfa and grass) (T1), and a full-tillage conventional organic feed-grain control (not intercropped) (T2), were compared to four feed grain intercropping system treatments differing in disturbance intensity: full-tillage with annual legume (crimson clover) inter-seeded following feed grain emergence (T3); strip-tillage establishment into living pasture (T4); minimum-till establishment into pasture following mowing and undercutting (T5); and minimum-till establishment following mowing only (T6). Aboveground plant community and corn biomass were measured at peak biomass. Weeds were sorted to species, dried to constant biomass and weighed. Annual weed abundance increased with tillage intensity, with higher weed abundance in conventionally tilled treatments (T2 and T3) compared to the minimally tilled intercrop treatments. Plant community composition also differed across treatments, with Amaranthus spp., Chenopodium album, Digitaria sanguinalis, and Setaria viridis dominating the conventionally tilled treatments and perennial pasture species dominating in the minimally tilled treatments. In contrast, corn biomass was highest in the conventionally tilled treatments and lowest in the minimally tilled treatments. Total plant biomass (corn, pasture, and weeds) was highest in T2 and T3. These results suggest that intercropping into established pasture using conservation tillage methods can decrease annual weed abundance; however trade-offs exist between disturbance intensity, maintenance of desirable pasture species, and corn yield.  

Seed vigor of the crop can influence crop competitive ability against weeds, and therefore would be an important tool for integrated weed management systems.  The main hypothesis is that low seed vigor produced plants with growth characteristics less competitive to weeds.  Competition studies were conducted on plum tomato high and low vigor seeds (HV, LV, respectively), with green foxtail (Setaria viridis) and Jimsonweed (Datura Stramonium) seeds.  Final emergence (E₉₀) was similar (6.8 vs. 7.2 d) in plants derived from HV and LV respectively.  Green foxtail had a lower (5.1d) E₉₀ whereas Jimsonweed had a higher (9.3d) E₉₀.  Uniformity (U=E₉₀ – E₁₀) was higher in plants from HV seeds compared to that from LV seeds (U=2.5 vs. 4.7d, respectively).  Green foxtail had a high uniformity (U=1.8d) whereas jimsonweed had a low one (U=5.2).  Seed vigor of plum tomato did not influence plant height of plants.  Green foxtail was more competitive than jimsonweed, for most growth characteristics, to the crop regardless of the vigor level.  These results demonstrated seed vigor effects (plum tomato) in relation to two important weeds for the crop; a narrow leaf (green foxtail) and a broadleaf (jimsonweed).

Cultural practices including fertilizer nitrogen (N) and crop seeding rates influence weed interference and crop yields. Beside crop-weed competition, fertilizer N can influence herbicide efficacy for weed control. To test these hypotheses in cereal production systems, field and greenhouse experiments were initiated at MSU Southern Agricultural Research Center, Huntley, Montana, in 2011 and repeated in 2012. Influence of fertilizer N and barley seeding rates on weed interference was evaluated in the field. A randomized complete block design (RCBD) with a factorial arrangement of treatments was used, with four replications.  Malt barley variety ‘Metcalf’ was planted. Treatments included fertilizer N at three levels (56, 112, and 168 kg/ha); seeding rates at three levels (38, 76, and 153 kg/ha) and four weed removal timings (at 3-to 4-leaf stage of barley, 8-to 10-leaf stage of barley, season-long weed free, and weedy check). Based on residual nitrate-N (NO₃-N), amount of urea fertilizer was adjusted to obtain the desired N levels. Weeds included wild buckwheat, common lambsquarters, kochia and redroot pigweed. Data on plant height, barley and weed density, barley biomass at anthesis, and weed biomass at each of the weed removal timings were recorded. Barley grain yield and grain quality (protein and plumpness) were recorded at harvest. To fulfill the second objective (effect of fertilizer N on herbicide efficacy for weed control), greenhouse experiments were conducted. Green foxtail, wild oat, kochia and Russian thistle were the target weed species. For each weed species, a randomized complete block design (RCBD) was utilized with a factorial arrangement of treatments and three replications. Treatments included fertilizer N at two levels (56 and 168 kg/ha); herbicides with different modes of action and doses of each herbicide at five levels (0, 1/8X, 1/4X, 1/2X and X; where X is the recommended rate of a herbicide). For grassy weeds, herbicides including fenoxaprop p-ethyl, tralkoxydim, imazemethabenz-methyl, pinoxaden, difenzoquat, flucarbazone, and clodinafop were evaluated. For broadleaf weeds, thifensulfuron-methyl plus tribenuron-methyl, metsulfuron, bromoxynil plus pyrasulfotole, bromoxynil plus MCPA herbicides were evaluated. Additionally, glyphosate and glufosinate were tested. Weed species were grown in pots containing field soil in the greenhouse. Data on visual control [7, 14, and 21 d after application (DAA)] and weed biomass (21 DAA) were used to develop dose response curves. Results from the field study suggest that higher rates of fertilizer N (112 to 168 kg/ha) along with higher seeding rates (76 to 153 kg/ha) increased crop competitiveness relative to weeds and increased barley yields. Under low N (56 kg/ha), weed removal at the 3- to 4-leaf stage of barley was critical to reduce weed interference, while it can be delayed up to 8- to 10-leaf stage of barley under high soil N. Preliminary results from greenhouse studies revealed that efficacy of some herbicides on selective weed species was higher under high soil N compared to low soil N, and higher herbicide doses were needed for weed control under low soil N. This research would aid in improving weed management decisions by understanding the impact of inputs especially N on herbicide efficacy and weed control failures.  

In order to examine the cumulative effects of reduced tillage treatments, all plots at a long-term study site were split in two, with one half receiving its usual tillage treatment, and the other half being moldboard plowed in the autumn of the 23^rd year (‘tillage reset’ factor). The experiment was conducted at La Pocatière, QC, on a Kamouraska clay (fine, mixed, frigid Typic Humaquept). The strip split-split plot design included cropping system, tillage, and tillage reset as factors, and four replicates. Tillage treatments initiated in autumn 1987 were: moldboard plow (MP), chisel plow (CP), and no till (NT). Previous cropping systems (2007-2010) 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. All plots were seeded to corn in 2011. Corn population and biomass, and weed biomass were measured on 9-12 July 2011 in two quadrats per plot. Crop yield was estimated at maturity. Variables were analyzed with PROC GLIMMIX of SAS, with tillage reset, cropping system, and tillage as fixed effects, and replicate as a random effect. Corn population and biomass were 13% and 86% greater, respectively, in plowed-NT compared to NT, but similar across plowed-CP, CP and MP treatments. Similarly, weed biomass in plowed-NT was also 48% greater than in NT (127 vs. 86 kg ha^-1), whereas weed biomass in plowed-CP was 21% lower than in CP (64 vs. 81 kg ha^-1). Silage corn yield in plowed-NT was 25% greater than in all other treatments (13.8 vs. 11.0 Mg ha^-1), regardless of previous cropping system. The yield benefit in plowed-NT was attributed to greater plant populations and increased fertility from the tillage operation, and occurred in spite of greater mid-season weed biomass which also benefitted from the fertility boost. However, corn yield in NT was only 9% lower than MP yield (9.6 vs. 10.6 Mg ha^-1) after 24 years of NT, confirming the feasibility of long-term NT even on a heavy clay soil, under a cool, humid climate. anne.legere@agr.gc.ca

A basic understanding of the spectral reflectance properties of crops and weeds is needed prior to implementing remote sensing strategies into weed management programs.  Research was conducted to determine the feasibility of using leaf hyperspectral reflectance properties to discriminate crops and weeds found in the lower Mississippi Delta.  Three crops and eleven weeds were evaluated in this study: cotton (Gossypium hirsutum L.),  soybeans (Glycine max L.), corn (Zea mays L.), velvetleaf (Abutilon theophrasti Medik.), Palmer amaranth (Amaranthus palmeri S. Wats.), giant ragweed (Ambrosia trifida L.), redvine, [Brunnichia ovata (Walter) Shinners], trumpetcreeper (Campsis radicans L.), common pokeweed (Phytolacca americana L.), common purslane (Portulaca oleracea L.), kudzu [Pueraria montana (Lour.) Merr var. lobata (Willd.) Maesen and S. M. Almeida], curly dock (Rumex crispus L.), johnsongrass [Sorghum halepense (L.) Pers], and horse purslane (Trianthema portulacastrum L.). Data were collected on plants during summer of 2012 at research farms located near Stoneville, Mississippi.  Leaf reflectance properties were measured with a contact probe attached to a spectroradiometer (spectral range, 350-2500 nm). The reflectance data were aggregated to 165 ten nanometer bands spanning the visible to shortwave infrared region (400-2350 nm) of the spectrum.  A leave-one-out cross validation procedure incorporating a correlated adjusted t-score to rank spectral bands and Fisher’s linear discriminate analysis was used for binary classifications (1 crop versus 1 weed) of crops and weeds.  Leaves of crops and weeds exhibited the classic green leaf reflectance characterized by an increase in reflectance within the visible green region (400-500 nm) of the spectrum and by the highest reflectance occurring in the near-infrared (770-1299 nm) region.  Nevertheless, distinct differences were observed in the amplitude of reflectance curves within the visible (400-670 nm), near-infrared, and shortwave-infrared (1300-2350 nm) regions of the spectrum for the crops versus weeds.  Overall, the misclassification error rate ranged from 0 to 0.1 for the classifications and the results indicated that one to eight spectral bands were needed as input into the classifier.  There were a number of spectral bands specific to the crop-weed comparison.  For example, visible bands ranked most influential variables for soybean and corn separation from redvine and kudzu, respectively.  Shortwave-infrared bands were important variables to input into the classifier for distinguishing soybean from velvetleaf and common purslane, cotton from giant ragweed, trumpetcreeper, and common purslane, and corn from trumpetcreeper and common purslane.  Results also include other band inputs for crop and weed separation.  These findings are encouraging and support further research on employing hyperspectral data to identify appropriate spectral bands for differentiating crops from weeds.

Experiments were conducted in 2012 at Dundee, MS and Robinsonville, MS to determine the effect of spray tip selection and herbicide program on glyphosate-resistant Palmer amaranth control.  Experiments were initiated in grower fields with heavy natural infestations of glyphosate-resistant Palmer amaranth.    Applications were initiated when Palmer amaranth plants were 10 to 15 cm in height.  Applications were made with a CO₂ backpack sprayer at a pressure of 324 kPa and an application volume of 140 L/ha.  Treatments utilized in these experiments included:  dicamba at 0.6 kg ai/ha; glufosinate at 0.6 kg ai/ha; dicamba + glufosinate at 0.6 kg ai/ha each; dicamba + glufosinate at 0.3 kg ai/ha each; and glyphosate + dicamba at 0.75 kg ae/ha and 0.6 kg ai/ha, respectively.  All herbicide treatments were applied using each of the following spray tips:  Extended Range Flat Fan, Greenleaf Asymmetric Dual Fan, Extended Range Air Induction, and Turbo Teejet Induction.  All tips utilized in these studies delivered 0.06 liters per minute (0.015 GPM) at 276 kPa.  Visual estimates of weed control, the number of Palmer amaranth plants per square meter, and height of Palmer amaranth plants in each square meter were collected weekly following herbicide application.  In addition, above ground plant biomass from each square meter was collected four weeks after application and dried in a forced air dryer for one week.  Experiments were conducted using a factorial arrangement of treatments in a randomized complete block design with four replications.  Visual estimates of weed control, number of plants per square meter, plant height, and plant biomass were subjected to analysis of variance and means were separated using Fisher’s Protected LSD at p = 0.05.    

Two weeks after application, dicamba + glufosinate at 0.6 kg ai/ha provided greater than 80% reduction in total plants compared to the untreated check.  Glufosinate alone, glyphosate + glufosinate, dicamba + glufosinate at 0.3 kg ai/ha, and dicamba alone provided 66, 55, 40, and 23% reduction in the total number of plants per square meter, respectively, two weeks after treatment.  No difference in plant height was observed two weeks after treatment.  All plant heights were reduced 15 to 38%.  Visual estimates of control indicated that dicamba + glufosinate at 0.6 kg ai/ha provided significantly greater control (90%) compared to all other treatments two weeks after application.  Similar control was observed following application of glufosinate alone of glyphosate + dicamba two weeks after treatment.  Four weeks after treatment, dicamba + glufosinate at 0.6 kg ai/ha reduced the total number of plants and plant height approximately 70% compared to the untreated check.  In addition, glyphosate + dicamba reduced the total number of plants by 60% and height plant height by 80%.  Visual estimates of weed control and reduction in above ground biomass were similar in that dicamba + glufosinate and glyphosate + dicamba each provided greater than 75 to 80% reductions compared to the untreated check. 

Spray tip selection did not impact efficacy of the herbicides tested on Palmer amaranth. The most consistent treatments were dicamba + glufosinate at 0.6 kg ai/ha and glyphosate + dicamba.  However, no single treatment provided adequate control four weeks after treatment.  A combination of herbicide applications and timings is recommended for season long control of glyphosate resistant Palmer amaranth. 

Glyphosate-resistant (GR) weeds continue to be the most problematic weeds to control in most cropping systems in the Mid-South region of the United States.  There are now no less than ten GR weed species in the Mid-South and no less than six confirmed species GR species in Tennessee. Of these, Palmer amaranth (Amaranthus palmeri) is the most difficult of these to control.  This dioecious, broad-leaf species has a robust growth habit, a wide germination window and will out compete crops for essential resources.  Successful management schemes for controlling GR weeds include the use of PRE-emergence (PRE) herbicides, overlaying residual chemistries, making timely applications of POST-emergence (POST) herbicide and integrating cultural control methods. Unfortunately, rainfall to activate PRE’s and residual herbicides can be sporadic at best in Tennessee.  Therefore, timely applications of POST herbicides are essential for many producers to grow a profitable crop.  This heavy reliance on POST herbicide applications increases selection pressure and the possibility of herbicide resistance.  Integrating cultural control methods, such as cover crops, is a viable option available for area producers to reduce selection pressure and gain early season weed control.  Since winter-annual cover crops have readily been used in the Southeastern United States as a conservational practice and have been proven to increase soil quality, as well as provide early season weed suppression. With more interest in cover crops a better understanding of herbicide and cover crop integration is essential for producers to make effective weed management decisions.  Thus a study was conducted in 2012 to investigate Palmer amaranth control in a cotton system where treatments of cover crops and POST applications of glyphosate and glufosinate were applied.  The cover crops evaluated were crimson clover (Trifolium incarnatum L.) and hariy vetch (Vicia vilosa L.).  Seeding rates were 16.8 kg hectare^-1 and 23.6 kg hectare^-1 of viable seed for crimson clover and hairy vetch, respectively. The cover crops were drilled on September 8, 2011 using a no-till drill and allowed to over winter. Approximately four weeks prior to estimated cotton planting date, all plots were desiccated using glyphosate + dicamba tank mixture.  However, adequate control of the cover crops was not achieved.  A sequential application consisting of paraquat + flumeturon was applied, which adequately controlled both cover crops and the winter-annual weeds present in the no cover plots.  Cover crop biomass yields were obtained by clipping a 0.1 m² quadrat above the ground.  The cover crop samples were dried in a forced-air oven at 60°C and weights were recorded after drying for 48 hours.  Herbicide applications commenced when Palmer amaranth populations were 10-12 centimeters in height.  Plots receiving herbicide applications were treated with a sequential herbicide application 7 days after initial application (7 DAA), as is common in these production scenarios to control GR Palmer amaranth.  Palmer amaranth control was assessed 7, 14, 21, and 28 DAA.  Experimental design was a randomized complete block design with four replications and a split plot arrangement of treatments.  Means were separated using Fisher’s Protected LSD at P ≤ 0.05.  Hairy vetch accumulated the more biomass than crimson clover, adding 6750 kg hectare^-1.  Crimson clover accumulated 4960 kg hectare^-1 of biomass, still adding to early season weed suppression.  Application of the first postemergence herbicide was 31 days after planting the cotton crop, or 45 days after termination of the cover crops.  This cover crop system effectively replaced a PRE or early POST application.

Palmer amaranth control was increased at 7, 14, 21, and 28 DAA by utilizing POST herbicide treatments.  Palmer amaranth population evaluated was variable in susceptibility to glyphosate, thus glyphosate did add some efficacy when applied POST.  However, a glufosinate based systems provided the highest amount of control throughout the assessment period, resulting in 94% control of Palmer amaranth.  Cover crop presence had no effect on Palmer amaranth control during the assessment period.  Cotton yield was impacted by both cover crop and herbicide application, but no interaction effect was observed.  Cotton yield was increased by using POST herbicides when compared to control.  However, yield was diminished in plots where cover crops were present.  These results indicate that cover crops may remove early season moisture from the soil profile and lessen yield potential.  In summary, effective early season control of Palmer amaranth is attainable in a system utilizing cover crops.  However, for season long control timely applications of POST herbicides are essential.

Since the introduction of glyphosate-resistant (GR) crops, growers often have relied on glyphosate-only weed control programs. As a result, multiple weeds have evolved resistance to glyphosate. Now, in many areas the value and viability of glyphosate-only herbicide programs are limited.  Long-term research is needed to assess the sustainability of herbicide best management practices (BMPs) to mitigate and/or manage evolved herbicide resistance. A long-term field-scale study called the Benchmark Study was implemented to compare weed management and economics of typical grower standard programs (SPs) versus academic-recommended BMPs. The study involved 641 grower fields in six states from 2006 through 2010. Crop yields, weed management costs, and weed population changes over time were compared for the SP versus BMP approach across states, years, crops, rotation and tillage systems, and geographical regions. The crops included in this study were maize (Zea mays L.), cotton (Gossypium hirsutum L.), soybean [Glycine max (L.) Merr.], and rice (Oryza sativa L.). Production systems included a continuously grown GR crop, a rotation of GR crops, and a GR crop rotated with a non-GR crop, such as rice or maize. The various tillage systems included conventional, minimum, and no-tillage. Data from this study suggest that the more intensive herbicide BMP (e.g., number of applications and diversity of herbicide mechanisms of action) do not result in economic loss to manage evolved herbicide resistances in weeds. Results also suggest that in the near-term the less herbicide intensive SPs provide equivalent economic returns while minimizing herbicide load in the environment and retain simplicity and convenience of weed management.

From 2010 to 2012, fall- and spring-applied herbicides were evaluated to determine their impact on control of suspected ALS-resistant common chickweed (Stellaria media) in winter small grain fields in southeastern Pennsylvania.  Treatments were applied in late October to mid-November (chickweed – 15-23 cm in diameter) and mid-March to late March (chickweed – 30 cm in diameter) with a hand-held boom sprayer that delivered 187 L ha-1.  Thifensulfuron plus tribenuron premix was applied at 31.4 g ai ha-1; fluroxypyr at 69.4 and 121 g; metribuzin at 105, 157, and 211 g; 2,4-D at 398 g; dicamba at 140 g; fluroxypyr plus dicamba premix at 183 g; pyrasulfotole plus bromoxynil premix at 266 g; and pyroxsulam at 18.4 g.  Some of these treatments were applied as a single active ingredient while others were tank-mixed or applied in sequence. All treatments contained the recommended adjuvants.  Plots were replicated and randomized and measured 3 m wide by 9 m long.  Ratings taken in late April/early May revealed that the chickweed population was ALS-resistant, since the thifensulfuron plus tribenuron premix provided no more than 70% control when applied in the fall and less than 37% when applied during the spring. Also pyroxsulam, another ALS-inhibiting herbicide, only provided 77% control when fall-applied. Treatments containing fluroxypyr provided 92-98% chickweed control when applied in the fall and 84-99% control when applied in the spring. In general, metribuzin alone or in combination provided greater than 90% chickweed control, regardless of rate or application timing. A tank-mixture of 2,4-D plus dicamba provided chickweed control ranging from 67 to 89%; whereas the pyrasulfotole plus bromoxynil premix ranged from 32 to 80% control. Fall-applied herbicide generally provided more consistent control of common chickweed. Metribuzin and fluroxypyr provide the most effective control of ALS-resistant common chickweed. However, currently, metribuzin is not labeled for use in small grains in the Mid-Atlantic region and potential crop injury has been evident on certain winter wheat and barley varieties. Fluroxypyr has good crop safety, but has a limited weed control spectrum. The thifensulfuron plus tribenuron premix still provides adequate control of other common weeds found in Pennsylvania small grains, thus using it in combination with other herbicides will likely occur in order to obtain broad-spectrum control while maintaining an economical solution. Crop rotation and the use of other weed control tactics including different herbicide programs and modes of action provides the most reliable means of controlling ALS-resistant common chickweed. The ALS-resistant chickweed populations are not yet widespread in Pennsylvania but have been documented in neighboring states to the south.

Glyphosate is the most widely used herbicide in the world for weed control in annual and perennial crops. Currently there are several cases of grasses and dicotyledonous species that are resistant to this herbicide in the world, including in Leptochloa virgata. In order to characterize the resistance level in this specie, dose-response (ED₅₀) and effective concentration (EC₅₀) assays were performed by using two biotypes: a susceptible (S) population collected in a sugar cane field, and the resistant (R) one collected in a citrus orchard with a long history of glyphosate usage. The results obtained in the dose-response curves showed a resistance index of 3.0, while the EC₅₀ showed a value of 4.9. Both results, confirm a low resistance level in the R population to the glyphosate herbicide; meaning that other options should be included in the weed management in order to reduce the pressure of glyphosate in this and other species associated with the crop.

Nutsedge (Cyperus spp. L) is a problematic weed in Florida bell pepper production, due to the phase out of methyl bromide and the few herbicides registered in bell pepper. In the spring of 2012, field studies were established to evaluate the efficacy of glyphosate and cultivation applied during the fallow season on nutsedge control in bell pepper. Locations included the Plant Science Research and Education Unit in Citra, FL and the Gulf Coast Research and Education Center in Balm, FL. Both sites initially had nutsedge populations in the range of 100 to 200 shoots/m². Experimental design was split plot randomized complete block design with 4 replications. Treatments included 8 fallow programs and 3 fumigant treatments. The fallow season was 18-weeks, with treatments occurring 4,6,9,12 and 14 weeks after initial (WAI) field cultivation. The 8 fallow programs included glyphosate (G) or cultivation (C) at 9 WAI: GG, CC, GC or CG at 6 and 12 WAI: GCG at 4,9 and 14 WAI: and a nontreated (NT). Glyphosate was applied at 5.51 kg ae/ha with a backpack sprayer calibrated to deliver 287 L/ha. The 3 fumigants included 1,3-dichloropropene+chloropicrin (337 kg/ha), dimethyl-disulfide (595 kg/ha), and a nontreated check. Bell pepper ‘Tomcat’ (Capsicum annuum L. ‘Tomcat’) were transplanted 26 WAI at both locations. Nutsedge counts were taken 0,14,28 and 42 days after planting (DAP) using a 1 m² quadrant. Bell pepper were harvested on October 31 in Citra and November 26 in Balm. Data were analyzed with analysis of variance and means were separated with Duncan’s multiple range test (P<0.05). Locations were not significantly different for nutsedge counts and locations were combined. The highest nutsedge counts were in the C (12 nutsedge/m²) treatment and was similar to NT (11 nutsedge/m²) and CC (9 nutsedge/m²) at 0 DAP. At 14 and 28 DAP, NT had the highest nutsedge counts and was similar to C. The lowest nutsedge population was GG (3 nutsedge/m²) and GCG (3 nutsedge/m²) 42 DAP, and was similar to CC (6 nutsedge/m²), CG (4 nutsedge/m²) and GC (4 nutsedge/m²) treatments 42 DAP.  In the NT fallow program, 1,3-dichloropropene+chloropicrin had the lowest nutsedge counts (4 nutsedge/m²). In plots with the GG and GCG fallow program, 1,3-dichloropropene+chloropicrin and dimethyl-disulfide were similar to the NT. Locations were different for yield (fruit number and weight) and locations were separated. The application of a fumigant resulted in higher yields compared to the nonfumigated in both locations. In Balm, total number (109.5 peppers/plot) and total weight (9.76 kg/plot) yield was highest with 1,3-dichloropropene+chloropicrin. In Citra, no difference in fruit number or weight between 1,3-dichloropropene+chloropicrin and dimethyl-disulfide was seen, while the application of a fumigant resulted in higher yields in both locations. Nutsedge counts in GG and GCG fallow programs did not differ between fumigated and nonfumigated plots. However, in reduced fallow programs the fumigant was required to reduce nutsedge populations. Growers may apply less fumigant with a fallow program of GG or GCG for controlling nutsedge.   

Lima bean producers in the mid-Atlantic States have struggled with control of ALS-resistant pigweed.  Most herbicides do not provide adequate crop safety to lima beans.  Sulfentrazone has been used successfully in regions with medium-textured soils but no work has been done with coarse-textured soils.  A series of trials were conducted in 2010 to 2012 examining crop safety and weed control when sulfentrazone is applied preemergence to lima beans.  Sulfentrazone was applied at rates of 35 to 209 g ai/ha immediately after planting.  In addition, sulfentrazone at 105 g ai/ha was applied with s-metolachlor at 1 kg/ha.  Lima bean injury at 105 g was consistent across sites and was 10% at 2 weeks after planting (WAP) and 6% at 5 WAP.  Higher rates were not consistent across sites, with 157 g ai/ha ranging from 16 to 29% injury 2 WAT.  Yield of shelled beans was not significantly different for any treatment, regardless of sulfentrazone rate or additional herbicides.  There was no indication that early-season injury delayed crop maturity.  At 5 WAP, sulfentrazone alone provided 84% Amaranthus control, but the addition of s-metolachlor improved control to 98%.  Sulfentrazone can be used on coarse-textured soil with caution, provided the grower avoids spray overlaps in the field, and no soil splashing occurs shortly after crop emergence.

EFFICACY OF POSTEMERGENCE HERBICIDES FOR THE CONTROL OF VINE WEEDS IN FLORIDA CITRUS. Analiza H.M. Ramirez*¹, Amit J. Jhala² and Megh Singh¹;  ¹University of Florida, Citrus Research and Education Center, Lake Alfred, FL; ² University of Nebraska, Lincoln, NE.

ABSTRACT

Vine weeds are problem weeds in citrus groves. They not only compete for nutrients but more importantly limit citrus’ photosynthetic capacity by smothering them. There is limited information on the control of vine weeds with postemergence herbicides in citrus.  Several greenhouse studies were conducted to evaluate the efficacy of postemergence herbicides currently being used and under investigation in citrus for the control of balsam apple (Momordica charantia L.), citron melon (Citrullus lanatus var citroides (Thunb.) Mats. & Nakai ), maypop vine (Passiflora incarnata L.) and milkweed vine (Morrenia odorata (Hook. & Arn.) Lindl). Treatments were applied at two- to four- and six to eight- leaf stage for balsam apple, citron melon and maypop vine while milkweed vine was treated at the two- to four- leaf stage only. Control of vine weeds varied with weed species, herbicides and growth stage. Balsam apple and citron melon, regardless of growth stage, was effectively controlled (> 90%) at 21 and 14 DAT, respectively with flumioxazin (Chateau), glyphosate (Roundup WeatherMax), glufosinate (Rely 280), paraquat (Gramoxone Inteon), saflufenacil (Treevix), and premix of 2,4-D and glyphosate (Landmaster II). The same herbicides controlled milkweed vine at the two- to four- leaf stage, while the premix of 2,4-D + glyphosate, paraquat and saflufenacil effectively controlled  maypop vine (78 to 92%) regardless of growth stage. Carfentrazone (Aim) was more effective in controlling young (2 to 4 leaf stage) balsam apple and citron melon but not milkweed vine and maypop. Rimsulfuron (Matrix) was ineffective for controlling all vine weeds except citron melon at the 2 to 4 leaf stage while control with 2,4-D was <65%. The results indicate that commonly used postemergence herbicides in citrus can effectively control vine weeds under greenhouse conditions however, more research is required under field conditions to evaluate the regrowth of vine weeds after a single herbicide treatment and the effectiveness of a sequential application of postemergence herbicides for controlling vine weeds in Florida citrus.

Field studies were conducted in 2011 and 2012 at Belle Glade, FL to evaluate the critical period of weed control (CPWC) in snap bean grown in high organic matter soils of the Everglades Agricultural Area (EAA) of south Florida. Treatments of increasing duration of weed interference and weed-free period were imposed at weekly intervals from 0 to 7 wk after snap bean emergence (WAE). The beginning and end of the CPWC based on 2.5, 5, and 10% snap bean acceptable yield loss was determined by fitting log-logistic and Gompertz models to represent increasing duration of weed interference and weed-free period, respectively. Based on 2.5% yield loss, the CPWC was 6.6 wk beginning 1.1 (first trifoliate leaf) and ending 7.7 WAE (mid pod set, 50% of pods had reached maximum length). At 5% yield loss, the CPWC was 4.9 wk, beginning 1.5 (first to second trifoliate leaf) and ending 6.4 WAE (early pod set, one pod had reached maximum length).  At 10% yield loss, the CPWC was 3.1 wk, beginning 1.9 (second trifoliate) and ending 5.0 WAE (early flowering, one open flower). Beginning of the CPWC was hastened while the end of the CPWC was delayed at the different yield loss levels showing that acceptable weed control in snap bean is required throughout much of the growing season to maximize on yields. Therefore, snap bean growers in the EAA should consider use of residual PRE or POST herbicides or a combination of both supplemented with tillage to minimize weed interference throughout much of the growing season. 

Short season cover crops can provide a number of benefits including reduced soil erosion and soil crusting, disruption of weed life cycles, and increased nutrient cycling. While a number of studies have looked at the benefits and costs of summer cover crops, very few have evaluated how those benefits differ when terminated and tilled in the fall versus spring. Field experiments were conducted in Michigan, New York, and Illinois to evaluate the effect of short season cover crops sown in late summer, combined with two timings of primary tillage (fall versus spring) on weeds and organic snap beans grown the following summer.  Cover crop treatments included mustard, buckwheat, and bare ground at all sites, and either oats (MI), or sorghum sudangrass (IL, NY).  Data collection included winter annual weed biomass, emergence of summer annuals, time required for hand weeding, and snap bean density and yield.  In Michigan, in both bare ground and buckwheat treatments fall tillage reduced winter annual weeds compared to spring tillage.  However, when mustard or oats were tilled in the spring, winter annual weed biomass was equal to or lower than fall tillage. Cover crops either had no effect or decreased summer annual weed emergence compared to bare soil.  In one site-year out of five, mustard and sorghum sudangrass decreased emergence of common lambsquarters.  Compared to fall tillage, spring tillage reduced weed emergence of pigweed in one out of five site-years, and decreased the time spent hand weeding in one out of four site-years.  Fall tillage decreased snap bean stands compared to spring tillage in four out of five site-years, and resulted in reduced snap bean yields in two out of five site-years.  Cover crops had little impact on snap bean stands or yields.  

Sweet corn growers in the mid-Atlantic States often grow processing sweet corn and then plant a second vegetable crop immediately after harvest.  As a result, herbicide selection for the sweet corn crop is important to ensure the second crop is not injured, and the rotational restrictions are followed.  The label for topramezone allows for planting crops shorter than what the label recommends, but the grower must be willing to accept any injury.  This study was conducted to evaluate the safety of vegetable crops often planted after sweet corn harvest.  A series of greenhouse trials evaluated the relative safety of snap beans, lima beans, and pickling cucumbers.  Snap beans were the most sensitive, followed by lima beans, and pickling cucumbers were the most tolerant.  Furthermore, four snap bean varieties were included and Envy and Dart were more sensitive than Caprice, with Slenderpack having an intermediate response.

 Under field conditions, snap beans, lima beans, and pickling cucumbers were planted approximately four weeks after the plots were treated with topramezone.  Two snap bean varieties, Envy and Slenderpack, and two pickling cucumbers, Vlaspik and Expedition were included.  The lima bean variety was Cypress.  Based on visual ratings taken 3 weeks after planting the vegetables, Envy averaged 27% injury, Slenderpack averaged 15% and lima bean and both pickling cucumber varieties were less than 5% injury. 

Topramezone has potential for use in sweet corn if lima bean or pickling cucumbers are used in rotation.  Snap beans should not be planted after sweet corn treated with topramezone.

Low-density polyethylene (LDPE) mulch is commonly used in transplanted vegetable crop production in the southeastern U. S.  Cantaloupe and watermelon growers use a system of hybrid transplants, grown on narrow LDPE mulch-covered seedbeds with overhead irrigation, and use the mulch cover for only one crop.  LDPE mulch offers many crop production advantages over bareground systems, including weed suppression.  However, LDPE mulches are costly to remove and dispose ($210 to $370/ha).  Discarded LDPE mulch is often burned, discarded in landfills, or piled in large unsightly mounds in bordering areas.  Biodegradable mulches that eliminate removal and disposal costs would be of significant value, provided that weeds are adequately suppressed.  Cotton gin trash is a waste product, composed of fiber fragments and seed pieces, and biodegradable.  Using a proprietary process, cotton gin trash can be pressed into a loosely woven mat and stored as a continuous roll.  Research trials were conducted from 2010 to 2012 to determine if the rolled cotton fiber mat made from gin trash could be applied as a seedbed cover using conventional application equipment and adequately suppress weeds.  Mulching materials (rolls 91 cm wide) were applied with a mulch layer that produced a finished seedbed 41 cm wide.  ‘Athena’ cantaloupe and ‘Crimson Sweet’ watermelon were transplanted using a waterwheel transplanter.  There was no pre-plant fumigation.  Mulching materials included nontreated rolled cotton fiber mat, rolled cotton fiber mat sprayed with boiled linseed oil after mulch application, rolled cotton fiber mat sprayed with black latex paint, rolled cotton fiber mat sprayed with tan-colored paint (derived from soybean), black LDPE, and bareground.  Herbicide treatments included ethalfluralin plus halosulfuron plus glyphosate applied as directed spray and nontreated with herbicides.  Rolled cotton fiber mat was easily applied with a conventional mulch-layer with no modification and minimal adjustment, producing no tears, rips, or holes.  The biodegradable cotton fiber mat performed best when treated with boiled linseed oil or black latex paint after mulch application.  Treated cotton fiber mat suppressed weeds equal to or slightly better than LDPE, with cantaloupe and watermelon yields responding similarly.

Purple nutsedge is one of the most troublesome weeds of fresh-market vegetable crops in the Southern U.S.  A perennial weed, purple nutsedge reproduces vegetatively by producing chains of tubers.  Halosulfuron is an effective means of controlling purple nutsedge foliage and is registered for use in several vegetable crops.  However, the effect of halosulfuron on purple nutsedge tuber production and tuber viability has not been evaluated.  A single pre-sprouted purple nutsedge tuber was transplanted into outdoor microplots in middle April in 2011 and 2012.  After six weeks of growth, six rates of halosulfuron (7 to 208 g ai ha^-1) were applied POST.  A nontreated control (NTC) was also included.  Treatments were arranged as a randomized complete block design, blocked by emerged shoot numbers at application, and had five replications.  All shoots emerged at the time of application were marked with plastic rings; this allowed for classification of tubers at exhumation of 1) tubers attached to shoots that were emerged at time of application, 2) tubers attached to shoots that emerged after application, and 3) tubers without an aerial shoot during the study.  Seven weeks after application, the tubers in the microplots were exhumed, tubers classified, quantified, and viability evaluated.  In the NTC, there were 530 total tubers, with a hyperbolic decay regression describing the tuber population with increasing halosulfuron dose.  At 52 g ha^-1 (common 1X dose in vegetables) there was a 79% reduction in total tuber population.  There were no differences among treatments in number of tubers attached to emerged aerial shoots (31 to 43) at the time of application.  However, the viability of these tubers was reduced to 16% at the 1X rate.  In the NTC, there were 200 tubers that were attached to shots that emerged following halosulfuron application, while the 1X dose reduced tuber numbers 75%.  However, this new shoot emergence may give the initial impression to the grower that the treatment was ineffective.  Viability of these tubers was 28% at the 1X rate of halosulfuron, suggesting the action of the herbicide may have rendered the tuber nonviable after new shoots were produced.  The final classification of tubers is the tubers that did not have an aerial shoot during the study.   These are tubers in which apical dominance suppressed shoot development or were the most recent tubers to develop.  Of the three classes, these were the most numerous in the NTC, with 294 tubers.  At the 1X rate of halosulfuron, tuber production was reduced 93%, with only 14% viability of the tubers that were produced.  Halosulfuron is an effective herbicide that control purple nutsedge foliage, but also reduces the number of new tubers produced and overall tuber viability.  This could be an important component used to reduce the long-term population density of this weed.

A study was conducted to address weed and root-knot nematode infestations in high tunnels at a central Florida organic farm.  The high tunnels provide for season extension for the production of frost-sensitive vegetable crops, but are not used for cropping during the summer when conditions inside are very hot and humid.  One bay of a two-bay 14.6 m x 61 m high tunnel was used to establish eight off-season treatments arranged in a randomized complete block design with four replications.  Treatments were applied to 0.9 m x 6.1 m plots on July 18, 2012.  A weedy control, a weed-free treatment covered with black polyethylene film, and four cover crop treatments: Iron Clay, US-1136, US-1137, and US-1138 cowpeas sown at 25 seeds m^-2 were terminated after eight weeks by rototilling in preparation for a cucumber crop.  A nine-week soil solarization treatment and US-1137 cowpea grown for four weeks followed by five weeks of soil solarization (US-1137SS) were terminated by removal of the solarization film.  Solarized plots were not rototilled.  Plots were mulched with white-on-black film (white side up) and three-week old cucumber seedlings were transplanted into each plot on October 3.  The three recently released cowpea germplasm lines (US-1136, US-1137, and US-1138) did not differ in biomass production from Iron Clay cowpea.  Grasses were the predominant weed species by mass and all off-season fallow treatments resulted in lower grass and total weed biomass than the weedy control.  Iron Clay was the only treatment with a higher fruit number than the weedy fallow.  Only US-1137 cowpea had a higher total marketable weight than the weedy fallow.  Using US-1137 in combination with soil solarization did not improve fruit weight over US-1137 alone.  Mean root-knot nematode population in July was, which was higher than the obtained in December at the end of the cucumber crop.  Lower root-knot nematode populations in December after the cucumber crop (5 per 100 cc) than in July (82 per 100 cc) prior to the experiment could not be attributed to the off-season treatments.  Additionally, root galling in cucumber with the alternative off-season treatments was not significantly different from that observed with the weedy control. Therefore, decreases in root-knot nematode occurrence were not the result of suppression of weeds with off-season cover crops and soil solarization. Corresponding author: cachase@ufl.edu

Weeds have a greater impact on crop yields than any other pests. In the past growers have turned to synthetic herbicides because they are the most effective deterrent against weeds. However, demand for organic food is rising, and public sentiment toward synthetic herbicides is increasingly negative. While demand for organic food has grown tremendously throughout the developed world, weed management remains the most significant agronomic problem associated with organic crop production. There is a need and a market for new, natural weed management tools. The objective of this study was to evaluate improved biological and lower-risk herbicides that are appropriate for use by organic growers to provide enhanced weed management in the organic production of tomato, sweet corn and pepper. The efficacy and safety of manuka oil, applied alone and tank-mixed with other organically-acceptable weed control products to control weeds in organic crop production was evaluated and the synergy/additive effect associated with tank-mix applications of manuka oil with currently approved essential oils was observed. Weed control with manuka oil (1%), tank mixed with Green Match Ex (10%), Weed Zap (5%) or Weed Pharm (30%), was superior to weed control with these products used alone. In most cases yields were also superior with tank-mix applications. The synergy/additive effect associated with tank-mix applications of manuka oil with currently approved essential oils has the potential to significantly improve weed management in organic crop production. Developing new natural weed control products with superior weed management properties to control or effectively suppress weeds will help the organic crop production industry remain competitive and sustainable into the future.  

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 January 2012 to December, 2012 for: Clomazone on Brassica, head and stem, Rhubarb and southern pea; Glyphosate on Root and tuber vegetable, group 1, except sugar beet, Oilseed group 20, Teff, Bulb vegetable group 3-07, Fruiting vegetable group 8-10, Citrus fruit group 10-10, Pome fruit group 11-10, Berry and small fruit group 13-07; Halosulfuron-methyl on Caneberry subgroup 13-07A and globe artichoke; Prometryn on dill and snap bean. From January 2012 through December 2012, EPA has published Notices of Filing in the Federal Register for: EPTC on Citrus fruit, group 10-10, Sunflower subgroup 20B, and watermelon; Ethalfluralin on Oilseed group 20; Flumioxazin on globe artichoke, cabbage, Chinese cabbage,  olive,pomegranate and prickly pear cactus; Fomesafen on cantaloupe, watermelon, cucumber, summer squash, winter squash, pumpkin and succulent pea; Imazosulfuron on Tuberous and corm vegetables, subgroup 1C and melon subgroup 9A; Simazine on Pome fruit group 11-10 and Stone fruit group 12-11; Trifluralin on oilseed group 20 and Teff. EPA established tolerances from January 2012 to December 2012 for: Clopyralid on apple, Brassica leafy greens, subgroup 5B, Rapeseed subgroup 20A, except gold of pleasure; Glufosinate-ammonium on sweet corn, Fruit, citrus group 10-10, Fruit, pome, group 11-10,Fruit, stone, group 12-12; 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-ethyl on rapeseed subgroup 20A, except flax seed, and sorghum; Quinclorac on Rhubarb and Berry, low growing, except strawberry, subgroup 13-07H; Rimsulfuron on Caneberry subgroup 13-07A and Bush berry subgroup 13-07B; Rimsulfuron + thifensulfuron-methyl on chicory; S-metolachlor on cilantro and garden beet leaves; Sulfentrazone on turnip, rhubarb, Wheat (PNW only), Sunflower subgroup 20B, and Cowpea, succulent (Tennessee only) and edamame.

EVALUATION OF FLORASULAM FOR BROADLEAF WEED CONTROL IN BERMUDAGRSS.  T. Reed and P. McCullough; Department of Crop and Soil Sciences, University of Georgia, Griffin, GA 30223.  A. Alexander; Dow AgroSciences Turf & Ornamental Business, Lawrenceville, GA 30042.

ABSTRACT

Field experiments were conducted to evaluate efficacy of florasulam applications with dithiopyr for annual and perennial broadleaf weed control in two common bermudagrass (Cynodon dactylon) lawns in Griffin, GA.  Treatments were applied on February 13 and March 12, 2012 and single versus sequential applications were evalauted.  Weeds evaluated included catsear dandelion (Hypochoeris radicata), common dandelion (Taraxacum officinale), common chickweed (Stellaria media), corn speedwell (Veronica arvensis), henbit (Lamium amplexicaule), parsley-piert (Aphanes arvensi), and white clover (Trifolium repens).  Bermudagrass had no injury from treatments and greenup was not inhibited from the untreated.  Single applications of florasulam at 15 g ai/ha with dithiopyr provided excellent control (>90%) of common chickweed and white clover and good control (80 to 89%) of henbit.  However, control was poor (<70%) on other weeds evaluated.  Sequential florasulam applications generally improved control compared to single treatments and provided excellent control of common chickweed, and white clover; good control of catsear dandelion, corn speedwell, and henbit; and fair control (70 to 79%) of parsley-piert and common dandelion.  

Creeping bentgrass (CBG) (Agrostis stolonifera L.) is the most widely used cool-season turfgrass species on golf course fairways and tees in the United States. However, CBG is tolerant of few postemergence herbicides. Preliminary research indicates CBG has tolerance to the HPPD-inhibiting herbicide topramezone, but improved tolerance is desirable. Two experiments were conducted at the University of Tennessee (Knoxville, TN) to evaluate safeners as a means to enhance CBG tolerance to the HPPD-inhibiting herbicide topramezone.

In Experiment 1, topramezone (37 g ha^-1) was applied alone or in combination with the herbicide safeners naphthalic anhydride (NA) and isoxadifen-ethyl (isoxadifen). Safeners were applied on the day of herbicide application or 3 days prior to herbicide application in a 5:1 or 10:1 safener:herbicide ratio. All treatments were applied with NIS at 0.25% v/v.  Treatments were applied with a water carrier at 221 L ha^-1 using a spray chamber to mature CBG grown in 6 cm cone-tainers filled with a peat moss, perlite, and vermiculite growing medium. Plants were maintained in a greenhouse under ambient light. Treatments for experimental runs A and B were applied on February 10 and June 1, 2012, respectively. Treatments were evaluated visually on a 0 (no injury) to 100% (complete control) scale at 7, 14 and 21 days after treatment (DAT). Plant were clipped to a 1.25 cm height at 21 DAT, verdure was collected, dried and weighed to quantify biomass production. Data were analyzed in a completely randomized factorial design with three replications in SAS 9.3 (α ≤ 0.05).

Application of NA and isoxadifen reduced injury from topramezone 14 DAT. Neither safener application timing nor safener rate were significant in either run. Therefore, it was determined that the lowest safener rate (5:1 safener:herbicide) applied at the time of herbicide application would be used in Experiment 2.

In Experiment 2, using the same methodology as experiment 1, benoxacor, cloquinctocet-mexyl, fenchlorazole-ethyl, isoxadifen-ethyl, NA, and mefenpyr-diethyl were investigated to determine their ability to reduce CBG injury from topramezone at 37 g ha^-1. Safeners were selected based on their commercial availability. The objective of this experiment was to identify optimal herbicide-safener pairings for candidate herbicides identified in Experiment 1.

In Experiment 2, application of topramezone alone at 14 DAT injured CBG 23%; injury was reduced to 12% when topramezone was applied with cloquintocet-mexyl. No other safener reduced CBG injury from topramezone. Further investigation of cloquintocet-mexyl in greenhouse and field trials to determine its ability to reduce CBG injury using lower safener rates and impacts on weed control is underway.

Herbaceous perennial producers typically start outdoor production with transplants from 72-cell trays (or similar). However, in an effort to improve production efficiency and reduce costs, some herbaceous perennial growers are transplanting smaller, 288-cell plugs directly into outdoor containers.  There is concern that preemergence herbicides applied after transplanting would injure the smaller plants. The objective of this experiment was to compare the safety of delayed preemergence herbicide applications on 288- and 72-cell transplants of Heuchera, a species that is commercially grown using both plug sizes. Heuchera ‘Palace Purple’ 72-cell and 288-cell plugs were transplanted into 4-L plastic pots using a pine bark substrate. Plants were treated with Snapshot TG (5 lb ai/A), Pendulum 2G (3 lb ai/A), or Freehand 1.75G (1.75 or 3.5 lb ai/A). Non-treated plants were included for comparison. Herbicide treatments were applied 0 (at potting), 1, 2, or 3 weeks after potting. Crop injury was visually evaluated weekly from 6 to 10 weeks after potting on a 0 to 10 scale where 0 = no injury (equivalent to the non-treated) and 10 = dead plants. Six weeks after potting, plant canopy heights and widths in two directions were measured to estimate canopy volume. Visual evaluations showed that 288-cell transplants were more sensitive to herbicide injury than 72-cell plants, regardless of potting-to-treatment interval. Delaying applications for three weeks reduced the severity of herbicide injury to 288-cell transplants, but crop injury was still greater than that observed when 72-cell transplants were treated the day of potting. Canopy volume of 288-cell transplants was reduced by all herbicide treatments; however, canopy volume and plant height of 72-cell transplants were reduced only by Snapshot, and treatment effects were not influenced by delayed herbicide applications. This research was unable to identify a potting-to-treatment interval that could provide adequate crop safety when starting with 288-cell transplants.

Amicarbazone is a new herbicide registered for use in turfgrass under the trade name Xonerate.  Most previous research with amicarbazone has been conducted on creeping bentgrass golf greens and fairways.  Amicarbazone could become the first herbicide for selective annual bluegrass control in Kentucky bluegrass athletic fields, sod, and golf fairways during spring when the weed is most problematic, but more work is needed to determine the best treatment programs.  The objective of this study was to determine the appropriate application rates and timings of amicarbazone for controlling annual bluegrass in Kentucky bluegrass without causing unacceptable turf injury.

The trial was initiated on May 23, 2012 on an annual bluegrass infested Kentucky bluegrass fairway maintained at 1.2 cm.  Treatments consisted of amicarbazone applied four times at 49.0 g ai/ha at one-week intervals, twice at 98.0 g ai/ha at a two-week interval, twice at 98.0 g ai/ha at a three-week interval, twice at 147 g ai/ha at a two-week interval, and twice at 147 g ai/ha at a three-week interval.  An untreated check was included for comparison. 

All amicarbazone treatments controlled annual bluegrass greater than 93% 12 weeks after initial treatment (WAIT), with the 98.0 g ai/ha rate applied twice at a 3-week interval being significantly less (93%) than amicarbazone applied four times at 1-week intervals at the 49.0 g ai/ha rate (98%).  Amicarbazone applied at 147 g ai/ha injured Kentucky bluegrass the most 4 WAIT (20%) after the first application but decreased to 13% by 6 WAIT and recovered completely by 12 WAIT and after both applications had been made.  These data suggest that amicarbazone controls annual bluegrass at several different application rates and timings; however, the second application of the 98.0 and 147 g ai/ha rates seemed to be unnecessary in regards to annual bluegrass control.  Temperatures exceeded 85 F during most of the later application times and may have increased annual bluegrass and Kentucky bluegrass response to amicarbazone.  It was also noted that higher and seemingly drier areas of the trial exhibited more severe Kentucky bluegrass injury and more rapid annual bluegrass control.  In order to avoid unacceptable turf injury, amicarbazone should be applied at the 49.0 g ai/ha rate four times at 1-week intervals or the 98.0 or 147 g ai/ha rates once.  In cases of high annual bluegrass infestations, 49.0 g ai/ha of amicarbazone applied four times appears to be the most appropriate treatment in order to phase out annual bluegrass and prevent large, dead or void areas in the turf which may be unsightly to spectators or users of the athletic field.  Other research conducted in cooler weather suggests these lower rates may not effectively control annual bluegrass.  Future research should seek to develop a model that will allow turf managers to predict appropriate amicarbazone rates based on measured or expected temperature fluctuations.

One of the major pest management costs for container nursery growers is weed control. The costs include the the product and labor to apply. However, the nursery must also factor in the cost to hand-weed the containers prior to applying all preemergent herbicides after the initial application at potting. This is partially due to the variability of herbicides under different environmental conditions resulting in shorter than expected residual control and partially due to the diversity of weed species found in nurseries that differ in their response to the herbicide residual. That is, some weeds may be more sensitive to a given herbicide and therefore controlled for a longer period while others may emerge sooner because the residual is no longer present at a sufficient concentration to be effective for control of that particular species. Another complication is that there are few herbicides that can be used over the top (OTT)safely. The uncertainty of knowing when an herbicide treatment is no longer effective results in two behaviors. One is to apply the preemergent before weeds start to emerge based on “best-guess” or other experience which would reduce the cost of hand-removal but may increase the overall amount of herbicide actually needed over the course of the production cycle. The second is to wait until the weeds start to emerge, hand weed as best as one can, and then apply the next preemergent herbicide treatment. The problem with the latter is that while obvious weeds are removed, small, newly germinated ones are not and these will not be controlled by the preemergent herbicide. The result is the need for subsequent hand weeding even though another application was made. I recently conducted trials examining an iron-based contact herbicide, with the active ingredient of Fe-HEDTA, currently labeled for broadleaf weed control in turf. When applied OTT to established nursery plants in 1-gal containers that also contained mature creeping spurge, petty spurge, common groundsel, common purslane, and/or northern willowherb, Fe-HEDTA provided moderate to excellent weed control with little to no crop injury. In in-ground tests of the herbicide on spotted spurge and woodsorrel there was excellent control for approximately one week before regrowth or new emergence.

BERMUDAGRASS CONTROL WITH TOPRAMEZONE IN TALL FESCUE.   C. Johnston and P. McCullough; Department of Crop and Soil Sciences, University of Georgia, Griffin, GA 30223. 

ABSTRACT

Field experiments were conducted in Griffin, GA to evaluate efficacy of topramezone alone or with triclopyr for bermudagrass (Cynodon dactylon) suppression in a tall fescue (Festuca arundinacea) lawn.  Three applications were made on a three-week interval beginning in July and half of each plot was overseeded with ‘Titan’ tall fescue two weeks after the third application.  Topramezone treatments alone controlled bermudagrass 6 to 54% but tank-mixtures with triclopyr increased control to 60 to 68% before overseeding in October.  All treatments provided excellent (>90%) control of smooth crabgrass (Digitaria ischaemum) except the lowest rate of topramezone alone.  Topramezone plus triclopyr treatments increased tall fescue cover to ≈50%, compared to 10% in the untreated, but overseeding after these applications increased tall fescue cover to >80% by December.  However, bermudagrass cover was similar across treatments and overseeding regimens at one year after initial treatments suggesting sequential applications in spring and the following summers will be needed for long-term bermudagrass control. 

COOL-SEASON TURFGRASS TOLERANCE TO METAMIFOP DURING ESTABLISHMENT.  S. Sidhu, Department of Crop and Soil Sciences, University of Georgia, Griffin, GA 30223; D. Gómez de Barreda, Polytechnic University of Valencia, Spain; P. McCullough, Department of Crop and Soil Sciences, University of Georgia, Griffin, GA 30223. 

ABSTRACT

Field experiments were conducted from 2011 to 2013 in Griffin, GA to evaluate injury potential of metamifop applications during establishment of ‘Penn A-4’ creeping bentgrass, ‘Manhattan V’ perennial ryegrass, and ‘Titan’ tall fescue.  Treatments evaluated included metamifop at 0, 200, 400, or 800 g ai/ha and fenoxaprop at 50 g ai/ha.  Applications were made 1, 2, 3, or 4 weeks after seeding (WAS).  Creeping bentgrass ground cover was reduced at 8 WAS from the untreated by fenoxaprop at 50 g ai ha^-1 and metamifop at 400 and 800 g ai ha^-1 at all application timings.  Metamifop at 200 g ha^-1 reduced creeping bentgrass cover from the untreated at 8 WAS when applied 1, 2, or 3 WAS but treatments at 4 WAS did not reduce cover.  Perennial ryegrass treated with fenoxaprop and metamifop at 800 g ha^-1 at 1 WAS had cover reduced on two and one dates, respectively, but cover was similar to the untreated from all other treatments and timings.  Tall fescue cover was reduced ≈5% at 8 WAS from fenoxaprop and metamifop at 800 g ha^-1 applied 4 WAS while all other treatments and timings did not reduce cover from the untreated. 

Research was designed to reduce the application rate of fenoxaprop-p-ethyl (Acclaim Extra) postemergence herbicide by applying it in combination with readily available ocean water to control large crabgrass (Digitaria senguinalis) in zoysia (Zoysia tenuifolia) turfgrass.  It was previously determined that crabgrass can be fully controlled when soil is saturated for 3 days with full strength ocean water (55 dS/m).  Zoysia could tolerate 3 days of salt-stress at salinity level 37 dS/m while 55 dS/m caused unacceptable and long lasting discoloration.  The combination of 3 rates of fenoxaprop-p-ethyl and 3 durations of salt stress (55 dS/m) on crabgrass control were evaluated.  Crabgrass was fully controlled with label recommended rate (1.96 kg/ha) of phenoxaprop-p-ethyl regardless of the salt stress presence.  Full control was also achieved when application rate was 0.63 kg/ha (1/3 X) and salt stress duration of 2 days.  Combination of 1.26 kg/ha (2/3X) and salt stress lasting only 1 day was ineffective with crabgrass fully recovered within two weeks.  Salt stress lasting 3 days or more resulted in unacceptable turfgrass discoloration regardless of herbicide application. In conclusion, crabgrass in zoysia turfgrass could be effectively controlled with reduced rate of fenoxaprop-p-ethyl applied in combination with short lasting salt stress.  

Topramezone is a herbicide labeled for broadleaf and grassy weed control in corn and is currently under evaluation by BASF for use in cool season turfgrass.  Topramezone functions by inhibiting HPPD (hydroxyphenylpyruvate dioxygenase) and the formation of plant carotenoids.  Topramezone effectively controls a broad range of weed species and is safe to cool season turfgrass species.  Combinations of topramezone with triclopyr have been found to reduce whitening symptoms on susceptible plant species while increasing both grass and broadleaf weed control.

This study was conducted on two sites in 2012.  Ground ivy (Glechoma hederacea) was evaluated in tall fescue (Festuca arundinacea) at Kentland Farm in Whitethorn, VA.  Nimblewill (Muhlenbergia schreberi)  and white clover (Trifolium repens) in Kentucky bluegrass (Poa pratensis) was evaluated at the Glade Road Research Center in Blacksburg, VA.  Both trials were initiated on July 21, 2012 and sequential applications were made on August 10, 2012.  Topramezone was applied at 36 g ai/ha alone and in combination with triclopyr at 561 g ai/ha or quinclorac at 841 g ai/ha.  All topramezone treatments contained methylated seed oil.  Mesotrione was included as a comparison at 280 g ai/ha.  Non-ionic surfactant was included with the mesotrione treatment.

Initial ground ivy cover ranged from 43 to 57%.  At 2 weeks after initial treatment (WAIT), topramezone plus triclopyr controlled ground ivy 97%, whereas all other treatments did not exceed 73% control.  At 4 WAIT, all treatments controlled ground ivy between 95 and 99%.  At the conclusion of the study, topramezone alone, plus triclopyr or plus quinclorac controlled ground ivy between 99 and 100%. Mesotrione applied alone controlled ground ivy 95%.

Initial nimblewill cover ranged from 15 to 38%.  At 2 WAIT, topramezone plus triclopyr or quinclorac controlled nimblewill 80 and 80%, respectively, whereas all other treatments did not exceed 57% control.  At 4 WAIT, topramezone alone, plus triclopyr or plus quinclorac controlled nimblewill 78, 99 and 90%, respectively. Mesotrione applied alone controlled nimblewill 58%.  At the conclusion of the study, control was between 75 and 100% across all treatments.  

Initial white clover cover ranged from 20 to 35%.  At 2 WAIT, topramezone plus triclopyr or quinclorac controlled white clover 97 and 100%, respectively, whereas all other treatments did not exceed 13% control.  At the conclusion of the study, all topramezone treatments controlled white clover 100%.  Mesotrione only controlled white clover 43%.  

In turfgrass systems, two and three-way herbicide combinations are popular and effective options for controlling a wide variety of annual and perennial broadleaf weeds.  The objectives of this study were to compare broadleaf weed control between several combination herbicides in bermudagrass and perennial ryegrass.  Four trials were initiated May 17^th in Blacksburg, VA, two in perennial ryegrass and two in bermudagrass.  For  perennial ryegrass trials, treatments were 1) QP 17202 at 1350g ai ha^-1, 2) QP 17203 at 1460g ai ha^-1, 3) a triclopyr + clopyralid combination at 420g ai ha^-1 and 4) a triclopyr + clopyralid combination at 840g ai ha^-1, 5) a dicamba + 2,4-D + mecoprop-p combination at 1390g ai ha^-1 and 6) a dicamba + 2,4-D + mecoprop-p combination at 1850g ai ha^-1,  7) a 2,4-D + mecoprop-p + dicamba combination at 1810 g ai ha^-1, and 8) a 2,4-D + clopyralid + dicamba combination at 1250g ai ha^-1.  For bermudagrass trials, there were slight variations in treatments.  Treatments 1-7 were the same, treatment 8 was excluded, and three new treatments were added: QP 16202 at 355g ai ha^-1, metsulfuron-methyl at 42g ai ha^-1, and a thiencarbazone + iodosulfuron + dicamba combination at 176 g ai ha^-1.  Weed control, weed cover, and turfgrass injury were measured at 7, 14, 28, and 35 DAT. 

In bermudagrass, metsulfuron-methyl controlled white clover and dandelion 99-100% at 35 DAT and better than other treatments.  Most other treatments had similar control.  Experimental treatment QP 17202 and QP 17203 varied in weed control by location.  In one location, QP 17202 controlled both weeds 94% or better at 35 DAT, while in another location, white clover and dandelion control decreased to 77 and 50%, respectively.  Similar results were seen with QP 17203.  There were little differences between QP 16202, triclopyr + clopyralid combinations, and the dicamba + 2,4-D + mecoprop-p combination treatments.  The thiencarbazone + iodosulfuron + dicamba combination controlled white clover 99-100%, but varied in dandelion control, ranging from 53% control in one location to 99% control in another.  Bermudagrass was not injured by any treatment.    

In perennial ryegrass, all treatments controlled white clover and dandelion greater than 94%.    Experimentals QP 17202 and 17203 controlled both weeds better than other treatments.   Perennial ryegrass was not injured.  These data suggest that there are several options for annual and perennial broadleaf control in warm and cool-season turf.  Variations in control could be attributed to environmental factors or differences in weed pressure.  Several of the treatments are commercially available.  Others, such as QP 17202, QP 17203, and QP 16202, are experimentals that can provide efficacious control of white clover and dandelion, potentially expanding the available options for broadleaf weed control in the near future. 

 Perennial woody weeds are often problematic in ornamental beds.  Hand removal may be the solution homeowners use to remove the unsightly weeds, but after pulling or cutting the weed, new shoots emerge quickly.  Hand removal of old growth often stimulates perennial weeds to produce more new shoots than existed before the plants were pulled.    

Treating perennial woody with herbicides can be a more effective long-term control solution than hand removal.  Soil active herbicides may be taken up by plant roots and damage desirable ornamentals. Using these products for control may cause more damage than good.  Herbicides with no soil residual activity are best to use in areas where desirable plants also exist, but application with no overspray onto desirable plants may be difficult.  Roundup (active ingredient glyphosate) is an ideal treatment for perennial weed control because it has activity on a wide variety of perennial weeds, it is not absorbed from soil by plant roots, is inexpensive, and it is widely available.  Roundup must be applied with extreme caution, however, to avoid overspray onto desired ornamentals because spray drift can cause serious damage or even kill desirable plants.  Wiping the Roundup solution onto the foliage of weeds can work with significantly less potential for drift compared to spraying, but wiping may not apply enough Roundup on the foliage of the undesirable plant for satisfactory control, especially if woody perennial plants are the target. 

A herbicide application often used to control trees can be used by homeowners to improve control of woody perennials. Immediately after a tree is cut, application of a herbicide to the stump often prevents the emergence of new sprouts from the stump.  This method works best for complete control if done in the fall when sugars produced by the plant are moving into roots in preparation for winter dormancy.  A modification of this application method that works well to control perennial woody weeds in ornamental beds involves the application of Roundup with a florist’s water-pick.  A water-pick is a plastic tube used by florists to maintain quality of cut stem flowers.  It has a rubber cap with a pre-cut opening that stretches around the stem for a water tight seal.  Water-picks vary in size, but those evaluated for this publication were 3 to 4 inches long and held approximately 0.7 fluid ounces.  To control the woody plant, fill the water-pick with undiluted (41% active ingredient of isopropylamine salt or 48% potassium salt) Roundup (approximately 0.3 to 0.7 fluid ounces), seal with the lid.  Find a stem on the target weed slightly larger than the hole in the water-pick cap.   Cut the stem with a pruning shear, then slide the Roundup filled water-pick onto the cut stem making certain the cut stem is positioned so the plant can absorb all Roundup in the water-pick.  To kill the entire plant, including the roots, remember to use this technique in the fall (August to late October).  This method of application has been used to successfully kill woody plants, including the roots.  The primary potential for damage to ornamentals is if the tube is dislodged from the stem to spill Roundup onto adjacent ornamentals or the stem that is cut is too small to seal tightly so the Roundup leaks onto ornamentals. 

Effectiveness of organic and reduced risk herbicides on lawns and playing fields. A. Senesac*¹, J. Kao-Kniffin²; ¹Long Island Horticultural Research & Extension Center, Riverhead, NY, ²Cornell University, Ithaca, NY.

Starting in 2011, schools and daycare centers in New York State were banned from using conventional pesticides on playing fields, lawns, and playgrounds. The NYS Child Safe Playing Fields Law, enacted to minimize pesticide exposure to children, restricts the use of pesticides to minimal risk ingredients that include clove oil, lemongrass oil, cinnamon oil, and other compounds listed under FIFRA 25(b). Many of the allowable pesticides are approved as organic products through the Organic Materials Review Institute (OMRI), yet few of the products have been tested for efficacy in turfgrass settings. The trial was conducted in weedy Kentucky bluegrass plots infested with Taraxacum officinale, Trifolium repens, Plantago lanceolata, Glechoma hederacea, and Artemisia vulgaris. Three of the treatments were organic herbicides (GreenMatch EX, Weed Zap, and Burnout II) that are allowable for use in schools and daycare centers. Two treatments were reduced risk herbicides (Fiesta and Ecosense Weed B Gone) that require one-time application approval from the local school board, NYS Department of Health, or NYS Department of Environmental Conservation. And one treatment was a thermal propane-fueled torch. Treatments were applied in June and July, biomass of harvested plants was measured, and percent cover of turfgrass and select weeds was evaluated. The fresh weight data collected two weeks after the first application indicated that broadleaf weeds were significantly reduced by most of the treatments. Grass weeds were reduced somewhat but not as significantly. However, after the second application, Fiesta, Ecosense, and BurnOut II were the only spray treatments that caused significant reductions in broadleaf weed fresh weight. More research is needed to determine if combining some of the better products would result in additive levels of control. A follow up study was conducted in the greenhouse with seedling tall fescue, Ambrosia artemisiifolia, and Glechoma hederacea.  Treatments included Adios, Avenger, Fiesta, Weed Zap, Burnout II, and GreenMatch EX.  Avenger resulted in the greatest injury to the seedling tall fescue.  Adios, Avenger, Weed Zap, Burnout II, and GreenMatch EX provided excellent control of the Ambrosia artemisiifolia. Avenger, Burnout II and GreenMatch EX provided acceptable control of Glechoma hederacea. Corresponding author: jtk57@cornell.edu

METSULFURON RESISTANT SPURGE IN GEORGIA.  J. Yu and P. McCullough; Department of Crop and Soil Sciences, University of Georgia, Griffin, GA 30223.  

ABSTRACT 

Spotted spurge (Euphorbia maculata) was collected in Adele, GA from a suspected population resistant to metsulfuron and a susceptible population in Griffin, GA.  Seed from plants were established in pots and treated with herbicides to evaluate resistance potential.  Susceptible plants collected were injured from metsulfuron applications at 21 g ai ha^-1 while resistant plants had no injury after four weeks.  Spotted spurge from Adele was injured ≤5% from six rates of metsulfuron ranging 21 to 672 g a.i. ha^-1 while amicarbazone, glyphosate, and 2,4-D + dicamba + MCPP caused 100, 89, and 40% injury at 4 weeks after treatment (WAT), respectively.  Trifloxysulfuron at 29 g a.i. ha^-1 injured spotted spurge 3% from Adele.  Dry weight reductions from the untreated for spotted spurge ranged 100, 72, and 46% from amicarbazone, glyphosate, and 2,4-D + dicamba + MCPP, respectively, while spotted spurge treated with metsulfuron and trifloxysulfuron had <10% dry weight reductions from the untreated.  

“Investigating Preemergence Herbicides for Arundo donax as a Bioenergy Crop”

Since the passing of the Biomass Research and Development Act of 2000 there has been encouragement to research new forms of biomass to be used as biofuel.  This has increased interest for the production of Arundo donax as a biomass source.  Other countries, such as Italy, are currently using Arundo donax as a source of biomass for their own production of biofuel.  Although there is increased interest for production as a crop there has been no research conducted on preemergence herbicide effects for the establishment of Arundo donax as a biomass source.  A greenhouse study was conducted using cut node sections of harvested Arundo donax.  The nodes selected were of consistent diameter and length and then were placed into 10.16 cm square pots filled with a sandy loam soil.  All nodes were placed horizontal with the opposite side of the leaf arrangement positioned upwards in the pots.  The nodes were watered to saturation and preemergence applications were applied the following day.  The treatment applications were as follows:  acetochlor @ 2.41 lb a.i./A, atrazine @ 1 lb a.i./A, diclosulam @ 0.024 lb a.i./A, diuron @ 0.8 lb a.i./A, flumioxazin @ 0.064 lb a.i./A, fomesafen @ 0.75 lb a.i./A, imazaquin @ 0.123 lb a.i./A, metribuzin @ 0.031 lb a.i./A, pendimethalin @ 1.71 lb a.i./A, pyroxasulfone @ 0.106 lb a.i./A, saflufenacil @ 0.053 lb a.i./A, simazine @ 1.44 lb a.i./A, S-metolachlor @ 1.91 lb a.i./A, sulfentrazone + carfentrazone-ethyl @ .154 lb a.i./A.  Although not statistically different after twenty eight days acetochlor, fomesafen, flumioxazin, and pyroxasulfone had greater than fifty percent control whereas imazaquin, metribuzin, and pendimethalin had less than twenty percent control.

Gene flow between Dalmatian toadflax (Linaria dalmatica ssp. dalmatica) (DT) and yellow toadflax (Linaria vulgaris) (YT), two aggressive invaders throughout the Intermountain West, is creating hybrid populations potentially more invasive than either parent species.  To determine the direction of gene flow in these hybrid populations, species-diagnostic markers were developed based on PCR-RFLP polymorphisms in the TrnT/D cpDNA region digested with Alu1, and SNPs in the matK and TrnL-F chloroplast barcoding regions.  Five hybrid toadflax populations sampled from CO, MT and WA contained both DT and YT cytoplasm with YT predominating; 25 individuals from a sixth hybrid population from ID all had identical YT cpDNA haplotypes. Thirteen plants from two CO populations assumed to be DT based on morphology and geographic isolation from any YT population were found to have YT cpDNA haplotypes. These results indicate that gene flow between invasive YT and DT populations is more widespread that previously realized, and that cryptic introgression of YT alleles has occurred in DT populations.  The presence of YT genetic material in presumed DT populations may negatively affect host recognition and establishment by biocontrol agents used for toadflax management.

Incorporation of a legume, such as red clover (Trifolium pratense), into grass pasture systems is very advantageous for both pasture health and animal nutrition.  However, red clover is susceptible to herbicides used in grass based pastures and, therefore, is limited in its practical incorporation into these systems.  Accordingly, pasture weed management guides state that “In grass pastures interseeded with clover or other forage legumes, selective herbicide options are not available for use as broadcast treatments”.  Selecting for red clover which is tolerant to herbicides currently used in grass based pastures would overcome this limitation.  A red clover which is tolerant to 2,4-D, ideally able to tolerate twice a typical use rate (1.12 kg/ha), would be particularly advantageous because products containing 2,4-D have been standards for pasture weed management for many years.  Although red clover is susceptible to 2,4-D, sufficient variability was identified in the species to suggest a 2,4-D tolerant variant could be selected.  This project expands on work initiated at the University of Florida by Dr. Ken Quesenberry and continued at the University of Kentucky by Dr. Norman Taylor.  A Florida red clover line with improved 2,4-D tolerance was crossed to Kenland (a 2,4-D susceptible red clover variety adapted to the transition zone), and the resulting population was selected in the field for 2,4-D tolerance in 2006, 2007, 2008, 2009, 2010, 2011, and 2012.  Plants were grown in the greenhouse from seed collected after the 2010 and 2011 seasons, and treated with 0.5, 1.0, 1.5, and 2.0 kg/ha of 2,4-D.  Responses of these plants were compared to those of the original Florida line and Kenland.  Fresh weights and injury ratings were taken two weeks after treatment.  The 2,4-D tolerance of the plants grown from the 2010 and 2011 seed, based on fresh weight reductions, was intermediate between Kenland and the Florida line.  Wheras, based on injury ratings, the 2010 and 2011 lines had 2,4-D tolerance similar to the Florida line.  We conclude that, while our cross to the 2,4-D tolerant Florida line increased 2,4-D tolerance compared to Kenland, we have made little further gain in 2,4-D tolerance beyond that of the Florida line.  This is despite numerous rounds of selection for 2,4-D tolerance in the population from the initial cross.

Perennial weeds such as Canada thistle (Cirsium arevense), smooth bedstraw (Galium mullogo), multiflora rose (Rosa multiflora), and wild blackberry (Rubus spp.) are difficult to be managed in pastures and hayfields. Field experiments in West Virginia from 2010 to 2012 evaluated the herbicide aminocyclopyrachlor, applied by itself (35-140 g/ha), or in combination with metsulfuron-methyl (7-14 g /ha) or with 2,4-D (532 -1064 g/ha), up to one year after treatment for weed control efficacy. Canada thistle and smooth bedstraw were cut along with hay in spring 2011 and treated following regrowth on July 14, 2011 under moist soil conditions. In two separate experiments, the herbicides were applied to multiflora rose (on May 20, 2010) and wild blackberry (on May 12, 2011) during the early bloom stage in pastures under moist soil conditions. All treatments contained a non-ionic surfactant @ 0.25% vol/vol. Excellent (>90%) control of Canada thistle and smooth bedstraw was recorded with aminocyclopyrachlor at 70 g/ha, one year after application. The comparison herbicide, aminopyralid (107 g/ha) used in the experiment, provided excellent control of smooth bedstraw but failed to provide satisfactory (60%) control of Canada thistle one year after application. Aminocyclopyrachlor (70 g/ha) or aminocyclopyrachlor + metsulfuron-methyl (47+7 g/ha) provided excellent control of multiflora rose, one year after application. Similar mulitflora rose control was recorded with the comparison treatment, a mixture of aminopyralid + 2,4-D (94 + 747 g/ha). Aminocyclopyrachlor + 2,4-D (70 + 532 g/ha) or aminocyclopyrachlor + metsulfuron-methyl (78 + 12 g/ha) provided excellent control of wild blackberry one year after treatment. Unacceptable wild blackberry control was recorded with the comparison treatment fluroxypyr  + picloram (40 + 40 g/ha) in this experiment.

In order to assess the potential of monoecious hydrilla to invade existing aquatic plant communities, monoecious hydrilla was grown in competition with four submersed plant species: Eurasian watermilfoil (Myriophyllum spicatum L.; invasive), curly leaf pondweed (Potamogeton crispus L.; invasive), Elodea canadensis Michx. (native), and Vallisneria americana Michx. (native).  Initial plant establishment occurred in fall 2010 in a glasshouse; plants were then moved to outdoor mesocosms, and the trial was initiated in March 2011. Competition treatments included all tested plant species alone, at two different densities, and in combination with sprouted monoecious hydrilla tubers, at two different introduction timings.  Treatments were replicated 3 times and completely randomized.  Stem lengths of the longest shoot of each plant were measured initially, and biweekly for 20 weeks.  At the termination of the experiment, all plant biomass was separated by species and harvested, separating root mass from shoot mass for dry weight determination. Vegetative reproductive structures were counted when present, and fresh weight was taken.  Study was repeated in 2012. 

While the introduction of monoecious hydrilla at both timings lowered the shoot biomass dry weight for all plant species, the decrease was only significant for the early introduction of hydrilla with Elodea, curly leaf pondweed, and Vallisneria; not for Eurasian watermilfoil and not the late introduction of hydrilla.  Hydrilla introduction had no effect on root biomass dry weight at either timing.   Plant density had no effect on biomass dry weight for all naturalized species, with or without monoecious hydrilla.  Elodea, at both densities, significantly hindered monoecious hydrilla shoot biomass for the late introduction only.  No other plant tested, at either density, had an effect on hydrilla biomass at either introduction timing.  This research illustrates what effects previous establishment of these four species may have on hindering monoecious hydrilla colonization.

Winter creeper is a nonnative invasive plant that was introduced from Asia in 1907 as an ornamental plant.  It is commonly planted as an ornamental, and because of ornamental planting and bird-dispersed seeds it has become prominent as a ground cover in disturbed forest areas and poorly managed landscapes.  Winter creeper is very competitive, in part, because it retains its leaves year round, in some environments.  Can application of foliar herbicides achieve selective control of winter creeper, after other desirable species have dropped their leaves?

This study was initiated in December, 2011 at the University of Kentucky Arboretum to answer the question asked above.  Coralberry (Symphoricarpus orbiculatus) was the primary desirable species of concern.  Herbicide treatments were applied with a single tipped CO₂ sprayer until the leaf surface of the entire plot (0.9 m x 0.9 m) was wet.  Most treatments were applied on December 17, 2011.  Visual data were collected on plots for percent wintercreeper foliar cover (0-100%) at 96 (3/22/2012), 112 (4/7/2012), and 267 (9/9/2012) DAT (days after treatment). 

The treatments included the following products (active ingredients):  Reward (diquat), Finale (glufosinate), and Roundup Pro (glyphosate) plus a non-ionic surfactant at 0.5% v/v.  Coralberry was not killed by any of the treatments but there was some damage to the new foliage visible 112 DAT in the glyphosate plots.  The best control of wintercreeper 112 DAT was with the glufosinate treatments (7 to 18% foliar cover) and the glyphosate treatments had poor control (35 to 53% foliar cover).   However, by 267 DAT the best glufosinate treatments had 12 to 25% foliar cover while the best glyphosate treatments had 5 to 10% foliar cover.

Lepidoptera larvae are a key food source for the declining population of nesting, migratory songbirds utilizing early successional and shrubland habitats.  Exotic shrub species are increasingly common in shrubland settings, and likely provide the same structural characteristics as native species.  It is not clear if exotic shrubs provide the same quality of foraging habitat as native shrubs.  An understanding of the relative value of native and exotic species would inform management prescriptions needed to increase available, quality habitat.  Larval counts were conducted at two Pennsylvania state parks on collected branch samples from native and exotic shrub species, and converted to larva/10 g foliage dry weight.  Native species evaluated were hawthorn (Crataegus spp.), silky dogwood (Cornus amomum), and arrow-wood viburnum (Viburnum dentatum) at Yellow Creek State Park, Penn Run, PA; and grey dogwood (Cornus racemosa) and arrow-wood viburnum at Bald Eagle State Park, Howard, PA.  The exotic species at both sites were autumn olive (Elaeagnus umbellata) and Morrow's honeysuckle (Lonicera morrowii).  Branch specimens were collected as netted (predator exclusion) and un-netted pairs, during the nesting period for migratory songbirds, after the nets had been installed for at least two weeks.  At Yellow Creek, there was no interaction between netting and species, and netting effect was not significant.  Shrub species larval counts/10 g foliage dry wt. (n=60) were hawthorn (1.97) > arrow-wood (1.18) > silky dogwood (0.54) = honeysuckle (0.36) = autumn olive (0.23).  At Bald Eagle, only a portion of the data was collected as netted vs. un-netted pairs (n=7).  There was a significant interaction between species and netting (p=0.04).  Analysis of netting by species was significant for autumn olive and honeysuckle, which both had low counts for either condition.  The data was analyzed without netting effect, and showed the same pattern as at Yellow Creek, with larval counts for arrow-wood (n=30, 1.42 larva/10 g dry wt) > grey dogwood (n=30, 0.44) = autumn olive (n=22, 0.25) = honeysuckle (n=23, 0.08).  Native species hosted a greater food resource than exotics species, but comprised a smaller portion of the woody population.  At Bald Eagle, a transect of 1107 plants in the study area showed that three exotic species, honeysuckle, autumn olive, and multiflora rose (Rosa multiflora) were 64 percent of the population.  Arrow-wood and hawthorn made up 10 percent of the population.  At Yellow Creek, these three species comprised 50 percent of 497 surveyed plants.

Art Gover, aeg2@psu.edu

The recent expansion of hydraulic fracturing for natural gas in the Marcellus Shale is creating a patchwork of vegetation removal across Pennsylvania forests. Drilling activity on these new inroads into the forest has the potential to vector the rapid spread of invasive plants. This study was conducted to document the presence and extent of invasive exotic plant spread on PA State Forests as well as to identify characteristics of the forest sites that may help explain the current state of invasion. The data collected will also be used as baseline measurements to monitor the long-term effects of disturbance related to natural gas extraction on invasive plant abundance. Sixty-seven drilling pads distributed across four PA State Forests (Tioga, Tiadaghton, Sproul, and Hyner Run) and the Allegheny National Forest were selected. For each pad, the abundance of a predefined list of 24 invasive exotic plants was recorded along the roads approaching the pad entrance (0.5km total), and around the pad perimeter (approximately 10m from the gravel edge of the pad). Overall, 70% of pads surveyed were invaded by at least one invasive exotic plant. Of those pads invaded, 62% harbored three or more species and 40% had individual species at abundance levels between 100 and 1000 plants around the pad perimeter. There were 11 instances of a species numbering in the 1000s on the pad perimeter. Invasive plant abundance along roads approaching the pad was a positive indicator of invasive plant abundance on the pad.  Differing seed dispersal mechanisms, such as spread by wind versus bird, likely play a role in the varying presence and abundance levels seen in species’ movement from nearby roads to the pad. Regional invasive plant pressure, surrounding forest type and forest fragmentation, and land-use history are being studied as covariates. Developing a greater understanding of how these new forest corridors are creating avenues for invasive plant encroachment into state forests is essential in creating best management practices to prevent future spread.

To assess risk to non-target plants from pesticide application, EPA requires that registrants conduct two 10-species non-target plant studies, one pre-emergence and the other post emergence.  Application rates which cause either no effect (NOEC) or a 25% reduction in plant height or weight (EC₂₅) are used in the risk assessment.  To assess risk, these effect rates are compared to estimated rates of pesticide depositing outside the field.  The exposure values outside the field are estimated from chemical drift deposition studies.  Deposition curves are fit from analytical measurements of spray drift deposited onto collectors set at various distances from the sprayed area.   The relevant effect rate is compared to the chemical deposition curve to determine if a buffer distance is required for protection of sensitive species.  Although this is the standard approach that has been used, deposition studies are subject to questions regarding collector efficiency, potential sample contamination, sufficient analytical sensitivity, and curve fitting assumptions; and greenhouse plant studies are subject to questions of greenhouse to field translation and environmental relevance.  As an alternative approach, sensitive crop plants grown uniformly in fields at high density can be used as an in situ bioassay to determine distances to which effects on plants are no longer observed. A series of studies will be described that used this field bioassay method to determine spray buffer distances needed to protect adjacent areas under a wide range of environmental conditions.  The advantages of this approach are that it results in an unambiguous measure of the no effect distance compared to the potential problems with the traditional method for buffer distance determination; and because the measurement methods are less expensive than chemical analysis, studies can be conducted at a number of sites under varying environmental conditions to provide a better understanding of off-site movement.

The Canadian Grain Commission (CGC) inspects export shipments of grains from Canada, part of which is the monitoring of cargo samples for the presence of weed seeds. Grains exported and moving in commercial handling systems are under increased scrutiny for many phytosanitary factors including regulated weed seeds. The CGC analyzed over 2300 samples from 2001 through 2011 to identify and classify weed seeds associated with western wheat, durum and canola. The results indicate that the most frequently found seeds from samples analyzed were wild buckwheat, wild oats, green foxtail and kochia in western wheat and durum while lambs quarters, green foxtail, cleavers, smartweed, wild mustard and stinkweed are most prevalent in canola. No prohibited noxious (class 1) weed seeds (Canadian schedule) were discovered in any of the samples. Weed seeds will always be part of commercial shipments of grains and information such as this can assist brokers and regulators to develop risk assessments to mitigate establishment of invasive species.

The On-Target Application Academy is a one-of-a-kind educational opportunity to provide growers extensive hands-on training for better awareness of herbicide application best practices that help mitigate spray drift – which is a continuous area of focus for the agricultural industry.  Understanding that today’s herbicide environment is more complex, BASF wants to continually support growers and help them achieve the most effective weed control possible with today’s emerging product and equipment innovations.

According to the BASF Grower Perception Survey conducting in 2011, 80% of the respondents indicated that they self-apply herbicides to their crops.  In addition, more than one-third said they were interested in taking a herbicide self-application training seminar.  Based on the responses from growers, BASF and TeeJet^® jointly initiated the On-Target Application Academy to provide field based training utilizing recognized application technology experts.  The Academy has focus areas that are derived from herbicide application best practices including proper nozzle selection, appropriate calibration and boom placement and impact of environmental conditions.  The On Target Application Academy will be conducted at various locations throughout the US in 2013.

Crop growth and development can vary dramatically within a field due to a variety of factors, including differences in soil properties, terrain, moisture, nutrients, plant stands, pest problems, and herbicide effects. Field patterns and the magnitude of differences in crop growth and development often can be difficult to assess at ground level.   Aerial photography has been used to get a better perspective on spatial and spectral patterns within fields.  Color and infrared photography can help discern differences in crop growth and development that may not be evident in the normal color ranges of the human eye.  However, there may be a number of limitations to using conventional aerial photography to assess crop conditions, including flight availability, costs, scheduling, flying conditions, and spatial resolution.  One alternative to conventional aerial photography to assess field conditions is to use remotely piloted, or small Unmanned Aircraft Systems (sUAS) , in combination with a high resolution color infrared digital camera.  Detailed aerial color infrared images of a simulated drift study were collected and produced using the following procedures.  A Canon Powershot S100 was modified to allow visible blue and visible green light between 400 nm and 580 nm, and the visible red edge to near infrared transition between 680 nm to 780 nm to pass to the camera sensor for image collection.  The camera was mounted on a Zephyr sUAS flying wing model aircraft manufactured by Ritewing RC.  The aircraft is powered by an outrunner brushless electric motor.  The airframe consists of extruded polypropylene (EPP) foam, with internal and external reinforcement using fiberglass spars and laminating film.  Control and stabilization surfaces are constructed from balsa wood and corrugated plastic. Electrical power for the autopilot, flight control servos, and electric motor is provided by two lithium polymer batteries in parallel.  Command and control is achieved through the use of the Hitec Aurora 9 R/C system, and Ardupilot Mega 2.0 autopilot system.  The camera was set to continuous shoot mode to record one image every four seconds.  The aircraft was flown over the test area several times and images recorded.  RAW format images were converted to TIFF format in Adobe Photoshop CS6 (ver. 13.0.1 x64). A photogrammetric model was then constructed from overlapping images using Agisoft PhotoScan Standard Edition (ver. 0.9.0 build 1586). The process included photo alignment, 3D model construction, and adding reflectance data to the 3D model to produce an orthophoto of the entire field.  The photogrammetry-derived orthophoto was converted to a data layer in ESRI ArcMap 10.0 (build 2414) for image analysis.  Pixel size at the altitude flown over the field was approximately 2 cm x 2 cm.  Multiple images with different color separations of the field were created to assess differences in crop growth and development.  Utilizing different color separations illustrated different patterns in the field.   The patterns of differential crop growth appeared to be primarily a function of variability in soil properties and available soil moisture rather than herbicide drift damage.  Hot, dry environmental conditions, the type of herbicide injury, and the timing of the photography may have minimized the ability to detect the drift injury.  Drift injury was primarily distorted growth and height reduction, and not chlorosis or dramatic biomass reductions. The aerial imagery was taken about 5 weeks after application, while herbicide response was probably greatest at 3 to 4 weeks after application. Remotely piloted aircraft systems and high resolution color infrared imagery appears to be an economical method to discern different patterns of crop growth within a field. The type of crop response, however, may influence its effectiveness, and the cause for different growth patterns may not always be easily determined. 

Dow AgroSciences has developed Enlist Ahead, a comprehensive stewardship initiative to promote responsible use and sustain the long-term performance of the Enlist^TM Weed Control System. Enlist Ahead focuses on educating and training retailers, farmers and applicators on the appropriate use of the technology.  Enlist Ahead is built upon three foundational pillars: 1) technology advancements, 2) management recommendations and resources, and 3) education, training, and outreach.  Stewardship of Enlist will be accomplished with a multi-faceted approach, including a variety of tools and delivery methods, plus working with customers, stakeholders and industry organizations.  Enlist Ahead is a benefits-based management resource designed to help growers and applicators succeed while promoting responsible use of the technology. 

 ™Trademark of Dow AgroSciences LLC. Components of the Enlist Weed Control System have not yet received regulatory approvals; approvals are pending. The information presented here is not an offer for sale. Always read and follow label directions. ©2013 Dow AgroSciences LLC

Liquid Yucca Extract is a 100% natural wetting agent derived from Yucca schidegera. These surfactant compounds help plants survive the extreme heat, drought and soil salinity found in harsh climates. Yucca schidigera extracts also contain natural saponins that promote beneficial microbial activity in the soil. Although pure yucca extracts are highly effective surfactants, Yucca is modified to enhance wetting and penetrant properties for outstanding performance. It is an ideal choice as an adjuvant for Integrated Pest Management (IPM) programs.  Due to biological source and biodegradability of yucca extract, application of this substance will lead to pesticide dosage and hazardous effects reduction in environment. This study was carried out to study yucca extract effects on efficiency of Nicosulfuron.  Four levels of herbicide were applied: recommended dosage (2lit/ha), 10% lower than recommended dosage (1.8lit/ha), 20% lower than recommended dosage (1.6 lit/ha) and 30% lower than recommended dosage (1.4lit/ha) without any adjuvant and mentioned treatments with yucca extract (1/1000). According to our results yucca treatment with 20% lower than recommended dosage showed no significant differences in comparison with application of recommended Nicosulfuron dosage (2lit/ha) (P=0.85). According to our observations yucca extract application as an adjuvant with herbicides will lead to herbicide efficiency Increase and dosage reduction, this property may decrease costs of herbicides application and environmental risk.

Adjuvants are substances used with a herbicide or other pesticide to enhance performance.Adjuvants may be added to the product at the time of formulation, or by the applicator to the spray mix just prior to treatment. Adjuvants include surfactants, compatability agents, anti-foaming agents and spray colorants (dyes), and drift control agents. Hydromax® is and adjuvant contains yucca extract with herbal source and in high biodegradability property. Gyahgate is a widely used adjuvant to increase efficiency of herbicides with chemical source in Iran.  Current study was carried out to compare efficiency of organic and chemical adjuvant. This study was carried out to compare chemical and organic adjuvant efficiency in corn field, Saveh, on Corn (Zea mays var.704).  Nicosulfuron efficiency (recommended dosage, 2lit/ha) with Gyahgate (5/1000), Nicosulfuron (recomnded dosage) with Hydromax (1/1000) and control (Nicosulfuron without adjuvant) was studied. According to our results significant differences between were observed in Gyahgate and Hydromax treatments (p<0.05), Hydromax treatment efficiency was 98.7±0.75% and Gyahgate treatment efficiency was 90.3±0.23%. According to our observations, due to biological source of Hydromax and none adverse effects on plants and environment can be considered as an appropriate alternative of chemical adjuvant with high efficiency.

Pelargonic acid (PA; nonanoic acid) has been used as a non-selective, foliar herbicide for many annual and perennial weeds. Vegetable oils have also been used as adjuvants to improve efficacy of herbicides. The objective of this study is to investigate the effect of gum arabic, gum tragacanth, and six vegetable oils on the herbicidal activity of PA in green foxtail (Setaria viridis  L.). Green foxtail seedlings were grown in a glasshouse, transferred to field, and sprayed (400 L/ha) with PA (2% v/v) with or without gum arabic or gum tragacanth. In a separate experiment, green foxtail seedlings were sprayed with PA with or without six vegetable oils (1 or 2% v/v) using a backpack sprayer. A completely randomized design with 10 replications per treatment was used. Fresh and dry biomass of the treated plants were measured at 3 and 14 d after spraying. Decrease in fresh weight due to moisture loss was used as a measure of herbicide damage. All experiments were repeated. Addition of Tween 80 increased efficacy of PA at 3 and 14 d after application. Gum tragacanth and gum arabic did decrease green foxtail’s fresh weight compared to control at 3 as well as 14 d after spraying. Gum arabic and gum tragacanth were less effective compared to Tween 80. Interestingly, gum tragacanth sprayed alone stimulated green foxtail seedling fresh weight at 14 d after application. Addition of vegetable oils (1% or 2% v/v) did not improve efficacy of PA; the herbicidal activity of PA actually decreased with addition of any of the six vegetable oils. The results show that Tween 80 is a more effective at increasing the herbicidal activity of PA compared to gum arabic and gum tragacanth. Despite their slightly lower effectiveness as adjuvants for PA, gum arabic and gum tragacanth could provide environmentally-friendly alternatives as emulsifiers for PA. The six vegetable oils employed in this study do not appear promising as adjuvants for PA.

 Field studies at the University of Nebraska-Lincoln: John Seaton Anderson Turfgrass Research Facility near Mead, NE were conducted to determine efficacy correlated between an ULV (Ultra-Low Volume) sprayer (Kamterter LLC, Waverly, NE 68462) and a conventional sprayer (Toro Multi-Pro 1200, The Toro Company, Bloomington, MN 55420). The first study contained two treatments for each sprayer and an untreated check arranged in a randomized complete block design with four replications.  The treatments selected were 2,4-D + dicamba + mecoprop (Trimec Classic, PBI/Gordon Corporation, Kansas City, MO 64101) at 2326 g ae ha^-1 +248 g ae ha^-1 + 622 g ae ha^-1_, respectively and mesotrione (Tenacity, Syngenta Crop Protection Inc, Greensboro, NC 27419) at 224 g ai ha^-1. The mesotrione treatments were made in split applications of 112 g ha^-1. The first application was made at the time of the 2,4-D + dicamba +mecoprop application on June 8^th, 2012 and then the second application was made three weeks later on June 28th, 2012 . Treatments with the conventional sprayer were applied at 561 L ha^-1 with XR11006 nozzles (Teejet Technologies, Wheaton, IL 60187) at 310 kPa and a speed of 5 km hr^-1. Treatments with the ULV sprayer were applied at 19 L ha^-1 with proprietary fixtures at 6 kPa air pressure and a speed of 5 km hr^-1. The ULV sprayer has negligible liquid pressure which differs from the conventional sprayer. The dandelion study was applied over a mixed stand of Kentucky bluegrass (Poa pratensis L.) and perennial ryegrass (Lolium perenne L.). The ground ivy study was applied over turf type tall fescue (Festuca arundinacea Schreb.). The established turf was maintained at 7 cm and irrigated to prevent drought stress. One study was selected to compare 2,4-D + dicamba + mecoprop and mesotrione efficacy between the two sprayers on dandelion (Taraxacum officinale G.H. Weber ex Wiggers) and the other study was selected to compare the efficacy on ground ivy (Glechoma hederacea L.). Dandelion and ground ivy counts were taken at the time of application, 14, 28, and 56 days after treatment.  Two additional studies were conducted to compare the efficacy between a conventional sprayer and an ULV sprayer. The first study compared a 2,4-D + dicamba + sulfentrazone + triclopyr (T-Zone, PBI/Gordon Corporation, Kansas City, MO 64101) solution at 1427 g ae ha^-1 + 109 g ae ha^-1 + 33 g ai ha^-1 + 377 g ai ha^-1 respectively on ground ivy suppression in established turfgrass between a conventional sprayer and an ULV sprayer. The second study compared the two sprayers with a pre-emergent herbicide to compare the efficacy of a 1736 g ai ha^-1 pendimethalin (Pendulum Aqua Cap, BASF Corporation, Research Triangle Park, NC 27709) solution on large crabgrass (Digitaria sanguinalis (L.) Scop.) suppression in established turfgrass.  Results showed no difference in weed suppression for sprayer type in all four studies. The ULV sprayer suppressed weeds similarly to the conventional sprayer even with a fifteen-fold decrease in carrier volume across different herbicide modes-of-action in all of the studies. Results indicate that the Kamterter ULV sprayer system would be a useful and effective management option for turfgrass managers for weed control.

Pending regulatory approvals, the Roundup Ready® Xtend Crop System includes the simultaneous launch of a new soybean product with tolerance to both glyphosate and dicamba Roundup Ready® 2 Xtend and a low volatility premix formulation of dicamba and glyphosate.  The system is designed to provide more consistent control of glyphosate-resistant and tough to control weeds. Monsanto also intends launch new low volatility formulations of dicamba for over-the-top use on Roundup Ready® 2 Xtend Soybeans.  A premix of dicamba and glyphosate will be branded as Roundup® Xtend, and a stand-alone formulation of dicamba will be branded as XtendiMax™. To ensure the highest level of on-target application and herbicide performance, Monsanto will also announce Application Requirements for the Roundup Ready Xtend Crop System.  Growers will continue to use residual herbicides in the Roundup Ready PLUS™ program to maintain a sound weed resistance management strategy.   Dicamba product labels will increase application accuracy compared to older products and uses.  Targeted weeds should be less than four inches tall.  Spray nozzles must provide very coarse, extremely coarse or ultra coarse droplets.  Spray gallonage must be at least 10 GPA, and spray ground speed must be less than 15 mph.  Drift reduction agents should be used, and spray boom height should be 20-24 inches above the canopy.  Roundup Xtend and XtendiMax should be applied when winds are 10 mph or less.  Growers are encouraged to check local sensitive crop registries (e.g. DriftWatch, others) before making applications, and to pay special attention to both wind direction and speed.  Growers will also be required to maintain the required label buffer to protect sensitive areas.  It is very important that growers triple rinse their sprayers according to label directions after using Roundup Xtend or XtendiMax.  

Few studies have investigated droplet size from glufosinate solutions and its effects on spray patterns, potential drift, and efficacy.  The objective of this study was to elucidate the effects of nozzle, herbicide concentration, and pressure on the droplet size of a glufosinate (Liberty at 0.594 kg ai ha-1) spray spectra.  Droplet size and distribution of four herbicide concentrations (47, 94, 140, and 187 L/ha) was measured using laser diffraction.  The spray droplet spectra of five commonly used nozzles (AI, AIXR, TT, TTI, and XR), using both medium and large orifices for each nozzle (11003, 11005), was investigated at low, medium, and high pressure (2.76, 4.14, 5.52 bar [40, 60, 80 psi]).  In nearly every case, droplet size increased as carrier volume increased.  The exception was the TTI nozzle which behaved inconsistently when compared to the other nozzles and in some cases carrier volume had an inverse effect on droplet size.  The droplet size of every combination of nozzle and GPA decreased as the pressure increased.  The most important factor in determining droplet size of a glufosinate spray spectra is the nozzle, followed by pressure, and lastly herbicide concentration.

The simple and effective weed management enabled by the use of glyphosate in glyphosate-resistant crops has arguably peaked and experienced a state of decline in regions infested with glyphosate-resistant weeds.  Initially, the high level of weed control provided by glyphosate would allow for some inadequate foliar application methods to be practiced without significant concern for herbicide failure.  However, the evolution and spread of several glyphosate-resistant weeds have some experts speculating that any factor, including poor application methods, which compromised glyphosate efficacy could have contributed to the proliferation of glyphosate-resistant weeds.  Field research was conducted over several years to identify and characterize some of the more frequent practices used in commercial glyphosate application that may result in sublethal activity.  As anticipated the weed species which have historically demonstrated less sensitivity to glyphosate provided some of the greatest differences in glyphosate application methods.  For instance, different size spray droplets produced through traditional flat fan and low-drift nozzle designs and drift control adjuvants resulted in relatively minor differences in control of common cocklebur (<9%).  However, control of waterhemp with glyphosate fluctuated by up to 24% with reduced efficacy stemming from the use of venturi style nozzles and drift control agents that increase the viscosity of the spray solution. The use of low-drift nozzles and viscosity-based drift control agents reduced spray coverage at the top of the target weed canopy and was correlated to reduced glyphosate efficacy.  Likewise, the use of higher carrier volumes (140 and 187 L/ha) resulted in less control of waterhemp compared with 47 L/ha.  Even though a trend was observed for lower spray coverage with lower carrier volumes, the higher concentration of glyphosate at 47 L/ha was able to overcome the lower spray coverage compared with higher carrier volumes.  Finally, the combination of a venturi style nozzle with higher carrier volumes tended to exacerbate the negative effects of applying glyphosate at suboptimal times of day in the early morning and evening.  Therefore, efforts to avoid spray drift by applying glyphosate in the early morning or evening during relatively lower wind speeds; the use of low-drift nozzles producing excessively large droplets; tank-mix adjuvants that dramatically increase spray solution viscosity; and higher carrier volumes necessitated by commercial applications being performed on dense weed infestations above recommended weed heights may have all contributed to the decline in glyphosate efficacy over time.

Field dodder (Cuscuta compestris) is one of the most problematic weeds that is widespread in many Iranian crop field such as alfalfa, potato, tomato, beet, etc. Studies were conducted to evaluate some germination characteristics of dodder seeds collected from different hosts. Dodder seeds were gathered from two host crops, potato (Solanum tuberosum) and sugar beet (Beta vulgaris); and two host weeds, camelthorn (Alhagi pseudalhagi) and prickly lettuce (Lactuca serriola) in late October 2010. Scarification in sulfuric acid (98%) for 5, 10, 15, 20, 25 and 30 min and stratification at 5°C for 1, 2, 3 and 4 weeks were used in order to break seed dormancy. Twenty-five seeds were placed on filter paper in 11 cm diameter Petri dishes. The filter paper was moistened with 5 ml of distilled water. The influence of salinity on germination was evaluated using sodium chloride (NaCl) solutions of 0, 50, 100, 150 and 200 mM. To determine the effects of osmotic potential on germination, dodder seeds were incubated in solutions with osmotic potentials of 0, -0.2, -0.4, -0.6, -0.8 and -1 MPa, which were prepared by polyethylen glycol (PEG) 6000. Results show that dodder seeds, collected from potato, beet, camelthorn and prickly lettuce have different reactions to different duration of sulfuric acid, but maximum germination was occurred in treatment of 20 min sulfuric acid in all dodder seeds. Germination of dodder seeds decreased by increasing time of sulfuric acid treatments more than 20 minutes, except those seeds collected from camelthorn. Stratification had no effect on dodder seed germination. Seed germination decreased with decreasing osmotic potential and increasing NaCl concentration. No germination happened in treatments -0.8 MPa osmotic potential. In -0.2 and -0.4 MPa dodder seeds collected from camelthorn and prickly lettuce had the highest percentage of germination. On the other hand, in -0.6 MPa, all of the seeds had about 5% germination. Furthermore, dodder seeds collected from camelthorn and prickly lettuce were more tolerant at 50 and 100mM NaCl concentration compared to other seeds. However, at 150 mM NaCl concentration, there were no significant differences between dodder seeds while no germination was observed in 200 mM of NaCl concentration. In conclusion, host plant species influence some characteristics of dodder seeds such as their dormancy and tolerance to salinity or drought stress. In this study dodder seeds collected from camelthorn and prickly lettuce were more tolerance to osmotic potential and NaCl concentration.

A class of phenolic compounds, ortho-dihydroxyphenols (hereafter “o-DHP”), has been implicated with seed survival.  Based on expectations of the growth-differentiation balance hypothesis, we predicted that seed o-DHP concentration exhibits a curvilinear response to increasing resource availability in the maternal environment, with maximum o-DHP occurring at moderate resource levels.  To test this hypothesis, velvetleaf seeds were produced under field conditions at two locations (Mead, NE; Havana,IL).  Each location included twelve maternal environments established through factorial combinations of soil compost (+ / -), species assemblage (velvetleaf with and without corn), and soil nitrogen fertilizer (0, 0.5x or 1x local recommendations for corn).  Resource availability with respect to velvetleaf growth was summarized by above-ground biomass at seed harvest (maternal biomass).  Results indicated that seed o-DHP concentrations increased then decreased in response to increasing maternal biomass.  This relationship was modeled with a unimodal function specific for location (Mead, NE, y = 1.18 + 0.03xe^-0.02x, pseudo-r² = 0.59, p = 0.003; Havana,IL, y = 1.40 + 0.006xe^-0.005x; pseudo- r² = 0.34, p = 0.05).  Seed protein concentrations remained constant across maternal biomass levels.  Because inherent vulnerability to predation is considered a consequence of chemical protection relative to nutritional offering, our results suggest that velvetleaf seed susceptibility to predation and decay is influenced by resource levels in the maternal environment.  However, such a claim requires further evidence that directly connects seed o-DHP concentrations with seed defense. More broadly, our results suggest that the growth-differentiation balance hypothesis can be extended to maternal effects on seed phenolics.

Diversified cropping systems can have high soil microbial biomass and thus strong potential to reduce the weed seed bank through seed decay. To evaluate the hypothesis that weed seed decay is higher in a more diverse 4-year corn / soybean / oat+alfalfa / alfalfa cropping system than in a conventional 2-year corn / soybean rotation, we conducted a study in Iowa, U.S.A. We buried mesh bags filled with either Setaria faberi  or Abutilon theophrasti  seeds and soil at two depths in the corn phase of the two cropping systems, and sampled them over a 3-year period. S. faberi seed decay was higher in the more diverse rotation than in the conventional rotation, and at 2 cm than at 20 cm burial depth, only during one year. A. theophrasti seeds, on the contrary, decayed very little over the three years. Separate laboratory and field experiments confirmed differences in germination and seed decay among the seed lots evaluated each year. Furthermore, laboratory analyses determined that Fusarium, Pythium, Alternaria, Cladosporium, and Trichoderma were the most abundant genera colonizing seeds of both species, and a greenhouse experiment determined a possible relationship between P. ultimum and S. faberi seed decay. These differences in seed susceptibility to decay indicate the necessity to evaluate weed population dynamics in different cropping systems in order to make weed management programs as effective as possible.

The carabid beetle Harpalus rifipes is a dominant weed seed predator in Maine agroecosystems.  H. rufipes is known to prefer sites with vegetative cover to fallow sites.  To test whether this preference is driven by predator avoidance behavior, we developed novel “hyperpredation assays,” in which live H. rufipes prey were presented to higher-order predators.  We conducted an experiment to determine whether a) vegetative cover affords H. rufipes protection from hyperpredators, and b) high hyperpredation rates correspond with decreased invertebrate seed predation rates.  We conducted two 72-hour trials (mid August and September 2012) at Rogers research farm in Stillwater, ME.  We measured hyperpredation in vegetated and fallow assays, invertebrate seed predation, and invertebrate activity-density.  Wildlife cameras were used to capture images of potential hyperpredators.

We found that H. rufipes likely falls prey to birds and small mammals.  There was a non-significant trend toward lower hyperpredation in vegetated assays, providing weak support for our hypothesis a).  We did not find a relationship between hyperpredation and decreased invertebrate seed predation; however, we expect that such a relationship may be detected with larger sample sizes.  This study is the first of which we are aware to consider carabid seed predation within the context of a larger food web.  Our results suggest that hyperpredation may contribute to the variability we see in seed predation.    

Control options for kochia can be developed and applied in a timely manner when emergence patterns and seed persistence in the field are known.  Since kochia has developed resistance to glyphosate herbicide in many parts of the central Great Plains, detailed studies of the basic biology are required.  Previous seed burial studies have determined that kochia seed persistence was very short, perhaps three years or less, and that viability declined more rapidly when seed was buried at a depth of 10 cm.  The objective of this study was to determine the length of time kochia seed from different emergence cohorts persists and is viable when placed at different depths in the seedbank in field sites across the central Great Plains.  In the fall of 2010 and 2011, seed were collected from kochia populations from multiple emergence cohorts (cohort 1, 2, and 3) or from contrasting environments located next to a field experiment studying the emergence profiles of kochia.  Seed persistence was monitored for two years after burial in fall 2010 and again in fall 2011 in Colorado (Fort Collins [irrigated and dryland cropland, 3 cohorts each]), Kansas (Garden City [cropland, 3 cohorts], Hays [cropland, non-cropland], Manhattan [non-cropland], and Stockton [non-cropland, 3 cohorts]), Nebraska (Mitchell [non-cropland, 3 cohorts] and Scottsbluff [non-cropland, 3 cohorts]), Wyoming (Lingle [non-cropland, 2 cohorts]), and South Dakota [cropland].  Collected seed were sent to Manhattan, KS to be cleaned with sieves and an air column separator.  Wire-mesh packets, each containing 100 kochia seed, were made to be buried in the soil.  Packets were sent back to each original location.  A 15-cm diameter wire cage was placed such that soil could be put inside and packets placed at three different depths within each cage at 10 cm, 2.5 cm and 0 cm and a wire cap placed on top to keep packets in place and deter predation.  A total of 16 cages per kochia cohort or environment were established (four replications with four removal times).  Four extractions were planned for March and October in each year after burial for two years. Extracted packets were sent back to Manhattan KS.  Seed were removed from each packet and placed in a petri dish with filter paper and water in a growth chamber set at 20/10 C day / night temperatures and a 12/12 hr photoperiod.  Germinated seed were counted and removed for 30 days and a press test was used to determine any remaining viable seed at that time.  Number of intact seed that were viable and ready to germinate was very high at the first extraction time (March, 4 mo after burial).  For example, at Nebraska 78% or more seed germinated from the extracted packets across cohorts and burial depths.  In an irrigated environment in Colorado, kochia viability ranged from 40 to 69% across on cohorts and in a dryland environment kochia viability ranged from 9 to 45% with the first extraction.  This first extraction date in March corresponded to time when kochia typically emerges across these locations.  Influence of cohort or burial depth on seed viability at the first extraction depended on geographic location but subsequent extractions (October yr1, March yr2, October yr2) had less than 5% viable seed left in the packets and in many cases, less than 1% viable seed were observed.  Alternative to herbicide control strategies might include tillage to bury seed at 2.5 to 10 cm depths.  These seed would experience fatal germination (too far from surface to become established) and very low seed persistence was observed with buried seed.

Weed seed collection and destruction at crop harvest can be an effective strategy in minimizing the weed seedbank size and greatly preventing the evolution of herbicide resistance in weed populations.  A key consideration to this strategy, however, is the weed seed retention potential at the time of harvest as weed seeds shattered prior to crop harvest are not available for collection using combine harvester. Palmer amaranth is a troublesome weed in the Midsouth soybean production systems. Because of the widespread resistance to glyphosate and ALS-inhibiting herbicides in this species, growers have limited options to effectively manage this weed in soybean. The overall objective of this research was to investigate the opportunities for employing weed seed collection at harvest, which was proven effective elsewhere, as a management tool to prevent seedbank addition from Palmer amaranth escapes in Midsouth soybean fields. A baseline survey was conducted in fall 2012 in five locations across the important soybean production region in eastern Arkansas to estimate the level of seed retention in Palmer amaranth escapes. In each location, five soybean fields were visited and within each field five representative Palmer amaranth escapes were randomly selected for sample collection. For each selected plant, the above-ground plant parts were carefully harvested by avoiding seed shattering and any seeds lying on the soil surface immediately around the plant were collected along with a thin soil layer using a soft brush and stored separately. The plant samples were dried, threshed, and total seeds retained were counted. The soil samples collected underneath each plant were placed in individual trays in a greenhouse and seedling emergence was documented at weekly intervals for a month period. On average, about 125 seedlings recruited from the soil samples (ranged from 0 to 1061), yet it was only a fraction of the total seed production. Overall, >99% of the Palmer amaranth seeds were retained in the plant at the time of soybean harvest, suggesting that seed collection is a feasible option for this species. Experiments are being conducted to standardize appropriate cage mills for effective seed destruction following collection.

Multiple-resistant (glyphosate- and ALS-resistant) Palmer amaranth was discovered in a Michigan soybean field in 2010.  Palmer amaranth is typically a southern weed species and little is known about its survival in northern climates.  In the fall of 2011, a field experiment was established to determine the effects of four soil amendments on the mortality of Palmer amaranth seed.  The soil amendments included rye, wheat, dairy compost, poultry compost, and a no amendment control. Rye and wheat were planted in the fall at 100 kg ha^-1.  Dairy and poultry compost were applied in the spring at 9234 kg ha^-1 and 2241 kg ha^-1, respectively, when compost applications would typically be made.  The carbon to nitrogen (C:N) ratio was 9.9:1 for dairy compost and 8:1 for poultry compost.  Soil amendments were incorporated into the soil to a 15 cm depth in late May. Two concentrations of each amendment were evaluated.  The normal concentration of rye and wheat were determined by the maximum expected biomass production of 600 g dry biomass per m² at an incorporation depth of 15 cm.  The normal concentration of dairy and poultry compost were based upon typical field rates when incorporated to a depth of 15 cm.   Soil amendments were also examined at a higher concentration that was equivalent to 23 times the calculated concentration.  Mesh bags containing 100 g sand, 100 Palmer amaranth seeds, and the soil amendment concentrations were buried to a depth of 15 cm in the corresponding amended plots.  Seed bags were recovered from the soil amended plots at 4, 8, 12, and 24 weeks after burial.  Palmer amaranth seeds were sieved from the sand and intact seeds were counted.  Intact seeds were germinated in petri dishes in the dark at room temperature for 1 wk and counted to determine non-dormant viable seed.  Remaining ungerminated seeds were subjected to tetrazolium chloride (TZ) testing to determine seed viability.  Seeds that tested positive were considered viable.  Percent seed mortality was determined by subtracting the germinated and viable seeds from the 100 initial seeds in each mesh bag.  At the normal concentrations of each soil amendment there were no differences in Palmer amaranth seed mortality.  However, at the higher soil amendment concentrations, Palmer amaranth seed mortality was higher (40%) with rye than the other soil amendments.  This research will be repeated in 2013.

Gene amplification confers glyphosate resistance in two populations of Amaranthus palmeri from New Mexico. However, the relative growth and development of these populations, compared with the susceptible populations, are unknown. Greenhouse experiments were conducted to compare the growth, relative competiveness and seed production of two glyphosate resistant (R) and susceptible (S) populations. Under non-competitive conditions the S populations had greater leaf area, height and biomass compared with the R populations. Further studies with one of the S populations under two different alternating temperature regiments indicated that in both conditions S population produced more biomass compared with R populations. Replacement series with three ratios of R:S (16:0, 8:8 and 0:16), under different alternating temperature regiments, indicated superior competitiveness of S population. Fertilization experiments revealed that the S population produced more seeds compared with the R populations. The seed production from crosses and reciprocal crosses was lower than the S population, but higher than the R populations. The data suggests that in the absence of herbicide selection, the R populations from New Mexico would be dominated by the S populations.

Strip tilled (ST) fields, particularly those with a cover crop, are heterogeneous environments—in-row (IR) zones have a crop, tilled soil, and incorporated cover crop residue, while between-row (BR) zones have no crop, no tillage, and a cover crop surface mulch.  Understanding how weeds respond to these different environments is helpful for identifying optimal tillage and cover cropping strategies for suppressing weeds.   A field experiment was conducted over two years in central Michigan to separate the effects of three different factors on weed growth—tillage [ST or chisel plow followed by field cultivation (CT)], cover crop [spring-planted oat (Avena sativa L.) or none], and crop competition (cabbage or no cabbage).  Powell amaranth (Amaranthus powellii) seedlings were transplanted IR and BR (or in the corresponding location when no crop was present) and sampled both at mid-season and at cabbage maturity.  Soil samples were collected biweekly from planting to harvest to measure moisture and nitrate content.  We hypothesized that the undisturbed BR zone in ST would have higher soil moisture and lower initial nitrogen availability compared to all tilled zones and that the interaction between these would regulate weed growth.  Surface mulch of the high carbon oat cover crop was expected to enhance these effects.  IR, we expected the cabbage to have a dominant role in regulating weed growth. Further, we anticipated that higher soil moisture and improved synchrony of N availability in ST would increase cabbage growth relative to CT, resulting in improved suppression of IR weeds.  Contrary to our hypothesis, final biomass of BR Powell amaranth was either unaffected by tillage (2011) or greater under ST compared to CT (2010). In 2010 the oat cover crop did not affect weed biomass in ST, but increased weed biomass in CT.  In 2011, oats did not affect weed biomass.  IR Powell amaranth biomass was either lower (2010 without cabbage), higher (2011 with cabbage), or equivalent (all other cases) under ST compared to CT.  In contrast, and contrary to our hypothesis, tillage had no effect on cabbage growth in either year.  Principal components analysis and ANOVA of the principal component scores suggested that tillage and the cover crop were typically the most important factors in determining soil moisture; ST, especially with oats, was associated with greater IR and BR soil moisture.  Soil nitrate was affected most by cabbage, with cabbage plots typically associated with less soil nitrate, particularly IR.  However, these differences in soil moisture and nitrogen were insufficient to explain differences in Powell amaranth biomass observed in the different zones in each year.

Invasion theory suggests that species coexistence is enhanced through niche partitioning and that species with overlapping use for limiting resources will be in competition with one another. Here we present a spatial model that allows us to assess the mechanism of competition between native and invasive grasses on established plots as well as the potential for restoration of native plant species as bio-control against invasive species establishment and spread. Our model considers both temporal and spatial differentiation in the calculation of niche differences between three focal C₄ grass species: King Ranch bluestem (Bothriochloa ischaemum), silver bluestem (Bothriochloa laguroides) and sideoats grama (Bouteloua curtipendula). KR bluestem, our focal invasive species, was originally planted throughout much of Texas and the Midwest to restore degraded rangeland but has since become a damaging invasive pest for both ranchers and private landowners. Silver bluestem and sideoats grama, our focal indigenous species, are two grasses commonly used in rangeland restoration. We collected data on a variety of response variables from relevant literature and then applied it to the model in order to determine niche differences between the three focal species. Our literature review led to inconclusive results because a lack of cohesion and precision in the data available in literature prevented the calculation of niche difference. Additionally, because this data has been collected from varying geographic locations and because there are different varietals of the three species throughout these different locations, application to our model is limited. We are currently designing an experiment where temporal and spatial data will be collected every two weeks for established monoculture and mixed plots of the three focal species. Data on little bluestem (Schizachyrium scoparium), a third native species that is a known poor competitor with KR bluestem, will also be collected in this experiment as a means of comparison to the more successful native competitors. This consistent set of data will allow us to more accurately model niche differences between native and invasive perennial grasses.

Moving Beyond Basic Risk Assessments: A Dynamic Spatio-Temporal Model to Mitigate Bioenergy Crop Invasion Risk.

Daniel R. Tekiela*, Eugene Dollete, Matthew W. Ho, Jacob N. Barney

Department of Plant Pathology, Physiology, and Weed Science

Virginia Tech, Blacksburg Va

Risk assessments such as the Australian and APHIS-PPQ Weed Risk Assessment are a critical step to assessing the invasion risk of potential new biofuel crop species being planted in the United States.  Despite their widespread adoption, they are limited to broad conclusions at a national scale that do not consider spatial heterogeneity.  Therefore, they should not be the only step taken in assessing biofuel crop invasion risk.  Assessments that better characterize risk at a finer spatial scale that consider landscape heterogeneity, species biology, propagule dispersal kernels, and the temporal dynamics of these factors are essential to better characterize the true risk of species invasion.

The Biofuel Invasion Risk Model (BIRM) is a site-specific stochastic simulation model that characterizes the potential risk of converting farmland into biofuel cropland. By integrating geographic and land-use data, species demographic characteristics, species-specific dispersal kernels, and land-use establishment probabilities this model will be capable of characterizing the relative risk of establishing biofuel crops in multiple locations, and with correct parameterization  will also be able to compare the risk of establishing different biofuel crop species in the same field location.

Currently our model only considers wind, water, and rhizomatous dispersal and spread, but our future plans are to add dispersal through biomass transportation, traffic currents, and other unique low probability events such as hurricanes and floods.  We will also implement various best management practices such as field border scouting and escaped population eradication to see how these various techniques affect the level of invasion risk. Because this tool could be useful to land managers across the United States, we plan to scale this model to a state or national level through optimized performance.

The Biofuel Invasion Risk Model is designed to complement current risk assessments already in use to determine the invasive status of plants.  Our model will allow for a much more spatially precise assessment of risk that has been impossible with current tools until now.

Propagule establishment is a quintessential step in the invasion process.  Information about the germination requirements of any invasive species could be critical for germination prediction and subsequent management efforts.  The C₄ perennial grass Miscanthus sinensis is an important ornamental grass and potential bioenergy crop in the United States.  If implemented as a bioenergy crop, the extraordinary influx of propagules would add an immense pressure to surrounding ecosystems.  Therefore, it is essential to develop predictive models for M. sinensis seed germination in order to assess the risk of invasion.

The hydrothermal time model combines three essential parameters for seed germination – water availability, temperature, and time, as a way to quantitatively assess and visualize germination requirements.  Controlled laboratory experiments were performed to develop a hydrothermal time model for Miscanthus sinensis using seed from five naturalized populations and one commercial cultivar.  Seeds from each population were placed in solutions of varying water potential (0.0MPa, -0.25MPa, -0.50MPa) along a temperature gradient (7.6 – 32.6°C) for a total of 30 treatment combinations per seed lot.  Miscanthus sinensis has a minimum germination temperature threshold at approximately 9.0°C and was tolerant of all water potential treatments at temperatures above this threshold.  Data from this model could be combined with geographical information system (GIS) models to develop a predictive visualization of high and low risk areas for M. sinensis germination and potential establishment.

Cyperus difformis L. (CYPDI) management has been complicated by the evolution of herbicide-resistant biotypes. In California rice weed management using the stale seedbed technique, spring irrigation is employed to encourage weed seed germination and growth, but growers face uncertainty regarding the adequate timing of control.  Timing of CYPDI control is also an issue with most available herbicides for use in rice given their narrow window of efficacy.  Estimating CYPDI germination and emergence dynamics could improve the efficacy of stale seedbed and postemergence CYPDI control timing. Our objectives were to (1) evaluate germination patterns of CYPDI biotypes R and –S to acetolactate synthase (ALS) inhibiting herbicides across varying temperature and moisture conditions in order to obtain cardinal temperatures and base water potential (Ψ_b ) for germination, and (2) validate a population-based threshold model capable of predicting CYPDI emergence in rice fields.

Wet chilled seeds germinated faster and at colder temperatures relative to dry chilled seeds, indicating wet overwinter conditions may play a role in overcoming dormancy.  Base temperatures for germination were not different between ALS-R and –S biotypes; the coldest temperature at which ALS-R CYPDI can germinate is 16.2 ºC.  R accessions require shorter (5.5 ºCd less) median thermal time to germination (θ_T(50)) and are able to germinate under dryer conditions (i.e. have more negative Ψ_{b (50)}) than S biotypes.  However, CYPDI seedling emergence was strongly suppressed by dry soil conditions; emergence was greater in flooded compared to saturated and daily watered soil.  Nevertheless, anoxia may delay germination or early seedling growth under flooded conditions, thus emergence was faster in the daily watered soil.  Suggested control dates are presented, based on 30-year weather data for California's Colusa County. 

Weedy red rice is a widespread, economically challenging problem in Southern U.S. rice fields.  The two major U.S. red rice types, strawhull and blackhull, are thought to have arisen independently from Asian rice populations in the distant past.  Red rice is a weedy relative of rice, a genomic model species, and thus can be exploited to better understand the genetic and evolutionary mechanisms by which weediness has evolved in this species.  Increased knowledge of the contemporary and longer-term evolution of this weed and its important weedy traits may help us improve its management.  In 2011, red rice populations were obtained from farm surveys of Arkansas rice fields with a history of imidazolinone-resistant (IR) rice production systems (Clearfield®).  Numerous instances of IR weedy rice populations were detected by sequential spraying of the imidazolinone herbicide, imazethapyr, suggesting recent gene flow between IR cultivated rice and red rice.  Almost all sampled fields with a history of Clearfield® rice produced some IR weedy rice.  These populations also ranged greatly in their plant size and shape, leaf dimensions, flowering date, color of plants, seeds, and awns, and seed shattering and germination.  Many of the populations appeared to be segregating for one or more of the above traits, further suggesting that gene flow had occurred recently.  In a different study, we used Asian strawhull indica rice, which is a putative cultivated progenitor of U.S. red rice, and made a cross (using cv Dee Geo Woo Gen) with two different red rice lines that had been obtained from southern U.S. rice farms.  These were a late-flowering blackhull line from Mississippi (PI 653419; MS-1996-9), and an early flowering strawhull line from Arkansas (PI 653435; AR-2001-1135).  Recombinant inbred mapping populations up to F₆ were generated from these crosses in a greenhouse, and evaluated in the field in 2012.  Phenotypic measurements of weedy traits and other important productivity traits from these populations were recorded.  These included plant height, flowering date, seed shattering, and resistance to blast disease.  QTL mapping using genotyping by sequencing, whole genome sequencing, and other analyses of key genomic regions will allow us to distinguish the DNA sequence variation in U.S. red rice from indica rice and how this is associated with weedy traits.  Ultimately, these findings may provide insights into management strategies for red rice.

Expanding the niche: the role of nutrient-limiting soils and invasiveness in perennial grasses

Matthew W. Ho, Larissa L. Smith, Jacob N. Barney

Abstract Perennial grasses considered for bioenergy production share many characteristics with known invasive species, which include rapid growth rates and tolerance of poor growing conditions.  Their use as bioenergy crops will depend on their ability to thrive on marginally productive soils, including having high nitrogen-use-efficiency. Many of the promising C₄ grasses being considered for bioenergy have potential associations with nitrogen-fixing bacterial endophytes, which may allow these crops to be productive on marginal soils with few inputs, but may also increase their ability to thrive in disturbed areas and become invasive. However, no experiments have been conducted to test the level of this association, and the impacts on establishment and performance.  Therefore, this study focuses on six grasses with varying tolerance to nutrient poor soils: weedy and ornamental M. sinensis, the bioenergy crops M. × giganteus and Panicum virgatum, Sorghum bicolor, and weedy Sorghum halepense. We tested the performance of each species in three soil types (local soil, sterilized soil to remove the resident microbial community, and sand) and two nitrogen levels (0 and 56 kg ha-1). Results show soil type as the primary driving factor for growth, with all species performing poorly in sand compared to soil (sterilized and non-sterilized). Average across all species, performance at the end of the experiment for individuals grown in sand was 16.3cm, while grasses in sterilized and non-sterilized soil was 43.9cm and 49.1cm, respectively. In all soil environments, the worst performing grass was weedy M. sinensis.  In sterilized soil, S. bicolor reached a height of 74.2cm and was 4.2 times greater than M. sinensis. In sand, P. virgatum reached a height of 23.9cm compared to M. sinensis at 8.6cm, and in non-sterilized soil, M. x giganteus has a height 3.4 times greater than M. sinensis at 80.1cm. Surprisingly, we did not find any differences in performance between the two nitrogen levels for any species. No difference in performance was found between nitrogen levels or between sterilized and non-sterilized soils, suggesting that an endophytic association may be present in all species tested. Continued research on nutrient-limited soil tolerance and potential nitrogen-fixing bacterial endophytes is needed to further elucidate the role this association plays in the establishment of invasive species.

Effect of Herbicide Application with Select Mechanisms of Action on Total Phenol Production in Wheat.  Tarouco, C. P*¹,  Nohatto, M², Oliveira, C³, Manica-Berto, R⁴, Agostinetto, D⁵, Senseman, S. A⁶; ^1,2,3,4,5Universidade Federal de Pelotas, Pelotas, Brazil, ^1,6Texas A&M University, College Station, TX, ⁶Texas A&M AgriLife Research, College Station, TX.

Plant competition determines the diversity and species abundance of natural communities as well as potential yields in agricultural systems. Herbicides constitute the most widely used method for weed control in winter cereals. In wheat herbicides are used with different mechanisms of action (ACCase, ALS, Synthetic auxin) to reduce weed plant competition from Lolium multiflorum, Avena strigosa, Raphanus raphanistrum and R. sativus.  The objective of this study was to investigate the effect of herbicide application with select mechanisms of action on total phenol production in wheat. This experiment was conducted in a greenhouse at the Federal University of Pelotas, in 2011. The experimental design was completely randomized with six replications. The factorial treatments  used were herbicides (clodinafop propargyl, iodosulfuron-methyl, 2,4-dichlorophenoxyacetic acid and untreated check)  and  sampling times of plants (0, 12, 24, 48, 72, 96 and 120 hours after application). The variable studied was total phenolic content, expressed as milligrams of gallic acid equivalents per gram of fresh weight (mg GAE g^-1 MF). The results may imply that wheat showed differences in the production of phenolic compounds at different sampling times when herbicides clodinafop propargyl, iodosulfuron-methyl and dichlorophenoxyacetic acid were applied. In general, the clodinafop propargyl and iodosulfuron-methyl caused the increased production of phenols at 120 hours after application, thereby suggesting alterations in metabolism of wheat plants.

In a previous study, glyphosate-resistant and -susceptible biotypes of giant ragweed were able to survive a higher rate of glyphosate when grown in sterile field soil, compared to unsterile field soil. Sampling of the roots revealed that the susceptible biotype was colonized by a greater number of soil microorganisms, specifically oomycete (e.g. Pythium spp. and Phytophthora spp.) pathogens, when treated with glyphosate, compared to the resistant biotype. The ability of the resistant biotype to tolerate a glyphosate application may involve differences in the susceptibility to soil microbial colonization, especially oomycetes. Therefore, the objective of this study was to investigate the potential shift in the soil microbial community within the rhizosphere soil of glyphosate-resistant and -susceptible biotypes of giant ragweed after a glyphosate application. A greenhouse study was conducted by growing giant ragweed biotypes in unsterile field soil, treating with either 0 or 1.6 kg ae ha^-1 of glyphosate, and sampling the rhizosphere soil adhered to the roots three days after the glyphosate treatment. Microbial DNA was extracted from the soil samples, purified, and sequenced utilizing next-generation sequencing (Illumina Genome Analyzer). The microflora of the rhizosphere of the glyphosate-resistant and -susceptible biotypes was compared. This study sheds further light on the relationship between specific soil microbes and the tolerance to glyphosate building an understanding of the microbial component of the mode of action of glyphosate and their potential role in the evolution of resistance.   

Historically, Europe has been viewed as a source for invasions in the new world, rather than vulnerable to invasions itself. However, as transportation has increased globally, the number of invasive plant problems in Europe has grown. Solidago gigantea was deliberately introduced to Europe from North America as an ornamental plant, approximately 250 years ago. From the initial introductions in London, it spread to nurseries across the European continent, reaching Hungary by the mid 1800s. In natural areas in Hungary, it is now one of the top invasive plants of concern. Combining data from a series of experiments performed in Hungary as well as using estimates from the literature, we developed a demographic matrix model to explore the dynamics of giant goldenrod and the efficacy of several management practices aimed at reducing local population density and/or controlling spread. The stages in the model are seeds, establishing individuals and clonal adult plants. Transitions between the stages are a combination of various vital rates, such as the number of seeds produced in a shoot, the probability that a seed germinates, the survivorship of seeds, the probability of an establishing individual surviving and growing to a clonal adult, and the number of shoots produced in clonal adults. The spread model is based on the wind dispersal of seeds as well as the local spread via rhizomes, which is thought to produce most local spread. Insights from the model  into what best controls the spread and suppresses local dynamics of giant goldenrod invasions can lead to more appropriately targeted management practices.

ALS Resistance in Prickly Lettuce after 30 Years of ALS Inhibitor Use

Barco, Mario; Raeder, Alan J ^*; Aramrak, Attawan; Bell, Jared L; Burke, Ian C; Washington State University, Pullman, WA

Since the introduction of acetolactate synthase (ALS) inhibitor herbicides in the 1980’s, the number of ALS-resistance weeds species has increased rapidly, and ALS-resistant biotypes outnumber resistance to other herbicide modes of action. ALS-inhibitors block the formation of the essential amino acids valine, leucine, and isoleucine that are necessary for a host of plant functions, and results in plant death. One or more amino acid substitutions in the ALS protein are sufficient to convert a herbicide-susceptible weed to a herbicide-resistance weed. Prickly lettuce (Lactuca serriola L.) was one of the first ALS-resistant species. Thirty years have passed since that first report, and ALS inhibitors have been in continuous use in the PNW. To assess the effects of that use, twenty Eastern Washington prickly lettuce biotypes from across the region were grown in a greenhouse and sprayed with multiple ALS-inhibiting herbicides. In conjunction with the greenhouse study, ALS mutations were studied by extracting DNA from the 20 biotypes and amplifying the nucleotide sequence containing domain A in each the ALS gene. Known amino acid substitutions in the ALS gene of resistant biotypes were observed – the originally observed Pro197His substitution and a novel (to North America) Pro197Thr substitution. Cross resistance patterns confirmed the nucleotide substitutions. Triasulfuron will control biotypes containing the Pro197His substitution, but not biotypes containing the Pro197Thr substitution. Florasulam controls all ALS-resistant biotypes. The results of this study confirm point mutations within the ALS gene of prickly lettuce in North America.

Since the 1990’s there have been 3 successive waves of new tools brought to the marketplace that have fundamentally changed weed control in row crops – the ALS herbicides, glyphosate tolerance, and most recently, auxin tolerance traits.  Each new tool brought or is anticipated to bring expectations for significant improvement in efficacy against troublesome weeds while at the same time lowering costs and simplifying management practices.  Early adopters of ALS herbicides, such as imazethapyr in soybeans, saw their expectations for improved efficacy versus older established herbicides met or exceeded.  Initial good product performance lead to over-simplified product use patterns, questionable crop rotational practices, and intense selection pressure for weeds resistant to ALS herbicides.   The same pattern of over-use, over-simplification, and resulting weed resistance was repeated with the advent of glyphosate-tolerant crops and is poised to repeat itself yet again with the auxin tolerance technologies.  Questions arise on how best to encourage product use patterns that extend the useful life of new technologies in spite of the fact that excellent initial effectiveness, reasonable cost, and simplicity will likely drive use patterns that promote short-term effectiveness.  It is important to recognize that a company’s product portfolio will likely contain a range of herbicide products designed for use with new technologies that are appropriate for addressing a wide range of field needs. Different products and use patterns may be appropriate for well-managed fields with routine weed control needs, fields containing “at-risk” weeds where the potential for resistance exists but where no immediate threat has been identified, or “high-risk” fields where resistance is an established problem that must be addressed.  DuPont Crop Protection believes key considerations for driving sustainable product use patterns include; designing single and multiple active ingredient products with efficacious use rates and realistic performance claims, pricing and servicing products so favorable behavior is incentivized and irresponsible use is penalized, and promoting and positioning products to meet specific field needs.

A study examined the feasibility of applying low input cropping systems to mature (20+ year old) tillage plots in a four-year crop rotation (barley-red clover-corn-soybean). One of the questions of interest concerned the relative efficacy of weed control methods applied to the various treatment combinations. For example, a comparison of POST vs. PRE total weed density in the corn year suggested that herbicide- and mechanical-based weed control systems provided good to marginal efficacy.  Weed control was generally inadequate in organic and no-till systems. We then examined how each weed species was responding to weed control in the various treatment combinations. Given the complexity of the treatment design, we explored the use of multiple contrasts to graphically summarize mean differences between PRE/POST density across levels of cropping system and tillage, and for each combination of cropping system by tillage. Graphs of the confidence intervals for these mean differences, i.e. the diffogram, illustrated their statistical importance (confidence intervals not overlapping with zero), and magnitude (distance from zero), and the direction of the difference (positive or negative). The diffogram provides a simple and elegant method of simultaneously looking at many comparisons for any given variable (in this case: POST vs. PRE density comparisons across various treatment combinations for each weed species), and quickly identifying treatments and species responsible for trends observed at the community level. anne.legere@agr.gc.ca

Ornamental Weed Control with Bio-herbicides and Bio-Rational Approaches.

Hannah M. Mathers^1*, Michele M. Bigger²

¹Associate Professor, Department of Horticulture & Crop Science Ohio State University, Columbus Ohio

²Graduate Student, Department of Horticulture and Crop Science, Ohio State University, Columbus Ohio

ABSTRACT

Heightened environmental and human health and safety concerns have driven the need for alternative weed controls in both nursery and landscape settings. 

The study initiated May 19, 2009, had two objectives 1) To determine the efficacy and duration of weed control of different control methods, including two bark sizes applied as a single layer on container surfaces; and 2) Assess the phytotoxicity of the different methods in containers.  Evaluations were conducted at Sheridan Nursery, Halton Hills, Ontario.  Initially bark was prepared by spreading a two inch (5 cm) thick layer on plastic sheets and over sprayed with 5 replication of each treatment.  Follow spraying, bark was allowed to stand for, chemical absorption, for 24 hours. Bark type and size consisted of pine bark greater than 1” (>2.54 cm) and less than 1” (<2.54 cm), from Gro-Bark Ltd., Caledon, Ontario.  Following the 24 hours bark was applied in a single layer application to the top of freshly planted 1 gallon containers.  Plants used in 2009 were Winter Creeper Euonymus, Euonymus fortune ‘Emerald Gaiety’, American Elderberry, Sambuscus Canadensis, and Mugo Pine, Pinus mugo.  Oxadiazon (Ronstar, Dow AgroSciences) and flumioxazin (BroadStar, Valent USA) were used at the 1X rate as industry standards for phytotoxicity and efficacy.   In addition two bio-herbicides (BH1 & BH2), extracts of plants with known alleopathic tendencies, were prepared and applied at 5% and 10% aqueous solution, lastly a 200 grain vinegar (Ohio State University Food Science Department) was applied to <1” (<2.54 cm) pine bark material.  Containers were arranged in a completely randomized block with 5 replications for phytotoxicity and a completely randomized design for efficacy.  Evaluations were conducted 90 days after treatment (DAT).  For efficacy, a visual rated scoring system 0 (no control) to 10 (complete control), with a rating of 7 being commercially acceptable.  For phytotoxicity a visual rated score of 1 (no injury) to 10 (complete kill), with 3 being commercially acceptable.

In 2010, the study was designed to be a continuation and had two objectives based off of the work conducted in 2009.  1) To determine the efficacy and duration of weed control of different control methods in the field including mulch applied at a 2” depth.  2) Assess the phytotoxicity of the different methods in the field. The study was begun June 8, 2010 at the Vineland Research and Innovation Centre, Victoria Road Farm, Vineland Station, Ontario.  Bark was prepared in the same manner as was done in 2009. Bark type and size consisted of pine bark less than 1” (<2.54 cm), hardwood bark and wood, and cedar bark and wood, all from Gro-Bark Ltd., Caledon, Ontario.  Following the 24 hour standing time, bark treatments were applied over freshly planted three foot (0.9 m) x three foot (0.9 m) plots.  Plants used in 2010 consisted of White Spruce, Picea glauca, English Oak, Quercus robur, and Moonbeam Coreopsis, Coreopsis ‘Moonbeam’.  Treatments in 2010 consisted of BH1 from 2009 in 5%, 10%, and 15% aqueous solution, 200 grain vinegar (similar to 2009 study), WeedPharm^TM (20% acetic acid) at 10% v/v (Pharm Solutions Inc., Port Townsend, WA), Munger Horticultural Vinegar Plus (20% acetic acid) (Engage Agro, Guelph, Ontario), Scythe^TM (pelargonic acid) at 10% v/v (Gowan Co., LLC, Yuma AZ.) and a control (No mulch & no herbicide).  Efficacy and phytotoxicity were done in the same manner as was conducted in 2009.

June 28, 2011 the study was again conducted at Sheridan Nurseries.  Objective were 1) To determine the efficacy and duration of weed control of different control methods in the field using liner material and containers. 2) Assess the phytotoxicity of the different methods in the field and containers. Hardwood mulch was prepared as described in 2009, then stored in black plastic bags for 1 week, before applying.  One gallon containerized plants of Summer Wine^TM Ninebark, Physocarpus opulifolious ‘Seward’ and Winter Creeper Euonymous, Euonymus fortunei were used as well as Spirea liner material planted in a three foot linear field manner.  Mulch was applied to field study in 12” (30 cm) wide bands. BH1 from 2009 again was used as a treatment along with two new bio-herbicides, 10% extract of Russian Olive, Eleagnus angustifolia (RO) and 20% extract of Tree of Heaven, Ailanthus altissima (TH).  Along with these other treatments included Weed Pharm 10%, Weed Pharm 100%, Scythe 20%, Munger Horticultural Vinegar Plus 10%, Munger Horticultural Vinegar Plus 100%, BroadStar 0.0102 lb./ 3 ft² , hardwood mulch and two controls; hand weeded initially only and hand weeded both initially and after evaluations. Evaluations for phytotoxicity and efficacy were conducted 40 DAT as done in previous years.

In 2009, on the < 1” pine bark the 200 grain vinegar was as efficacious as Ronstar with less than half of the phytotoxicity.  Similarly the BH1 5% and 10% were as efficacious as Ronstar and 200 grain vinegar, however the BH1 had close to half of the phytotoxicity that the vinegar displayed.  In 2010 Munger Horticultural Vinegar, Scythe and BH1 with bark proved to be most efficacious.   In 2011 BH1 did not display as much efficacy this is attributed to deterioration of the sample over this period of time.   Both RO and TH had commercially acceptable levels of weed control 40 DAT.  BH1, RO, and TH plant extracts developed at Ohio State University merit more assessment as alternative bio-herbicides in ornamental containers, nursery fields, and landscapes.  

The development of low-input agriculture involves the use of alternative weed management. Biological control is a tool to develop under this new approach. Sorghum halepense is one of the ten species of perennial weeds more important in the world. It is necessary to advance the knowledge of potential biological control agents. Thus, the aim of this study was to evaluate the effect of Sporisorium cruentum on total biomass (aerial and rhizomes) of S.halepense to determine its potential utility as a biological control agent. Aerial biomass (AB) was evaluated (BA) at maturity (in two growth cycles, C1 and C2) and rhizome biomass (RB) in C2 maturity. The pathogen was inoculated by three treatments: T1) dipping sprout in liquid culture of S.cruentum for 20 minutes., T2) dipping sprout in liquid culture of S.cruentum at 1 atm vacuum  for 5 minutes, and T3) immersion in water with teliospores suspension during 20 minutes. The pathogen decreased C1 AB in T1. While in C2, caused a significant decrease in AB and RB when used T2 and T3. S.cruentum emerges as a potentially useful agent of S.halepense.

Mile-a-minute weed (MAM) [Persicaria perfoliata (L.) H. Gross] (Polygonaceae) is a rapidly growing herbaceous vine native to eastern Asia.  In temperate climates, MAM has an annual life cycle.  Since its accidental introduction in the 1930s at a southeastern Pennsylvania nursery, MAM has spread across PA and into several nearby states.  The presence of MAM in Connecticut was confirmed in 2000 when a population was found at the southwestern corner of the state.  In subsequent years, MAM has invaded many locations in CT.  Some MAM populations are along streams or in dense thickets where mechanical or chemical control methods may be impractical or inappropriate.  Fortunately, a biological control option for MAM is available.  The biocontrol agent is a tiny weevil species (Rhinoncomimus latipes Korotyaev) native to China.  R. latipes is highly host specific for MAM.  Adults (~2 mm long) feed on MAM leaves and growing tips.  Females lay eggs on stems and underside of leaves.  Hatching larvae bore into a node and feed within the stem, mature larvae drop to the ground to pupate, then adults emerge and fly to MAM plants to feed.  Generation time during the summer is about 4 weeks, and adults overwinter in the ground.  Beginning in 1996, extensive testing by USDA-APHIS and other labs determined that this weevil depends solely on MAM as its food source.  The first field releases of R. latipes were approved in 2004 in Delaware and New Jersey, and weevils have been released in several other states since 2005.  Following protocols established by USDA Forest Service and the University of Delaware, we initiated a biocontrol program in 2009 for MAM in Connecticut.  The Philip Alampi Beneficial Insects Laboratory in Trenton, NJ has provided us with R. latipes adults.  The first weevil release in CT occurred on July 2, 2009 in a MAM stand in Quinnipiac River State Park (North Haven); we released 500 weevils at each of two locations within the park.  Through 2012, we have released 24,000 R. latipes adults at 25 MAM sites within 12 towns in CT.  Release sites include river banks, floodplains, open meadows, utility rights of way, town and state parks, nature preserves, residential properties, neighborhood open space, and a golf course.  Property owners and managers have been cooperative and often have assisted with our evaluations.  At each release site, we have monitored several times per year for weevil numbers, feeding activity by adults and larvae, damage to MAM and production of fruits.  No feeding by R. latipes has been observed on any other plants, including native species of Polygonaceae.  The weevils have survived a variety of winter conditions and flooding at some sites.  They have demonstrated a keen ability to locate MAM plants in outlying areas.  We have found R. latipes adults on MAM up to 2 miles away from the nearest release site.  Control in terms of reducing growth and reproduction of MAM has been better at some locations than at others.  The greatest growth in weevil numbers, feeding damage and reduction in MAM fruit production has been at one of the Newtown sites, a sunny open space not subject to flooding.

EFFECT OF WATER QUALITY ON GLYPHOSATE EFFICACY. M. R. Manuchehri*¹, P. A. Dotray¹, T. S. Morris², J. W. Keeling²; ¹Texas Tech University, Lubbock, TX, ²Texas A&M AgriLife Research and Extension Center, Lubbock, TX.

Water is the main carrier used in most herbicide applications. The quality of water plays a critical role in the success or failure of herbicide treatments, especially for weak acid herbicides such as glyphosate. In an attempt to offset potential antagonism of herbicides due to poor water quality, systems utilizing reverse osmosis (RO), a filtration process to remove dissolved inorganic solids from water, are being used by some growers in the Texas High Plains. Defining the role of water quality on glyphosate efficacy is important due to its increased use over the past 15 years. The effects of water quality and water conditioning agents on glyphosate efficacy were assessed in five field trials established near Lubbock, TX in 2012. Test plants included volunteer winter wheat (Triticum aestivum L.), Palmer amaranth (Amaranthus palmeri S. Wats.), and kochia (Kochia scoparia L.). All trials were organized in a randomized complete block design with four replications. Five water samples, ranging in cation concentrations of 519-1,046 ppm, were selected from a collection of 23 wells throughout the Texas High Plains. The selected five sources plus a RO water source were used as carriers for the following four herbicide treatments: glyphosate applied alone at 0.43 and 0.86 kg ae ha^-1 and glyphosate applied at 0.43 and 0.86 kg ae ha^-1 with dry ammonium sulfate (AMS) at 20.37 g L^-1. Injury was recorded at 14, 21, and 28 days after treatment. In three of the five trials, differences in efficacy due to water source or a water source by glyphosate rate interaction were observed. Additionally, efficacy across trials improved with increasing glyphosate rate and the presence of AMS.

Shikimic acid accumulates to high levels in susceptible plant tissue after treatment with glyphosate.  The detection of shikimic acid, then, is a diagnostic marker for glyphosate injury and for discriminating between glyphosate sensitive and resistant weed biotypes.  We have developed a colorimetric assay method for shikimate detection.  It is a coupled enzyme assay employing shikimate dehydrogenase and diaphorase with a tetrazolium dye to produce a colored end-product.  The assay is simple and fast: color development begins immediately and full color development is usually achieved in 10 minutes.  This assay can be used in the laboratory to quantify shikimic acid in plant extracts in a microtiter plate.  It is especially useful for detection and quantification of shikimic acid in whole plant tissues collected in the greenhouse or the field.

Two glyphosate-resistant Palmer amaranth biotypes (R and G) from Mississippi (MS) were compared with glyphosate-resistant (C7) and –susceptible (C3) biotypes from Georgia (GA).  The target site of glyphosate is 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) and plants that possess multiple copies of EPSPS display resistance to glyphosate.  We randomly selected 10 plants of each biotype population from the two geographic regions and cloned these plants for long-term evaluation.  Tolerance to glyphosate was determined using leaf disk bioassays and herbicidal injury was analyzed using a visual rating scale and by digital imaging software.  EPSPS copy number determined by Q-PCR generally showed that resistance was directly correlated with increasing copy number.  However, certain clones with high copy number did not exhibit a high degree of resistance in leaf disc bioassays; conversely some clones with very low copy number demonstrated moderately high resistance to glyphosate.  Based on these bioassay results, several intact resistant (R, G and C7, with high copy number and high resistance) and susceptible (C3, with low copy number and variable resistance) clones were spray-treated with glyphosate.  These whole plant spray tests corroborated the results from the bioassays.  Although elevated copy number of the EPSPS gene generally instills resistance to glyphosate, other factors or resistance mechanisms may contribute to the overall glyphosate resistance of Palmer amaranth in some of the plants tested.  Results also demonstrate the variability associated with herbicide resistance in individual plants within a given population.

Investigations were undertaken using four biotypes (one glyphosate-sensitive, one resistant and two of unknown tolerance) of Palmer amaranth (Amaranthus palmeri) to examine bioassay techniques for the rapid detection and level of resistance in populations of this weed and to comparatively characterize these plants with respect to inherent protein, chlorophyll and betalain levels, and immunological responses to an EPSPS protein antibody.  After resistance determination, selected plants were cloned to facilitate further characterization of individuals over a long-term time course.  Only slight differences were found in the four biotypes grown under greenhouse conditions regarding extractable soluble protein and chlorophyll content, but one biotype was found devoid of the red pigment, betalain.  Seed bioassays at various glyphosate concentrations showed that measurement of early growth of seedlings could be useful to detect resistance.  A leaf disc bioassay (using visual ratings and/or chlorophyll analysis) and an assay for shikimate accumulation were effective methods for determining resistance levels.  The two unknown biotypes were found to be resistant to glyphosate.  The effects of glyphosate application to intact plants corroborated findings demonstrated via the bioassays. Some differences were found in the electrophoresed protein profiles of the biotypes, and western blots demonstrated only weak antibody labeling of EPSPS in the glyphosate-sensitive biotype, whereas strong labeling occurred in the resistant plants thus supporting results by others that resistance in this species is due to increased EPSPS gene copy number.  Results indicate the utility of certain bioassays for the determination of resistance and provide useful comparative information on the levels of inherent constituents among closely related plants.

Ryegrass (Lolium sp.) is a common weed 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. 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 peroxidase activity of glyphosate-resistant and susceptible Lolium perenne L. biotypes. Perennial ryegrass plants were grown in a greenhouse and treated with 1,020 g ae ha^-1 of glyphosate. The last expanded leaves were sampled at 0, 24, 48 and 72 hours post-application (HPA). Peroxidase activity was measured by spectrophotometer at 430nm in a reaction medium consisting of 50 mM potassium phosphate buffer (pH 6.5), 45 mM pyrogallol and 8 mM H₂O₂. The activity was estimated from the reduction of pyrogallol to purpurogallin.  

At 72 HPA, peroxidase activity increased one fold in susceptible treated plants compared to their controls, while glyphosate-resistant plants showed no significant changes in the enzyme activity during all experiment. These results are consistent with previous reports which involved the generation of reactive oxygen species after glyphosate application that provoke oxidative damage. However, it was a relatively later event compared to the glyphosate effects on leaf gas exchange reported previously.

The current study thus provides evidences in the phytotoxic effects that are triggered in response to glyphosate application. In addition, it specifies the mechanisms by which the herbicide affects susceptible plants and it characterizes the glyphosate-resistant L. perenne plants physiologically.

Greenhouse and laboratory studies were conducted to confirm and quantify glyphosate resistance, and to investigate molecular mechanism of glyphosate resistance in spiny amaranth from Mississippi. The GR₅₀ (herbicide dose required to cause a 50% reduction in plant growth) values for two glyphosate-resistant biotypes, R1 and R2, and a glyphosate-susceptible (S) biotype were 0.66, 0.70, and 0.15 kg ae ha^-1 glyphosate, respectively. This indicated that the R1 and R2 biotypes were 4- and 5-fold resistant to glyphosate, respectively, compared with the S biotype. Both resistant biotypes, R1 and R2 accumulated less shikimate compared to the S biotype. 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 (50%) of the S biotype compared to the R1 (24%) and R2 (10%) biotypes, possibly, indicating a reduced movement of glyphosate in the resistant biotypes. Genomic DNA and total RNA were extracted from the three biotypes.  The epsps cDNA was amplified from each biotype and sequenced.  Epsps copy number and gene expression levels were determined using real-time PCR. There was no mutation at the Pro106 site in the resistant biotypes.  Copy number assays revealed that resistant biotype R1 had 26 copies of epsps and biotype R2 had 37 copies.  Gene expression levels were also increased in the resistant biotypes: R1 had a 17 fold increase in expression and R2 had a 23 fold increase in expression. These data show that glyphosate resistance in R1 and R2 is due to amplification of epsps.

Insights into molecular mechanisms regulating vegetative growth and dormancy may lead to new strategies for inducing uncontrolled bud growth in perennials, making them more susceptible to alternative control techniques. Glyphosate is known to induce witches’ brooming (a form of uncontrolled growth) in perennials such as leafy spurge, which has been proposed to interfere with correlative inhibition. To enhance our understanding of glyphosate’s effect on molecular mechanisms regulating vegetative development in underground adventitious buds (UABs), we sprayed leafy spurge plants with 0 or 2 lb/acre glyphosate+0.25% surfactant. These plants were returned to growth-conducive greenhouse conditions and UABs were collected at 3h, 1-, 3-, and 7-d post-application. A duplicate set of treated plants were also decapitated 7d post-application to monitor weekly vegetative growth from UABs. After six weeks, aerial tissue from these plants were harvested and used for hormone profiling. Glyphosate application resulted in regrowth from UABs typical of witches’ brooming and a significant (P<0.05) reduction in shoot height compared to controls. We performed qRT-PCR to monitor effects of glyphosate on molecular mechanisms involved in regulating various pathways associated with hormones and cell cycle. Overall, the most striking effect of glyphosate on molecular mechanisms occurred for ethylene and gibberellic acid (GA) biosynthesis and signaling, and auxin transport and degradation pathways, all of which were mostly down-regulated. Aerial tissue showing witches’ brooming from glyphosate treated plants had higher levels of bioactive auxin and inactive GA. New insights on how plant growth regulators impact plant growth and development could lead to next generation weed management strategies.

Physiological Analysis of  Lolium multiflorum Resistant to Iodosulfuron-methyl sodium Herbicide. F. Mariani*¹, L. Vargas², D.S. Fraga³, S.A. Senseman⁴, D. Agostinetto⁵; ^1,2,3,5Universidade Federal de Pelotas, Pelotas, Brazil, ²EMBRAPA Trigo, Passo Fundo, Brazil, ^1,4Texas A&M University, College Station, TX, ⁴Texas A&M AgriLife Research, College Station, TX.

Weeds resistant to herbicides do not necessarily phytotoxicity symptoms in response to herbicide treatment. But they may have physiological changes that are visually imperceptible. Therefore, the objective of this study was to evaluate physiological parameters in ryegrass (Lolium multiflorum L.) biotypes resistant and susceptible to iodosulfuron-methyl sodium herbicide. The experiment was conducted at the Universidade Federal de Pelotas, Brazil. The doses of the herbicide evaluated were: 0, 0.36, 0.72, 1.05, 1.41, 2.14, 2.83 and 5.66 g ai acre^-1. The dose indicated on the label for ryegrass control is 1.42 g ai acre^-1. Physiological evaluations were made at 15 days after application of the herbicide treatments with an infrared gas analyzer (IRGA). The photosynthetic rate (Pn), stomatal conductance (gs) and the transpiration rate (E) were determined. Between the biotypes, the differences in the variables occured from 50% of the dose, with the exception of E where the difference occured after the first dose. The Pn was not affected by increasing levels of the herbicide in resistant biotypes. However, starting with 25% of the recommended dose photosynthesis was affected negatively in the susceptible biotype. The variables gs and E decreased at the highest dose of the herbicide to resistant biotype compared with the intermediate doses. However, they not differ statistically of from untreated. The same variables for the susceptible biotype, decreased significantly after the first dose of the herbicide. Therefore, the increase of the herbicide dose was not enough to adversely affect the resistant biotype.

Waterhemp (Amaranthus tuberculatus) is a difficult-to-control weed in Illinois soybean and corn production, which is in part due to 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 applied PRE- and POST-emergence.  Metabolism studies using excised leaves from vegetatively-cloned lines revealed a significantly shorter DT₅₀ (time for 50% of absorbed mesotrione to degrade) for MCR relative to mesotrione-sensitive ACR and WCS populations, which correlates with phenotypic responses to mesotrione applied POST in maize and in these waterhemp populations.  A cross was made between the male clonal line MCR₆, which metabolized mesotrione most rapidly, and the female clonal line WCS₂, which metabolized mesotrione the slowest among all clonal lines examined, to determine phenotypic responses and quantify DT₅₀s in the F₁ in comparison with MCR₆ and WCS.  Excised leaves of MCR₆, WCS, and the F₁ were treated with radiolabeled mesotrione for metabolism time-course studies, and whole-plant dose-response studies were conducted in the greenhouse with these same lines.  The F₁ displayed an intermediate phenotype (DT₅₀) in the metabolism study as well as in determinations of GR₅₀, GR₂₀, and GR₈₀ values in whole plant dose-response experiments_.  Metabolism studies using excised leaves of primisulfuron-resistant (via an unknown mechanism; MCR), primisulfuron-resistant (due to a target-site mutation; ACR) and primisulfuron-sensitive (WCS) waterhemp populations indicated the DT₅₀ of radiolabeled primisulfuron in MCR was significantly shorter than in ACR and WCS.  Our results demonstrate that the gene(s) associated with rapid mesotrione metabolism in MCR is/are incompletely dominant, and that rapid metabolism via P450 activity may also contribute to primisulfuron resistance in MCR.  Additional research is needed to determine if other non-target site mechanism(s) contribute to mesotrione resistance and if the same gene(s) contribute to both mesotrione and primisulfuron resistance in MCR.

The noxious weed lespedeza dodder (Cuscuta pentagona) is an obligate stem parasite that is a threat to many crops such as alfalfa, tomato, potato, carrot, sugar beets, cranberry, and citrus. Our research has been focused on understanding macromolecular movement between hosts and dodder that occur via haustoria that function to link the plants and transfer nutrients to the parasite. Our previous research has demonstrated that specific phloem-mobile mRNAs are trafficked from host plants to dodder, but nothing is known about the mechanisms regulating cross-species transfer or its biological significance to the parasite. One approach to addressing these questions is to use Illumina high-throughput sequencing to assess the presence of host mRNAs in the parasite, as well as potential for parasite mRNAs in the host. Dodder was grown on Arabidopsis or tomato hosts because their sequenced genomes facilitate bioinformatic identification of transcripts moving between the plants. We focused on three regions of interaction: the dodder alone, the region of attachment between dodder and the host plant, and the host stem adjacent to the attachment site. More than 1.5 billion sequence reads (75bp and 100bp long) were generated from three tissues from the dodder-Arabidopsis system and three from the dodder-tomato system. By informatic analysis of RNA reads in parasite tissue growing in the different hosts we detected a large number that correspond to host sequences and represent approximately 11,000 Arabidopsis transcripts and 3,000 tomato transcripts. Also, we found evidence for bidirectional movement of mRNAs between host and parasite by finding approximately 3,000 putative dodder unigenes in both hosts. The mobile RNAs from hosts and parasite were functionally categorized using GO-slim terms and represent a broad cross-section of the transcriptome. This work is providing insight into mechanisms of mRNA mobility and parasite biology, and holds potential to lead to new strategies for dodder management. 

Pyroxasulfone is a new pre-emergent herbicide for control of grasses and small-seeded broadleaf weeds on corn, soybeans, wheat and other crops.  Pyroxasulfone kills plants by inhibiting the biosynthesis of very-long-chain fatty acids, the same mechanism of action as the acetanilide herbicides.  This study was done to determine the effect of soil adsorption on the movement of pyroxasulfone in different soils utilizing a small (5 cmX1.5 cm) column under simulated rainfall.  Six Australian soils were tested (York, Mangoplah, Mingenew, Pithara, Corrigin, and Kalkee) ranging from a loamy sand to a clay.  The adsorption of pyroxasulfone to these soils was York>Mangoplah>Kalkee=Corrigan>Mingenew=Pithara.  To measure the movment of pyroxasulfone in each soil, enough water was added to air-dried soil to bring the soil water potential to either -33 kPa or -500 kPa.  The herbicide was applied to the surface of each soil at a rate corresponding to 300 g/ha.  The soil surface was covered with sand and the columns incubated in the dark for 5 days.  The columns were then treated with 10 mm of simulated rainfall.  The leachate and soil water was collected (by centrifugation) and then the soil was divided into two sections (0-2.5 and 2.5-5 cm).  The pyroxasulfone in the leachate, soil water, and soil segments was extracted into toluene and measured by GC/MS.  The soil water potential had limited effect on the movement of pyroxasulfone, but there was a major effect of soil type.  The amount of pyroxasulfone leached from the columns ranged from 0.5 to 9% and the order of leaching was Pithara>Migenew>Corrigan>York=Kalkee=Mangoplah.  The distribution of the herbicide within the column was also correlated to soil binding.  The amount of pyroxasulfone retained in the upper 2.5 cm was York>Mingenew>Kalkee=Corrigin>Pithara.

Imidazolinone Leaching in Different Rice Paddy Soils

ABSTRACT

The imidazolinone herbicides used in Clearfield^® rice have high leaching potential. However, chemicals have different behavior depending on soil characteristics. The objective of the study was to evaluate leaching of imidazolinone herbicides in different lowland soils. Undisturbed soil cores were sampled from different locations in the state of Rio Grande do Sul, southern Brazil, corresponding to five distinct soils. An experiment with the samples was conducted in a greenhouse in a randomized complete block design in factorial arrangement with three replications. Factor A included the five soil types and factor B included the herbicides imazethapyr (100 g ai ha^-1), imazapic (100 g ai ha^-1) and imazapyr (100 g ai ha^-1), applied on the surface of the lysimeters. Factor C included six soil depths (0-5, 5-10, 10-15, 15-20, 20-25 and 25-30 cm). Sixty days after herbicide applications, during which the soils were flooded with a 6-cm water layer, the lysimeters were cut longitudinally. In each soil layer it was seeded the non-tolerant cultivar IRGA 417 used as a bio-indicator. There was significant difference in leaching in different soils, layers and herbicides. The results showed that soils with low clay content had higher herbicide leaching, with herbicide symptoms been detected at 30 cm-depth. Lesser leaching was observed in soil with higher clay and organic matter. The results suggest that there are differences between soils from different locations on the imidazolinone leaching potential, and that such information should be considered in the recommendations of herbicides for weed control.

The mechanisms determining success of non-indigenous, invasive species are still up for discussion in much of the ecological literature. Research suggests that non-indigenous, invasive grass (NIIG) species may have the potential to alter soil species composition or may benefit from changes in soil species composition due to long-term land-use or major soil disturbance. In this study, we compared soil microbe species compositions of soils dominated by a focal NIIG (KR Bluestem, Bothriochloa ischaemum, hereafter referred to as KR) and a focal indigenous grass (IG) species (Little Bluestem, Schizachryium scoparium, hereafter referred to as LBS) that often grows in proximity to KR. We hypothesized that the microbial species in KR’s rhizosphere would be different than those of the rhizosphere of LBS. Amplified fragments of the V3 region from 16s rDNA in bacteria and 18s rDNA in fungi was analyzed by denaturing gradient gel electrophoresis (DGGE).The microbial community profiles between NII and I soils were consistently different for each site and for both bacterial and fungal communities. Further research is needed to confirm if the change in composition is a cause or an effect of NIIG invasion.

In recent years, mycorrhizal fungi have emerged as a potential tool for restoration of degraded rangelands. These microbial symbionts facilitate plant growth by associating with roots to increase nutrient uptake. It is thought that inoculating natural ecosystems with mycorrhizal fungi could assist them in resisting potential invasions of unwanted plant species. In other words, plant community dynamics may be manipulated with the intentional application of mycorrhizal fungi. Furthermore, with an increased understanding of how mycorrhizal fungi specifically affect host plants, restoration techniques could be modified to achieve desired results. In this experiment we aimed to determine if the presence of mycorrhizal fungi alters competitive dynamics between an indigenous and non-indigenous grass species. Claims made by manufacturers of commercially available fungal inoculants led us to predict that the fungi would facilitate the growth of indigenous species and assist them in resisting invasion by non-indigenous species. We grew our two focal species, King Ranch Bluestem (Bothriochloa ischaemum, non-indigenous) and Sideoats Grama (Bouteloua curtipendula, indigenous), in a greenhouse experiment, whereby half the pots were inoculated with a commercially available mycorrhizal fungal mixture and half were not. Seedlings were harvested weekly over the course of a month to record biomass response and randomly selected roots were stained to confirm the presence of fungal colonization using microscopic analysis. We found that the non-indigenous grass species showed a larger positive biomass increase when grown in the presence of mycorrhizal fungi than the indigenous grass species, suggesting that the commercial use of fungal inoculant may be facilitating invasion. Our observations, in which we detected more mycorrhizal fungal structures in the non-indigenous plant roots than the indigenous plant roots supports this theory. This result suggests that the use of broad-spectrum fungal inoculants in rangeland management and restoration may actually be facilitating invasion by harmful non-indigenous species.

Palmer amaranth is a serious production problem for alfalfa growers in the southern Great Plains region.  An experiment was conducted in 2012 near Clay Center, KS to evaluate several dormant and between cutting herbicide treatments for residual control of Palmer amaranth under dryland and irrigated conditions.  Dormant treatments were applied on March 9 with 21 C, 16% relative humidity, and clear skies as alfalfa began to actively regrow.  Dormant season treatments included labeled rates of several registered herbicides, including flumioxazin, hexazinone, diuron, trifluralin, and terbacil.  Experimental treatments included sulfentrazone and pyroxasulfone herbicides.  Between cutting treatments were applied three days after the first cutting and harvest on April 23 with 22 C, 40% relative humidity, and clear skies.  Between cutting treatments included flumioxazin, imazethapyr, imazamox, and sulfentrazone.  The experimental design for the irrigated and dryland experiments was a randomized complete block with three replications.  Palmer amaranth emergence was monitored in 0.25 m² quadrats at the four corners of each experiment by removing emerged plants and recording them at weekly intervals throughout the season.  Alfalfa injury and Palmer amaranth control were also evaluated at regular intervals throughout the growing season.  Several dormant season treatments caused substantial necrosis shortly after application, but new growth was unaffected.  Regrowth of alfalfa appeared to be delayed, but alfalfa eventually resumed growth and no injury was evident by the time of the first cutting.  Total Palmer amaranth emergence was greater on the dryland experiment than the irrigated experiment with 436 and 136 plants m^-2, respectively, but emergence patterns through the season were similar.  Palmer amaranth began emerging May 1, with 20% cumulative emergence by June 3 (33 d), 80% cumulative emergence by July 8 (35 d later), and 100% emergence by August 5.  The best late season Palmer amaranth control was achieved with sequential treatments that included flumioxazin at 0.14 kg/ha or diuron at 2.7 kg/ha as dormant applications followed by a between cutting treatment of flumioxazin at 0.07 kg/ha, which was still providing 85 to 96% control on September 18.  Several other treatments provided good early season Palmer amaranth control, but control diminished as the season progressed.  Palmer amaranth emerges throughout the growing season and therefore, sequential herbicide treatments with good residual activity may be necessary for season-long control.

The later planting date of dry edible beans offers growers a larger window for incorporating cover crops into the rotation. Decreased weed pressure and improved nutrient cycling are two potential benefits that dry bean growers, especially organic growers, may realize from the use of a cover crop. In 2011 and 2012 field experiments were conducted to determine the effect of cover crops on weed populations in organic dry beans. This research was designed as a two level experiment (main and satellite sites). The two main sites (4 site-years) were located on Michigan State University research farms and included four cover crops treatments: medium red clover, oilseed radish, rye, and no cover. The 9 satellite sites (totaling 13 site-years) were located in Michigan organic farmers’ fields. Each satellite site had one cover crop treatment (clover, oilseed radish, or rye) and one no cover treatment. Both main and satellite sites were organized as randomized complete blocks with three to four replications. Weeds were managed uniformly by producers at each site using various cultivation tools. Weed density and biomass within the bean rows were sampled using three 0.12 m² quadrats (15 cm wide by 76 cm long) at both the V2 and R1 stages of bean development for all sites. At the main sites, beans planted following a clover cover crop were more likely to exhibit higher weed densities and weed biomass than the other cover crop treatments. At the satellite sites, there was rarely a difference between any of the cover crops studied and the no cover crop treatment with regards to weed density or weed biomass. This experiment will be conducted for a third and final year in 2013.  

Appropriate rotation system is an agronomical means of weed management. In order to assess the reaction of weeds to a number of different rotations, a six-years experiment was conducted based on a randomized complete block design with four replications at Agricultural Research Station of Khorasan Razavi, located in Jolgeh Rokh. Experimental treatments were included: annual alfalfa-potato, vetch-potato, berseem clover-potato, canola-potato, barley-potato, purple loosestrife-potato,
fallow with chicken manure-potato, fallow with cow manure-potato, fallow with compost-potato and fallow-potato (control). Each of the rotations was repeated in three times during the 6-years course of the experiment. The results indicated that the
canola-potato rotation proved highly successful in controlling the weeds during the growth season, and interestingly, did not suffer from bindweed unlike other rotation systems. The highest density of perennial weeds was observed in the fallow-potato rotation. The barley-potato rotation made an appropriate control of the weeds. The majority of weeds observed in sampling were spring annual ones, with lambsquarter and pigweed being the dominant species. In rotations which included a legume crops, weed management was not fully achieved. The inclusion of compost, chicken manure and cow manure in the fallow year had no significant impact on weed management. In conclusion, it can be suggested that identification of the appropriate rotation for each specific region can be applied as a means to sustainable weed control.

New tools for controlling weeds would be useful for soybean and corn production in organic systems or in systems in which weeds developed resistance to multiple herbicides. Here we report on two developments: (i) the safety to soybean seedlings of using air-propelled abrasive grit (PAG) for managing weeds, and (ii) fabrication of a four-row implement that uses PAG to manage weeds (PAGMan). PAG performs well for in-row weed control in corn, but crop safety in soybean is unknown. Consequently, we examined responses to abrasion by corn-cob grit of soybean seedlings at VE, VC, VU, V1, V2, and combinations of these growth stages in both greenhouse and field settings. Seedling leaf areas and dry weights in greenhouse experiments were reduced by treatments that included abrasion at VC, with the primary effect expressed through reductions in the size of the unifoliate leaf.  In the field, soybean stand also was reduced by grit applications at VC, especially if followed by a second application at VU or V1. However, soybean yield was not reduced by grit applied at any soybean stage of growth. End-of-season weed dry weights did not differ from hand-weeded checks and did not impact soybean yields. Thus, abrasive grit for in-row weed control can be applied at least twice at VE through V2 growth stages without lowering soybean yield, but applications at VC probably should be avoided. The second development, PAGMan, is an implement that was designed, constructed, and fine-tuned at the Agricultural and Biosystems Engineering Department at South Dakota State University during winter through summer 2012. It is tractor-mounted with a PTO-driven air compressor that delivers PAG at adjustable pressures through four pairs of nozzles aimed at either side of the bases of crop rows. The abraded swath resulting from each nozzle is about 5 to 10 cm wide, which creates a 10 to 20 cm-wide band of shredded weed seedlings centered on the crop row. At typical implement settings, PAGMan delivers about 84 ± 5.2 g per sec of grit. At the slowest conceivable operational speed of 1 m per second, this rate equates to 275 kg grit per hectare. Two to three abrasion events are needed for season-long control of annual weeds, thus 500 to 1000 kg per hectare of grit may be required. Much additional testing of PAGMan is necessary to verify its utility.

Fineleaf sheep fescue (Festuca filiformis) is an introduced perennial grass in Maine wild blueberry (Vaccinium angustifolium) fields, and growers in the Jonesport, ME area recently reported an herbicide-resistant population that has begun taking over local fields.  In a study initiated in November 2011, herbicides registered for use on wild blueberry as well as unregistered herbicides were evaluated for control of fineleaf sheep fescue and other weeds, and injury to blueberry.  Pronamide (2 lb/a; all rates in product per acre) was applied in fall 2011 and pre-emergence in spring 2012. Terbacil (2 lb/a)/diuron (2 lb/a)/hexazinone (1 lb/a) = “Trimix”, rimsulfuron (4 oz/a), and linuron (2 lb/a) were also applied pre-emergence, and clethodim (8 oz/a) and foramsulfuron (1.5 oz/a) were applied twice post-emergence.  Fall pronamide application resulted in the highest blueberry cover. Linuron and foramsulfuron had significantly higher initial phytotoxicity but overall levels were not unacceptably high, and the plants grew out of it with the exception of minor phytotoxicity in August in the linuron treatment. The Trimix was most effective on broadleaf weeds, while foramsulfuron was the least effective.  Fall pronamide was also significantly and consistently most effective in controlling fineleaf sheep fescue over time, followed closely by rimsulfuron, while clethodim and linuron were consistently ineffective.  In conclusion, fall application of pronamide and pre-emergence application of rimsulfuron controlled fineleaf sheep fescue, and Trimix could be effective with low fineleaf sheep fescue pressure.  Clethodim, linuron, foramsulfuron and spring application of pronamide were not effective control options under sheep fescue and/or broadleaf weed pressure.  The study will continue through the 2013 growing season; percent cover of wild blueberry and weeds, and yield, will be assessed in August 2013.

Flufenacet is widely used in the Pacific Northwest (PNW) of the U.S. to control Italian ryegrass in winter wheat (Triticum aestivum L.) production fields. Recently, four populations of Italian ryegrass in Oregon were identified that survived flufenacet applications under typical winter wheat production conditions. Seed from these populations was collected and greenhouse studies were conducted to determine the resistance patterns and levels of resistance to existing management options. Another objective of this study was to determine the response of the suspected flufenacet resistant Italian ryegrass-populations to pyroxasulfone, an herbicide in the same group, which is expected to be effective for management of Italian ryegrass in various crops. Our results indicate that the four populations were resistant to flufenacet, but were not resistant to pyroxasulfone. These are the first documented flufenacet resistant Italian ryegrass populations in Oregon. The four populations were controlled by pyroxasulfone at rates greater than 7.5 g ai ha^-1. The estimated flufenacet doses required for 50% growth reduction (GR₅₀) were 438 g ai ha-1 (R2) and 308 g ai ha-1 (R4). Resistance indices (RI) for the R2 and R4 populations were 8.4 and 5.9, respectively, compared to a known susceptible population (S). Two populations selected for further studies, R2 and R4, were resistant to mesosulfuron-methyl, pinoxaden, quizalofop, clethodim, but not to metolachlor, glyphosate, acetochlor or dimethenamid-p. R4 was also resistant to diuron.

Waterhemp (Amaranthus tuberculatus) is an annual weed reducing the yield of several crops including maize and soybean that is particularly present in the Midwestern United States. Palmer amaranth (Amaranthus palmeri) is a common competitive weed often found in cotton and soybean fields in the southern United States. The high reproduction potential of both weeds and their obligate outcrossing as dioecious species make them especially suited for evolving herbicide resistance. Resistances to herbicides that inhibit acetolactate synthase (ALS), photosystem II (PSII), protoporphyrinogen oxidase (PPO) and glyphosate have been observed, as well as multiple resistance stacked in populations. Herbicides that inhibit 4-hydroxyphenylpyruvate dioxygenase (HPPD; EC1.13.11.27) provide a solution with an alternative mode of action (MoA) to control Amaranthus weeds. Their broad-spectrum weed control and excellent crop tolerance are key factors to their integration into maize and other crop production systems. The evolution of HPPD resistance will increase the complexity of Amaranthus weed control. A better understanding of the spatial and temporal evolution of HPPD resistance in Amaranthus populations will contribute to select the best strategy to control these weeds and contain and delay as much as possible the development of resistance to the inhibitors of this new MoA. Case studies have been started in 2011 in three locations in Nebraska, Kansas, and Illinois and will be continued over 3 to 5 years. In each case, populations have been harvested from a fields suspected of resistance due to failure of HPPD herbicides (central point) and fields around it with increasing distances. Biotests were performed in the greenhouse using pre-emergence and post-emergence HPPD inhibitors. First biotest data will be reported. So far the resistance to HPPD inhibitors appears to remain localized to the central point(s) of the sampling areas. 

The application of plant protection products is becoming more regulated at every turn. Plant protection products labels are more complicated with the development of the new DRT Verification Program. The industry is already seeing labels that require the use of medium, coarse or very coarse spray quality for legal applications to be made. One of the major concerns is maintaining efficacy of the plant protection products after application as we meet the label requirements for spray quality. Of specific concern are the current labeled phenoxy herbicides to be applied in primarily a coarse spray quality.

Herbicide application in the 21^st century will present many challenges and exciting opportunities for innovation.  Feeding the increasing world population that is now more than seven billion, expected to be nine billion by 2050, will be an enormous task. Arable land and adequate quality water will become increasingly limiting.  Developing strategies to increase the production of food on the acres available will be critical.  The high value of crops will mean that losses due to weeds will increase and place additional incentives to eliminate weed losses.  Eliminating herbicide resistant weeds will need to occur as early as possible. 

Applicators will face a formidable challenge to improve product stewardship to eliminate losses from herbicide damage that may occur.  The risk increases because the value of non-target organisms will increase, there will be more regulations. less patience and understanding from neighbors and the public as the likelihood of litigation increases. 

An opportunity for innovation in herbicide application is increased precision and automation.  Sensors coupled with diagnostic programs will monitor plants to spray when and where needed.  Presently there are many electronic systems to perform functions such as GPS positioning and steering, spray controllers, recording instruments to document the spatial information and factors that are present as the application is being made. Weather information from near the application or on the spray equipment is being tried.  A consequence of the electronic recording of application and weather information is that if the applicator misapplies a product the electronics will document it and it can be used as a legal document against the applicator in litigation. This has already occurred with current technology.

Sprayers will be designed so each nozzle is guided electronically.  Multiple spray booms will be simultaneously spraying different herbicides, insecticides, fungicides, nutrients and plant growth enhancers and quality improving products.  Automation can provide greater safety through lower applicator and handler exposure to products.

New herbicide genetic traits will be developed.  New herbicide modes of action and weed control technologies will present both opportunities and challenges. Advances in weed science and stewardship need to be made create and to continue to provide selectivity.  

Information such as electronic labels and decision aids will become increasingly interactive and useful. This electronic information may be integrated with the automation of spray equipment to increase efficiency, effectiveness and minimize unintended consequences.

The US Environmental Protection Agency proposed for review and comment the Drift Reduction Technology Program with the goal of encouraging the agriculture sector to develop, market, and use spray application technologies verified to significantly reduce pesticide spray drift. The focus is on application technologies for ground boom and aerial application to row and field crops, and participation would be voluntary. The proposal includes a draft test protocol, description of the operation of program for industry, EPA, and applicators and is available at http://www.epa.gov/oppfead1/cb/csb_page/updates/2012/drift-reduction.html. The DRT Program would provide industry with a standard protocol to test technologies to verify drift reduction potential as compared to a standard. EPA would review test results and assign a DRT rating based on potential drift reduction and post results on its webpage. EPA would encourage pesticide registrants to label their products for use with rated technologies and could credit those products with less stringent application restrictions for managing spray drift. EPA will address all comments and as appropriate and revise the proposal before initiation of the program in 2013

Design, conducting and interpreting drift studies is challenging. For drift studies conducted in the field, it requires large areas, many people, lots of planning and a little bit of luck (since the weather cannot be controlled). Field drift studies can be conducted in a variety of ways, but should seek mass balance closer. Field drift studies should be conducted such that we have the ability to show at a minimum the amount of product that has deposited at various distances “off-target” so that relationships between the amount of product and injury or loss can be calculated in conjunction with biological studies.

The Spray Drift Task Force conducted numerous studies which have gone into the development of AgDrift and AgDISP. Both of these models require droplet size data in order to generate the expected amount of drift that would occur under various application conditions. However, to generate droplet size data, equipment such as laser diffraction or high speed videography. These pieces of equipment are highly sensitive and require significant quality assurance testing to retain full confidence in the data generation.

Particle size data are very useful in understanding drift potential as smaller droplets are more prone to drift. In order to help make applicators more aware of the droplet sizes from their applications, the USDA:ARS Areawide Pest Management Research Unit in College Station, TX and the University of Nebraska-Lincoln have developed iPhone/Android apps which allow applicators to input parameters of their applications and see what the impact is on droplet size. As drift becomes ever more scrutinized, tools like these and others will give applicators rapid feedback on their potential for drift.

The Winfield Spray Analysis System, which uses laser diffraction in a low speed wind tunnel to measure droplet size of agricultural sprays, has been fully operational for over a year. In this time we have tested more than 600 spray nozzles with a variety of pesticide products and adjuvants. We have gained numerous insights into product development, drift reduction technologies, droplet size distribution, nozzle effects, and pesticide interactions. For instance, we have demonstrated that tank mixtures affect droplet size distributions, and that these effects vary with nozzle type. We are adding to our extensive database of droplet size data and developing innovative ways to deliver these insights. In addition to laboratory research, we conduct over 200 field trials every year to validate our findings in the field.

Our extensive training and education program reaches retailers, commercial applicators, and growers. Over the past three years we have reached over 22,000 growers with Winfield Grower Sprayer Clinics, half of these in 2012. We have trained over 2,000 custom applicators in sprayer calibration, nozzle selection, and drift management. Our 200 Answer Plot locations across North America and R7 software tool support efforts to educate retailers, applicators, and growers by providing localized recommendations for seed and crop protection products that match the potential of each field. We have observed increasing demand for training among our customers to improve stewardship by maximizing herbicide efficacy while minimizing spray drift losses.

Spray applicators have many choices in selecting a spray nozzle to make an application to an agricultural product.  They must balance flow rate, spray pressure, and nozzle type and setup to deliver their agrochemical in the right droplet size for their particular needs.  The information presented will focus on the physical forces, such as viscosity and surface tension, involved in droplet formation, then discuss the role of spray pressure and solution effects on droplet size and velocities for a variety of commonly-used spray nozzles.  By gaining a better understanding of the basics of the droplet formation process, applicators will be able to make more informed decisions during a spray application.

ASTM International Subcommittee E35.22 on Pesticide Formulations and Delivery Systems develops and maintains standards that cover pesticide formulations, their application, and the adjuvants that are used to enhance the performance of the active ingredient.  There are separate terminology standards for pesticide formulations, their application, and tank mix adjuvants.  Formulation performance standards include how well an emulsifiable concentrate emulsifies, the suspensibility of suspension concentrates, and the dispersibility of water dispersible granules.  Application standards include field sprayer calibration, granular applicator calibration, and hydraulic spray nozzle testing.  Adjuvant standards include physical compatibility tests, pH control, spreading, and defoaming.  When a new term or performance standard is required, E35.22 will develop the definition and perform round robin testing on the method.  One of the most recent standards developed was for the performance evaluation of spray drift reduction adjuvants.

Spray drift reduction agents are adjuvants used in pesticide spray mixtures to reduce spray drift.  Spray drift is the physical movement of an agrochemical through the air at the time of application or soon thereafter to any off-target site. Spray drift does not include movement to off-target sites caused by erosion, migration, volatility or wind blown soil particles that occurs after application.  The U.S. EPA recently solicited comments on information collection activities relating to pesticide spray drift reduction technologies.  The EPA is implementing a voluntary program that encourages the practice of reducing spray drift as much as possible with the use of no-spray buffer zones.   While this program recognizes the benefits of using built-in and tank mix adjuvants to reduce drift, the proposed process of certification could be optimized.  ASTM International Subcommittee E35.22 on Pesticide Formulations and Delivery Systems developed Standard Test Method E2798 for the Characterization of Performance of Spray Drift Reduction Adjuvants for Ground Application.  This test method provides guidelines for the measurement of parameters pertaining to the performance of drift reduction adjuvants under simulated field ground application conditions.  The measurements can be made in a wind tunnel or spray chamber.  The method describes the preparation, composition and test/application conditions for the direct measurement of droplet size distribution and the volume of driftable fines generated.  The performance of a drift reduction adjuvant is enumerated by how much it reduces driftable fines.  These results could be used to determine appropriate buffer zones and verify spray drift reduction adjuvant performance directly, eliminating the need to use intractable field experiments or empirical correlations.  curtis_elsik@huntsman.com

keywords:  Adjuvant, Pesticide, Application, Spray drift reduction

Antagonistic salts present in spray water can reduce herbicide phytotoxicity. The type and concentration of salts in spray water varies widely across geographies. Many regions have greater than 1000 ppm hardness. Spray water should be tested to determine spray quality. When cations are present in high levels in the water source, they can antagonize the effectiveness of most weak-acid herbicides. Extensive research has been conducted with various water conditioners to overcome the antagonism. Glyphosate, in particular, is antagonized by several cations, including potassium, sodium, calcium, magnesium, and iron. Water conditioners that contain the equivalent of 8.5 lbs/100 gallon of water or more of ammonium sulfate (AMS) are effective in overcoming antagonistic cations. The ammonium ion binds with glyphosate to enhance absorption and translocation.  The sulfate anion binds with the cations and will precipitate as water evaporates from the spray droplet. Bernards et al. reports that sunflower and velvetleaf efficacy ratings increased from 5% to 80% with the addition of ammonium sulfate to water containing 1000 ppm of Ca²⁺ as compared to no water conditioner. Further, as sulfate binds with cationic salts in the spray droplet this makes the order in which AMS is added to the spray tank irrelevant. Nalewaja et al. observed no differences in flax or sunflower efficacy when AMS was added to the spray solution before or after glyphosate was included. This research was conducted with other weak acid herbicides and similar results were observed.

Configuring methods for foliar herbicide applications to serve the needs of optimizing herbicide efficacy while minimizing physical spray particle drift can develop into a complex set of issues.  During the era of glyphosate-resistant crops the robust efficacy of glyphosate on a host of target weeds resulted in little detriment for having extra coarse or larger droplets that may have compromised spray coverage, but were consistent with methods to reduce spray drift.  Current trends point towards the use of arguably less forgiving herbicides to control some of our most problematic weed species with greater attention required for sufficient spray coverage on target leaves with smaller spray droplets which presents a challenge for drift mitigation. A compilation of field research trials along with limited spray droplet spectra analysis has been conducted to derive the most effective application methods that preserve herbicide efficacy while contributing towards lower off-target drift.  The application factors evaluated included different nozzle types, adjuvant products, carrier volumes, travel speeds, and application time of day. Weed control from glyphosate, glyphosate plus clethodim, and glufosinate fluctuated 20 to 30% depending on the nozzle, adjuvant, and target weed.  These herbicides represent applications in which only a single herbicide was active on the target weed being reported.  The inclusion of drift control agents that increase spray solution viscosity tended to have a greater impact on reducing weed control when used in combination with air inclusion nozzles, relative to standard XR flat fan nozzles.  This observation was even more pronounced when used with the non-systemic herbicide glufosinate.  A premix formulation of glyphosate, mesotrione, and s-metolachlor includes two foliar herbicides with activity on the weed species evaluated.  Applications of this herbicide premix had much more consistent weed control (less than 10% deviation) under the same nozzle/adjuvant configurations as the other herbicides.  Spray coverage is essential for any herbicide application and the production of extremely coarse or larger droplets were inadequate for achieving sufficient spray coverage to optimize weed control.  Based on this research droplet sizes in the range of coarse to very coarse may provide the most consistent and/or greatest level of weed control while not allowing for excessive driftable fine droplets during foliar herbicide applications. Furthermore, combining two effective foliar herbicides instead of just one active ingredient may provide greater consistency and be less prone to herbicide failure due to aggressive drift management tactics producing extremely large droplets resulting in poor coverage.

Topramezone is a promising new herbicide for bermudagrass control in cool-season turf.  It is similar to mesotrione (Tenacity®) in that it controls many grassy and broadleaf weeds and is safe to many cool-season turfgrasses.  Topramezone can effectively control crabgrass, goosegrass, and white clover with a single application and is more effective than mesotrione for bermudagrass control.  Topramezone should be marketed in the coming year, but its trade name is unknown at this time.  The objective of this study was to determine if topramezone alone or in combination with triclopyr (Turflon® Ester) or quinclorac (Drive XLR8®) is effective in controlling bermudagrass in cool-season turfgrasses, and how these treatments compare to the industry standard of fenoxaprop (Acclaim® Extra) plus triclopyr (Turflon® Ester).

A study was initiated on July 20, 2012 on a ‘Kelly’ Kentucky bluegrass lawn maintained at 7.6 cm at the Turfgrass Research Center (TRC) of Virginia Tech in Blacksburg, and infested with approximately 70-80% bermudagrass.  Treatments consisted of topramezone applied alone, with triclopyr, or with quinclorac and compared to fenoxaprop + triclopyr and mesotrione + triclopyr.  All treatments were applied three times.  Rates of topramezone were 0.04 kg ai ha^-1 for the first two applications and 0.02 kg ai ha^-1 for the third application.  Rates of triclopyr, quinclorac, fenoxaprop, and mesotrione were 1.12, 0.42, 0.10, and 0.21 kg ai ha^-1, respectively.  All sequential treatments were applied at three-week intervals.  All topramezone treatments included a methylated seed oil surfactant (0.5% v/v).  An untreated check was included for comparison. 

Topramezone + triclopyr controlled bermudagrass 94% and significantly better than topramezone + quinclorac, fenoxaprop + triclopyr, and mesotrione + triclopyr, which only controlled bermudagrass less than 71%, 57 days after initial treatment (DAIT).  Topramezone applied alone controlled bermudagrass 85%, 57 DAIT, but not significantly different from topramezone + triclopyr, topramezone + quinclorac, or mesotrione + triclopyr.  For the three treatments that contained triclopyr, white leaf tissue (mostly weedy bermudagrass) comprised less than 5% of plot area.  Topramezone alone and topramezone + quinclorac had over 30% white leaf tissue in plots.  Kentucky bluegrass was not injured at any timing in this study.

Annual bluegrass (Poa annua) is the most common weed found in creeping bentgrass putting greens.  Attempts to remove annual bluegrass from putting greens usually prove futile, and thus the weed is generally accepted as part of the turf sward.  A major component of annual bluegrass maintenance is seedhead suppression.  Annual bluegrass seedheads generally occur in the spring, but sporadic seedheads may be found any time in winter.  For seedhead suppression, applications of mefluidide + foliar iron or ethephon + trinexapac-ethyl are commonly applied at 50 growing degree days at base 50 (GDD₅₀).  Seedhead suppression from these applications is often inconsistent and additional applications may lead to turf injury.  Given annual bluegrass plasticity and variations in seedhead initiation, the objectives of this study were to determine if early-winter applications of ethephon applied before a 50 GDD₅₀ initiated spring program would improve annual bluegrass seedhead suppression. 

Two trials were conducted on creeping bentgrass putting greens mowed at 3mm at the Virginia Tech Golf Course in Blacksburg, VA and the Spotswood Country Club in Harrisonburg, VA.  Treatments consisted of a base program of ethephon at 3.8 kg ai ha^-1 + trinexapac-ethyl at 0.048 kg ai ha^-1 applied first at 50 GDD₅₀ and again 4 WAIT.  This basic program was augmented to form the following treatments: 1) No early treatment, 2) ethephon at 3.8 kg ai ha^-1 in January, 3) ethephon at 3.8 kg ai ha^-1 in February, or 4) ethephon at 3.8 kg ai ha^-1 in March.  Treatments 5 and 6 included a comparison of mefluidide at 0.007 kg ai ha^-1 + foliar iron applied at 50 GDD₅₀ and again 4 WAIT, and a nontreated control.  On April 6, at the Virginia Tech Golf Course, the nontreated plots averaged 66% seedhead coverage.  Ethephon + trinexapac-ethyl initiated at 50 GDD₅₀ averaged 45% coverage, and early treatments of ethephon initiated in January, February, and March averaged 6, 10, and 25% coverage, respectively.  Mefluidide + foliar iron averaged 48% seedhead coverage.  Similar trends were seen at Spotswood Country Club on April 26^th.  Ethephon early treatments initiated in January, February, and March averaged at 7, 6, and 18% coverage, respectively.  Ethephon + trinexapac initiated at 50 GDD₅₀ averaged 58% coverage, and mefluidide + foliar iron averaged 20% coverage with 10% turf injury.  The nontreated plots averaged 91% seedhead coverage.  These data suggest that January or February applications of ethephon can significantly improve seedhead suppression when applied with a 50 GDD₅₀ ethephon + trinexapac-ethyl program.        

Methiozolin is a new herbicide developed for the safe and selective removal of annual bluegrass from creeping bentgrass on golf course putting greens and fairways.  If annual bluegrass is controlled too quickly, it can leave voids in the putting green canopy.  The objective of this trial was to determine how quickly voided creeping bentgrass recovers following applications of methiozolin and as influenced by cultural practices common to golf course putting green management.  Two trials were initiated at the Glade Road Research Facility in Blacksburg, VA, on February 20, 2012 on ‘Penn A-1’ and ‘Tyee’ creeping bentgrass maintained at 0.4 cm.  The experimental design was a split plot with 6 cultural treatments as the main plots, and 3 methiozolin treatment programs as the sub-plots. All treatments were replicated 3 times on both ‘Penn A-1’ and ‘Tyee’ sites.  In addition to basic greens fertility, cultural treatments (main plots) are as follows: no cultural treatments, vertical mowing at 3 week intervals and increased fertility using a commercial foliar feed N+P+K product supplying an additional 6 kg N/ha (V+F), V+F where fertility increases over the base program are supplied by Floratine biostimulant products, V+F and trinexapac-ethyl (47 g ai/ha) applied at 200 GDD base 32 °F, V+F and seeding at 3 weeks after conclusion of methiozolin applications, and V+F and seeding at 6 weeks after conclusion of methiozolin applications.  Each sub-plot was treated as follows: no methiozolin treatment, methiozolin applied at 500 g ai/ha at two week intervals (6 total), and methiozolin applied at 1000 g ai/ha at 4 week intervals (3 total).  Voids were created in the canopy of each sub-plot by severing stolons then dabbing glyphosate to create 7 circles of dead bentgrass ranging in size from 1.9 cm to 12.8 cm diameter.  These circles served to mimic voids that would be left behind following control of annual bluegrass with methiozolin.  The biostimulant program provided the same level of macronutrients as other increased fertility programs.  Light-box images and normalized differential vegetative index (NDVI) were taken weekly and as the season progressed, biweekly.  Digital images were analyzed for percent green cover by isolating voided turf areas using an automated batch process in Adobe Photoshop and analyzing for green pixels using Sigmascan.

The interaction of methiozolin treatment and cultural treatment was not significant for percentage void recovery at 98 days after treatment (DAT) but both main effects were significant at P=0.05.  Thus, creeping bentgrass recovery seems to respond the same way to methiozolin treatments regardless of the cultural treatments applied and vice versa.  Methiozolin applied at 500 g ai/ha allowed turfgrass to recover more quickly when compared to the nontreated and methiozolin applied at 1000 g ai/ha.  The biostimulant program was the only program that allowed creeping bentgrass to completely recover the four smaller canopy voids by August 5.  When calculating the total turf recovery over all seven canopy voids, the biostimulant program recovered 87% of the lost canopy and significantly more than other cultural treatments. 

Abstract: Monitoring stations were established in April 2010 to
determine monoecious hydrilla growth and life stage as correlated to
water temperature and light intensity.  Five spatially separated
locations were established on Lake Gaston, NC and VA to enable
sampling across a gradient of conditions.  Another study location as
established on Lake Raleigh, North Carolina.  All six locations were
selected to avoid herbicide applications for hydrilla management.  At
Lake Gaston, fenced exclosures were built at the sample points, to
allow hydrilla to mature without herbivory from grass carp.  No grass
carp have been historically stocked in Lake Raleigh, therefore, an
exclosure was not necessary.  Temperature and light pendant data
loggers were placed at each location to record water temperature and
light intensity values every six hours throughout the year.  All sites
were monitored biweekly from April 2010 until late fall 2010, after
hydrilla senesced.  Data collected included hydrilla life stage,
hydrilla turion density, and hydrilla shoot length.  Soil cores were
collected and sifted to determine the number of tubers and turions.
In addition, tuber or turion sprouting was noted and length of sprout
was measured.  Stations were reestablished at the same points in 2011
and 2012, and monitoring continued until late fall 2012.  On Lake
Raleigh, monoecious hydrilla tubers were found sprouting from March
through July, with mean water temperature 28.1ºC for sprouting.  Newly
formed tubers were found in September through mid-October in 2010, at
mean water temperature 23.4ºC, and no newly formed tubers were found
in 2011.  On Lake Gaston, at the westernmost study location,
monoecious hydrilla tubers were found sprouting from April through
July, with mean water temperature 20.8ºC.  Newly formed tubers were
found in mid-August through October, at mean water temperature 25.4ºC.
 This study will enable the generation of a ‘story’ of the monoecious
hydrilla life cycle throughout the year. A predictive model will be
generated to allow lake managers to better time management practices
to the hydrilla life cycle based on environmental conditions. This
information will be crucial in creating monoecious hydrilla management
plans in North Carolina and elsewhere.

Palmer amaranth (Amaranthus palmeri) is a weed species that is found in almost all row crops in the southern United States farmland and is moving toward the northeast.  Due to resistance across many herbicides/ modes of action (for example glyphosate and ALS) in Palmer amaranth, new technologies and formulations are needed to properly deal with the problem at hand that many growers struggle with on a daily basis.  The research conducted in this study looks to utilize new chemical mixes of an herbicide and include alongside this herbicide with a plant growth regulator or metabolism inhibitor.  The modes of action looked at in this study are PPO or protox inhibitors, auxin growth regulators, and HPPD inhibitors, applied in combination with growth regulators such as uniconazole-P (14 g/ha), abscisic acid (140 g/ ha), salicylic acid (48.3 g/ha), jasmonic acid (157.08 g/ ha), a salicylic acid analog 2,6 dichloro-isonicotinic acid (13.44 g/ ha)(INA), diflufenzopyr (DFF)(0.56 g/ ha), alanap(560 g/ha), and cyclanilide (560 g/ ha).  The study was conducted in a greenhouse at North Carolina State University and the herbicides were applied at lower than field rates (lactofen at 2.24 g/ha, fomesafen at 5.49 g/ha, aciflurofen at 1.12 g/ha, 2,4-D at 79.81 g/ha, endothall at 14 g/ha, glufosinate at 34.75 g/ha  saflufenacil at 44.84 g/ ha, carfentrazone-ethyl at 7.84 g/ ha and mesotrione at 104.25 g/ ha) via a spray chamber.  Herbicide activity increase, compared to the specific herbicide in question alone, has been observed in fomesafen plus DFF or uniconazole-P, glufosinate plus INA or DFF.  Also a significant increase (α=.05) was observed with saflufenacil plus cyclanilide within 24 hours of treatment.  These combinations have a promising future in expanding the tools necessary to combat the growing resistance problem facing agriculture today, thus more research is needed to insure their success in the future.

Pokeweed (Phytolacca americana) Biology and Management in Pennsylvania Field Crops. K. Patches*, W. Curran; Penn State University, University Park, PA.

Common pokeweed is a perennial broadleaf weed with a large persistent taproot that is also capable of abundant seed production. It has become a frequent problem in agronomic crops in Pennsylvania. Traditionally, plowing was used to manage pokeweed; however, the wide-spread adoption of conservation tillage and a decline in the use of soil residual herbicides may have allowed pokeweed populations to increase in recent years.

Our objective is to identify opportunities to better manage pokeweed in corn, soybean, and other Northeast cropping systems. We believe that an integrated approach which includes both cultural and chemical tactics could be successful in conservation tillage systems. We are conducting a number of experiments that investigate the biology and control of common pokeweed in Pennsylvania. Plant biology experiments examined emergence periodicity, seed longevity, and plant growth and fecundity. Herbicide experiments were also conducted in both corn and soybean. For today’s presentation, we will report on some preliminary biology research and management results with herbicides in corn.

In the emergence timing experiment, pokeweed seeds were scattered in plots in the fall of 2011. Fifty berries, or about 500 seeds, were placed in each plot. Throughout the spring and summer of 2012, the number of emerged pokeweed seedlings were counted and removed every two weeks. Results show peak seedling emergence in mid-May, with new seedlings continuing to emergence through early October. The total number of seedlings counted in this first season only accounted for about 19 percent of the total number of seeds; the other 79 percent may have died, not yet germinated, or fallen prey to predators or diseases.

Corn herbicide efficacy experiments were conducted in State College, Pennsylvania, in 2011 and in Mt. Joy, Pennsylvania, in 2012. Herbicides were applied POST emergence to both the corn and pokeweed. The pokeweed ranged from seedling to about one meter in height. A total of 14 treatments were tested, including herbicides alone and in combination. Most treatments provided at least 80 percent control throughout the season and reduced biomass by 85 to 98 percent when compared to the control treatment. Combining glyphosate with another herbicide such as mesotrione, halosulfuron, or atrazine may be important especially for control of new seedling emergence.

With soybean prices remaining at historic highs, growers are willing to consider intensive management strategies to maximize yields and profits.  This includes the application of herbicides to soybeans for purposes other than weed control.  It has been suggested that the application of protoporphyrinogen oxidase (PPO) inhibitor herbicides to young soybeans can increase yields.  These herbicides are thought to damage the soybean apical meristem which stimulates increased lateral branching thereby increasing the number of reproductive nodes and potential yield.  However, published evidence of increased lateral branching resulting from early application of PPO herbicides is limited.  A small plot-study was initiated in 2012 at two locations in Kentucky to investigate the physiological effects of early-applied PPO inhibitor herbicides on soybean yield and yield components.  The studies were conducted in a randomized complete block design and maintained weed free.  Lactofen was applied to soybeans at 240 g ai ha^-1 at V2 and V4 as well as at 420 g ai ha^-1 at V4.  Aciflurofen and fomesafen were applied to soybeans at 600 grams ai ha^-1 and 420 g ai ha^-1 respectively at V4.  Treatments for comparison were an untreated control and a treatment where the soybean apical meristems were manually removed at V4. All treatments were conducted with no additional fertility and with an additional 168kg ha^-1 of nitrogen applied as equal parts urea and slow release encapsulated nitrogen applied at V4.  Branches plant^-1, pods plant ^-1, pods branch^-1, seeds m^-2, seed mass and seed yield were measured at harvest.  Additional nitrogen did not have an effect on any yield component or seed yield.  Removal of the apical meristem increased branches plant^-1 and pods branch^-1 but did not increase seed yield when compared to the untreated control.  Herbicide treatments did not change branches plant^-1.    The only herbicide treatment that significantly increased seed yield was lactofen applied at V2.  This yield increase resulted from an increase in seeds m^-2.  These analyses indicate any yield increase observed from applications of PPO herbicides to early vegetative soybeans may not be due to increased branching but because of other unknown mechanisms.  

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 and 2012 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 year, nitrogen source, and weed removal height effects were observed for corn yield. Differences based on year are not surprising considering the differences in weather patterns between the two seasons.  Significance based on source could also have been predicted due to the different sources being used with an organic source, and two synthetic sources one of which was a time release fertilizer.  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. 

Weed control remains a major challenge for economically viable sorghum production in North Carolina because sorghum is highly sensitive to weed competition during early growth stages. Moreover, herbicides able to suppress grasses are extremely limited due to sorghum sensitivity. Besides grass weeds, Palmer amaranth (Amaranthus palmeri) is one of the broadleaf weeds that may be the most problematic in sorghum production. As previously demonstrated by different studies, a potential response to improve weed control in sorghum production would be to narrow the spacing between rows and to increase the density at which sorghum is planted. Three separate field studies have been conducted in 2012 at the Upper Coastal Plain Research Station near Rocky Mount, NC, at the Caswell Research Farm near Kinston, NC, and at Clarkton, NC, to determine which row spacings and which plant populations would increase crop competitiveness sufficiently to allow the reduction of POST herbicide applications. The experiment has been conducted in a factorial arrangement of treatments in a randomized complete block design with row spacing (19, 38, and 76 cm), plant population (40,000, 80,000, 120,000, 160,000 plants, and 300,000 plants per acre), and herbicides (non-treated, PRE application of S-metolachlor at  1412 g ai.ha^-1 + atrazine at 1824 g ai.ha^‑1, and PRE application of S-metolachlor at 1076 g ai.ha^-1 + atrazine at 1390 g ai.ha^-1 followed by POST application of 2,4-D amine at 333 g ai.ha^-1) as main factors. Sorghum was rated for the percentage of Palmer amaranth, sicklepod (Senna obtusifolia), and large crabgrass (Digitaria sanguinalis) control 4 weeks after PRE,  and 1, 3 and 7 weeks after POST. Weed density and biomass were evaluated before harvest as well as yield at the harvest. Palmer amaranth control averaged 98% for both herbicide strategies at Clarkton and Rocky Mount. At Kinston, sicklepod control averaged 42% for PRE herbicide alone and 66% for PRE herbicide followed by POST herbicide whereas heterogeneity of large crabgrass infestation prevented to draw conclusions about the efficacy of the two herbicide strategies. Overall, Palmer amaranth density increased with wider row spacings. For 19 cm rows, its density decreased from 8 plants.m^-2 to 2 plants.m^-2 when sorghum population increased from 80,000 to 300,000 plants per acre. Its biomass has been primarily affected by plant population and reached a maximum dry weight of 1420 g.m^-2 for 76 cm rows and 40,000 plants per acre, and a minimum of 400 g.m^-2 for 19 cm rows and 300,000 plants per acre. Sicklepod control tended to increase with plant population for both the 19 and 38 cm row spacings. For 76 cm row spacing, percentage of control at a given date remained similar between the different plant populations. Sorghum yields were shown to present significant differences at Clarkton and Rocky Mount. The highest yields were associated with the combination of narrow rows (19 cm) and high plant densities (120,000 to 160,000 plants per acre). For both the 38 and 76 cm row spacings, 80,000 plants per acre produced optimal yields.

tebesanc@ncsu.edu

Weedy plant species in and around agricultural fields greatly increase the plant diversity in these ecosystems.  Plants provide necessary pollen and nectar resources for pollinators, and it is hypothesized that a more diverse plant community will support a more abundant and diverse pollinator community.  Apples are highly dependent on animal pollination to produce fruit, and with the decline of the European honey bee (Apis mellifera) from Colony Collapse Disorder there is increasing scientific and producer interest in promoting wild bee populations in apple orchards. 

We measured bee abundance and diversity in six Pennsylvania apple orchards weekly in 2011 from April to October using Solo brand bowl traps.  We also surveyed plant diversity and abundance in 0.1 ha plots in the orchard floor, an adjacent forested parcel, and the orchard-forest edge ecotone in the same six orchards.  We found that the edge ecotones were the most diverse plant communities, with a mean of 62.2 species, but highly variable, ranging from 36 to 86 species.  Orchard and forested plots had an average of 36.75 and 35.56 species, respectively.  For these six orchards plant diversity was not found to be a significant predictor of bee abundance or species richness, but was found to influence pollinator community composition.

         Field edges, old fields, and other semi-natural habitats in agricultural landscapes support diverse plant communities that help sustain pollinators and other beneficial insects. Plant communities in these habitats may be at persistent ecotoxicological risk from herbicides applied to crop fields. Recent innovations in herbicide-resistant crop biotechnology may lead to major increases in the use of the herbicides dicamba and 2,4-D. These herbicides selectively impact broadleaved plants, and non-target exposures may therefore lead to a net reduction in the functional diversity and floral resources provided by semi-natural habitats. In multi-year experiments at two sites (a field edge and an old field), we exposed replicated plots to low doses of dicamba designed to simulate herbicide spray drift. At the field edge site, we observed a significant decline in herbaceous cover (but not floral resource production) in plots treated with low doses (0.1% to 1% of the field application rate). At the old field site, drift-level doses did not affect the plant communities. Factors including the successional age of the plant community and water stress at the time of herbicide exposure likely explain the differing responses at the two sites to simulated drift. The response of natural plant communities to herbicide drift is complex and highly variable and warrants additional research.

Natural pines are a concern for both forest managers and utility R.O.W. managers. The more commonly used site preparation tank mixtures in the South do not provide consistent control of naturally occurring pine on regeneration sites. A variety of treatments containing Viewpoint, Streamline or Krenite were applied to areas containing naturally occurring loblolly pines 1-6 feet tall in September, 2011. Applications were completed using a CO2 - powered sprayer to simulate a helicopter  opertion and treatmentts were replicate three times in a randomized complete block deign. Pines and all hardwoods in treatment plots were recorded by species and height class prior to treatment application and 1YAT. Control varied by product and rate of application, and results for all treatments will be presented.

 A site near Atoy (Cherokee County), TX was selected for testing foliar treatments of Streamline and Viewpoint mixtures for the brownout and control of trumpet creeper, Japanese honeysuckle and greenbriar.  Seven treatments were tested.  Test treatments and ounces of product per acre rates were:  (1) MAT28+Escort XP (Streamline) 3.75+1.2+1% NIS, (2) MAT28+Escort XP+Arsenal (2SL)  (Viewpoint) 2.88+0.92+4.0+1% NIS, (3) MAT28+Escort XP (Streamline) +glyphosate 3.75+1.2+64+1% NIS, (4) MAT28+Escort XP+Arsenal (2SL)  (Viewpoint)+Roundup (SL 4.0) 2.88+0.92+4.0+64.0+1% NIS, (5) MAT28+Escort XP (Streamline) 3.75+1.2+1% MSO, (6) MAT28+Escort XP+Arsenal (2SL)  (Viewpoint) 2.88+0.92+4.0+1% NIS, (7) Surmount 2.0+0.5% NIS.  Treatments plots were 10-ft X 20-ft with an internal 10-ft evaluation plot leaving a 5-ft buffer on each end.  Three replications of all treatments were installed.  Treatments were applied on 7-Sep-12 using a Teejet XP Boomjet 10L nozzle and visually evaluated for brownout on 19-Oct-12.  Five weeks after treatment, trumpet creeper brownout was >77% and statistically similar for all herbicide treatments.  The untreated check had significantly less  brownout (33%).  Japanese honeysuckle brownout was best and similar for MAT28+Escort XP mixtures.  Brownout was numerically >90%.  Surmount brownout was 65%, significantly less than MAT+Escort XP mixtures and significantly greater than the untreated check.  Greenbrier brownout was highest (88%) by MAT28+Escort XP+glyphosate mixtures.  Other herbicide treatments were similar and intermediate with the untreated check exhibiting significantly least brownout (5%).  Control will be evaluated in September 2013.

Basal bark applications offer an alternative for herbicide application in areas where broadcast operations are not desirable. In the past, basal application have proven to be more effective that foliar applications using the same herbicide. In this study, MAT-28 (aminocyclopyrachlor) was applied in five different treatments to a variety of hardwoods growing in a loblolly pine stand in September, 2011. All treatments were replicated three times in a randomized complete block design. Prior to application and 1 YAT, all woody stems in the treatment plots were recorded by species and groundline diameter (GLD). Control was based on a percentage reduction of the stems by species at the 1YAT evaluation.  Statistical analysis was used to determine significance of responses and to sepaarate treatment means. Results will be presented to demonstrate variation by treatment, with some of the applications being very effective on the species on the site.

Industrial and right-of-way sites, such as guiderails, roadside signage and culverts, gravel yards, and railroad ballast areas are unique safety areas that require weed free accessibility in order to maintain sight distance, ensure proper drainage, eliminate fire hazards, maintain aesthetic value, while managing overall maintenance costs. Presently herbicide tank mixes are the cost-effective approach to eliminate existing weeds and ensure vegetation-free zones throughout the growing season. Bayer Environmental Science recently developed a new active ingredient, indaziflam, labeled as “Esplanade 200 SC” for this application.  Previous experiments have shown indaziflam to be effective in controlling a host of unwanted plant species.  Within two separate experiments, each repeated at two locations in central Pennsylvania, indaziflam was applied alone and combined with other non-crop herbicides to validate its efficacy at providing season-long control for a spectrum of plant species.  Additionally, pendimethalin and prodiamine were compared to indaziflam for bareground applications.

Treatments containing 73 or 102 g indaziflam/ha alone and indaziflam, prodiamine, or pendimethalin in combination with other non-crop herbicides provided excellent control of the species present throughout the growing season at all four locations.  The only significant differences noted for these three active ingredients were a decrease in kochia (Kochia scoparia) control for combinations of 73 g indaziflam plus 158 g sulfometuron plus 42 g metsulfuron/ha and 1679 g prodiamine plus 210 g imazapic plus 421 g glyphosate/ha compared to the best performing treatments.  Overall, both indaziflam and pendimethalin, where applied, provided season-long control in bareground situations and prodiamine also demonstrated effectiveness.  Continued investigation of these products with assorted rates, common tank mix partners, in a variety of sites, and for a host of target species will help to identify the weaknesses and strengths of these materials.

As trees and shrubs mature, they can cause sight-distance and safety issues on the roadside right-of-way.  The removal of these woody plants is a priority for the vegetation manager.  The most cost-effective approach is to eliminate woody vegetation while the populations are still young and beginning to establish.  Basal bark treatments are one option for controlling sparse populations of small caliper (less than 15.24 cm basal diameter), woody plants.  Once the trees begin to mature, removal is often necessary and cut surface herbicide treatments are used to reduce or eliminate the re-sprouting that can occur.  The active ingredient, triclopyr ester, found in Garlon 4 or Pathfinder II has a proven track record and is the standard herbicide used for both basal bark and cut surface treatments.  A newer active ingredient, aminocyclopyrachlor, has shown promise and is currently labeled and sold in premixes with other herbicides for controlling woody vegetation.  A formulation that includes 1 lb aminocyclopyrachlor/gal (MAT28 OL) and is more miscible in oil has been developed for basal bark and cut surface treatments.  The efficacy of this product was tested at 0.05, 0.10, 0.15, and 0.20 lb aminocyclopyrachlor/gal for basal bark and 0.005, 0.01, 0.02, 0.04, and 0.08 lb aminocyclopyrachlor/gal for cut surface and compared to 0.8 lb triclopyr/gal on a host of tree species using either treatment method.  All herbicides were mixed in basal oil.

In the basal bark study black locust (Robinia pseudoacacia), sugar maple (Acer saccharum), and red oak (Quercus rubra) were treated.  Both control and mortality were assessed and are reported.  Control values were based on the observed amount of chlorosis, necrosis, malformation, and loss of leaves while mortality reflects absolute defoliation of the canopy.  It was found that rates of 0.05 lb aminocyclopyrachlor/gal or greater provided control similar to the standard triclopyr treatment, except on black locust at approximately 1 year after treatment, YAT.  Black locust required a minimum of 0.10 lb aminocyclopyrachlor/gal to achieve similar results.  The mortality of black locust trees ranged from 70 to 100 percent at 1 YAT for trees treated with 0.10 to 0.20 lb aminocyclopyrachlor/gal or triclopyr.  However, mortality sometimes varied from the control ratings, especially for red oak with 20 to 80% mortality because treatments may have significantly impacted the canopy (control) but not completely defoliated the tree (mortality).  It would be prudent to evaluate these trees at 2 years after treatment to determine whether the lingering foliage was sufficient to allow survival of the trees, especially at the lower rates of aminocyclopyrachlor used.

The three species in the cut surface trial included red oak, red maple (Acer rubrum), and boxelder (Acer negundo).  At approximately 1 year after treatment, aminocylcopyrachlor caused 70 to 80% mortality (the complete absence of stump sprouts) on red oak and 100% mortality on boxelder when applied at a rate of 0.01 lb/gal and above.  Complete mortality of red maple stumps occurred only at rates of 0.04 lb aminocyclopyrachlor/gal or greater.  Triclopyr at 0.8 lb/gal caused 100% mortality to all three species tested.

Aminocyclopyrachlor (MAT28) is a new herbicide currently under development by DuPont Crop Protection. MAT28 belongs to the pyrimidine carboxylic acids (synthetic auxins). It provides a broad spectrum of activity on difficult to control weeds such as ALS and glyphosate resistant weeds with selectivity to most grasses. Blends of MAT28 with other herbicides including sulfonylureas, 2,4D and triclopyr are being evaluated for broadleaf weed control and crop safety of pasture grasses. Results of several trials across the country indicate an excellent control of cocklebur, sunflower, nightshade, wild carrot, clovers, thistles, wooly croton (0.5-2 oz ai/A), marestail, leaf spurge, common ragweed (1-2 oz ai/A), buttercup, dogfennel, horsenettle, spiny amaranth and ironweed (2-3 oz ai/A) among others. Additionally MAT and MAT blends have shown to be safe to the most common warm and cold-season grass species (Bermudagrass, Timothy, Bluegrass and Fescues). Registration for three aminocyclopyrachlor blends is pending.  

Spontaneous hybridization between Dalmatian toadflax (Linaria dalmatica ssp. dalmatica) (DT) and yellow toadflax (Linaria vulgaris) (YT), both aggressive invaders throughout the Intermountain West, was first reported in Montana in 2009; additional hybrid toadflax populations have since been identified in Idaho, Washington and Colorado. Although initiation of plant invasion has been repeatedly documented following hybridization between colonists or between a colonist and a native congener, the consequences of novel hybridization between two non-native species already exhibiting invasive behavior are less clear.  In a multi-year common garden experiment replicated at different latitudes, F1, BC1 and field-collected toadflax hybrids consistently grew larger, were more fecund, and had lower mortality than either parent species. In replacement series experiments, toadflax hybrids were highly competitive with both parent species, consistent with field observations of expanding hybrid toadflax populations displacing the parents.  With limited herbicide options for YT and DT, and unknown effects of novel hybrid genotypes on biocontrol agents currently used on YT and DT, hybrid toadflax may present significant management challenges.

Aminopyralid (Milestone^® herbicide) was developed by Dow AgroSciences for rangeland, pastures, and non-cropland weed management systems. The herbicide provides excellent efficacy against important noxious and invasive plant species and has a good fit in rangeland improvement, prairie restoration and pasture renovation programs. Aminopyralid is a pyridine carboxylic acid that is formulated as a 240 g acid equivalent (ae)/liter product and has an auxinic mode of action.  Aminopyralid has very low acute and chronic toxicity (practically nontoxic) to mammals, birds, fish, and aquatic invertebrates, with no evidence of teratogenicity, mutagenicity, carcinogenicity, or adverse endocrine or reproductive effects.  Aminopyralid is only slightly toxic to algae and aquatic vascular plants and substantially below EPA’s levels of concern for adverse effects on these organisms.  Aminopyralid has a very favorable environmental fate because of rapid degradation in soil (t_1/2 = 34 d) and photolysis in aquatic habitats (t_1/2 = 0.6 d) with CO₂ and NH₃ as the only metabolites.  Aminopyralid provides preemergence and postemergence control of many broadleaf noxious and invasive plants with little to no injury to most rangeland and pasture grasses.  Aminopyralid is effective at rates between 53 and 120 g ae/ha, which is about 1/4 to 1/20 of the use rates for currently registered rangeland and pasture herbicides including, 2,4-D, picloram, clopyralid, triclopyr, and dicamba. Invasive plants in the Acroptilon, Carduus, Centaurea, Chondrilla, Cirsium, Croton, Dipsacus, Hieracium, Hypericum, Leucanthemum, Melilotus,Microstegium,Onopordum, Pueraria, Senecio, Solanum, and Vicia genera are among those controlled by aminopyralid. In collaborative investigations with state and federal land management and research institutions, many native broadleaf plant species were determined to be moderately tolerant to tolerant to aminopyralid and their populations recovered following treatment. Many native cool-and warm-season grass species commonly used in restoration programs are tolerant to aminopyralid applied pre- and post-emergence. Aminopyralid serves as a catalyst to manage invasive plants and facilitate recovery of desirable plants when used as a component of integrated rangeland and grassland restoration systems.

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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?

For the second year, 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 (December 3, 2011) and the same 10 treatments applied in the spring (March 27, 2012) 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 9 inches tall at the fall application and 12 inches at the spring application. 

Visual percent seedhead suppression was assessed by comparison to the running check strips 16 (4/12/2012), 31 (4/27/2012), 54 (5/20/2012), and 83 (6/18/2012) days after spring application (DASA). Tall fescue color was assessed by comparison to the running check strips 16, 31, 54, and 83 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 at all assessment dates.  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 in both years.  Fall applications of four effective treatments ranged from 92 to 73% seedhead suppression 54 DASA.  This was more than in the previous year’s trial.  These same four treatments applied in the spring reduced seedheads from 100 to 85% 54 DASA.  The two spring applied treatments with 100% seedhead suppression, in both years, were GF-2703 (Dow AgroSciences) + aminopyralid and imazapic + 2,4-D.  Green color of these two spring applied treatments was less than the check strips 16 and 31 DASA.

Canada thistle (Cirsium arvense) is a common and aggressive perennial noxious weed found throughout the continental U.S. that spreads by seed and vegetatively.  Mowing is often the standard approach to curb seed dispersal; however, mowing does not prevent continued colony expansion by the root system.  The recent rise in fuel prices has prompted some highway department maintenance programs to reduce mowing cycles to manage and reduce operational costs.  The result has been a release of Canada thistle along roadways through both increased seed distribution and overall colony expansion.  In an effort to address Canada thistle expansion while effectively managing costs, a long-term study of alternative management strategies was initiated. This study consists of a two-season two-step program, a spring treatment of either mowing or herbicide applications, specifically chemical mowing treatments which included 2,4-D (1335 g ai/ha) + mecoprop-p (353 g ai/ha) + dicamba (123 g ai/ha). Followed by a fall mowing or application of one of the following herbicides or herbicide combinations; aminopyralid (123 g ai/ha), combinations of aminocyclopyralid (123 g ai/ha) and dicamba (140 g ai/ha) + diflufenzopyr (56 g ai/ha), or combinations of aminocyclopyrachlor (55 g ai/ha) + chlorsulfuron (22 g ai/ha) and dicamba (140 g ai/ha) + diflufenzopyr (56 g ai/ha) was undertaken in fall of 2010.  Two trial sites were established in central Pennsylvania with one in Lancaster county near the Mountville exit of SR 30 and the other in the Laurel Highlands of Indiana County near an entrance ramp to SR 422 near Indiana, PA.   Initial cover by Canada thistle was 5.5% and 44% at the Mountville and Indiana sites, respectively.  Approximately one year after initial treatment (370 days after initial treatment, DAIT, for the Mountville site and 362 DAIT for the Indiana site), all treatment sequences reduced Canada thistle populations compared to the initial stem counts.  At one year after the initial treatment, the number of Canada thistle stems was significantly lower at the Indiana site for plots treated with a fall herbicide application as compared to fall mowing.  This trend continued through a second season of evaluation and treatments.  It appears the incorporation of fall applied herbicide treatments enhanced the control of Canada thistle compared to mowing alone.  Mowing two times per season without the incorporation of herbicide treatments was effective only where turf and other existing vegetation was able to compete against the Canada thistle stand.  Overall, a competitive grass cover may have contributed to the effectiveness of the treatments at both sites.  Continued treatment and assessment of the sites will determine if complete elimination of the Canada thistle stand can be achieved and maintained.

Widespread occurrence of herbicide resistance in arable weed populations can be greatly attributed to the movement of resistance alleles from one field to another, through pollen and/or seed dispersal. In this respect, roadside habitats (including road shoulders, ditchbanks, and field shoulders) can serve as important corridors for the spread of herbicide resistance at landscape scales. Movement of equipment and seed transport are important avenues for the long-distance dispersal of resistant weed seeds to the roadside habitats. These latent populations can serve as sources of resistance alleles for pristine populations, as well as reservoirs for the persistence and further spread of resistance in the landscape. A survey was conducted in fall 2012 in the Mississippi Delta region of eastern Arkansas to understand the level of herbicide resistance in roadside populations of johnsongrass, Palmer amaranth, and barnyardgrass, three of the most important herbicide-resistant weeds in this region. Five hundred sites were pre-selected randomly using global positioning system waypoints. In total, 186, 353, and 425 populations were collected respectively for johnsongrass, Palmer amaranth, and barnyardgrass. The plants were established in greenhouse in a replicated pot trial and were treated with herbicides as per the label instructions. Barnyardgrass was treated with propanil, quinclorac, imazethapyr, and glyphosate, johnsongrass with glyphosate, fusilade, and nicosulfuron, and Palmer amaranth with glyphosate and pyrithiobac. Control for each treatment was assessed at 14 (barnyardgrass), 14 (Palmer amaranth), or 21 (johnsongrass) days after application and any surviving populations were subsequently treated with 4x the field rate. Preliminary and partial screening results suggest that herbicide resistance is more widespread in roadside arable weed populations than usually thought, particularly in Palmer amaranth where >95% of the tested populations survived the applications of glyphosate and pyrithiobac. This research urges the need for landscape-level considerations in herbicide resistance management.

Since the introduction of glyphosate tolerant crop varieties and the almost exclusive use of glyphosate to control weeds, the evolution of glyphosate resistance has increased dramatically. It is today in the Southeast U.S. the most important threat to cropping systems.

The response to the herbicide glyphosate of several Amaranthus palmeri populations, collected across the Southeast U.S., was studied and for most populations resistance was detected or confirmed in greenhouse dose response experiments. The analysis of EPSPS gene copy number revealed that almost all glyphosate resistant populations possessed variable but high EPSPS gene copy number which was also correlated with the resistance level observed in the greenhouse. In A. palmeri EPSPS gene amplification is the most common and most important resistance mechanism found so far as shown by its widespread geographical occurrence through the U.S. and by the high resistance factors conferred, but it is not the only resistance mechanism evolved by this weed species.

Molecular genetic diversity analysis of 8 glyphosate-sensitive and -resistant A. palmeri populations using Random Amplification of Polymorphic DNA (RAPD) markers reveals a heterozygosity between H_S = 0.10 and H_S = 0.18 within each Population based on between 78 and 164 polymorphic markers per population.  In an Analysis of Molecular Variance (AMOVA) a stronger relationship was found based on the response to glyphosate than based on geographical separation. The most genetic variation was found within each population (84 %). Around 2.3 % of the genetic variation was based on the different glyphosate resistance levels, while no significant influence of the geographic distance was found between glyphosate resistant and sensitive populations. This suggests that the glyphosate resistant populations share a more recent common ancestor with each other than with glyphosate sensitive populations.

These data indicate the occurrence of plant migration, in particular plant seed dispersal, among fields and regions. These findings stress the importance of farm and field hygiene for weed management to prevent introduction of herbicide resistance from other regions and to protect efficient crop production.

In Greece, a long history (more than 30 years) of glyphosate use and an increasing overreliance on this herbicide, with limited application of herbicides with a different mechanism of action, use of suboptimal glyphosate application rates, and little alternative integrated weed management approaches (such as crop rotation and use of mechanical weed control) have resulted in the development of glyphosate resistant Conyza spp. biotypes in perennial crops. The problems are especially focused on horseweed (Conyza canadensis) and tall fleabane (C. bonariensis). This presentation will provide data under development regarding: 1) characterization of seed germination patterns of contrasting biotypes; 2) the level of resistance on a large number of field collected biotypes from 11 regions and different perennial crops in Greece; 3) three years of field experiments with glyphosate mixtures in 4 perennial crops (olives, citrus, grapes, pomes); and 4) molecular studies to understand the mechanism of glyphosate resistance. Results from these studies could help understanding the mechanisms of glyphosate resistance, the ecophysiology of resistant biotypes and developing control strategies to manage and prevent glyphosate resistant Conyza spp. in perennial crops in South Europe.

            Canada fleabane (Conyza canadensis (L.) Cronq. var. canadensis) is a surface-germinating ruderal facultative winter annual with recruitment that is highly susceptible to changes in microsite conditions.  Temperature and light play the largest roles in germination and emergence timing of this species.  Base germination temperatures for Canada fleabane are unknown and have only been estimated at 13⁰C in a Knoxville, Tennessee population.  In this experiment the germination of Canada fleabane germination was investigated using the Thermo-gradient Plate (TGP) at the University of Saskatchewan in Saskatoon, SK, Canada in January and February of 2012. The TGP machines consist of 96 and 176 individually controlled cells that are accurate within 0.1⁰C.  An international collection of seed from varying climatic zones was used.  Seed sources included populations from San Joaquin Valley, CA, Hertfordshire, UK, Shiraz, Iran, and Southern Ontario, Canada. Seeds from each of the 4 populations were counted and counted and placed into 40 petri dishes with wet filter paper within the Thermo-gradient Plate cells. The seeds were subjected to temperatures from 6.5-20⁰C at 1.5⁰C increments. Cumulative daily germination counts for 30 days were recorded.  Results indicated that temperature and source have a significant effect on germination.  Base germination temperatures were significantly different between all populations (Ontario (~9.5⁰C), Iran (~11⁰C), Spain (~14⁰C), UK (~12.5⁰C)) as well as literature values.  The results suggest a genetic difference between these international populations and suggest rapid evolutionary change since the introduction of Canada fleabane to Europe and the Middle East 200-300 years ago.   The results also have implications for management especially in no-till situations where Canada fleabane populations are the most problematic.  Germination at such low temperatures may require altered approaches to controlling this species.

Genotypic analysis was conducted on an F2 segregating prickly lettuce population to discover genetic regions linked to traits associated with weediness. A total of 461 EST-SSR derived primers were screened against the crossed parents. Of the screened markers, 89 polymorphic markers were selected and used to create a genetic linkage map. Three markers were not linked to any linkage group and five dominant markers did not map leaving 81 mapped markers in 12 linkage groups. Seventeen phenotypic measurements were taken from three main categories, phloem chemical components, leaf measurements, and growth patterns. Interval mapping (IM) and multiple QTL mapping (MQM) identified several QTL in the mapping population that had significance based on LOD score thresholds. Leaf perimeter and leaf lobbing, similar traits, both had QTL on Grp 8 near markers WSULs-102 and WSULs-212. Stem counts and growth habit both had a similar QTL on Grp 4 near marker WSULs-304. Herbivory which was scored as plants that had been grazed or not grazed, most likely by deer, had a surprising QTL on Grp 8 between markers WSULs-12 and WSULs-21. Rubber molecular weight, a component of prickly lettuce phloem, had a QTL on Grp 8 near markers WSULs-21, WSULs-374.2, and WSULs-210. The discovered QTL and the corresponding local markers are genetic resources for understanding traits that confer weediness in prickly lettuce.

Carbon dioxide (CO₂) is a principle resource for plant growth; as such, the ongoing increase in its concentration may differentially affect the growth of cultivated and wild types of the same species.  In this presentation I will provide a summary of work related to selection of feral and domesticated cereal lines to recent and projected changes in atmospheric carbon dioxide. Specifically, I will discuss the evidence for wild lines having a greater response, and outline the next steps in a comprehensive selection/breeding program.  Overall, this approach may provide a straightforward, short-term approach to begin adaptation of crop production to an uncertain climate.

Often in predicting the response of weeds or crops to rising CO₂, photosynthetic pathways are used.  How different photosynthetic pathways respond to rising levels of atmospheric carbon dioxide (CO₂) is particularly relevant to crop/weed interactions in agricultural systems; in part because many of the most troublesome weedy species are C₄ plants, while a number of major crops are C₃ plants.  However, in this overview I will discuss a number of relevant studies that examine both crops and weeds, and both types of pathways.  I will discuss recent findings demonstrating that while C₃ vs. C₄ pathway is relevant from a biochemical standpoint, photosynthetic pathway per se, may not be a good indicator of predicting crop-weed competitive outcomes at the whole plant or field level in a future, higher CO₂ environment.

Although recent and projected increases in anthropogenic carbon dioxide are likely to alter plant phenological development, these changes have not been quantified in terms of floral outcrossing rates or gene transfer.  Yet, such rates, particularly between genetically altered crops and wild relatives, could increase the spread of novel genes, potentially altering evolutionary fitness.   Here we show that increasing CO₂, from an early 20^th century concentration (300 µmol mol^-1) to current (400 µmol mol^-1) and projected (600 µmol mol^-1) values, increased the flow of genes from wild, weedy rice to the genetically altered, herbicide resistant, cultivated population, with outcrossing increasing from 0.22% to 0.71% over the range of CO₂ values.  The increase in outcrossing and gene transfer was associated with differential increases in plant height, as well as greater tiller and panicle production in the wild, relative to the cultivated, population.  In addition, increasing CO₂ also resulted in a greater synchronicity in flowering times between the two populations.  These results demonstrate that increases in anthropogenic CO₂ per se can alter phenological development with subsequent changes in outcrossing and the direction of gene flow.  These observed changes resulted in a subsequent increase in rice dedomestication, and a greater occurrence of weedy, herbicide-resistant hybrid progeny.  Given the genetic similarity between crop species and feral populations often found in agroecosystems, the ongoing increase in atmospheric CO₂, and differential responses to that increase, could result in a greater flow of novel genes between populations. 

Jointed goatgrass (JGG) is a difficult to control winter annual grass weed, which infests winter wheat (Triticum aestivum L.) in the Pacific Northwest and Great Plains of the USA. Wheat (2n = 6x = 42; ABBDD) and JGG (2n = 4x = 28; CCDD) are genetically related and have a common ancestor, which donated the common D genome. Thus, wheat and JGG can cross and produce hybrids and backcross generations. Clearfield wheat varieties carry the Imi1 gene, which confers resistance to the imidazolinone (IMI) herbicide imazamox. The advent of IMI-resistant wheat varieties raised the question of how quickly gene flow between IMI-resistant wheat and JGG would occur. In 2008, IMI-resistant wheat by JGG hybrids (F₁) were identified in a commercial wheat field in Eastern Oregon. In 2009 and 2010, surveys were conducted in Eastern Oregon in order to understand how widespread the imazamox-resistant hybrids were. Tissue and spikes from hybrids were collected and PCR assays were performed in order to detect the presence of the Imi1 gene. Average hybrid seed production was assessed. A total of 128 sites were surveyed in the two years, and 57.4% of them had at least one hybrid plant. Of 1,216 hybrids that were analyzed, 921 were IMI-resistant. We processed more than 2,500 hybrid spikes to determine seed production. The average seed number produced per plant was 1.5, although there were plants that had higher seed number, which indicated the possibility of having backcross generations among the hybrids. Our results demonstrate that the Imi1 gene is moving from IMI-resistant wheat to hybrid plants and potentially to backcross generations. This movement is taking place not only in commercial wheat fields with a history of IMI-resistant wheat but also in non-crop sites close to these fields. Information about site management and JGG control history will help predict hybrid occurrence and spread of the imazamox resistance trait from Clearfield wheat.

Weedy rice is a difficult to control con-generic weed of Oryza sativa (crop rice).  Until 2003, weedy rice was not present in California since eradication in the 1970’s. In contrast, weedy rice has never been eradicated and persists as a very serious weed in the southern U.S., especially in Arkansas, Louisiana, and Mississippi. California weedy rice (CAWR) is genetically distinct from sampled AA genome Oryzas.  Coalescent-based divergence population genetics analyses of STS loci sequences and molecular evolution analyses of candidate genes indicate that CAWR is most recently diverged from the O. sativa subgroup temperate japonica rice which is cultivated in California.  This suggests that a newly derived weedy red rice biotype differentiated from a cultivated ancestor, in contrast to how weedy red rice biotypes in the southern U.S., which appear to derive from global import of weedy genotypes.  Our results indicate that CAWR is a newly established, weedy rice population distinct from other weedy rice in the U.S. and from the globally-sampled Oryzas. Together, these results suggest that CAWR represents a potential feralized genotype from cultivated rice.

Common waterhemp and Palmer amaranth are troublesome pigweed species that can reduce crop yields significantly.  They are both dioecious species and can produce more than one million seeds per plant.  Common waterhemp was first confirmed to be resistant to glyphosate in northeast Kansas in 2006.  Glyphosate-resistant Palmer amaranth is a major problem in the southeastern United States, but has not been previously confirmed in Kansas.  The objective of this research was to document the presence and scope of glyphosate-resistant common waterhemp and Palmer amaranth in eastern Kansas.  Seed from 15 populations of common waterhemp and 8 populations of Palmer amaranth were collected from soybean and cotton fields throughout eastern Kansas in the fall of 2011.  Seed was threshed and placed in storage at -5ºC until planted.  Seed was sown into separate flats and allowed to germinate.  Susceptible check populations of each species were grown simultaneously.  Individual seedlings were transplanted into 0.25 L pots when plants were at the cotyledon stage of growth and watered as needed.  Plants measuring 10 to 14 cm in height were treated with glyphosate at rates of 0, 840, 1,680, and 3,360 g ae ha^-1, respectively.  The experiment had a randomized complete block design with 8 replications and was repeated.  Percent injury and mortality was determined 7 and 14 days after treatment (DAT) where 0 = no effect and 100 = complete plant death.  Glyphosate effectively controlled the susceptible check populations resulting in complete plant mortality.  However, multiple populations of common waterhemp survived applications of glyphosate up to 4 times the suggested use rate.  Visual injury varied 10 to 100% depending on the population, and rate.  Two populations of Palmer amaranth showed similar resistance characteristics, with some plants surviving 4 times the suggested use rate of glyphosate.  Glyphosate-resistant common waterhemp is present across much of eastern Kansas and appears to be spreading.  Glyphosate-resistant Palmer amaranth is now present in south central Kansas and will likely become more widespread in the future.     

Conservation agriculture (CA) practices are threatened by glyphosate-resistant Palmer amaranth. Integrated control practices including PRE herbicides and high-residue CA systems can decrease Amaranthus emergence. Field experiments were conducted from autumn 2006 through crop harvest in 2009 at two sites in Alabama to evaluate the effect of integrated weed management practices on Amaranthus population density and biomass, cotton yield, and economics in glyphosate-resistant cotton. Horizontal strips included four CA systems with three cereal rye cover crop seeding dates and a winter fallow (WF) CA system compared to a conventional tillage (CT) system. Additionally, vertical strips of four herbicide regimes consisted of: broadcast, banded, or no PRE applications of S-metolachlor (1.12 kg ai ha⁻¹) followed by (fb) glyphosate (1.12 kg ae ha⁻¹) applied POST fb layby applications of diuron (1.12 kg ai ha⁻¹) plus MSMA (2.24 kg ai ha⁻¹) or the LAYBY application alone. Early-season Amaranthus density was reduced in high-residue CA in comparison to the CA WF systems in 2 of 3 yr. Amaranthus densities in herbicide treatments that included a broadcast PRE application were lower at three of five sampling dates compared to banding early-season PRE applications; however, the differences were not significant during the late season and cotton yields were not affected by PRE placement. High-residue conservation tillage yields were 577 to 899 kg ha⁻¹ more than CT, except at one site in 1 yr when CT treatment yields were higher. CA utilizing high-residue cover crops increased net returns over CT by $100 ha⁻¹ or more 2 out of 3 yr at both locations. High-residue cover crop integration into a CA system reduced Amaranthus density and increased yield over WF systems; the inclusion of a broadcast PRE application can increase early-season Amaranthus control and might provide additional control when glyphosate-resistant Amaranthus populations are present.

Waterhemp (Amaranthus tuberculatus) and Palmer amaranth (Amaranthus palmeri) are annual weeds reducing the yield of several crops including maize, soybean and cotton and are mainly present respectively in the midwestern and the southern United States. Resistance to herbicides that inhibit acetolactate synthase (ALS), photosystem II (PSII), protoporphyrinogen oxidase (PPO) and glyphosate has been observed as well as multiple resistance stacked in populations. Herbicides that inhibit 4-hydroxyphenylpyruvate dioxygenase (HPPD; EC1.13.11.27) provide a solution with an alternative mode of action (MoA) to control Amaranthus weeds. Their broad-spectrum weed control and excellent crop tolerance are key factors to their integration into maize and other crop production systems. The evolution of HPPD resistance will increase the complexity of Amaranthus weed control. A better knowledge of the mechanism(s) of HPPD inhibitor resistance will allow the design of fast diagnostic tests. Among several mechanisms, herbicide resistance occurs often via the metabolism of the herbicide in the resistant plants or the selection of plants showing mutation(s) in the gene(s) encoding the target enzyme. The metabolism of HPPD inhibitors was studied in Amaranthus plants. Gene(s) encoding HPPD were cloned and sequenced.  Differences in the metabolism of an HPPD inhibitor between a sensitive and an HPPD resistant Amaranthus biotype will be presented.

Organic and low-external-input farmers typically focus their weed management efforts on seedlings, relying on early cultivation events to reduce weed density and thereby crop yield loss.  Late in the season, weeds are often ignored, and abundant seed rain perpetuates the weed problem.  Furthermore, fall cover cropping is widely recommended to protect the soil from erosion and to capture excess nutrients.  Despite these benefits, an unintended consequence of fall cover cropping is burial of weed seed rain, likely protecting seed from predation.  To test this hypothesis we examined the effects of several post-harvest weed management strategies on weed seedbanks in Maine: 1) flail mowing weeds and crop debris; 2) flail mowing followed by no-till cover crop sowing; 3) fall tillage and cover crop sowing; 4) a zero-seed rain (ZSR) control; and 5) moldboard plowing.   Treatments 1-4 were examined over four years (2007-10), while treatment 5 was added only in the final year of the study.  Unexpectedly, flail mowing, with or without a cover crop, did not reduce the germinable weed seedbank compared to a tilled cover crop.  The ZSR control consistently resulted in the lowest spring germinable weed seedbank, except in the final year of the study, where ZSR and moldboard plow similarly reduced the seedbank compared to other treatments.  Mesh exclosures were used to measure the effects of predators on the seedbank, over the period from September to May each year.  Predator effects were large, but inconsistent, causing a 42% reduction in the germinable weed seedbank in one year, but no effect in the remaining three years.  This large, but variable effect of predation warrants further research to describe the sources of intra-annual variation.  Also, diversified vegetable farmers could exploit the large and consistent effect of ZSR: short-season crops can both produce a marketable crop and preempt weed seed rain. 

Weeds are a major challenge for organic farmers, yet we know little about the factors influencing organic farmer weed management decisions. We hypothesized that 1) farmers and scientist “experts” differ in fundamental areas of knowledge and perceptions regarding weeds and weed management and 2) farmer knowledge and perceptions are associated with their on-farm weed pressure. An expert mental model was constructed primarily from interviews with research scientists and extension professionals. We interviewed 23 organic farmers in northern New England, yielding farmer mental models to compare to the expert model. To characterize weed pressure on each farm, we collected 5 soil samples from each farm and measured germinable weed seedbank density. Farmers demonstrated knowledge of the major concepts discussed by experts regarding ecological weed management, but differed in emphasis. Farmers placed less emphasis on ecological complexity than experts and more emphasis on managing the weed seedbank. Farmers emphasized the role of experience, both their own and that of other farmers, rather than knowledge derived from scientific research. Weed seed density per farm ranged from 2,775 seeds per m-sq to 24,678 seeds per m-sq to a soil depth of 10 cm. Farmer knowledge and perceptions were associated with on-farm weed seedbank densities. Farmers who mentioned the risks of weeds more often, for instance biological competition and harvest interference, had lower seedbank densities. Farmer knowledge was negatively associated with seedbank density. Targeted education efforts could potentially lead to improved success of ecological weed management in the future.

Effects of Soil Fertility and Tillage on Weeds in Long-Term Organic Grain Cropping Systems Experiments. M. R. Ryan*; Cornell University, Ithaca, NY. 

Long-term experiments that compare different cropping systems are useful for understanding how weeds respond to various crop and soil management practices over time. Research on organic cropping systems is particularly interesting because of the inherent challenge of managing weeds without synthetic herbicides. Organic cropping systems experiments also provide the opportunity to test the effects of physical and cultural practices that can be employed to manage herbicide-resistant weeds and reduce the potential for water pollution and non-target effects from herbicides. In this research, results from several long-term organic grain cropping systems experiments are compared in order to synthesize information about the effects of soil fertility and tillage practices on weed management. Specifically, strategies are explored that address the weed management–soil quality paradox: although effective weed management and enhancement of soil quality are both necessary components of sustainable crop production, practices focused on enhancing one component often inhibit the other. Results suggest that simply increasing the rate of soil amendments favors increased weed growth, but that integrating perennial legume forage crops into crop rotations can effectively decrease weeds and increase organic grain crop yields. Management strategies that reduce soil tillage frequency can perform as well as, or better than, standard organic practices, but low weed seed bank densities, experience with reduced-tillage crop and soil management, and proper equipment are essential to maintain low weed populations and high organic crop yields. 

Impact of a two year crop rotation and mechanical control on weeds in tomato

Carolina Zamorano-Montañez ¹, Kevin Gibson¹

Limiting weed seed production by late emerging weeds can be a particular challenge in fresh market tomatoes. A split plot experiment was conducted in 2011 and 2012 to evaluate the effect of crop rotation (tomato –soybean, soybean-tomato) and seeding a cover crop between crops rows late in the growing season on weed growth and crop yields.  The clover subplots were mowed in both years but clover establishment was poor in 2012 due to drought conditions.  Additional subplot treatments included removing all weeds every two weeks to prevent any seed production and only removing weeds during the first 6 to 8 weeks (control).  Weed biomass at the end of the 2011 growing season in the clover plots was less than 30% of biomass in the control treatment for tomatoes.  However no differences were detected between the mowing and critical period treatments in 2011 for soybeans; weed biomass was low for both treatments. The clover treatment reduced weed biomass in both tomatoes and soybeans in 2012 relative to the control. Tomato yields were lower in both years in the clover plots than in the control; soybean yields were not affected by mowing.  The mechanism by which the tomato yields were reduced is unclear but warrants further research. 

 ¹ Graduate Student and Associate Professor, Botany and Plant Pathology Department, Purdue University, West Lafayette, IN 47907.Correponding author’s E-mail: czamoran@purdue.edu

Resistance is a biological phenomenon that results from environmental selection on the genetic diversity of living organisms; it is also universal and has been found in bacteria to antibiotics, fungi to fungicides, insects to insecticides, and plants to herbicides.  Random mutations are common and resistant genes likely already exist in weed populations.  Under selection by the environment the best adapted plants will leave more offspring; thus, when an herbicide is present in the environment, any plants resistant to that herbicide will be best adapted, survive, and leave more offspring than susceptible plants.  Resistant plants are thus genetic variants of the same species as susceptible biotypes.  Although resistance is widespread among weeds, our research suggests that selection of resistance is not random but exhibits some taxonomic and life history bias.  All agricultural practices, including non-chemical ones, have the potential to kill weeds that are susceptible and select weeds that are best adapted to those practices.  The result of this selection can be very rapid evolution (genetic change within populations of a species) or very rapid succession (shifts in entire species to others that are better adapted to the agricultural practices).  In addition to evolution of herbicide resistance, there are many examples of rapid weed succession that have been observed in a variety of cropping systems.  Any herbicide chemistry or use pattern that increases selection pressure on weeds constitutes a high risk for evolution of resistance.  The general principle that should guide all weed management is to reduce the selection pressure caused by repeatedly using the same method of control (chemical or non-chemical).  In other words, care should be taken to manage selection pressure on weeds.

Since 2009 the National Institute of Food and Agriculture and the Agricultural Research Service of the US Department of Agriculture have collectively invested more than $19 million in research, education and extension programs that focus on herbicide resistant weeds.  Has this been a wise investment?  How would one measure success for these programs?  These are critically important questions considering the increasingly tight federal budgets and the role of accountability.  This presentation will focus on possible metrics of success for programs on herbicide resistant weeds, and how those metrics might be viewed by scientists, program administrators and policy makers. 

Weed resistance is not a new problem. As production agricultural practices have developed, grower practices continually select for the weed species best adapted for each system. However, with changes in production agriculture toward large farm size, reduced tillage, and reliance on herbicides and herbicide resistant crops, the evolution of weeds resistant to herbicides has had a devastating impact on production. This problem is a game changer. Experts differ in opinion regarding how to best address this problem of herbicide resistant weeds.  However, weed scientists agree that research is needed to understand the biology of these driver weeds and to develop integrated strategies for management based on identified vulnerabilities in the life cycle of each species and aimed at reducing selection pressure. Best Management Practices have been developed based on our current knowledge and growers recognize the need to diversify weed management practices. However, adoption of diverse practices on a wide scale has been hindered by a number of issues.  Poor adoption of best management practices has been driven in large part by sociological, management and economic realities and regulatory/farm program constraints.  Best Management Practices need to be adapted by experts to fit with regional and local practices.  In addition, extension outreach is critical to providing growers and consultants with the knowledge to adopt diverse practices. New technologies are being developed which may provide much needed and innovative tools for managing herbicide resistance within production agriculture.  However, these tools will need to be integrated into diversified production practices designed to reduce selection pressure on specific weed populations. Weed scientists must also develop collaborative research programs with economists and social scientists.  Research is critically needed to understand the financial, time management and behavioral constraints that have reduced widespread adoption of Best Management Practices by the grower community. We need broad, interdisciplinary and public/private sector collaboration to develop program and market options that address herbicide resistance on both a farm and area-wide basis but do not compromise other conservation, environmental, and economic goals.

A design for selecting novel biocontrol agents from soil. K. Panke-Buisse*, J. Kao-Kniffin; Cornell University, Ithaca, NY.

Advancements in the study of plant-associated microorganisms offer new sources of biocontrol agents for weed management. The greatest challenge has been the isolation of single microbial strains responsible for weed control from a pool of hundreds of potential microbial species.  We developed a method for the artificial selection of microbial communities that induce a controlled effect on plants. We used flowering regulation in a model dicotyledonous weed, Arabidopsis thaliana, as the controlled effect demonstrating how plant-associated microorganisms alter plant performance. After 10 generations of selection for diverging flowering times, we analyzed the soil microbial community for population changes using 16s bacterial community profiling. The plant and soil methods included analysis of soil extractable nitrogen (ammonium and nitrate), plant tissue C:N ratios, soil extracellular enzymes, and ¹⁵N isotopic analysis. We found a highly significant difference in both carbon- and nitrogen-accessing soil enzymes between the early and late flowering communities. The ¹⁵N isotopic values of soil and plant tissues, along with plant tissue C:N ratios added additional support for the concept of microbial coordination in soils driving flowering regulation. The 16s bacterial profiling analysis is still in progress, and should allow us to assess changes in population structure between the divergent flowering times. Analysis of the culturable members of the enriched microbial communities (also in progress) will allow us to test isolated strains responsible for flowering regulation. The preliminary findings demonstrate the abilities of selected soil microbial communities to control plant traits and performance. The selection method shows promising potential for isolating biocontrol agents from soil. Corresponding author: jtk57@cornell.edu

 The Sustainable Dairy Cropping Systems Project is an interdisciplinary experiment consisting of two diverse six-year crop rotations designed to produce all feed, forage, and fuel to sustain an average-sized Pennsylvania dairy herd. Managing weeds in these diverse mostly no-till rotations with less herbicide is our focus.  For this presentation, we will discuss an integrated strategy to control weeds in no-till corn (Zea mays L.) and soybean (Glycine max L.).  The ‘Standard Herbicide’ (SH) treatment in these crops employs an herbicide-based program to manage weeds, while the ‘Reduced Herbicide’ (RH) treatment uses less total herbicide by incorporating herbicide banding, growing a weed suppressive cereal rye (Secale cerale L.) cover crop, and using high residue inter-row cultivation for post weed control. Corn is seeded in 76 cm rows; soybeans are seeded in 76-cm rows in the RH treatment and in both 19 and 76-cm in the SH treatment.  The experiment was initiated in 2010 and we are reporting on results from two crop entry points (corn and soybean) repeated twice since 2010.

For no-till corn, weed control was better in SH vs. RH management in one of three years, although weed biomass never exceeded 21 g*m^-2, generally not enough to impact yield.  In fact, corn grain yields were equal in SH and RH management all three years indicating that differences in weed management did not impact yield.

Over three years, weed control in soybean was either equivalent or better in SH vs. RH management.  Only in 2011, was weed biomass greater in RH vs. SH management, although end of season dry matter levels were still less than 100 g*m^-2.   Achieving adequate soybean plant populations proved to be problematic in two of three years and drilled soybean were reseeded in both 2011 and 2012.  Soybean populations in 76 cm rows were reduced in 2012.  Soybean grain yield was reduced in 2011 and 2012 in RH management compared to SH 19-cm row soybean.  However, differences in weed control were likely not responsible for the differences in observed yield, but rather reduced soybean population, differing planting dates, and depleted soil moisture reserves resulting from inter-row cultivation may have contributed to these differences. 

The “roll-killed” cover-crop system has been successful in reducing weed pressures in organic soybeans.  This study examined six-rye cultivars as cover crops to determine which were most suitable for use in the rye roll-killed organic soybean system for the Southern US.   Six rye cultivars, three facultative, non-winter hardy Southern cultivars, and three non-facultative, winter hardy Northern cultivars, were planted at three locations over the 2009 and 2010 growing seasons.  Non-facultative winter hardy rye cultivars require vernalization offered by a fall planting in order to complete their life cycle.  However, facultative rye cultivars do not require vernalization to complete their lifecycle and can be planted in spring or fall (Reberg-Horton et al., 2003).  Each rye cultivar was roll-killed at soft-dough and soybeans (Glycine Max L. ‘NC Roy’) of maturity group VI were planted on two separate dates (i.e. early and late roll-kill).  Favorable weather through out the 2009 growing season combined with early rye planting resulted in all rye cultivars being roll-killed with 100% kill rating for both dates. All rye cultivars produced greater than 9000 kg ha^-1 rye biomass with exception of Rymin at Tidewater.  Weed control during the 2009 growing season was excellent and there was no rye cultivar effect on soybean yield.    Due to an unseasonably cold and wet winter, after the early roll-kill date in 2010, only the Southern cultivars were rated at 100% kill.  Northern cultivar Aroostook, a Northern cultivar, along with all the Southern cultivars were the only rye cultivars rated at 100% kill by the late roll-kill date.  Weed pressures were more variable during 2010. Wheeler, despite producing sub 9000 kg ha^-1 biomass, had the lowest broadleaf densities, which could be explained by Wheeler’s reported allelopathic activity.  Soybean yield in 2010, was modeled with rye biomass (kg ha^-1) and soybean stand count (counts m^-1) where rye biomass and soybean stand count were used as covariates.  Due to a dry and hot summer, soybean stand count negatively effected soybean yield during the late roll-kill date.  Overall, Wheeler was found to be the most suitable rye cultivar for organic soybean production using the roll-killed system in the Southeast US based on its good biomass production, allelopathic properties, and a termination date that closely synchronizes with soybean planting dates (Mid May-June).

Cover crops have a crucial role to play in reducing tillage in organic grain production systems.  Crop rotations that prioritize timely fall cover crop planting and allow for adequate biomass accumulation in spring prior to termination with a roller-crimper eliminate the need for spring tillage.  In these reduced-tillage organic rotations, the cover crops included must be winter hardy, grow quickly in the spring, and be susceptible to control with a roller-crimper.  Hairy vetch (Vicia villosa) is a leguminous species currently under investigation as a cover crop before corn in a 3-year organic rotational no-till cropping systems experiment being conducted in central Pennsylvania, central Maryland, and southern Delaware.  In 2011 and 2012, a hairy vetch cover crop was terminated at three different phenological stages and vetch biomass was collected.  Hairy vetch biomass ranged from 3342-6415 kg ha^-1 and from 4455-6083 kg ha^-1 in Delaware in 2011 and 2012, respectively; from 4152-6680 kg ha^-1 and from 5880-6438 kg ha^-1 in Maryland in 2011 and 2012, respectively; and from 5258-5336 kg ha^-1 and from 4396-5479 kg ha^-1 in Pennsylvania in 2011 and 2012.  Growing degree days alone was a significant predictor (p<0.0001) of hairy vetch biomass and explained 18.14% of the variation in vetch biomass when all sites and both years were included in the regression.  Warmer-than-average spring temperatures in 2012 did not appear to result in vetch maturing earlier in 2012 than in it did during the cooler spring of 2011.  In 2012 two weeks after vetch termination by rolling, percent control of the cover crop was visually estimated and regrowth biomass was collected.  Hairy vetch regrowth declined as vetch maturity at rolling increased with, for example, regrowth amounts of 173, 87, and 18 kg ha^-1 observed for the early, intermediate, and late termination timings, respectively, in Pennsylvania.   The influence of hairy vetch maturity at termination on control differed by site and resulted in varying levels of control achieved by rolling-crimping.  Until a number of management challenges posed by including hairy vetch in an organic grain rotation are resolved, adoption of hairy vetch in such rotations will be limited.

The objectives of my research are to: (1) determine the reproductive growth stage at which three summer annual weeds can be terminated and still produce viable seeds; and (2) quantify the effect of termination method on the viability of the weed seeds produced. Three common summer annual weed species: Abutilon theophrasti Medic. (velvetleaf), Chenopodium album L. (common lambsquarters) and Setaria faberi Herm. (giant foxtail) were used in this study. Plants of the three weed species were grown under greenhouse conditions. The flowering phenology of each plant was recorded throughout the experiment. Each species was classified according to four or five developmental stages based on their seed or capsule color or days after flowering (DAF). Three cutting methods were used for each weed species: (a) cutting the entire plant from its base and leaving the plant material to dry on the greenhouse bench, (b) individual capsules (velvetleaf) or inflorescences (common lambsquarters and giant foxtail) were harvested and left to dry on the greenhouse bench, and (c) capsules or inflorescences were harvested and seeds tested immediately for germination and viability. After four weeks, seeds from plants in treatments (a) and (b) were cleaned and tested for germination and viability testing. For freshly harvested seeds in treatment (c), seeds within each capsule or inflorescence were divided into three groups for germination, viability testing and observations on morphology. Velvetleaf seeds from the first stage of development (2-6 DAF) were not viable. Viability began to appear during the second development stage (7-13 DAF), and reached 100% during the third (14-16 DAF) and later stages of development. However, the rate at which full viability was approached differed significantly among treatments, with speed of development ranked c> b> a. In common lambsquarters, black-colored seeds were viable and poorly developed brown-colored seeds were not viable. This species did not produce seed at 3 DAF and seeds from 13 DAF had lower viability than later stages of development. Seeds of S. faberi at 0 and 5 DAF were not viable, but seed viability increased from 15 DAF to 20 DAF. This experiment was repeated in the field during the 2012 growing season. Findings from this research will directly benefit agricultural producers who rely on hand labor or mowing to prevent late-season seed production of summer annual weeds.

Is Controlling Japanese Stiltgrass Worth It? Forest Understory Community Response.

Daniel R. Tekiela*, Angela R. Post, Shawn A. Askew, and Jacob N. Barney

Department of Plant Pathology, Physiology, and Weed Science

Virginia Tech, Blacksburg Va

Invasive species are drivers of significant changes in ecosystem functioning and processes.  The economic and ecological losses globally imposed by invasive species are detrimental to human society.  In the Eastern U.S. Japanese stiltgrass (Microstegium vimineum) is considered one of the worst invaders by local, state, and federal agencies.  Japanese stiltgrass is shown to reduce biodiversity, alter nutrient cycling, and most importantly change successional patterns in hardwood forests.  Therefore, it is critical to develop a management program to effectively control this species.

Current studies show the effectiveness of single application control measures, yet no studies exist (for Japanese stiltgrass or other invasive plant species) that demonstrate the effectiveness of single application measures on the long-term eradication of Japanese stiltgrass.  With a seedbank known to survive at least three years, single applications methods currently utilized are ineffective at eradicating populations of Japanese stiltgrass.  Therefore, any management program that does not have an objective of population eradication is wasting resources trying to control this species.  Finding an effective management protocol that can eradicate Japanese stiltgrass, while not negatively impacting the surrounding native plant community is desired by many land managers.

This eradication study shows the effects of controlling Japanese stiltgrass on the surrounding plant community both pre and post treatment application, and on an annual basis.  Treatments included full rate glyphosate, low rate glyphosate, sethoxydim, pendimethlin, and mechanical control applied in September in year one and July in year two.  All treatments except mechanical removal were effective (>95%) at controlling Japanese stiltgrass each year, but the effect on the surrounding plant community was not the same for all treatments.  Full rate glyphosate applications reduced overall vegetation ground cover.  Sethoxydim effectively removed Japanese stiltgrass while leaving the surrounding plant community relatively untouched.

This study shows that single year application is not enough to eradicate Japanese stiltgrass. Continued years of research will result in conclusive evidence of how long is required to eradicate Japanese stiltgrass.

Vincetoxicum rossicum (pale swallow-wort) and V. nigrum (black swallow-wort) are invasive, perennial vines that have become problematic in natural areas in the northeastern United States and neighboring southeastern Canada.  Both species reproduce primarily via wind-dispersed seeds in the form of achenes with a coma.  To better characterize seed dispersal of these vining herbaceous species, two studies were initiated.  First, settling velocities of seeds of pale swallow-wort and black swallow-wort were measured by dropping individual achene-coma units (pale swallow-wort, n = 106; black swallow-wort, n = 97) down a clear plastic tube measuring 1.22 m in length and 8 cm in diameter.  Falling time in seconds was converted to settling velocity in meters per second.  The settling velocity of pale swallow-wort seeds was 0.797 m sec^-1 (±  standard deviation (SD) = 0.219), while black swallow-wort had a slightly slower settling rate of 0.670 m sec^-1 (SD = 0.230).  The slower settling rate of black swallow-wort was expected because of the larger coma present in this species.  A wind tunnel experiment was also performed to collect additional data that can be used to model swallow-wort seed dispersal.  The wind tunnel measured 1.22 by 1.22 m with a 2 m test section.  Seeds were released into the wind tunnel from a thin tube.  Release heights included 0.6 and 1 m.  Wind speeds were 10 and 16 km h^-1.  Seeds were trapped on mesh fabric coated with adhesive spray, placed 0.75 and 1.5 m from the release point.  Data are currently being analyzed.  Settling rate, release height, wind speed, distance from the release point, and vertical height at the point of collection will be used in conjunction with a linear model to describe seed movement through the wind tunnel. 

     Flame cultivation is a nonchemical method of weed control where target plants are damaged by brief exposure to high temperature.  The utility of flame cultivation on perennial weeds in cranberry systems is currently being investigated to determine if it could be a useful practice for cranberry weed control.  Woody perennial weeds such as dewberry (Rubus spp.) are particularly problematic in cranberry production. Infestations will crowd out cranberry vines and seriously decrease yield.  Efficacious management tools for dewberry are limited.

     Past work with dewberry plants (Rubus spp.) has shown that a single exposure with a hand-held flame cultivation tool will cause a reduction of dewberry biomass by the end of a single growing season.  Our objective in the present study was to test the effects of multiple treatments within a single growing season, as well as the effects of varying the timing of these treatments.  Utilizing dewberry plants transplanted from commercial cranberry farms to a prepared area at the UMass Cranberry Station, treatment areas 0.25 m x 0.25 m were arranged in a randomized complete block design with four replications, with treatment blocked by replicate to account site difference. Plots were exposed to one of seven treatments using an open flame torch: a single 9-s exposure (June, July, or August) or two 9-s exposure (June/July, June/August, or July/August) or untreated control.  Dewberry stems were counted and measured prior to treatment, and again at end of the season after the plants has entered dormancy as a quantitative estimate of weed cover.  In the year following treatment, all stems were counted and measured, and above and belowground biomass was collected, dried, and weighed.  

     Cumulative dewberry stem lengths from the end of the season of treatment showed that all treatments had significantly less stem length than the untreated control except for the single June treatment, indicating that all other treatments were effective at reducing weed cover in the year of treatment.

     Biomass collected in the year after treatment showed that treatments with two exposures were more effective at reducing total, shoot, and root dewberry biomass than treatments with a single exposure.  Plants receiving a single exposure in June or August did not differ significantly in total biomass from the control, while plants receive a single exposure in July did.  All treatments had significantly less aboveground biomass than the untreated control, however only the June/July and July/August treatments showed a significant reduction in root biomass.  The efficacy of flame cultivation on dewberry control is impacted by both the timing and the frequency of treatments. 

The Invasion Cliff: The Interaction Between Propagule Pressure and Invasiveness

Matthew W. Ho, Larissa L. Smith, Jacob N. Barney

Abstract Success of an invasive species relies on the individual traits of the species, such as growth rate and dispersal characteristics; the environment the species will be introduced to; and the number of arriving propagules to the site. Since these factors can be quantified, an equation can be formulated to estimate the probability of establishment of at least one individual in a dispersal event, termed the invasion cliff. Despite the simple nature of this empirical model no data exists on the propagule pressure requirements of most invasive species, especially as it may vary as a function of habitat. Therefore, we examined the effects of propagule quantity (1, 10, 250, 750, and 1250 seeds) and competitive environments (no competition, full competition, forb-only competition, and grass-only competition) on establishment and invasibility of the C₄ grasses Miscanthus sinensis (ornamental and weedy), Panicum virgatum, and Sorghum halepense at two locations. When averaged across all treatments, S. halepense and P. virgatum have germination rates of 1.2% and 0.8%, respectively; weedy and ornamental M. sinensis have germination rates of 0.3% and 0.1%, respectively. The higher density levels (750 and 1250) result in more established plants than lower density levels (1 and 10). However, following germination, introduced propagule density shows no relationship to growth, but competition and species are both related to growth. Across all treatments, Sorghum halepense is the only grass with a significant difference from the other grasses with a final height of 260.1cm, while we found that weedy M. sinensis has a height of 16.5cm, 16-fold smaller than S. halepense. As expected, plants in full competition have the lowest performance, while species in grass-only competition performed the best. Overall, individuals in the grass-only competition outperformed those in full competition by >220%. We can conclude that the ability of grasses to recruit into a site depends on the propagule pressure to that site, as well as species characteristics. However, the level of competition and species-specific characteristics represent the factors that influence establishment and performance. To adequately measure the interactions between population density, establishment, and invasiveness, further ecological studies need to be conducted which include a wider range of species and a broader range of propagule numbers and types (e.g., seeds vs. rhizomes). 

Goals of energy independence and the mandated increase in production of transportation fuel from renewable sources encourage the development of novel species as crops. Miscanthus × giganteus has emerged as a promising cellulosic bioenergy crop due to its rapid growth rate, high aboveground yields, and tolerance to poor growing conditions. Newly developed, fertile varieties may reduce establishment costs, but may increase the likelihood of escaping field boundaries and establishing invasive populations, which must be evaluated.

            In our effort to evaluate the first stage of invasion of propagule establishment for seeded M. × giganteus in the Southeast, we compared seedling establishment in seven habitats: no-till soybean field, agricultural field edge, forest understory, forest edge, pasture, riparian and roadside.  This experiment was conducted in Blacksburg and Hampton Roads, Virginia and Tifton, Georgia. We use a novel head-to-head comparison of M. × giganteus against eight grass species; six species were introduced and are known invasives in the US (positive controls), and two species that are known not to be invasive (negative controls). At each site, 250 seeds of M. × giganteus and two positive and two negative controls, suited for the habitat and geographic location, were sown in early January 2012.  Plots were monitored every two weeks beginning February 20 for germination, survival, height, culm and inflorescence number. Soil samples were taken at the onset of the experiment to characterize soil nutrient availability, pH and percent organic matter. Soil moisture, light availability, and percent bare ground were also recorded bimonthly. Despite early germination of M. × giganteus seedlings in the forest understory, riparian, no-till soybean field and agricultural field edge habitats, only one, 5 cm seedling remained at the end of the experiment.  Comparatively, 62.5% of remaining johnsongrass, (Sorghum halepense, positive control), seedlings reached reproductive maturity at the end of the experiment.  At the conclusion of the experiment, 0.1% of M. × giganteus which germinated during the experiment remained while 21% of Microstegium vimineum (positive control) remained. Percent bare ground or lack of resident vegetation and organic matter had a significant effect on seed establishment of M. × giganteus in all habitats, while light availability was positively correlated with height and culm number.  Knowledge gained from our results may help prepare for widespread commercialization, while helping to identify susceptible habitats to seedling establishment and aiding in the development of methods for improved stewardship.

The recent trend in bioenergy feedstock development is the use of large-statured perennial grasses that pose a relatively high risk of becoming invasive species due to the similarity in desirable agronomic traits with those of many of our worst invaders.  Thus, it would be prudent to evaluate the potential economic and ecological benefits and consequences of widespread cultivation of potentially invasive species.  Miscanthus sinensis and its sterile daughter species, Miscanthus × giganteus, are two prominent bioenergy feedstock candidates due to their low input requirements and significant biomass production in a broad range of growing conditions.  Despite being an extremely popular ornamental grass, and naturalizing in over half of US states, little is actually known about the ecology and niche requirements of M. sinensis. Previous studies on the biology and ecology of M. sinensis have suggested that enhanced tolerance to shade and poor soil conditions may be significant mechanisms for invasion in the United States. Therefore, we conducted a greenhouse study to compare shade and soil moisture tolerance among common ornamental cultivars and naturalized populations, where we found enhanced plant growth and vigor in naturalized biotypes compared to ornamentals across varying levels of light stress, from 5% to 100% light availability.  We also found that both naturalized and ornamental biotypes were not significantly affected by soil moisture stress, and thus express significant drought tolerance. Significantly greater vigor and performance in naturalized biotypes compared to ornamental cultivars suggests naturalized populations have evolved enhanced shade tolerance, most likely from hybridization and natural selection across generations. Finally, we subtle, yet significant, differences in the vigor and vitality amongst ornamental cultivars, meaning some ornamental varieties may be more or less potentially invasive than others. These basic ecological studies will help refine and support future evaluations and weed risk assessments of both Miscanthus sinensis and Miscanthus × giganteus, which is critical in prevention of major ecological invasions.

“Tolerance of Arundo donax to Postemergence Herbicides”

Although many states include Arundo donax on their noxious weed list, it is being considered as a source of biomass for biofuel production in North Carolina.  Since there is little to no information on the effects of herbicides for establishment of Arundo donax, field and greenhouse studies were conducted in the summer and fall of 2012 to observe the tolerance of Arundo donax to Postemergence (POST) herbicides.  Our objective was to screen POST herbicides for potential use in the establishment of Arundo donax as a biomass crop.  Arundo donax was planted in a field setting, and after establishment POST applications were made with an average plant height of 83.82cm.  Treatments consisted of 2,4D @ 0.475 lb a.i./A, aminopyralid @ 0.109 lb a.i./A + NIS 0.50% v/v, atrazine @ 0.5 lb a.i./A+ COC 1% v/v, atrazine @ 1 lb a.i./A + COC 1% v/v, bentazon @ 1 lb a.i./A + COC 0.25% v/v, bispyribac-sodium @ 0.0285 lb a.i./A, bromoxynil @ 0.375 lb a.i./A, carfentrazone @ 0.0313 lb a.i./A + COC 1% v/v, clethodim @ 0.0682 lb a.i./A + NIS 0.25% v/v,  clopyralid @ 0.188 lb a.i./A, cloransulam @ 0.016 lb a.i./A + NIS 0.25% v/v, clorimuron @ 0.012 lb a.i./A + NIS 0.25% v/v, diacamba @ 0.25 lb a.i./A, fluazifop @ 0.141lb a.i./A + NIS 0.25% v/v, glufosinate @ 0.402 lb a.i./A + AMS 8.5lbs/100 gal, glyphosate @ 0.473 lb a.i./A + NIS 0.25% v/v, halosulfuron @ 0.031 lb a.i./A + NIS 0.50% v/v, imazamox @ 0.039 lb a.i./A + NIS 0.25% v/v, mesotrione @ 0.094 lb a.i./A + COC 1% v/v, nicosulfuron @ 0.016 lb a.i./A + NIS 0.25% v/v, nicosulfuron @ 0.031 lb a.i./A + NIS 0.25% v/v, pyraflufen ethyl @ 0.001 lb a.i./A, quinclorac @ 0.492 lb a.i./A + MSO 1.5 pt/A, quinclorac @ 0.984 lb a.i./A + MSO 1.5 pt/A, rimsulfuron + thifensulfuron @ 0.018 lb a.i./A, sulfosulfuron @ 0.031 lb ai ac + NIS 0.50% v/v, tembotrione @ 0.082 lb ai ac + MSO 1% v/v, tembotrione + thiencarbazone-methyl @ 0.081 lb a.i./A + COC 1% v/v, thifensulfuron @ 0.004 lb a.i./A + NIS 0.25% v/v,  topramazone @ 0.016 lb a.i./A + MSO 1% v/v, trifloxsulfuron @ 0.005 lb a.i./A + NIS 0.25% v/v.  In the field study glyphosate, fluazifop, topramazone, and both rates of nicosulfuron showed greater than thirty percent injury and stunting with bentazon, bromoxynil, bispyribac-sodium, clorimuron, halosulfuron, rimsulfuron + thifensulfuron, sulfosulfuron, thifensulfuron showed no injury and stunting less than twenty percent.  All other treatments fell between these two percentages. Additionally a greenhouse study was conducted using greenhouse propagated plants.  All plants were established from cuttings into 10.16 cm square pots.  All treatments were similar for greenhouse study as the field study with the addition of chlorsulfuron @ 0.047 lb a.i./A + NIS 0.25%v/v, fomesafen @ 0.353 lb a.i./A + NIS 0.25% v/v, imazapic @ 0.063 lb a.i./A + NIS 0.25%v/v, metsulfuron methyl @ 0.038 lb a.i./A, pinoxaden @ 0.054 lb a.i./A, quinclorac @ 0.75 lb a.i./A + MSO 1.5 pt/A, sulfometuron @ 0.094 lb a.i./A + NIS 0.25% v/v  and the removal of atrazine @ 0.5 lb a.i./A + COC 1% v/v, glyphosate @ 0.473 lb a.i./A + NIS 0.25% v/v, nicosulfuron @ 0.016 lb a.i./A + NIS 0.25% v/v, quinclorac @ 0.492 lb a.i./A + MSO 1.5 pt/A, quinclorac @ 0.984 lb a.i./A + MSO 1.5 pt/A, rimsulfuron + thifensulfuron @ 0.018 lb a.i./A.  The greenhouse study resulted in clethodim, fluazifop, sulfometuron, imazapic having greater than thirty percent injury, with clopyralid, tembotrione + thiencarbazone-methyl, and pinoxaden having less than fifteen percent injury.  All other treatments fell between these two percentages.

Demographic matrix modeling of plant populations can be a powerful tool to identify key life stage transitions that contribute the most to population growth of an invasive plant and hence should be targeted for disruption (weak links) by biological control and/or other control tactics.  Therefore, this approach has the potential to guide the selection of effective biological control agents.  We have parameterized a five life-stage matrix model in order to generate pre-release agent recommendations for the swallow-wort biological control program.  Pale swallow-wort (Vincetoxicum rossicum) and black swallow-wort (Vincetoxicum nigrum) are herbaceous, perennial, viny milkweeds introduced from Europe (Apocynaceae-subfamily Asclepiadoideae).  Both species are becoming increasingly invasive in a variety of natural and managed habitats in the northeastern United States and southeastern Canada.  Black swallow-wort appears restricted to higher light environments, whereas pale swallow-wort infestations occur from the high light environments of open fields to low light forest understories.  We quantified demographic transitions for marked individuals of the five life stages over 3-4 years of both swallow-wort species in field and, for pale swallow-wort, forest habitats in New York State (N = six populations).  Vital rates estimated include germination, survival, growth to the next life stage, and fecundity (viable seeds produced per plant). All open field populations of both swallow-wort species as well as a high-light forest population of pale swallow-wort are increasing (population growth rates > 1). However, a heavily shaded (low-light) forest population of pale swallow-wort is only persisting (population growth rate = 1).  Elasticity analyses have identified several potentially important transitions for one or both species of swallowwort: survival of vegetative juvenile, small flowering and large flowering plants; growth of seedlings, juveniles and small flowering plants to the next life stage; and reproduction of small and large flowering plants. This information in combination with published herbivory impact data will be used to assess the potential efficacy of candidate biological control agents. Successful biological control of long-lived perennials like the swallow-worts will likely require targeting a combination of either survival and growth transitions or survival and reproduction transitions.

Since the early 2000's, discoveries of new infestations of the monoecious variety of the invasive submersed aquatic weed Hydrilla verticillata in several northern US states have presented an increasing new threat to the ecology of northern lake systems and other critical waterways.  Early hydrilla infestation of smaller, contained bodies of water in multiple US states including Wisconsin, Indiana, Ohio, New York, Connecticut, Massachusetts, and Maine been managed in a variety of ways including herbicide use, handpulling, sterile grass carp stocking, and even simple filling.  However, in the late 2000's up to today, there is a growing number of infestations in more open, much larger aquatic systems where eradication and containment is much more difficult.  The aquatic herbicide Sonar^®  (active: fluridone) has been a common tool in efforts to achieve eradication of monoecious hydrilla at both smaller and now larger scales of infestation.  The mode of action of Sonar (phytoene desaturase inhibition), the extreme sensitivity of hydrilla to the herbicide, and its longer dissipation time and extended impact to invasive hydrilla all support Sonar's use for hydrilla eradication.  Successful, season-long treatment programs with Sonar can prevent vegetative hydrilla growth and spread as well as, when used over multiple annual cycles, gradually eliminate an extensive accumulation of subterranean turions or tubers, the extremely successful long-term survival mechanism of hydrilla.   Successful operational hydrilla eradication efforts for northern infestations are being implemented, and monitoring of tuber densities shows that 5 to as many as 10 successive seasons of Sonar treatment may be required to achieve complete tuber bank depletion.  Hydrilla eradication efforts with Sonar herbicide since 2007 on Manitou Lake (325 ha) in north central Indiana and starting in 2012 for a new 66 ha infestation of an inlet tributary of Cayuga Lake, New York will be highlighted.

Desired characteristics of herbicides for use in wildland settings include broad species spectrum, reduced soil activity, and aquatic labeling.  The combination of glyphosate plus triclopyr meets these criteria, and is a standard treatment in state parks in Pennsylvania.  Another desired trait would be safety to grasses to increase selectivity.  Glyphosate-free foliar herbicide combinations were evaluated against burning bush (Euonymus alata) and privet (Ligustrum obtusifolium) at Gifford Pinchot State Park, Lewisberry, PA; and Morrow's honeysuckle (Lonicera morrowii), autumn olive (Elaeagnus umbellata), and Japanese barberry (Berberis thunbergii) at Bald Eagle State Park, Howard, PA.  Candidate herbicides to combine with triclopyr were 2,4-D (aquatic labeling, reduced soil activity), and the pre-mixed herbicides aminopyralid plus metsulfuron methyl and aminocyclopyrachlor plus metsulfuron methyl.  The pre-mixed herbicides are broad spectrum, and have useful, but terrestrial-only labeling.  They are also soil-active and will require low application rates for widespread adoption. Glyphosate plus triclopyr at 3.4 plus 1.7 kg ae/ha was used as a standard.  Alternate treatments included triclopyr alone at 3.4. kg ae/ha, or in combination with 2,4-D at 2.2 kg ae/ha, and triclopyr at 1.7 and 3.4 kg ae/ha combined with a pre-mix of aminopyralid plus metsulfuron methyl at 0.12 kg ae/ha plus 0.021 kg/ha, or a pre-mix of aminocyclopyrachlor plus metsulfuron methyl at 0.13 plus 0.042 kg/ha, respectively.  Treatments were applied individually to five plants each at 700 L/ha, based on canopy basal area, with an oil-based surfactant included at 1.0 percent, v/v.  Treatments were applied September 1 and September 16, 2011, and final evaluations recorded September 12 and September 7, 2012, at the Gifford Pinchot and Bald Eagle sites, respectively.  The glyphosate plus triclopyr standard averaged 98 to 100 percent reduction across the five species.  There was no significant treatment effect for autumn olive and privet, with reduction ranging from 98 to 100 percent and 93 to 100 percent, respectively.  Differences in Japanese barberry were numerically small, but significant.  Triclopyr plus 2,4-D was rated at 95 percent reduction, compared to 98 to 100 percent for the remaining combinations.  Triclopyr plus 2,4-D was rated significantly lower than the other combinations for honeysuckle as well, 92 percent compared to 97 to 100 percent.  Triclopyr alone performed better than expected against honeysuckle at 97 percent reduction.  This treatment has historically not been operationally acceptable.  The greatest differences were observed on burning bush.  Triclopyr alone or with 2,4-D was rated at 76 or 81 percent reduction, compared to 96 to 99 percent for the other combinations.  The combinations including the aminopyralid or aminocyclopyrachlor pre-mixes with metsulfuron were highly effective, regardless of triclopyr rate, suggesting there is latitude to investigate further dosage reduction.

Art Gover, aeg2@psu.edu

Reed canarygrass is a cool-season, rhizomatous grass that forms persistent, near-monotypic stands in riparian and seasonal wetland sites.  Current practice to suppress reed canarygrass to revegetate riparian sites with a spring seeding or planting is to treat two to three times with glyphosate between the preceding spring and the spring of planting, with the key timing the fall prior to planting.  This regimen provides a window to establish the alternate vegetation, but reed canarygrass typically rebounds from rhizome remnants or seed.  To determine if enhanced suppression could be achieved with tank mixtures, glyphosate was applied alone at 3.4 or 4.5 kg ae/ha, and alone at 3.4 kg ae/ha with triclopyr at 1.7 kg ae/ha, imazapic at 70 or 140 g ae/ha, or sulfometuron methyl at 52 or 105 g/ha.  Treatment combinations were applied to a mixed stand of partially senesced reed canarygrass and goldenrods (Solidago spp.) that averaged 75 and 23 percent cover, respectively, on October 18, 2011.  Suppression was rated August 31, 2012, and cover in untreated plots for total vegetation, reed canarygrass and goldenrod was 57, 33, and 23 percent, respectively.  Only treatments with sulfometuron significantly reduced total vegetative cover (37 and 27 percent for 52 and 105 g/ha, respectively).  All herbicide treatments significantly reduced reed canarygrass cover compared to the controls.  Glyphosate alone or with imazapic produced similar results, with reed canarygrass cover ranging from 2 to 3 percent, and goldenrod cover increased from the controls, ranging from 38 to 52 percent.  Adding triclopyr to glyphosate resulted in increased reed canarygrass cover (15 percent) and reduced goldenrod (24 percent) compared to glyphosate alone.  The addition of sulfometuron at 52 or 105 g/ha resulted lower goldenrod cover (22 and 9 percent), and similar reed canarygrass cover compared to glyphosate alone.

Art Gover, aeg2@psu.edu

Tamarisk is one of the most common woody plant species along waterways in the arid and semi-arid western United States. Intensive efforts to manage tamarisk have occurred since the 1950s, but there have been very few studies that quantitatively assessed tamarisk control and non-target ecological impacts of common management strategies. In 2009 we established four sites in the Arkansas River watershed of southeastern Colorado to simultaneously investigate the effectiveness of tamarisk removal methods, and their impacts on passive understory re-vegetation patterns. Primary treatment plots (aerial imazapyr applications, mulching, excavation, untreated controls) were installed at each site the first year, and secondary treatments (releases of Diorhabda carinulata beetles, and individual plant treatments (IPTs) of imazapyr and triclopyr) were installed in 2010. Within each treatment plot multi-scale, nested sampling plots were randomly located to monitor tamarisk survival and understory vegetation recruitment and establishment.

Results three years after treatment indicated that whole tree extraction caused 20% higher tamarisk mortality than aerial imazapyr applications or mulching. Increased tamarisk mortality from secondary treatments was slightly higher from IPT imazapyr applications than from IPT triclopyr applications or beetle defoliation. Cost effectiveness analyses indicated that tamarisk biomass removal followed by biological control releases was more cost effective than either aerial or targeted herbicide treatments. In regards to ecosystem impacts, aerial imazapyr applications resulted in a depauperate plant community dominated by kochia (Bassia scoparia). Plant species richness and diversity was slightly higher in plots where mechanically-removed tamarisk was treated with Diorhabda beetles compared to those that received IPT herbicide applications. Overall, data indicated that plant community re-vegetation patterns were more strongly affected by drought than by tamarisk removal. This study provides evidence that it is possible to effectively control tamarisk and similar species using integrated strategies that do not detrimentally affect the extant plant community. However, our results also indicate that it is critical to holistically address underlying causes of site degradation to ensure desirable passive re-vegetation following tamarisk removal.

Understanding the factors that determine how plant communities assemble is needed if progress is to be made toward optimizing invasive plant management. Community assembly theory invokes geographic, abiotic, and biotic selection factors that filter plant species based on their traits from the regional species pool into the local community. In addition to dispersal and physiological traits that allow plants to overcome geographic and abiotic constraints and successfully arrive and establish in a community, understanding the traits that allow plants to persist in the face of generalist herbivores is also important. The enemy release and biotic resistance hypotheses highlight the importance of herbivory in determining the success or failure of exotic species. The enemy release hypothesis predicts that exotic species succeed because they leave their enemies in the native range, whereas biotic resistance occurs when the native community prevents invasion of exotic species via antagonistic species interactions. Here, we use community assembly theory, a regional mega-analysis, and controlled herbivore preference trials to elucidate the role of the regionally abundant white-tailed deer (Odocoileus virginianus) in exotic plant invasion. We found that deer feeding preferences help explain regional invasive plant abundance patterns. Deer appear to indirectly facilitate the invasion of species with anti-herbivore traits via avoidance (e.g., garlic mustard Alliaria petiolata, Japanese barberry Berberis thunbergii, and Mary's-grass Microstegium vimineum), supporting the enemy release hypothesis. Conversely, deer exhibited preference for other invasive plants (e.g., oriental bittersweet Celastrus orbiculatus, European privet Ligustrum vulgare, and Morrow's honeysuckle Lonicera morrowii) and we observed that deer presence significantly reduced the abundance of such palatable species in forest understories, supporting the biotic resistance hypothesis. However, the counteractive traits of animal-mediated dispersal and a high tolerance for herbivory could outweigh the negative impacts of browsing. Our data suggest the selective browsing of abundant deer results in a community of species that have predictable resistance or tolerance traits. We conclude that white-tailed deer herbivory is an important biotic community assembly factor that influences the success of exotic species in the Mid-Atlantic Region. Additional research should aim to determine if deer population management strategies reduce exotic invasive plant abundance.

A Novel Method to Detect and Quantify Non-riparian Water Dispersal of the Invasive Grass Microstegium vimineum.

Daniel R. Tekiela* and Jacob N. Barney

Department of Plant Pathology, Physiology, and Weed Science

Virginia Tech, Blacksburg Va

Microstegium vimineum is a shade tolerant annual C₄ grass that is an invasive species in the Mid-Atlantic and upper Southeastern US, and has been shown to negatively impact species diversity and composition in eastern hardwood forests.  To date, empirical studies have shown that local dispersal is limited to ~1m yr^-1, which is largely driven by gravity dispersal. However, this likely does not fully account for the mechanisms of population-scale dispersal, which clearly expand much greater than 1 m yr^-1. Though water, both riparian and ephemeral overland flow, has been a speculated mechanism for dispersal of M. vimineum, no studies have been conducted to empirically test this hypothesis. 

We designed an experiment along the slopes of a Southwest Virginia hardwood forest to see if marked seed would be dispersed downslope by means of non-riparian water dispersal (i.e., ephemeral overland flow resulting from precipitation). We used a novel seed marking technique by coating seed lots in an ultraviolet powder that did not affect buoyancy to aid in recapture of seed, which is difficult at low densities.  Additionally, a new image analysis protocol was developed to automate seed identification from UV-based photos. Labeled seeds were surface sown and initial UV photos were taken to establish an initial location. Subsequent UV photos were collected after rain events in a downslope transect using a custom designed UV photo box. In general, seed populations moved unidirectionally downslope with a maximum dispersal event of 0.62m over a single rain event and 1.83m over a one-month period. 

Our spatially limited study, while not showing broad population expansion, is the first to document overland seed dispersal in a forest ecosystem, which is a new mechanism for local population expansion of M. vimineum once it has established.

Genetic analysis of invasive weeds can provide important insights into their origin, biology and adaptive capacity to assist with their control and management. For example, comparing genetic structure between native and introduced populations can help determine whether single or multiple introductions have occurred. It can also help delineate source populations (or regions) to narrow the search for biological control agents, based on the premise that co-evolving natural enemies are more damaging. Indeed, the failure of numerous biocontrol projects in Australia (e.g. lantana, skeleton weed and European blackberry) has been attributed to a mismatch between invasive species’ genotypes and their natural enemies. Finally, determining the levels of genetic variation in introduced populations may provide insights into the likelihood of success of a potential biocontrol project given that these have been most successful against clonal species with minimal genetic variability. Delta arrowhead, Sagittaria platyphylla (Alismataceae) an emergent aquatic plant introduced to Australia from the southern USA during the early 1900’s. It is now widely established in south-eastern Australia where it invades and chokes shallow waterways. Genetic analyses using AFLPs were used to assess 20-30 populations from the invaded Australian range for comparison with populations in the southern USA to determine (i) how is genetic diversity in S. platyphylla partitioned between individuals, populations and continents? (ii) can we identify the source populations from which S. platyphylla invaded Australia? (iii) how do levels of genetic diversity compare between the invaded and home ranges?

Students in the University of Nebraska–Lincoln Doctor of Plant Health field of study needed a course on Pesticide Application Technology. The DPH program is only the second of its kind in the US. It was established as a result of input from a broad spectrum of employers who strongly support the need for this professional training. Graduates from the program will be in great demand in a broad job market. We are excited to be involved in educating students who will have great potential to contribute to these critical needs worldwide. A course, AGRO 896, 1 credit, was taught on Friday afternoon and evening and all day Saturday to keep from conflicting with the students’ class schedules. The goal of the course was to provide the student with an in-depth background and hands-on experience with pesticide application technology in use today. The students were also to gain an understanding of current spray drift regulations, and understand how to manage application technology for best performance while meeting regulations. The course outline was as follows:  calibration of application equipment; spray nozzle selection and demonstration; ANSI/ASAE S572.1 Standard; how the pesticide, pressure, nozzle tips, and additives affect spray particle size; managing spray drift; balancing particle size and efficacy; EPA spray drift regulations; doing a professional job; sprayer set-up; equipment calibration (hands on); solving equipment problems (hands on). The entire course was completed during the two sessions, thus attendance for the entirety of both sessions was mandatory. An exam was given at the conclusion of the second day which constituted 75% of the final grade. An additional homework assignment which was to develop a PowerPoint on one of several topics dealing with pesticide application (25% of final grade) was completed after the course session.

Studies to evaluate the response of non-target, sensitive plants to foliar active herbicides have been conducted for at least the past 60 years.  It is accepted that inadvertent foliar exposure of a non-target, sensitive plant resulting directly from a liquid spray can occur primarily in two ways: 1. Direct application to the non-target plant due to sprayer contamination from a previous use of the equipment or accidental addition of an unintended herbicide to the spray tank; or 2. Droplet movement (spray drift) from the target area during an application to a non-target area where the sensitive plants are growing.  There are distinct differences in what occurs in these two situations.  The direct application from a contaminated sprayer is delivering a spray volume in the range of 100 to 200 L/ha with a highly diluted concentration of the unintended herbicide in the spray solution in droplets mostly larger than 200 microns.  In addition, the non-target plants are generally evenly covered by the spray solution.  The spray drift situation involves the movement of the original spray solution for some distance from the target area.  The droplets that drift off-target typically are small (< 100 microns) and contain a concentration of the herbicide that is equal to the original spray solution or higher.  Coverage of the non-target plants is generally not even and when calculating the actual amount of herbicide being delivered it can be less than 1% of the original dosage that was applied to the target field.  Despite the obvious differences in how plants are exposed to the unintended herbicides, researchers continue to conduct and publish “simulated drift” studies that use highly diluted carrier volumes which do not vary with herbicide dosage and in no way simulate spray drift.  Several herbicides have been shown to be more injurious to sensitive plants when applied at lower carrier volumes or when droplet concentrations are higher or as droplet size decreases.  Several simulated spray drift studies in the early 2000’s demonstrated that injury to sensitive crops was greater when the dosages were delivered in carrier volumes that were proportional to the change in dosage which kept the herbicide concentration constant.  Studies that do not make an effort to adequately simulate actual drift are most likely under estimating the effects of the herbicide on the non-target plants and in reality are producing results that are consistent with spray tank contamination.

A wind tunnel study was conducted to determine the effects of nozzle selection, nozzle orifice size, and spray pressure on spray droplet size of four dicamba/glyphosate mixes.  The study included 14 nozzles, three orifice sizes for each nozzle (03, 04, and 05), two spray pressures and a total of four dicamba/glyphosate mixes, including two tank mixes (TM1, TM2) and two premixes (PM1, PM2).  Spray pressures were adjusted to correspond to application volumes of 10 and 15 GPA.  Droplet size distributions for all possible combinations of the four factors were measured using a laser in a wind tunnel at the University of Queensland in 2012.  The data were statistically analyzed using a full factorial response surface model. The application parameters of nozzle selection and spray pressure had the largest effect on droplet size of the four primary factors evaluated in the model.  Nozzle x pressure and nozzle x orifice size interactions were also highly significant. Percent driftable fines (% volume < 150 µm) was primarily influenced by nozzle and pressure with nozzle selection being the most critical factor for reducing driftable fines. Larger orifice sizes and lower pressures resulted in fewer driftable fines. Formulation effects were similar for TM1, TM 2, and PM1. PM2 generally resulted in higher percent fines generation. The results from this study highlight the importance of proper nozzle selection for controlling off-target migration of driftable fines.

An Ultra-Low Volume (ULV) sprayer was developed to decrease carrier volume required for pesticide applications in crop production. A field study was conducted at the University of Nebraska-Lincoln West Central Research and Extension Center Dryland Farm near North Platte, NE to determine efficacy of herbicide active ingredients when atomized by a ULV sprayer compared to a conventional sprayer. Ten active ingredients with each sprayer and an untreated check (21 total treatments) were arranged in a randomized complete block design with four replications.  The ten herbicides chosen were glyphosate, glufosinate, 2,4-D ester, dicamba, atrazine, saflufenacil, mesotrione, chloransulam-methyl, sodium salt of bentazon, and clethodim. Treatments with the conventional sprayer were applied at a carrier volume of 76 L ha^-1 and treatments with the ULV sprayer were made at 19 L ha^-1. The effect of four drift reducing adjuvants on glyphosate efficacy with the ULV sprayer at two pressures was also evaluated. Four drift reducing adjuvants, a glyphosate check and an untreated check were arranged in a randomized complete block design with four replications. The four adjuvants selected were hydroxyethyl cellulose (HEC), polyethylene oxide (PEO), methylated soybean oil (MSO) and glycerin. Treatments were applied across a 12 row plot planted to six different plant species. Plant species used were non-glyphosate-resistant corn (Zea mays L.) non-glyphosate resistant soybeans (Glycine max (L.) Merr.), amaranth (Amaranthus hypochondriacus L.), quinoa (Chenopodium quinoa Willd.), velvetleaf (Abutilon theophrasti Medik.), and green foxtail (Setaria viridis (L.) Beauv.). Treatments in both studies were analyzed for their relative particle size on a laser diffraction instrument to compare droplet size spectra and determine if differences in droplet sizes exist between the two sprayers. Five plants of each species per plot were harvested four weeks after application, dried for 48 hours at 60°C and dry weights were recorded. The active ingredient study yielded no difference in efficacy between sprayer types across all six species in 2011 but was different in corn in 2012. Simple effect differences of treatment by sprayer type were observed in both years. The adjuvant study had no difference in glyphosate efficacy across the four adjuvants or the glyphosate check over the six species in 2011 and corn and soybean in 2012. Additionally, operating pressure did not affect efficacy across all treatments. The results indicate that the ULV sprayer is potentially an effective method for delivering herbicides.

Monsanto is currently developing transgenic cotton and soybean varieties capable of withstanding postemergence applications of dicamba.  This technology facilitates effective control of many troublesome weed species, including many that have exhibited resistance to glyphosate.  The ability to control glyphosate-resistant weeds like Palmer Amaranth will likely result in rapid adoption of this new technology.  As adoption increases, incidences of off-target deposition will likely increase as well.  The potential for increased off-target deposition of dicamba coupled with the fact that soybean are very sensitive to low concentrations of dicamba has resulted in many concerns relative to its use as an in season weed control option.  Monsanto will  require the use of spray tips that produce very coarse to ultra coarse spray droplets in an effort to mitigate spray particle drift.  Two such spray tips available from Spraying Systems is an air induction (AI) and turbo teejet induction (TTI). 

In 2012, an experiment was designed to evaluate the potential for off-target deposition of dicamba when applied with these tips under wind speeds of 5 to 10 miles per hour (MPH).  The experiment was conducted in Brooksville, MS, Jackson, TN, Keiser, AR, and Scott, MS.  The two treatments consisted of a comparison of off-target movement of a premix candidate when applied at 1.5 lbs ae/A with 11004 AI and 11004 TTI nozzles calibrated to deliver 15 gallons per acre (GPA).  The premix candidate was composed of 2.67 lbs ae glyphosate with 1.33 lbs ae dicamba per gallon of product.  Each treatment was replicated three times.  Non-transgenic soybeans were utilized as a bio-indicator because of their sensitivity to dicamba.  Treatments were applied to soybean at the V5-V6 stage of growth.  In general, wind direction was perpendicular to each area sprayed and speeds averaged 6.2, 4.2, 5.0, and 5.4 MPH at Brooksville, Jackson, Keiser, and Scott, respectively.  Plots were 100 feet long at all locations and width was dependent upon sprayer type and ranged from 28 to 60 feet.  A 100 ft nontreated buffer was left between each sprayed plot.  Data were collected in upwind and downwind transects segmented into 4 row wide plots that were 25 ft long.  Plots were contiguous throughout the transects and were adjacent to both the treated and nontreated buffer areas.  This approach was utilized to capture the effect of non-right angle movement of driftable particles.

Visual estimates of injury and plant heights were collected from each downwind and upwind experimental unit 14 and 28 days after treatment.  Malformation data were fitted as a function of log(distance) using linear regression.  At 28 DAT, the distance beyond which malformation was less than 5% with the AI tip was 187, 85, 248, and 141 ft while with the TTI tip it was 225, 85, 248, and 161 ft at Brooksville, Jackson, Keiser, and Scott, respectively.  AT 28 DAT, the distance beyond which malformation was less than 15% with the AI tip was 59, 18, 179, and 11 ft while with the TTI tip it was 80, 31, 109, and 19 ft at Brooksville, Jackson, Keiser, and Scott, respectively.

Plant heights were fitted with a segmented regression technique to determine the hinge point at which the data reaches a plateau of no effect.  Plant heights were reduced with drift out to a distance of 71, 36, and 45 ft with the AI tip and 71, 19, and 46 ft with the TTI tip at Brooksville, Jackson, and Keiser, respectively.  Plant heights at the Scott location did not result in the detection of a hinge point when fitted to this model.

When yield data were subjected to the hinge point model to determine the distance to which yield reductions occurred only two were detectable.  The AI tip at Keiser and the TTI tip at Scott resulted in drift that caused yield losses out to 40 and 36 ft, respectively.  When subjected to an analysis of variance yield reductions could be determined to approximately 25, 12, 12, and 24 feet with the TTI tip at Brooksville, AI tip at Keiser, AI tip at Scott, and the TTI tip at Scott.

These data indicate that malformation can be observed a considerable distance downwind from an application of dicamba.  They also show that plant height may be reduced at moderate distances from the treated area.  However, even where visual estimates of injury and plant heights were reduced, yields were not reduced beyond 40 ft from the treated area.  Additional data are needed to allow the development of buffer restriction relative to applications around sensitive species.

Decreasing the particle size of herbicides can influence biological activity in several ways including improved cuticular penetration and stomatal uptake.  Decreased particle size can also result in improved coverage on the leaf surface.  The combination of these effects can improve efficacy of herbicides at lower rates.  The objective of this research was to compare the standard (Excel Super, 80.5 gai/L EC) and nano (37% WP) formulations of fenoxaprop-p-ethyl for the control of selected annual monocot species.  Species selected included green foxtail (Setaria viridis) , corn (Zea mays)) and oat (Avena sativa).  These species were selected based on known susceptibility to fenoxaprop-p-ethyl with green foxtail the most susceptible, corn, (moderate susceptibility) and oat being the most tolerant of the three species tested.  The nano formulation of fenoxaprop-p-ethyl had greater efficacy consistently on green foxtail and corn than the standard formulation. For green foxtail and corn, the dose required of the nano formulation to reduce plant biomass by 50 % (GR₅₀) was approximately 50% of the commercial formulation of fenoxaprop-p-ethyl.   In addition, the nano-formulated fenoxaprop-p-methyl was equal to or better for the control of the more tolerant oat species compared to the standard commercial formulation.

The terminology for herbicidal additives is confusing. It is often assumed that any material that lowers the surface tension of water in the spray mixture or increases the wetability of the spray solution on plant leaf surfaces is an adequate adjuvant. Due to side effects of chemical pesticides on the environment, one of the facing challenges of human is finding a solution to reduce the risks and harmful effects of these substances. One of the most important cases in reducing these harmful effects may be using chemical pesticides with lower doses than recommended doses; but In this case, one of the most important problems is lesser efficiency of chemical pesticides. This study was carried out to study various adjuvants efficiency in reducing Nicosulfuron dosage with Citogate, Gyahgate and D-octil in 5 levels of herbicide. Recommended dosage (2lit/ha), 10% lower than recommended dosage (1.8lit/ha), 20% lower than recommended dosage (1.6 lit/ha) and 30% lower than recommended dosage (1.4lit/ha) and control (without any adjuvant) in 30 plots and in four replications. According to our results Citogate efficiency with Nicosulfuron (20% lower than recommended dosage) showed no significant differences in comparison with control (Nicosulfuron in recommended dosage) (P<0.05). Gyahgate and D-octil application can show appropriate efficiency in an integrated weed management.

Recent developments within unmanned aircraft systems (UAS) add new perspectives to efficacy assessments of herbicides.  Cameras mounted on UAS offer a bird's-eye view of large plots and are especially useful in field trials with logarithmic sprayers, because plots are large and responses change continuously.   The objective of this presentation is to demonstrate how images from a standard RGB camera (Canon G12), mounted on a hexakopter from Microkopter™ can be used to asses herbicide efficacy. After applying herbicides of various modes of action in different crops with a logarithmic sprayer, plots were photographed at 40 m altitude.  This altitude ensured that 35 m long plots were covered in one image with a ground resolution of 14 mm/pixel.  A MATLAB script was used to estimate the excess green index (ExG), which expresses the greenness in each pixel. Based on ExG, dose response curves were fitted to estimate key parameters reflecting herbicide efficacy.  Results showed that images from UAS offer high precision  parameter estimates, easy access to visual control of experimental treatments and cost effective assessments.   The results can be used in R & D of herbicides, be it in Industry or research institutes. In the future UAS may help farmers check the success or failures of weed control and to map weed infestations.

Early physiological mechanisms that occur in crop plants in response to neighboring weeds are not well understood. In this experiment, it was hypothesized that, in the absence of direct competition for resources, low red to far red ratio (R:FR) reflected from neighboring weeds will modulate the phenylpropanoid pathway, increase hydrogen peroxide (H₂O₂)_, and up-regulate the expression of ethylene biosynthesis and auxin transport genes. Laboratory experiments were conducted under conditions of non-limiting resources using perennial ryegrass as a model weed species. We discovered that the detection by phytochrome of low R:FR signals reflected from both biological and non-biological sources triggered an up-regulation of ethylene biosynthesis genes and stimulated an auxin transport gene. The low R:FR also modulated the phenylpropanoid pathway resulting in a reduction in anthocyanin content and an enhancement of lignin synthesis. The presence of neighboring weeds also caused an accumulation of H₂O₂ in the first leaf and crown root tissues of the maize seedling. Stomata were observed to be closed as H₂O₂ accumulated in leaf tissue. This is the first study to report the modulation of phenylpropanoid pathway and the accumulation of H₂O₂ attributed to low R:FR. We further suggest that these physiological changes which occur in response to early weed competition, result in a physiological cost to the crop plant, which contributes to the rapid loss in yield observed in weed competition studies conducted under field conditions.

Early season weed control in maize is essential to protect yield potential. The presence of uncontrolled weed seedlings is known to trigger a shade avoidance response in maize seedlings. This response has been observed to delay in reproductive development and a subsequent decline in kernel number. Such changes in reproductive development and kernel number may limit the ability of a maize hybrid to express novel traits such as drought tolerance. In this study, we hypothesized that if weed control was delayed, an increase in the anthesis-to-silking interval (ASI) would occur in both a drought tolerant and non-drought tolerant maize hybrid compared to these hybrids growing under weed free conditions. In order to test this hypothesis, we compared a drought tolerant hybrid with its non-drought tolerant isoline. Field studies were conducted over two years at the Ridgetown Campus (2011 and 2012) and one year at the Woodstock Research Station (2012).Weed control treatments included a season long weedy and weed-free treatment, and weed removal at the 1^st, 3^rd, 5^th, 7^th and 10^th leaf tip stage of maize development. No differences were observed in height or rate of leaf appearance in either of the two years of study. ASI was found to be shorter in the drought tolerant hybrid when compared to the non-drought tolerant hybrid across all treatments. A delay in weed control, however, increased ASI and kernel number loss for both hybrids. No difference in final yield was observed between hybrids in 2011. The lengthening of ASI caused by delayed weed control may limit the effectiveness of the drought tolerant trait. Further studies are required to confirm this result. 

Thiamethoxam, is a broad-spectrum neonicotinoid insecticide which when applied to seed, has been observed to enhance seedling vigour under environmental stress conditions. Stress created by the presence of neighbouring weeds is known to trigger the accumulation of hydrogen peroxide (H₂O₂) in maize seedling tissue. No previous work has explored the effect of thiamethoixam as a seed treatment on the physiological response of maize seedlings emerging in the presence of neighbouring weeds.  In this study, we hypothesized that the enhancement in seedlings vigour reported in seedlings emerging from seeds treated with thiamethoxam is the result of a reduction in H₂O₂ accumulation. We further hypothesized that the mode of action of thiamethoxam involves the alteration of gene expression linked to anthocyanin biosynthesis pathway and antioxidant scavenging genes. In this study, thiamethoxam was found to enhance seedling vigour and to overcome the expression of typical shade avoidance characteristics in the presence of neighbouring weeds. These results were attributed to an increase in seed germination, the maintenance of anthocayanin content, and the activation of scavenging genes which reduced the accumulation of H₂O₂ in maize seedling tissues. These results suggest the possibility of new chemistries and modes of action be explored as novel seed treatments to up-regulate free radical scavenging genes and to maintain the antioxidant system within plants. Such an approach may provide an opportunity to enhance crop competitiveness with weeds.

Palmer Amaranth Management in Enlist Cotton Systems in the Texas High Plains. M. R. Manuchehri*¹, P. A. Dotray¹, J. D. Reed², J. W. Keeling², and J. A. Lee³; ¹Texas Tech University, Lubbock, TX, ²Texas A&M AgriLife Research, Lubbock, TX, ³Dow AgroSciences, Lubbock, TX.

Russian-thistle (Salsola tragus L.) and Palmer amaranth (Amarathus palmeri S. Wats.) control presents many challenges in Texas High Plains cotton. Burndown treatments such as glyphosate can be inconsistent in controlling Russian-thistle while resistant escapes are a concern in Palmer amaranth management. Enlist technology, utiliziting 2,4-D + glyphosate crop tolerance, has the potential to effectively control Russian-thistle, Palmer amaranth, and other difficult to manage weeds in Texas High Plains cotton. Field studies were established in 2012 near Lubbock and Halfway, TX to 1) evaluate 2,4-D Choline alone, glyphosate alone, and 2,4-D + glyphosate (Enlist Duo) for preplant burndown control of glyphosate-susceptible Russian-thistle and 2) evaluate Enlist Duo alone and in combination with glufosinate and several soil-residual herbicides for postemergence control of glyphosate-susceptible Palmer amaranth in Enlist Cotton. Preplant burndown treatments included glyphosate, glufosinate, 2,4-D Choline, Enlist Duo, and 2,4-D Choline + glufosinate. Postemergence treatments following a preemergence application of fluometuron included glyphosate followed by (fb) glyphosate, glufosinate fb glufosinate,  Enlist Duo (1.64 kg ae ha^-1) fb Enlist Duo (1.64 kg ae ha^-1), Enlist Duo (2.20 kg ae ha^-1) fb Enlist Duo (2.20 kg ae ha^-1), Enlist Duo + glufosinate fb Enlist Duo, Enlist Duo + glufosinate fb glufosinate, Enlist Duo + glufosinate fb Enlist Duo + glufosinate, Enlist Duo + S-metolachlor fb Enlist Duo + glufosinate, Enlist Duo + pyrithiobac fb Enlist Duo + glufosinate, Enlist Duo + acetolachlor fb Enlist Duo + glufosinate, and 2,4-D Choline + glufosinate fb 2,4-D Choline + glufosinate. Visual injury of target weed species was recorded at 14 and 21 days after application. Enlist Duo improved Russian-thistle control (93-95%) compared to glyphosate or 2,4-D alone (68-79%). Enlist Duo controlled Russian-thistle 95%, which was similar to Enlist Duo + glufosinate or 2,4-D Choline + glufosinate (91-93%). In Lubbock, Palmer amaranth control was achieved with glyphosate, Enlist Duo, or Enlist Duo + glufosinate applied early postemergence (EPOST) (93-99%). In Halfway, Enlist Duo control EPOST was improved (83-94%) with the addition of a soil-residual herbicide compared to Enlist Duo alone (68%). Weed pressure was greater in Halfway compared to Lubbock; however, Enlist Duo fb mid-postemergence achieved greater than 94% Palmer amaranth control at both locations. 

Limited data is available comparing weed control systems in glyphosate-resistant soybean to glufosinate-resistant soybean in a glyphosate-resistant weed population.  A small-plot research trial was established to address the following objectives:  1. Determine effectiveness of various herbicide programs in glyphosate- and glufosinate-resistant soybean; 2. Determine effectiveness of various preemergence herbicides in glyphosate- and glufosinate-resistant soybean; and 3. Determine yield differences between herbicide programs in glyphosate- and glufosinate-resistant soybean.  The trial was established in a glyphosate-resistant waterhemp population near Holloway, MN and a glyphosate-resistant common ragweed population near Buxton, ND.  The herbicide programs included glyphosate (1.68 kg ae/ha followed by 0.84 kg/ha) alone and glufosinate (0.59 kg ai/ha followed by 0.59 kg/ha) alone, glyphosate and glufosinate plus an additional postemergence herbicide, preemergence followed by glyphosate and glufosinate alone, glyphosate and glufosinate applied early postemergence plus an acetamide herbicide and plus an additional postemergence herbicide, preemergence followed by glyphosate and glufosinate plus an additional postemergence herbicide, and preemergence followed by glyphosate and glufosinate plus an acetamide herbicide plus an additional postemergence herbicide.  Glyphosate and glufosinate were applied at the same rates when in mixtures as applied alone.  All herbicide treatments were applied with a bicycle sprayer calibrated to deliver 159 l/ha at 276 kPa.  Glyphosate- and glufosinate-resistant soybean were planted on April 25 and May 3, 2012 at Holloway, MN and Buxton, ND, respectively and all preemergence herbicides applied after planting.  Postemergence herbicides were applied at various weed stages for the initial application and as needed in the second application for each treatment.

At the time of the postemergence application following preemergence herbicides the rank of effectiveness of the preemergence herbicides were as follows:  saflufenacil plus dimethenamid (Verdict) plus pyroxasulfone, saflufenacil plus pyroxasulfone, metribuzin plus s-metolachlor (Boundary), fomesafen plus s-metolachlor (Prefix), flumioxazin plus metribuzin, and flumioxazin plus pyroxasulfone (Fierce) controlled 95, 94, 89, 87, 77, and 69% glyphosate-resistant waterhemp, respectively and flumioxazin plus metribuzin, saflufenacil plus dimethenamid (Verdict) plus pyroxasulfone, saflufenacil plus pyroxasulfone, saflufenacil plus pyroxasulfone, fomesafen plus s-metolachlor (Prefix), and flumioxazin plus pyroxasulfone (Fierce) controlled 77, 69, 69, 65, 56, and 48% glyphosate-resistant common ragweed, respectively.  Just before harvest at Holloway, MN, all treatments in glufosinate-resistant soybean controlled 96% of glyphosate-resistant waterhemp compared to all treatments in glyphosate-resistant soybean controlling 89% of glyphosate-resistant waterhemp.  Just before harvest at Buxton, ND, all treatments in glufosinate-resistant soybean controlled 98% of glyphosate-resistant common ragweed compared to all treatments in glyphosate-resistant soybean controlling 79% of glyphosate-resistant common ragweed.  The herbicide program ranking for control of glyphosate-resistant waterhemp was as follows:  preemergence followed by glufosinate plus an acetamide herbicide plus an additional postemergence herbicide (99%), preemergence followed by glufosinate plus an additional postemergence herbicide (99%), glufosinate alone (99%), glufosinate plus an additional postemergence herbicide (98%), glufosinate applied early postemergence plus an acetamide herbicide and plus an additional postemergence herbicide (97%), and preemergence followed by glufosinate alone (93%) for glufosinate-resistant soybean and preemergence followed by glyphosate alone (94%), preemergence followed by glyphosate plus an additional postemergence herbicide (93%), preemergence followed by glyphosate plus an acetamide herbicide plus an additional postemergence herbicide (91%), glyphosate plus an additional postemergence herbicide (90%), glyphosate alone (75%), and glyphosate applied early postemergence plus an acetamide herbicide and plus an additional postemergence herbicide (71%) for glyphosate-resistant soybean.  The herbicide program ranking for control of glyphosate-resistant common ragweed was as follows:  preemergence followed by glufosinate plus an acetamide herbicide plus an additional postemergence herbicide glyphosate (99%), preemergence followed by glufosinate plus an additional postemergence herbicide (99%), preemergence followed by glufosinate alone (99%), glufosinate plus an additional postemergence herbicide (97%), glufosinate alone (97%), and glufosinate applied early postemergence plus an acetamide herbicide and plus an additional postemergence herbicide (97%) for glufosinate-resistant soybean and preemergence followed by glyphosate plus an acetamide herbicide plus an additional postemergence herbicide (99%), preemergence followed by glyphosate plus an additional postemergence herbicide (95%), preemergence followed by glyphosate alone (78%), glyphosate plus an additional postemergence herbicide (73%), glyphosate applied early postemergence plus an acetamide herbicide and plus an additional postemergence herbicide (68%), and glyphosate alone (58%) for glyphosate-resistant soybean.  At Holloway, MN the glyphosate-resistant soybean out-yielded the glufosinate-resistant soybean across all treatments 2529 to 1917 kg/ha.  At Buxton, ND the glufosinate-resistant soybean out-yielded the glyphosate-resistant soybean across all treatments 733 to 659 kg/ha.

Over the past 3 years, tall waterhemp (Amaranthus tuberculatus Moq. Sauer) resistance to 4-hydroxyphenyl-pyruvate dioxygenase (HPPD) inhibiting herbicides has been confirmed in Illinois, Iowa and Nebraska seed corn production fields.  Resistance to HPPD-inhibiting herbicides in Palmer amaranth (A. palmeri S. Wats.) has also been reported in Kansas and Nebraska. These populations are also resistant to other herbicides with different mechanisms of action (e.g. atrazine), and can therefore, be considered multiple-herbicide, resistant populations. The existence of these HPPD-resistant populations illustrates the propensity of different species within this genus, to evolve resistance to HPPD-inhibitors, in addition to other mechanisms of action.

The evolution of HPPD-inhibitor resistance in these seed corn production fields has been attributed to the limited diversity of cultural practices and of mechanisms of action of herbicides used, necessitated by the sensitivity of inbred lines to herbicides that are more widely available for use in field corn production. Nevertheless, this development is an early warning of potentially more widespread occurrences. In common with resistance to other herbicides, the risk of HPPD-resistance development is high if there is exclusive reliance on HPPD-inhibiting herbicides for weed control, particularly in species with high genetic diversity and which are obligate out-crossers, such as A. tuberculatus or A. palmeri, in which resistance to other herbicide mechanisms of action has already evolved.

Considerable resources have been employed in research to understand the mechanism of resistance and to assess the probability of evolution of further resistance to HPPD-inhibitors in waterhemp. In addition, research continues to explore the options for managing this issue from both proactive and solution-based approaches, in corn and soybean production systems.  A diverse approach, which includes the use of multiple mechanisms of action and other methods of weed management, is critical to the sustainable use of HPPD-inhibiting herbicides.

Post-emergence weed control from protoporphyrinogen oxidase (PPGO) herbicides is highly dependent on weed size at the time of herbicide application. The intraspecific variability in the control of Palmer amaranth (Amaranthus palmeri or AMAPA) accessions with fomesafen applied as Flexstar® at 3 and 6 inch height of plants was evaluated in the greenhouse. Additionally, AMAPA and waterhemp (Amaranthus tuberculatus or AMATA) accessions were screened for fomesafen sensitivity. Three and six inch tall plants of ten different AMAPA accessions were treated with 0, 2, 4, 8.2, 16.4, 32.8, 65.7, 131.5, 263 g a.i. per ha of fomesafen. Furthermore, to test fomesafen sensitivity three inch tall AMAPA and AMATA plants were treated with 65 and 7 g ai of fomesafen, respectively, to obtain 80% control. Percent control and biomass evaluations were recorded 21 days after treatment. Significant differences in control and biomass were observed between AMAPA accessions treated at the same rate of Flexstar. As expected, the control for all accessions in all treatments decreased significantly from the application made to plants 6 inches in height versus 3 inch plants. The variability in control of AMAPA at the same rate of herbicide indicates that there are inherent differences in the sensitivity of AMAPA populations to PPGO herbicides with respect to both origin and height. These data clearly suggest that fomesafen provides most effective and consistent control of smaller AMAPA plants. All AMAPA accessions tested in this test were fomesafen sensitive. All AMAPA accessions were controlled (>90%) with 65 g rate of fomesafen. However, reduced fomesafen sensitivity was observed in seven AMATA accessions when treated with 7 g rate of fomesafen.

In summer, 2011, we investigated suspected glyphosate-resistant (GR) kochia (Kochia scoparia (L.) Schrad.) in three chem-fallow fields (designated F1, F2, F3, each farmed by a different grower) in southern Alberta. This study characterizes glyphosate resistance in those populations, based on data from dose-response experiments. In a greenhouse experiment, the three populations exhibited a resistance factor ranging from 4 to 6 based on shoot biomass response (GR₅₀ ratios), or 5 to 7 based on survival response (LD₅₀ ratios). Similar results were found in a field dose-response experiment at Lethbridge, Alberta in spring, 2012 using the F2 kochia population. In fall, 2011, we surveyed 46 fields within a 20-km radius of the three chem-fallow fields for GR kochia. In the greenhouse, populations were screened with glyphosate at 900 g ae ha^-1. Seven populations were confirmed as GR, the farthest site located about 13 km from the three originally confirmed populations. An additional GR population more than 100 km away was later confirmed. Populations were screened for acetolactate synthase (ALS)-inhibitor (thifensulfuron:tribenuron) and dicamba resistance in the greenhouse, with molecular characterization of ALS-inhibitor resistance in the F1, F2, and F3 populations. All GR populations were resistant to the ALS-inhibiting herbicide, but susceptible to dicamba. ALS-inhibitor resistance in kochia was conferred by Pro197, Asp376, or Trp574 amino acid substitutions. This study confirms the first occurrence of a GR weed in western Canada.

We have recently (2012) confirmed the presence of glyphosate-resistant kochia in Montana.  The two suspected kochia populations in fallow fields from northern Montana in 2012 were tested (whole plant bioassay) and found to be 8- to 10-fold more resistant to glyphosate compared to a known susceptible biotype.  We are currently investigating other cases of suspected glyphosate-resistant kochia populations from MT.  There is a need for development of alternative (non-glyphosate) herbicide programs for control of glyphosate-resistant kochia in wheat-fallow systems.  Field experiments were conducted at the MSU Southern Agricultural Research Center, Huntley, MT, in 2011 and 2012, to evaluate herbicide options for kochia control in spring fallow and in wheat stubble (post-harvest).  Herbicides were applied with a hand-held boom calibrated to deliver 94 L ha^-1 at 276 kPa.  Except the post-harvest treatments, all POST treatments were applied to 8- to 10-cm tall kochia plants.  Experiments were conducted in a randomized complete block design with 4 replications.  Kochia control with PRE applications of dicamba (0.56 kg ae/ha) and sulfentrazone (0.210 kg ai/ha) averaged 92% compared with 82 and 71% control from KIH 485 (0.175 kg ai/ha) and flumioxazin (0.07 kg ai/ha), respectively, 6 wk after application.  Among POST herbicide programs, fluroxypyr + bromoxynil at 0.361 kg/ha, pyrosulfutole + bromoxynil at 0.109 kg/ha, carfentrazone-ethyl + 2, 4-D at 1.716 kg/ha, and paraquat (0.84 kg ai/ha) plus linuron (0.84 kg ai/ha) provided effective control of kochia, which averaged 96% 21 DAA.  Kochia control from POST applications of diflufenzopyr + dicamba at 0.024 kg/ha, saflufenacil (0.025 kg/ha) plus 2,4-D ester (0.282 kg/ha), diflufenzopyr + dicamba at 0.024 kg/ha along with 2,4-D (0.183 kg/ha) averaged 84%.  Glyphosate at 1.26 kg ae/ha provided 82% control of kochia (population was susceptible to glyphosate) 21 DAA.  Among the post-harvest (wheat stubble) herbicide programs, paraquat (0.42 kg ai/ha) plus linuron (0.84 kg ai/ha) and paraquat (0.42 ka ai/ha) plus metribuzin were the best treatments with 95% average kochia control 25 DAA.  Kochia control in wheat stubble with diflufenzopyr + dicamba plus 2,4-D LV4 was 70%, which was higher than the control (55%) obtained from dicamba plus 2,4-D LV4.  In conclusion, these non-glyphosate based post-harvest, early spring residual, and alternative POST burndown herbicide programs could be utilized to manage glyphosate-resistant kochia in no-till wheat-fallow systems.  However, potential injury to wheat crop from these soil residual herbicides especially under dry conditions of Montana needs further investigation.

Prohibiting pesticides on turf: What we have learned from New York State. J. Kao-Kniffin; Cornell University, Ithaca, NY.

New York State (NYS) has been experiencing a change in the regulatory landscape in the past 12 years that places far more restrictions on weed management of turf and grounds. The first wave of restrictions occurred in the late 1980s requiring the notification of pesticide applications on commercial turf. Amendments to the law followed soon after, culminating in the 2000 Neighbor Notification Law that expanded written warnings of pesticide use on residential and commercial turf. More recently, the 2010 Child Safe Playing Fields Law limits pesticide use on school grounds and daycare centers to products containing active and inert ingredients that are deemed minimal risk under FIFRA 25(b) and 4a. For weed management, we identified only 10 post-emergent herbicides adhering to the strict requirements of the new law. Examples of active ingredients include citric acid, clove oil, eugenol, lemongrass oil, and 2-phenethyl propionate. All of the allowable herbicides are non-selective and show considerable variation in their effectiveness in vegetation control. As an alternative to chemical control, we found that thermal weeding with a propane torch showed greater total vegetation control compared to the organic herbicides. Although the 2010 law covers only school grounds and daycare centers in NYS, we expect an increase in the demand for organic land care management beyond the intent of the law. Initial survey results show that 27% of respondents working in turf management primarily in NYS have been requested by clients to provide organic land care services, with an additional 25% of respondents anticipating requests of organic services in the future. Ongoing survey work will provide greater understanding of changing land care management in NYS and implications for regional weed management in the Northeastern U.S. Corresponding author: jtk57@cornell.edu

Efforts to decrease supplemental nitrogen (N) applications to turfgrass justify alternative fertility strategies such as legume inclusion. Legumes such as clovers (Trifolium spp.) are present within many turfgrass scenarios. Legume persistence is partly due to an ability to biologically fix atmospheric N, which is incorporated into the plant as proteins and other compounds. N is subsequently shared with associated grasses through the decomposition of legume -roots and -foliage. For this reason, turf health is often improved rather than diminished. Our research estimates biological N fixation within mixed bermudagrass (Cynodon spp.) -white clover (T. repens) swards.

A three-year study (2010 to 2012) was conducted to test the effects of clover inclusion upon N fixation and transfer within an existing bermudagrass (C. dactylon x C. transvaalensis) lawn at Auburn University’s Turfgrass Research Unit in Auburn, AL. Treatment factors were clover inclusion and supplemental N rate (0 to 8 g N m^-2 month^-1) applied as CaNO₃, with Ca applied to uniformity via CaSO₄. White clover was seed-established in October prior to each year (3 g live seed m^-2). Supplemental N was applied monthly, April to August. Clover population densities were quantified monthly via subsample plant counts. Plots were harvested monthly during active bermudagrass growth (April through September). Clippings were air-dried, weighed, and representative samples were partitioned into their constituent grass or clover parts. Grass-only and grass-plus-clover mixtures were analyzed for N composition. N fixation was calculated using the difference method, by subtracting N-yield of grass-alone plots from the total N-yield of grass-plus-clover mixtures. Furthermore, the apparent N transfer was estimated during 2011 and 2012 as the difference between grass-alone N-yield of mixtures and that of grass monocultures. Means were separated using mixed models analysis. Adjusted 95% confidence intervals were used to detect significant differences between treatments.

During the three-year study, N fixation was estimated to be 8.6 g m^-2 year^-1 regardless of supplemental N rate. However, N rate was an important factor within all years, having impacted grass yield, clover density, N fixation and N transfer. N fixation was generally suppressed at the high and low extremes of supplemental N rate and decreased during summer months, presumably due to decreased clover populations and increased competitiveness of bermudagrass.

Unlike fixation, transfer of N actually increased with increasing supplemental N, though these results differ from those reported by others. N transfer between clover and bermudagrass was higher than that commonly reported within other scenarios (~30%). We observed 46 and 64%, respectively, during 2011 and 2012. These results may overestimate N transfer due to a lag between early season N fixation and the beginning of bermudagrass growth.

These results and others are evidence of white clover’s ability to supplement turfgrass N requirements. Ongoing research evaluates N contributions of foliage deposited during mowing occurrences and soil C change as a result of mixed grass-clover swards.

SELECTIVITY OF METHIOZOLIN FOR ANNUAL BLUEGRASS CONTROL IN CREEPING BENTGRASS GOLF GREENS AS INFLUENCED BY TEMPERATURE AND APPLICATION TIMING.  P. McCullough; Department of Crop and Soil Sciences, University of Georgia, Griffin, GA 30223; D. Gómez de Barreda, Polytechnic University of Valencia, Spain; J. Yu, Department of Crop and Soil Sciences, University of Georgia, Griffin, GA 30223.

ABSTRACT

Methiozolin controls annual bluegrass in creeping bentgrass but application timing and temperature could influence efficacy in turf.  In field experiments, sequential methiozolin applications totaling 3.36 kg ai ha^-1 provided excellent (>90%) annual bluegrass control at 8 weeks after initial treatment when treatments were initiated in Feb./March or May but programs totaling 0.84 and 1.68 kg ha^-1 provided poor control (<70%) at both timings.  Methiozolin at all rates caused minimal turf injury (<8%) but creeping bentgrass was only injured from Feb./March applications.  In growth chamber experiments, creeping bentgrass injury from methiozolin at 10 C was 2 and 4x greater than at 20 C and 30 C, respectively, while annual bluegrass injury was similar across temperatures.  In laboratory experiments, annual bluegrass had more foliar absorption of ¹⁴C-methiozolin than creeping bentgrass at 30/25 C (day/night), compared to 15/10 C, but translocation was similar at both temperatures as >90% of absorbed ¹⁴C remained in the treated leaf after 72 hours.  Annual bluegrass distributed and recovered more radioactivity to shoots from root-applied ¹⁴C-methiozolin than creeping bentgrass while both species had about 2x more distribution to shoots at 30/25 C than 15/10 C.  Metabolites were not detected in annual bluegrass or creeping bentgrass at 1, 3, or 7 days after treatment when grown at 15/10 C or 30/25 C suggesting uptake and translocation contributes to methiozolin selectivity in turfgrass. 

Methiozolin (PoaCure) a new herbicide developed by the Moghu Research Center in Daejeon, Korea for safe and selective removal of annual bluegrass (Poa annua) from creeping bentgrass (Agrostis stolonifera) turf.  Methiozolin is a member of the isoxazoline class of chemistry and works by either inhibiting cell wall biosynthesis or through inhibition of the enzyme tyrosine aminotransferase.  Ethephon (Proxy) is a plant growth regulator which is used on putting greens to temporarily suppress annual bluegrass seedheads.  Applications of ethephon improve the aesthetic quality and playability of putting greens during peak seedhead production on putting greens.  Previous research conducted on two Virginia golf courses in 2011 indicated ethephon may negatively impact methiozolin efficacy for annual bluegrass control and creeping bentgrass response.  The objective of this study was to determine whether or not the addition of ethephon to methiozolin programs would influence annual bluegrass control and creeping bentgrass safety.  This trial was initiated on March 13, 2012 at the Blacksburg Country Club in Blacksburg, Virginia on a mixed variety creeping bentgrass putting green.  Sequential applications were made on March 13 and April 16.  Methiozolin was applied alone at 500, 1000 and 2000 g ai/ha, and 500, 1000 and 2000 g ai/ha + 3818 g ai/ha ethephon.  A comparison treatment of 1000 g ai/ha methiozolin + 3818 g ai/ha ethephon+ 48 g ai/ha trinexapac-ethyl as well as an untreated check were also included.

Initial annual bluegrass cover ranged from 43 to 57%.  At the time of the first application, 82% of the annual bluegrass plants were producing seedheads.    At two weeks after the initial treatment (WAIT), methiozolin at 1000 and 2000 g ai/ha controlled annual bluegrass 22 and 53%, respectively, and all other treatments controlled annual bluegrass less than 15%.  At 4 WAIT, methiozolin at 2000 g ai/ha controlled annual bluegrass 73% when applied alone and 53% when applied in a mixture with ethephon.  At 6 WAIT, all treatments except methiozolin at 500 g ai/ha controlled annual bluegrass over 87%. At 8 WAIT, methiozolin alone did not significantly injure bentgrass regardless of rate while combinations of ethephon with 1000 or 2000 g ai/ha methiozolin injured creeping bentgrass 23 and 80%, respectively.  In addition, normalized difference vegetative index was significantly decreased when ethephon was added to any rate of methiozolin.   By mid- October (28 WAIT), methiozolin with or without ethephon or trinexapac ethyl at 1000 and 2000 g ai/ha controlled annual bluegrass 85% or higher.  Methiozolin at 500 g ai/ha with and without ethephon controlled annual bluegrass 43 and 40%, respectively.  All bentgrass injury had recovered and voided areas of turf caused by removal of annual bluegrass had recovered.  Visually estimated bentgrass texture, however, was significantly lower in plots previously injured by ethephon + methiozolin.  These data suggest ethephon should not be mixed with methiozolin to avoid increased creeping bentgrass injury and delayed recovery of areas voided by controlled annual bluegrass.

Amicarbazone and methiozolin are herbicides with efficacy for annual bluegrass (Poa annua L.) control in creeping bentgrass (Agrostis stolonifera L.). Greenhouse research was conducted at the University of Tennessee (Knoxville, TN) to determine the effects of rooting depth and soil type on creeping bentgrass injury with amicarbazone and methiozolin. The effects of soil texture on annual bluegrass control efficacy were evaluated in field studies conducted on golf greens in Knoxville, TN and Lubbock, TX.

‘Penncross’ creeping bentgrass was established in sand- or soil-based rootzones using mini-rhizotrons in the greenhouse. Plants were treated with amicarbazone (49, 98, 196 g ha^-1) or methiozolin (500, 1000, 2000 g ha^-1) once root growth reached depths of 5, 10, and 15 cm. Amicarbazone was more injurious than methiozolin in both rootzones. Creeping bentgrass injury with amicarbazone measured 62% in soil compared to only 38% in sand. In addition 54 to 69% reductions in root length density were observed in the sand-based compared to 42 to 81% reductions in soil. Methiozolin resulted in ≤ 12% creeping bentgrass injury, regardless of rootzone type or application rate, and reduced root length density ≤ 25%. Amicarbazone injury was lower at the 15 cm rooting depth compared to the 5 and 10 cm rooting depths. Responses indicate that methiozolin is less injurious to creeping bentgrass than amicarbazone and that rooting depth and soil type affect creeping bentgrass injury with amicarbazone.

Field experiments evaluated annual bluegrass control efficacy with methiozolin using two application rates (500 and 1000 g ha^-1) and six application regimes [October, November, December, October followed by (fb) November, November fb December, and October fb November fb December] on sand- and soil-based putting greens. Annual bluegrass control with methiozolin at 1000 g ha^-1 on sand-based greens ranged from 70 to 72% compared to 87 to 89% on soil-based greens. Treatment at 500 g ha^-1 controlled annual bluegrass 57 to 64% on sand-based greens compared to 72 to 80% on soil-based greens. Sequential application programs controlled annual bluegrass 70 to 79% on sand-based greens and 85 to 92% on soil-based greens. Responses indicate that soil type and rooting depth affect the activity of amicarbazone and methiozolin applications for weed control on creeping bentgrass putting greens.

Roughstalk bluegrass (Poa trivialis) is a perennial cool season grass often found as a weed of desirable cool season turfgrasses such as Kentucky bluegrass (Poa pratensis).  It is difficult to selectively control roughstalk bluegrass in cool season turf since its physiology and life cycle are similar to the desirable species.  Primisulfuron can suppress roughstalk bluegrass without injuring cool season turf and methiozolin is a new herbicide developed for the selective control of annual bluegrass in cool season turf that also has activity on roughstalk bluegrass. 

The objective of this research was to evaluate combinations of primisulfuron and methiozolin for control of the perennial roughstalk bluegrass in a Kentucky bluegrass turf maintained at 1.5cm.  The study was initiated April 6^th 2012 in Blacksburg VA.  There were 12 treatments including a nontreated control.  Four were applied at weekly intervals for 8 weeks including methiozolin alone at 1000 g ai/ha, primisulfuron alone at 13.1 g ai/h, and methiozolin + primisulfuron at 1000 + 13.1 and 500 + 5.25g ai/ha.   Six treatments were applied at two week intervals for eight weeks including methiozolin alone at 2000 g ai/ha, primisulfuron alone at 26.3 g ai/h, and methiozolin + primisulfuron at 1000 + 13.1, 1000 + 26.3, 2000 + 13.1 and 2000 + 26.3g ai/ha.   The final treatment was primisulfuron applied at 4 week intervals for 8 weeks at 39.4 g ai/ha.  Visual cover, injury, control and NDVI ratings were taken 0, 3, 5, 6, 7, and 12 weeks after initiation (WAI). 

Three WAI primisulfuron at 26.3 g ai/ha controlled roughstalk bluegrass 83%.  Methiozolin + primisulfuron combinations of 500 + 5.25, 2000 + 13.1 and 2000 + 26.3 g ai/ha controlled roughstalk bluegrass 63, 52, 78% respectively, and were equivalent to one another.  No treatments controlled annual bluegrass 3 WAI.  By 7 WAI all primisulfuron and primisulfuron + methiozolin treatments controlled roughstalk bluegrass 92-100% and were equivalent to one another.  Methiozolin alone at both rates only controlled roughstalk bluegrass 30-38% 7 WAI.  Primisulfuron alone at 13.1, 26.3 and 39.4 g ai/ha controlled annual bluegrass 69, 83, and 71%, respectively 7 WAI.   All combinations of primisulfuron and methiozolin controlled annual bluegrass 88-98% except the 1000 + 13.1 g ai/ha which only controlled it 30%.  The most important rating will be one year after initiation to determine the level of control for this perennial weed.  However, based on this research spring applications of primisulfuron alone or in combination with methiozolin effectively controls roughstalk and annual bluegrass in the same season. 

UPTAKE, TRANSLOCATION, AND METABOLISM OF DITHIOPYR IN LARGE AND SMOOTH CRABGRASS AS INFLUENCED BY ENVIRONMENT, GROWTH STAGE, AND ADJUVANTS. D. Gómez de Barreda, Polytechnic University of Valencia, Spain; P. McCullough and J. Yu, Department of Crop and Soil Sciences, University of Georgia, Griffin, GA 30223.

ABSTRACT

Dithiopyr provides preemergence and early postemergence control of crabgrasses (Digitaria spp.) in turfgrass but postemergence applications often have inconsistent efficacy.  Experiments were conducted to evaluate effects of growth stage, temperature, and adjuvant use on absorption and translocation of dithiopyr in smooth and large crabgrass (Digitaria ischaemum and D. sanguinalis).  Multi-tiller smooth crabgrass absorbed more root-applied ¹⁴C-dithiopyr than multi-leaf and one-tiller plants but radioactivity concentration (Bq/g) across growth stages from high to low measured: multi-leaf > one-tiller > multi-tiller.  Smooth crabgrass had approximately twofold more total radioactivity concentrations at 15/10 C compared to 30/25 C from root applications.  Distribution of root-applied dithiopyr to shoots was twofold greater in multi-leaf smooth crabgrass compared to multi-tiller plants and increased at 30/25 C compared to 15/10 C.  Across growth stages, smooth crabgrass had more foliar absorption of ¹⁴C-dithiopyr at 15/10 C compared to 30/25 C and >90% of absorbed ¹⁴C was retained in shoots.  The addition of a nonionic surfactant (Activator 90) at 0.25% v/v increased foliar absorption of ¹⁴C-dithiopyr in large and smooth crabgrass at one-tiller compared to treatments without a surfactant.  

Oxadiazon is a preemergent herbicide that has been used commercially for control of annual grasses, including goosegrass (Eleusine indica) in warm season turf since it was registered in the late-1970’s. During 2009 and 2010, a golf course superintendent in the Richmond, VA area began to experience lack of goosegrass control with oxadiazon applied at 3.4 to 4.5 kg ai/ha. This golf course had successfully used oxadiazon for preemergence goosegrass control since it opened in the early 1990’s. In 2011, Virginia Tech and Bayer CropScience LP independently sampled escaped goosegrass plants/seed and tested to determine if herbicide resistance might explain the lack of product performance. Six unique ecotypes or seed sources were tested. Seed of native goosegrass was collected near Clayton, NC and Blacksburg, VA in areas known to have no prior history of oxadiazon use to serve as wild type comparisons. Three mature goosegrass plants collected from the Richmond, VA golf course served as seed donors for three suspected resistant ecotypes that were evaluated in the study by Bayer. A composite of seed from plants growing at random locations on previously oxadiazon-treated fairways at the same golf course was collected for use in the Virginia Tech trial. Approximately 100 seeds were evenly spread over a soil-mix (3 part sand: 1 part potting soil) packed lightly, then irrigated with enough water to allow soil to settle and drain for 24 hrs. Seed was then topdressed lightly with dry sand and irrigated lightly to encourage seed/soil settling. Pots were treated with Ronstar FLO (380 g oxadiazon/L) in a spray chamber equipped with flat fan nozzles at a spray volume of 373 L/ha. Treatments included oxadiazon applied at rates of 4.48, 3.4, 2.2, 1.1, 0.56, 0.28, 0.14, 0.07, and 0.03 kg ai/ha. Specticle FLO (indaziflam at 0.05 kg ai/ha) and Barricade (prodiamine at 0.84 kg ai/ha) were included as reference standards. Pots were then placed in a greenhouse and irrigated regularly to encourage seed germination. Emerged seedlings were counted weekly. Seedling counts were transformed to percent reduction of counts in nontreated pots and oxadiazon rate responses were fit to the hyperbolic function using Proc Nlin in SAS. Estimated i values and LC95 values that were subjected to ANOVA to test for differences in lethal concentration required to reduce seedling counts between ecotypes/seed sources. Seedling population reductions for all seed sources fit the hyperbolic function in response to oxadiazon rate with wild-type plants (WT) having rapid ascent to 100% reduction compared to slower ascents from suspected resistant plants (SR). Estimated i values from WT seed were several orders of magnitude higher than i values from SR plants. The SR population in Virginia Tech trials required an estimated 16.5 kg ai/ha oxadiazon to kill 95% of the population at 9 WAT while the Virginia Tech WT seed required only 0.5 kg ai/ha. Likewise, WT seed was 24, 45, 87, and 105 times more susceptible to oxadiazon than SR plants in the studies conducted by Bayer in North Carolina. Seedlings were never observed in the pots treated with prodiamine or indaziflam at any time in any study. Based on these results, the goosegrass collected from the Richmond golf course has tested positively for oxadiazon resistance. Oxadiazon is a PPO inhibitor with no documented cases of annual grass resistance globally. This is the first reported case of herbicide resistance development of an annual grass to oxadiazon. It is not known if this is an isolated biotype or if other sites may also be at risk. However, it does indicate that the potential to develop resistance is relatively low given the ~20 years of use at the golf course where resistant goosegrass was found and over 40 years of general use after introduction, but resistance management strategies should be implemented before options become limited.

Uptake, Translocation, and Metabolism of Methiozolin in Five Weed Species. D. Gómez de Barreda, Polytechnic University of Valencia, Spain; P. McCullough, J. Yu, and S. Sidhu, Department of Crop and Soil Sciences, University of Georgia, Griffin, GA 30223.

ABSTRACT

Experiments were conducted to evaluate application placement and timing, uptake, translocation, and metabolism of methiozolin on turfgrass weed species.  In greenhouse experiments, preemergence applications of methiozolin provided excellent control (>90%) of annual bluegrass (Poa annua), goosegrass (Eleusine indica), smooth crabgrass (Digitaria ischaemum), large crabgrass (Digitaria sanguinalis), and yellow nutsedge (Cyperus esculentus).  In postemergence experiments, soil and soil + foliar applications of methiozolin reduced biomass of annual bluegrass, goosegrass, smooth crabgrass, and yellow nutsedge more than foliar only applications.  In lab experiments, annual bluegrass, goosegrass, smooth crabgrass, and yellow nutsedge did not metabolize ¹⁴C-methiozolin at 7 days after treatment.  Annual bluegrass, smooth crabgrass, and goosegrass retained >90% of foliar applied ¹⁴C-methiozolin in treated leaves and had minimal translocation to nontreated shoots and roots.  Annual bluegrass translocated more root-absorbed ¹⁴C-methiozolin to shoots than smooth crabgrass but was similar to goosegrass and yellow nutsedge.  

Seedling Broadleaf Weed Control with MBI-005.  J. C. Neal*, R. Schiavone, and C. Harlow; North Carolina State University, Raleigh NC

MBI-005 is a biopesticide produced by fermentation of Streptomyces acidiscabies RL-110.  The active ingredient is thaxtomin, a non-systemic plant toxin.  This class of chemistry has been reported to have herbicidal activity on dicot weeds with significantly less activity on grasses.  In this research we investigated preemergence and postemergence efficacy of MBI-005 on seedling dicot weeds and compared application concentrations and spray volumes for optimum control.  Experiments reported herein were conducted in outdoor containers.  Increasing the dose of MBI-005 from 19 to 38 L/ha improved preemergence and postemergence efficacy on most species tested.  Applied preemergence, 38 L/ha MBI-005 provided greater than 90% control of eclipta (Eclipta prostrata), spotted spurge (Chamaesyce maculata), henbit (Lamium amplexicaule), dandelion (Taraxacum officinale), marsh yellowcress (Rorippa islandica), pearlwort (Sagina procumbens), common groundsel (Senecio vulgaris) and annual bluegrass (Poa annua).  Postemergence applications were less effective on marsh yellowcress, annual bluegrass , dandelion and pearlwort than were preemergence treatments. Common chickweed (Stellaria media) and hairy vetch (Vicia villosa) were not controlled preemergence or postemergence.  Control of flexuous bittercress (Cardamine flexuosa) was less than 60%.  Sequential treatments improved efficacy of both preemergence and postemergence treatments.  Increasing spray volume and concentration improved postemergence control of flexuous bittercress, common groundsel, dandelion, henbit, and eclipta.  Results suggest that the percent control observed was more a function of the actual dose of MBI-005 (L/ha) than spray volume or concentration.    joe_neal@ncsu.edu

Most lawn care professionals use phenoxy-based herbicides to control broadleaf weeds in the spring but applications are often ineffective when temperatures are suboptimal.  This research was initiated to determine if florasulam (N-(2,6-difluorophenyl)-8-fluoro-5-methoxy(1,2,4)triazolo(1,5-c)pyrimidine-2-sulfonamide) when mixed with dithiopyr (S,S'-dimethyl 2-(difluoromethyl)-4-(2-methylpropyl)-6-(trifluoromethyl)-3,5-pyridinedicarbothioate) would be effective for broadleaf weed control during these conditions.  Field studies were conducted from 2007 through 2012 to determine the effect of florasulam and dithiopyr applied alone and in tank mixtures on broadleaf weed control in both cool and warm season turfgrass.  Applications were made prior to or at typical preemergence crabgrass, Digitaria sp., timing acrss the eastern and midwestern US.  Studies were conducted in locations that contained white clover, Trifolium repens, and dandelion, Taraxacum officinale, to assess efficacy of these herbicides applied at this early timing on key weeds common in residential turf.  Florasulam applied alone or in combination with dithiopyr controlled white clover, dandelion and other broadleaf weeds.  At this early timing, other herbicides mixtures containing 2,4-D were less effective.  Florasulam combined with dithiopyr improved weed control in an additive or symergistic manner.  These two herbicides applied together may reduce or eliminate the need for a later season postemergent herbicide treatment.

Several products have been introduced recently for broadleaf weed management in warm-season turfgrass. Studies were conducted at the University of Florida West Florida Research and Education Center to determine the utility of selected products for both summer and winter broadleaf control. Herbicides were applied with a back-pack sprayer with a hand-held boom calibrated to deliver 20 gallons per acre at 20 psi. Weed control and turfgrass injury were visually evaluated at intervals of 3 to 6 wk following treatment. A three-way combination of thiencarbazone + iodosulfuron + dicamba applied postemergence provided 80 to 90% control of several broadleaf weeds including dollarweed (Hydorcotyle sp.), Virginia buttonweed (Diodia virginiana L.) and chamberbitter (Phyllanthus urinaria L.) with minimal injury to hybrid bermudagrass or St. Augustinegrass. Repeat applications often provided better control than a single application. Winter weeds including Carolina geranium (Geranium carolinianum L.), oxalis (Oxalis stricta L.), white clover (Trifolium repens L.) and dandelion (Taraxacum officinale F.H. Wigg.) were also controlled with this combination. Another three-way combination, quinclorac + mecoprop + dicamba, was effective for controlling Carolina geranium, dandelion, cutleaf eveningprimrose (Oenothera laciniata Hill) and white clover. Sulfentrazone + metsulfuron applied postemergence provided 70 to 90% Virginia buttonweed and dollarweed control with minimal injury to bermudagrass. Carfentrazone + quinclorac provided 90 to 100% control of dollarweed, Carolina geranium, white clover and dandelion. These results indicate that there are several options now available for postemergence broadleaf control in turfgrass.

The success of pre-emergent weed control measures, such as the stale seedbed technique, may be enhanced through accurate predictions of seedling emergence timing, which are in part determined by environmental factors like temperature, moisture and oxygen levels, as well as by seed dormancy and early seedling growth. We used population-based threshold models to establish the temperature, moisture and oxygen conditions for optimum germination of multiple-herbicide–resistant and –susceptible late watergrass (Echinochloa phyllopogon), and applied them to predict emergence from field soil. We combined hydrothermal time for germination, accounting for within-population variation in base water potentials (Ψ_b), with thermal time for early growth to predict the quantity and proportional size of the flushes that constitute final recruitment. Emergence in field soils was reduced by moisture stress and flooding, especially for the R population. Germination rates in all populations increased between 9.5 and 31 C, Ψ_b was < -1.0 MPa, and there was no sensitivity to oxygen supply. We evaluated wintertime moisture conditions necessary for optimizing dormancy release by stratifying seeds under a range of water potentials and determined that three weeks’ saturation in ~5 C water is required for full dormancy release. To foster rapid and uniform seedling growth in spring, we recommend saturating field soil for three weeks in winter, then flooding fields in spring for 50 thermal units above a base temperature of ~9.3 C to obtain maximum germination and draining fields for 100-120 additional thermal units to promote early growth. These steps should combine to decrease the time between initial field irrigation and the application of herbicides in a stale seedbed establishment system.

Rice is an essential food crop for more than half of humanity. However, rice yield is lower than the genetic potential of rice varieties throughout the world. Weeds reduce the capacity of rice seedlings to exhibit their genetic potential depending on the age at the time of transplanting. Farmers need to know how the critical period of weed management in rice varies with change in seedling age at transplanting time. A factorial experiment was undertaken for two consecutive years (2010 and 2011) to determine the influence of seedling age on the critical weed-crop competition period, in terms of growth and yield of rice. Main plots had seedling age treatments, imposed by rice nursery transplantation ages of 14, 21 and 28 days. Subplots consisted of competition treatments including no competition, competition for 20 days after transplanting (DAT), competition for 40 DAT, competition for 60 DAT, competition for 80 DAT and weedy check. The minimum total weed dry weight (9.3 g m^-2) value was recorded in 21-day-old seedlings with competition for 20 DAT; highest (106.2 g m^-2) weed weight was found in 28-day-old seedlings with weedy check. We observed the highest growth trend, at grain formation stage, in 21-day-old seedlings with weed-free conditions, with CGR of 24.5 g m^-2 day^-1. This CGR value was 5.6 percent higher than that recorded in the interaction of 21-day-old seedlings and competition for 20 DAT and 76.2 percent higher than that in 28 days old seedlings with weedy check (the minimum). Moreover, kernel yield (5.6 tons ha^-1) was highest for 21 day-old seedlings and weed-free plots which was 4.3 percent higher than that of 21 day-old seedlings interacting weed competition for 20 DAT. Whereas, the minimum kernel yield (1.8 tons ha^-1) was recorded in 28 day-old seedlings and the weedy check. After economic analysis, transplanting 21-day-old seedlings is recommended, with weed management starting not later than 20 DAT for obtaining high and economical yields of rice.

In production agriculture, it is not uncommon for a crop seedling to experience both intra- and inter-specific interference during the normal course of growth and development.  Although the interference between crop seedlings (intraspecifc) is often considered independently of that among crop and weeds (interspecific), the physiological mechanisms through which yields are reduced may be common to both. In this study, we will compare and contrast the impacts of intra and interspecific interference on the growth and development, stand uniformity and their potential impact on yield determination of maize. We will review literature and data pertaining to the two widely recognized critical periods of maize development: 1) the critical period for weed control (4-13 leaf tips), and 2) the critical period for kernel set (one month centered on silking time). We hypothesize that the type and timing of the stress will differentially impact the advancement of developmental stages, biomass accumulation and yield. Overall, a better understanding of the factors associated with direct competition for limited resources will help elucidate mechanisms underlying stress tolerance of modern maize.

Effective cultivation is critical for weed management on organic farms.  To assess the percentage kill, we counted weeds before and after cultivation operations in the Cornell Organic Grain Cropping Systems Experiment.  The experiment uses a corn-soybean-winter spelt/red clover crop rotation to compare High Fertility, Low Fertility, Intensive Weed Management, and Reduced Tillage systems.  Counts were made in four randomly placed 0.5 m² quadrats in each plot.  The experiment has a diverse and patchy weed flora so for purposes of analysis, weeds were grouped into categories, with only common ragweed and yellow nutsedge, the initially most abundant species, treated separately.  Percentage control was better in corn (80% and 91% at 1^st and 2^nd cultivation) than in soybean (77% and 70%), and effect of crop interacted with cultivation timing. Control varied greatly among taxa, with a single cultivation controlling seedlings of perennials 97%, various annuals 80-87%, and yellow nutsedge and perennial broadleafs only 61% and 55%. Effectiveness of tine weeding was assessed by counting weed seedlings in and outside of subplots protected by plywood sheets. Tine weeding was relatively less effective against common ragweed than against other dicots and annual grasses (primarily giant foxtail), possibly due to the former’s larger seed size.  Annual grasses were better controlled in corn and soybeans by pre-emergence tine weeding (92% control) than by post-emergence tine weeding (65% control).   An experiment in which some subplots were watered immediately after weeding showed that the proportion of seedlings dying due to desiccation as opposed to other causes varied greatly among taxa.  Although the percentage control by a single cultivation event is often small to moderate, the cumulative effect of multiple operations through the season can provide effective weed management.        

Members of the Brassicaceae family are known to contain glucosinolates that once hydrolyzed release compounds that can inhibit germination and cause stunted growth of other plant species. Tansymustard, a winter annual weed member of the Brassicaceae family, is becoming prevalent in no-till fields in the Midwestern USA. Farmers have complained that corn growing in the presence of this weed can be stunted. A greenhouse study was conducted to evaluate the negative feedback effect of tansymustard on corn emergence and growth. Tansymustard plants were grown for 5 weeks in square plastic pots (13 x 13 x 15 cm). At the end of this period, shoots were clipped at the soil surface, cut into 2 cm segments, and placed back to the soil surface and soil + roots were left intact. Five corn seeds were then planted at 4 cm depth in each pot. An additional set of pots with no tansymustard residues was used as control.  Treatments included pots with only tansymustard roots (R), only tansymustard shoots (S), whole tansymustard plant (roots + shoots; W), non-cut tansymustard plants treated with glyphosate two days after planting corn seeds (T), and control (no tansymustard residues; C). Corn emergence was evaluated for 15 days after planting. Corn plants were grown for 4 weeks; at the end of this period, plant height was measured, final density recorded, and shoot dry weight pot^-1 determined. The experiment was arranged in a randomized complete block design with 4 replications per treatment, and was repeated in time. The number of emerged corn plants pot^-1, total corn biomass pot^-1, and corn height were not influenced by the presence of tansymustard residues (R, S, W, or T), leading to the conclusion that tansymustard residues had no negative feedback effect on corn growth in this study. The stunted corn development observed by farmers in the field might have been due to competition, since this weed is often controlled just after crop emergence. 

Plants perceive their neighbours through changes in light quality. This change in light quality is brought about by alterations in the red/far-red ratio detected by plant phytochrome, which in turn will induce a shade avoidance response. The shade avoidance response has been reported to be an important variable defining the critical period for weed control. Previous work has shown that this period occurred from the first to third trifoliate of soybean development. No work, however, has been done to quantify how early a soybean seedling can detect the presence of neighbouring weeds. We hypothesized that a soybean seedling can detect the presence of aboveground neighbouring weeds upon emergence and this detection will be evident through changes in seedling morphology. Growth chamber studies were conducted using the soybean cultivar OAC Wallace grown in the presence of ryegrass. Seedling measurements were recorded at 72 hours after planting, VE, VC, unifoliate, 1^st trifoliate, and 2^nd trifoliate stage of growth. Morphological changes in stem height were observed upon seedling emergence. This alteration in carbon allocation between weedy and weed free treatments persisted throughout all growth stages sampled. The results of this study suggest that detection of changes in light quality induced by aboveground neighbouring weeds occurs at time of seedling emergence. The ability of soybean seedlings to detect changes in light quality at such an early stage of development further suggests that molecular and physiological changes were occurring prior to seedling emergence.

Genotypic variation in early ground cover has been observed in multiple crop species and is implicated as an important predictor of crop-weed competition.  Most of the research on the topic has been conducted using a uniform crop plant density, similar to how most agronomic trials are conducted.  However, this practice can be called into question in the study of early season phenomena, particularly in crops such as soybean where seed size is highly variable amongst genotypes.  This experiment was undertaken with the goal of determining whether holding the mass of seed planted on a plot, while allowing plant density to fluctuate accordingly, would yield different results when screening soybean genotypes.  The alternative method has a large effect, sometimes reversing trends amongst genotypes.  A reevaluation of how to screen germplasm for early season traits may be needed.  There are also implications for making seeding rate recommendations in environments with marginal weed control.  Soybean seeding rates have increasingly been expressed in seeds per acre, whereas the older mass per acre recommendations are likely more predictive of crop-weed competition.

Title: THE NON-NATIVE VASCULAR FLORA AT BROOKHAVEN NATIONAL LABORATORY, LONG ISLAND, NEW YORK.

Abstract:

The objective of this study was to collect and document the non-native vascular plant species at Brookhaven National Laboratory. Collecting trips were made to the laboratory at two-week intervals beginning in April, 2007, terminating on October, 2009 for the purpose of collecting voucher specimens. Ninety eight introduced species have been identified, 30% of the flora. The Asteraceae (19 species) and Poaceae (16 species) contributed the greatest number of non-native species.

Invasive plants have become synonymous with displacement of native species and negative impacts on our ecosystem processes and services. Despite this dogmatic understanding of invasions, the overwhelming majority of studies focus on single consequences in specific locations, with few attempts to scale or integrate impact metrics. In fact there has only been a single attempt to scale ecological impacts, but it suffers from defining impact on a per capita basis and has ironically only been calculated for a single species (Heracleum mantegazzium). Therefore, we are incapable of knowing what the total impact of an invasion is on a system (i.e, impacts to diversity, structure, functions, etc.). To overcome the limitations of current models, we have created a novel functional relationship that is capable of integrating all metrics of interest, and allows a more holistic accounting of ecological impact.

To achieve an integrated impact value, we designed each metric (eg, richness, nitrogen pool, liter production) to be calculated in the common currency of percent difference between the invaded and uninvaded (reference) sites. Metrics that were once examined independently can now be combined into a common unit of measure. An integrating function combines a possible infinite number of metrics, which approaches a theoretical true total ecological impact value. Achieving the actual ecological impact value is therefore non-linearly proportional to the number of metrics measured, which suggests that simply measuring a single metric grossly oversimplifies the “actual” impact. Interestingly, our model also suggests that it may not matter what metrics are quantified from a site as long as enough metrics are sampled.

                  Measuring impact on a per capita basis precludes interspecies comparisons due to the tremendous differences in size among invaders (annual grasses to large trees). By using percentage cover, interspecies comparisons to other invaders and natives with dramatically different size is achievable, which also allows measurements to be taken across the range of possible densities to create an impact curve. This curve is then scaled over invaded area size to create a species-specific impact surface.  With this surface it will be possible to make interspecies impact comparisons, and to estimate population level impacts. Testing this conceptual model with empirical evidence may lead to an understanding of the true impact an invasive species has on its surrounding habitat previously unavailable.

The thistles Carduus nutants L. and C. acanthoides L. have both been implicated as allelopathic species.  These Eurasian native plants are invasive in the U.S. and other parts of the world, competing well with many native species.  Bioassay-guided isolation of phytotoxins from shoots and roots of this plant revealed that a chemical found in the roots, aplotaxene (heptadeca-1,8,11,14-tetrane),  to be the most likely candidate as an allelochemical.  Contrary to the published work of others, we found that this compound to be moderately phytotoxic.  It was also found in relatively large amounts in the roots of both Carduus species, and we found the compound to be exuded by the roots into the soil.

Control of non-indigenous, invasive, C4 grasses (NIIG) in perennial C4-dominated rangelands presents a unique challenge as management approaches designed to target the invasive can result in collateral damage to resident perennial, C4 grasses.  In addition, restoration of indigenous high forage species is often foiled by novel biotic and abiotic conditions that limit re-establishment.  Arid and semi-arid rangelands throughout the Southwestern and Midwestern U.S. have been altered by intensive grazing pressure and fire suppression.  The native seed bank has been reduced and throughout much of the region indigenous species of high forage value do not readily re-establish.  In an attempt to identify non-herbicide approaches to NIIG control we have utilized a three-pronged approach employing prescribed burns, mycorrhizal fungi addition, and indigenous species restoration as biocontrol.  In this talk our work to date on these control strategies will be summarized.  In preliminary soil foodweb analyses, we found that sites dominated by our focal invasive, KR bluestem (Bothiochloa ischaemum, hereafter referred to as KR), were dominated by bacterial species and lacking in mycorrhizal fungi.  In addition, rhizosphere analysis of KR and sympatrically growing indigenous species demonstrate divergent microbial communities.  Competition studies in the field and greenhouse designed to assess the effect of commercial mycorrhizal inoculants suggest that mycorrhizal addition initially increases indigenous species establishment but eventually favors KR.  It has also been shown that growing season (late summer/early fall) burns may serve to control KR.  Nonetheless, our experimental work demonstrates that soil water status, plant physiology and phenology, and fire condition must be taken into account to avoid collateral damage to resident indigenous species.  Finally, in a manipulative experiment we assessed the value of restoration as a biocontrol tool.  We found that species identity was critical, particularly under drought conditions, and that restorationists would maximize their success in controlling KR by focusing on those species that established at the highest rates.    

Atrazine is a foundational herbicide for broad-spectrum weed control in corn in the United States. It is commonly applied at the time of corn planting to provide residual control into the growing season. Some field locations in the United States occur in low-lying river bottoms, which are prone to flooding. These fields can be highly productive given their fertile soils and high water holding capacity. However, there is a chance that some of these low-lying fields may flood and thus terminate the previously planted corn crop. If a short time interval has elapsed, and it is early enough in the season, the farmer can simply re-plant corn. However, the corn yield penalty due to later planting or the lack of available adapted corn seed varieties may discourage  farmers from this practice. The atrazine label clearly states that planting soybeans in the same year as an atrazine application will cause excessive soybean injury. However, in warmer southern environments where atrazine persistence is not as extensive, farmers would like the flexibility to consider planting soybeans in this particular situation. A field study was conducted in Knoxville Tennessee in 2012 to examine the effect of flooding on atrazine dissipation under field conditions and its resultant affect on a soybean crop. 

Plots were established with berms to separate the various plots which were 12 m x 12 m for each main plot, and the subplots were 3 m x 10 m.  The study utilized a 2 x 3 factorial with the main factor being level of flooding (yes or no) and the second factor being atrazine application rate (0, 2.2 or 4.4 kg per ha).  Immediately after herbicide application the entire study area was sprinkler irrigated with 2.0 cm of water to move the atrazine into the soil. After that a flood of 7 to 12 cm was established on the flooded plots and maintained for five days. After the plot area drained sufficiently, (seven days) the berms between the main plots were removed and soybeans (Asgrow AG4531) were no-till planted in all plots in 76 cm wide rows. All plots were maintained in a weed free status with post emergent applications of glyphosate as needed.  Soil samples were collected to a depth of 0 - 8 cm at the time of soybean planting and analyzed for atrazine concentration. Data included visual evaluations of soybean injury at 25, 33, and 44 days after atrazine application, and soybean yield at crop maturity. 

Atrazine concentrations followed expected trends, although some atrazine was detected in the untreated check plots in both flooded and non-flooded situations.  Soon after soybean emergence the visual injury was minimal in all plots (< 5 %), but as the soybeans grew there was much more soybean injury in the flooded plots (~75%).  Soybean yield was highest in the plots that had received no atrazine, and were lowest in those plots that had received atrazine although yield was more affected in the flooded plots.

Adsorption and Desorption of Pyroxsulam in Inland Pacific Northwest Silt Loam Soils

Raeder, Alan J ^*1; Burke, Ian C ¹; Yenish, Joe ²; Gast, Roger E ²; Washington State University ¹, Pullman, WA; Dow AgroSciences ², Indianapolis, IN

Pyroxsulam is used for postemergence control of primarily annual grass weeds in winter and spring wheat. When applied in the spring to winter or spring wheat, pyroxsulam residues can cause injury to lentil grown the following year in the inland Pacific Northwest (PNW) – the phenomena is seldom observed anywhere else in the world. Soil characteristics, such as organic matter (OM), pH, and clay content, and environmental conditions are considered to be largely responsible for the adsorption and desorption of herbicides to soils. In this study, the adsorption and desorption of pyroxsulam to and from seventeen inland PNW silt loam soils with varying levels of OM, pH, and clay content were evaluated. The analysis was carried out using a batch equilibration method and a 1:1 soil: solution ratio. Duplicate test samples were dosed with 0.0075 µg ¹⁴C-pyroxsulam g^-1 soil, placed on a rotating shaker, and evaluated by removing triplicate aliquots after 4, 4.5, 18, 39, and 61 hours of shaking. Scintillation fluid was added to each aliquot and ¹⁴C-pyroxsulam in solution was determined using liquid scintillation spectroscopy. A multiple regression analysis revealed that clay content coupled with OM or pH was not a predictor of pyroxsulam adsorption or desorption, but that an OM and pH interaction was a significant predictor of both adsorption and desorption. The adsorption of pyroxsulam was more heavily influenced by pH, whereas, the desorption of pyroxsulam was more heavily influenced by OM. Pyroxsulam carryover in inland PNW silt loam soils appears to be affected by both OM and pH. Further work addressing the effect of temperature on the degradation should be sufficient to model the fate of pyroxsulam in inland PNW soils and predict carryover situations.

Halauxifen-methyl (XDE-729 methyl) is a novel arylpicolinate synthetic auxin herbicide being developed by Dow AgoSciences LLC for post-emergence broadleaf weed control in several crops. Halauxifen-methyl readily degrades in plant tissues and exhibits selectivity to multiple crops including cereals, brassicas, turf and forage grasses, etc…

The phytotoxicity of straw of Triticum aestivum (wheat) and clippings of Festuca arundinacea (Tall fescue) treated with halauxifen-methyl was investigated on vegetable and legume crops which are highly sensitive to halauxifen-methyl. The sensitive crops Lycopersicon esculentum (tomato), Lens esculentum (lentil), Medicago sativa (alfalfa), and Vicia faba (field bean) grown on soil mixed with straw or clippings of halauxifen-methyl-treated Triticum aestivum and Festuca arundinacea, respectively, showed no sign of herbicidal phytotoxicity to Lycopersicon esculentum, Lens esculentum, and Vicia faba. Analysis of the straw and clippings revealed only trace to no detectable residues of halauxifen-methyl, halauxifen-acid and a hydroxyphenyl metabolite.

Under aerobic soil conditions in the laboratory halauxifen-methyl was rapidly converted to halauxifen-acid by microbial degradation with an average DT₅₀ of 1.5 days. Halauxifen-acid, which had an average DT₅₀ of 14 days  was further degraded to form a hydroxyphenyl metabolite, as well as non-extractable residues (NER) and CO₂. 

Under anaerobic soil conditions in the laboratory halauxifen-methyl was also rapidly transformed to halauxifen-acid with an average DT₅₀ of 1.8 days. Further degradation of halauxifen-acid produced the hydroxyphenyl metabolite, NER and CO₂. However, CO₂ levels were negligible. 

Photodegradation on soil surfaces was negligible compared to biodegradation in soil. 

Emerging rhizosphere molecular techniques for selective weed control. S. M. Carver*, J. Kao-Kniffin. Cornell University, Ithaca, NY.

With increased weed resistance to common herbicides, comes greater demand for new herbicides targeting novel modes of action. Previous research of natural products from microorganisms using traditional culturing and solvent extraction techniques resulted in the discovery of several new herbicides, including the popular glufosinate. Metagenomic techniques offer the potential to isolate more weed suppressive compounds from soil microorganisms. Our work focuses on using established metagenomic techniques on genomic material extracted from the rhizosphere soil surrounding common ragweed (Ambrosia sp.). The DNA, up to 40kbp, is placed into fosmid vectors and each vector is stored in separate Escherichia coli cells yielding a library of 125,000 clones. E. coli allows for high-throughput screening of small molecules which most natural products are classified. Using a basic screen of clones for small molecule production (pigmentation, changes in morphology, and antibiosis activity), we found 56 clones with unusual morphology and one clone with pigmentation out of a subpool of 5000 clones. After checking the DNA inserts, clone redundancy was eliminated leaving 10 unique clones. These clones have been tested against germination and seedling growth of two model plant species: annual bluegrass, Poa annua, and lettuce, Lactuca sativa L. cv. Grand Rapids. While research and optimization is still underway, our bioassays have shown two clones with the ability to slow P. annua germination and growth. Also, two different clones showed some slowing of L. sativa L. early growth. Future work will focus on optimizing bioassays for high-throughput screens and establishing efficiency of the techniques. Corresponding author: jtk57@cornell.edu

Northwest Frontier region of Pakistan covers an area of 74,521 km². It includes 25 districts with elevation ranging between 173 m to 7700 m. Some of the high altitude mountains are Himalayas \"Home of the Snow, Tirich Mir and Nowshaq. The geological formations are mainly composed of alluvial and loess. The major soil groups distributed in the region are sandy, sandyloam, clay and clayloam. Dominant plant cover of trees includes the species like Dalbergia sisoo, Acacia nilotica, Acacia modesta, Pinus spp and Zizyphus jujuba. The percentage of endemics in the region lies around 80.

Due to its geographical borders with Afghanistan the region is experiencing a great unrest and severe land degradation. These factors coupled with the climate change  and social instability is resulting in the disruption of the high altitude ecosystems as well. The changes in the climatic conditions have lead to the dominance of many weeds. Later produce large number of seeds which are therefore overtaking the native flora. The devastating floods in summer 2010 accelerated the problem of diversity disturbance as millions of animals, wildlife and pollinators were disturbed which have proved detrimental for the biodiversity of the area together with the changing rainfall pattern and these need to be properly addressed. The temperature changes are pushing the weeds adapted to low temperatures towards the areas with higher temperatures and vice versa. As weeds play a vital role in the household economy of millions of farmers in the region, therefore the yield and biodiversity losses due need greater attention. 

Currently, the unrest in the area has totally disrupted the daily life and living style of the inhabitants. Thus the social issues have lead towards the negligence of conservation strategies of flora and fauna. Internally  displaced people use herbs for different diseases therefore the migrants and war affected people carry the seeds with them. This adds further to the spread of weeds. The homeless people collect the plants for fuel purposes which also accelerates the weed dispersal. The growth and development of weeds was promoted when Army banned cultivation of crops on the roadsides to avoid the ambush. In this way the weed diversity as well as the diversity of pollinators has been disturbed which can pose many social, economical and political problems in the days to come. This paper presents an overview of all these aspects and possible suggestions to address the problem. 

In recent years, a rapid increase in the adoption of herbicides has been occurring in countries in Asia. In India, herbicide sales doubled in the past five years. In China, close to 100 million hectares of cropland are treated with herbicides today- an increase from about 10 million treated hectares in the 1980s. A driving force in the adoption of herbicides in these countries has been rapid economic growth which has created job opportunities for rural laborers in urban industrial zones. Traditional weed control in China and India has been handweeding. Today, acute labor shortages are occurring throughout rural India and China and farmers find it difficult to find workers who will do the drudgery of handweeding. Because of labor shortages and increased cost of labor, the cost of handweeding in China is 6.5 times greater than the cost of using herbicides. These trends are expected to continue with China’s rural population projected to decline by 400 million people by the year 2050.Herbicide use has led to reduced losses to weeds and higher crop yields. In China in the early 2000s, 43 million crop hectares were estimated to be heavily infested with weeds causing a loss of 18 million tons of grain. Surveys of farmers rice fields in the early 2000s in tropical Asia showed that uncontrolled weeds were the biggest factors reducing yields with yield losses of 20% resulting both from weeds growing above and below the rice canopy(considered individually).Today, in China the losses to weeds in rice fields from weeds is estimated at  2% from both above and below canopy weeds. Significant yield losses are still occurring in rice fields in Bangladesh with almost 50% of the yield gap for rice being accounted for by weed infestations. In Bangladesh 30% of the farmers are estimated to lose more than 500 kilograms of rice per hectare due to weeds. Research has shown the herbicides would cut the losses, increase yields and lower the cost of rice production with farmers doubling their net income. A significant increase in herbicide use in Bangladesh is inevitable. Pulse crops (pigeon pea, lentil, mungbeans) are a neglected crop in India. Despite being the largest producer of pulses in the world, India’s yields are among the lowest. Herbicides are hardly used. Research has shown that by using herbicides, pulse crop yields in India could triple.

Occasionally in our career's we are given the opportunity to make a difference.  For me one such opportunity came through Pyongyang University of Science and Technology (PUST), a privately funded university in the heart of DPRK.  Classes for the first 160 PUST students commenced in October 2010. Currently about 300 Korean men study at PUST including a handful at the graduate level.  Majors, in addition to Agriculture and Life Science, include International Finance, Information Technology, and Engineering.  Faculty are drawn from several western countries and all are volunteers.  My involvement with PUST began by being copied on an email from Dr. Robert Shanks to tri-society members, recruiting a weed science teacher.  Dr. Shanks is the Dean of Agriculture and Life Science at PUST, and teaches most of the plant science courses offered.  I arrived in Pyongyang on September 10th carrying 10 Kg of textbooks, an undergraduate weed science course outline and lab manual, a ziplock bag full of disposable bulb-pipettes, a hand lens and 50 ml each of atrazine, glyphosate, clopyralid and glufosinate.  Teaching began the following day and continued Monday through Friday from 12-230 PM for 3 weeks.  Labs were 2 to 3 days per week and consisted of weed-identification and -collection walks on the 40 ha campus, an attempt at soil weed seedbank quantification, and herbicide mode of action in corn and soybean.  Students completed a weed collection and wrote reports on the herbicide mode of action lab as well as several papers from Weed Science.  Two tests were also administered.  Teaching in a 'modern lab' without the benefit of running water, pots and media for growing plants, or a suitable growing environment created unique challenges that my 20 students helped me to meet with their unique ingenuity and hard work. Their English language skills were excellent.  They were bright, highly motivated and endearing; we had a lot of fun.   Teaching at PUST was an 'experience of a lifetime' and one that I hope to repeat. If you would like to learn more about teaching opportunities at PUST please contact me.

Our group has been attempting to research and demonstrate herbicide persistence and carryover principles particularly related to fall cover crop establishment since 2010.  In 2010 and again in 2011, we conducted a rather large herbicide-cover crop trial in corn.  Our focus has been looking at herbicides in corn with the idea of establishing fall cover crops in early September.  Herbicides included active ingredients potentially problematic and also some thought to be short residual.  The trials were conducted in central Pennsylvania on silt loam soils with approximately 3% organic matter and a soil pH of 6.5.  About 25 herbicides were applied PRE and/or POST in corn.  In both years, corn was harvested for silage in September and a number of annual species including winter cereals, brassicas, and legumes were no-till seeded.  Most cover crops were seeded in 1.5 m wide strips using a no-till drill perpendicular to the direction of herbicide application.   A few cover crops were inter-seeded into corn in mid June. Cover crops were evaluated for % stand reduction on a 0 to 100% scale in late fall and again in early May of the following year.

In 2011, slug herbivory reduced the success of both the brassicas and legumes.  In 2012, soil compaction during the silage harvest operation impacted the success of cover crop establishment.  In the two year trial, only a few cover crop species established in both years and were successfully evaluated including annual ryegrass (Lolium multiflorum Lam.), cereal rye (Secale cereal L.), wheat (Triticum aestivum L.), and hairy vetch (Vicia villosa Roth).  The end result showed that metolachlor and nicosulfuron can reduce annual ryegrass stand when inter-seeded, but most herbicides did not affect the cover crops.  Neither atrazine nor simazine at rates up to 2.2 kg/ha PRE reduced cover crop establishment.    The results from these field experiments suggested that many herbicides believed to be problematic for cover crop establishment were not.

Because of problems we encountered in conducting this research, the lack of negative results, and the small inference space, we pursued other opportunities to demonstrate these relationships.   In 2012, we conducted a nonreplicated trial to demonstrate herbicide selectivity for 18 different herbicides or combinations.  In this demonstration the field was tilled in early May and cover crops including legumes, grasses, and brassicas were seeded again using a drill.  Herbicide were applied PRE perpendicular to the direction of cover crop seeding and the trial was irrigated.  We utilized a log sprayer for this demo applying the herbicides at rates ranging from 1/16X to 1X the normal rate.  An individual plot and herbicide rate was 3 by 6 m in size and included 8 different crop species.  We evaluated the plots for % stand reduction about 4 weeks after establishment and conducted a field day at about the same time.  At the field day, we utilized the half-life values from the literature along with the herbicide stand reduction ratings to discuss the potential for carryover injury based on herbicide and application rate. Each reduction in herbicide rate represented a half-life of the herbicide and we were able to apply rates theoretically up to 4 half-lives.   This technique was very useful especially for longer-lived herbicides but also showed positive results for herbicides with less soil activity.  Short-lived herbicides with high soil activity (e.g. rimsulfuron) were not accurately represented in this demonstration since they impacted plant growth at very low rates, yet are short-lived.  In future research, we would like to bridge herbicide persistence research with practical demonstration activities that better show how soil persistence, activity, and susceptibility are all involved in predicting rotational crop safety.

Glyphosate resistant sugar beet (Beta vulgaris L.) became commercially available in 2008. The adoption rate was very rapid and in Idaho approximately 96% of the sugar beets grown that year were glyphosate resistant. The primary reason for the rapid adoption rate was due to the lack of effective herbicides used for weed control in conventional beets. It was not uncommon for growers to make 3 to 5 herbicide applications, cultivate two times and still rely on hoeing crews to handweed later in the season. Weed control costs often ranged from $40 to $55 dollars per hectare ($100 to $135/acre). Initially, weed control costs in glyphosate resistant sugar beets were slightly more than average weed control costs in conventional sugar beet. However, weed control was much more effective, much easier and sugar beet yields were higher. Typically, sugar beets are grown once every three or four years in rotation. Other crops commonly grown in rotation include potatoes, small grains, corn, alfalfa, dry beans, and onions. In 2012, 145,700 ha (360,000 acres) of field corn and 154,000 ha (380,000 acres) of alfalfa was grown in Idaho. Nearly all of the corn and about 11% of the alfalfa are glyphosate resistant. The concern for glyphosate resistance is greater where glyphosate resistant corn and even alfalfa are grown in rotation with sugar beets. Since 2007, we have included information about glyphosate resistance management in extension presentations to sugar beet growers. Crop rotation and herbicide tank mixtures with glyphosate were among the earliest recommendations in addition to the many other resistance management recommendations that have been encouraged by weed scientists. Much like other areas, Idaho and eastern Oregon growers were reluctant to spend more money adding a tank mix partner to glyphosate when glyphosate was working so well by itself. Using the experience of growers in the Midwest, southern and eastern states, we have strongly encouraged growers to adopt resistance management strategies. Slowly, growers are beginning to adopt some resistance management practices, including tank mixing other sites of action with glyphosate. In early 2012, glyphosate resistance management recommendations from Kansas, North Dakota State, Indiana and Tennessee were utilized in extension presentations to sugar beet growers. Since December 2012, photos of fields with glyphosate resistant crops infested with glyphosate resistant weeds from the Midwest, eastern and southern US also have been used in extension meetings. These graphic examples appear to be making a tremendous difference in growers and crop advisors/crop consultants perspective of glyphosate resistant weeds. Only time will tell if Idaho and eastern Oregon farmers respond to these warnings about glyphosate resistant weeds.

Evolved herbicide resistance in common waterhemp (Amaranthus tuberculatus) has been a serious issue in Iowa agriculture when this weed first began to show up as a major production problem in soybeans in the 1980’s.  At that time, ALS inhibitor herbicides (Group 2) were applied to a majority of the corn and soybean acres across the Midwest and common waterhemp populations quickly evolved resistance.  In the 1990’s, concerns focused on the inevitability of evolved resistance to glyphosate (Group 9) and the first glyphosate-resistant common waterhemp populations were identified coincidentally in Badger and Everly, Iowa in 1997.  However, glyphosate resistance in common waterhemp was generally scattered in fields and had not become a major concern to agriculture.  This changed as the adoption of glyphosate-based corn and soybean production systems became the dominate practice.  It was clear that common waterhemp had become the major concern in soybean production and ultimately in corn production.  The more recent identification of common waterhemp populations with evolved resistance to auxinic herbicides (Group 4) and the HPPD inhibitor herbicides (Group 27) as well as the historic resistance to the PSII inhibitor herbicides (Group 5) and PPO inhibitor herbicides (Group 14) leaves few herbicide options for the control of common waterhemp, particularly for postemergence strategies. 
In order to assess the extent of herbicide resistant common waterhemp populations in Iowa, a project was initiated in 2011 with support from the Iowa Soybean Association. This project supplements a study conducted in 2008 where resistance to glyphosate was detected in 16% of approximately 220 common waterhemp populations collected arbitrarily.  In 2011, the Iowa Soybean Association funded a proposal to evaluate herbicide resistance in Iowa with an emphasis on glyphosate.  More than 200 common waterhemp populations were collected in fall 2011 and similar collections were made in fall 2012.  Together, more than 600 common waterhemp populations in Iowa have been sampled to assess the evolution of herbicide resistance.  Evaluations of the populations are currently underway and approximately 60% of 2011 populations have been evaluated for resistance to the ALS inhibitor herbicides (Group 2), PSII inhibitors (Group 5), EPSPS (Group 9), PPO inhibitor herbicides (Group 14) and HPPD inhibitor herbicides (Group 27).  Resistance was assessed on the relative control of the populations when compared to a known susceptible common waterhemp populations.  Evaluations were on a 0 to 100% control where 0 indicated no herbicide activity and 100% indicated all plants were sensitive.  Values below 90% control when compared to the susceptible population were deemed to indicate that resistance had evolved in the specific population.  Most of the populations that were designated as resistant still contain sensitive plants. 
More than 93% of the populations evaluated thus far demonstrate a resistant phenotype to Group 2 herbicides.  Surprisingly, resistance to the Group 5 herbicides was identified in 58% and 57% of the common waterhemp populations for 1X and 4X atrazine rates, respectively.  Glyphosate (Group 9) resistance was found in 53% of the common waterhemp populations but only 6% of the populations evaluated thus far were resistant to the Group 14 herbicide.  Resistance to mesotrione (Group 27) was found in 27% of the common waterhemp populations evaluated. Given the fact that HPPD herbicides were the last site of action without resistant weed populations, this is significant.
One important aspect of the research sponsored by the Iowa Soybean Association was the opportunity to assess multiple herbicide resistances in the populations.  Given that common waterhemp has demonstrated the ability to evolve resistance to six different sites of herbicide action, it is critically important to know exactly which herbicides are still effective when planning a common waterhemp management program.  Eighty-five percent of the common waterhemp populations from the 2011 collections evaluated thus far demonstrated multiple resistances.  The most prevalent multiple resistant phenotype was resistance to Groups 2, 5, and 9.  Common waterhemp populations that had evolved resistance to two sites of herbicide action accounted for 32% of the populations, resistance to three herbicide sites of action included 37% of the populations while resistance to four herbicide sites of action included 14% of the populations.  Three populations (2%) were resistant to all herbicide sites of action.
Of great concern is the resistance to the Group 27 herbicides.  It is important to recognize that while the data are preliminary, if the trend established thus far holds when all of the common waterhemp collections are evaluated; the prevalence of resistant phenotypes will make common waterhemp management in corn and soybean extremely difficult if only herbicidal tactics are used. Recognize that this screen thus far is only for the postemergence application of these herbicides; there is a possibility the common waterhemp populations may respond differently to soil-applied herbicides.  Furthermore, the heritability of resistance, particularly the HPPD inhibitor herbicides, will influence how quickly this phenotype emerges in common waterhemp.  Regardless, these preliminary data indicate that better management of weeds in Iowa is of utmost importance and alternatives strategies must be quickly adopted in order to maintain effective weed management.

In 2012, cotton, peanut, and soybean were harvested on 1,285,000, 725,000, and 205,000 acres in Georgia, respectively.  Because these crops are grown in close proximity, off-target movement and sprayer contamination problems are often encountered which results in unintentional crop injury.  Recent increases in the use of Liberty-Link® crops and the future use of 2,4-D or dicamba-resistant crops has caused growers some concern about the potential effects that these herbicides may have on the growth, development, and yield of peanut.  To assess these effects, numerous weed-free peanut tolerance trials have been conducted In Georgia since 2008.  In these field trials, ‘Georgia-06G’ peanut were treated at 30, 60, and 90 days after planting with various rates of dicamba, glufosinate, or 2,4-D.  Rates evaluated included 1, 2, 4, 8, and 16 oz/A of Clarity 4SL (dicamba) and 2, 4, 8, 16, and 32 oz/A Liberty 2.34SL (glufosinate) or 2,4-D Amine 3.8SL.  Generally, peanut yield sensitivity to these herbicides was as follows: dicamba > glufosinate > 2,4-D.  Actual peanut yield losses ranged from 4-100%; 7-100%, and 3-31% with dicamba, glufosinate, and 2,4-D, respectively.  Results of this research have been presented at various educational meetings and appropriate extension publications have been developed or are in production.  Growers must be conscious of wind speed/direction and utilize drift reduction strategies when applying dicamba, glufosinate, or 2,4-D near peanut fields.  Additionally, herbicide containers must be properly labeled and stored to minimize potential mixing errors that could result in sprayer contamination.  Sprayers should be adequately cleaned of dicamba, glufosinate, and 2,4-D residues before utilization in peanut fields.

The spread of herbicide resistance (HR) in weeds represents a serious threat to crop production and the environment. The dominant U.S. management approaches have not slowed the increase in HR weeds or in their occurrence across the landscape. Ratcheting up the same efforts with more manpower and funding will not likely reverse that outcome. Nor should we expect new herbicide technologies to magically rescue the situation. The root problem lies in farmer behaviors around weed management, and the solution, therefore, is finding novel ways to change those behaviors that will endure through volatile economic and other conditions. This formidable challenge involves more complexity than just altering single farmer decisions because one farmer’s actions or inaction on herbicide use and weed control have effects beyond their farm’s boundaries. Effective solutions must confront those community externalities head on. In natural resource management terms, assuring a weed gene bank with susceptibility to effective and environmentally friendly herbicides becomes a “common pool” resource management challenge.

This paper delves into farmer behavior affecting common pool herbicide resistance problems. Research and practice have demonstrated that effective mechanisms to control such “common pool” resources can emanate from the private or public sectors, or collaborations of both.  Key lessons from other attempts to manage common pool resources should inform the search for novel institutions and programs to make progress on this complex task. Examples include cheap and easy conflict-resolution mechanisms and minimal recognition of rights of parties to organize. To apply such lessons to HR weed challenges will require much more social science research at the individual and community levels to understand the heterogeneous nature of those decisions. Moreover, that research agenda must be interdisciplinary and have meaningful involvement of all stakeholders in HR issues to yield productive approaches that stand the test of time.

The selection and management of herbicide resistant weed populations was not a concern for the first 20 years of herbicide use, even though resistance had been predicted to occur in the 1950s.  The discovery of triazine resistant common groundsel in 1968 was the first serious case of herbicide resistance.  However, herbicide resistance was not considered an extremely important problem in spite of the increasing cases of resistance to the triazines and other mechanisms of action through the 1970s.  At that time most of the resistant weed populations were well controlled by other herbicides.  The explosion in herbicide resistance occured in the mid-1980s with the selection of ALS inhibitor and ACCase inhibitor resistant weed populations.  More attention was given to this increasing problem and guidelines for managing resistance were proposed.  Industry responded by organizing the Herbicide Resistant Action Committee in 1989.  The International Herbicide Resistance website, managed by Dr. Ian Heap, was established and continues to be the primary repository of information on the selection and spread of herbicide resistant weed populations.  The classification of herbicides by mechanism of action soon followed.  Since the early 1990s there have been extensive efforts to educate growers, as well as the general public and regulatory agencies, on the phenomenon of herbicide resistance.  These efforts include the labelling of herbicide packages by their mechansism of action.  When glyphosate-resistant varieties became available in many of the major crops, the initial perception was that herbicide resistance would not be a serious problem in these crops.  However, this has not been true and the increasing number of glyphosate resistant weed populations is raising new concerns.  In looking back of the last 40 years, it is interesting, and discouraging, to note that the guidelines for managing herbicide resistance have not substantially changed, but the problem continues and appears to be growing.  Herbicide resistance will always be a problem that has to be considered and managed as long as herbicides remain the foundation of weed management.

Herbicide resistance management should rely on best management practices (BMP’s) to delay, mitigate, and control the evolution and proliferation of herbicide-resistant weeds.  Federal policies should encourage and not hinder the use of BMP’s for herbicide resistance management.  For example, rotating herbicide use is hampered because registrations of older herbicide chemistries are difficult to maintain under the Federal Insecticide Fungicide and Rodenticide Act and registration costs can be prohibitive for herbicides used on small acreage crops.  Also, while tillage can be an effective tool for managing herbicide resistance, many growers have been encouraged to essentially eliminate tillage by policies within the Farm Bill.  In addition, Farm Bill commodity support programs and insurance programs can discourage the practice of crop rotation, another BMP for herbicide resistance management.  Problems with herbicide resistant weeds will not be solved by prescriptive federal regulations or policies such as restricting the sale and interstate movement of herbicides under the noxious weed provisions in the Plant Protection Act as has been suggested.  Mandating that refuges be provided for herbicide susceptible weeds for managing herbicide resistant weeds will also not work.  Federal policies for herbicide resistance management should include provisions for incentives to growers for following BMP’s.  Federal funds should be used to bolster research on improving BMP’s for herbicide-resistant weeds and to support Cooperative Extension education and outreach to decision makers.

To combat glyphosate-resistant Palmer amaranth, growers rely heavily on herbicides, tillage, and hand weeding.  Herbicide use has increased sharply with 2.5 times more herbicide active ingredient applied in cotton today as compared to before resistance.  Use of most herbicides, except glyphosate, have risen sharply, although the residual herbicides (acetochlor, diuron, flumioxazin, fomesafen, pendimethalin, S-metolachlor, trifluralin) and glufosinate have increased the most.  Although growers spend $68/A on herbicides, control is not adequate.  Thus, ninety-two percent of Georgia cotton growers are hand weeding 52% of the crop with an average cost of $11.40 per hand weeded acre.  In addition to increased herbicide use and hand weeding, growers are relying on soil disturbance for the control of Palmer amaranth; presently, in-row cultivation, deep turning, and tillage for the incorporation of herbicides are each being used on 20 to 30% of the cotton acreage.  Current management programs are diverse, complex, and expensive, but were more successful at controlling glyphosate-resistant Palmer amaranth in 2012 as compared to the strategies employed during the previous eight years.   In fact, hand weeding costs were reduced by half in 2012 as compared to 2011, saving Georgia cotton growers nearly $7.7 million.  Several factors were critical in obtaining better management during 2012, but growers being more aggressive and making wise decisions had the greatest influence.

Although these management programs are more effective, they are not economically sustainable and are still too dependent on herbicides.  Therefore, an effort is underway to help growers integrate a heavy rye cover crop into their weed management program.  Research results show that, if an adequate stand is achieved, rye itself, after being rolled, can reduce Palmer amaranth emergence 65 to 95%.  Although the rye cover does not provide sufficient control when used alone, the rolled rye cover in conjunction with a sound herbicide program has proven extremely effective.  In two large on-farm (4-8 A) dry land cotton studies conducted during 2012, the addition of a heavy rye cover crop reduced Palmer amaranth populations at harvest 70 to 95% and increased yields 16 to 23%, when all other variables, including herbicide program, were held constant.  In addition to improving Palmer amaranth control and increasing yields, the rye cover crop system also has the potential to reduce herbicide input overtime, prevent or at least delay additional herbicide resistance, reduce labor needs compared to conventional tillage, mitigate wind and water erosion, improve moisture conservation, and likely reduce impact from other pests such as thrips, ryegrass, and horseweed.  Although numerous benefits from this system exist, there are challenges that must be addressed including: finding time to get the rye cover established, increased nitrogen requirements, purchasing or building a roller, and obtaining a uniform cotton stand.  Large-acreage on farm studies will be used to determine the overall economics of the heavy rye system and these results should be available by winter of 2013/2014.

Herbicide-resistant weed populations have evolved rapidly in response to the selection pressures imposed upon them in current agricultural production systems.  Specifically, in the Midwest the number of acres impacted by glyphosate-resistant (GR) weeds has increased dramatically in recent years due to the rapid adoption of GR crops and extensive use of glyphosate.  The GR weed species that currently have the largest impact on corn and soybean production systems in the Midwest include waterhemp (Amaranthus rudis Sauer), horseweed [Conyza canadensis (L.) Cronq.], giant ragweed (Ambrosia trifida L.), common ragweed (Ambrosia artemisiifolia L.), kochia [Kochia scoparia (L.) Schrad.], and palmer amaranth (Amaranthus palmeri S. Wats.).  In addition to glyphosate resistance, several of these species have evolved multiple resistances to the acetolactate synthase (ALS)-, protoporphyrin oxidase (PPO)-, and hydroxyphenylpruvate dioxygenase (HPPD)-inhibiting herbicides as well.  Results from recent grower surveys indicate a greater awareness of glyphosate resistance in weeds, but the adoption of best management practices for the prevention of GR weed biotypes still remains much higher among growers who report having a GR weed biotype on-farm compared to those who do not.  To date, the primary way in which Midwest growers, land managers, crop consultants, and other decision-makers have responded to the problem of GR weed biotypes is through the application of herbicides that act at alternate sites of action.  In soybean production systems, for example, there has been a dramatic shift back to the use of pre-emergence, residual herbicides, which had virtually disappeared in most areas soon after the introduction of glyphosate-resistant soybean.  However, as a result of the increasing problem of multiple herbicide resistance in species like waterhemp, it seems clear that this practice alone will not mitigate the evolution of herbicide resistance, and that a multi-faceted approach will be required.  Based on the available data, there does not appear to be major changes in the use of different tillage or cultural practices for the management of herbicide-resistant weed biotypes at this time.

Although glyphosate-resistant weeds occur in the west, they are not currently as prevalent or as difficult to manage as in other regions of the USA.  This is largely due to fewer glyphosate-resistant crops in the diverse cropping systems of the region which results in less reliance on glyphosate and, thus, reduces selection pressure on weed populations.  The exceptions are glyphosate-resistant Palmer amaranth which was selected in glyphosate-resistant cotton in Arizona, California, and New Mexico and junglerice in glyphosate-resistant corn in California.  In the west, the first glyphosate-resistant weeds occurred in perennial cropping systems such as orchards or vineyards.  In California and Oregon, glyphosate-resistant rigid ryegrass and Italian ryegrass were selected in nut orchards where glyphosate had been applied frequently over multiple years.  Glyphosate-resistant weeds are frequently reported to occur along roadsides and in other nonagricultural sites where glyphosate is a preferred herbicide. Glyphosate-resistant weeds in these situations are an issue but can be managed through cultural and mechanical means, or by changing the herbicide active ingredient utilized for vegetation management.  In many crops, preplant tillage and preemergence herbicides have likely been important in delaying glyphosate resistance.  In addition, many acres are still planted to nonRoundup Ready crops in which case glyphosate has a built in resistance management strategy because herbicides with a different site of action must be utilized during the cropping year. For example in a wheat/fallow system, glyphosate could be used preplanting or post-harvest and in the fallow year but not in the wheat crop itself where herbicides with a different site of action would be required for weed control.  Because of the limited number of herbicides available for use in specialty and horticultural crops, tillage, handweeding, and cultural control methods are used which reduces the risk of resistance in these systems. There are no confirmed reports of glyphosate resistant species in Idaho, Montana, and Washington.

Hugh J. Beckie (AAFC Saskatoon, SK), Peter H. Sikkema, Nader Soltani (University of Guelph Ridgetown Campus, Guelph, ON), Robert E. Blackshaw (AAFC Lethbridge, AB), and Eric N. Johnson (AAFC, Scott, SK).                                                                            Glyphosate-resistant (GR) giant ragweed, horseweed, and common ragweed were confirmed in southwestern Ontario, Canada in 2008, 2010, and 2011, respectively. In the western prairie provinces of Alberta and Saskatchewan, GR (plus acetolactate synthase inhibitor-resistant) kochia was confirmed in 2012. This symposium paper estimates the environmental impact (EI) of the top herbicide treatments or programs used to manage these GR weed species in the major field crops grown in each region. For each herbicide treatment, EI (per ha basis) was calculated as the environmental impact quotient (EIQ), which quantifies toxicological properties of a herbicidal active ingredient, multiplied by the application rate (kg ai ha^-1). Total EI is defined as EI (per ha basis) multiplied by the application area (i.e., land area affected by a GR weed). It was assumed that all herbicide treatments would supplement the continued usage of glyphosate because of its broad spectrum weed control. For the control of these GR weeds, most treatments contain auxinic or protoporphyrinogen oxidase (PPO)-inhibiting herbicides. The majority of auxinic herbicide treatments result in low (EI <10) to moderate (11 to 20) EI, whereas all treatments of PPO inhibitors have low EI. Total EI of GR horseweed and kochia will generally be greater than giant or common ragweed because of rapid seed dispersal over time. For recommended herbicide treatments to control GR weeds (and herbicide-resistant weeds in general), EI data should be routinely included with cost and site of action so that growers have the information needed to assess the environmental impact of their actions.

Soil microbial community structure and activity are clearly linked to plant communities established in natural and agricultural ecosystems. A limited number of studies confirm that weeds alter their soil environment and select for specific microbial communities in the rhizosphere. Such rhizosphere modification is well documented for many crop and horticultural plants. However, the impact of weeds, especially those in agroecosystems, on soil biology and ecology has received less attention because effective weed management practices were developed to minimize the impacts of these plants on crop production. The recent development of herbicide resistance in several economically important weeds leading to unexpected and widespread infestations in crop fields treated with a single herbicide has prompted a re-evaluation of the effects of weed growth on soil biology and ecology. The objective of this paper is to review the potential impacts of herbicide-resistant weeds on soil biological and ecological properties based on previous and on-going studies on crops, weeds and invasive plants. Persistent weed infestations likely establish extensive root systems and release various plant metabolites into soil through root exudation. Many of these exudates are selective for specific soil microbial groups that mediate certain biochemical and nutrient acquisition processes. The exudate chemicals may stimulate development of microbial groups beneficial to weed growth and detrimental to crop growth or beneficial to both crop and weed. Changes in the interactions with symbiotic and associative microorganisms are known, especially for arbuscular mycorrhizal fungi (AMF) that are important in aiding the plant in uptake of nutrients and water, and in protection from soilborne pathogens. Mechanisms used by weeds to potentially disrupt AMF symbioses with adjacent crop plants are not clearly described. However, many herbicide-resistant weeds including Amaranthus and Chenopodium species do not support AMF symbioses and may reduce the density of AMF propagules in soil necessary for establishment of the symbiosis with crop plants in current and subsequent seasons. Impacts of herbicides applied to control herbicide-resistant weeds may compound the effects of weeds on the soil microbial community. Systemic herbicides released through weed roots may select additional microbial groups that mediate detrimental processes such as nutrient immobilization or serve as opportunistic pathogens. An understanding of the complex interactions of weeds with soil microorganisms under extensive and persistent infestations is important in developing effective management systems for controlling herbicide-resistant weeds.

With the development of weed resistance from repeated herbicide applications in agricultural fields, areas adjacent to cropland (edge-of-field) are vulnerable to the spread of herbicide-resistant plant species.  This issue is a growing concern, and there are several research areas of emphasis that need to be addressed.  First, if there is no active weed management in the edge-of-field areas, they may become nurseries for resistant plant species.  Second, the resistant plants are often invasive and may crowd out desirable plants in edge-of-field areas.  Third, edge-of-field areas within a locale may have several owners with differing management philosophies.  One owner may implement effective management practices, but a neighbor may not.  Fourth, as edge-of-field areas become more difficult to manage, extreme measures may be used that are not environmentally friendly, including (a) over-use of herbicides; (b) destruction of desirable plants along with undesirable plants; (c) tillage; or (d) converting non-cropland areas back to cropland.  USDA conservation programs have successfully removed marginal lands from crop management in order to improve water quality and conserve soil.  Proper management of resistant plant species in these and other edge-of-field areas is needed in order to preserve gains in environmental quality accomplished by implementing these conservation programs. 

Tillage has been an integral element of crop production since crop cultivation began. A number of benefits have often been noted, but none more important than weed management. However, tillage also promotes soil loss and adversely affects surface water quality. Weed management has always been the primary purpose of tillage, and tillage was essential until the development of effective herbicides for weed control. The ability to reduce or eliminate tillage was enhanced tremendously with the development of herbicide-resistant crops, particularly glyphosate-resistant (GR) crops. GR crops are planted on the majority of canola, corn, cotton, soybean, and sugarbeet hectares in the United States. However, this has also placed tremendous and unprecedented selection pressure for the development of GR weeds. Several weed species have now evolved resistance to glyphosate, some of which previously had evolved resistance to other herbicide mechanisms of action. This poses a serious threat to soil conservation gains, since in some cases tillage is the only option available to manage these resistant populations. Research is demonstrating, however, that there are situations where the farmer will not have to abandon current conservation tillage practices in order to manage a resistant weed population. Best management practices (BMPs) have been established for either proactive or reactive management of HR populations, still considering support for conservation tillage systems. USDA/NRCS has determined a number of herbicide resistance BMPs that qualify for programs such as the Environmental Quality Incentive Program. For example, Palmer amaranth (Amaranthus palmeri) is the most important weed problem in southeastern U.S. cotton production because of glyphosate resistance. Inversion tillage is an effective tool in helping manage this weed. Programs have been demonstrated that meet conservation compliance, and at the same time carefully use tillage in a highly prescriptive manger as an element for Palmer amaranth management.

Environmental stewardship refers to responsible use and protection of the natural environment through conservation and sustainable practices. Aldo Leopold (1887–1948) championed environmental stewardship based on a land ethic "dealing with man's relation to land and to the animals and plants which grow upon it”.  Environmental stewardship as it relates to weed science has taken on varying roles as chemical weed control took hold in managing crops as a general practice soon after World War II and became an issue at the forefront of human awareness during the Vietnam War with the extensive use of Agent Orange.  As technology both in chemistry and genetics have evolved, chemical weed control became safer with the advent of less toxicologically damaging materials.  Combining toxicologically safe herbicides with genetic manipulation made it possible to apply chemicals that previously would have caused plant death seemingly providing a “magic bullet” that simplified weed control for many producers during the mid to late 1990’s.  As university scientists were guarded during the introduction of this technology, many understood that the “magic bullet” had flaws.  By dominating postemergence applications to weed species, genetic selection has given rise to substantial resistance, therefore, providing weed scientists with a grand challenge for the future.  As new genetic technology is introduced for existing and future weed management problems, how will environmental stewardship be addressed and how can this technology be better preserved?  How can a producer afford it and how can they afford not to use it? If we have weeds present that used to be managed by herbicides and genetic technology, then society will deal with the same social, economic, agronomic, and environmental issues that they dealt with prior to herbicide/genetic technology.  Herbicide-resistant technology and the concomitant herbicide-resistant weeds have provided a perfect case study to learn from if those in academia, extension, and industry will pay attention.  Continuing education of the producer will be perhaps the biggest key in meeting the challenge to produce the safe and productive food supply for a growing population with minimal adverse effects of weeds while providing a desirable degree of environmental stewardship.

There is the need and motivation for consideration of environment stewardship by all who are involved in agriculture and the crop protection and seed industry is no exception. From an industry perspective environmental and product stewardship are important to increasing shareholder value. Industry is committed to providing effective stewardship programs for the products and services it provides to farmers to manage weeds and, in general, to produce a crop in an efficient manner, while optimizing yield.  The increasing incidence of herbicide resistance in weeds in the major crops in North America has driven the need for a close examination of their environmental impact. This is particularly relevant in assessing the risks and benefits of new trait development, changing herbicide use patterns and the drive for greater diversity in weed management to help limit the spread or delay the onset of herbicide resistance. Examples of initiatives by the industry to provide outreach and education to stakeholders and to support sustainable herbicide-resistance management practices will be discussed.

Evaluation of Weed Management Programs and Response of FG72 Soybeans to HPPD-inhibiting Herbicides. John Schultz*, Michael Weber, Jayla Allen, and Kevin W. Bradley, Graduate Research Assistant, Senior Technical Service Representative, Trait Development Manager, Bayer CropScience, Research Triangle Park, NC, Associate Professor, Division of Plant Sciences, University of Missouri, Columbia, MO 65211

Separate field trials were conducted in 2012 near Columbia and Moberly, Missouri to determine the response of FG72 soybeans to various HPPD-inhibiting herbicides, and to evaluate weed control programs for use in these systems. Treatments in the FG72 tolerance experiment included isoxaflutole, tembotrione, mesotrione, or topramezone at a standard (1X) and twice the normal use rate (2X). Treatments were applied pre-emergence (PRE) to soybeans and at the V3 and R1 stages of soybean growth. Visual crop injury and soybean height and fresh weight reduction were taken 7, 14, and 28 DAA. All treatments were arranged in a randomized complete block design with six replications. A non-treated control was included for comparison. When averaged across all herbicide treatments, the PRE application timing resulted in less visual crop injury than either the V3 or R1 application timings.  Across all application timings, tembotrione at the 1X and 2X rates resulted in the highest visual crop injury 7, 14, and 28 DAA, but no more than 14% visual soybean injury was observed in these experiments with any herbicide treatment or application timing.  Across all application timings, no differences in soybean fresh weight reduction were observed between herbicide treatments 7, 14, and 28 DAA.  In the weed management experiments, PRE followed by POST herbicide programs resulted in at least 74% control of glyphosate-resistant (GR) waterhemp 28 DAA while POST applications of glyphosate alone or glyphosate plus isoxaflutole, fomesafen, or S-metolachlor provided only 22% to 28% control of GR waterhemp. At locations with and without GR waterhemp and a variety of other summer annual weed species, PRE followed by POST programs generally provided higher levels of weed control when compared to two-pass POST programs and one-pass POST programs that contained isoxaflutole.  Results from these experiments indicate that FG72 soybeans exhibit acceptable tolerance to isoxaflutole, mesotrione, and topramezone, and that the incorporation of HPPD-inhibiting herbicides will provide a novel mechanism of action in soybean to aide in the management of resistant and susceptible weed biotypes.

A New Mesotrione, Glufosinate and Isoxaflutole Tolerant Trait for Soybean Weed Management

Syngenta and Bayer CropScience are developing new herbicide tolerant technology for soybeans consisting of a molecular stack of a gene conferring tolerance to HPPD-inhibiting herbicides as well as a gene for glufosinate tolerance.  This multiple mode-of-action herbicide tolerant trait will enable the use of herbicides such as mesotrione and isoxaflutole pre- and post-emergence in soybean in addition to glufosinate-ammonium post-emergence.

This new trait technology will provide growers with a valuable tool to improve weed management options in soybeans.  HPPD-inhibitors are a leading, selective class of herbicide chemistry and provide unprecedented broadleaf and grass weed control with proven residual and application flexibility.  Glufosinate-ammonium has a unique mode of action and provides control of a broad-spectrum of weeds.  This technology will therefore enable herbicide programs with more options for multiple modes-of-action and superior residual control for sustainable weed management including ALS-, triazine-, PPO-, and glyphosate resistant biotypes.

The technology has shown consistent efficacy and agronomic performance for seven field seasons in North and South America.  During 2012, it demonstrated excellent yield and agronomic performance as well as tolerance to mesotrione, isoxaflutole and glufosinate across numerous elite genetic backgrounds and many environments.  Regulatory dossiers have been submitted for cultivation and import approval in key countries and further studies to support approvals and commercialization are on-going with a target for commercial launch after the middle of the decade. brett.miller@syngenta.com

Field trials were conducted in 2012 to assess potential weed control programs for mesotrione use in HPPD-tolerant soybeans.  Several programs provided near complete control of important weed species, including targeted glyphosate resistant populations.  The most successful programs included preemergence residual weed control with multiple, overlapping modes of action. The use of these chemically diverse and novel programs offers effective, safe and sustainable weed management options for soybean growers.

Weed Control Options in Enlist^TM Soybean. Eric. F. Scherder, Jeff M. Ellis, Ralph B. Lassiter, Bradley W. Hopkins, Larry L. Walton, Jonathon H. Huff and Bobby B. Haygood, Dow AgroSciences, 9330 Zionsville Road, Indianapolis, IN 46268.

 The Enlist™ Weed Control System, developed by Dow AgroSciences, incorporates Enlist herbicide tolerant traits and associated Enlist™ herbicides, including Enlist Duo™ (2,4-D choline + glyphosate DMA).  Components of the Enlist™ system are under review for regulatory approval.  Weed control programs that utilizes preemergene herbicide treatments followed by postemergence applications of mixed modes of action provide consistent, highly effective control and is an effective approach to manage resistant weed species.

 A total of 30 research trials were conducted in 2011 and 2012 in Enlist soybean within the U.S. to evaluate weed control delivered by a systems approach composed of preemergence followed by postemergence herbicide applications. Preemergence treatments consisted of cloransulam + sulfentrazone, flumioxazin, flumioxazin + chlorimuron ethyl or S-metolachlor + fomesafen.  Enlist Duo™ herbicide was applied at 1092, 1640, and 2185 g ae/ha at about 30 days after planting soybean.  Experiments were conducted in the U.S. at 5 locations in 2011, and 20 locations in 2012, to evaluate a total postemergence weed control program consisting of Enlist Duo alone or in combination with micro-encapsulated acetochlor, fomesafen or S-metolachlor + fomesafen.  Treatments were applied at the V3 soybean growth stage or V3 growth stage followed by a second application 17 to 21 days later. 

 Enlist Duo™ provided greater than 95% control of several key broadleaf weed species (AMAPA, AMBEL, AMBTR, SIDSP, CHEAL, and ABUTH) that are difficult to control or resistant to glyphosate. 

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

Enlist E3^TM soybeans, jointly developed by Dow AgroSciences and M.S. Technologies, provide for the first time, three herbicide tolerance genes stacked together as part of a single genetic event in the soybean genome, and Enlist^TM RR2Y soybeans (AAD12/PAT + Roundup Ready 2 Yield® traits in a breeding stack) developed by Dow AgroSciences both confer tolerance to 2,4-D, glyphosate and glufosinate. In 2012, trials were initiated to evaluate Enlist E3 soybeans and Enlist RR2Y soybeans injury following applications of 2,4-D, glyphosate, glufosinate, 2,4-D + glyphosate or 2,4-D + glufosinate.  The herbicides rates were 1x and 2x rates with the 1x rates of 1065 g ae/ha  for 2,4-D , 1120 g ae/ha  for glyphosate and 542 g ae/ha  for glufosinate .  The 2,4-D + glyphosate treatments were an Enlist Duo™ herbicide formulation, a proprietary blend of 2,4-D choline and glyphosate,  applied at 2185 and 4370 g ae/ha.  Single herbicide treatments were applied at V2, V6 and R2 growth stages.  A second study evaluated tolerance of Enlist E3 soybeans to sequential applications of Enlist Duo at 2185 or 4370 g ae/ha at V2 followed by V6 or V6 followed by R2 soybean growth stages.

Enlist E3 soybeans and Enlist RR2Y soybeans demonstrated robust tolerance to all herbicide treatments across all application timings and rates.  Enlist E3 soybeans and Enlist RR2Y soybeans had equivalent tolerance to 2,4-D, glyphosate, glufosinate, 2,4-D + glyphosate or 2,4-D + glufosinate treatments. Overall injury with Enlist Duo™ herbicide at 2185 g ae/ha was less than 5% at any single application timing or in a sequential program seven days after final treatment.  Increasing Enlist Duo rate to 4370 g ae/ha (2X the anticipated maximum use rate) increased initial crop injury slightly compared to 2185 g ae/ha rate at 7 days after treatment (DAT). Crop  injury was negligible at 14 DAT.  Enlist E3 or Enlist RR2Y soybeans yields were not affected by herbicide applications made at V2, V6 or R2 growth stages.  Sequential applications of Enlist Duo at 2185 or 4370 g ae/ha applied at V2 followed by V6 or at V6 followed by R2 applications did not affect soybean yield.

Roundup Ready 2 Yield® is a trademark of Monsanto Technology LLC and used under license from Monsanto Company.  Enlist™, Enlist Duo^TM, and Enlist E3^TM are trademarks of The Dow Chemical Company (“Dow”) or an affiliated company of Dow.  Components of the Enlist Weed Control System have not yet received regulatory approvals; approvals are pending. The information presented here is not an offer for sale.  Enlist E3 soybeans jointly developed by Dow AgroSciences and M.S. Technologies.  ©2013 Dow AgroSciences LLC

Separate field protocols were conducted in 2012 to evaluate herbicide options for the control of glyphosate-resistant (GR) and hard-to-control weeds in Roundup Ready® 2 Xtend soybean in soybean growing regions.  A total of 43 locations focused on weed management benefits in the Midwest, 14 locations in the South, and 7 locations in the Northeast.  Treatments evaluated include burndown, pre-emergence (PRE) and post-emergence applications (POST) when plants measured 8 to 10-cm in height.  Dicamba was evaluated as a premix formulation consisting of dicamba plus glyphosate.  Visual weed control was determined approximately 21 days after application (DAA) of the final POST applications.  In the Midwest, overall weed control averaged across all species ranged between 73 and 94% control.  All dicamba-containing treatments averaged 89 to 94% control across all weed species.  Overall weed control ranged between 92 to 96% when a residual herbicide was included in the burndown treatment.  Incorporating dicamba into the burndown treatment significantly improved overall weed control compared to a glyphosate only or glyphosate plus 2,4-D burndown treatment.  In the South, a dicamba system utilizing a strong PRE residual product followed by the dicamba premix formulation provided improved or equivalent Palmer amaranth control compared to current standards.  This research confirms findings that incorporating dicamba into current weed management recommendations as burndown, PRE or POST treatment can provide an additional tool for effective, season-long weed management.

Glyphosate-resistance (GR) weeds are now widespread across much of the U.S. Alternative control options in soybean, as well as other crops, are desperately needed. Dicamba-tolerant soybean (DTS) offers an alternative mechanism-of-action (MOA) for the control of many GR weeds including Palmer amaranth (Amaranthus palmeri S. Wats.). The DTS system will allow producers the option of applying dicamba as an additional MOA in-season and prior to planting for control of GR Palmer amaranth along with other broadleaf weeds. With the commercialization of DTS nearing, dicamba preemergence (PRE) and postemergence (POST) efficacy on GR Palmer amaranth must be evaluated to determine the most effective means of utilizing this technology. Dicamba rates of 0, 0.28, 0.56, and 1.1 kg ae/ha were applied PRE and POST to determine the most efficacious rates and timings for the control of Palmer amaranth. Research was conducted on fields with naturally occurring populations of GR Palmer amaranth in 2011 and 2012. POST applications of glyphosate alone at 0.86 kg ae/ha provided 30% control of 5 cm Palmer amaranth. Dicamba applied with and without the addition of glyphosate were not significantly different for all rates of dicamba observed on 5 cm Palmer amaranth providing at least 80% control. However, as dicamba rate decreased to 0.28 kg ae/ha and weed size increased, dicamba plus glyphosate provided greater control when compared to dicamba alone and gave 65 to 60% control of 10 and 15 cm weeds, respectively. At 28 DAT, control of Palmer amaranth was 95, 86, and 79% when dicamba was applied alone at 1.1 kg ae/ha to 5, 10, and 15 cm weeds, respectively. At 14 DAT, PRE applications of dicamba at 1.1 kg ae/ha provided between 85 and 95% control and 0.56 kg ae/ha dicamba provided 90% control when applied at either 0 or 15 DPP. Dicamba at the lowest rate of 0.28 kg ae/ha provided 80 to 85% control 14 DAT, when applied at 0 and 15 DPP. Dicamba at 0.56 and 1.1 kg ae/ha applied at 0, 15, and 30 DPP provided between 65 and 85% control 21 DAT with the exception of 0.28 kg ae/ha dicamba 30 DPP which provided 50% control. By 28 DAT, all rates and timings provided some residual control for Palmer amaranth greater than 45% control. When 0.56 and 1.1 kg ae/ha dicamba were applied, density was reduced by 65% and biomass declined by 90% when averaged across rates. Results from this research demonstrate the importance of application timing when targeting Palmer amaranth with dicamba. POST control of Palmer amaranth can exceed 90% control when dicamba is applied at 0.56 or 1.1 kg ae/ha to 5 cm weeds. Residual efficacy of dicamba, applied PRE for the control of Palmer amaranth, diminishes as time progresses but provided at least 90% control 14 DAT with a rate of 1.1 kg ae/ha.

Pending regulatory approval, the first generation of dicamba tolerant soybean varieties is anticipated to be commercially introduced in 2014 and will be marketed under the trade name Roundup Ready® 2 Xtend.  A new low volatile premix formulation of glyphosate plus dicamba is being developed for preplant or in-crop use and is expected to be branded as Roundup® Xtend.  The use of dicamba in soybeans will provide an additional mode-of-action for managing the selection and control of herbicide resistant weeds. A summary of 2 years of small plot research shows dicamba and glyphosate applied preplant to Roundup Ready® 2 Xtend soybeans provides improved residual weed control versus a glyphosate plus 2,4-D LV ester burndown treatment.  Additional residual herbicide improved residual weed control of both treatments.  Glyphosate plus dicamba also provided enhanced POE control of glyphosate resistant horseweed (Conyza canadensis) verses glyphosate plus 2,4-D LV ester.

Dicamba has been a highly effective weed management tool for nearly 50 years.   Engenia™ herbicide is a new experimental formulation (pending regulatory approval, commercialization anticipated in 2014) based on the BAPMA (N, N-Bis-(aminopropyl) methylamine) form of dicamba. Engenia herbicide reduces the volatilization potential of dicamba beyond the improvement achieved with Clarity^® herbicide over Banvel^®  herbicide.  Engenia herbicide has been shown in research trials to effectively control 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).  The auxin agonist mechanism of action of Engenia herbicide will provide growers the opportunity to effectively control broadleaf weeds resistant to EPSPS, triazine, ALS, and PPO herbicides. Weed management programs should be designed to take advantage of dicamba’s postemergence and moderate residual activity. Combining dicamba with preemergence herbicides preplant will provide burndown with critical broad spectrum early season residual control.  Postemergence use of dicamba with glyphosate and other effective herbicides following a PRE or preplant residual herbicide often provides the most consistent and effective control.  Optimum postemergence control has been shown when Engenia herbicide is applied to small weeds no larger than four inches.  Integration of weed management strategies that combine herbicide, cultural and mechanical control techniques such as alternative herbicide mechanisms of action, crop rotation, and sanitation are critical to effectively manage herbicide resistant weeds and protect the utility of dicamba-tolerant cropping systems.

            Cultivars of soybean and cotton genetically modified with resistance to the synthetic-auxin herbicides dicamba and 2,4-D will allow these compounds to be used with greater flexibility but may expose susceptible varieties to non-target herbicide drift.  From past experience, it is well known that soybean and cotton are both highly sensitive to low-dose exposures of dicamba and 2,4-D. In this study, we use a meta-analysis approach to synthesize data from over seven decades of simulated drift experiments in which investigators treated soybean and cotton with low doses of dicamba and 2,4-D and measured the resulting yield loss.  We use these data to produce global dose-response curves that plot crop yield loss against herbicide dose.  Our analysis shows that soybean are most susceptible to dicamba in the flowering stage and relatively tolerant to 2,4-D at all growth stages.  Conversely, cotton is tolerant to dicamba but extremely sensitive to 2,4-D, especially in the vegetative and square stages. Both crops are highly variable in their responses, with soil moisture and air temperature at the time of exposure identified as key factors. Visual injury symptoms, especially during vegetative stages, are not predictive of final yield loss. Our global dose-response curves can provide producers and agricultural professionals with a benchmark of the mean and range of crop yield loss that can be expected from 2,4-D or dicamba drift incidents.

New weed control options are needed to help manage an evolving weed resistance problem.  Dicamba-tolerant soybean and cotton will enable the use of dicamba to manage these problematic broadleaf weeds with an additional herbicide mechanism-of-action.  These dicamba tolerant cropping systems will allow for application of dicamba as a preplant burndown without a planting interval and postemergence over the top of the crop.  Engenia herbicide, currently under evaluation by the US EPA, is an advanced formulation based on the novel BAPMA (N, N-Bis-(aminopropyl) methylamine) form of dicamba that reduces potential secondary loss more than Clarity^® herbicide, which in itself was an improvement over other formulations.  In addition to addressing secondary loss through formulation innovation, a comprehensive stewardship strategy will be implemented to focus on weed management and effective control, weed resistance management, and maximizing on-target application. 

In order to maximize on-target deposition, many parameters related to equipment setup and environmental conditions should be considered.  Proper nozzle selection offers the opportunity to dramatically reduce the potential for spray drift.  Research shows that venturi-type nozzle technology can greatly reduce drift potential compared to standard hydraulic flat-fan nozzles.  Other application parameters that should be considered include wind speed and direction, temperature inversions, travel speed, boom height, application volume, use of a deposition aid, and proximity to sensitive crops.  BASF has initiated the ‘On Target Spray Academy’ training series to educate applicators on best application practices to optimize herbicide performance and limit off-target movement. The combination of Engenia herbicide and dicamba-tolerant crops plus a stewardship strategy will provide growers with an effective system to control herbicide-resistant and difficult to control broadleaf weeds.  Pending regulatory approvals, commercialization of Engenia herbicide is anticipated to coincide with the launch of dicamba tolerant soybean in 2014.

The presence of glyphosate-resistant weeds in agricultural fields has forced many growers to use other herbicides with alternative modes of action.  Proper selection of carrier volume and droplet size may help to improve the efficacy of these herbicides.  The objective of this study was to measure the influence of carrier volume on droplet size and weed control using four commonly used soybean postemergence herbicides.  The effects of five carrier volumes (47, 70, 94, 140, and 187 L/ha) and four herbicides (glyphosate [Roundup PowerMAX] at 37g ae/ha, glufosinate [Liberty] at 97g ai/ha, lactofen [Cobra] at 36g ai/ha, 2,4-D [Weedone] at 87g ae/ha) on droplet size was evaluated at the wind tunnel facility in North Platte, NE, and weed control ratings were recorded at four field sites located across Nebraska (Lexington, O’Neill, Platte Center and David City).  Generally, the performance of systemic herbicides (glyphosate and 2,4-D) on weed control was not influenced by different carrier volumes.  An interaction between the effect of carrier volume and the contact herbicides glufosinate and lactofen was observed for most weed species used in this study.  Herbicide efficacy increased by 51 and 67%, respectively, for these two contact herbicides as carrier volume increased from 47 to 187 L/ha.  Using an appropriate carrier volume and targeting an effective droplet size can increase weed control when using contact herbicides.          

EFFICACY OF AMINOCYCLOPYRACHLOR FOR CONTROLLING CRABGRASS, SWINECRESS, and VIRGINIA BUTTONWEED IN TALL FESCUE.  T. Reed and P. McCullough; Department of Crop and Soil Sciences, University of Georgia, Griffin, GA 30223. 

 ABSTRACT

Field experiments were conducted to evaluate efficacy of aminocyclopyrachlor and other herbicides for controlling swinecress (Coronopus didymus (L.) Sm.), smooth crabgrass (Digitaria ischaemum Shreb.), and Virginia buttonweed (Diodia virginiana L.) in tall fescue (Festuca arundinacea Schreb.). Aminocyclopyrachlor at 0.05 and 0.10 kg a.i./ha provided <35% control from February applications but both rates gave >90% control with April applications.  Fluroxypyr at 0.26 and 0.52 kg a.i./ha provided poor (<70%) control from February applications but control increased to 71% and >90% from April treatments, respectively. Triclopyr at 0.56 and 1.12 kg a.i./ha provided >90% swinecress control at both application timings and was comparable to 2,4-D + dicamba + MCPP.  In other experiments, single applications of aminocyclopyrachlor at 0.05 and 0.08 kg ai ha^-1 provided poor (<70%) and fair (70 to 79%) control of Virginia buttonweed, respectively, but sequential applications improved control 83 to 99%.  Single and sequential applications of aminocyclopyrachlor at 0.11 kg ai ha^-1 provided good (80 to 89%) and excellent (>90%) control of Virginia buttonweed, respectively.  Aminocyclopyrachlor at 0.11 kg ha^-1 provided fair control of smooth crabgrass at the multi-leaf stage but control was poor when applied at the multi-tiller stage.  Aminocyclopyrachlor at 0.05 and 0.08 kg ha^-1 provided poor control of crabgrass at both timings and were less effective than fenoxaprop at 0.10 kg ai ha^-1.

Physiological effects of temperature on turfgrass injury to amicarbazone.  J. Yu and P. McCullough; Department of Crop and Soil Sciences, University of Georgia, Griffin, GA 30223.

ABSTRACT

Amicarbazone effectively controls annual bluegrass (Poa annua L.) in cool-season grasses with spring applications but summer applications are too injurious for selective control.  Experiments were conducted to evaluate uptake, translocation, and metabolism of ¹⁴C-amicarbzone in hybrid bermudagrass (Cynodon dactylon x C. transvaalensis), tall fescue (Festuca arundinacea), and annual bluegrass.  Grasses were grown in growth chambers set for 25/20 C (day/night) or 40/35 C.  At the cool temperature, annual bluegrass absorbed more foliar applied amicarbazone than tall fescue and bermudagrass after 72 hours.  Foliar absorption increased at 40/35 in all species, compared to 25/20, and tall fescue had similar absorption to annual bluegrass at the high temperature.  Bermudagrass had less foliar absorption than annual bluegrass at both temperatures and less absorption than tall fescue at the high temperature only.  Annual bluegrass and tall fescue had approximately twofold greater root absorption of ¹⁴C-amicarbazone than bermudagrass after 72 hours. Annual bluegrass had less metabolism of amicarbazone than tall fescue at 25/20 but both species recovered similar levels of parent herbicide at the high temperature. Bermudagrass had more metabolism of amicarbazone than annual bluegrass and tall fescue at the high temperature but metabolism was similar to annual bluegrass at the low temperature.  Results suggest bermudagrass tolerance to amicarbazone is attributed to less absorption than cool-season grasses while increased sensitivity of tall fescue to amicarbazone at high temperatures results from greater foliar and root absorption.   

Annual bluegrass (Poa annua L.) is a troublesome weed on golf greens.  As the intensity of golf turf management increases, so do populations of perennial biotypes of annual bluegrass.  Annual bluegrass patches, which may represent different biotypes, are commonly observed to differ in regards to color, texture, growth rate, and number of seed heads.  It is not known whether these visual differences are promoted by management strategies, and/or whether morphologically diverse annual bluegrasses respond differentially to control programs. We designed a study to examine these questions.  Annual bluegrass plugs were collected in 2011 from greens at the Lexington Country Club and The University Club of Kentucky, both located in Fayette County Kentucky. The samples were collected based on their having one of two appearances while on the same green: 1.) dark green, with few to no flower heads (“dark” biotype) or 2.) light green, with numerous flower heads ("light" biotype).  Two plant growth regulators (PGRs), paclobutrazol and flurprimidol, and two herbicides, bispyribac-sodium and amicarbazone, were applied to the plants both in the field and the greenhouse.  Quality ratings were collected in the summer and fall of 2011 and 2012 on a scale from 1-9, with 1= a dead plant and 9= excellent quality.  The rates and application frequency were as follows: paclobutrazol (270 g a.i./ha applied every 3 weeks); flurprimidol (490 g a.i./ha applied every 3 weeks); bispyribac-sodium (25 g a.i./ha applied once in the summer and once in the fall); amicarbazone (49 g a.i./ha applied weekly for the first 4 weeks).  In 2011, we found that in the field, the “light” biotypes tended to have a higher overall turf quality than the “dark” biotypes.  Paclobutrazol reduced the quality of “light” biotypes collected from both locations more than the “dark” biotypes.  In contrast, flurprimidol reduced the quality of the “dark” biotypes from both locations more than the “light” biotypes.  In the greenhouse, paclobutrazol and flurprimidol reduced quality of the “dark” biotypes more than the “light” biotypes from the University Club.  However, bispyribac-sodium reduced quality of the “dark”
 biotypes more than the “light” biotypes from both locations.  The “dark” biotypes had higher overall quality than the “light” biotypes in the field in 2012.  Also in the field experiment in 2012, the quality of annual bluegrass collected from the Lexington CC, both “light” and “dark”, was reduced more by all treatments, except flurprimidol, than the quality of annual bluegrass collected from the University Club.  Flurprimidol reduced the quality of annual bluegrass from the University Club, both “light” and “dark” biotypes, more than the annual bluegrass from the Lexington CC.  In the greenhouse, flurprimidol reduced the overall quality of the “light” biotypes from the Lexington CC versus those collected from the University Club.  Our studies are continuing but these results demonstrate both the potential for different responses between annual bluegrass biotypes to PGRs and herbicides and that these differences, like all things about annual bluegrass, may be complex.

Silvery threadmoss has become a major weed problem on creeping bentgrass putting greens.  Carfentrazone is the only herbicide labeled for use against silvery threadmoss on putting greens and it requires repeated applications throughout the season for effective suppression of moss.  Several fungicides also have supplemental registrations for silvery threadmoss control.  After preliminary screening in the laboratory, selected treatments were field-tested to determine their potential silvery threadmoss control.  The objective of this study was to test the efficacy of several herbicide, fungicide, and herbicide + fungicide combinations for season long control of silvery threadmoss on golf course putting greens.

This study was initiated on three creeping bentgrass putting greens in Blacksburg VA in May18^th 2012 at the Turfgrass Research Center & Glade Road Research Facility, Virginia Tech.  The three creeping bentgrass cultivars were A4, L-93 and Tyee. Twenty six herbicide, fungicide or herbicide + fungicide combinations were applied in a randomized complete block design.  Any combination including a fungicide but not carfentrazone was applied every two weeks.  Any combination including carfentrazone was applied every three weeks.  All other products were applied once at study initiation.  See table 1 for treatments listed by application timing.  Visual cover, control, and injury ratings were taken monthly throughout the season as well as whole plot NDVI readings. 

At 8 weeks after initial treatment, three treatments performed equivalent to carfentrazone.  They included carfentrazone + chlorothalonil Zn + fosetyl-Al, 2,4-D amine, and Experimental #1.  In addition four treatments outperformed carfentrazone.  They included flumioxazin, sulfentrazone, Experimental #2, and oxyfluorfen.  Unfortunately those products which are more effective than carfentrazone can also be quite injurious to putting green turf.  Experimental #2 and sulfentrazone may have potential for turf safety and improved moss control; however, bentgrass variety testing needs to be performed to demonstrate safety to most varieties. 

Table 1.  Treatments listed in each box according to season long application timings.

FALL APPLICATIONS OF PRODIAMINE + SULFENTRAZONE FOR PREEMERGENCE CONTROL OF ANNUAL BLUEGRASS AND CRABGRASS.   C. Johnston and P. McCullough; Department of Crop and Soil Sciences, University of Georgia, Griffin, GA 30223. 

ABSTRACT 

Preemergence herbicides are applied in fall for annual bluegrass (Poa annua) control and residual effects may control summer annual weeds.  The objective of this research was to evaluate efficacy of fall applications of Echelon (prodiamine + sulfentrazone) at 1.25 kg ai/ha applied as a granular (G), suspension concentrate, or water dispensable granule compared to prodiamine at 0.56 or 0.84 kg ai/ha, F9001 (0.3G) at 1 kg ai/ha, and indaziflam at 53 g ai/ha.  Applications were made on October 3, 2011 to a ‘Tifway’ bermudagrass (Cynodon dactylon x C. transvaalensis) fairway.  All treatments provided complete control of annual bluegrass at 203 days after applications (DAA).  Echelon, F9001, and prodiamine treatments provided poor control of parsley-pert (Aphanes arvensis) but indaziflam provided complete control at 203 DAA.  At 332 DAA, the granular Echelon formulation and F9001 provided excellent control (≥90%) of smooth crabgrass but control was (<70%) from other treatments.  Results suggest all Echelon formulations provided comparable control of annual bluegrass to prodiamine and indaziflam in fall while the granular formulation and F9001 had enough residual to control smooth crabgrass at the rates tested.   

Dimension® 2EW is a new formulation of dithiopyr widely used for pre-emergence control of crabgrass in the Transition Zone and Northern United States.  Dithiopyr also controls crabgrass post-emergence and up to the tillering stage.  Defendor™ (florasulam) is a new herbicide from Dow® AgroSciences, utilizing low use rates for post-emergence control of many winter annuals and perennial broadleaf weeds.  Defendor™ should be available to the public in early 2013 as a co-pack with Dimension® 2EW offering pre-emergence crabgrass control and broadleaf weed suppression during the lag time between pre-emergence crabgrass treatment and late season broadleaf treatments.      

A study was initiated on March 16, 2012 that evaluated the following treatments for broadleaf weed control: dithiopyr (280 g ai ha^-1) + florasulam (14.6 g ai ha^-1) applied in mid-March + 6 weeks after initial treatment (WAIT), dithiopyr (280 g ai ha^-1) + florasulam (14.6 g ai ha^-1) + Trimec Classic (1330 g ai ha^-1) at 6 WAIT, dithiopyr (426 g ai ha^-1) + florasulam (14.6 g ai ha^-1) applied in mid-March, dithiopyr (426 g ai ha^-1) + florasulam (14.6 g ai ha^-1) applied in early May, dithiopyr (426 g ai ha^-1) + Trimec Classic (1330 g ai ha^-1) applied in early May and dithiopyr (280 g ai ha^-1) applied mid-March + 6 WAIT.  A second study, also initiated March 16, 2012, evaluated dithiopyr alone for smooth crabgrass control applied at 426 g ai ha^-1 in mid-March, 280 g ai ha^-1 applied in mid-March and mid-May, and 560 g ai ha^-1 applied in mid-March.  Both studies were arranged as a randomized complete block design with three replications.  All treatments were applied at 280 L ha^-1 using Teejet turbo twin injection 11004 nozzles at 262 kPa.  An untreated check was included for comparison. 

In the first study, all treatments controlled white clover greater than 93% when evaluated on June 15 (4 months after initial treatment), with the exception of dithiopyr (426 g ai ha^-1) + florasulam (14.6 g ai ha^-1) applied at 6 WAIT, and dithiopyr (280 g ai ha^-1) applied twice, which controlled white clover 30% and 10%, respectively.  On the same evaluation date, dithiopyr + florasulam treatments and treatments that contained Trimec Classic controlled dandelion > 93%, and the remaining treatments controlled dandelion < 25%.  These results indicate that dithiopyr plus florasulam controls white clover, but only when applied early in the season.  Dithiopyr applied alone does not control white clover.  Acceptable control of dandelion was achieved when dithiopyr was paired with florasulam at 6 WAIT and when treatments contained Trimec Classic.  In the second study, smooth crabgrass was completely controlled by all treatments on August 17, 2012, indicating dithiopyr applied alone and as a sequential application will provide season-long control of smooth crabgrass in the Transition Zone.  At a second location, single treatments of dithiopyr controlled smooth crabgrass less than the split treatment of 280 g ai ha^-1 applied in March and May.

Postemergence Control of Creeping Lilyturf, Liriope spicata.

K. Adams*, C.H. Gilliam, G.R. Wehtje, S.F. Enloe;  Auburn University, Auburn, AL.

ABSTRACT

Liriope spicata is an evergreen groundcover classified as a perennial, popularly found in the ornamental landscape setting.  L. spicata is commonly referred to as creeping liriope, creeping lilyturf, and creeping monkeygrass.  Native to eastern Asia, creeping liriope spreads aggressively through an underground rhizome root formation.  When incorporated into the homeowner landscape, the aggressive nature of L. spicata can become a problematic maintenance issue when trying to contain an area of establishment.  Listed as an exotic forb species by the Invasive Plant Atlas of the United States, creeping liriope has been reported to be invasive in natural areas within the U.S.  Little research has been documented on the control methods of L. spicata within the horticulture industry.  The objective of this research is to determine the efficacy of post emergence spray applications of seven different herbicide sprays for control of L. spicata.  Herbicide treatments in this study include selective and non-selective chemistries, available to the public through homeowner, forestry, or agricultural use.  In May 2012, seven herbicides were applied to L. spicata at two rates each.  Each treatment consisted of ten single pot replications.  A randomized block experimental design was used. Visual injury ratings were collected at 30 and 60 days after treatment (DAT).  Shoot regrowth and root assessments were made by measuring each replication for dry shoot and dry root weights.  All data were subjected to analysis of variance (ANOVA).  Duncan’s Multiple Range Test was used for a comparison between treatment means at a p-value ≤ 0.05.

At 30 DAT, only metsulfuron at both rates and sulfometuron at the higher rate had greater   injury than the non-treated control liriope.  All other treatments had injury similar to the non-treated control.   At 60 DAT, both rates of metsulfuron, both rates of imazapyr, and the higher rate of glyphosate had significantly injury greater than that of the non-treated control.  Maximum control (91%) as determined by dry weight reduction at 63 DAT, was obtained with metsulfuron at the 2 oz./acre rate.  Metsulfuron at the 1 oz./acre rate provided 84% control.  Control of foliage regrowth at 90 DAT was consistent with both injury ratings and with dry weight reduction.  Metsulfuron application at both rates had similar foliar regrowth control (97% - low rate) (100% - high rate).  Imazapyr had similar control for foliar regrowth at both the low rate (85% control) and the high rate (86%).  Root tissue control at 90 DAT again showed that metsulfuron was most effective.  Metsulfuron at 1 and 2 oz./acre controlled root tissue 66% and 80%, respectively.  Glyphosate at the high rate (171 oz./acre) provided 61% control.  Registered for non-crop control of weeds and woody plants, metsulfuron demonstrated the greatest control of shoot reduction, shoot regrowth, and root formation of L. spicata.

Liverwort (Marchantia polymorpha) can be a serious impediment to commercial perennial production in much of the country and is often found infesting plants throughout the year. In the Northeast, it is common to over-winter perennials in unheated covered houses. Close inspection of liverwort in these conditions indicates that it is still actively growing and capable of spreading to new areas during the season when the crops have become dormant. This represents an opportunity to manage liverwort with non-selective broadcast applications of contact herbicides without significant harm to the crop. In 2012, a study was conducted to evaluate five nonselective herbicides at two application rates: d-limonene at 14% and 28% v/v solution (Avenger Ag Burndown), oregano oil extract at 1% and 2% (Mossbuster), ammonium nonanoate at 3% and 6%(Emery Agro), pelargonic acid at 3% and 6% (Scythe) and acetic acid 25% and 50%(Weed Pharm). All treatments were applied at 100 gpa. The ornamental species evaluated were: Delosperma nubigenum 'Basutoland', Heuchera villosa 'Caramel', Dryopteris erythrosora, Hosta x 'Gold Standard', Hemerocallis x 'Mini Pearl' and Hydrangea macrophylla 'Blue Danube'. Applications were made twice, in late February 2012 when the ornamentals were dormant, and again 8 weeks later when new growth had emerged. The plots were arranged so that 0.25 inch of irrigation could be applied to half of the plot immediately after treatment. This post treatment irrigation was applied to determine if the water could reduce phytotoxicity to actively growing ornamentals and still allow the herbicides to control liverwort. Liverwort was exposed to all treatments and timings. The results suggest that good to excellent control can be attained with all of the treatments. In general, post treatment irrigation did not decrease liverwort control, but did increase safety of some of the treatments on actively growing ornamentals. The implications for further research and practical implementation will be discussed.

Marchantia polymorpha L. (a thalloid liverwort) is estimated to cost MI nurseries $650,000 is loses annually due to ineffective control.  In MI, the rapid growth and dissemination of liverwort has resulted in heavy thallus mats on the surface of pots, restricting water penetration, competing for nutrients, and providing habitat for other pests and disease vectors.  To date there are no registered products that are used by nursery or greenhouse growers for effective liverwort control in enclosed structures.  In 2011, with funding provided by the USDA, Specialty Crop Block Grant (SCBG) program through Michigan Nursery and Landscape Association (MNLA) and Michigan Department of Agriculture (MDA) and the IR-4 program, we compared six control products (listed below) in the USDA/ IR-4 liverwort protocols plus a 1/3 (4oz/ac) rate of SureGuard (flumioxazin, Valent U.S.A.) and WeedPharm™ (20% acetic acid) at 10% v/v (Pharm Solutions Inc., Port Townsend, WA), to Baking Soda (sodium bicarbonate) (2.24 g/ ft²)(not part of IR-4).  In 2012, in the MDA/ MNLA SCBG, we evaluated SureGuard at a ¼ (3 oz/ac) rate and a 1/3 rate (4 oz/ac) and WeedPharm in the IR-4 program, to Baking soda and MilStop^® (Potassium Bicarbonate 85%, BioWorks^®, Victor, NY) as a powder 5 gram/ft² and liquid at 2.5 lb/100 gallons.  MilStop is an OMRI listed sprayed broad spectrum fungicide (with no registration as an herbicide).  Cooperating nurseries located near Grand Haven, MI [Berry Family Nurseries (BFN) (2011) and Spring Meadow Nursery (SMN), Inc. (2011-12)] and West Olive, MI (Northland Farms, LLC.) (2011-12) were selected as sites.  Phytotoxicity and efficacy evaluations were conducted in 2011 and 2012 on ten ornamental species which varied by year.  In 2011, the six additional liverwort control products tested mentioned above were Tower (dimethenamid-p) at 32 oz/ac, Racer™ (Ammonium nononanoate) at 10% v/v, SureGuard (flumioxazin) at 12 oz/ac, GreenMatch (d-limonene) (an extract of lemon grass) at 20% v/v, Bryophyter (Oregano Oil Extract) at 2% v/v and Terracyte Pro G (Sodium carbonate peroxyhydrate) at 10 lb/1000 ft². Evaluations of phytotoxicity and efficacy were taken at 1, 2, 4, 5, 6, 7, 8, and 9 WAIT (weeks after initial treatment).  Phytotoxicity was evaluated on a scale of 0-10 with 0 being no phytotoxicity and 10 death and ≤3 commercially acceptable.  Efficacy was evaluated on a scale of 0-10 with 0 being no control, 10 perfect control and ≥7 commercially acceptable.  MillStop^® as a sprayable had O efficacy.  However, MilStop^® as a powder warrants further evaluations in 2013 as it ranked #1 in 2012 efficacy treatments at SMN and NF with minimal damage to 8 or 10 species tested. Further reductions in MilStop^® phytotoxicity on the two species observed may be possible by knocking the dust off the foliage immediately following application, as is the procedure used by Northland Farms when applying Baking Soda to active growth.  Also testing with new formulations of K-bicarbonate and application methods are planned for 2013.  The SureGuard at ¼ the normal rate also warrants further evaluations in 2013 due to its efficacy and low phytotoxicity.  The WeedPharm at 10% will also be tested further in 2013; however, not 5%. Tower, Racer™, GreenMatch, Bryophyter and Terracyte were not tested in 2012 due to low efficacy and/ or high phytotoxicity.  SureGuard testing at 1/8 (1.5 oz/ac) rate will be conducted in 2013.

In our research at Imperial Nurseries in Granby, CT we always are looking for sprayable herbicides that can be used over the top on container grown plants. The objective was to see if indaziflam can be used as a spray on some herbicide sensitive plants.

Three plants of five species were included in each experimental unit. Newly potted plants were put in one gallon container two days prior to application. Five different herbicide treatments and a control were replicated four times in randomized complete blocks. Plants included were; dwarf burning bush (Euonymus alatus ‘Compactus’), emerald green arborvitae (Thuja occidentalis ‘Smaragd’), rhododendron ‘Chionoides’; hydrangea macrophylla (The Original Endless Summer ‘Bailmer’) and butterfly bush (Buddleia ‘Tutti Fruitti’). Two herbicide applications were made, first on July 25^th and second on September 12^th.

The treatment were sprays of 1) isoxaben (Gallery 75 DF at 1 lb/A) plus prodiamine (Barricade 4FL at 21 oz/A), 2) dimethenamid-P (Tower at 21 oz/A), and indaziflam 3) Alion at 5.437 oz/A, 4) Alion at 10.874 oz/A and 5) Alion at 21.748 oz/A). Sprays were applied with a calibrated CO² powered hand-held boom equipped with two Tee Jet 8004-VS nozzles, operating at 41 psi and 2.5 ft/sec speed, applying 50 gallons/A. Foliage was wet before spraying. The temperature was 71° F, sunny and calm for the first application and 65° F in a sunny day with little wind for second application. Following applications the experiment was irrigated for 15 minutes.

Plants were held in a hoop house. After each application several ratings for injuries were done. Injury was rated in a scale (0-10) with zero no injury and ten dead.

            With the exception of 21.748 oz/A rate of Alion on the rhododendron, all the other applications of Gallery 75 DF plus Barricade 4FL, Tower and Alion 1X, and 2X did not cause any or caused very little injuries on the emerald green and rhododendron. Application of Alion 10.874 oz/A rate on the rhododendron caused very little dark spotting on the leaves, but the growth was not effected. Tower caused little injuries on buddleia and hydrangeas. Alion on all rates injured significantly the burning bush, hydrangea and buddleia.

            The results show that indaziflam on the recommended rate can safely be used over the top as a spray on emerald green (Thuja occidentalis’Smaragd’) and rhododendron ‘Chionoides’. Based on those results sprays of indaziflam over the top on container grown plants may have potential on other plants, research needed.

(saizba@yahoo.com)

We conducted field experiments in 2012 to evaluate the herbicide indaziflam (Alion 1.67SC) for safety to three conifer species.  Research plots were established in Enfield, CT in commercial Christmas tree fields of Fraser fir [Abies fraseri (Pursh) Poir.] planted in 2010, eastern white pine (Pinus strobus L.) planted in 2010, and Colorado spruce (Picea pungens Engelm.) planted in 2011.  Most trees were 1.5 to 2.5 ft tall prior to bud break in 2012.  Soil texture is a fine sandy loam.  Each plot consisted of four to five trees spaced 5 ft apart in a row.  Tree rows were 6 ft apart.  Herbicide treatments and the untreated control were replicated four times in a RCB design.  Each plot was treated once.  Herbicides were applied over the top of trees using a CO₂-pressurized sprayer equipped with two Teejet 8003VS nozzles and calibrated to deliver 30 gallons per acre at a pressure of 32 psi.  The following treatments were applied on March 30 (pre bud-break / dormant):  indaziflam at 1.14 oz ai / A (0.08 kg ai / ha), indaziflam at 2.28 oz ai / A (0.16 kg ai / ha), glyphosate alone, glyphosate plus indaziflam at 1.14 oz ai / A, and glyphosate plus indaziflam at 2.28 oz ai / A.  Glyphosate doses were 0.75 lb ae / A (0.84 kg ai / ha) for Fraser fir and Colorado spruce, and 0.375 lb ae / A (0.42 kg ai / ha) for white pine.  The following treatments were applied on May 23 (post bud-break / active growth):  indaziflam at 1.14 oz ai / A and indaziflam at 2.28 oz ai / A.  Plant injury and weed control were evaluated on several dates.  The most severe injury occurred on Fraser fir treated with indaziflam on May 23.  Symptoms of chlorotic, stunted new needle growth were not observed at 2 weeks after treatment (WAT) but were obvious at 5 WAT and beyond.  The only other lasting injury occurred on white pine treated on March 30 with glyphosate plus indaziflam at 2.28 oz ai / A.  Colorado spruce was tolerant of all treatments.  Indaziflam applied on March 30 provided much better weed control than when applied on May 23.  Pre-emergent control of large crabgrass [Digitaria sanguinalis (L.) Scop.] was excellent at both doses, but control of yellow foxtail [Setaria glauca (Poir.) Roemer & J.A. Schultes] was not as complete or consistent.  Indaziflam activity on horseweed [Conyza canadensis (L.) Cronq.] and common ragweed (Ambrosia artemisiifolia L.) was in the range of suppression rather than control.  Indaziflam stunted growth of some perennial weeds, such as hemp dogbane (Apocynum cannabinum L.) and common milkweed (Asclepias syriaca L.).

Two separate experiments were conducted in 2012 at the Valley Laboratory in Windsor, CT to evaluate herbicides applied over the top of ornamentals grown in nursery containers.  Plants were potted in 1-gallon containers in late May to early June 2012.  A granular formulation of indaziflam was the focus of Experiment 1.  Dimethenamid-p in sprayable form was evaluated in Experiment 2. 

For Experiment 1, plants were hosta (Hosta ‘Gold Standard’), daylily (Hemerocallis ‘Stella de Oro’ and ‘Happy Returns’), azalea (Rhododendron ‘Delaware Valley White’), hydrangea (Hydrangea macrophylla ‘Endless Summer’), and common lilac (Syringa vulgaris).  Each plot contained three pots of each species.  Treatments were replicated four times in a RCB design.  Granules were applied with a calibrated auger-feed drop spreader over the top of dry foliage.  Treatments consisted of indaziflam (0.0224G) granules applied at one of three doses:  0.0448, 0.0896 or 0.179 lb ai / A (50, 100 or 200 g ai / ha).  Granules were applied on June 18 (T-1) and again on July 31 (T-2).  At 2 h after treatment application, all plants were watered with overhead sprinklers for 45 min.  Plant injury (0 to 10 scale) was evaluated several times.  The hydrangeas were extremely sensitive to indaziflam.  By July 17 (4 WAT-1), hydrangeas treated with indaziflam, even at the lowest dose, were dead or nearly dead.  All treated hydrangeas died before the second application.  No significant injury was observed on any of the other plants after the first treatment application.  By September 5 (5 WAT-2), injury was observed on azalea, hosta, and ‘Happy Returns’ daylily, but only on those plants treated with the highest dose of indaziflam.  Lilac and ‘Stella de Oro’ daylily were tolerant of indaziflam.  Weeds were counted and pulled from all containers on July 31 prior to T-2.  At all doses, indaziflam provided excellent control of annual weeds present.

For Experiment 2, plants and plot layout were the same as above, except lilacs were not included.  Dimethenamid-p (5.9EC) treatments were applied in a volume of 100 gallons per acre by spraying over the top of dry foliage at 50 gal / A twice.  A CO₂-pressurized spray boom with Teejet 8004VS tips was used.  Treatments consisted of dimethenamid-p at one of three doses [0.97, 1.94 or 3.88 lb ai / A (1.09, 2.17 or 4.35 kg ai / ha)] applied once on June 27.  Overhead irrigation for 45 min began 20 min after treatment application.  Plant injury was evaluated several times on a 0 to 10 scale.  On August 2 (5 WAT), an average injury rating of 2.5 was recorded for hydrangeas treated with the highest dose of dimethenamid-p.  All other plant injury ratings were less than 2.  Daylilies and hostas exhibited tolerance to all doses.  Prostrate spurge [Chamaesyce humistrata (Engelm. ex Gray) Small] was the most prevalent weed that emerged in containers.  The high dose of dimethenamid-p provided excellent control of spurge, but the low and medium doses only suppressed the number of spurge seedlings.  The medium and high doses provided adequate control of other weeds.

In the summer of 2011, indaziflam 0.622SC at 40, 80, and 160 grams per hectare and flumioxazin at 0.28 kg. per hectare were applied as directed sprays to established woody ornamentals grown in Riverhead sandy loam. The following spring, buckwheat and oats were sown on one side of the plots and herbicide application was repeated on the opposite side. The cover crops were broadcast seeded at the standard rate for cover crop; buckwheat at 70 lb./A and oats at 110 lb./A. Establishment of cover crop and phytotoxicity to ornamentals were evaluated by visual observation. The ornamental species, Althea syriacus 'Boule de Feu', Betula nigra, Cupressocyparis leylandii 'Leighton Green', and Ligustrum ovalifolium, Fothergilla gardenii and Ilex glabra 'Densa', were rated for phytotoxicity and height. (Fothergilla and Ilex were planted during the fall of 2011 so were not treated at the first timing in the summer of 2011.) Some very minor leaf speckling was observed on lower foliage of Betula and Althea and no significant height differences were observed. Cover crop germination and growth was affected. Oat germination was poor and not sufficient to collect reliable data. For buckwheat, all treatments resulted in a significant reduction of percent ground cover. In the treated plots, buckwheat plants were smaller and less vigorous throughout the season. By two weeks after seeding, significant reduction in establishment of buckwheat was observed. At the highest rate of indaziflam, an average of 11% ground cover was observed compared to 55% in the untreated plots. At six weeks after seeding, buckwheat was well established in the untreated plots with an average of 83% ground cover. The lowest rate of indaziflam and the SureGuard treatment were at 58% and 54%, respectively. The mid-rate of indaziflam had 35% ground cover and the highest rate had 14% ground cover. These results indicate that both indaziflam and flumioxazin can have negative effects on cover crop establishment in the year following the application.

Leaching Behavior of Two Pendimethalin Formulations in a Soilless Mix.  J. F. Derr, Virginia Tech, Virginia Beach, VA.

Pendimethalin is commonly used for control of annual grasses and certain broadleaf weeds in nursery crops, including container production.   Container trials and column leaching studies were used to compare herbicide effectiveness and movement of two pendimethalin formulations, an emulsifiable concentrate (EC) and a microencapsulated (ME) form in a pine bark growing medium.   Pendimethalin leaching was determined using both a southern crabgrass (Digitaria ciliaris) bioassay as well as chemical extraction and quantification.  The EC formulation provided greater southern crabgrass control than the ME form.  The ME form of pendimethalin had lower persistence and greater movement than the EC formulation in 100% pine bark. After applying 3.4 kg ai ha^-1 pendimethalin and 17.8 cm of irrigation water, the ME formulation showed significant downward movement in pine bark through the 12-cm depth, as indicated by the southern crabgrass bioassay.  Using chemical extraction,  0.91 ppm of pendimethalin was found at the 3- to 6-cm depth below the surface when the EC form was applied compared to 4.0 ppm when the ME formulation was used.  Below the 6-cm depth, no pendimethalin was detected when the EC form was applied compared to 0.5 ppm when the ME formulation as used.  No pendimethalin was detected in effluent collected from the bottom of the soil columns when the EC form was applied.  However, 3.0 ppb was collected from the leachate for the ME formulation.  Pendimethalin ME is leaching much deeper in the pine bark profile than the EC form, which results in lower weed control and may potentially cause adverse root effects to sensitive nursery crops.  The greater leaching seen for the ME formulation may be due to capsule movement in the irrigation water flowing downward through pores in the bark substrate prior to release of the pendimethalin.

jderr@vt.edu

Continuous glyphosate use has contributed to an increasing number of problematic glyphosate-resistant weeds. The mechanism of resistance in many glyphosate-resistant weeds is poorly understood, in part, due to a poor understanding of how exactly glyphosate kills a plant. In previous research, the efficacy of glyphosate on giant ragweed (Ambrosia trifida) biotypes was shown to be greater when plants were grown in unsterile soils compared to sterile soils due to soil-borne plant pathogens infecting and damaging the roots of glyphosate-treated plants. A series of experiments were conducted to investigate the role of soil microbes in the resistance of giant ragweed to glyphosate. Glyphosate-resistant and -susceptible biotypes of giant ragweed were grown separately in sterile and unsterile field soil and treated with glyphosate at two sublethal rates. Soil microbes were isolated from the roots onto sterile media three days after the glyphosate treatment. The susceptible biotype grown in the unsterile soil was colonized by a greater number soil microbes when treated with glyphosate, compared to the resistant biotype. Oomycete (e.g. Pythium spp. and Phytophthora spp.) pathogens were also more prevalent in the roots of the susceptible biotype grown in the unsterile soil, when glyphosate was applied. Giant ragweed biotypes were then planted in sand-cornmeal that was either inoculated with Pythium ultimum or not inoculated, and tolerance of each biotype was measured in the absence of glyphosate. The ability of giant ragweed to tolerate a glyphosate application may involve differences in the susceptibility to soil microbial colonization, especially oomycete pathogens.

The dominance of glyphosate in global agriculture has arguably contributed to the number of glyphosate resistant weeds found today, numbering 24 species (1/2013, www.weedscience.org).  Interestingly several genera have at least two species and further some of these species are found on multiple continents.  The independent selection of these resistant biotypes strongly suggests that the “genome” of these plants has a trait that can be selected for glyphosate resistance.  This is quite contrary to the random generation and frequency of point mutations in populations that give rise to highly effective target site resistant weeds for several sites of action mechanisms.  However glyphosate’s transition state inhibition mechanism so far has not allowed effective target site point mutations (as originally predicted).  The selection for glyphosate resistance is more akin to the resistance provided by metabolism seen in other chemistries in that some species can and others can not.  There is limited chemical evidence glyphosate is metabolized in plants generally (but legumes can produce AMPA) and so far not as a means for a resistance mechanism.  The mechanisms of glyphosate resistance are more exclusion type systems where vacuole sequestration (horseweed, ryegrass) or cellular exclusion (slower cellular uptake, Johnsongrass, waterhemp, Palmer) involving active transport has long been predicted but never demonstrated until now.  The novel gene duplication of EPSPS providing resistance in Palmer, waterhemp, ryegrass and Kochia is really a “sequestration” type mechanism too.  In this case the EPSPS enzyme can together with S3P form a “dead-end” complex and effectively lower the concentration of glyphosate available to inhibit the normal shikimate pathway.  Data supporting the various mechanisms will be discussed with an eye toward yet other possible resistance mechanisms.

Amaranthus palmer resistance to glyphosate results from the amplification of the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene.  However, the gene amplification mechanism is unknown.  We sequenced the EPSPS gene and genomic regions flanking EPSPS loci in A. palmeri, and searched for mobile genetic elements or repetitive sequences.  The EPSPS gene was 10,229 bp, containing 8 exons and 7 introns.  The gene amplification likely proceeded through a DNA-mediated mechanism, as introns exist in the amplified gene copies and the entire amplified sequence is at least 30 kb in length.  Our data support the presence of two EPSPS loci in susceptible (S) A. palmeri, and that only one of these was amplified in glyphosate-resistant (R) A. palmeri.  The EPSPS gene amplification event likely occurred recently, as no sequence polymorphisms were found within introns of amplified EPSPS copies from R individuals.  Sequences with homology to miniature inverted-repeat transposable elements (MITEs) are present in the genomes of both S and R individuals, but are found within 500 bp from both ends of EPSPS gene copies only in R individuals.  Additionally, a putative Activator (Ac) transposase and a repetitive sequence region are consistently located downstream of amplified EPSPS genes.  We propose two potential mechanisms that may have contributed to the gene amplification: DNA transposon-mediated replication, and unequal recombination between different genomic regions resulting in replication of the EPSPS gene.

Herbicide resistance due to non-target site resistance (NTSR) mechanisms, including increased metabolism, is not well understood at the molecular level.  A transcriptomics approach was used to study a diclofop-methyl NTSR Lolium rigidum population produced through recurrent selection.  A reference transcriptome was produced by sequencing a cDNA library using the Roche/454 GS FLX+ Titanium platform.  One pico-titer plate produced 1,069,238 reads with an average length of 448 bases.  Read assembly produced 19,623 contigs of greater than 100 bp and a mean contig size of 1,049 bp.  The reference transcriptome was annotated using both UniProt and Pfam and included genes involved in herbicide modes of action, detoxification pathways, and signal transduction, including 57 cytochromes P450, 56 glutathione-S-transferases, and at least 58 protein kinases.  Next, an RNA-Seq experiment was conducted, using vegetative clones of 4 individuals each from the recurrent-selected resistant (R) and progenitor susceptible (S) populations as 4 biological replicates, and 3 treatments including an untreated control, a surfactant treatment (sprayed with water and surfactant only) and a diclofop-methyl treatment (375 g/ha + surfactant).  The 24 mRNA samples were sequenced using the Illumina HiSeq 2000 platform with 100 bp paired-end reads, producing an average of 75 million reads per sample.  Reads were aligned to the reference transcriptome using Bowtie.  Differential expression (DE) analysis was conducted using the BaySeq and DESeq packages in R.  Between R and S prior to treatment, 11% of all contigs had DE.  Surfactant treatment induced DE in 9% and 3% of contigs in R and S, respectively.  Diclofop-methyl treatment did not induce DE in R relative to the surfactant treatment, but diclofop-methyl did induce DE in several contigs in S including heat shock proteins.  Twenty-eight contigs were selected for functional validation using qRT-PCR on cDNA, including 5 cytochrome P450 contigs, and 4 reference genes for normalization.  These results demonstrate the utility of RNASeq to study NTSR mechanisms.

A tall waterhemp population from Missisippi was suspected to be resistant to glyphosate. Glyphosate dose response experiments resulted in GR₅₀ values of 1.28 and 0.28 kg ae ha^-1 glyphosate for the glyphosate-resistant (GR) and -susceptible (GS) populations, respectively, indicating a 5-fold resistance. The absorption pattern of ¹⁴C-glyphosate between the GR and GS 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% vs. 29%) and shoot fresh weight reduction (73% vs. 34% of nontreated control) of the GS plants compared to the GR plants, possibly, indicating a reduced movement of glyphosate. The amount of ¹⁴C-glyphosate that translocated out of the treated leaves of GR plants (19.8% of absorbed at 24 HAT and 23.3% of absorbed at 48 HAT) was significantly lower than the GS plants (30.9% of absorbed at 24 HAT and 31.9% of absorbed at 48 HAT). The IC₅₀ values for the GR and GS populations were 480 and 140 µM of glyphosate, respectively, resulting in more shikimate accumulation in the GS than the GR population. Sequence analysis of 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), the target site of glyphosate, transcript from GR and GS plants identified a consistent single nucleotide polymorphism (T/C, thymine/cytosine) between GR/GS plants, resulting in a proline to serine amino acid substitution in the GR population. The GR and GS plants contained equal genomic copy number of EPSPS, which was positively correlated with EPSPS gene expression. Thus, glyphosate resistance in the tall waterhemp population from Mississippi is due to both altered target site and non-target site mechanisms.

Common ragweed (Ambrosia artemisiifolia) is an almost ubiquitous weed throughout Ohio, and can cause considerable yield loss when competing with crops.  Common ragweed is typically well-controlled in soybeans with various herbicide programs, but is becoming a larger concern as options are reduced due to the evolution of herbicide-resistant biotypes.  The molecular basis for glyphosate-resistance in Ohio common ragweed populations is unclear.  Our current research seeks to elucidate potential mechanism(s) of resistance, through studies of expression and sensitivity of the target enzyme for glyphosate, 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS).  Sequence analysis of epsps gene PCR products does not show any target-site mutations in samples from glyphosate-resistant populations, in comparison to “wild-type” glyphosate-sensitive plants.  This sequence also demonstrates that there are 2 or more copies of epsps in common ragweed.  An immunoblot assay with common ragweed total soluble protein, as well as Palmer amaranth (Amaranthus palmeri) and kochia (Kochia scoparia) controls, was inconclusive in that no EPSPS expression could be detected except in the Palmer amaranth and kochia over-expressing controls.  Current research focuses on epsps genomic and mRNA transcript copy numbers.

Investigation into the molecular and biochemical mechanisms of resistance to glyphosate in two populations of giant ragweed (Ambrosia trifida)

Taylor Jeffery, Chris Hall, Mark Lawton, Peter Sikkema, François Tardif, Michael McLean

There are two phenotypes associated with resistance to glyphosate in giant ragweed (Ambrosia trifida). The most common in Canada is the “rapid necrosis response” which shows treated leaves rapidly reacting to glyphosate while the growing point remains unaffected. Plants with the “slow recovery response” stop growing for about 14 days and turn slightly chlorotic before resuming growth. Our aim is to examine the genetic and biochemical factors that confer resistance. The target site of glyphosate has been PCR amplified and sequencing analysis is being conducted. We are also examining the role free radicals play in the rapid response plants. Using spectrophotometry we are examining free radical production in response to glyphosate application. In addition semi-quantitative PCR we will be used to investigate changes in expression of several genes associated with free radical production. Finally crosses have been made between resistant and susceptible plants, as well as between resistant plants with the two phenotypes. We will determine the inheritance and dominance of the resistant traits. Results from this study will provide insight on new resistance mechanisms that will lead to a better understanding of the selection process leading to resistance..

Palmer amaranth (Amaranthus palmeri S. Wats.) is a common agronomic weed in the southern U.S., and several populations have developed resistance to glyphosate. This study explored the potential of using hyperspectral sensors to distinguish glyphosate-resistant (GR) from glyphosate-sensitive (GS) plants. A Pika II hyperspectral camera (394 – 900 nm, 240 bands) was used in a greenhouse/laboratory setting to collect plant images. Three GR and three GS Palmer amaranth populations from Mississippi and Georgia raised from seed and clone in greenhouse were used in the study. A total of 185 plants (97 GR and 88 GS plants) were imaged at 6 to 7-leaf stage. Though, there is not a single narrow wavelength band that has a good enough signal-to-noise ratio to reliably separate GS and GR Palmer amaranth plants, overall, they have different reflectance spectral properties. There are a few windows in the spectrum where the signal-to-noise ratio is best; 400-500 nm, 650-690 nm, 730-740 nm, and 780-900 nm. Selecting several bands from these ranges and computing a weighted average with weights obtained from Fisher’s Linear Discriminate Analysis algorithm produces a feature that provides excellent separability of GS and GR Palmer amaranth. To test the classification potential of unknown plants using the hyperspectral features, 138 plants were randomly selected to use for band selection and classifier (maximum likelihood) training, and the remaining 47 plants were used for validation. The number of bands used was varied from 1 to 20, and repeated 100 times to get a mean and variance for the confusion matrix for each number of bands. Fourteen spectral bands (features): 394, 402, 407, 444, 449, 459, 480, 486, 489, 642, 669, 682, 688, and 890 nm were selected and used in classification of unknown plants. Overall, classification (GR from GS plants) accuracy of about 94% was achieved. These results demonstrate that hyperspectral sensors have potential to separate GR from GS Palmer amaranth (without a glyphosate treatment). However, further investigations are needed to refine this detection technique. Krishna.Reddy@ars.usda.gov

Website of the Center for Invasive Species and Ecosystem Health (www.invasive.org) has 1596 species in its “Full List” of “Exotic and Invasive Plants”.  This list is made up of species that appear either on an invasive species list or are considered in a noxious weed law in North America.  The number of species in this list is greater than what can be managed with the present complement of personnel and current funding level, so triage and focus of effort seems in order.  Which species need to be managed, and in what manner would that be best accomplished?  Only a minority of introduced weeds cause the disproportionately large changes in ecosystems and agriculture, and detrimental effects are not always possible to define monetarily.  Also, for some “invasives” there might be useful or beneficial traits, and distinctions about “good” or “bad” are usually synthesized from a dearth of information, i.e., there is an incomplete understanding of ecology and economics.  What is the role of “science” in such cases, and how can information generated from scientific research be integrated into the complex of considerations associated with non-native species? 

Despite their numbers and a certain level of publicity, invasive weeds remain a seemingly cryptic part of our culture and society.  Within the scientific arena, there is a great deal of information, but most is narrow in focus and of limited application; there are important information gaps that complicate communication with regulators and the public.  Furthermore, processes for dealing with invasive weeds are diffuse, uncoordinated, and conducted in a social and regulatory environment that is risk-averse.  Decisions about policy, regulations, and management, are almost always made with incomplete and generalized information, and they require integration of complex perspectives from outside of science into what is known from science.  An even greater challenge facing decision-makers is how to include aspects of nuance and variability that is known about ecosystems.

The objective of the symposium, “Holistic invasive weed management”, is to consider these issues in a very broad, even national, context that attempts to consider the place and involvement of science, statutes, and society.  Success in invasive weed management has been achieved a number of times, and three case studies will be reviewed in light of the issues described.  Possible outcomes envisioned in an holistic approach include:  1) identification of the most important species,  2) determination of the best management strategies,  3) coordination of scientific research,  4) establishment of support, i.e., monetary, public, and regulatory, for such, and  5) development of the means to enlist society and improve public confidence.

The United States Executive Order 13112 defines, as a matter of policy, an invasive species as “an alien species whose introduction does or is likely to cause economic or environmental harm or harm to human health.”  Species so defined cause major environmental damages and losses that may cost the US economy as much as $120 billion per year.  According to Pimentel et al. (2005) there are approximately 50,000 alien species in the US. With the number of invasive species introductions increasing, it is worth noting that about 42% of the species on the Threatened or Endangered species lists are at risk primarily because of alien, invasive species.
Because, to paraphrase Bertrand Russell, everything is vague (fuzzy) to a degree we do not realize until we have tried to make it precise, the factual information of the policy definition is scientifically incomplete. Notwithstanding this secret of science, information is transmitted to policy makers wrapped in an aura of certainty.  In reality, however, the world's socio-economic-environmental problems, challenges and choices, as described by Winthrop (1972), are comprised of "...multi-loop, nonlinear feedback systems whose structures run counter to the intuitive, simplistic models usually invoked for studying and dealing with our global, environmental problems."  
Information about invasive species, accordingly, is simplified to facilitate decisions and involves assumptions that policy makers use to set parameters about that action.  Paradoxically, the same simplifications ultimately frustrate our ability to describe, understand and respond to issues arising from complex ecological systems.  Our system of decision-making is based upon logical positivism and its implicit dependency on bivalence, i.e. A or NOT-A (either/or), and is, accordingly, poorly equipped to accommodate nuance, uncertainty and degree.  Ironically, this uncertainty may then be exploited to challenge regulation and to circumvent risk management in complex systems.  
When science simplifies by rounding-off to good-enough (linear approximations), it is used to support policy based on either/or. This in turn leads to the classic political debates, which, on issues involving invasive species, are supported on all sides by 'science',  thus resulting in paradoxes, inaction and, ultimately, policy gridlock. Describing invasive species and their attendant risks and benefits in terms of fuzzy logic is more instructive at a policy level since it reflects factual truth that maps better onto reality. Science should not become entangled in the space of social and ethical valuation; doing so only confuses and confounds already complex questions.  

Before any objective management decision can be made, it is critical to first identify and prioritize which species need to be managed or eradicated. While there are models to assist with this task, the outcome can vary depending on the overall objective of the site. In some cases, it may be inevitable that an invasive species be accepted as part of the community if it provides reasonable ecosystem services and causes minor harm. Once one or more priority species has been determined, the overall objectives of the management approach must begin with the desired end outcome in mind.  Choosing the most effective approach for management will be spatially dependent, as a large regional or national scale may require a more economic and sustainable solution that could involve restoration programs, such as biological control and revegetation, whereas small scale eradication projects may be more chemical or mechanical intensive without the need for restoration considerations. To be successful in the implementation of a management strategy, a broad perspective of stakeholders must be involved in defining the acceptable approaches, solutions, and outcomes. This includes both public and regulatory input and ownership of the proposed outcomes.  Diverse stakeholder groups bring different values to any problem and the solutions employed will need to consider these if a project is to be successful and sustainable.  It may also be critical to understand and accept the concept that sustainability can require short-term harm to non-target organisms.  In the long-term, successful and sustainable management of invasive plants will depend on environmental, social and economic factors.

Leafy spurge (Euphorbia esula L.) is a widely established weed in North America and is found on a variety of terrain from flood plains to river banks, grasslands, ridges, and mountain slopes.  Chemical, cultural, and biological methods have been developed to control leafy spurge, but no single control method can be used across all areas the weed is found.  In the four state region (North Dakota, Montana, South Dakota, and Wyoming) of the Little Missouri National Grassland (LMNG), leafy spurge occupied over 1 million ha in the late 1990s and caused over $130 million in losses each year.   Managing leafy spurge in a cost-effective manner in such a large and diverse area was a hopeless situation for most land managers prior to 2000.  In 1997 under leadership from USDA-ARS, The Ecological Area-wide Management (TEAM) Leafy Spurge project was initiated to research and demonstrate IPM strategies to effectively manage leafy spurge in this four state area.  TEAM Leafy Spurge was coordinated and funded by the USDA-ARS and USDA-APHIS, and conducted in cooperation with the BLM, Forest Service, National Park Service, Bureau of Indian Affairs, Bureau of Reclamation, USGS, USDA Cooperative Extension Services, land grant universities, state agencies, county weed managers, and landowners.  This five year research and demonstration program helped reduce the size of the leafy spurge infestation by approximately 75% by the end of the decade.  At the North Dakota site, leafy spurge stem density decreased by 94%  and leafy spurge seed declined from nearly 70% to only 2% of the soil seedbank in 2009.  As leafy spurge was successfully controlled in the LMNG, native species seed and diversity increased.  Controlling the invasive weed also helped the recovery of the endangered western prairie fringed orchid (Platantlgera praeclara Sheviak and Bowles).  Quinclorac applied in the fall controlled leafy spurge and did not affect regrowth or fecundity of the western prairie fringed orchid 1 or 2 yr after treatment.  Orchids treated with quinclorac were as tall, had racemes as long as, and produced as many flowers and seed capsules as untreated orchids.  Nearly 90% of the public land managers and decision makers in the region attended at least one TEAM leafy spurge research and extension event and subsequently incorporated an integrated approach into their weed management programs.  Multiple agencies working together to provide research and extension coordination met the goal of implementing a long lasting invasive weed control program that would have been difficult, if not impossible, to accomplish without the USDA Area-wide Pest Management Program.

The highly invasive marine alga Caulerpa taxifolia was discovered in a 350 acre tidal lagoon near Carlsbad, CA (USA) in June of 2000.  This was the first documentation of C. taxifolia in the Western Hemisphere; however its aggressive growth characteristics were well known from populations of the same alga that were allowed to spread to over 20,000 ha in the Mediterranean beginning in 1985.   The clear threat to California coastal habitats, coupled with the fortuitous consortium of highly motivated state federal, private industry and local agency representative resulted in the initial containment and treatment actions within three weeks of the discovery.   The  “Southern California Caulerpa Action Team” (SCCAT) operated by consensus-driven decisions and incorporated both technical and public inputs throughout the project period even though there initially was no single  “lead” agency.  This rapid response –using bleach applications contained under bottom barriers- and intensive follow up monitoring, containment, and public outreach led eventually to successful eradication of C. taxifolia  from Aqua Hedionda Lagoon (Carlsbad) and Huntington Harbour (near Long Beach, CA) over a 6 year project period.   Eradicating C. taxifolia was expensive-$7million- but given the extent of susceptible coastline from Baja California to Monterey (ca. 1200-1500 miles), one could argue that the cost of protecting that valuable habitat was well worth it at less than a dollar per foot.   The success can be attributed to not only dedicated individuals, but also to a willingness to openly weight risks and long-term benefits of proposed actions, flexibility with regulatory agencies, and sustained authority to restrict access and use in and around the eradication sites.    Buy-in from the public stakeholders- and skeptics- required proactive engagement, open workshops and forums, and reliance on science-based decision making that eventuated in the social support needed to sustain the program long enough for successful completion. 

The invasive riparian shrub tamarisk (Tamarix spp.; a.k.a. saltcedar) is the target of one of the most widespread and successful weed biological control programs in North America.  The northern tamarisk beetle, Diorhabda carinulata, was released into the open in 2001 and has since expanded its range in Utah, Colorado, Wyoming, Oregon, Idaho, New Mexico and Arizona. A closely related species, D. elongata, has been established in Texas and California and two other Diorhabda species, D. sublineata and D. carinata, are now established in Texas.  Beetles regularly defoliate tamarisk over a wide area of the western US and at some sites tamarisk has begun to die back with tree mortality exceeding 50%.

The tamarisk biocontrol program is controversial because an endangered bird subspecies, the southwestern willow flycatcher (Empidonax traillii extimus) nests in tamarisk over part of its range.  It was initially thought that the spread of the tamarisk beetles would be slow, especially into the southern range of tamarisk where the flycatchers use it to nest.  Rapid evolution of traits that allow the northern tamarisk beetle to survive and reproduce in more southern areas has accelerated the movement of beetles into areas where flycatchers use tamarisk for nesting, igniting a controversy over the value of tamarisk in riparian ecosystems.  It is clear that tamarisk may provide habitat for native species when the ecosystem includes a native plant component.  It is equally clear that tamarisk monocultures have little or no value as habitat for native species. One way to resolve this controversy is to restore a native component to the plant communities where Tamarix is the dominant species.

The Virgin River, which flows from southern Utah through Arizona and enters Lake Mead in Nevada, is the first drainage where the northern tamarisk beetle has moved into areas where the southwestern willow flycatcher nests in tamarisk.  Periodic defoliation of tamarisk along the Virgin River has intensified the need to closely monitor the impact of biocontrol on the riparian ecosystem and to restore native plant communities.  These components are integrated into a multidisciplinary program designed to restore the Virgin River system, particularly with respect to native plant communities.  Restoration is ongoing with the establishment of “islands” of native plants which will act as seed sources to cover the entire river system (propagule islands).  Restoration will also include an evaluation of hydrology and geomorphology in order to establish native plants in areas less prone to washing out during flooding.  The goals also include the enhancement of wildlife habitat, including habitat for the southwestern willow flycatcher.  The restoration program utilizes D. carinulata as a tool for the suppression of tamarisk while replacing tamarisk with high value native species.  In this way we can utilize biocontrol, manage tamarisk and enhance wildlife habitat.           

Congress is an exceptionally busy body, having to deal with the myriad issues facing the nation at any given point in time. While the representatives do what they can to fix certain issues, others go generally unaddressed or left inadequately addressed by existing laws. This is the current status of biological control of invasive weeds. Congress has recognized and legislated to adress many environmental issues, yet it has not fully considered how best to deal with biological control techniques. While statutes such as the Plant Protection Act and the Endangered Species Act directly influence decisions of whether biological control may be used in certain instances, there has never been an explicit policy announced by Congress for a specific process to implement biological control. Rather, it exists in a world between environmental statutes, being subject to many of them but fully covered by none. This paper serves as an introduction to these major statutes, discussing their specific goals and how they impact use of biological control. In addition to briefly looking at these statutes, this paper explores what other options—currently existing or still theoretical—may be preferable to the existing statutory framework.

Taking a holistic approach to invasive species: Science, society, and adaptation to change

Over the past few decades, invasive species have been one of the bugbears of biodiversity conservation.  While they are often considered a biological problem, they are interwoven with myriad social complexities.  In this presentation, I review several examples of this interweaving to demonstrate that our traditional approach to invasive species is inadequate and that we require a more holistic, nuanced, and pragmatic one.  Specifically, I argue that we require i) a broader and more inclusive approach that incorporates the views of diverse stakeholders; ii) more positive language rather than previous fear-mongering (e.g., “invasional meltdown”); and iii) greater acknowledgement of ongoing global change and the uncertainties and limitations it introduces.  While this agenda may seem defeatist, it instead seeks to align with social-ecological complexities and points towards a more workable and hopeful vision for the future.

Growers rely solely on glyphosate for weed control in glyphosate-resistant sugar beet, which could potentially enhance glyphosate-induced selection pressure for resistance development in weeds. Over reliance on glyphosate has already led to increase in glyphosate-resistant weed species including kochia (Kochia scoparia L.) in the northern Great Plains. Glyphosate-resistant kochia biotypes have been confirmed in Kansas, Nebraska, Colorado, North Dakota, and South Dakota in US and Alberta in Canada. Lack of effective alternative herbicide programs for broad-spectrum weed control in sugar beet further exacerbates the problem. To develop glyphosate resistance management strategies in glyphosate-resistant sugar beet, it is imperative to understand the response of individual weed cohorts to glyphosate and their overall impact on weed seed bank. A field experiment was initiated at the MSU Southern Agricultural Research Center near Huntley, Montana, in 2012, to determine the effect of glyphosate timing(s) on kochia demographics and sugar beet yields in glyphosate-resistant sugar beet. Glyphosate-resistant sugar beet variety ‘BTS 36RR50Pro200’ was planted at a seeding rate of 52,000 seeds ha^-1. Kochia seeds were uniformly broadcasted prior to sugar beet planting. A randomized complete block design (RCBD) was utilized with 4 replications. Treatments included single and sequential applications of glyphosate at three different timings relative to sugar beet growth stages along with a non-treated check for comparison. Glyphosate timings included single application at the 2-, 6-, or 10-leaf (lf) stage of sugar beet and sequential applications at 2-lf followed by (fb) 6-lf, 6-lf fb 10-lf, and 2-lf fb 6-lf fb 10-lf stages of sugar beet. Glyphosate was applied at 1.26 kg ha^-1 at the 2-lf and 6-lf application timings, while 0.84 kg ha^-1 of glyphosate was applied at the 10-lf timing. Glyphosate applications were made using handheld boom calibrated to deliver 94 L ha^-1 at 276 kPa. Permanent 1 m² quadrats were established at the center of each plot to monitor kochia emergence cohorts during the growing season. Weed cohort 1 emerged from planting to the 2-lf stage of sugar beet, cohort 2 emerged from 2- to 6-lf stage of sugar beet, and cohort 3 emerged after the 10-lf stage of sugar beet. Data on density, percent survival, height, and leaf number were collected for kochia plants in each cohort at biweekly intervals. At physiological maturity, biomass and seed production of each cohort was recorded. Sugar beet root and sucrose yields were recorded at harvest. Data were subjected to ANOVA using PROC MIXED in SAS. Preliminary analyses of the data suggest that sequential applications of glyphosate were better than single applications for kochia control and biomass and seed reductions in cohort 1 and 2. Kochia survival did not differ between the sequential application timings; however, three applications (2- fb 6- fb 10-lf stages of sugar beet) were needed to prevent seed bank additions from cohort 1 and 2. Since cohort 3 emerged after the 10-lf stage of sugar beet, plants escaped glyphosate application.  Although plants in cohort 3 were beneath the sugar beet canopy, those plants did produce seeds. This warrants the need for weed control programs to extend beyond the 10-lf stage of sugar beet to prevent replenishment of the soil seed bank from kochia escapes (late-emerging cohorts) in glyphosate-resistant sugar beet. This research will generate valuable information for simulation models to predict evolution of glyphosate-resistant kochia in glyphosate-resistant sugar beet, which would aid in designing herbicide resistance management programs.

Waterhemp is becoming an increasing problem in sugarbeet in Minnesota and North Dakota.  The biggest reason is the selection of glyphosate-resistant waterhemp in glyphosate-resistant corn and soybean.  Several small plot (2 m [wide] by 9.1 m [length]) sugarbeet research trials have been conducted since 2010 investigating the management of glyphosate-resistant waterhemp with soil-applied and postemergence herbicides in glyphosate-resistant sugarbeet.  All applications were applied with a bicycle sprayer calibrated to deliver 159 L/ha at 275 kPa.  One trial investigated preplant incorporated versus preemergence applications of cycloate [4 EC formulation] (4.5 kg ai/ha), cycloate [4 SB formulation] (4.5 kg/ha), cycloate (2.8 kg/ha) plus EPTC (2.2 kg ai/ha), ethofumesate (4.2 kg ai/ha), S-metolachlor [Dual Magnum] (1.6 kg ai/ha), and acetochlor [Warrant formulation] (1.3 kg ai/ha) followed by two postemergence applications of glyphosate (1.3 kg ai/ha to 7 to 10 leaf sugarbeet followed by 0.84 kg/ha 14 to 23 days later).  A second trial investigated three soil-applied herbicides at two rates followed by four postemergence treatments at three locations, one glyphosate-susceptible waterhemp, another limited glyphosate-resistant waterhemp and the third having good presence of glyphosate-resistant waterhemp, but resistant to phenmedipham and desmedipham.   Cycloate [SB formulation] (3.4 and 4.5 kg/ha) and ethofumesate (3.4 and 4.2 kg/ha) and S-metolachlor (0.95 and 1.6 kg/ha) were applied preplant incorporated and preemergence, respectively.  The postemergence treatments were applied starting at the 2-leaf sugarbeet stage and applied two additional times every 14 days.  Treatments included:  1. Glyphosate (1.3 followed by 0.95 followed by 0.84 kg/ha); 2. Glyphosate (1.3/0.95/0.84 kg/ha) plus ethofumesate (140/140/140 g/ha); 3. Glyphosate (1.3/0.95/0.84 kg/ha) plus ethofumesate (140/140/140 g/ha) plus phenmedipham plus desmedipham [1:1] (137/183/274 g ai/ha); and 4. Glyphosate (1.3/0.95/0.84 kg/ha) plus ethofumesate (140/140/140 g/ha) plus phenmedipham plus desmedipham [1:1] (137/183/274 g/ha) plus dimethenamid (737/527/0 g ai/ha).  Ammonium sulfate was added to all postemergence treatments at 7.7 kg per 378 L of spray solution and Destiny HC (1.75 L/ha) was added when conventional sugarbeet herbicides were included with glyphosate. Over a three year period, ethofumesate (at various rates) plus glyphosate has been applied postemergence once and up to three times in trials.

At the time of the first postemergence glyphosate application in the soil-applied trial, ethofumesate (4.2 kg/ha) and S-metolachlor (1.6 kg/ha) applied preplant incorporated and preemergence and cycloate (2.8 kg/ha) plus EPTC (2.2 kg/ha) applied preplant incorporated controlled waterhemp 78 to 87%.  All remaining soil-applied treatments controlled fewer than 74% of waterhemp.  Cycloate and EPTC must be incorporated to maximize efficacy.  Due to a limited frequency of glyphosate-resistant waterhemp at each location over a three year period, two applications of glyphosate controlled waterhemp on average 65% and waterhemp control was improved at least 3% for all soil-applied treatments followed by glyphosate compared to glyphosate alone.  Sugarbeet yield was not reduced by any soil-applied treatment.  In the second trial cycloate (3.4 and 4.5 kg/ha), S-metolachlor (0.95 and 1.6 kg/ha), and ethofumesate (3.4 and 4.2 kg/ha) controlled waterhemp 76, 83, 81, 86, 90, and 92%, respectively at the time of the first postemergence application at three locations.  Limited rainfall at one location reduced waterhemp control with S-metolachlor.  Near harvest, the waterhemp control averaged across the four postemergence treatments at the site with the greatest frequency of the glyphosate-resistant biotype was 57, 81, 89, 88, 94, 97, and 97% for no soil-applied herbicide, cycloate (3.4 and 4.5 kg/ha), S-metolachlor (0.95 and 1.6 kg/ha), and ethofumesate (3.4 and 4.2 kg/ha), respectively.  Near harvest, the waterhemp control averaged across all soil-applied herbicides for glyphosate alone, glyphosate plus ethofumesate, glyphosate plus ethofumesate plus desmedipham plus phenmedipham, and glyphosate plus ethofumesate plus desmedipham plus phenmedipham plus dimethenamid was 84, 88, 83, and 89%, respectively.  Few treatment differences were observed with yield in this second trial sugarbeet. When the total amount of ethofumesate exceeded 2.5 kg/ha in a single application or multiple applications with glyphosate, waterhemp control ranged from 77 to 99% over a three year period.  The most effective herbicide strategy to managing glyphosate-resistant waterhemp in glyphosate-resistant sugarbeet is to apply effective soil-applied herbicides.

Pyroxasulfone 85WG (formerly known as KIH-485) is a residual herbicide developed for use in several agronomic crops such as corn, soybean, wheat, and sunflower.  However, little information is known about peanut tolerance and its potential fit in peanut weed management systems.  Therefore, field trials were conducted in Georgia during 2012 to evaluate peanut cultivar response to preemergence (PRE) applications of pyroxasulfone and to compare pyroxasulfone based weed management systems to systems currently used in Georgia. 

PRE tolerance. A field trial was conducted during 2012 at the UGA Ponder Research Farm near Ty Ty, GA on a Tifton loamy sand.  Experimental design was a split-plot consisting of three pyroxasulfone 85WG rates (0, 2, and 4 oz/A) and three peanut cultivars (GA-06G, Georgia Greener, and Tifguard). Treatments were replicated four times and the plot area was maintained weed-free.  Plant population, visual estimates of peanut stunting, and peanut yield  were recorded.  All data were subjected to ANOVA and means separated using Fisher’s Protected LSD Test (P≤0.10) when appropriate.  At 10 days after planting (DAP), there was a significant interaction between peanut cultivar and pyroxasulfone rate for peanut injury.  Peanut stunting was greater when pyroxasulfone was applied PRE at 2 oz/A to Tifguard (50%) than GA-06G and GA Greener (38 to 40%). Peanut stunting was not influenced by cultivar when pyroxasulfone was applied PRE at 4 oz/A (44 to 55% stunting). By 119 DAP, peanut had recovered substantially from PRE applications of pyroxasulfone.  Peanut stunting at this time ranged from 4 to 7%.  When averaged over cultivar, peanut yield was not significantly reduced by any pyroxasulfone rate even though early season injury was severe (5,825 to 6,480 lbs/A).         

Weed management systems. Two field trials were conducted during 2012 at the UGA Ponder Research Farm near Ty Ty, GA on Tifton loamy sand and the UGA Attapulgus Research and Education Center near Attapulgus, GA on Dothan loamy sand.   Pyroxasulfone based weed management systems were compared to commonly used systems in Georgia. Four standard systems including pendimethalin 3.8SC (34 oz/A) plus diclosulam 84WG (0.23 oz/A) plus flumioxazin 51WG (3 oz/A) PRE or paraquat 2SL (12 oz/A) plus bentazon/acifluorfen 4SL (16 oz/A) plus S-metolachlor 7.62EC (16 oz/A) EPOST (20 DAP) were compared to five systems with pyroxasulfone 85WG.  Systems included pyroxasulfone 85WG (1 or 1.5 oz/A) and flumioxazin PRE or pyroxasulfone 85WG (1 or 1.5 oz/A) as a substitute for S-metolachlor in standard EPOST or POST systems.  All systems included imazapic 2SL (4oz/A) POST. Also included was a non-treated control.  Visual estimate of peanut stunting and Palmer amaranth control were recorded throughout the season.  Peanut yield data was also obtained.  Statistical analyses were performed as previously discussed. Pyroxasulfone based systems had similar crop stunting, Palmer amaranth control (>95%), and yield to current standard systems (4,900 to 5,500 lbs/A).    

Previously, 20 years of corn herbicide efficacy studies conducted by university weed scientists and published in the North Central Weed Science Society Research Report were analyzed to compare corn yields with treatments containing atrazine to treatments lacking atrazine but containing atrazine alternatives.  All treatments had to control both broadleaf and grass species, be applied at label rates, and registered for use at the time of the analysis.  For the 236 studies analyzed for the period, 1986-2005, corn yielded an average 5.7 bushels/acre higher or 5.1% higher with atrazine than with alternatives.  The North Central Weed Science Society discontinued publishing the Research Report after 2005.  Therefore, to investigate the potential yield benefits of atrazine for years after that date, herbicide efficacy studies were obtained directly from universities or from a Syngenta Crop Protection database summarizing studies conducted by universities.  Unlike the 1986-2005 analysis, which involved only Corn Belt states, the new analysis covered 22 states in all major corn-growing regions of the U.S.  A total of 449 qualifying studies containing 5,991 qualifying treatments were analyzed for the years 2006-2010.  Corn yielded an average 4.9 bushels per acre or 3.3% higher with atrazine than with atrazine alternatives.  The yield benefit with atrazine was greatest with no-till systems, with a yield increase of 8.1 bushels per acre or 6.7%, compared to 4.6 bushels per acre (3.1%), and 4.4 bushels per acre (2.7%) for conventional and reduced tillage, respectively.  Thus, atrazine continues to provide a yield benefit similar to that provided over the previous 20 years, despite the introduction of new herbicide actives and technologies such as herbicide-resistant corn.  In addition to analyzing corn studies, sorghum yield studies were also analyzed.  A total of 12 qualifying studies containing 131 qualifying treatments were analyzed for the years 2006-2010.  Sorghum yielded an average 5.7 bushels per acre or 6.4% higher with atrazine than with atrazine alternatives.

ALS-resistant grain sorghum cultivars are expected to be available for farmers within the next few years. This technology has the potential to improve sorghum production by allowing the postemergence control of grassy weeds and is likely to be adopted by a high percentage of sorghum producers. However, shattercane x sorghum hybridization has been reported and is a concern regarding this upcoming technology. The objective of this study was to evaluate the herbicide resistance levels of two ALS-resistant sorghum inbred lines (6001 and 6002), a wild shattercane population (SH), and their respective hybrids (SH x 6001 and SH x 6002; total of 5 genotypes). A field study was conducted in 2012 near Mead, NE. Fifty seeds of each genotype were planted in 3 m rows. At 34 days after planting, rows were treated with nicosulfuron, rimsulfuron, or nicosulfuron + rimsulfuron (mixture) at 1, 2, or 4 times the expected recommended rate (nicosulfuron at 26.3 g ai ha^-1 + rimsulfuron at 13.2 g ai ha^-1). A set of untreated rows were left as controls. At 7 and 28 days after treatment (DAT), visual injury data (ranging from 0 [no injury] to 100% [plant death]) was collected. At 7 DAT, sorghum inbred, hybrid, and shattercane injury ranged from 0 to 12%, 13 to 24%, and 38 to 58%, respectively. At 28 DAT, no injury was observed in the sorghum inbreds, whereas hybrids and shattercane injury ranged from 0 to 10% and 94 to 100%, respectively. Injury in the hybrid was more prominent as herbicide rate increased. The mixture and rimsulfuron treatments caused slightly more injury to the hybrids than nicosulfuron. By 28 DAT, the sorghum inbreds and hybrids recovered from any injury, indicating that these genotypes were highly resistant even to high herbicide application rates, and shattercane plants were basically dead. The results of this study show that these inbred lines were resistant and that the resistance trait is likely to be transferred to the F1 population (hybrids) if hybridization occurs. While these two ALS herbicides will control susceptible shattercane populations, it is widely known that ALS resistant shattercane is present in many sorghum production areas. Therefore, this weedy relative of sorghum must be managed by alternate methods before and during the adoption of this technology.

Halauxifen-methyl (XDE-729 methyl) is a novel arylpicolinate herbicide currently being developed by Dow AgroSciences LLC for post-emergent, broadleaf weed control in global cereals and several other crops. Halauxifen-methyl was first discovered by Dow AgroSciences in 2005 and has been evaluated in all major cereal cultivating regions. When combined with the safener cloquintocet-mexyl, halauxifen-methyl is selective in winter and spring wheat (including durum), barley and triticale. Postemergence use rates in cereals will typically range from 5 – 10 grams ae/ha depending upon target weed species and geography. Field trials have shown that halauxifen-methyl can be tank mixed or preformulated with various cereal herbicides to provide broader levels of weed control at various application timings. Halauxifen-methyl, with an auxinic mode of action, will provide a new option for the control of key broadleaf weeds including those with resistance to other herbicides. Halauxifen-methyl has shown favorable environmental and toxicological profiles. Dow AgroSciences is seeking to widely register halauxifen-methyl for use in all major cereal producing countries with first registrations anticipated in 2014.

Halauxifen-methyl (development code XDE-729 methyl) is a novel arylpicolinate synthetic auxin herbicide being developed by Dow AgroSciences for post-emergence broadleaf weed control in western Canadian cereal crops.  This active has been formulated into two herbicide mixtures for the Canadian market, halauxifen-methyl + florasulam formulated as a wettable granule and halauxifen-methyl + fluroxypyr-meptyl formulated as an emulsifiable concentrate.   Field trials were conducted between 2010 and 2011 to characterize performance of these herbicide mixtures in western Canada.   Both halauxifen-methyl + florasulam and halauxifen-methyl + fluroxypyr-meptyl provided excellent control (>90%) of key broadleaf weeds, including chickweed (Stellaria media), cleavers (Galium aparine), hemp-nettle (Galeopsis tetrahit), common lambsquarters  (Chenopodium album), redroot pigweed (Amaranthus retroflexus), and wild buckwheat (Polygonum convolvulus).  Crop safety of both mixtures was exceptional, with early season injury to spring wheat, durum wheat, and spring barley seldom exceeding 1% and no injury observed late season.  In weed-free tolerance trials, no crop yield loss was observed at up to 2X proposed label rates of either herbicide mixture.  Herbicide mixtures containing halauxifen-methyl offer resistance management by controlling Group 2 resistant biotypes of weeds such as cleavers, chickweed, and hemp-nettle.  Halauxifen-methyl is efficacious at very low rates and will be utilized in mixtures at rates <10 g ae/ha.  Halauxifen-methyl breaks down quickly in the environment, predominantly via microbial degradation, enabling broad follow crop flexibility, including to pulses and oilseeds, the season after application.  Halauxifen-methyl will provide growers in western Canada with effective new tools for selective weed control in spring cereal crops, while also offering resistance management, low use rate, and a favorable environmental and toxicological profile.

Miscanthus giganteus has been considered as a potential bioenergy crop in the US for over a decade. However, very limited information concerning available PRE herbicides for M. giganteus stand establishment from seed is available. Therefore, the objective of this research was to screen PRE herbicides, and evaluate herbicide tolerance of M. giganteus seed. Herbicide screening in petri dishes indicated that M. giganteus seed was tolerant to atrazine, flufenacet plus metribuzin, mesotrione, tembotrione and acetochlor for all application rates evaluated with no significant reduction in germination as compared to the NTC. Dinitroanilines, PPO inhibitors and several chloroacetamide herbicides tested caused significant seed germination reduction, up to complete seed germination failure. Dose response experiments in petri dishes indicated seed germination was not affected by acetochlor, atrazine and mesotrione up to 4480, 4480, and 224 g ai ha^-1, respectively.  S-metolachlor significantly decreased seed germination at 1108 and 2216 g ai ha^-1. However, dose-response study in soil suggested, compared to the non-treated control (NTC), any rate of S-metolachlor evaluated significantly reduced shoot height and weight of M. giganteus seedling 50 days after treatment. Acetochlor at 4480 g ai ha^-1 and mesotrione 224 g ai ha^-1 significantly reduced dry weight or caused significantly lower heights than NTC. Results of this experiment suggested several preemergence herbicides have the potential to be evaluated during the establishment of seeded-type M. giganteus in large field trials. 

Annual bluegrass (Poa annua) invades newly established and established grasses grown for seed in OR causing significant production and economic challenges for grass seed growers.  Field experiments were conducted from 2007-2012 to determine the potential for using carbon seeding techniques and fall- applied applications of indaziflam, rimsulfuron, pyroxasulfone and a commercial premix of pyroxasulfone and flumioxazin  to control annual bluegrass in perennial ryegrass and tall fescue grown for seed.  A range of application rates of these  products were compared to current industry standards including applications of diuron and flufenacet plus 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 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.  Applications of the pyroxasulfone and flumioxazin premix at rates of 106-160 g ai/ha provided excellent annual bluegrass control.  These studies suggest that these active ingredients provide adequate annual bluegrass control as well as crop safety when applied to carbon seeded and established perennial ryegrass and tall fescue and are reasonable alternatives to diuron use in grass seed production systems.  Additional trials are ongoing to build needed efficacy and crop safety data sets with these herbicides should industry choose to pursue uses of these materials in grasses grown for seed.

Effect of Ambient Temperature on Thermal Weed Control using Microwave Radiation.  A. Rana* and J. F. Derr, Virginia Tech, Virginia Beach, VA.

The effect of ambient temperature on thermal weed control using microwave radiation was investigated at Virginia Tech’s Hampton Road Agricultural Research & Extension Center. Irradiation with nonionizing microwaves causes dielectric heating in plant tissues where sufficient moisture is available. A running belt prototype with variable speed control and two microwave radiations generators called magnetrons (2450 MHz) of output 900W each was built to determine weed control effectiveness. Approximately 4 to 6 week old seedlings of  southern crabgrass (Digitaria ciliaris), dallisgrass (Paspalum dilatatum), fragrant flatsedge (Cyperus odoratus), false green kyllinga (Kyllinga gracillima), yellow nutsedge (Cyperus esculentus), common ragweed (Ambrosia artemisiifolia), field bindweed (Convolvulus arvensis), henbit (Lamium amplexicaule), white clover (Trifolium repens), and pitted morningglory (Ipomoea lacunosa), representing monocots and dicots, were transplanted into 10 cm-diameter pots containing a peat-based medium. These weeds were treated with microwave radiation for 5 or 10 seconds at three different ambient temperatures (13^oC, 24^oC, or 35^oC) in a greenhouse. Ambient temperature at the time of microwave radiation exposure had a substantial effect on plant injury. In general, injury increased as temperature increased for the 5 second exposure treatment. Increasing the exposure time to 10 seconds decreased the impact of temperature.    One week after treatment, a 5 second exposure to microwave radiations completely controlled the sensitive weed species pitted morningglory at all three temperatures and injured the other 9 weed species.  White clover was the most tolerant of the ten species, showing regrowth by 4 weeks after treatment. The exposure time required for weed control appears to be a limiting factor for this technique. Repeat treatments would be needed for complete control of certain weed species, especially ones.  This technique may be applicable for weed control in situations in which other physical methods or chemical means are inconvenient or undesirable.

amanrana@vt.edu

Since 1963 the IR-4 Project has been the primary resource in the United States for facilitating specialty crop registrations of: conventional pesticides, pesticides for organic production, and biopesticides.  IR-4 has facilitated the registration of over 25,000 crop uses (14,000 food uses, with just over 30% of those for herbicides/PGRs, and 11,000 for ornamental uses).  Throughout the fifty years, IR-4 has adapted and modified its mission to provide the best service possible to US Specialty crop growers.  Initially it provided registrations of the then newly developed chemical products to growers of fruits and vegetables, then expanded to include ornamental and biopesticide registrations to support the ornamental industry and organic production.  The IR-4 Program provides crucial support to specialty crop growers by developing residue and other data that is required by law for U.S. EPA to register pesticides. This work is important because the cost of the data required for specialty crops and minor uses far exceeds the potential return on investment to the crop protection industry and therefore the data will not be generated without IR-4’s assistance.  In the late 1980s and early 1990s, Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) reregistration was a major effort of the IR-4 food program.  The passage of the Food Quality Protection Act (FQPA) shifted IR-4’s focus to reduced risk products and IPM.  Each year, IR-4 engages stakeholders in a transparent priority setting process by garnering potential research projects through project clearance requests, surveys and regional meetings, a process that culminates at national priority setting workshops with growers and other pest management professionals, researchers, registrants and EPA to set the annual research plan. The Michigan State University Center for Economic Analysis (Dec. 2011) reported that for a combined total budget of $18 million, the IR-4 Project contributes over $7.2 billion to annual US Gross Domestic Product and support 104,650 jobs throughout the United States. 

In 2012, the IR-4 Ornamental Horticulture Research Program sponsored research on two weed science projects: 1) crop safety of over-the-top herbicide applications, and 2) crop safety and efficacy of over-the-top herbicides targeting liverwort. The goal of the over-the-top herbicide application evaluations was to screen herbicides [Biathlon (oxyfluorfen + prodiamine), F6875 4SC (sulfentrazone + prodiamine), Freehand G (dimethenamid-p + pendimethalin), Gallery 75DF (isoxaben), Indaziflam 0.0224%G (indaziflam), and Tower EC (dimethenamid-p)] for safety on woody and herbaceous perennials grown primarily in container nurseries.

Applications were made at dormancy and approximately 6 weeks later for all products. Biathlon was applied to 11 crops; F6875 4SC was applied to 33 crops; Freehand was tested on 10 crops; Gallery was applied to 22 crops; and Tower was applied on 23 crops. The goal of the liverwort herbicide product evaluations was to determine whether immediate irrigation after application reduces crop injury while maintaining efficacy with herbicides effective for managing liverwort. Seven products were evaluated: Avenger Ag (d-limonene), Bryophyter (oregano oil), Racer Herbicide (ammonium nonanoate), Scythe (pelargonic acid), Sureguard 51WDG (flumioxazin), Tower (dimethenamid-p), and Weed Pharm (acetic acid). Applications were made to pots containing liners with or without liverwort followed by irrigation or no irrigation.

Data on efficacy and crop safety were collected. With results received thus far, non-selective herbicides applied over the top generally provided good to excellent efficacy, but commercially unacceptable injury was observed even with immediate irrigation on several species. The results from this research will aid in the development of product labels and will help growers and landscape care professionals make more informed product choices.

Field studies were conducted in 2010 and 2011 at Belle Glade, FL to evaluate the influence of phosphorus (P) application (98, 196, and 293 kg P ha^-1) on the critical period of weed control (CPWC) in lettuce. Natural populations of mixed weed species were allowed to interfere with lettuce in a series of treatments of both increasing duration of weed interference and duration of weed-free period imposed within 98, 196, and 293 kg P ha^-1 levels added to the soil. The beginning and end of the CPWC for each P level based on a 5% acceptable marketable fresh lettuce yield loss level was determined by fitting log-logistic and Gompertz models to represent increasing duration of weed interference and duration of weed-free period, respectively. The beginning of the CPWC in lettuce was estimated to be 2.2, 2.3, and 2.9 WAE at 93, 196, and 293 P kg ha^-1, respectively which corresponded to the four- to six-leaf stage of lettuce development. The end of the CPWC in lettuce was 6.8, 5.7, and 5.2 WAE at 93, 196, and 293 P kg ha^-1, respectively which corresponded to the cupping to heading stage of lettuce development. Beginning of the CPWC was delayed at high P level (293 kg P ha^-1) while the end of the CPWC was hastened at high P level. Our study shows that reduced levels of P fertilization in lettuce will result in the need for more intensive weed management practices to attain acceptable yields. 

When a single herbicide is used, for decades, such as the herbicide Hexazinone, resistance and weed shifts occur.  There is a need to develop alternatives with different modes of action to alternate or in combination with herbicides now used to prevent resistant weeds from developing. In order to assess the effects of new pre-emergence herbicides with different modes of action both alone and in combination with currently used herbicides on wild blueberry an experiment with a Split-Block RCBD design with six replications was established at Blueberry Hill Farm in Jonesboro, ME.  Premerergence application of Indaziflam at 5 and 10 oz product/a, Halosulfuron-methyl at 1 and 2 oz product/a split by 0, Hexazinone at 1 lb product/a or Terbacil at 2lb product/a were applied on 18 April (early) and the Indaziflam and Halosulfuron-methyl applied over either, none Hexazinone or Terbacil treatments on May second (mid) and 24 May (late) just a blueberries were beginning to emerge. Blueberry Cover, phytotoxicity, broadleaf weed cover, grass cover were evaluated at one, two, and three months post-treatment.  A combination of treatments was most effective in controlling weeds. Indaziflam or Halosulfuron-methyl alone was not effective in suppressing broadleaf weeds but improved suppression when combined with Hexazinone and Terbacil. The Indaziflam and especially Halosulfuron-methyl treatments resulted in higher phytotoxicity due to late application timing and the higher rate, so earlier application timing will be needed to prevent the stunting and delay in growth of the wild blueberries. Since with the Hexazinone and Terbacil treatments the broadleaf weeds were higher than the untreated check the, addition of other herbicides is needed. Since Hexazinone and Terbacil are Group 5 herbicides and Indaziflam is Group 29 and Halosulfuron-methyl is in Group 2, the use of these herbicides will prevent the development of resistant grasses.

Evaluation of Hexazinone Alternatives and Tankmixes for use in Lowbush Blueberry (Vaccinium spp.). N. S. Boyd^*1, E. Clegg²;  ¹University of Florida, Balm, Florida, ²Dalhousie University, Truro, Nova Scotia.

Weeds are a major yield-limiting factor in lowbush blueberry production.  The broad spectrum herbicide Hexazinone is applied bi-annually in most commercial fields.  Reliance on a single herbicide chemistry over extended periods of time has altered the weed spectrum and may have led to the development of herbicide resistance.  A 2x8 Factorial experiment was conducted at three sites in Nova Scotia, Canada to evaluate the efficacy of hexezine (1920 g ai ha^-1) alone or in combination with oxyfluorfen, dichlobenil, pyroxsulam, florasulam, flumioxazin, amniopyralid, glufosinate, or glufosinate+indazaflam at 480, 3200, 15, 10, 214, 91.2, 375, and 375+75 g ai ha^-1, respectively,.  All herbicides were broadcast applied in 2m x 20m plots in the spring  preemergence to the blueberry crop.  Hexazinone significantly reduced ground cover by grass and broadleaf weeds and controlled a broader spectrum of weed species than all other herbicides evaluated.  Aminopyralid caused significant crop damage.  The remaining products were safe for use on lowbush blueberry.  All of the herbicides evaluated controlled or suppressed problematic weed species and were more effective when tank mixed with hexazinone. The most effective tank mix partner for hexazinone varied with site and depended upon the weed spectrum present.

Florida blueberry production requires raised pinebark beds; growers have begun to incorporate sand into the planting bed to reduce the cost.  The change in soil structure may effect herbicide efficacy and weed control.  Conducting fields trials would be large and costly so smaller studies must be conducted. The objective is to evaluate the effectiveness of two columns.  Soil columns were constructed of polyvinyl chloride pipes 25.4 cm tall and 7.6 cm wide.  The pipe was cut in half vertically or horizontally into 5 segment 5.1 cm tall.  The columns were filled with pine bark mulch and then soaked in water overnight.  Simazine at 2.3 kg/ha was applied over the top of columns with a CO₂ backpack calibrated to deliver 280 L/ha.  The soil was irrigated 2.54 cm per day for 4 weeks.  At 4 weeks after treatment (WAT), redroot pigweed (Amaranthus retroflexus L.) was planted at the surface of each horizontally cut pieces and the length of the vertically cut pieces.  Pigweed emergence was least at 5.1 cm using the horizontal cutting.  Using the vertical cut pigweed emergence was lowest 4.7 to 5.6 cm deep.  Not measured were the ease of separating sections of the soil column. The horizontal cut provided an easier method of separating each unit. Cutting the soil column either vertically or horizontally provided weed control at the same depth.  However, the vertical cut provides a wider range of depth control rather than a singular depth received from the horizontal cut.    

Cranberry vines are usually planted as unrooted cuttings that are scattered onto the ground and pushed in with a disk.  Typically, two to three years are needed to achieve adequate colonization of the production surface.  During this period, weeds will establish in any available bare ground and retard cranberry vine colonization.  The objective of this study was to evaluate the weed control provided by various combinations of napropamide (Nap; dry flowable) and mesotrione (Mes; emulsion) on newly planted and 1-yr-old cranberry farms during the establishment years. 

            Six sites were studied over a 4-yr period (2009-2012); each individual site was treated for a 2-yr period.  Three sites were treated in the year of planting plus the subsequent year (called “new plantings”): Sites NP1 (cv. Demoranville), NP2 and NP3 (cv. Stevens.  Three sites were treated in their second year of growth (or their first full season and called “second-year plantings”) plus the subsequent year: Sites SY1 (cv. Ben Lear), SY2 (cv. Crimson Queen) and SY3 (cv. Howes) and.  There were ten treatments administered each year: Nap at 3.37 kg ai/ha applied once, twice, thrice or once followed by (fb) one application of Mes at 210 g ai/ha; Nap at 5.05 kg ai/ha applied once, twice or once fb one application of Mes at 210 g ai/ha; Mes at 210 g ai/ha applied once or twice; and untreated (10 treatments total).  A nonionic surfactant was added to the Mes treatments (0.25% v:v).  Plots, always separated by at least 0.5 m, were 2 by 4 m, except those at the 1-year old plantings treated in 2009, which were 2 by 7 m. Applications simulated chemigation (delivered in 3,735 L water/ha) via 11.3 L CO2-powered backpack with flat fan nozzle (Teejet 1004vs).  Visual assessments of weed species abundance and percent weed and cranberry cover were conducted each year.  Biomass samples (random 930-cm2 quadrats) were taken in late summer and processed for cranberry and weed biomass.

            The effect of treatment varied by site, year, and age of the planting.  Overall, the composition of the weed community (which varied by site) influenced the effectiveness of the herbicides.  Weed biomass reduction was directly related to controlling grasses.  In 2009, weed biomass was reduced by all treatment combinations at SY1 and SY3 (second-year plantings in the first year of treatment).  Mes treatments typically performed the best on most sites in 2009 and 2010 (both new plantings and second-year plantings); in 2011, Nap treatments reduced biomass similar or better than Mes in two of the four trial sites (NP2 and NP3 in their first year of growth and treatment) in terms of % weed cover.  Nap-fb-Mes treatments were usually similar (in terms of weed biomass reduction) to Mes-only treatments.  No negative impact was noted on cranberry growth overall.  Applying an herbicide to new cranberry plantings for weed control is a good management practice as weed pressure was reduced in almost all circumstances compared to the untreated plots.  2012 samples are still being processed as of this writing.

Field tests were conducted to evaluate a prototype steam applicator designed to deliver steam to raised strawberry beds. In previous work we concluded that existing designs from foreign manufacturers were impractical, requiring development of a new design for California strawberry. With funding from the Propane Education and Research Council (PERC) in October 2011 we built an automatic steam applicator. The objective of this research was to compare preplant soil disinfestation of raised strawberry beds with our custom designed steam applicator to standard soil fumigation in strawberry.

Materials and methods

Equipment description.  The initial prototype consisted of a tractor-towed wagon with a propane fueled Clayton 100 HP steam generator (Clayton Industries, City of Industry, CA) capable of steaming one 1.32 m wide raised bed per field pass.  Steam was injected and mixed into the soil through a bed shaper equipped with a rototiller, multiple steam injection shanks in front and behind the tiller, and steam injection nozzles above the tiller. Water was supplied to the steam generator through a 400 m long hose reel.

Field tests. Two tests were done in October 2011, one at Salinas, CA Oct. 12, 13, 2011 and the second at Watsonville, CA Oct. 25, 2011. Soil at both Salinas and Watsonville sites were a sandy loam soil. Soil temperatures were measured with Hobo temperature loggers (Onset Computer Corp.
Pocasset, MA).  At Watsonville weed seed bags were installed in the strawberry beds as soon as the steam applicator passed. At both sites Pic-Clor 60 EC (56.7% chloropicrin, 37.1% 1,3-dichloropropene; TriCal, Hollister, CA) was included as a fumigant standard at 392 and 280 kg ha^-1 in Watsonville and Salinas, respectively.  Weed seed were removed after fumigation and tested for viability with tetrazolium.  The trials were arranged in a randomized complete block design with 5 reps at Salinas and 4 reps at Watsonville.

Weed densities were measured periodically and weeding times were recorded as described in Samtani et al. 2012. Fruit harvest was measured by a commercial harvest crew once or twice weekly as needed during the April to September 2012 interval.

Results and discussion

At both locations the soil temperature at 15, 30 and 45 cm from the bed shoulder reached >70ËšC for >20min. The 60 cm probe marks the low end of heat penetration into the bed and temperatures were cooler at the bottom of the bed. Fuel consumption was measured at 14,595 L ha^-1 propane, which means that 163 MJ m^-3 of energy were applied which is comparable to that listed in Baker and Roistacher (1957). Estimated machine, fuel and labor costs are $14,146 ha^-1 based on the single bed prototype and the field application rate was 76 hours ha^-1. We estimate the cost of a two bed unit would be $12,298 ha^-1 based on our current design and the rate of application would be 37 hours ha^-1.  The comparable 2012 price of methyl bromide plus chloropicrin broadcast fumigation in California was $10,000 ha^-1.

Viability of chickweed, knotweed and yellow nutsedge were reduced by steam and Pic-Clor 60 fumigant compared to the control (Table 1). Only steam killed the bluegrass seed. Measurements of hand weeding times, weed densities, weed fresh weights and fruit yield assessments indicate that steam and Pic-Clor 60 performed similarly (Tables 1, 2).

References

Baker, K.F. and C.N. Roistacher. 1957. In:Baker, K.F. The U.C. system for producing healthy container-grown plants. California Agr. Expt. Sta. Ext. Serv. Manual 23.

Fennimore, S.A. and R.E. Goodhue. 2009.  Estimated costs to disinfest soil with steam. In: Annual International Research Conference on Methyl Bromide Alternatives and Emissions Reductions. San Diego, CA.  Proceedings 3.

Samtani, J.B., C. Gilbert, J.B. Weber, K.V. Subbarao, R.E. Goodhue and S.A. Fennimore. 2012. Effect of Steam and Solarization Treatments on Pest Control, Strawberry Yield and Economic Returns Relative to Methyl Bromide.  HortScience 47:64-70.

Table 1. Weed seed viability at Watsonville steam test and subsequent hand weeding time in 2011-12.

^a Means with the same letter within columns are not significantly different according to Fisher’s LSD at P = 0.05

Table 2. Weed densities, seasonal hand weeding times and season long fruit yields at Watsonville, CA in 2011-12.

^a Means with the same letter within columns are not significantly different according to Fisher’s LSD at P = 0.05

Onion weed control experiments were conducted on mineral and muck soils using labeled herbicides at maximum annual rates to obtain maximum weed control and greatest yields.  Pendimethalin may be applied preemergence to onion on muck soil at 2.1 kg/ha a.i. with a maximum of 6.7 kg/ha/yr.  S-metolachlor may be applied after the 2 leaf stage (LS) at 1.4 kg/ha with a maximum of 2.8 kg/ha/yr.  Dimethenamid-P may be applied once after the 2 LS at 1.1 kg/ha.  Flumioxazin is labeled for a maximum of 0.11 kg/ha between the 3 and 6 LS. 

Pendimethalin was applied preemergence to seeded onions on muck soil at 2.1 or 4.2 kg/ha.  The treatments were reapplied at the 2 LS and at the 4-5 LS.  In other treatments, pendimethalin at 4.2 kg/ha was followed by S-metolachlor at 2.99 kg/ha at the 2 LS and dimethenamid-P at 1.1 kg/ha at the 4-5 LS.  The total annual rate of flumioxazin, 0.11 kg/ha, was applied in three applications of 0.036 kg/ha (preemergence, 2LS, 4-5 LS) plus pendimethalin at 2.1 kg/ha.  Onions were tolerant of the high rates and repeated applications of pendimethalin, S-metolachlor, dimethenamid-P, and flumioxazin.  Onions were stunted slightly after some applications but outgrew the injury.  At harvest, none of the onions treated with maximum rates of the four preemergence herbicides had reduced yield.  The improved weed control from maximum use rates resulted in higher yields.

In postemergence treatments, oxyfluorfen was applied at 0.07 or 0.14 kg/ha with fluroxypyr at 0.07 or 0.14 kg/ha or flumioxazin at 0.036 kg/ha.  All treatments were applied three times at the 1 LS, 2 LS, and 4-5 LS.  Onions treated at the 1 LS were not permanently injured by any of the treatments.  Oxyfluorfen at 0.14 kg/ha applied three times plus fluroxypyr at 0.14 kg/ha provided good ladysthumb and redroot pigweed control and had high onion yield. Onions treated with oxyfluorfen at 0.07 kg/ha plus bromoxynil at 0.14 kg/ha applied at the 2 LS and the 4-5 LS had good yield.  

On mineral soil, pendimethalin applied preemergence and at the 2 LS at 0.84, 1.1 and 1.68 kg/ha was safe on onion and all the treatments had good yield.  Pendimethalin at 1.68 kg/ha gave almost complete weed control for the growing season.  Pendimethalin at 0.84 kg/ha preemergence followed by flumioxazin at 0.036 at the 2LS gave season long weed control and high yield.

Use of maximum seasonal rates of pre- and postemergence herbicides provides better weed control, causes minimal onion injury, and results in maximum dry bulb onion yields.

Today in agriculture, herbicides are widely used as an integral weed management tool.  With genetically modified crops such as Roundup Ready (glyphosate) corn and soybean, herbicides that normally would have killed a crop can be used for weed control.  Over years of use, certain weeds have developed a resistance to glyphosate and require new management tools.  New technologies, including 2,4-D and dicamba tolerant crops, will add the tools needed for corn and soybean farmers to better manage weeds; however, herbicides can drift from the target area and damage sensitive crops such as grapes, tomatoes, and peppers.  Research over the last 30+ years has shown some of the effects of these herbicides on sensitive crops.  With the impending introduction of new resistance traits in agronomic crops, the use of 2,4-D and dicamba will change and, therefore, the severity and frequency of damage seen on sensitive crops may also change.  Grapes are an important crop in Ohio for table and wine production.  The wine industry attracts millions of tourists each year with a measureable positive economic effect.  Grapes are extremely sensitive to 2,4-D and dicamba down to rates as low as 0.33% of the label rate for row crops. Grape growers are very concerned about the potential for damage to their vineyards.  Greenhouse experiments on common varieties of grapes being planted in Ohio showed that vinifera varieties were slightly more sensitive than hybrid varieties.  In the field, one variety (Riesling) was tested for the effects of timing (pre-bloom, full-bloom, and post-bloom) and rate (1/30, 1/100, 1/300) of simulated herbicide drift. Grape yield and quality data were collected in 2011 and 2012.  In 2011 1/100 and 1/30 rates at all timings affected shoot length and visual injury to the vines; however, only the 1/30 pre- and post-bloom and 1/100 post-bloom treatments had an effect on yield.  The post-bloom 1/30 and 1/100 also had significant loss of yield in the year following the herbicide treatments (due in part to complete vine death in some reps).  In 2012, the 1/30 rates at all timings caused much greater injury and effect on yield then in 2011.  Other stresses such as weather may play a large role in the severity of damage due to simulated herbicide drift.  The damage caused by the combination of 2,4-D and glyphosate was almost always more severe than that with either herbicide alone.

A field study was conducted in 2012 at the Malheur Experiment Station, Ontario, OR to evaluate the response of several rotational crops to fomesafen soil residues applied in 2011 to control weeds in potato. Fomesafen was applied prior to potato emergence in May 2011 at 280 or 560 g ai ha^-1 alone or at 280 g ai ha^-1 tank-mixed with S-metolachlor plus pendimethalin at 1,420 and 1,060 g ai ha^-1, respectively. A grower standard of S-metolachlor 1,420 g ai ha^-1 plus pendimethalin 1,060 g ai ha^-1 was included. No injury was observed on winter wheat var. ‘Stephens’ and spring wheat var. ‘Alturas’ planted 179 and 293 days after herbicide application, respectively. Similarly, pinto bean var. ‘Windbreaker’ was not injured by fomesafen soil residues when planted 360 days after herbicide application. However, spring barley var. ‘Millennium’ planted 293 days after herbicide application was injured 48 to 72% by fomesafen soil residues and the grain yield was reduced 19% compared to the grower standard. Also, sugar beet hybrid ‘27RR20’ planted 324 days after herbicide application was injured 13 to 95% across fomesafen containing treatments. Residues from fomesafen applied at 560 g ai h^-1 injured sugar beet the most and reduced beet root yield and estimated recoverable sugar by 35% and 41%, respectively, compared to the grower standard. Soil residues from fomesafen at 280 g ai ha^-1 did not injure rotational dry bulb onion var. ‘Vaquero’ planted 296 days after herbicide application. However, residues from 560 g ai ha^-1 caused 92% onion injury and the U.S. no. 1 bulb yield was reduced 60% compared to the grower standard. The results suggested that winter and spring wheat, direct-seeded bulb onion, as well as pinto bean could be planted safely at 179 and 293, 296, 360 days, respectively, following application of fomesafen 280 g ai ha^-1 to control weeds in potato.

In Ontario, the occurrence of pigweed populations resistant to herbicides is a significant threat to carrot producers on muck and mineral soils. Linuron and prometryne are the only broad-spectrum herbicides registered in carrots. Alternative herbicides were evaluated for efficacy on redroot pigweed and crop tolerance in carrots grown on muck and mineral soil. Trials were conducted at 3 sites in Ontario: on muck soil at MCRS (70-80% O.M) near Bradford; and mineral soils at Ridgetown (82.4% sand; 1.5% silt; 7.1% clay; 4.1% O.M.); and Harrow (82.5% sand; 5% silt; 12.5% clay; 2% O.M.). Preemergence treatments of pendimethalin (ME formulation), ethofumesate, pyroxasulfone, flufenacet, and s-metolachlor were applied at 1X the proposed use rate:  3000, 3960, 89, 450, and 1373 g ai ha^-1, respectively, for control of redroot pigweed. Herbicide efficacy and crop tolerance was influenced by soil type. At MCRS all herbicides gave <50% control of pigweed at 2 WAT (weeks after treatment) compared to 75-90% control at 5 WAT (weeks after treatment) on mineral soils except for reduced control with flufenacet and s-metolachlor at Harrow. When applied PRE to carrots at 2X, herbicide tolerance was excellent at MCRS and Ridgetown. At Harrow, however, all herbicides except pendimethalin caused injury and yields were reduced except with pendimethalin and ethofumesate. When applied POST to carrots at the 2-3 leaf stage, tolerance was excellent and no yield loss incurred at all locations with 2X rates of pendimethalin (ME formulation), pyroxasulfone, flufenacet, and s-metolachlor. Below label treatments of oxyfluorfen (EC formulation), acifluorfen, fluthiacet-methyl, and fomesafen, at doses of 60, 18.75, 1.875, and 5 g ai ha^-1, respectively, gave postemergence control of 2-4 leaf 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, and did not reduce total or marketable carrot yield.

Florida potato producers utilize seepage irrigation as a means to supply water to their crop. Seepage irrigation furrows run the length of the field and provide an environment for weeds to grow, set seed, and contribute to the seedbank. The objective of this study was to quantify weed populations and movement from irrigation furrows into the potato crop rows. In 2012, four commercial potato fields (identified as sites A through D) in Flagler County, Florida, were included for this study. A bed of sixteen rows constituted a replication with three replications per field. Sampling sites were in two directions- within the crop row starting at the beginning of the crop row to the center of the field (every 15.2 m for 91.4 m) and across the beds (every 1.14 m from irrigation furrow for 9.12 m) from the irrigation furrow for a total of sixty-three sample sites. Weeds were counted in field (30 cm x 30 cm area) during the crop season and soil cores were taken at each of the sample sites. Soil cores (11.5 cm wide x 18 cm deep) were collected, bagged, refrigerated (4°C), and grown in a greenhouse during the summer and winter. Weeds in the field and from the soil cores were counted and analyzed with Duncan’s multiple range test and lack of fit to quantify weed movement. Due to significant location interactions, locations were analyzed separately for both field and greenhouse weed counts. The three most common weeds in the field were yellow nutsedge (Cyperus esculentus L.), Rumex sp., and bermudagrass (Cynodon dactylon [L.] Pers.). In greenhouse weed counts, old world diamond- flower (Oldenlandia corymbosa L.), low falsepimpernel (Lindernia dubia [L.] Pennell), and winged waterprimrose (Ludwigia decurrens Walt.) had the highest densities.  Field weed counts for distance from irrigation furrow showed higher populations of weeds in the furrow (at least 1 weed) and the eight distances into the field being significantly lower. At sites A and C, 0 m from the start of the row contained the highest weed density 4.9 and 6.9 weeds, all other sample sites within the row being significantly less. Lack of fit analysis for distance from furrow fit a linear and quadratic model for field weed counts.  Sites A and C fit a linear and quadratic model for distance from the start of the row while the other two fields fit neither. Greenhouse weed counts were lower in the crop row compared to the furrow at site B. At sites B and C, distance from the start of the row showed the 0 m. distance contained the highest weed population (70- 98 weeds/ soil core). For site D, the farthest distance from the beginning of the crop row had the greatest number of weeds (272.2 weeds/ soil core). All fields fit a linear model and all sites except site D fit a quadratic model relating weed density to the start of the crop row (a= 0.05). Irrigation furrows and ends of crop row are among the heavier populated areas of the fields with the crop rows having lower densities. The inclusion of two methods to quantify weeds in the field shows the impact of weeds in the irrigation furrow may have minimal impact on weeds in the crop row. Differences in the three most dominate weed species between the field and greenhouse studies indicate the problems in determining weed populations from seedbank analysis. Further research must be completed to evaluate the enumeration methods in order to accurately predict weed populations in this type of study. 

Redflower ragleaf (Crassocephalum crepidioides) grows throughout tropical and subtropical areas in the world as a weed and minor vegetable. Growth characteristics, distribution, seed germination and seedling emergence of the plant were evaluated under various climatic and edaphic factors to understand biology and degree of infestation. Several survey studies carried out from 2007 to 2012 in the islands of Okinawa and Kagoshima prefecture, Japan indicate that the plant grows well in fallow lands, and various crops and vegetables under sunny and partial shade conditions with the temperature range of 15-25 C. The plant was a severe weed in various crops and vegetables in Kourijima island of Okinawa in 2007, but not in the following years. Shoot biomass of the plant was three-time higher in gray soil (pH 6.9) as compared to that in dark-red soil (pH 6.0) or red soil (pH 4.8) in a pot experiment; and the plant showed earlier heading in dark-red soil and red soil than in gray soil. In incubator experiments, the seeds germinated at the temperature range of 10-30 C and pH range of 2-12, and the germination rate was highest with a temperature range of 15-20 C and pH range of 4-10. High seed germination was recorded under both saturated and flooded conditions. The germination of seeds from opened (mature) capitula was significantly higher than from partially opened or unopened capitula. The germination of seeds without a pappus was significantly higher than for seeds with a pappus. The germination rate of 1-year-old seeds decreased drastically. The seedlings did not emerge from the soil-depth of 1 cm or above in a pot experiment. The seed-germination was significantly influenced by the climatic and edaphic factors, and the seeds were found to be easily dispersed by wind and rainfall. A single plant produced as much as 90,000 seeds in a life cycle in field, but regeneration was very few in the following season, indicating that the plant regeneration is significantly controlled by natural factors, and it could not be a troublesome weed in Japan.

Post-dispersal seed predation is a desirable ecosystem service that could support weed management efforts in organic and low-external-input cropping systems.  However, the magnitude of seed predation is known to vary greatly across time, space, and habitat.  To measure the relative importance of these sources of variability, we conducted a series of spatially-explicit, farmscape-level seed predation assays across crop and non-crop habitats of a typical small, Maine organic mixed vegetable farm with diverse habitat features.  Specifically, a 20-meter grid was placed over the farm, and a random site location was selected within each of the 240 cells.  Seed predation assays, with and without vertebrate exclosures, were used to estimate invertebrate and total seed predation in mid October 2011, August 2012, September 2012 (N=132), and October 2012 (N=132).  Concurrently, we measured invertebrate activity-density and habitat attributes at each sample site. 

As expected, we observed significant inter- and intra-annual variation in seed predation.  Total seed predation was greater in October 2011 (22.7%) than October 2012 (13.8%).  Within year, total seed predation decreased from 40.5% in August 2012 to 13.8% in October 2012. 

We also found significant habitat type and vegetative cover effects.  Specifically, seed predation was greater in crop and riparian forest than in softwood forest, meadow, or mowed grass habitats.  Within the crop habitat only, seed predation was positively correlated with leaf area index and other measures of vegetative cover.  Across habitat types, however, vegetative cover did not support higher seed predation rates. 

We expected seed predation to be spatially aggregated in such a heterogeneous landscape, with “hotspots” located in or near desirable habitat.  Surprisingly, seed predation appeared randomly distributed across the landscape.  It is possible that our system was so heterogeneous that habitat was confounding.  We conclude that time and habitat attributes were much more important regulators of seed predation than space in our study system.  

Invertebrate and vertebrate consumers are thought to play an important role in reducing soil surface weed seed banks via post-dispersal seed predation, but quantifying how much seed can be removed and under what conditions is challenging. Field experiments were conducted during 2011 and 2012 in Fargo, ND to assess the effects of vegetative cover and soil ambient seed bank on vertebrate and invertebrate weed seed predation rates. Spring wheat was sown at typical agronomic densities in May of each year. The experiment was an RCBD with four replications and three factorial treatments: weed control or no weed control, cover crop or no cover crop, and short vs. tall wheat stubble. The cover crop consisted of canola (14 kg ha^-1) and radish (7 kg ha^-1) seed hand-broadcasted into plots several weeks prior to wheat harvest. These treatments were intended to alter amounts of post-harvest vegetative cover and dispersed weed seed. After wheat harvest, at three or four day sampling intervals during September and October, one artificial seed arena, consisting of a 57 sq cm Petri  plate filled with finely sieved field soil and 25 yellow foxtail (Setaria glauca L.) seeds pressed into the soil surface, was installed in each plot. At each sampling interval and in every plot, leaf area index (LAI) was measured with a ceptometer, the soil surface ambient seed bank was sampled by sweeping all surface material from a 143 sq cm area, and the invertebrate population was sampled using pitfall traps. Seeds recovered from the soil surface seed bank were separated into two groups, wheat seed and all other small seeds, and bulk seed mass was measured. Invertebrates were separated into carabids (family: Carabidae), crickets (family: Gryllidae), and grasshoppers (suborder: Caelifera). LAI measured during the first week of measurements did not differ among treatments. Soil surface small seed mass measured during the first week of measurements was greater in plots that had not been sprayed with herbicide, but the total soil surface seed mass did not differ among treatments because wheat seed was evenly dispersed during harvest in every plot. There were fewer carabids in plots sprayed with herbicides. When plots were not sprayed with herbicide, cover crop presence was associated with more grasshoppers. In general, crickets seemed to prefer short stubble and no cover crop. Since the treatments meant to impose differences in LAI and soil surface seed bank were largely unsuccessful, seed removal rates did not differ among treatments, either for vertebrates or invertebrates. However, considerable quantities of seed were removed from the artificial seed arenas by both vertebrate and invertebrate predators in all plots. Scaled up, these measurements indicate that considerable seed should have been removed from the soil surface. However, no differences in soil surface seed bank were detected over time during either year of the experiment. This result suggests that seed removal rates measured from artificial seed arenas may not be well correlated with true weed seed predation rates.

The Virginia Weed Clinic, an extension service provided by Virginia Tech through the department of Plant Pathology, Physiology & Weed Science, has been receiving and processing weed identifications and control recommendations for over 30 years.  The clinic receives up to 400 weed samples each year from all commodities grown in Virginia including those grown by private residents.  Spatial and demographic data for the weed clinic has been collected every year including weed common and botanical name, commodity of origin, county, and date received.  This information will be useful to horticultural and agronomy extension agents and to any commodity grower where an abundance of data has been collected for their crop.

 Data from 2002-2012 has been compiled and analyzed to illustrate demographic and spatial data for weeds submitted by growers and extension agents in the state of Virginia.  Submitted samples represent 147 families, 428 genera and 729 unique species.  The largest families represented based on number of individual submissions are Poaceae, Asteraceae, Fabaceae, Brassicaceae, Lamiaceae, Polygonaceae, and Caryophyllaceae.  Of 428 genera, 399 contained 3 unique species submitted or less, 15 genera had 4 unique species submitted, 9 genera had 5 unique species, and 3 genera had 6 unique species.  The genera Veronica and Bromus had the largest number of unique species containing 8 and 7, respectively. 

Most samples are submitted in the months of May and September accounting for 35% of all submissions. The majority of submissions come from only 6 commodities including 28% from turfgrass, 21% from pasture, 10% aquatic, 7% each from fallow areas and ornamental beds, and 4% from gardens.  Up to 7% of growers submit samples without specifying their crop.  The remaining 16% come from various commercial crops and forested areas.   The number one weed submitted by our state agents over the last 10 years was Japanese stiltgrass (Microstegium vimineum).  This is a weed of growing concern in forest understories, roadsides, pastures, and other non-cropland.  The top ten weeds received by the Virginia weed clinic were Japanese stiltgrass, Japanese clover, nimblewill, tall fescue, roughstalk bluegrass, bermudagrass, common chickweed, sericea lespedeza, yellow nutsedge, and smooth crabgrass.   Many of these are also very common weeds of turfgrass, which accounts for the largest proportion of samples submitted. 

After introduction as a horticulture plant, Japanese knotweed (Fallopia japonica) has invaded disturbed areas, riparian ecosystems, and wetlands across the US. Disturbance often creates rhizome and shoot fragments that can easily root at the nodes, and once established, the infestation spreads mainly through rhizome growth. There are few mechanistic data on development of the rhizomes for perennial species, including Japanese knotweed, despite the importance for understanding population dynamics. Predicting the change in population size based on shoot emergence, survival and, implicitly assuming asexual reproduction, is a first step to modeling Japanese knotweed population dynamics and identifying plant vulnerabilities.

Four new infestations of Japanese knotweed (densities ranged from 0.43 to 2.47 shoots/m²) were selected to study population growth rates. Japanese knotweed crowns (shoots emerging at same location) were first marked in 2010 and new shoots were marked in 2011 and 2012. During the growing season, shoot height was measured every 3 weeks until leaf senescence in fall when we obtained dry shoot biomass. Following senescence in fall 2012, the soil was excavated to a depth of 25 cm to reveal the rhizome network among shoots.

Crowns and new shoots emerged at similar times in March through May, but crowns grew more quickly and achieved greater height by July 15^th, when shoot growth stopped. Shoot height is a critical measure because it predicts dry biomass in the fall, plant height in the following year, survival to the following year, and number of rhizomes produced per shoot. Once established, more than 75% of shoots will re-emerge in the following year. Since new shoots can emerge from nearly anywhere along a rhizome length, we modeled reproductive output as the number of rhizomes produced per shoot. More than half of the observed shoots (57%, n=327) did not produce any rhizomes and 33% only produced a single rhizome.

An integral projection matrix with plant height or biomass as a predictor of survival and reproduction was constructed for each site. The models predict populations are changing at a per capita growth rate of -15% to +150% 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 select biological control agents that will have the greatest per capita effect.

Models based on thermal time describing seedling emergence are valuable not only to understand important aspects of the biology of a weed species, but also for decision making when implementing weed control practices. Most seedling emergence models have been developed in temperate regions where extreme temperatures during the winter and summer prevent seed germination and seedling growth of summer and winter weed species, respectively, creating relatively defined seedling emergence periods. Conversely, to the extent of our knowledge, there are no weed seedling emergence models for tropical conditions, and it is unknown how the absence of extreme temperatures throughout the year might affect weed seedling emergence patterns in agroecosystems. We studied seedling emergence of itchgrass (Rottboellia cochinchinensis), which is an aggressive grass weed in multiple agronomic crops such as corn, rice, cotton, and sugarcane in the tropics. Field experiments were conducted in several locations in Costa Rica from March to August and August to December in 2010 and 2011. Itchgrass seedling emergence timing and soil temperature were monitored after tillage. Most of the emergence occurred two weeks after tillage, regardless of the location and time of the year, suggesting that tillage promoted itchgrass germination. Gompertz and Weibull models were adjusted to the observed cumulative seedling emergence based on thermal time using growing-degree days (GDD) with a base temperature of 20 C, which was determined using an iteration procedure. The models satisfactorily described the observed emergence (r²=0.79 to 0.93) although the Weibull model best fitted the data based on the Akaike information criterion (AIC). Fifty percent emergence (E₅₀) occurred approximately at 115 GDD although there were differences between locations and time of the year, thus E₅₀ ranged between 64 to 300 GDD. Additionally, two phases of rapid seedling emergence occurred consistently in all sites and years, suggesting the presence of two groups of itchgrass individuals with different seed germination requirements within the evaluated populations. The present study illustrates how predictive seedling emergence models can be generated using GDD for tropical conditions. 

The replacement series experimental design is a widely used approach to answer questions related to resource complementarity. In this design, the total density of individuals remains constant while the proportions of two species vary. Species-specific and total yields in mixture are compared to yields in monoculture to determine the competitiveness of each species and extent of niche differentiation. However, results from this design can be influenced by species density, initial size, and resource use differences between species, and overall experimental duration. Using species specific functional densities (i.e., nitrogen and water uptake, or light capture) may address these limitations. Therefore, monocultures of corn (Zea mays L), smooth pigweed (Amaranthus hybridus L.) and giant foxtail (Setaria faberi L.) were grown in soils with contrasting management histories. Shoot and root biomass, N uptake and leaf area, and water uptake were measured on each species grown across different densities and experimental durations. The responses of each species across density and time gradients were used to determine functional species-specific densities and harvest times to minimize the density dependence, size bias and temporal dependence. The methods we used to select appropriate replacement series experimental conditions may prove to be a useful model for other researchers seeking to use this design.

Cropping systems research has shown that organic systems can have comparable yields to conventional systems at higher weed biomass levels. Higher weed tolerance in organic systems could be due to differences in labile soil organic matter and nitrogen (N) mineralization potential. The objective of our study was to test whether inherent soil N mineralization differences in organic and conventionally-managed soils from a long-term cropping systems experiment resulted in different early-season weed-crop competition relationships. A greenhouse experiment was conducted using corn (Zea mays L), smooth pigweed (Amaranthus hybridus L.) and giant foxtail (Setaria faberi L.) grown in crop:weed mixtures of 100:0, 75:25, 50:50, 25:75 and 0:100 and harvested at 24, 35 and 43 days after planting. Averaged across species, the monocultures grown in soil under organic management had significantly higher shoot N content at the two later harvest dates (p<0.05). Competition over N was not apparent at the first harvest date, but corn was more competitive than both weed species at the later harvests. However, the competitiveness of corn did not differ between the two soils. We found little evidence of resource partitioning when the mixtures were in competition. The results indicate that greater weed tolerance in organic systems is not likely due to differences in soil mineralizable N. 

Altered title:  Weed Biomass and Density Responses to Fertility and Weed Management Gradients in a Long-Term Organic Grain Systems Trial.  A long-term experiment at the Cornell University Musgrave Research Farm was initiated in 2005, comparing four organic cropping systems that differed in soil fertility inputs and intensity of weed management.  Soil fertility management in the High Fertility (HF) system was based on soil testing and Cornell University soil fertility recommendations, whereas fewer inputs were used in the Low Fertility (LF) system. Standard physical and cultural weed management including inter-row cultivation and delayed planting was used in both  systems. An enhanced weed management (EWM) system combined low nutrient inputs with extra cultivations, specialized equipment and denser plantings, while a reduced tillage (RT) system focused on building soil health through minimization of soil disturbance from tillage and cultivation and moderate nutrient inputs. A three-year rotation of corn, soybeans, and spelt/red clover was grown in all systems, and the experiment included two crop rotation entry points, enabling two of the three crops in the rotation to be grown every year. Weed density and biomass data were collected annually in all systems and crops.  Data were subjected to a repeated measures ANOVA and mean separation. 
We hypothesized that annual weed density and biomass would be greater in the High Fertility compared with the Low Fertility system, and that perennial weed density and biomass would be greater in the Reduced Tillage system compared with the Intensive Weed Management system.  Total weed density and biomass were greater in the High Fertility and Reduced Tillage systems. We found partial support for our hypothesis about annual weeds, as annual weed density was greater in the High Fertility system in one entry point, but the effect on biomass was less clear.  Perennial weed density was greater in the Reduced Tillage system compared with the Intensive Weed Management system in one entry point, and perennial weed biomass was greater in both entry points.  Across all systems and entry points, weed biomass was lower during the first three years of the experiment during the transition to organic (mean 302 kg ha-1) compared with the second rotation cycle (mean 808 kg ha-1).  Interestingly, corn yield was similar between High Fertility, Low Fertility and Intensive Weed Management systems, but weed biomass in the High Fertility system was more than double that of the Low Fertility and Reduced Tillage systems in the second crop rotation cycle.  Our results suggest that managing soil fertility and avoiding over-application of nutrients in organic cropping systems is an important weed management strategy.

Growing interest in sustainable, local food production has created incentives for crop producers in urban areas to grow food for local consumption using low chemical inputs and sustainable or organic management techniques. Weeds represent a major obstacle to any organic crop production system and for small-scale producers in urban environments there is a need for organic weed control methods that are inexpensive, sustainable, and effective. Mulch has been successfully used for weed control in numerous fruit and vegetable crops. Cucurbita pepo has a high pollination demand and the native, ground-nesting bee, Peponapis pruinosa, provides the majority of the crop's pollination requirement. Peponapis pruinosa nests directly in crop fields and the nests can be disturbed by tillage operations used for weed control. Mulches that utilize municipal waste materials may provide a sustainable weed control strategy for application in urban C. pepo plantings that is more benign to P. pruinosa than tillage. Novel mulch materials remain to be investigated for their effects on weed suppression, crop performance, crop nectar and pollen production, and bee nesting. Field and greenhouse studies of pumpkin and zucchini were conducted in 2011 and 2012 to determine the effects of polyethylene black plastic, woodchips, shredded newspaper, a combination of shredded newspaper plus grass clippings (NP+grass), and bare soil on soil characteristics, C. pepo pollination, fruit production and overall crop performance, weed abundance, pest and disease pressure, and P. pruinosa nesting. Woodchip, newspaper and NP+grass mulches conserved soil moisture, with newspaper mulch resulting in the highest and plastic in the lowest soil moisture levels overall. NP+grass mulch accumulated the most soil growing degree days over the course of a season and had a positive effect on pumpkin and zucchini plant growth, producing plants greater in size and with higher leaf chlorophyll content than plants grown on bare soil. All mulch treatments resulted in higher pumpkin yield than bare soil. Misshapen, unmarketable zucchinis occurred more frequently in black plastic than in the other mulch treatments. No measurable differences in floral resource production or crop pollination were found among mulch treatments, so misshapen fruits present in black plastic may have been due to high soil temperatures. During the critical period for weed control, four to six weeks after planting, suppression of weed biomass ranged from 74% by NP+grass to 100% control by black plastic in 2011, and from 99% in woodchips to 100% control by plastic, newspaper, and NP+grass mulch in 2012. NP+grass mulch may have been compromised in 2011 due to wet weather conditions leading to more rapid degradation of grass clippings and higher weed emergence. Bee nests were located within bare, newspaper, and NP+grass plots, so P. pruinosa nesting was not prevented by these mulches. Shredded newspaper and shredded newspaper combined with grass clippings should be considered for further research because of their potential to increase sustainability within urban agricultural systems by providing adequate weed suppression and improving crop performance of C. pepo with no apparent negative impacts on pollination or P. pruinosa nesting.

Eight-four populations of previously confirmed ALS-resistant Palmer amaranth from Georgia were analyzed to determine the percentage of target-site and nontarget-site resistance. Thirty percent of the populations were target site resistant. Of these, 16% contained a substitution at Trp574, 12% at Ser653, and 2% at Ala122. The remaining non-target site resistant populations have been characterized to determine if enhanced metabolism is the mechanism of resistance or another resistance mechanism. These data reveal the large diversity present in a herbicide-resistant weed population.

Herbicide resistance has travelled a well trod path laid by antibiotics, chemotherapy agents, insecticides, fungicides etc.  Herbicide metabolism and target-site mechanisms account for most resistance, but this is not the case with glyphosate.  Recently horseweed (C. canadensis) and ryegrass (L. multiflorum) were shown to be resistant through active sequestration of glyphosate into the vacuole.  Additionally, Palmer amaranth (A. palmeri) resistance has been found to result from an unusual MOA of extensive gene duplication of 5-enolypyruvyl shikimate 3-phosphate synthase (EPSPS).  Herbicide resistance has been managed by changing or combining active compounds with different modes of action (MOA) to control weeds and reduce selection pressure.  However, the paucity of new herbicide MOA’s and multi MOA-resistant weedy species are threatening economical weed control in some row crops. A review of current strategies and discussion of new strategies to control herbicide resistant weeds will be presented as a means to create a weed management system with sustainable weed control.

Algae can be cultivated using seawater and industrial carbon dioxide with much greater fertilizer efficiency and far higher yields than conventional crops.  They would be an ideal crop for sun-rich deserts near the sea, without competing with agriculture for land and fresh water. Many naïve groups are attempting to cultivate wild type undomesticated algae, contrary to human experience.  Many biological problems must be solved before algae can be efficient crops, including contamination by other algae.  As with conventional crops, the solution would be transgenically engineering selective herbicide resistance.  The huge numbers of wild type algae contaminating crop algae precludes using mutationally-derived resistance; the mutation would probably be in the weedy algal population.  Marine microalgae, unlike their freshwater counterparts are not killed by micromolar concentrations of most herbicides (due to the ionic strength of the media?).  The most effective herbicides seem to be highly hydrophobic herbicides either used for rice weed control or for waterweed control.  The purported successes for marine microalgae, found mainly in the patent literature are for transgenic strains containing the protox inhibitor butafenacil and others with the phytoene desaturase inhibitor fluorochloridone active on wild-type at less than 1 micromolar.  Glufosinate resistance was also engineered into marine algae requiring 30 micromolar to kill wild type as was glyphosate resistance requiring 1000 micromolar.  This would require 17 kg glyphosate per hectare for each cm of photobioreactor depth, and some are 50 cm deep.  It will probably be imperative to use algae with two transgenic herbicide resistances and apply two herbicides in order to preclude weedy algae from rapidly evolving resistance, as well as to treat when contamination rates are still very low to further reduce the likelihood of selecting for resistant mutations.

This presentation is dedicated to the memory of Homer LeBaron, a pioneer in bringing the awareness of herbicide resistance to the WSSA.

Roundup Hybridization System (RHS) is based on glyphosate-mediated male sterility and replaces mechanical detasseling with glyphosate spray during hybrid seed corn production. RHS not only simplifies but also increases the efficiency of hybrid seed production. RHS relies upon differential expression of the CP4-EPSPS (5-enolpyruvyl-shikimate 3-phosphate synthase), a glyphosate insensitive EPSPS enzyme commonly used in Roundup Ready® crops, and targeted delivery of glyphosate to the tassel. In this presentation, I will describe results from molecular biology studies to minimize expression of CP4-EPSPS in male reproductive tissues to render them sensitive to glyphosate and also from physiology studies using spray applications to optimize glyphosate delivery to the tassel for efficient induction of male sterility. 

Purple nutsedge (Cyperus rotundus L.) is one of the most troublesome weeds in vegetable crops of the southeast US.  Studies have indicated that tubers are the primary means of reproduction and spread of purple nutsedge.  Basal bulb formation occurs simultaneously with tuber development on rhizomes.  Basal bulbs can sprout and differentiate into plants, while remaining attached to the parent plant.  This reproduction mechanism for purple nutsedge results in rapid proliferation in vegetable production due to use of polyethylene mulch, season long fertilization, and daily irrigation.  Glyphosate has been shown to reduce purple nutsedge proliferation, and the dose necessary has been established.  Research has indicated that topical applications of glyphosate at 0.95 kg ae/ha, made to eight week old plants, reduced tuber and basal bulb plant biomass production five weeks after application.  Glyphosate remains as the parent molecule once it has been absorbed and translocation can occur throughout a treated plant.  Purple nutsedge forms extended rhizomatous chains from a parent plant and these produce daughter plants from the basal bulbs and tubers.  Parent and daughter plants will remain connected over time by these rhizomatous chains.  The rate for reduction of tuber and daughter plant formation has been established, but the mobility of glyphosate in this system has not been examined.  Therefore, a study was conducted to determine the absorption and translocation of ¹⁴C-glyphosate from parent purple nutsedge plant threw the tuber chain to daughter plants, and vice versa.

A single purple nutsedge tuber was planted into sand soil in an 11.3 L pot, and allowed to grow for eight weeks.  Nutsedge shoot emergence was monitored and daughter shoot emergence marked with date of soil surface protrusion using a plastic sheath slid to the base of the shoot.  The study was arranged as a completely random design with 5 replications and the study was repeated.  At eight weeks after planting, glyphosate was applied at 0.95 kg ae/ha.  Prior to glyphosate application, a single uppermost leaf on a parent or daughter plant was selected for ¹⁴C-glypohsate treatment.  This leaf was covered with a plastic sheath to prevent spray contact.  Daughter plants were selected based on date of emergence with the same or closest date for each replication.  This ensured that ¹⁴C-glyphoste treated daughter plants were similar in age.  After the sprayed glyphosate application had dried, the plastic sheath was removed, and 2.0 kBq of ¹⁴C-glyphosate was applied in 10 uL of the initial spray solution to the nontreated leaf surface using a Burkard microapplicator set to deliver a 1.0 uL/drop.  One treatment consisted of the parent plants, while the other treatment was daughter plants.  At five days after application, the ¹⁴C-glyphoste treated leaf was excised, and washed with 20 ml of a 1:1 solution of distilled water/methanol for one minute using a swirling action.  Then two separate 1 ml aliquots of this solution were measured for ¹⁴C-glyphoste quantification using liquid scintillation spectrophotometery (LSS) for counts per minute that were corrected for efficiency and converted to disintegrations per minute (DPM).  ¹⁴C-glyphoste not recovered in the wash was assumed to be absorbed by the leaf tissue.  The leaf sample was then dried in an oven, weighted, then oxidized using a Harvey biological oxidizer.  The ¹⁴CO₂ was quantified using LSS as previously described.  That same day, soil was washed away to separate the plants and tuber chains from the soil.  A plant map was generated to indicate the location of the parent and all daughter plants from the initial tuber were mapped by formation order.  All plant material was then frozen for later testing.  The initial ¹⁴C-glyphoste treated plant was then partitioned by roots and shoots, dried, weighed, and then oxidized as previously described.  Plants in the rhizomatous chains joined to the ¹⁴C-glyphoste treated parent or daughter, were then selected according to the map, portioned as previously described, and ¹⁴C-glyphoste quantified by oxidation.  All ¹⁴C-glyphoste was then budgeted as a percentage of the initial application.  This was done to establish the level of mobility of ¹⁴C-glyphoste from the parent or daughter tissue to the plants connected by rhizomatous chains.

Data was combined across studies for presentation.  Total leaf wash recovery was 45 and 36.2% for the parent and daughter treated plants, respectively.  The treated leaf for the parent and daughter contained 10.4 and 6.7% of the ¹⁴C-glyphoste while their respective roots and shoots contained 1.0 and 0.9%, and 1.14 and 4.29%.  ¹⁴C-glyphoste was translocated from the parent and daughter treated plants in a similar pattern.

The methylerythritol-4-phosphate (MEP) pathway leading to the synthesis of isopentenyl-phosphate in plastids was discovered fairly recently. It is an alternative pathway to the mevalonate pathway in the cytosol. In plastids, this pathway is necessary for the synthesis of carotenoids and the phytyl tail of chlorophyll. The first step in the pathway, DOXP synthase, is the target of ketoclomazone, the primary metabolite of the herbicide clomazone. Additionally, inhibition of DOXP reductase, the second step in the pathway, is also herbicidal, though no commercial herbicide affecting this step has been developed to date. Nonetheless, this pathway clearly has a number of steps that could be used as new herbicide target sites. The activity of the enzymes of this pathway is very difficult to measure in vivo and require cloning and heterologous expression. We have developed a simple leaf discs bioassay that can identify inhibitors of the early steps in the carotenoid biosynthesis pathway. Leaf discs are incubated in the presence of a phytoene desaturase inhibitor to induce phytoene accumulation. The level of phytoene accumulation is used as a measure of the carbon flow in this pathway.  Any compounds reducing the level of phytoene accumulation are likely to interfere with either one of the steps in the MEP pathway or subsequent synthesis of geranylgeranyl pyrophosphate. This assay may enable the rapid screen of new inhibitors of the MEP pathway on plants. 

One strategy to find more active or crop selective herbicides is to make structural changes to currently registered compounds, especially those with few cases of herbicide resistance and that have transgenic traits for crop tolerance.  Bromoxynil is a photosystem II inhibitor currently registered for control of broadleaf weeds in several agronomic and specialty crops. In 2012, research was conducted at the University of Tennessee-Knoxville to synthesize a previously patented pyridine analogue (2-6 dibromo-5-hydroxy-pyridine-2 carbonitrile sodium salt) of bromoxynil (Gullbenk and Ruetman, 1975, Dow Chemical Company, US patent 3,956,338) along with novel pyrimidine (4-6 dibromo-5-hydroxy-pyrimidine-2-carbonitrile sodium salt) and pyridine N-oxide (2,6-dibromo-1-oxido-pyridin-1-ium-4-carbonitrile) analogues of bromoxynil in order to evaluate their activity on multiple crops and weed species.  A bromoxynil sodium salt compound was also synthesized for a direct comparison to these heterocyclic compounds.  In addition, technical grade samples of both bromoxynil and bromoxynil octanoic acid ester [(2,6-dibromo-4-cyano-phenyl)octanoate] were purchased and included in this research for direct comparison. The pyridine analogue and the bromoxynil sodium salt analogue were synthesized starting with 5-hydroxypyridine-2-carbonitrile and 4-hydroxybenzonitrile, respectively, which were mixed separately with sodium bromate and sodium bromide and reacted with hydrochloric acid under nitrogen gas.  The pyrimidine analogue was synthesized starting with 5-benzyloxypyrimidine-2-carbonitrile, which was then mixed with methanol and a carbon palladium catalyst and reacted under hydrogen gas to remove the ethylbenzene. The end product of this reaction (2,6-dibromopyridine-4-carbonitrile) was then reacted as described previously with the pyridine analogue and the bromoxynil sodium salt.  The pyridine-N-oxide was synthesized starting with 2,6-dichloropyridine-4-carbonitrile which was mixed with hydrogen bromide and phosphorous tribromide and reacted with acetic acid at 130ÌŠ C.  The end product, 2,6-dibromopyridine-4-carbonitrile, was then further reacted with hydrogen peroxide and acetic acid under microwave conditions.

All six herbicides were applied POST to soybean (Glycine max), cotton (Gossypium hirsutum), redroot pigweed (Amaranthus retroflexus), velvetleaf (Abutilon theophrasti), large crabgrass (Digitaria sanguinalis) and pitted morningglory (Ipomoea lacunosa) grown in mum pans containing a high organic matter potting media in the greenhouse. All compounds were dissolved in acetone and applied in an enclosed spray chamber at 280 g ai/ha^-1 using 430 L ha^-1 of water carrier containing 0.25% non-ionic surfactant 10 days after seeding. Percent injury and plant height was recorded 7 days after treatment (DAT).  Only the pyrimidine analogue of bromoxynil provided less than 20% response to both crops; however, it did not provide greater than 20% control of any weed species.   Bromoxynil and bromoxynil octanoic acid ester were the most effective at controlling pitted morningglory, however both provided less than 25% control of redroot pigweed and velvetleaf. The pyridine-N-oxide analogue provided the best control of redroot pigweed and velvetleaf, and along with the pyridine analogue, were the only herbicides that reduced large crabgrass height.  Given the activity of the novel pyridine-N-oxide bromoxynil analogue future research should evaluate optimizing synthesis routes, formulation development, and additional evaluations of this active ingredient on a broader array of weeds and crops.

Indaziflam is a recently introduced herbicide for pre-emergent grass and broadleaf weed control in perennial cropping systems. Indaziflam is proposed to be a cellulose biosynthesis inhibitor (CBI) based on the radial swelling phenotype of treated plants. To explore this claim, we employed a combination of physiological, chemical, and cell biological assays. Dose response studies conducted on annual bluegrass (Poa annua) and Arabidopsis thaliana indicated both species were highly susceptible to indaziflam and exhibited characteristic radial swelling. The GR₅₀ values of light grown annual bluegrass and light or dark grown Arabidopsis plants was 667 and ~180 picomolar, respectively. However, isoxaben-resistant Arabidopsis mutants (ixr1-2 and ixr 2-1) did not display resistance to indaziflam suggesting an alterative mechanism of action. To explore this, we used laser assisted confocal microscopy to examine the behavior of fluorescently labeled cellulose synthase subunits (YFP:CESA6) in living cells treated with or without indaziflam. Analysis of the results indicates indaziflam possesses a novel mechanism of action in comparison to known CBIs by disrupting the association between cortical microtubules and cellulose synthase complexes. Thus, confirming indaziflam as a potent CBI.  

Halauxifen-methyl (XDE-729 Methyl) is a new postemergence herbicide being developed by Dow AgroSciences LLC for control of broadleaf weeds in the global cereals market.  Wheat selectivity to halauxifen-methyl was evaluated in comparison to a sensitive weed species (Lamium purpureum) and tolerant weed species (Veronica persica).  Parameters assessed included uptake, translocation, metabolic pathway, rate of metabolism and safener effect on uptake, translocation and metabolism. 

It was found that there was no difference in amount of uptake between wheat and weed species and there was no effect of safener on uptake.  In contrast, there was  greater amounts of translocation in L purpureum, the sensitive weed species, than in wheat or V. persica.  Halauxifen-methyl was de-esterified in all plants to halauxifen acid.  In wheat, the amount of halauxifen acid was lower than in L purpureum  likely due to a lower rate of de-esterification.  V persica formed halauxifen acid faster than wheat but was able to metabolize the acid quickly to inactive metabolites.  As the acid was the likely mobile form of halauxifen in plants, a faster rate of de-esterification was the cause of the difference in translocation.  The safener increased wheat's ability to conjugate halauxifen-methyl before the acid was formed but did not affect the metabolism in L purpureum.

Indaziflam is labeled as a non-selective herbicide for row crop use. It has exhibited excellent weed control. Indaziflam is unique because it has a low volatility index, providing potential use in other areas. Currently there are no labeled herbicides for enclosed structures, such as greenhouses. Reluctance to establish such a product arises from the small market and high volatility risk. The initial step in targeting the greenhouse industry is to determine if potential injury exist for sensitive greenhouse crops. This study was conducted with sensitive crops under extreme environmental conditions to explore the possibility of Indaziflam use in greenhouses. Our objective was to evaluate Indaziflam herbicide for potential use as a pre-emergent herbicide on gravel in greenhouses. Fifteen ground beds 90 square feet by 14 inches deep with metal support walls and a gravel floor were used. Mini-greenhouses, measuring 8ft. by 8ft. by 46 in. tall, were constructed with ½” PVC pipe and covered with Klerk’s K-1 white 70% co-poly. The species evaluated include: Better Boy Tomato Lycopersicon esculentu,‘Extreme Orange' Impatiens walleriana  and Petunia x hybrida (Dreams White-Experiment  1; ‘Dreams Neon Rose’ Experiment 2). Two rates of Indaziflam were applied at x (40 grams ai/ha) and 2x (80 grams ai/ha) with 374.2 L/ha of water. Each rate was applied to three areas: treated gravel only in ground bed; over-the-top of plants on gravel inside the ground beds; and over-the-top of plants outside the ground beds on adjacent gravel. Two non-treated control treatments were maintained: plants placed on the non-treated gravel inside the ground beds; and plants placed outside the ground beds on adjacent non-treated gravel without cover. Experiments were conducted under a worst-case scenario where air temperatures rose between 100 to 108  ÌŠF with no ventilation for three days. Overall, the study determined that under these extreme conditions treatments where gravel only was sprayed with Indaziflam had little to no injury, while OTT treatments had fatal injury on impatiens and tomatoes by 30 DAT.  Fresh weights confirm that the treatments sprayed OTT were severely injured, while the gravel only and non-treated control treatments exhibited no signs of injury or stunted growth.