EXAMINING COMMERCIAL SEED MIXTURES FOR THE PRESENCE OF WEED SPECIES. E. G. Oseland*, M. Biggs, M. D. Bish, K. W. Bradley; University of Missouri, Columbia, MO (1)


Examining Commercial Seed Mixtures for the Presence of Weed Species

Eric Oseland*, Meghan Biggs, Mandy Bish, Kevin Bradley; University of Missouri-Columbia

Palmer amaranth (Amaranthus palmeri) is one of the most economically important weed species in the U.S.  The weed is native to the southern U.S. but has expanded its distribution into more northern geographies in recent years.  Some of this recent movement has been attributed to contaminated machinery, livestock feed, and waterfowl dispersal. New infestations of Palmer amaranth were also discovered in Illinois, Iowa, and Ohio in 2016 and the source of these plants were traced back to commercial seed mixes used for conservation reserve program (CRP) areas and/or pollinator plantings. The goal of this research is to determine if commercially available birdseed, pollinator seed mixes, CRP seed mixes, and wildlife food plot mixes contain weed seed and if so, to identify the weed species present, their abundance, and viability. Twelve sources of birdseed from nine different companies, seven sources of wildlife food plot seed mixes from six companies, five sources of pollinator seed mixes from five companies, and four sources of CRP seed mixes from two companies were examined for the presence of weed seed. All seed mixes were sorted through a series of sieves and visually examined for the presence of weed seed.   Each individual weed seed was removed, counted, identified by species, and stored for future viability testing.  Preliminary results have shown that Amaranthus species were present in all 12 bags of birdseed examined.  The smallest amount detected was 1 pigweed seed per kilogram of birdseed mix for one source while the most was 2,012 pigweed seed per kilogram of birdseed mix in another source.  Common ragweed (Ambrosia artemisiifolia L.), kochia (Bassia scoparia) shattercane [Sorghum bicolor (L.) Moench ssp. arundinaceium (Desy) de Wet & Harlan], wild buckwheat (Polygonum convolvulus L.) large crabgrass (Digitaria sanguinalis) and Setaria spp. were also among the weed species present in the birdseed mixes. The largest amount of grass seed detected to date has been 1,694 seed per kilogram of birdseed.  Amaranthus seed was also discovered in small quantities in 2 wildlife food plot mixes. Amaranthus seed was found in 5 of the CRP and pollinator mixes with the smallest quantity of 2 pigweed seeds per kilogram and the largest quantity of 172 pigweed seeds per kilogram. Viability testing has shown as high as 73% of Amaranthus seed and 47% of grass species discovered in birdseed mixes are capable of germinating. This test will also provide definitive results of which species of Amaranthus was present in the seed mixes.  Results from this study will provide information about the potential involvement of commercial seed mixes to spread economically important weed seeds throughout the United States. Future work includes testing weed species for herbicide resistance as well as examining more birdseed mixes, pollinator mixes, and cover crop seed for weed species presence. 


EFFECTS OF SUB-LETHAL RATES OF DICAMBA AND 2,4-D ON SUGARBEET. M. A. Probst*, C. L. Sprague; Michigan State University, East Lansing, MI (2)


Dicamba- and 2,4-D-resistant soybean will provide growers with previously unavailable herbicide options for selective control of broadleaf weeds in soybean. However, as the potential uses for dicamba and 2,4-D expand, the possibility for exposure of these herbicides to sensitive crops through tank contamination will increase as well. Misapplication of these herbicides to sugarbeet, a sensitive crop, is of great concern to Michigan growers. To gain a better understanding of how sublethal rates of dicamba and 2,4-D influence sugarbeet, studies were conducted in East Lansing and Richville, MI. Five rates ranging from 0.0625-2% of the field use rates of dicamba and 2,4-D were sprayed on sugarbeet at the 2-leaf, 6-leaf, and 14-leaf growth stages. The field use rates for dicamba and 2,4-D were 1.1 kg ae ha-1. Applications to 6-leaf sugarbeet were excluded from the East Lansing location. All treatments included 0.84 kg ae ha-1 of glyphosate to simulate tank contamination. A glyphosate-only control treatment was included at each application timing. Herbicide injury was evaluated at 7, 14, and 21 days after treatment (DAT) and at the end of the season. Sugarbeet yield and quality were measured at harvest. Injury levels were higher from lower rates (<0.5% field use rate) of dicamba and 2,4-D when applications were made to 2-leaf sugarbeet compared with applications to 6- and 14-leaf sugarbeet, 14 DAT. The rate required to injure sugarbeet 20%, 14 DAT, was greater than 1% of the dicamba field use rate for the 2-, 6-, and 14-leaf applications at Richville, and the 14-leaf application at East Lansing The rate of 2,4-D that caused 20% sugarbeet injury was >1, 0.79, and 0.58% of the field use rate when applications were made to 2-, 6-, and 14-leaf sugarbeet, respectively, at Richville. At East Lansing, >1% of the 2,4-D field use rate was needed to injure sugarbeet 20%. Sugarbeet recovered from early season dicamba and 2,4-D injury when these applications were made to 2- and 6-leaf sugarbeet, and injury was generally less than 5% at the end of the season from these applications. Sugarbeet yield and recoverable white sucrose (RWS) was only impacted at the Richville location. Sugarbeet yield was reduced 24 and 18% when 2% of the field use rate of dicamba was applied to 6 and 14-leaf sugarbeet respectively. At the same application timings, 2% of the field use rate of 2,4-D reduced sugarbeet yield 56 and 46%, respectively. Reductions in RWS followed similar patterns to yield. These findings are of concern to Michigan sugarbeet growers since these sublethal doses can lead to reductions in sugarbeet yield and RWS, ultimately leading to economic losses. Further research needs to be conducted to determine if residues from these herbicides can be detected in the harvested sugarbeet.  


EFFECTIVE WEED MANAGEMENT SYSTEMS USING XTENDFLEX COTTON. K. R. Russell*1, P. A. Dotray1, J. Keeling2, S. L. Taylor2, J. D. Everitt3; 1Texas Tech University, Lubbock, TX, 2Texas A&M AgriLife Research, Lubbock, TX, 3Monsanto, Lubbock, TX (3)


EFFECTIVE WEED MANAGEMENT SYSTEMS USING BOLLGARD II XTENDFLEXTM COTTON K.R. Russell1* P.A. Dotray1,2, J.W. Keeling2, S.L. Taylor2, J.D. Everitt3 1Texas Tech University, Lubbock; 2Texas A&M AgriLife Research, Lubbock; 3Monsanto, Shallowater


Herbicide resistant weeds are becoming an increasing problem and are likely present on every farm in the Texas Southern High Plains. With the recent federal registration and state approval of XtendiMaxTM with VaporGripTM Technology for use in Bollgard II XtendFlexTM cotton, producers have an additional mode of action that can be used preplant (PP), preemergence, and postemergence to control glyphosate-resistant Palmer amaranth (Amaranthus palmeri S. Wats) and other troublesome weeds. The XtendFlexTM technology also allows growers to apply glufosinate and glyphosate in-season.  Prior to XtendFlexTM cotton, dicamba was not used PP in the Southern Texas High Plains due to rainfall limitations. The objective of this research was to evaluate season-long weed control in Bollgard II XtendFlexTM cotton using several weed management systems that include XtendiMaxTM.  A field study was established in a randomized complete block design in a drip-irrigated field at New Deal, Texas using a variety of herbicides in different applications to determine herbicide efficacy of Palmer amaranth.  Herbicides treatments used were; paraquat at 0.2802 kg/ha, prometryn at 1.1208 kg/ha, glufosinate at 0.5941 kg/ha, acetochlor at 1.2666 kg/ha, dicamba at 0.5604 kg/ha, glyphosate at 1.2666 kg/ha, dicamba+glyphosate at 1.6813 kg/ha, and trifluralin at 1.1208 kg/ha.  The greatest weed control in early season was observed in weed management systems that included two or more residual modes of action.  Mid-season weed management was greatest on systems that included dicamba and or glyphosate following residual treatments of trifluralin or prometryn.  Late season observations suggested systems that included dicamba+glyphosate had greater than 95% control of Palmer amaranth.  Plot lint yield ranged from 0 to 2219 kg/ha and were greatest following dicamba-based systems.




Palmer amaranth’s season long emergence, rapid growth rate and ability to develop herbicide-resistance make it extremely difficult to manage. Incorporating the use of additional cultural practices, such as narrow row widths and cover crops, may improve the management of herbicide-resistant Palmer amaranth. This experiment was established in the falls of 2014 and 2015 near Middleton, Michigan in a field with glyphosate-resistant Palmer amaranth. The objectives of this research were to examine the effects of: 1) a cereal rye cover crop, 2) cover crop termination method, 3) soybean row width and 4) herbicide programs on Palmer amaranth management and soybean yield. The experiment was a split-split-plot design with the main plots: 1) cereal rye cover crop terminated in the spring with flail mowing, 2) cereal rye cover crop terminated in the spring with glyphosate, and 3) no cereal rye cover. The sub-plots were soybean planted in two different row widths: 19 cm and 76 cm rows. The sub-sub-plots included three different Palmer amaranth herbicide management strategies: no management, low management (flumioxazin PRE fb. glufosinate POST), and high management (flumioxazin PRE fb. glufosinate + acetochlor POST). Cereal rye biomass averaged 120 g m-2 of dry biomass (1200 kg ha-1) in 2015 and 218 g m-2 of dry biomass (2186 kg ha-1) in 2016 which suppressed winter annual and early summer annual weed biomass 77% and 84%, respectively, compared with the no cover control at the time of rye termination. Cereal rye was not controlled by flail mowing in either year and produced an additional 128 g m-2 and 58 g m-2 of dry biomass in 2015 and 2016, respectively, before being terminated by glyphosate prior to soybean planting. Soybean canopy closure occurred at least two weeks earlier in the 19 cm row width compared with the 76 cm row width in both years. In 2015, Palmer amaranth was controlled in both the low and high Palmer amaranth management systems; however, a lack of precipitation in 2016 resulted in poor control in the low management system. Soybean yield in the low and high management systems were greater compared with the no management treatments in both years; however, in 2016 soybean yield was 574 kg ha-1 higher in the high management compared with the low management system. Low cereal rye biomass at the time of termination (late-April/early-May) may limit Palmer amaranth suppression in Michigan because of later emergence. The most effective treatment in managing Palmer amaranth is the use of a residual preemergence herbicide followed by a postemergence application, regardless of soybean row spacing.

HERBICIDE TREATMENT OPTIONS FOR DOUBLE CROP GRAIN SORGHUM. J. J. Albers*, D. E. Peterson, C. R. Thompson, M. M. Hay, A. Dille; Kansas State University, Manhattan, KS (5)


A common cropping practice in the southern plains region is double cropping; one example is planting grain sorghum after winter wheat.  In double crop fields in Kansas, Palmer amaranth (Amaranthus palmeri) and large crabgrass (Digitaria sanguinalis) are among the most troublesome weeds, especially if herbicide resistant weeds are present, and drive many weed management decisions.  The objective of this study was to provide a basis for growers to make herbicidal weed management decisions for Palmer amaranth and large crabgrass in double crop grain sorghum.  Field experiments were established near Hutchinson and Manhattan KS in recently harvested wheat stubble fields in late June 2016.  Fourteen different herbicide treatments were assessed; eight of which PRE only and six were PRE followed by a POST 3 weeks after (WA) PRE application.  All plots received a burn down treatment of glyphosate following wheat harvest to control emerged large crabgrass.  All PRE treatments were applied after planting and tank mixed with paraquat for control of glyphosate-resistant Palmer amaranth.  Weed control was visually evaluated at one week intervals, recorded as percent control (0-100%) and statistically evaluated using ANOVA and a priori orthogonal contrasts.  At 3 WA PRE application, the treatments with three effective residual sites of action (SOA) had better AMAPA control (94%) when compared with PREs having two or fewer SOA (84%).  At 4 WA POST application, a PRE followed by a POST had better AMAPA control (83%) when compared with a PRE alone (63%).  At 4 WA POST application, all treatments with three SOA provided greater AMAPA control (79%) when compared with treatments having two or fewer SOA (69%).  At 3 WA PRE application, DIGSA control across all treatments was (92%) and at 4 WA POST application DIGSA control was (86%) with no difference in control among treatments.  At 3 WA PRE, the best treatment for both species were atrazine + s-metolachlor + mesotrione (96%).  At 4 WA POST application, the best AMAPA treatment was an encapsulated acetochlor + atrazine PRE followed by an encapsulated acetochlor + atrazine POST (94%).  At 4 WA POST application, dimethenamid-P + saflufenacil PRE was the least effective PRE treatment for AMAPA control (36%).  However, 4 WA POST application the treatment dimethenamid-P + saflufenacil + atrazine control was nearly doubled (70%), showing the value of atrazine.  In summary, a sequential weed control program consisting of an effective burndown, the use of atrazine, the use of a PRE followed by a timely POST, and using more than two SOA in an herbicide application can provide effective weed control in double crop grain sorghum. 

OPTIMIZING HERBICIDE AND COVER CROP PROGRAMS FOR INTEGRATED WEED MANAGEMENT IN NO-TILL SOYBEANS. J. M. Bunchek*1, J. M. Wallace1, M. J. VanGessel2, W. Curran1, D. A. Mortensen1; 1Pennsylvania State University, University Park, PA, 2University of Delaware, Georgetown, DE (6)


As the rise in herbicide resistance increasingly challenges weed management, adopting an integrated weed management (IWM) approach becomes ever more important. IWM utilizes knowledge of weed biology to design multi-tactic weed management strategies that effectively control pests and remove selection pressure away from herbicides. In many regions of the United States, conservation tillage is a growing practice, therefore reducing or eliminating tillage as a weed management tool.  Cover cropping is also increasing on annual croplands and may be utilized as an IWM tool that potentially targets all phases of the annual weed life cycle via physical suppression, allelopathy, and competition. Thus, optimizing cover cropping and herbicide inputs is an IWM approach of interest in continuous no-till systems. A multi-state project was developed with the objective of integrating cover crop and herbicide strategies to diversify weed management. We hypothesized that: (1) fall-planted cover crops would decrease weed density and size at key times of herbicide application, and (2) integrating cover crops with targeted herbicides would increase overall weed control efficacy. To test these hypotheses, a field experiment was established at the Russell E. Larson Agricultural Research Center (PSU-RELARC) near State College, PA, and the Carvel Research & Education Center (UD-CREC) near Georgetown, DE. This experiment was conducted in 2015-2016 and will be repeated in 2016-2017 using a randomized complete block split-plot design. Main plots included cover crop treatments of a no cover control, cereal rye (Secale cereale L.) (135 kg ha-1), and a mixture of cereal rye + hairy vetch (Vicia villosa Roth) (100 kg ha-1 + 22 kg ha-1), which were drill-seeded following corn silage harvest (Oct. 1-15). In the spring, cover crop treatments were top-dressed with 45 kg ha-1 ammonium sulfate (21% N, 24% S) and terminated at the early heading stage of rye with a burndown (BD) mixture ten days prior to planting glufosinate-resistant soybean. Four herbicide program treatments were imposed in split-plots: (1) a control program of BD only (1.26 kg ae ha-1 glyphosate + 0.56 kg ae ha-1 2,4-D LVE), (2) BD + PRE-residual (1.7 kg ha-1 S-metolachlor + 56 g ai ha-1 flumetsulam), (3) BD + POST (0.74 kg ai ha-1 glufosinate), and (4) BD + PRE-residual + POST. Each split plot contained 0.5 m2 individual weed microplots of smooth pigweed (Amaranthus hybridus L.) and horseweed (Conyza canadensis [L.] Cronquist). Weed seeds were collected from local populations prior to establishing the microplots, and both locations had natural populations of the weed species of interest. Notable first-year results (p ≤ 0.05) from UD-CREC showed that horseweed density at BD was 81% lower in the rye + hairy vetch treatment than the rye and control treatments, likely due to rye + hairy vetch having greater biomass and percent ground cover at BD. At the time of POST application, treatments that included a cover crop had 61% fewer horseweed without the PRE-residual and 88% fewer horseweed when a PRE-residual was included. In addition, including a cover crop had a 59% reduction in horseweed height. Results from PSU-RELARC showed that relative to the control, the rye and rye + hairy vetch treatments had 51% lower late-summer smooth pigweed biomass without the PRE-residual and 66% lower late-summer smooth pigweed biomass when a PRE-residual was used. Further, at the time of POST application, including a PRE-residual resulted in lower smooth pigweed densities across all three cover crop treatments. Smooth pigweed density was highest in the rye + hairy vetch treatment, possibly attributed to the decomposition and subsequent N mineralization of the cover crop residue stimulating smooth pigweed establishment. The results from the first field year suggest that cover crops have the potential to lower weed population densities and size, but the extent to which this suppression occurs is dependent upon the species of cover crops being integrated.


INTEGRATING BIOLOGICAL CONTROL WITH CONVENTIONAL METHODS FOR ENHANCED TAMARIX MANAGEMENT. L. M. Murray*, E. A. Lehnhoff, B. J. Schutte, C. A. Sutherland; New Mexico State University, Las Cruces, NM (7)


Tamarix spp., invasive riparian shrubs, are ecological and economic threats in the southwest as they displace native vegetation and necessitate costly management. Tamarix control typically consists of chemical and mechanical removal, but these methods can prove to have negative ecological and economic impacts. Tamarisk beetles (Diorhabda spp.) released for biocontrol provide another form of control. While there is abundant research on each of these treatment methods, no research has been conducted on integrating these methods to improve management. Our question was, could Diorhabda herbivory be combined with mechanical and chemical treatment to achieve greater control with fewer non-target impacts. A field experiment was conducted by testing the impacts of mowing, herbicide at standard and low rate (2.78 lb ae ha-1 and 0.93 lb ae ha-1 respectively), and a control, each either with or without (via Malathion) beetle herbivory. Each treatment was replicated five times at both a dry and a seasonally flooded site. Green foliage percent and gas exchange (via LI-COR 6400) were measured, and water use efficiency (WUE) was calculated to assess plant stress. Results showed herbicide treatments, regardless of beetles present, resulted in reduced transpiration rates at both sites. Green foliage was influenced at both sites by adults and larva beetle numbers (p<0.01 and p<0.001 respectively), and towards the end of growing season at both sites, control plots showed a high green foliage percent recovery, while mowing and herbicide treatments all displayed a severely reduced percentages of green foliage.  While data collection will continue this summer, first year data show combining conventional management methods with biocontrol can result in additional stress through a combination of reduced green foliage recovery and a lower WUE in late summer. Incorporating this new knowledge into land management objectives for Tamarix control can result in more effective overall management plans. 


THE EFFECTS OF MULCHING, TILLAGE, AND HERBICIDES ON WEED CONTROL AND WATERMELON YIELD. A. J. Price1, S. Li2, B. Guertal3, J. McElroy3, J. P. Williams*3; 1USDA-ARS, Auburn, AL, 2Alabama Cooperative Extension Service, Auburn, AL, 3Auburn University, Auburn, AL (8)


Currently few producers in the Southeast US have adopted conservation tillage practices in specialty crop production. The lack of conservation adoption is likely due to the added challenges in producing vegetables in cover crop residues, especially high biomass cover crop systems. The objective of this experiment was to determine if conservation tillage practices could be incorporated into watermelon production (Citrullus lanatus (Thunb.) Matsum. & Nakai). A three year watermelon experiment was established in fall 2013 at Auburn University’s Plant Breeding Unit, near Shorter, AL. Four agronomic systems were evaluated: 1) conventional tillage with no polyethylene mulch, 2) conservation tillage with a cereal rye cover crop, 3) conventional tillage with polyethylene mulch, 4) conservation tillage with a rye cover crop integrated with polyethylene mulch. Within each system, herbicide treatments included 1) halosulfuron applied at 26.3 grams ai ha-1 PRE, 2) halosulfuron applied at 26.3 grams ai ha-1 POST, 3) halosulfuron applied sequentially at 26.3 grams ai ha-1 PRE and POST, and 4) a non-treated control. Results revealed that the agronomic system was the most important factor in determining yield, likely due to adequate herbicide control in most systems. Both polyethylene mulch treatments consistently yielded higher than treatments without polyethylene, regardless of the herbicide system used. Polyethylene use resulted in yields was significantly higher than all other mulching systems in 2014 (30,661 kg ha-1) and 2015 (61,223 kg ha-1). In 2016, polyethylene and polyethylene integrated with rye were not different (36,275 kg ha-1 polyethylene and 31657 kg ha-1 polyethylene over rye, respectively), and yielded significantly higher than treatments without polyethylene (10,938 kg ha-1 conventional tillage and 5,311 kg ha-1 conservation tillage). In all years, there was no interaction between yields by herbicide system. The effect of the polyethylene was again apparent in the yield interaction between mulching system and herbicide. Increasing herbicide intensity did not increase yield, and polyethylene use was still the most important effect in increasing yield. Crabgrass weed control was difficult regardless of agronomic system or herbicide system. Utilizing sequential PRE and POST applications did not significantly affect weed control in the interaction between herbicide and mulching system for any of the weeds rated. The results of this experiment show that progress still needs to be made in developing integrated conservation systems for watermelon production. However, the results of the polyethylene integrated with rye reveal that this mulching system could have potential in conservation specialty crop production.

STALE SEEDBEDS FOR SUMMER ANNUAL WEEDS IN NEW MEXICO CHILE. A. Sanchez*, B. J. Schutte, L. Beck, O. J. Idowu; New Mexico State University, Las Cruces, NM (9)


Chile peppers (hereafter “chile”) are pungent cultivars of Capsicum annuum L.  New Mexico has a heritage of chile production that dates back approximately four centuries.  However, since the mid-1990s, the amount of chile planted and harvested in New Mexico has declined. A prominent reason for the decrease in New Mexico chile production is high labor costs for removal of weeds that emerge mid-to-late season.  The goal of this project was to reduce reliance on hand labor for weeding by developing a stale seedbed technique that specifically targets mid-to-late season weeds in chile.  Our experimental objective was to measure the effects of fallow-season stale seedbeds on weed seedling densities and hoeing requirements in subsequent chile production.  Stale seedbeds (sequences of irrigation and tillage that eliminate weed seeds and seedlings) were implemented during August and September 2015.  In April 2016, chile was mechanically seeded at 6.6 kg seeds ha-1.  Prior to seeding, a soil-residual herbicide (napropamide at 1.1 kg ai ha-1) was applied to control early-season weeds.  Weeds that emerged after crop emergence were controlled with combinations of cultivation, hand hoeing, and post-emergence herbicide for grasses (clethodim at 0.14 kg ai ha-1).  Experimental treatments were 0, 2, and 3 fallow-season stale seedbeds.  Data collected included: weed emergence in stale seedbeds, weed emergence in chile, time required for hand hoeing in chile, and chile yield.  Results indicated that fallow-season stale seedbeds targeted late-season weeds including: junglerice, Wrights groundcherry, and Palmer amaranth.  Results also showed that fallow-season stale seedbeds: (1) reduced weed densities in chile on May 13, July 5 and July 15, and (2) reduced hoeing times in chile on June 2 and August 15.  Reductions in weed seedling density and hoeing time were similar between the 2 and 3 stale seedbed treatments.  Compared to the 0 stale seedbed treatment, the 2 stale seedbed treatment reduced green chile yield.  This reduction in yield may have been a consequence of early-season salt injury caused by rain, unimpeded by weeds, splashing saline groundwater on chile leaves.  Red chile yield was not affected by stale seedbed treatment.  Early results indicate that fallow-season stale seedbeds are a promising method for reducing requirements for hand hoeing in chile.  We expect that our study conclusions will be strengthened and clarified with both second-year data and forthcoming cost-benefit analyses.

FATE OF SULFENTRAZONE APPLIED TO COVER CROP SPECIES PRIOR TO SOYBEAN PLANTING. D. M. Whalen*, E. Oseland, S. Farrell, B. R. Barlow, Z. Trower, M. D. Bish, M. Biggs, K. W. Bradley; University of Missouri, Columbia, MO (10)




In 2016, the majority of the cotton acreage in the mid-South were planted with dicamba-tolerant (DT) varieties, and a limited number of DT soybean varieties were also planted in the mid-South and Midwest.  However, during the 2016 growing season, the Environmental Protection Agency had not approved any dicamba herbicide formulations for post-emergence application to these varieties.  Although investigations are ongoing, apparently some subset of growers made illegal applications of dicamba to a variety of sensitive crops, including non-DT soybean.  In southeastern Missouri alone, over 120 dicamba injury complaints were filed with the Missouri Department of Agriculture.  In non-DT soybean, previous and extensive research has been conducted that identifies specific yield loss relationships as it relates to the dose of dicamba and the stage of the plants when contacted.  However, in field settings, practitioners never know the specific dose of dicamba that contacted the non-DT soybean.  Additionally, plants may be injured multiple times by more than one off-target dose of dicamba.  All of these factors complicate estimations of soybean yield loss.  The objective of this research was to determine if late-season visual injury evaluations can predict yield loss on a field-scale level after off-target movement of dicamba has occurred.  In 2016, 4 separate non-DT soybean fields reported with injury from off-target movement of dicamba were visually rated for dicamba injury using a previously established scale developed by Richard Behrens and W.E. Lueschen. (1979).  The fields ranged in size from 30 to 48 hectares.  Field boundaries were mapped and uploaded to SMS Mobile AgLeader software for sample grid creation.  Sample locations were established within each field using a center grid format at spacings of 25 meters.  Handheld GPS units were used to navigate to the predetermined grid locations and record visual soybean injury ratings once soybean reached the R6-R7 stage of growth.  Site-specific yield information was then obtained through combine yield monitors.  Soybean yield and visual injury ratings at each predetermined sample location were compared in SAS using the MEANS procedure at a 0.05 level of significance.  Visual injury ratings were grouped to estimate yield loss ranges based on the MEANS procedure results then compared back to the actual yield.  Results from this study will help farmers and agriculture professionals to better visualize and understand the effects that off-target movement of dicamba can have on soybean yield.  


NOVEL MOLECULAR MARKERS FOR MONITORING THE GENE FLOW FROM HERBICIDE-RESISTANT CROPS TO CLOSELY RELATED SPECIES. J. J. Ziggafoos*1, R. Werle2, A. Jhala3, J. Lindquist1, M. K. Yerka1; 1University of Nebraska - Lincoln, Lincoln, NE, 2University of Nebraska, Lincoln, North Platte, NE, 3University of Nebraska-Lincoln, Lincoln, NE (12)


Concerns about gene flow from sorghum to sympatric weedy relatives have hindered regulatory approval of genetically modified traits in the crop. ‘Inzen’ sorghum hybrids were developed by DuPont-Pioneer with a non-GMO ALS-inhibiting herbicide-resistance trait and are in the final stages of commercialization. They will inevitably cross-pollinate weedy relatives, including shattercane and johnsongrass. Since no previous herbicide-resistance trait has been introduced into grain sorghum, commercialization of Inzen hybrids may serve as an effective landscape-level indicator of agroecosystem choice dynamics and weed population response (ecology and genetic diversity) when a new crop trait increases weed fitness and has high expected rates of on-farm adoption. As ALS-resistance alleles are neutral mutations that may persist indefinitely in weedy Sorghum populations once introduced, and increased use of ALS-inhibitors will apply selective pressure for both crop-derived and de novo resistance alleles, there is an urgent need to 1.) Identify cropping strategies that will delay herbicide-resistance evolution in Sorghum, 2.) Characterize the baseline genetics of existing Sorghum populations, and 3.) Develop high-throughput genotyping approaches to accurately monitor ALS-resistance alleles across the U.S. In the absence of such efforts, rapid fixation of ALS-resistance alleles in weedy Sorghum may be expected throughout the Great Plains, permanently altering the genetic composition of wild populations, reducing the lifespan of post-emergence weed control options in sorghum, and forfeiting the opportunity for Federal regulatory agencies to collect statistically-relevant data on the unintended consequences of DNA sequence modification (evolved herbicide resistance) of wild relatives due to nuclear sorghum technologies. Here we present genetic tools that meet the needs of a high-throughput regional monitoring program for crop-to-weed gene flow in Sorghum. Similar tools could be developed for any crop species with sympatric wild relatives.

A STUDY OF CYTOCHROME P450 MEDIATED METABOLIC RESISTANCE IN KOCHIA SCOPARIA . A. Barker*, O. Todd, F. E. Dayan, T. A. Gaines; Colorado State University, Fort Collins, CO (13)


Cytochrome P450s have been extensively connected to herbicide metabolism in monocots such as wheat and corn, but only recently have been investigated for herbicide resistance in dicot species including Kochia scoparia. They pose a unique threat for the evolution of herbicide resistance in weeds due to the ability of a single P450 to metabolize herbicides with different modes of action, which could mean a reevaluation of the current mode of action system used to recommend herbicide rotation in crops. Gene constructs were synthesized for expression in yeast to study the effects of plant P450s in vivo. The yeast line WAT21 was used because it expresses a plant P450 reductase and is sensitive to chlorsulfuron. A known chlorsulfuron-metabolizing protein from wheat, CYP71C6v1, and the closest homolog in Kochia scoparia were chosen for initial testing to evaluate chlorsulfuron-resistance due to P450 expression in WAT21. A liquid assay was used with chlorsulfuron concentrations of 0, 500, and 1,000 µM, and the growth rate of yeast was measured by the OD600 to obtain growth response curves. Results indicate this system has potential to screen new and existing herbicides for cytochrome P450 metabolism.


EFFECT OF DEGREE OF WATER STRESS ON THE GROWTH AND FECUNDITY OF PALMER AMARANTH. P. Chahal*1, S. Irmak1, A. Jhala2; 1University of Nebraska - Lincoln, Lincoln, NE, 2University of Nebraska-Lincoln, Lincoln, NE (14)


Palmer amaranth is the most problematic weed in agronomic crop production fields in the United States. The objective of this study was to determine the effect of degree of water stress on the growth, development, and fecundity of two Palmer amaranth biotypes under greenhouse conditions. Palmer amaranth plants were grown in the soil maintained at 12.5%, 25%, 50%, 75%, or 100% field capacity (FC) using irrigation sensors in 20 cm wide and 40 cm deep plastic pots. Water was regularly added based on moisture level detected by sensors to maintain desired stress level. No difference was observed in the growth, development, and seed production between Palmer amaranth biotypes, except root biomass weight, and between two experimental runs; therefore, data were combined over biotypes (except root biomass weight) and experimental runs. Palmer amaranth plants maintained at ≤ 25% FC did not survive more than 5 weeks after transplanting and were not able to produce seeds. Growth parameters such as number of leaves plant-1, plant height (cm), growth index (cm3), number of seeds plant-1, aboveground biomass (g plant-1), dry root biomass (g plant-1), and total leaf area plant-1 (cm2) were influenced by water stress treatments. Plants maintained at ≥ 75% FC produced the highest number of leaves (≥ 664 plant-1) and plants at ≥ 50% FC capacity produced highest dry root biomass (≥ 2.3 plant-1). The highest plant height (211 cm), seed production (41,696 plant-1), and growth index (120,272 cm3) was observed among plants maintained at 100% FC and reduced with increasing water stress. Additionally, seeds were harvested and germination test was accomplished to determine effect of water stress on germination. A cumulative seed germination (%) was similar (18 to 26%) when plants were exposed to ≥ 50% FC.




Investigating Palmer amaranth response to glufosinate in a North Carolina population

Drake Copeland*

W.J. Everman

A.C. York

North Carolina State University

Raleigh, North Carolina


Palmer amaranth (Amaranthus palmeri) is the most problematic weed in row-cropping systems in the southern United States. The summer annual has evolved resistance to herbicides from six different mechanisms of action in the U.S. In this study, a Palmer amaranth population of concern from McFarlan, NC in 2015 was collected and screened for glufosinate resistance against a susceptible population. Four seed lots (seed from individual females) from the putative glufosinate-resistant population (A19, CG6, CG8 and CG16) were tested versus the glufosinate-susceptible population (GS). Each population was treated with glufosinate at 10, 20, 40, 60, 90, 120, 180, 240, 480, 720, 960, 1200 g a.i. ha-1. A non-treated check was included. Percent mortality and shoot dry biomass were recorded 21 DAT (days after treatment). Treatments were replicated 5 times and repeated in time.

Little to no difference was observed between CG6, CG8, CG16 and the GS population, with respect to mortality or dry weight biomass 21 DAT. However, A19 (680 g) had a significantly greater LD90 (lethal dose, 90%) than GS (250 g). Differences in GI50 (growth inhibition, 50%), with respect to dry biomass, were observed between A19 (162 g) and GS (62 g).

Further experiments were conducted at the field site in McFarlan, NC. Plots were 4-96 cm rows, 6 m in length. Palmer amaranth were treated when plants were 5-8cm in height with glufosinate at 595, 660, 880, 1190, 1310, 1475, 1760 and 2355 g a.i. ha-1. Treatments of glufosinate followed by (fb) sequential applications of glufosinate 7 days after the initial (DAI) were utilized and included: 660 fb 660 g, 880 fb 660 g and 880 fb 880 g. A non-treated check was included. Percent control and mortality were recorded 7 DAT. Treatments were replicated 4 times and repeated in time.

In the first run, control of Palmer amaranth was greater than 93 % for all treatments that included a single application. However in the second run, single applications only provided 90 % or greater control with rates 1475, 1760 and 2355 g of glufosinate. Palmer amaranth was controlled in both runs when sequential applications of glufosinate at 660 or 880 g where made 7 DAI of 660 or 880 g of glufosinate. Research is ongoing to determine why this biotype survived rates of glufosinate known to be lethal to glufosinate-susceptible Palmer amaranth.


THE EFFECTS OF PALMER AMARANTH COMPETITION ON SOIL MOISTURE AVAILABIILITY IN SOYBEAN. D. D. Joseph*1, M. W. Marshall2; 1Clemson University, Clemson, SC, 2Clemson University, Blackville, SC (16)


TOLERANCE OF GLYTOL®/LIBERTYLINK® COTTON TO VARIOUS HERBICIDE TANK MIX COMBINATIONS. M. T. Plumblee*1, D. M. Dodds1, C. A. Samples2, A. B. Denton2, S. Davis2, L. X. Franca1, B. R. Wilson2; 1Mississippi State University, Starkville, MS, 2Mississippi State University, Mississippi State, MS (17)


Tolerance of GlyTol® /LibertyLink® Cotton to Various Herbicide Tank Mix Combinations. Michael T. Plumblee*1, Darrin M. Dodds1, Chase A. Samples1, Andrew B. Denton1, Savana S. Davis, Lucas X. Franca, and Bradley R. Wilson; 1Mississippi State University, Mississippi State, MS




Glufosinate-resistant cotton (LibertyLink®) was commercialized in 2004 by Bayer Crop Science. LibertyLink® cotton was developed through the insertion of the bialaphos resistance (BAR) gene, which provides resistance to glufosinate. In 2011 GlyTol® was commercialized by Bayer Crop Sciences which provided season-long, in plant tolerance to glyphosate herbicide which is the first Roundup Ready® alternative to be commercialized. Due to the popularity of cotton varieties with these traits and the ongoing battle with resistant weed species, applications of single post-emergence herbicides are becoming uncommon. Therefore, the objective of this research was to evaluate the effects of various herbicide tank mix combinations on a commercially available GlyTol®/LibertyLink® cotton.


This experiment was conducted in 2016 at the R.R. Foil Plant Science Research Center in Starkville, MS and the Black Belt Experiment Station in Brooksville, MS to evaluate GlyTol® /LibertyLink® cotton tolerance to glufosinate and glufosinate tank mix combinations. Stoneville 4946 GLB2 was planted May 7, 2016 in Starkville and May 11, 2016 in Brooksville in 4-row plots 3.86 m wide x 12.2 m long. Applications of glufosinate (Liberty) at 0.65 kg ai ha-1, glyphosate (Roundup PowerMax) at 1.26 kg ae ha-1, S-metolachlor (Dual Magnum) at 2.13 kg ai ha-1, glyphosate + S-metolachlor (Sequence) at 0.3 kg ae ha-1 glyphosate and 0.42 kg ai ha-1 S-metolachlor, glufosinate (Liberty) at 0.65 kg ai ha-1 + S-metolachlor (Dual Magnum) at 2.13 kg ai ha-1, glyphosate (Roundup PowerMax) at 1.26 kg ae ha-1 + glufosinate (Liberty) at 0.65 kg ai ha-1, and glyphosate (Roundup PowerMax) at 1.26 kg ae ha-1 + glufosinate (Liberty) at 0.65 kg ai ha-1 + S-metolachlor (Dual Magnum) at 2.13 kg ai ha-1 were made to 4-leaf cotton on June 7, 2016. Visual injury ratings consisting of chlorosis, necrosis, and stunting data were collected at 7, 14, and 28 days after application. End of season data collected included plant height, total nodes, and node above cracked boll, and lint yield. Data were subjected to analysis of variance using PROC Mixed procedure in SAS 9.2 and means were separated using Fishers protected LSD at p = 0.05.


The greatest visual injury 7 days after application occurred when S-metolachlor (Dual magnum) (13% injury) was applied and the lowest total injury was where glyphosate (Roundup PowerMax) (6% injury) was applied. Visual injury at 14 days after application was greatest from glufosinate (Liberty) + S-metolachlor (Dual Magnum) and glyphosate (Roundup PowerMax) + glufosinate (Liberty) + S-metolachlor (Dual Magnum) (3.6% injury) and glyphosate (Roundup PowerMax) and S-metolachlor (Dual Magnum) (2.3% injury) treatments having the lowest injury. At 28 days after application visual injury was not significant among treatments. Plant heights were significantly different at 1st bloom where S-metolachlor (Dual Magnum) treated plots had significantly taller plants than plots treated with glufosinate (Liberty) or glyphosate + S-metolachlor (Sequence). Plant heights were not significantly different at defoliation. Total nodes were not significantly different at 1st bloom but were different at defoliation where plots treated with glufosinate (Liberty) and glyphosate + S-metolachlor (Sequence) had more nodes than plots treated with glufosinate (Liberty) + S-metolachlor (Dual Magnum). No significant differences were observed in nodes above white flower. Plots treated with glyphosate (Roundup PowerMax) + glufosinate (Liberty) and S-metolachlor (Dual Magnum) had more nodes above cracked boll than plots treated with glufosinate (Liberty). Lint yield was significant is greater when glyphosate (Roundup PowerMax), glyphosate + S-metolachlor (Sequence), and glyphosate (Roundup PowerMax) + glufosinate (Liberty) was applied compared to glyphosate (Roundup PowerMax) + glufosinate (Liberty) + S-metolachlor (Dual Magnum).

SEED SHATTERING OF SIX PREVALENT WEED SPECIES IN NORTH CAROLINA. T. A. Reinhardt*, W. J. Everman; North Carolina State University, Raleigh, NC (18)


WATER-SEEDING WITH ANAEROBIC GERMINATION TOLERANT CULTIVARS IN IMPROVING CROP ESTABLISHMENT AND WEED MANAGEMENT IN WET DIRECT SEEDED RICE. B. S. Chamara*1, B. Marambe2, V. Kumar3, B. S. Chauhan4; 1Weed Science, Crop and Environmental Sciences Division, International Rice Research Institute, Philippines, Los Banos, Philippines, 2Department of Crop Science, Faculty of Agriculture, University of Peradeniya, Sri Lanka, Peradeniya, Sri Lanka, 3International Rice Research Institute, Los Banos, Philippines, 4The University of Queensland, Gatton, Australia (19)


FIELD PERFORMANCE OF A NOVEL 2,4-D TOLERANT RED CLOVER (TRIFOLIUM PRATENSE). M. Barrett, L. P. Araujo*, L. D. Williams, G. L. Olson; University of Kentucky, Lexington, KY (20)


Incorporation of a legume, such as red clover (Trifolium pratense), into grass-based pasture systems offers many benefits. However, available red clover lines are highly susceptible to herbicides, in particular 2,4-D (2,4-dichlorophenoxyacetic acid), which has been widely used for broadleaf weed management in pastures. A novel red clover line, UK2014, was developed at University of Kentucky through conventional breeding and expresses higher tolerance to 2,4-D than Kenland, a common variety used by Kentucky’s forage producers. Adopting this new tolerant line would broaden weed management options in a legume-grass mixed pasture. The main objective for this study was to assess the field performance of UK2014, in terms of yield and 2,4-D tolerance level, compared to Kenland in Kentucky’s environment. To accomplish this, both UK2014 and Kenland were seeded in April of 2016 and 2,4-D (both the 1.12 and 2.24 kg/ha rates) was applied either early (June 29, 2016), mid (August 8, 2016) or late (October 3, 2016) season.  Each plot received only one 2,4-D treatment and treated plots were compared to those that were not treated with 2,4-D.  Visual herbicide injury was evaluated one week after spraying and one week after harvest.  The red clover was harvested approximately one week after the 2,4-D applications were made.  Both individual harvest and total season yield (dry matter ton/ha) were determined.  Data was subjected to analysis of variance and means were separated using Fisher’s Protected LSD at α = 0.05.  Visual injury one week after 2,4-D treatment to UK2014 was less than that of Kenland, especially at the 2.24 kg/ha 2,4-D rate. Similarly, in plots treated earlier with 2.24 kg/ha 2,4-D, visual estimates of regrowth one week after harvest were higher for UK2014 than Kenland.  However, there were no differences in yield between UK2014 and Kenland at individual harvests or in the season total.  While this indicated that the performance of UK2014 is equal to Kenland in terms of yield, it also indicated that the 2,4-D injury to Kenland was not enough to reduce its yield.  Future research will follow the effects of 2,4-D on the persistence of these two lines in both monoculture and mixed species pastures.


MANAGEMENT STRATEGIES OF JOHNSONGRASS (SORGHUM HALEPENSE (L.) PERS.) RESISTANT TO GLYPHOSATE IN THE ARGENTINE AGRICULTURAL PRODUCTION SYSTEM. E. Bracamonte1, E. Actis2, G. Aiassa2, R. Montserrat2, F. Pussetto2, D. Ustarroz3, P. T. Fernandez-Moreno4, R. De Prado*5; 1Faculty of Agricultural Sciences, University of Cordoba, Cordoba, Argentina, 2Faculty of Agricultural Sciences-UNC, Cordoba, Argentina, 3INTA EEA Manfredi, Cordoba, Argentina, 4University of Cordoba, Cordoba, Spain, 5Department of Agricultural Chemistry and Edaphology, University of Cordoba, Cordoba, Spain (21)


The objectives of this study were a) to determine the bio-ecological and agronomic causes of johnsongrass resistance to glyphosate, b) evaluate the efficiency control over johnsongrass with glyphosate and/ or other active ingredients c) design and propose alternative strategies management of johnsongrass resistant to glyphosate (SHGR). For the bio-ecological study, were used the following sources: INTA, Rem AAPRESID, Weed Science, Weed Technology, Weed Research and HRAC (Herbicide Resistance Action Committee). In order to evaluate the alternative strategies and management SHGR, three different levels of management SHGR was considered. First level: plots where the SHGR has not been established, preventive measures should be practiced to prevent their arrival. Second level: it includes plots with presence of isolated individuals or grouped SHGR, corresponding to early stages of invasion, and a third level: plots completely affected by the SHGR, in which the distribution of plants does not allow the definition of a sector. According to the results it is concluded that the agronomic practices and bio-ecological characteristics of johnsongrass favor its spread on agricultural region of Argentina. The determination of the chronological stages of invasion is a simple and effective tool for the management of johnsongrass resistant to glyphosate. The chemical control as the only control tool is insufficient for effective weed management. The early vegetative stage is the optimal moment for an effective chemical control. The optimum growth stage for the chemical control is more important than the moment of germination, region, or soil and climate conditions for efficient management. The use of cultural and mechanical techniques, alone or in combination, provide equal or superior effective to chemical control.

Keywords: Sorghum halepense, resistance, glyphosate, management control.


MORE COMPLEX NATIVE FORAGE MIXTURES REDUCE WEED SEED BANK DENSITY BASED ON THEIR COMPETITIVE ABILITIES. M. Serajchi*1, M. P. Schellenberg2, E. G. Lamb1; 1University of Saskatchewan, Saskatoon, SK, 2Agriculture and Agri-Food Canada, Swift Current, SK (22)


More Complex Native Forage Mixtures Reduce Weed Seed Bank Density Based on Their Competitive Abilities. M. Serajchi1, M. P. Schellenberg*2, E. G. Lamb1; 1 University of Saskatchewan, SK Canada, 2 Agriculture and Agri-Food Canada, Swift Current, SK Canada.

To evaluate the effect of forage mixtures on the weed seedbank, seven perennial forage species were seeded in monoculture and binary mixtures at the Agriculture and Agri-Food Canada in Swift Current, SK. Species included: bluebunch wheatgrass (Pseudoroegneria spicata), nodding brome (Bromus porter), western wheatgrass (Pascopyrum smithii), little blue stem (Schizachyrium scoparium), side-oats grama (Bouteloua curtipendula), purple prairie clover (Dalea purpurea) and white prairie clover (Dalea candida). The weed seedbank was assessed four and five years after seeding the forages, from three depths: 0-5, 5-10 and 10-15 cm. Depth 0-5 cm contained the highest number of germinating seeds. About 57%, 37% and 6% of germinated seeds had biennial, annual and perennial life cycle, respectively. Biennial wormwood (Artemisia biennis), stinkweed (Thlaspi arvense), purslane (Portulaca oleracea) and flixweed (Descurainia sophia) comprised 86% of the total germinated seeds Our results supported the idea that mixtures of forage species promote lower weed densities in the seedbank compared to monocultures. Among mixtures, those containing western wheatgrass had the smallest weed seedbank, thus the species composition of mixtures may have a strong effect on weed seedbank. Western wheatgrass, a perennial rhizomatous grass, decreased weedy species in both monoculture and mixtures more than other grasses. Western wheatgrass demonstrated the ability to suppress weeds and their presence in the seedbank in monocultures and mixtures, another positive quality for its use as a forage species.

Email: Mike.Schellenberg@AGR.GC.CA

GLYPHOSATE RESISTANCE IN GIANT RAGWEED (AMBROSIA TRIFIDA L.). K. Segobye*1, S. C. Weller2, B. Schulz1; 1University of Maryland, College Park, MD, 2Purdue University, West Lafayette, IN (23)


Giant ragweed (Ambrosia trifida L.) is a competitive, annual weed. The introduction of glyphosate resistant agronomic crops (“Roundup®-ready”) in 1996 provided an effective tool to manage giant ragweed. The physiological mechanism of glyphosate’s herbicide effect is inhibition of EPSPS, a key enzyme in the shikimate pathway. The use of glyphosate drastically increased after 1996 in glyphosate resistant crops. This resulted in tremendous selection pressure for glyphosate resistant giant ragweed (GRGR). The development of glyphosate resistance in weeds continues to be agronomic threat in herbicide based weed management systems hence the importance of weed control. We are investigating the mechanism(s) of glyphosate resistance in GRGR biotypes. The goal of our project is to discover glyphosate resistance genes. We hypothesize that the basis of resistance in GRGR biotypes is related to reduced translocation of glyphosate and a rapid response of glyphosate treated leaves in GRGR, which show a hypersensitive-like (HR) reaction to herbicide treatments. This HR results in leaf abscission within few days of treatment. GRGR plants do not die from glyphosate treatments but re-grow from shoot and axillary meristems and reproduce. Glyphosate sensitive plants transport the herbicide throughout the entire plant, which leads to leaf chlorosis and eventual death of the treated plants after 2-3 weeks.

The progression of the response and symptoms in GRGR when treated with glyphosate resemble a typical hypersensitive response similar to that observed on some plants after pathogen attack. To assess the reaction of sensitive and resistant biotypes to glyphosate on the molecular level we analyzed the total transcriptome of treated and untreated plants after glyphosate application. We have identified a list of genes that were differentially expressed between the two biotypes as the first step in identifying genes responsible for the glyphosate resistance observed. We also study the pathogen response pathway in plants and assess the role of defense hormone salicylic acid (SA) and secondary messengers like reactive oxygen species (ROS) particularly hydrogen peroxide as basic immune signals and how they are involved plant’s response to glyphosate treatment. We further study the inheritance of resistance of giant ragweed to glyphosate though classical genetic approaches. F1 hybrids exhibited similar level of injury to the R parental population at all four glyphosate dosages. Segregation analysis of F2 and backcross populations indicate that a single, completely dominant nuclear gene confers the resistance to glyphosate in this giant ragweed biotype. F2 populations segregated in a 3:1 ratio of R and S phenotypes while backcross populations segregated in a 1:1 (R:S). The single dominant gene inheritance observed in this study is consistent with the inheritance of herbicide resistance in most weeds. This implies that glyphosate resistance in giant ragweed will spread rapidly and continue to be selected if glyphosate is continued to be used as a sole weed control tool. With this information on inheritance of glyphosate monogenic resistance in giant ragweed, the R biotype offers an exceptional system for mapping and characterization of this gene. 


2,4-D DISLODGE FROM TURFGRASS VEGETATION VARIES BY SAMPLE COLLECTION METHOD. M. Jeffries*, T. Gannon; North Carolina State University, Raleigh, NC (24)


Established turfgrass canopies inherently intercept foliar-applied pesticides, which can be dislodged through various routes onto humans.  For this reason, dislodgeable pesticide residue experiments are required for registration and re-registration.  However, limited specificity is required pertaining to pesticide dislodge measurement.  Field research was conducted (Raleigh, NC) to quantify 2,4-D dislodge via three measurement approaches across three treated turfgrass species. Dislodge measurements included cotton glove hand wipe, modified California roller (moving a roller over cotton cloth) and soccer ball roll (wrapped with sorbent strip), which were conducted on creeping bentgrass (Agrostis stolonifera L.; 0.4 cm), hybrid bermudagrass (Cynodon dactylon x C. transvaalensis; 5 cm) and tall fescue (Lolium arundinaceum [Schreb.] Darbysh.; 9 cm).  Results suggest 2,4-D dislodge varies across sampling methods and turfgrass species.  Overall, 2,4-D dislodged ranked hand wipe > modified California roller > soccer ball roll, while turfgrass species ranked hybrid bermudagrass > creeping bentgrass > tall fescue.  This information may be used to preserve 2,4-D use in turfgrass systems through improved approaches for human pesticide exposure risk assessments.

INFLUENCE OF BIOCHAR AMENDMENTS ON THE SORPTION&NDASH;DESORPTION OF AMINOCYCLOPYRACHLOR IN AGRICULTURAL SOILS. K. F. Mendes*1, K. A. Spokas2, V. L. Tornisielo3; 1Center of Nuclear Energy in Agriculture - University of São Paulo, Piracicaba, Brazil, 2University of Minnesota, Saint Paul, MN, 3University of São Paulo, Piracicaba, Brazil (25)




Widespread occurrence of glyphosate-resistant (GR) weeds in the Midwestern United States, especially species with certain degree of open pollination, have warranted to determine the role of pollen mediated gene flow (PMGF) in dispersal of resistance genes. Field experiments were conducted in 2014 and 2015 at the South Central Agricultural Laboratory (SCAL), Clay Center, NE to quantify PMGF from GR to –susceptible (GS) giant ragweed under non-crop field conditions using GR phenotype as a selective marker. The experiments were conducted by using a modified Nelder wheel design with the pollen source (GR giant ragweed) planted in the center and the pollen receptors (GS giant ragweed) planted surrounding the center in eight directional blocks (cardinal: N, S, E, and W; ordinal: NE, NW, SE, and SW) at specified distances (0.1, 0.5, 1, 2, 4, 10, 15, 25, and 35 m for all cardinal and ordinal directions; and additional 50 m for the ordinal directions) from the pollen source. Seeds were harvested from the pollen receptor blocks from all distances and a total of 100,938 giant ragweed plants were screened with 2× (× = 1,260 g ae ha–1) rate of glyphosate and 16,813 plants were confirmed resistant to glyphosate. The frequency of PMGF from all the distances and directions were fit to a double exponential decay model selected by information-theoretic criteria using Generalized Nonlinear Model (gnm) library in R. The highest frequency of gene flow (0.43 to 0.60) was observed at ≤ 0.5 m distance from the pollen-source and the frequency of gene flow reduced rapidly with increasing distances from the pollen source; however, gene flow (< 0.05) was detected even up to 50 m distance, the highest distance evaluated in this study. Averaged across all directions, PMGF reduced by 50% (O50) at ≤ 7 m distance from the pollen source, whereas 90% reduction (O90) occurred at < 107 m distance. The results of this study are important to understand the reproductive biology of giant ragweed and confirmed that PMGF is an important means for dispersal of resistance genes in this species.



Studies were carried out for identification and quantification of phenolic compounds present in sunflower shoot and root extracts at different growth stages (1 week, 1 month, 2 month and mature stage). High performance liquid chromatography (HPLC) was used for identification and quantification of phenolic compounds. Four phenolic acids present in root extracts from 1 week 1 month, 2 month and mature stage were identified and quantified.  These were: protocatechuic acid, catechol ferulic acid, caffeic acid and trans-cinnamic acid. Five phenolic acids were identified in sunflower shoot 1 week old: protocatechuic acid, catechol, ferulic acid, caffeic acid and trans-cinnamic acid. Twelve phenolic acids were identified in sunflower shoot extracts from 1 month, 2 months and mature stage: gallic acid, syringic acid, vanillic acid, protocatechuic acid, catechol, 4-hydroxybenzoic acid, p-coumaric acid, sinapic acid, ferulic acid, caffeic acid, chlorogenic acid, and trans-cinnamic acid). The study showed that sunflower shoot 2 months old produces the highest concentration of total phenolic acids. Also, the investigation of individual phenolic acids identified within sunflower 2 month old on seed germination and seedling growth of Brassica napus, Cephalaria syriaca, Triticum aestivum and Secale cereale were investigated in petri dishes. Results indicated that total phenolic acids, sinapic acid, ferulic acid, gallic acid, p-coumaric acid ferulic acid and caffeic acid significantly reduced seed germination (P < 0.001). Shoot and root length were significantly affected by the most phenolic acids (P < 0.001). Total phenolic acids significantly reduced shoot dry weight of S. cereale .Root dry weight was significantly reduced by total phenolic acids, chlorogenic acid, caffeic acid, and protocatechuic acid (P < 0.001).  In conclusion, results indicated that total phenolic acids had the greatest significant reduction in seed germination and seedling growth followed by chlorogenic acid and caffeic acid. 



Intensive use of herbicides has led to the evolution of herbicide resistant weed populations that cause substantial crop yield losses and increase production costs. The multiple herbicide resistant (MHR) Avena fatua L. populations utilized in these studies are resistant to members of all selective herbicide families, across five modes of action, available for A. fatua control in small grain crops, and thus pose significant agronomic and economic threats. Resistance to ALS and ACCase inhibitors is not conferred by target site mutations, indicating that nontarget site resistance (NTSR) mechanisms are involved. To investigate the physiological mechanisms of NTSR, we compared the transcriptomes, proteomes, and known herbicide-metabolizing enzymes of untreated MHR and herbicide susceptible (HS) A. fatua populations. For the transcriptome study, RNA samples were subjected to Illumina HiSeq high-throughput sequencing, differentially regulated proteins were identified by two-dimensional difference gel electrophoresis (2D-DIGE) analyses, and kinetic enzyme assays were conducted to compare enzymes of GSH conjugation and related activities. Enzyme assays showed that MHR plants contain slightly elevated rates of glutathione S-transferases and dehydroascorbate reductase activities. Compared to HS plants, MHR plants contained constitutively elevated levels of a number of differentially expressed genes (DEGs) with functions in xenobiotic catabolism, stress response, redox maintenance, and transcriptional regulation. Comparisons of abundant soluble proteins via 2D-DIGE revealed functionally similar suites of elevated proteins in MHR plants, as well as biosynthetic enzymes and multifunctional proteins. Of 25 DEGs validated by RT-qPCR assay, differential regulation of 21 co-segregated with flucarbazone resistance in F3 families. A subset of 10 of these were induced or repressed in flucarbazone-treated HS plants, indicating that both groups could be considered as candidate NTSR genes. These three independent but complementary surveys of transcripts, proteins, and enzymes from MHR and HS A. fatua plants revealed key insights into the physiological alterations associated with the MHR phenotype. Although their individual and collective contributions to MHR remain to be determined, our results support the idea that MHR plants possess an altered, constitutively-regulated system of stress-related gene expression. 

INVESTIGATING THE 2,4-D RESISTANCE MECHANISM IN INDIAN HEDGE MUSTARD (SISYMBRIUM ORIENTALE) FROM AUSTRALIA USING RNA-SEQ. A. Kuepper*1, C. Preston2, M. Figueiredo1, T. A. Gaines1; 1Colorado State University, Fort Collins, CO, 2University of Adelaide, Adelaide, Australia (29)


Indian Hedge Mustard (Sisymbrium orientale) is a major weed of cereals in Australia due to crop competition, physical blockage of harvesters, and seed contamination in grain. In 2013 a population from Port Broughton, South Australia was reported to be resistant to 2,4-D and MCPA, requiring 22 times more herbicide for equivalent control when compared to a susceptible population from Roseworthy, South Australia. The Port Broughton population was also resistant to the sulfonylurea and sulfonamide herbicide groups due to a target-site ALS mutation. However, the mechanism of resistance to the auxinic herbicides remains unknown. Metabolism, absorption, and translocation studies were conducted by applying 14C-labelled 2,4-D on two expanded leaves of plants at the 4-5 true leaf stage. Radioactivity was quantified for translocation and 2,4-D metabolites were measured in the treated leaf and other tissues at 3, 6, 12, 24, 48, 96 and 192 h after treatment. Further, in-situ studies on reactive oxygen species in plant tissue were performed over the course of 13 days. No differences between susceptible and resistant individuals were identified for translocation or metabolism. Next, the transcriptomes of untreated leaf tissue of six homozygous resistant and six homozygous susceptible recombinant inbred individuals were examined to identify candidate genes for 2,4-D resistance. Differential gene expression and variant calling analyses were performed. The results suggest the involvement of genes related to the regulation of transmembrane transporters in the mechanism of 2,4-D resistance.



Authors: Rebecka Dücker1,2, Peter Zöllner1 & Roland Beffa1
1Bayer AG , Frankfurt am Main, Germany; 2General Plant Pathology and Crop Protection, Göttingen, Germany

Sustainable weed control is a major factor protecting crops from yield losses. In an Integrated Weed Management approach (IWM), herbicides are a corner stone technology to ensure an efficient weed control at reasonable costs in modern agriculture. The use of chemistries representing few modes of action during the past years as well as simplified cropping systems have led to the development of herbicide resistance in numerous weeds worldwide. In cereals for example, the development of resistance against post-emergence herbicides, mainly against the inhibitors of ACCase (Group A or 1) and ALS (Group B or 2), has led to increased use of pre-emergence herbicides, including inhibitors of the synthesis of very-long-chain fatty acids (VLCFAs, Group K3 or 15). Among five grass weeds that have developed resistance against this mode of action, two of them are reported as resistant to flufenacet. While the Alopecurus myosuroides field populations reported to have elevated resistance levels to flufenacet could still be controlled by >90% with the registered field rate, this was not the case in several Ryegrass Lolium spp. populations from the United States. A better understanding of the resistance mechanism(s) may help planning an adequate resistance management as well as designing new herbicide structures.  Previous studies on crop tolerance and the structure of the herbicidal target suggest non-target-site resistance as a mechanism. Ryegrass populations carefully characterized in the greenhouse were used to study the flufenacet fate in planta. Using radioactive labelled flufenacet in HPLC and LCMS analyses, we showed enhanced metabolism in flufenacet resistant Lolium spp. and detected flufenacet-glutathione conjugates, suggesting glutathione S-transferase activity as the key step in flufenacet detoxification.


BARNYARDGRASS RESISTANT TO ACETOLACTATE SYNTHASE AND ACETYL-COA CARBOXYLASE INHIBITORS IN PADDY RICE FIELDS OF KOREA. O. Won*1, I. Park2, Z. Andreas3, S. Vinod4, J. Lee5, K. Park1; 1Chungnam National University, Daejeon, South Korea, 2Syngenta Korea Limited, JinCheon, South Korea, 3Syngenta Crop Protection AG, Basel, Switzerland, 4Syngenta Asia Pacific Pte. Ltd, Singapore, Singapore, 5National Institute of Agricultural Sciences, Wanju, South Korea (31)


Barnyardgrass Resistance to Acetolactate Synthase and Acetyl-CoA Carboxylase Inhibitors in Paddy Rice Fields of Korea

 Ok Jae Won1*, Inkon Park2, Vinod K. Shivrain3, Jeongran Lee4, Kee Woong Park1

 1 Department of Bio-Environment, Chungnam National University, Daejeon 34134, Korea

2 Syngenta Korea Limited, JinCheon 27855, Korea

3 Syngenta Asia Pacific Pte. Ltd., No. 1 Harbour Front Avenue #03-03 Keppel Bay Tower Singapore 098632

4 National Institute of Agricultural Sciences, RDA, Wanju 56365, Korea

 The continuous use of acetolactate synthase (ALS) and acetyl-CoA carboxylase (ACCase) inhibiting herbicides has led to the selection of herbicide resistant barnyardgrass (Echinochloa crus-galli) populations in rice (Oryza sativa) fields. In Korea, the first resistance to ALS inhibitors was reported in Monochroria korsakowii in 1998 (Park et al. 1999). Since then, 14 weed species have developed resistance to ALS inhibitors (Heap, 2014). This study was conducted to identify herbicide-resistant barnyardgrass and to determine cross- and multiple-resistance in Korea. We collected barnyardgrass seeds from 1,435 survivor individual plants at 66 sites in seven locations from Sep. to Oct. 2015. Collected barnyardgrass seeds were immersed in 4℃ water for 30 days to break the dormancy of seeds. Seedlings were grown in a glass house and herbicides were applied 14 days after sowing. Three ALS inhibitors, sulfonylurea (flucetosulfuron), pyrimidinyoxybenzoic acid (pyriftalid), and trizolopyrimidine (penoxsulam), and two ACCase inhibitors, cyclohexanediones (sethoxydim) and aryloxyphenoxypropionate (cyhalofop-P-butyl), were used to determine the presence or absence of resistance. Seedling response to herbicides was rated visually 14 days after treatment. Four hundred and eight plants out of 1,435 were resistant to at least one of the ALS or ACCase inhibiting herbicides. Among those, the highest number of resistant plants was found in Jeonbuk region (56.6%). Out of 408 resistant plants, 371 were resistant to ALS inhibitors and 37 plants were resistant to ACCase inhibitors. Approximately 56% of plants showed resistance to a ALS inhibitor, penoxsulam (the maximum percentage for ALS inhibitors). Ninety-nine plants were resistant to at least two ALS inhibitors and 11 plants were resistant to three ALS inhibitors. Twenty-five plants were resistant to both ALS and ACCase inhibitors. The continuous use of these herbicides in rice fields will increase populations of herbicide-resistant barnyardgrass. Alternative control methods should be used to control herbicide-resistant barnyardgrass in the infested fields.

 * This research was supported by Syngenta.

INVESTIGATING MULTIPLE RESISTANCE MECHANISMS OF AMARANTHUS PALMERI POPULATIONS FROM ARKANSAS. R. A. Salas*1, C. Oliveira1, J. Refatti1, L. Piveta1, R. Scott2, N. R. Burgos1; 1University of Arkansas, Fayetteville, AR, 2University of Arkansas-Cooperative Extension Service, Lonoke, AR (32)


Amaranthus palmeri is a highly competitive, prolific weed that has become one of the most troublesome weeds in several cropping systems throughout the Unites States. Its extensive genetic variability coupled with intense herbicide selection pressure resulted in the evolution of herbicide-resistant populations. While resistance to a single mode of action (MOA) is a concern, resistance to multiple MOA poses a larger threat. Glyphosate and ALS- resistant A. palmeri is widespread in the southern United States. Recently, resistance to PPO-inhibiting herbicides in A. palmeri was identified in Arkansas. The objectives of this research were to (1) confirm multiple resistance to glyphosate, ALS- and PPO-inhibiting herbicides and (2) investigate herbicide resistance mechanisms in two A. palmeri populations from Arkansas. Dose response assays were conducted to evaluate the resistance level to fomesafen, glyphosate, and trifloxysulfuron. Quantitative PCR was performed to determine EPSPS copy number. A PCR-based assay was used to detect the presence of PPO Gly210 mutation known to confer resistance to PPO-inhibiting herbicides. Trifloxysulfuron metabolism was evaluated indirectly using known P450 enzyme inhibitors- carbaryl, malathion, and piperonyl butoxide. Population 15-CLA-A was 25-, 78-, and 4-fold more resistant to fomesafen, glyphosate, and trifloxysulfuron, respectively, compared to the sensitive population (SS). The 15-CRI-B population exhibited 3-, 34-, and 4-fold resistance level to fomesafen, glyphosate, and trifloxysulfuron, respectively, relative to SS. Resistance to glyphosate in 15-CLA-A and 15-CRI-A populations is due to EPSPS gene amplification with copies ranging from 24 to 167. PPO-resistant plants in 15-CLA-A carried the PPO Gly210 mutation; however, resistant plants from 15-CRI-B did not carry the Gly210 mutation. Trifloxysulfuron controlled 15-CLA-A only 26%; the addition of malathion and piperonyl butoxide enhanced its activity to 50%. The P450 inhibitors did not completely overcome the resistance indicating that P450-mediated metabolism is partially responsible for resistance to trifloxysulfuron, or that other P450 enzymes besides those inhibited by these pesticides, are involved. Therefore, some A. palmeri populations from Arkansas such as 15-CLA-A have both target-site and nontarget-site resistance mechanisms to three modes of action. Multiple herbicide-resistant A. palmeri is a serious threat to sustainable weed management because metabolism-based mechanism can convey broader resistance. Integrated weed management programs should be implemented to curtail further spread of resistance. 




Since the mid 1940’s herbicides have been the most cost effective and efficient method of weed control in agronomic crops.  Today herbicide-resistant weeds, in combination with a decline in industry discovery programs and a cessation in discovery of new herbicide sites of action, threaten the continued utility of herbicides.  The International Survey of Herbicide-Resistant Weeds records the occurrence of herbicide-resistant weeds globally and is online at  There are currently 478 unique cases (species x site of action) of herbicide resistant weeds globally, with 252 species (147 dicots and 105 monocots). Weeds have evolved resistance to 23 of the 26 known herbicide sites of action and to 161 different herbicides. Herbicide-resistant weeds have been reported in 91 crops and in 67 countries.  In the 1970’s triazine-resistant weeds presented problems in corn production, followed by resistance to ALS and ACCase-inhibitor resistant-weeds in corn, soybean, wheat, and cotton.  The introduction of Roundup Ready crops in 1996 initially solved many of the existing problems of PSII, ACCase, and ALS inhibitor resistant weeds, but over reliance on glyphosate without sufficient integration of management practices resulted in selection of 36 glyphosate resistant weeds. Half of these were selected in Roundup Ready crops, and the others appeared in orchards, vineyards, non-crop areas and fallow.  Industries response to the growing list of glyphosate-resistant weeds is to genetically engineer crops to resist existing herbicides (particularly synthetic auxins) so that they can be used in new situations.  This will only be a temporary solution, as weeds already resistant to glyphosate will quickly evolve resistance to these other herbicides if they are used as the primary method of weed control.  Weeds will evolve resistance to any selection pressure and we should aim to diversify the number of ways in which weeds are controlled (using all available economic weed control measures) to destabilize evolution.  Herbicides are likely to remain the backbone of agronomic weed control for the next 30 years, however their utility will steadily decline, and we need to begin working on new weed control technologies that will eventually replace herbicides.



Glyphosate-resistant (GR) weeds pose a serious threat to no-till, GR cropping systems and cereal production systems of the Northern Great Plains, including Montana. During summer/fall 2015, seeds of one putative GR Russian thistle (GR-RT) population and one GR horseweed (GR-H) population were collected from wheat-fallow fields in Choteau and McCone counties, MT, respectively. The objectives of this research were to confirm and characterize the levels of glyphosate resistance in these GR populations relative to known glyphosate-susceptible (GS-RT from MT and GS-H from NE, respectively) populations, and to determine the effectiveness of POST herbicides (labelled in wheat-fallow rotation) for controlling these GR populations. Whole-plant glyphosate dose-response experiments indicated that the GR-RT population exhibited 4.5-fold resistance to glyphosate relative to the GS-RT population on the basis of shoot dry weight response (GR50 values). On the basis of percent control ratings (I50 values), the GR-H population exhibited 3.1-fold resistance to glyphosate relative to the GS-H population. Among alternative POST herbicides to control GR Russian thistle, bicyclopyrone + bromoxynil, bromoxynil + fluroxypyr, bromoxynil + pyrasulfotole, bromoxynil + MCPA, paraquat alone, paraquat + metribuzin, saflufenacil alone, saflufenacil + 2,4-D, and 2,4-D + bromoxynil + fluroxypyr provided effective control (≥95%) and shoot dry weight reduction (up to 98%) of GR population. In a separate greenhouse study, POST herbicides including bromoxynil + pyrasulfotole, dicamba alone, dicamba + diflufenzopyr + 2,4-D, 2,4-D alone, fluroxypyr + clopyralid + MCPA, glufosinate, paraquate alone, paraquat + metribuzin, saflufenacil, saflufenacil + 2,4-D, thifensulfuron + tribenuron + clopyralid + fluroxypyr   provided ≥ 90% control of GR horseweed at 21 d after treatment (DAT). This study confirmed the first global case of GR Russian thistle and occurrence of GR horseweed in Montana, and also revealed the effective POST herbicides for controlling these GR populations. Growers should utilize these herbicide programs (based on multiple mechanisms of action highlighted in this study) to manage GR Russian thistle and horseweed populations in their production fields.




DISSIPATION OF CLOMAZONE IN ORGANIC AND MINERAL SOILS OF SOUTH FLORIDA. D. Odero*, J. V. Fernandez; University of Florida, Belle Glade, FL (36)


Clomazone is used for preemergence control of many broadleaf weeds and grasses in sugarcane. Understanding the persistence of clomazone in Florida sugarcane fields is important for determining timing of subsequent weed management programs. However, currently there is no information on dissipation of clomazone in Florida sugarcane fields. Therefore, field studies were conducted in 2015-2016 to determine field dissipation of clomazone applied preemergence in sugarcane grown in mineral soils in Florida. Clomazone was applied at 1.12 kg/ha immediately after sugarcane planting. Clomazone initially dissipated rapidly in Florida sugarcane mineral soil. The half-life of clomazone in the mineral soil was 32 days. Further studies on dissipation of clomazone on other mineral and organic soils used for sugarcane cultivation in Florida will be used to corroborate the present results. 


MECHANISMS INVOLVED IN GLYPHOSATE-RESISTANT PERENNIAL RYEGRASS (LOLIUM PERENNE L.) AND ITALIAN RYEGRASS (L. MULTIFLORUM L.) BIOTYPES FROM IBERIAN PENINSULA AND FITNESS COST ASSOCIATED TO NTSR MECHANISM. P. T. Fernandez-Moreno*1, R. Roldan-Gomez2, M. D. Osuna3, R. J. Smeda4, R. De Prado5; 1University of Cordoba, Cordoba, Spain, 2Department of Agricultural Chemistry and Edaphology-UNC, Cordoba, Spain, 3Agrarian Research Center “Finca La Orden” Valdesequera, Badajoz, Spain, 4University of Missouri, Columbia, MO, 5Department of Agricultural Chemistry and Edaphology, University of Cordoba, Cordoba, Spain (37)


Multiple mechanisms of glyphosate-resistance are exhibited by perennial (Lolium perenne) and Italian ryegrass (L. multiflorum) populations worldwide.  Association of resistance with growth and reproductive fitness cost is an important predictor for long-term success of glyphosate-resistant (R) versus glyphosate-susceptible (S) biotypes. Numerous studies were conducted on R and S biotypes of Italian ryegrass and perennial ryegrass to characterize the underlying mechanism of glyphosate resistance. For Italian ryegrass (Douro), the R:S LD50 value for biomass accumulation was 4.2.  The underlying resistance mechanism is associated with a 40% reduction in 14C-glyphosate uptake at 96 hours after treatment (HAT) and up to 34% less translocation from treated leaves to other plant tissue.  Non-target site mechanisms was involved in R glyphosate Douro biotype. In perennial ryegrass (Golf), the R:S LD50 was 5.9; uptake of the R versus S biotype was 26% lower at 96 HAT and translocation out of treated leaves was 30% lower. R Golf biotype exhibited 5.3-fold higher constitutive levels of EPSPs activity and a mutation in 106-Pro was identified. Target site mechanisms was involved in R glyphosate Golf biotype. Reduced fitness cost of plant biomass and height for R versus S into Douro biotypes was evident over two growing seasons. This resulted in S Douro producing up to 47 and 38% more seeds in 2014 and 2015, respectively.  However, there were no differences found in both plant biomass and production seeds between Golf biotypes. Non-target site mechanisms of glyphosate resistance can place Lolium spp. at a competitive disadvantage.  This has long-term implications for the success of glyphosate-resistant plants in the absence of selection pressure.

Keywords: Italian ryegrass; perennial ryegrass; glyphosate; resistance; fitness cost


DIFFERENT LEVELS OF GLYPHOSATE-RESISTANT RIGID RYEGRASS (LOLIUM RIGIDUM L.) BIOTYPES FROM SOUTHERN SPAIN AND FRANCE. P. T. Fernandez-Moreno1, R. Roldan-Gomez2, M. D. Osuna3, R. J. Smeda4, R. De Prado*5; 1University of Cordoba, Cordoba, Spain, 2Department of Agricultural Chemistry and Edaphology-UNC, Cordoba, Spain, 3Agrarian Research Center “Finca La Orden” Valdesequera, Badajoz, Spain, 4University of Missouri, Columbia, MO, 5Department of Agricultural Chemistry and Edaphology, University of Cordoba, Cordoba, Spain (38)


Herbicides are the most effective weed control tools ever developed, controlling almost 99% of the weeds. However, herbicide-resistant is the primary concerns in modern agriculture. Glyphosate is one of the many other herbicides which herbicide-resistant in several weeds has been documented. The resistance characterization in new areas and elucidate their mechanisms is of vital importance. Nine populations from olive groves, vineyards and wheat crops from southern Spain and France were characterized as glyphosate-resistance (R) with diversity of results. The Line-3 population obtained the maximum fresh weight reduction and survival values with respect to the susceptible (S) population, showing 16.05 and 17.90-fold higher resistance. The wide range of values in fresh weight reduction, survival, shikimic acid and EPSPS enzyme activity indicate that there can be different mechanisms of resistance involved in these R-populations. The results range from 32% (lower absorption) for the R-populations to 85% (higher absorption) for the S-population. There were significant differences in 14C-glyphosate translocation between R and S-glyphosate populations. Even there were differences between the nine R-glyphosate populations, but all of them exhibited a reduction in glyphosate translocation remaining in the treat leaf. There were no significant differences in glyphosate metabolism between R- and S-populations.  EPSPS gene sequence revealed a Pro-106-Ser substitution in four populations. Therefore, these four populations were characterized as R-glyphosate with non-target-site and target-site resistance mechanisms involved.




Conservation agriculture hecterage in the mid-south and southeastern US has decreased because of herbicide resistant and other hard to control weeds. Producers have increasingly utilized tillage, the majority either using a moldboard plow to deeply bury weed seed and decrease emergence, or ‘vertical tillage’ to decrease surface residue in an effort to increase soil active herbicide placement and subsequent activity; soil health consequences be damned.  However, high residue cover crops integrated with efficacious herbicide systems could protect yield, and preserve conservation agriculture practices and salvation for associated soil health indicators.  Two nearly identical, four year conservation tillage cotton experiments, were established in fall 2012 at Auburn University’s EV Smith Research and Extension Center, near Shorter, AL.   Plots were maintained with the same treatment each subsequent year until experiment completion.  Both experimental fields contained majority glyphosate susceptible Palmer amaranth, among other weeds, at initiation. In both experiments, cereal rye (Secale cereale L.) was established in half of the plots and managed for maximum biomass, while the remainder was managed herbicide fallow.  In the glyphosate tolerant cotton experiment, for the first three years of the experiment, the factorial herbicide treatments included: 1) glyphosate applied at 1.12 kg ae/ha plus metolachlor applied at 1.12 kg ai/ha EPOST at cotton 2-leaf growth stage, 2) glyphosate applied at 1.12 kg ae/ha plus metolachlor applied at 1.12 kg ai/ha POST at cotton 8-leaf growth stage, or 3) flumioxazin 0.071 kg ai/ha applied as a PDS when cotton reached 45 cm height.  In the glufosinate tolerant cotton experiment, for the first three years of the experiment, the factorial herbicide treatments included: 1) glufosinate applied at 0.59 kg ai/ha plus metolachlor applied at 1.12 kg ai/ha EPOST at cotton 2-leaf growth stage, 2) glufosinate applied at 0.59 kg ai/ha plus metolachlor applied at 1.12 kg ai/ha POST at cotton 8-leaf growth stage, or 3) flumioxazin 0.071 kg ai/ha applied as a PDS again when cotton reached 45 cm height.  A non-treated control was included in both studies for comparison.  In the fourth year, dicamba (applied at 0.56 kg ai/ha) replaced glyphosate or glufosinate in all treatments in each respective experiment.  In 2013, in both experiments, early Palmer amaranth control exceeded 95% in rye and fallow systems following glyphosate or glufosinate EPOST.  However by late season, glyphosate applied EPOST fb POST fb flumioxazin provided 83% in plots containing a rye cover crop, and control was substantially lower in all other treatments.  In 2013 in the glufosinate experiment, sequential glufosinate applications EPOST fb POST or glufosinate applied EPOST followed by flumioxazin PDS when a rye cover was present, provided 99% late season control.  However, in the winter fallow system, glufosinate EPOST fb POST fb flumioxazin PDS was needed to attain 99% control Palmer amaranth full season.  Following decreasing Palmer control in 2014, in 2015 in the glyphosate experiment, no herbicide treatment provided >80% early control in cereal rye containing plots, and plots without three herbicide applications resulted in ≤ 67% control in all plots.  Control late season never exceeded 30% in the glyphosate experiment. In the glufosinate system, 95% or 93% late season control was attainable only in rye or fallow containing plots, respectively, when glufosinate was applied EPOST fb POST fb flumioxazin PDS.  In 2016, Palmer amaranth control with dicamba was increased across all treatments following both glufosinate and glyphosate experiments, levels observed at the initiation of this experiment or higher late season.  Cotton yield followed observed weed control; averaged over herbicide treatments, cereal rye containing plots yielded higher one out of three comparisons in the glufosinate treatments, and were equal following glyphosate in all three years of comparison.  In 2016, averaged over dicamba herbicide treatments, yields were again equivalent between cereal rye plots and winter fallow, following either glufosinate or glyphosate experiments.  One notable observation:  when glyphosate resistance in the glyphosate experiment increased, control in the adjoining glufosinate experiment decreased, likely due to weed seedbank additions, and loss of control due to sheer population size attributes.  




PRE-EMERGENCE HERBICIDE LONGEVITY ON PALMER AMARANTH CONTROL IN COTTON. S. Steckel*, J. Reeves, L. E. Steckel; University of Tennessee, Jackson, TN (41)


Longevity of herbicides is one key goal to long-term sustainability for a farmer.   In 2016 fomesafen in numerous cases did not provide the length of residual Palmer amaranth control seen in previous years. More weed control diversity is clearly needed which makes necessary that new herbicides and different approaches be utilized in the years ahead.  Applications of burndown, pre-emergence, and post emergence choices are necessary to survive a cotton season.  Stretching out these applications can be risky business, but with the right herbicide choices could this be possible? 

Fluridone + fluometuron has the potential to be a new choice for consistent pre-emergence control of Palmer in cotton.  This group 12 & 7 herbicide needs at least 0.5 inch of rain or irrigation to be activated.  It is also suggested to make a post herbicide application of choice 12-16 days after planting.   The longevity of this pre-emergence herbicide was assessed in comparison to other commonly used pre-emergence herbicides in hopes it will eventually be a good option for cotton farmers. 

A field study was conducted in 2016 at the West TN Research and Education Center in Jackson, TN.  The objective of this trial was to compare the residual activity of the pre-mix herbicide fluridone + fluometuron to five other commonly used pre-emergence herbicides in cotton for the control of Palmer amaranth.  Multiple visual ratings were taken to determine crop safety and the control of Palmer amaranth. 

Two rates of fluridone + fluometuron were applied as a pre; a 1x rate (32 oz/a) and a tank mixture of .5 x rate (16 oz/a) + 16 oz/a of dicamba.  Both treatments provided longer residual control of Palmer amaranth and caused similar or less injury to cotton when compared to local standards.  This showed that fluridone + fluometuron can have a longer lasting residual and the potential to be a good option as a pre-emergence herbicide.

CROP SAFETY AND WEED CONTROL FOLLOWING DICAMBA AND ACETOCHLOR AAPPLICATIONS IN XTENDFLEX® COTTON. L. X. Franca*1, D. M. Dodds1, J. Bond2, D. B. Reynolds3, A. Mills4, C. A. Samples1, M. T. Plumblee1, A. B. Denton3; 1Mississippi State University, Starkville, MS, 2Mississippi State University, Stoneville, MS, 3Mississippi State University, Mississippi State, MS, 4Monsanto Company, Memphis, TN (42)


Crop Safety and Weed Control Following Dicamba and Acetochlor Applications in XtendFlexTM cotton. L. X. Franca*1, D. M. Dodds1, C. A. Samples1, D. B. Denton1, D. B. Reynolds1, J. A. Bond1, A. Mills2; 1Mississippi State University, Mississippi State, MS, 2Monsanto Company, Saint Louis, MO.


Given the proliferation of glyphosate-resistant Palmer amaranth (Amaranthus palmeri S. Wats) and tall waterhemp [Amaranthus tuberculatus (Moq.) Sauer] throughout the United States, efficacious and cost effective means of control are needed. XtendFlexTM Technology from Monsanto allows postemergene application of dicamba, glyphosate, and glufosinate to cotton containing this technology. Herbicide programs with multiple site of actions (SOAs) generally have the greatest effect in delaying herbicide resistance yet optimizing weed control. Research was conducted to evaluate herbicide efficacy and crop injury of acetochlor (WarrantTM) and dicamba (XtendiMaxTM) applied PRE and POST for Palmer amaranth and tall waterhemp control in XtendFlexTM cotton. 

Experiments were conducted at Hood Farms in Dundee, MS, the Delta Research and Extension Center in Stoneville, MS, and the R. R. Foil Plant Science Research Center in Starkville, MS. The following PRE and POST herbicide programs were evaluated for Palmer amaranth and tall waterhemp control: 1) dicamba at 0.56 kg ae/ha + acetochlor at 1.26 kg ai/ha (PRE) fb dicamba + glyphosate at 1.68 kg ae/ha + acetochlor at 1.26 kg ai/ha (3-4 leaf cotton) fb dicamba + glyphosate at 1.68 kg ae/ha (6-8 leaf cotton); 2) dicamba at 0.56 kg ae/ha + acetochlor at 1.26 kg ai/ha (PRE) fb dicamba + glyphosate at 1.68 kg ae/ha (3-4 leaf cotton) fb dicamba + glyphosate at 1.68 kg ae/ha + acetochlor at 1.26 kg ai/ha (6-8 leaf cotton); 3) dicamba at 0.56 kg ae/ha + acetochlor at 1.26 kg ai/ha (PRE) fb dicamba + glyphosate at 1.68 kg ae/ha (3-4 and 6-8 leaf cotton); 4) dicamba at 0.56 kg ae/ha (PRE) fb dicamba + glyphosate at 1.68 kg ae/ha + acetochlor at 1.26 kg ai/ha (3-4 leaf cotton) fb dicamba + glyphosate at 1.68 kg ae/ha (6-8 leaf cotton); 5) dicamba at 0.56 kg ae/ha (PRE) fb dicamba + glyphosate at 1.68 kg ae/ha (3-4 leaf cotton) fb dicamba + glyphosate at 1.68 kg ae/ha + acetochlor at 1.26 kg ai/ha (6-8 leaf cotton); 6) dicamba at 0.56 kg ae/ha (PRE) fb dicamba + glyphosate at 1.68 kg ae/ha + acetochlor at 1.26 kg ai/ha (3-4 and 6-8 leaf cotton); 7) dicamba at 0.56 kg ae/ha (PRE) fb dicamba + glyphosate at 1.68 kg ae/ha (3-4 and 6-8 leaf cotton). The PRE application was applied immediately after planting followed by a 3-4 leaf cotton application two weeks after, followed by a 6-8 leaf cotton application two weeks after the first post application. DP 1522 B2XF was planted in Dundee, MS and Stoneville, MS, and DP1646 B2XF was planted in Starkville, MS. Visual control ratings and cotton injury were taken two weeks after each application. Cotton yield data were also collected from all locations. Data were subjected to analysis of variance and means were separated using Fischer’s Protected LSD at α = 0.05.   

Treatments containing dicamba + acetochlor (PRE) provided greater Palmer amaranth control at mid-post application. Conversely, dicamba + acetochlor (PRE) and dicamba only (PRE) did not significantly differ with respect to tall waterhemp control prior to 14 days after mid-post application. At 14 days after 6-8 leaf cotton application treatments containing acetochlor provided significantly greater Palmer amaranth control, regardless of application timing. Treatments with acetochlor applied PRE and 3-4 leaf cotton, and 6-8 leaf cotton only, provided the greatest Palmer amaranth control at 28 days after 6-8 leaf cotton application. In addition, applications of acetochlor PRE and 6-8 leaf cotton, and 3-4 and 6-8 leaf cotton, resulted in the greatest tall waterhemp control 28 days after 6-8 leaf cotton application. Cotton injury was significantly greater from treatments containing acetochlor. However, no injury was observed 28 days after 6-8 leaf cotton application. Yield differences were not observed on DP 1522 B2XF. Nevertheless, DP 1646 B2XF had significantly greater seed cotton yield on treatments containing two applications of acetochlor, regardless of application timing. The use of acetochlor as part of the XtendFlexTM resulted in effective Palmer amaranth and tall waterhemp control in Mississippi.


WEED MANAGEMENT SYSTEMS IN ENLIST COTTON IN THE TEXAS HIGH PLAINS. P. A. Dotray*1, J. Keeling2, S. L. Taylor2, M. Lovelace3; 1Texas Tech University, Lubbock, TX, 2Texas A&M AgriLife Research, Lubbock, TX, 3Dow AgroSciences, Lubbock, TX (43)


EnlistTM cotton was fully approved for export in August 2016.  The US EPA federally registered Enlist DuoTM herbicide with Colex-DTM Technology in January 2017. Enlist Duo is now registered for use in over 30 states on Enlist cotton, corn, and soybean.  Enlist Duo will be effective on a number of annual and perennial weeds.  PhytoGen has plans to sell several Enlist cotton varieties in the 2017 growing season.  The objective of this study was to evaluate several weed management systems using Enlist Duo and/or 2,4-D Choline in Enlist cotton.  A field study was established at the Texas Tech University Research Farm near New Deal in a field with sub-surface drip irrigation. Plots, 4 rows by 30 feet, were arranged in a randomized complete block design with 4 replications.  Natural populations of glyphosate-susceptible and glyphosate-resistant populations were present.  All plots received a blanket application of Trifluralin at 1 lb ai/A.  Early-postemergence (EPOST) applications were made on June 14 and mid-postemergence (MPOST) treatments were made on July 1.  At 2 weeks after the EPOST application (June 29), Enlist Duo (1.95 lb ai/A) + Dual Magnum (0.955 lb ai/A), 2,4-D Choline (0.95 lb ai/A) + Liberty (0.53 lb ai/A), and 2,4-D Choline + Liberty + Dual Magnum controlled Palmer amaranth at least 91%, while Roundup WeatherMax (1.22 lb ai/A), Liberty, and Enlist Duo controlled this weed 71, 67, and 82%, respectively.  On July 15, 2 weeks after the sequential application, several treatments achieved at least 94% Palmer amaranth control that involved the use of Enlist Duo or 2,4-D Choline:  Enlist Duo EPOST followed by (fb) Enlist Duo MPOST, Enlist Duo + Dual Magnum EPOST fb Enlist Duo MPOST, Enlist Duo EPOST fb 2,4-D Choline + Liberty MPOST, Enlist Duo EPOST fb 2,4-D Choline + Liberty + Dual Magnum MPOST, Liberty + Dual Magnum EPOST fb 2,4-D Choline MPOST, 2,4-D Choline + Liberty EPOST fb Enlist Duo MPOST, 2,4-D Choline + Liberty + Dual Magnum EPOST fb Enlist Duo MPOST, and 2,4-D Choline + Liberty EPOST fb 2,4-D Choline + Liberty MPOST. At 4 weeks after the MPOST treatment (July 28) and just prior to harvest (October), 8 weed management “systems” that involved one or two Enlist Duo and/or 2,4-D choline treatments controlled Palmer amaranth 91 to 94%.  Cotton lint yield ranged from 0 to 1783 lb/A, and the greatest yield tended to follow the most successful Palmer amaranth control.  This study suggests that several effective weed management systems exist when using Enlist Duo/2,4-D Choline in Enlist cotton.  These systems involved 1 or 2 Enlist Duo and/or 2,4-D Choline inputs.  Proper application stewardship will be critical when applying Enlist Duo and/or 2,4-D Choline.  The longevity of this technology from a weed resistance standpoint will involve the use of other herbicide modes of action that include the use soil residual herbicides as part of the “system”.

DICAMBA DOSE IMPACTS ON VARIOUS MATURITY GROUP VI SOYBEAN CULTIVARS. A. M. Growe*, W. J. Everman; North Carolina State University, Raleigh, NC (44)


Dicamba-tolerant crop varieties have the potential to become utilized in North Carolina as a tool to control glyphosate-resistant weeds.  Because of North Carolina's diverse agricultural landscape, and there is growing concern of off-site movement of this broadleaf herbicide to sensitive crops.  Previous research has determined that  soybean cultivars, commonly glyphosate or glufosinate-tolerant varieties, are highly sensitive to dicamba.  Tank contamination, wind drift, and volatility of dicamba can cause injury and reduce soybean yields. To date, there has been little information reported on soybean varietal responses to sub-lethal doses of dicamba. 

The objective of this study was to evaluate the effects of sub-lethal rates of dicamba on five maturity group VI soybean cultivars at the vegeatative and reproductive growth stages.  Effects of dicamba were determined by collecting visual injury ratings, height reductions and yield.  Experiments were conducted in Lewiston, Kinston, and Rocky Mount, North Carolina during 2015 and 2016.  These locations were chosen to represent two different soil types with Kinston being a Portsmouth loam and Lewiston/Rocky Mount consisting of a Rains sand. Five soybean varieties were treated with dicamba at 1.1, 2.2, 4.4, 8.8, 17.5, 35, and 70 g ae ha (1/512 to 1/8 of the labeled use rate for weed control in corn) during the R2 growth stage.  Experiments were conducted using a factorial arrangement of treatments in a randomized complete block design, with factors being dicamba rate, timing and soybean cultivar. Location was considered a fixed effect and all data were subjected to analysis of variance and means were separated using Fisher’s Protected LSD at p= 0.05.

Analysis showed a wide range of visual injury and height reduction 2 and 4 WAT for all 5 varieties.  Higher levels of height reductions and injury were associated with increasing dicamba rates.  When data was pooled across all soybean varieties, timings and soil types, height reductions and visual injury 4 WAT ranged from 8-43 and 16-65%, respectively.  Height reductions 2 and 4 WAT were greater for the vegetative growth stage compared to the reproductive stage. Yield reductions ranged from 7-67% as rate increased from 1.1-70 g ae ha-1.  Analysis revealed a variety soil and timing interaction for yield reduction.  On sand soils, greater yield reduction was observed for the reproductive application but the inverse effect was observed on loam soils.  Not only does the data suggest there is a varietal response, there are also implications that environmental factors (such as soil type, precipiatation, temperature) heavily influence soybeans response to dicamba drift.


WEED MANAGEMENT PROGRAMS IN OKAHOMA SOYBEAN. T. A. Baughman*, D. L. Teeter, C. D. Curtsinger, R. W. Peterson; Oklahoma State University, Ardmore, OK (45)


Weed Management Programs in Oklahoma Soybean.  T. A. Baughman1, K.E Cole2, M. R. Manuchehri2, R. W. Peterson1, and D. L. Teeter1. 1Oklahoma State University, Ardmore, OK and 2Oklahoma State University, Stillwater, OK.


Balance™ GT and Roundup Ready 2 Xtend® soybeans have the potential to effectively manage difficult-to-control weeds in Oklahoma soybean, including glyphosate resistant Palmer amaranth (Amaranthus palmeri S. Wats.). Weed management systems trials assessed the effectiveness of these two technologies at Bixby and Chickasha, OK in 2016. The Balance™ GT trial consisted of various preemergence (PRE) treatments followed by a post emergence (POST) application of glufosinate + S-metolachlor + fomesafen. Three Xtend® trials, two evaluating XtendiMax™ and one assessing Engenia™, included PRE, early postemergence (EPOST) and mid-postemergence (MPOST) applications. Visual crop injury and weed control were evaluated 2, 4, 6, 8, and 10 weeks after planting (WAP) and yield was recorded for the two Xtend® trials that evaluated XtendiMax™. Target weed species included ivyleaf morningglory (Ipomoea hederacea Jacq.), large crabgrass (Digitaria sanguinalis L.), and Palmer amaranth. One to 3% percent soybean injury was observed in Balance™ GT trials 6 WAP; however, no injury was noted by 8 weeks. All treatments controlled ivyleaf morningglory 100% 10 WAP. Palmer amaranth was controlled 99% with isoxaflutole at 0.105 kg ai ha-1 + metribuzin; flumioxazin + pyroxasulfone; chlorimuron + flumioxazin + thifensulfuron; and acetochlor + metribuzin applied PRE. Soybean injury was 1 to 5% in the Xtend® trials evaluated 6 WAP; however, minimal injury (0 to 1%) was observed by 8 weeks. Soybean injury in the Engenia™ trial was 6% or less 2 WAP, but injury decreased to 3 to 4% by 10 weeks. Palmer amaranth was controlled 94 to 100% 10 WAP in the Xtend® trial evaluating various tank-mixes EPOST. For the Xtend® trial evaluating weed management programs, all treatments controlled Palmer amaranth 99 to 100% 10 WAP with the exception of glyphosate applied alone EPOST; and chlorimuron + flumioxazin + thifensulfuron PRE followed by glyphosate + fomesafen MPOST. All treatments in the Engenia™ trial controlled large crabgrass and Palmer amaranth 98 to 100% 10 WAP with the exception of glyphosate applied alone EPOST and MPOST. Soybean yield for the Xtend® tank-mix trial ranged from 2,600 to 3,100 kg ha-1 for all treatments. Yield for the Xtend® program trial ranged from 2,600 to 3,300 kg ha-1 except glyphosate applied alone EPOST, which yielded 1,800 kg ha-1. Overall, several effective systems were identified using these new technologies. The most effective programs included multiple application timings, multiple herbicide modes of action, and soil residual herbicides.


ROUNDUP READY 2 XTEND SOYBEAN SYSTEMS. S. A. Nolte*; Monsanto, St. Louis, MO (46)


ROUNDUP READY 2 XTEND® SOYBEAN SYSTEM.  Scott A. Nolte. Monsanto Company, St. Louis, MO


Managing tough-to-control and herbicide-resistant weeds economically, has been and continues to be a challenge that soybean growers are faced with. Successful integrated weed management systems require an understanding of crop and weed interactions. Weeds impact soybean yield potential by competing for limited light, water, and nutrient resources. Nearly complete weed control is needed during the first weeks after soybean emergence to avoid potential yield losses due to early emerging weeds. Soybeans are especially sensitive to moisture deficiencies in late summer and even a few large weeds left in the field can severely reduce yield potential. Roundup Ready 2 Xtend® soybean is the industry's first biotech-stacked soybean trait with both dicamba and glyphosate herbicide tolerance. Use of the Roundup Ready® Xtend Crop System can help maximize weed control and increase yield potential by enabling the use of multiple modes of action on soybean products built on the high yielding Genuity® Roundup Ready 2 Yield® Soybean technology.

Field studies were conducted in 2016 at 10 Northern and 6 Southern locations across multiple states to evaluate weed control, grain yield and the economic return of three levels of herbicide input within the Roundup Ready® Xtend Crop System for soybean as compared with a competitor soybean system. Roundup Ready 2 Xtend® soybeans and LibertyLink® soybeans were planted in a conventional tillage system. The study was a split plot design with the main plot being trait and herbicide input being the subplot. Herbicide input levels were low, medium and high based on the addition of sites of action to the system.  

At canopy, regardless of herbicide input level, total weed control was 97% or greater in the Roundup Ready® Xtend Crop System for soybean, while in the LibertyLink® system weed control ranged from 80.9 to 96.9% at the low to high input levels. Yield was significantly higher in the Roundup Ready® Xtend Crop System for soybean, regardless of herbicide input level, at 71.0-72.4 bu/ac, compared to the LibertyLink® system at 63.1-67.1 bu/ac, in the Norther region. The Roundup Ready® Xtend Crop System for soybean also provided significantly greater economic return at the low and high herbicide input levels of 543.7 and 533.8 $/ac, compared to the LibertyLink® system at 481.7 and 476.1 $/ac, respectively in the Northern region. Optimizing profitability and management of tough-to-control and herbicide-resistant weeds can be achieved by selecting a high yield potential soybean product matched to the appropriate weed control program, for weed species present in the field. The Roundup Ready® Xtend Crop System for soybean provided, in trials, consistent weed control, high yield and maximized profit, while using multiple sites of action and practicing good weed resistance management.


EVALUATION OF RESIDUAL HERBICIDES IN SOYBEAN. D. L. Teeter*, T. A. Baughman, C. D. Curtsinger, R. W. Peterson; Oklahoma State University, Ardmore, OK (47)


Evaluation of Residual Herbicides in Soybean. D. L. Teeter*, T. A. Baughman, R. W. Peterson, C.D. Curtsinger; Oklahoma State University, Ardmore, OK

Glyphosate resistant weeds are becoming more prevalent in Oklahoma soybeans, the most troublesome being Palmer amaranth (Amaranthus palmeri).  New technologies are currently being developed to assist in dealing with these problematic issues.  Studies were established in Oklahoma to compare the new Roundup Ready 2 Xtend soybean technology to the already existing Roundup Ready and Liberty Link technologies.

Trials were established during the 2016 growing season at the Oklahoma State University Research Stations near Bixby, Chickasha, Fort Cobb, and Lane. Trials were planted with each of the three soybean technologies.  Within each of the three technologies the following herbicide treatment regimens were established:  Rowel FX applied PRE at 0.036 kg ai ha-1 (flumioxazin + chlorimuron) followed by Roundup Xtend at 1.68 kg ai ha-1 (dicamba + glyphosate), Roundup Powermax at 1.27 kg ae ha-1 (glyphosate), or Liberty at 0.594 kg ae ha-1 (glufosinate), early POST; Rowel FX + Warrant at 1.267 kg ai ha-1 (acetochlor) followed by Warrant at 1.267 kg ai ha-1 + Roundup Xtend, Roundup Powermax, or Liberty; Rowel FX + Warrant + Tricor 0.258 kg ai ha-1 (metribuzin) followed by Warrant Ultra at 0.57 kg ai ha-1 (acetochlor + fomesafen) + Roundup Xtend, Roundup Powermax, or Liberty.  Engenia 0.701 kg ae ha-1 + Roundup Powermax 1.27 kg ae ha-1 was substituted for Roundup Xtend at Chickasha, Fort Cobb, and Lane.  All treatments were applied with a CO2 backpack sprayer calibrated at 93.457 L ha-1.  Typical small plot techniques were employed at all locations throughout the growing season.  Soybean were visually evaluated for stand reduction and injury.  Herbicide treatments were evaluated for weed efficacy at each of the four locations.  Soybean were harvested to determine yield at each location with a small plot combine and adjusted to 13% moisture.

Soybean stand reduction and injury was less than 10% season long with all treatments at all locations.  The only treatments that resulted in injury greater than 5% was in the Roundup Ready system with the Rowel FX + Warrant and Rowel FX + Warrant + Tricor preemergence treatments mid-season at Bixby.  Palmer amaranth control (AMAPA, Amaranthus palmeri) was 99% or greater season long at Bixby when Rowel FX + Warrant or Rowel FX + Warrant + Tricor was followed early POST with Roundup Xtend or Liberty.  Late season AMAPA control with Rowel FX followed by Roundup Xtend was 100% compared to 88% when followed by Liberty and 76% followed by Roundup Powermax.  AMAPA control was at least 98% late season at Chickasha and Fort Cobb and season long at Lane with all treatments.  This was due to the fact that AMAPA was not glyphosate resistant at these locations and populations were low at Fort Cobb and Lane.  Large crabgrass (DIGSA, Digitaria sanguinalis) was controlled 100% season long at Fort Cobb.  DIGSA control was at least 98% late season with all treatments except Rowel FX followed by Liberty at Lane and any of the PRE herbicide programs followed by Liberty at Chickasha.  Ivyleaf morningglory (IPOHE, Ipomoea hederacea) control was greater than 98% at Lane and Chickasha with any of the PRE herbicide programs followed by Engenia + Roundup Powermax early POST. Prostrate pigweed (AMABL, Amaranthus blitoides) was controlled at least 97% season long with all treatments at Lane.  No treatment controlled cutleaf eveningprimrose (OEOLA, Oenothera lacinata) over 95% late season at Fort Cobb.  Carpetweed (MOLVE, Mollugo verticillata) control was 99% or greater season long with all treatments at Fort Cobb. Soybean yields were increased over the untreated check with all treatments at Bixby, Chickasha, and Lane.  Deer depredation likely influenced the lack of a yield response at Fort Cobb.  Soybean yields were higher with the Roundup Ready Xtend and Liberty Link systems compared to the Roundup Ready system at Bixby due to the presence of glyphosate resistance AMAPA at this location.  These studies indicated that when the Roundup Ready 2 Xtend soybean system is used in combination with a sound preemergence foundation successful control of a wide array of weed species can be accomplished.  


WEED MANAGEMENT SYSTEMS IN DICAMBA-TOLERANT SOYBEAN. M. W. Marshall*, C. H. Sanders; Clemson University, Blackville, SC (48)


Recent introduction of soybean with genetic tolerance to over-the-top applications of dicamba has given producers another tool for managing glyphosate-resistant Palmer amaranth, a common and troublesome weeds present in South Carolina soybean production fields.  Field experiments were conducted in 2016 at Edisto Research and Education Center located near Blackville, SC to evaluate preemergence and postemergence herbicide programs for weed control in dicamba tolerant soybean. At-plant herbicide treatments include dicamba, flumixoazin, pyroxysulfone, sulfentrazone, and metribuzin. Postemergence treatments included glyphosate, dicamba, fomesafen, dual magnum, acifluorfen, and bentazon. Experimental design was a randomized complete block design with 3 replications. Wet conditions were present shortly after the preemergence herbicides were applied which reduced the length of dicamba residual control.  In the flumixoazin, pyroxysulfone, sulfentrazone, and metribuzin treatments, Palmer amaranth control was greater than 95% at the time of the first postemergence application. In the glyphosate followed by glyphosate postemergence program, Palmer amaranth control was significantly less compared to the dicamba plus glyphosate programs. The standards PRE treatments (excluding dicamba)followed by glyphosate plus dicamba provided excellent Palmer amaranth control (100%) when evaluated at the second postemergence application timing. Overall, there was a significant difference among the dicamba and standard herbicide treatments when evaluated 2 weeks after second postemergence application. In general, all treatments (with the exception of glyphosate followed by glyphosate program) provided effective control of Palmer amaranth. These results showed that a foundation preemergence program followed by glyphosate and dicamba as the most effective treatment in Palmer amaranth when applied at the correct weed size (less than 10 cm in height).


RELATIONSHIP BETWEEN ABOVEGROUND BIOMASS AND RELATIVE COVER OF WEEDS IN WINTER FALLOW SOYBEAN. G. Picapietra1, M. V. Buratovich2, M. E. Cena3, H. A. Acciaresi*4; 1Instituto Nacional de Tecnología Agropecuaria, Pergamino, Argentina, 2ECANA-UNNOBA, Pergamino, Argentina, 3CIC, Pergamino, Argentina, 4Instituto Nacional Tecnologia Agropecuaria, Pergamino, Argentina (49)


Fallow weed community can adopt different structures, depending of winter crops, the rotation between them, and the control method used. An experiment was carried out in Pergamino (Argentina) during four cycles (2013/14, 2014/15, 2015/16, and 2016/17), in which soybean has cultivated with two fallow alternatives: rye as a cover crop (CC) versus application of residual herbicides (RH). In September 2016 before rye drying, CC decreased significantly (p <0.05) the aboveground dry matter (ADM) of weeds Bowlesia incana, Conyza spp., Gamochaeta spp., Stellaria media, Capsella bursa-pastoris, Coronopus didymus, Lamium amplexicaule, and Lolium perenne var. multiflorum. In addition, Bowlesia incana, and Stellaria media both has increased their ADM according to the total production per area, while Gamochaeta spp., and Conyza spp. were hardly affected, decreasing their ADM nearly to zero when the total ADM reached values ​​of 500 g.m-2. The results showed the interaction between fallow weeds: species such as Bowlesia incana, and Stellaria media can generate an important production of ADM to suppress the growth of competitive and time persistent species as Conyza spp. These relationships prove to be interesting because the possible competitive adjustment between the species would allow rationalizing the use of fallow herbicides.



The control of glyphosate-resistant (GR) Canada fleabane (Conyza canadensis L. Cronq) in soybean has been variable with glyphosate plus saflufenacil. The objective of this research was to determine the biologically effective rate (BER) of saflufenacil, saflufenacil mixed with glyphosate, and metribuzin mixed with saflufenacil and glyphosate applied preplant (PP) for the control of GR Canada fleabane in no-till soybean; a study was conducted to determine each of the three BER’s. For each study, seven field locations were completed used over a two-year period (2014, 2015) in fields previously confirmed with GR Canada fleabane. The saflufenacil BER found 25, and 36 g a.i. ha-1 provided 90 and 95% control of GR Canada fleabane 8 WAA, while the BER for 98% control was outside of the treatment range tested. The saflufenacil/glyphosate (900 g a.i. ha-1) BER found less saflufenacil to be required as 25, 34, and 47 g a.i. ha-1 provided 90, 95, and 98% control of GR Canada fleabane respectively. The metribuzin BER found 61, 261, and 572 g a.i. ha-1 was required to provide 90, 95 and 98% control of GR Canada fleabane, respectively, mixed with saflufenacil (25 g a.i. ha-1) and glyphosate (900 g a.i. ha-1). The addition of metribuzin mixed with saflufenacil plus glyphosate, improved control with the Ontario soybean rate of saflufenacil (25 g a.i. ha-1) and provided a second effective herbicide mode of action for the control of GR Canada fleabane. The use of a three-way herbicide mixture can be an effective weed management strategy to control GR Canada fleabane in soybean.

HALOSULFURON ABSORPTION, TRANSLOCATION, AND METABOLISM IN DRY BEAN. P. H. Sikkema1, Z. Li1, K. C. Kessler2, M. Rodrigues Alves2, S. J. Nissen2, T. A. Gaines2, P. Westra2, R. C. Van Acker3, D. E. Robinson1, N. Soltani*1; 1University of Guelph, Ridgetown, ON, 2Colorado State University, Fort Collins, CO, 3University of Guelph, Guelph, ON (51)


Halosulfuron-methyl, a sulfonylurea herbicide, was registered for broadleaf weed control in dry beans. This herbicide has an adequate margin of crop safety in white bean (Phaseolus vulgaris), but causes unacceptable injury to adzuki bean (Vigna angularis). Halosulfuron-methyl absorption, translocation, and metabolism were evaluated in white and adzuki bean using radiolabeled herbicide to determine if differences in these parameters could explain the difference in crop safety between these two species. Adzuki bean had more rapid halosulfuron-methyl absorption than white bean. Adzuki bean reached 90% absorption (t90) 26.2 HAT, while white bean required 40.1 HAT to reach t90. The maximum halosulfuron-methyl absorption (Amax) was significantly higher in adzuki bean (75.7%) than in white bean (65.3%). More 14C-halosulfuron was translocated to the apex, 1st trifoliate, stem above the treated leaf, and roots in aduzki bean than in white bean. The maximum radioactivity translocated out of treated leaf (Tmax) was significantly higher in adzuki bean (17.7%) than in white bean (12.1%). Halosulfuron-methyl was broken down to the same metabolites in white and adzuki bean. The half-life of halosulfuron-methyl in adzuki bean was 16 HAT, compared to less than 6 HAT in white bean. More herbicide remained as the free acid in adzuki bean compared to white bean over the entire 48 h time course. The differential tolerance of white and adzuki bean to halosulfuron can be attributed to greater absorption and translocation and decreased metabolism in adzuki bean.



No postemergence broadleaf herbicides are currently registered for use in chickpeas in the U.S.  Producers are at risk of crop failure if preemergence herbicides fail to control broadleaf weeds well. Field trials were conducted in chickpeas, var. Sierra, at Prosser and Paterson, Washington in 2016 to evaluate chickpea tolerance and weed control following postemergence application of seven herbicides. Chickpeas averaged 15 to 20 cm tall at the time of herbicide application. Pyridate applied alone at 0.8 or 1 kg ai ha-1 with or without nonionic surfactant (NIS) did not significantly injure chickpeas. Pyridate tank mixed with 50 g ai ha-1 metribuzin also did not significantly injure chickpeas. At both locations, chickpea injury was greatest with treatments containing fomesafen, acifluorfen, sulfentrazone, and bicyclopyrone. Tank mix treatments of fomesafen, acifluorfen, sulfentrazone, and flumetsulam with pyridate delayed chickpea maturity at Prosser and tank mix treatments of sulfentrazone and flumetsulam with pyridate delayed chickpea maturity at Paterson. Fomesafen applied alone and tank mixes of bicyclopyrone with pyridate also tended to delay chickpea maturity at both locations. Broadleaf weed density was low at Prosser and all treatments reduced common lambsquarters and Russian thistle counts compared to nontreated controls.  All treatments controlled Russian thistle greater than 90% and hairy nightshade greater than 93% at the Paterson location.  Despite early season visual injury to chickpeas and delay in maturity with some herbicide treatments, chickpea yield and 100 seed weight were not adversely affected by herbicide treatments at both locations. Chickpea yield was greater at Paterson (2394 kg ha-1) than at Prosser (1411 kg ha-1) most likely due to a higher plant stand, whereas 100 seed weight was greater at Prosser (49.5 g) than at Paterson (43.0 g).

EVALUATION OF CORN HERBICIDE PROGRAMS IN OKLAHOMA. C. D. Curtsinger*, T. A. Baughman, D. L. Teeter, R. W. Peterson; Oklahoma State University, Ardmore, OK (53)


Evaluation of Corn Herbicide Programs in Oklahoma.  T. A. Baughman1, J.A. Crose2, M. R. Manuchehri2, D. L. Teeter1, R.W. Peterson1; 1Oklahoma State University, Ardmore, OK, 2Oklahoma State University, Stillwater, OK


Successful weed control in irrigated corn can be challenging and requires a systematic approach of premergence and postemergence herbicides. Two studies were conducted at Chickasha and Fort Cobb, OK in 2016 to evaluate weed management systems in corn. One study evaluated the efficacy of one and two-pass herbicide programs while a second study addressed complete herbicide systems.  In both studies, herbicide treatments consisted of applications made at the preemergence (PRE), early postemergence (EPOST) and/or mid-postemergence (MPOST) timing. Corn injury and weed control were evaluated 2, 4, 6, and 10 weeks after planting (WAP). Target weed species included ivyleaf morningglory (Ipomoea hederacea, Jacq.), large crabgrass (Digitaria sanguinalis L.), Palmer Amaranth (Amaranthus palmeri S. Wats.), and Texas millet [Urochloa texana, (Buckl.) R. Webster]. In the 1 and 2-pass study at Chickasha, corn injury ranged from 1 to 6% for treatments that included a PRE application 2 WAP; however, injury decreased to 1% or less by 8 weeks. For the same trial at Fort Cobb, crop injury ranged from 4 to 13% 6 WAP with the highest level of corn injury (9 to 13%) following PRE applications of saflufenacil + dimethenamid; saflufenacil + pyroxasulfone; saflufenacil + dimethenamid + topramezone; and saflufenacil + dimethenamid + pyroxasulfone. This increase in injury at Fort Cobb was likely due to the coarse textured soil at this location and the colder temperatures resulting from an earlier planting date compared to Chickasha.  By 10 WAP, injury for the previously mentioned treatments decreased to 5% or less. Corn injury for the systems study was 5% or less 8 WAP at both Chickasha and Fort Cobb. When evaluating weed efficacy for the 1 and 2-pass study at Chickasha, large crabgrass was controlled 95 to 100% for all treatments 10 WAP with the exception of PRE only systems of saflufenacil + dimethenamid; and saflufenacil + dimethenamid + topramezone. Palmer amaranth was controlled 99 to 100% for all treatments. At Fort Cobb, ivyleaf morningglory was controlled 97 to 100% 10 WAP with the exception of acetochlor + flumetsulam + clopyralid applied PRE. Palmer amaranth was controlled 99 to 100% with the exception of saflufenacil + dimethenamid + topramezone + atrazine + glyphosate applied EPOST. Texas millet was controlled 93 to 100% with the exception of saflufenacil + dimethenamid; and saflufenacil + dimethenamid + topramezone applied PRE and saflufenacil + dimethenamid + topramezone + atrazine + glyphosate applied EPOST. All treatments for the systems trial at Chickasha controlled large crabgrass and Palmer amaranth 94 to 100% and 97 to 100% 10 WAP, respectively. At the Fort Cobb systems trial, Texas millet, Palmer amaranth, and ivyleaf morningglory were controlled 98 to 100% 10 WAP.  These studies indicated that effective control of a diverse weed population can be achieved when a programmatic use of PRE and POST herbicides are employed.



THIFENSULFURON RESISTANT MOUSE-EAR CRESS (ARABIDOPSIS THALIANA) MANAGEMENT IN WINTER WHEAT. R. S. Randhawa*1, M. L. Flessner1, C. W. Cahoon2, J. H. Westwood1; 1Virginia Tech, Blacksburg, VA, 2Virginia Tech, Painter, VA (54)


Thifensulfuron Resistant Mouse-ear Cress (Arabidopsis thaliana L.) Management in Winter Wheat. Ranjeet S Randhawa*, Michael L Flessner, James H Westwood, Charles W Cahoon; Virginia Polytechnic Institute and State University, Blacksburg, VA.


Thifensulfuron resistant mouse-ear cress was recently reported in production wheat fields in Virginia. Currently, there is little information regarding alternative herbicides for mouse-ear cress control. 

Two field trails were conducted in 2015 on farmers’ field in Essex County, Virginia to assess the pre- and post-emergence alternative control options for thifensulfuron resistant mouse-ear cress (Arabidopsis thaliana L.). Pre- and post-emergence studies consisted of 7 and 11 treatments, respectively, including a nontreated check. Studies were arranged in randomized complete block with four replications per treatment and were duplicated in space. For the pre-emergence study, herbicide treatments included thifensulfuron (Harmony) at 17.5 g ai ha-1, metribuzin (Tricor) at 105 g ai ha-1, flumioxazin (Valor) at 71.5 g ai ha-1, saflufenacil (Sharpen) at 50 g ai ha-1, pyroxasulfone (Zidua) at 119 g ai ha-1 and pendimethalin (Prowl H2O) at 1600 g ai ha-1.  Flumioxazin and saflufenacil were applied a week before wheat planting followed by pyroxasulfone and pendimethalin that were applied (at spiking) a week after planting. Thifensulfuron and metribuzin were applied at three weeks after planting. For the post-emergence study, herbicides treatments included thifensulfuron at 17.5 g ai ha-1, thifensulfuron + tribenuron (Harmony Extra) at 26.6 g ai ha-1, 2,4-D (2,4-D LVE) at 1060 g ae ha-1, dicamba (Banvel) at 560 g ae ha-1, metribuzin  at 105 g ai ha-1, bromoxynil + pyrasulfotole (Huskie) at 244 g ai ha-1 + ammonium sulfate at 1120 g ai ha-1, bromoxynil (Buctril) at 420 g ai ha-1, fluroxypyr (Starane Ultra) at 157 g ai ha-1, pyroxsulam (Poweflex HL) + ammonium sulfate at 18.4 + 3360 g ai ha-1 and nitrogen (Urea) at 56.8 Kg ai ha-1. All post treatments included non-ionic surfactant (NIS) (Activator 90) at 0.25% v v-1. Herbicide application was made using a hand held spray boom equipped with four AIXR nozzles spaced at 47 cm and calibrated to deliver 140 L ha-1 at 207 kPa. For pre-control study visible control and crop injury were assessed on 0 (no control/injury) to100 (complete necrosis) scale at 6, 11, and 15 and 11, 15 and 20 weeks after initial treatment (WAIT) for both sites respectively, for the post-emergence study visible control was assessed 3, 5, and 7 weeks after treatment (WAT) followed by yield data for both studies. Data were analyzed using JMP 1.1.0. ANOVA was performed followed by multiple comparison test using Fisher’s protected LSD at significance level of P < 0.05.

In the pre-emergence study, flumioxazin, pyroxasulfone and metribuzin resulted in >75% control 15 weeks after treatment (WAT) at both sites. No crop injury was observed in the pre-emergence study and no differences in yield were observed. In the post-emergence study, 2,4-D, dicamba and metribuzin resulted in >75% control 5 WAT at both sites. Dicamba and pyroxsulam resulted in 20% crop injury 3 WAT. However, none of the treatments resulted in increased yield relative to the non-treated check except dicamba at site 1. The results indicate that flumioxazin and pyroxasulfone can be applied as pre-emergence herbicides to control thifensulfuron resistant mouse-ear cress. Metribuzin is equally effective when applied either pre- or post-emergence. 2,4-D and dicamba can be used as post-emergence alternatives. Future research should focus on evaluating the density at which mouse-ear cress results in a yield loss and determine the critical weed free period, if any, to avoid yield loss.


EFFECT OF PRE-PLANT NITROGEN (N) RATES ON WHEAT YIELD IN CORN/SORGHUM-WHEAT ROTATION. M. K. Bansal*, W. J. Everman; North Carolina State University, Raleigh, NC (55)


Sorghum production has gained interest in recent years as regional grain demands increased which lead swine producer to offer a competitive sorghum grain price. Sorghum can be a good alternative for corn in rotation with wheat. Sorghum has ability to tolerate hot dry weather, a condition that can be challenging for corn in drought season. However, with the advantages, sorghum has some disadvantages as well when used in rotation. Grain sorghum is known to have negative impact on the following crop. Sorghum residue when incorporated in soil can make N immobilize making it less available to following wheat.

Experiments were conducted in 2013-14 at Rocky Mount, 2014-15 at Rocky Mount and Kinston (two locations), and 2015-16 at Rocky Mount and Kinston, North Carolina to evaluate the effect of different rates of pre-plant nitrogen (15, 30, 45, and 60 lbs per acre) applied to wheat following different hybrids either sorghum (DKS 53-67, P83P17) or corn (DKC 60-67) on wheat yield. There was no significant effect of pre-plant nitrogen on wheat yield in both 2013-14 and 2015-16. In 2013-14, there was significant effect of hybrids on wheat yield. Wheat yield was not significantly different when planted after either DKC 60-67 or DKS 53-67. Yield was significantly different when planted after DKC 60-67 and P83P17. In 2014-15 and 2015-16, there was no significant effect of different hybrids on wheat yield at all locations. Pre-plant nitrogen had significant effect only at one location in Kinston in 2014-15. Results suggests that wheat yield is not affected when planted after sorghum (DKS 53-67) compared to corn (DKC 60-67). At Rocky Mount, each year there was no significant effect of pre-plant nitrogen on wheat yield


GRASSY WEED MANAGEMENT IN OKLAHOMA WINTER WHEAT. M. R. Manuchehri*1, T. A. Baughman2, A. R. Post3; 1Oklahoma State University, Stillwater, OK, 2Oklahoma State University, Ardmore, OK, 3North Carolina State University, Raleigh, NC (56)


GRASSY WEED MANAGEMENT IN OKLAHOMA WINTER WHEAT. M. R. Manuchehri*1, T. A. Baughman2, A. R. Post3; 1Oklahoma State University, Stillwater, OK, 2Oklahoma State University, Ardmore, OK, 3North Carolina State University, Raleigh, NC.

The use of preemergence (PRE) herbicides in Oklahoma winter wheat may improve the control of acetolactate synthase resistant Italian ryegrass [Lolium perenne L. spp. multiflorum (Lam.) Husnot]. Three studies were conducted at the Cimarron Valley Research Station near Perkins, OK in 2016 to evaluate weed management systems that included flufenacet + metribuzin; pyroxasulfone; and pyroxasulfone + carfentrazone applied PRE. Visual weed control and crop injury were evaluated 4, 6, and 9, and 13 weeks after planting (WAP). Winter wheat injury in the flufenacet study was 46% 9 WAP following a PRE application of flufenacet + metribuzin at 380 g ai ha-1. In the pyroxasulfone studies, very early post (VEPOST) treatments that included metribuzin at 105 g ai ha-1 or axiom at 286 g ai ha-1 had the highest levels of injury (7 to 14%). Flufenacet + metribuzin applied PRE at 380 g ai ha-1 controlled Italian ryegrass 95% 9 WAP. Italian ryegrass control did not improve when mesosulfuron followed flufencaet + metribuzin. Italian ryegrass control in the pyroxasulfone study was at least 98% for all treatments that included pyroxasulfone PRE or VEPOST or pinoxaden VEPOST. In the pyroxasulfone + carfentrazone study, Italian ryegrass was controlled 95 to 100% for all treatments with the exception of pyroxasulfone + carfentrazone at 35 g ai ha-1 applied alone PRE. Overall, several successful systems were identified using flufenacet + metribuzin; pyroxasulfone; and pyroxasulfone + carfentrazone. Wheat response to these products is influenced by planting depth, application timing, herbicide rate, soil type, and rainfall following application. To reduce crop injury, plant seed to a depth of at least 2.5 cm and closely follow herbicide labels with regard to application rate and timing.


PREHARVEST HERBICIDE APPLICATION EFFECTS ON WINTER WHEAT. G. E. Powell*, K. M. Rogers, C. L. Sprague; Michigan State University, East Lansing, MI (57)


Preharvest Herbicide Application Effects on Winter Wheat

Late plantings due to delays in crop harvest and early winters do not bode well for good establishment of winter wheat. These later plantings combined with wetter than normal springs can narrow the window for spring herbicide applications in winter wheat and, in some cases, can prevent them. These situations can lead to the presence of weeds at the time of winter wheat harvest, reducing harvest efficiency and causing lower grain prices at the point of sale. A field experiment was conducted at the Michigan State University Agronomy Farm in 2015 and 2016 to evaluate the effect of preharvest herbicide applications on winter wheat. Preharvest herbicide treatments included: dicamba, 2,4-D amine, carfentrazone, saflufenacil, glyphosate, and glyphosate in combination with carfentrazone and saflufenacil. Applications were made when wheat was physiologically mature (<30% moisture). In 2016, two additional treatments of glyphosate at 0.84 and 1.68 kg ae ha-1 were included and applied at an earlier application time when grain moisture was ~40%. All treatments were compared with a nontreated control. In 2015, common lambsquarters and common ragweed desiccation were evaluated 3, 7, 10 and 15 days after treatment (DAT). At the time of harvest yield was recorded, and each plot was assigned a harvestability score. Low weed populations in 2016 prevented the evaluation of weed desiccation and wheat harvestability. Wheat grain samples were collected to measure grain moisture, test weight, percent foreign material, weight of 100 seeds, and wheat seed viability. In 2016, herbicide residue levels were tested in grain treated with glyphosate. Saflufenacil alone and in combination with glyphosate caused over 85% common ragweed desiccation 3 DAT in 2015. All other treatments did not adequately desiccate common ragweed, with the exception of glyphosate and glyphosate combinations. Glyphosate and glyphosate combinations were the only treatments that caused adequate desiccation of common lambsquarters 15 DAT. However, these applications needed 15 days for maximum desiccation. Harvestability scores were highest with treatments containing glyphosate in 2015. These treatments also resulted in the highest test weights, lowest grain moistures, and lowest amount of foreign material in the harvested crop. In 2016, regardless of treatment there were no difference in any of the grain parameters measured compared with the nontreated control. Preharvest treatments had little effect on wheat yield in both seasons. Glyphosate residues varied based on application rate and application timing. The highest glyphosate residue level found in the grain was 796 ppb, when glyphosate was applied at 2-times the normal application rate and applied prior to physiological maturity (39% grain moisture). This glyphosate level was 37.5 times lower than the maximum residue level allowed in wheat. Data from this research suggests that glyphosate and glyphosate combinations were the only treatments that resulted in overall effective weed desiccation, improved wheat harvestability, and reduced factors that can lead to price dockages at the point of sale. 


EFFICACY AND CROP TOLERANCE OF BUTTE HERBICIDE (BENZOBICYCLON + HALOSULFURON-METHYL) ON CALIFORNIA WATER-SEEDED RICE. A. S. Godar*1, W. Brim-DeForest2, K. Al-Khatib1; 1University of California, Davis, Davis, CA, 2University of California, Davis, CA (58)


Butte® herbicide is a co-formulated granular mixture of 3% benzobicyclon + 0.64% halosulfuron-methyl and is currently pending registration for into-the-water herbicide use in California water-seeded rice. The benzobicyclon component of Butte® is a new mode of action (HPPD-inhibitor) to the rice herbicides in California. Since there are currently eight weed species confirmed resistant to five modes of action in the CA rice system, the addition of a new mode of action will assist in resistance management. During the 2014, 2015 and 2016 rice growing seasons Butte® was tested under a continuous flood system (10 cm water depth) applied at the 1 leaf stage of rice. All experiments were conducted in the field under controlled conditions at the California Rice Experiment Station, in Biggs, CA. Populations of weeds were those found naturally in the field, and no additional weed seeds were planted. The rice varieties were California medium grains. Butte® was applied both alone and in a program with clomazone applied at seeding or other POST herbicides applied at 1 tiller stage of rice for crop tolerance and control of common California rice weeds. An into-the-water application of Butte® (at 250 + 52.2 or 303 + 63 g ai/ha, benzobicyclon and halosulfuron-methyl, respectively) applied alone provided complete control of ricefield bulrush (Schoenoplectus mucronatus L.) Palla) and smallflower umbrella sedge (Cyperus diformis L.). Late watergrass (Echinochloa oryzicola (Vasinger) Vasinger) control with the Butte® alone applications was less than 90% in 2014 and 2016; however, it was excellent in 2015. The lower rate of Butte® followed by clomazone (560 g ai/ha) improved late watergrass control compared to the Butte® alone; however, this herbicide combination caused significant (up to 20%) crop stand reduction affecting crop yield. A follow-up application of cyhalofop-butyl (280 g ai/ha + 2.5% v/v COC), bispyribac-soduim (37 g ai/ha + 2.0% v/v UAN + 0.2% v/v NIS), propanil + triclopyr (6726 + 58 g ai/ha + 1.25% v/v COC) or penoxulam (40 g ai/ha + 2.25% v/v COC) after application of the lower rate of Butte® provided excellent control of the all the weed species evaluated. Butte® followed by these POST-applied herbicides caused no or little crop injury and provided higher crop yield (10.8 t/ha) compared to Butte® alone (10.2 t/ha). This study showed that Butte® herbicide has great potential to control several important weeds in California water-seeded rice.




Widespread distribution of glyphosate-resistant (GR) weeds in soybean-growing areas across Mississippi has economically affected soybean planting and follow-up crop management operations. Several of the GR weeds, especially pigweeds (Amaranthus spp) including Palmer amaranth, are also resistant to acetolactate synthase (ALS) inhibiting herbicides. Thus, protoporphyrinogen oxidase (PPO) inhibitors are one of the few remaining postemergence control herbicide options for soybean growers in Mississippi. Resistance to PPO inhibiting herbicides in Palmer amaranth has very recently been reported in Arkansas and Tennessee, states where soybean production practices are similar to Mississippi and share a border. Under these conditions, prolonging the sustainability of PPO herbicides for MS soybean producers is of paramount importance. The objective of this research was to evaluate quality of spray carrier (water) and its effect on efficacy of selected formulations of fomesafen on Palmer amaranth populations collected in Mississippi. City and well water samples from sources used by agricultural aviation pilots were collected, analyzed for physico-chemical properties, and used to mix herbicide treatments to test for efficacy on pigweed populations. Analysis of city and well water samples indicated a range of values for pH, hardness, iron, carbonate, bicarbonate, sodium, and chloride ion concentrations. Water quality, for the most part, did not influence efficacy of fomesafen or its formulations on Palmer amaranth.

WINTER SOWED COVER CROPS AND DIVERSITY OF NATURAL WEED POPULATIONS. M. V. Buratovich1, M. E. Cena2, G. Picapietra3, H. A. Acciaresi*4; 1ECANA-UNNOBA, Pergamino, Argentina, 2CIC, Pergamino, Argentina, 3Instituto Nacional de Tecnología Agropecuaria, Pergamino, Argentina, 4Instituto Nacional Tecnologia Agropecuaria, Pergamino, Argentina (60)


The objective of this study was to determine the effect of different cover crops and level of fertilization on the diversity of natural winter weed populations. The species used as cover crops (CC) were bromegrass (Bromus unioloides L.), oats (Avena sativa L.), ryegrass (Lolium multiflorum L.) and barley (Hordeum vulgare L.). A sector was left without cover crop used as negative control. Two levels of fertilizer (F) were applied (0 and 32 kg N.ha-1). In each experimental unit, total number and species of weeds at CC tillering and corn sowing were quantified. Abundance and frequency of each weed specie were quantified. Diversity (H´) and equitative (E) index of Shannon and specific richness effective (eH´) were estimated. Bromegrass showed major H´, E and eH´ at CC tillering, and H´and eH´ at corn sowing.  Conversely, oats, ryegrass and barley showed no significant differences (P>0.05). Fertilization showed significant differences only at tillering of CC. The interaction CC*F has no significant difference in all treatments. The use of bromegrass as CC would favor the diversity of the community of winter weeds. It would lead to decrease dominant species, favoring the competitiveness of winter crops.

POST HERBICIDE EFFICACY SCREEN ON MARESTAIL. D. Lingenfelter*, W. Curran; Pennsylvania State University, University Park, PA (61)


A field study in a fallow setting was conducted in 2016 in Pennsylvania (Landisville, Lancaster Co.) to evaluate glyphosate-resistant horseweed/marestail (Conyza canadensis) control with POST herbicides. Studies were arranged in a randomized complete block design with three replications. Herbicides were applied with a small-plot, CO2-backpack sprayer system that delivered 15 GPA thru TeeJet AIXR110015 nozzles on June 10 and marestail ranged from 4 to 14 inches tall (8 inch average height). Treatments included: glyphosate (1.13 lb ae/A), cloransulam (0.0315 lb ai), chlorimuron (0.0105 lb), imazamox (0.039 lb), fomesafen (0.25 lb), lactofen (0.195 lb), acifluorfen (0.375 lb), fluthiacet (0.0064 lb), saflufenacil (0.0223 lb), glufosinate (0.66 lb), bentazon (1 lb), dicamba (0.25), dicamba + diflufenzopyr premix (0.175 and 0.35 lb ae), 2,4-D ester (0.5 lb ae), fluroxypyr (0.14 lb), clopyralid + flumetsulam premix (0.196 lb), mesotrione (0.094 lb), topramezone (0.0164 lb), bromoxynil (0.375 lb), pyrasulfotole + bromoxynil premix (0.241 lb), halosulfuron (0.314 lb), and atrazine (0.5 lb). All of the spray mixtures included liquid AMS at 2.5% v/v; all contained COC at 1% v/v except glyphosate, glufosinate, and fluroxypyr; and the dicamba and 2,4-D ester treatments contained NIS at 0.25% v/v. In addition, all treatments except glyphosate, contained 0.375 lb glyphosate to control other weed species present. Visual weed control ratings were taken periodically throughout the growing season.

Preliminary results from end of season ratings (approx. 8 WAA) revealed that glyphosate and the ALS-inhibitor (Group 2) herbicides provided only 47 – 67% marestail control. The contact and PPO (Group 14) herbicides had variable results. Bentazon provided only 50% control while the PPO herbicides ranged from 8 – 13% except for saflufenacil which provided 81% and glufosinate gave 92% control. The PGR (Group 4) herbicides were variable and ranged from 62 to 98% control. The 0.175 and 0.35 lb dicamba premix provided 96 and 98% control respectively. Dicamba alone and 2,4-D provided 86 and 75% control respectively. Control from the other two PGR herbicides was <73%. Mesotrione, topramezone, bromoxynil, and atrazine all were <53% control. However, the pyrasulfotole + bromoxynil premix was rated at 93% marestail control.

In summary, although the average marestail height was greater than what is suggested for good control it was realistic to when most are sprayed. We assume better control might have been observed by some (possibly all of the Group 4 herbicides, atrazine, cloransulam and chlorimuron) but not all of the treatments if applied to smaller weeds. Furthermore, saflufenacil may have provided better control if MSO instead of COC was used as recommended on the product label but none of the other Group 14 herbicide provided acceptable control of marestail. Some of the treatments (e.g., glufosinate) may have been less active if applied earlier in the year due to cooler temperatures. Higher spray volumes and different nozzles could potentially influence control as well. In general, herbicide combinations were not evaluated in this study but certain tankmixes may have provided some enhanced control. We plan to expand this study to assess some of these factors and other herbicides in the future.

HYPERSPECTRAL IMAGING TO DETECT GLYPHOSATE-RESISTANT VS. GLYPHOSATE-SUSCEPTIBLE KOCHIA SCOPARIA: IMPLICATIONS FOR SITE-SPECIFIC MANAGEMENT. P. Jha*1, V. Kumar1, P. Nugent2, A. Donelick2, B. Scherrer2, J. Shaw2; 1Montana State University, Huntley, MT, 2Montana State University, Bozeman, MT (62)


Advanced optics-based hyperspectral imaging could be a potential tool for early detection of herbicide-resistant weeds in-crop and for site-specific precision weed control. A hyperspectral image has large number of pixel spectra; therefore, image segmentation is executed pixel by pixel. This technology has the possibility of weed detection at a high rate of accuracy because the image contains more detailed spectral information and much higher resolution compared to Red, Blue, Green (RGB) or multispectral imaging. This project is focused on the development of hyperspectral imaging and smart algorithms to distinguish between herbicide-resistant and susceptible kochia in-crop. The crops include wheat, barley, and sugar beet. Our hyperspectral imager in the wheat/barley/sugar beet field was used to record hyperspectral data cubes with 240 spectral channels per spectrum over the wavelength range of 396 – 885 nm (visible to near-infrared). Such images obtained from the ground or from an aerial platform (UAVs), can be used to create maps that show growers where spot spraying (site-specific weed control) is required. This allows much more economical application of herbicide than broadcast spraying and also helps identify problem spots/patches with herbicide-resistant weeds in-crop. The pixel discrimination model between crop and kochia biotypes consisted of normalization, generation of explanatory variables and discrimination, and different types of models were developed and validated. The smart algorithms were based on machine learning classifiers, where various spectral features were used to map the locations of different biotypes of kochia in a crop field. The results indicate that glyphosate-resistant and dicamba-resistant kochia biotypes can be differentiated from a susceptible kochia biotype in a sugar beet, barley, or wheat field based on differential spectral reflectance across visible (520 to 650 nm) and near-infrared (720 nm) wavelengths.

WHEAT CANOPY STRUCTURE INCIDENCE IN NATURAL WEED POPULATIONS EMERGENCE. M. E. Cena1, M. V. Buratovich2, G. Picapietra3, H. A. Acciaresi*4; 1CIC, Pergamino, Argentina, 2ECANA-UNNOBA, Pergamino, Argentina, 3Instituto Nacional de Tecnología Agropecuaria, Pergamino, Argentina, 4Instituto Nacional Tecnologia Agropecuaria, Pergamino, Argentina (63)


The objective of this study was to evaluate the competitive ability of wheat (Triticum aestivum) varieties thought of emergence fluxes and the relations with canopy structure. The experiment was realized with different varieties of wheat with natural weed population. Four wheat varieties were used whit differences in height, foliar angle, width and length of the last expanded leaf and tillage number. Emergence fluxes were observed biweekly between August and December. The variables were measured from crop emergence during growing cycle (1152°D, 1750°D y 2300°D (growing degrees) (base temperature: 0°C). The varieties whit higher number of tillage.m-2 had registered a smaller numbers of emerged weeds (.m-2). Foliar variables did not affect the number of emerged weeds. The results obtained allow concluding that the number of tillers has an inverse relationship with the number of emerged weeds. According to this, the tiller number appeared as an important trait to be incorporated in breeding program to obtain wheat varieties with higher competitive ability.

DYNAMICS OF EMERGENCE OF NATURAL WEED POPULATIONS UNDER WINTER COVER CROPS. M. V. Buratovich1, M. E. Cena2, G. Picapietra3, H. A. Acciaresi*4; 1ECANA-UNNOBA, Pergamino, Argentina, 2CIC, Pergamino, Argentina, 3Instituto Nacional de Tecnología Agropecuaria, Pergamino, Argentina, 4Instituto Nacional Tecnologia Agropecuaria, Pergamino, Argentina (64)


The objective of this study was to characterize the emergence of weeds in different monocultures and mixtures of winter cover crops (CC). The species used as CC were oats (Avena sativa), triticale (Triticosecale) and vetch (Vicia villosa). These were sown in monocultures and mixtures doubles and triples, with 250 pl.m-2, except in vetch were 160pl.m-2 were used. A sector was left without CC to use as negative control. In each experimental unit during August-Novemberperiod, total number and species of emerged weeds were quantified fortnightly. Frames of 0.25m-2 were established in each treatment, with three replications. CC showed significant differences with fallow, in all treatments. Oats, oats/vetch, oats/triticale and triticale/vetch showed significant differences with vetch. Accordingly, CC appeared as an interesant alternative of cultural management that allow maintain weeds populations in low densities.

SEED GERMINATION OF JUNLERICE (ECHINOCHLOA COLONA) IN RESPONSE TO POST-HARVEST DORMANCY. G. Picapietra1, M. V. Buratovich2, M. E. Cena3, H. A. Acciaresi*4; 1Instituto Nacional de Tecnología Agropecuaria, Pergamino, Argentina, 2ECANA-UNNOBA, Pergamino, Argentina, 3CIC, Pergamino, Argentina, 4Instituto Nacional Tecnologia Agropecuaria, Pergamino, Argentina (65)


Junglerice seeds have a great dispersion capacity through different ways, mainly animals, machinery and water. After dispersal from mother plant, seeds have a dormancy that varies between two to seven months. To determine the time of dormancy and the pre-germination treatment that allow to overcome it, two experiments were carried out in the Agricultural Experiment Station of the National institute of Agricultural Technology (Pergamino-Argentina). Initially, seed samples were collected from mature plants in field, cleaned and stored. The first experiment consisted in planting seeds every 3 weeks from harvest, for 30 weeks (11 times). The second experiment was to sowed the seed with different pre-germination treatments: water 70°C washing, manual scarification, potassium nitrate, water 7°C for 48 hours immersion, and immersed in gibberellic acid 0.8% m/v. After post-harvest 21 weeks seeds began to germinate and at 30 weeks the 20% of germinated seedlings were obtained. The washing, scarified, and gibberellins treatments had no significant response, while the use of potassium nitrate and pre-sowing immersion were able to significantly increase the number of germinated seedlings.



Velvetleaf (Abutilon theophrasti Medik) is a problem weed in cotton (Gossypium hirsutum L.) production systems. There is a growing interest in using machine learning techniques for distinguishing velvetleaf from cotton. A greenhouse study was conducted to evaluate canopy multispectral reflectance data as input into the random forest machine learner to differentiate velvetleaf from cotton.  Cotton near-isogenic lines that have bronze, green, and yellow leaf colors were used in the study. Canopy reflectance measurements of velvetleaf and cotton plants were obtained with a hyperspectral spectroradiometer. The hyperspectral reflectance measurements were aggregated to sixteen multispectral bands: coastal, blue, green, yellow, red, red edge, near infrared 1 and 2, and shortwave infrared 1 thru 8. The multispectral data were entered into the random forest classifier to complete three binary classifications: velvetleaf versus cotton bronze, velvetleaf versus cotton green, and velvetleaf versus cotton yellow. Random forest algorithm achieved classification accuracies ranging from 44% to 83% for distinguishing velvetleaf from the cotton near-isogenic lines. Green, yellow, red, red edge, near infrared 1, and near infrared 2 spectral data were ranked as important variables for the algorithm to use for velvetleaf and cotton discrimination. When using canopy multispectral reflectance data as input, random forest had weak to moderate potential as a tool for differentiating velvetleaf from cotton.

ENHANCED WEED MANAGEMENT FOR ORGANIC VEGETABLE CROP PRODUCTION. J. O'Sullivan*1, R. C. Van Acker2, R. N. Riddle1, P. H. White1; 1University of Guelph, Simcoe, ON, 2University of Guelph, Guelph, ON (67)


The application of synthetic herbicides has become the primary method for weed management in conventional agriculture.  The perception of increased weed pressure and inadequate weed control methods in organic systems are major barriers to adopting organic crop production practices. Weed control remains a major concern for organic farmers. Only a few products, with limited weed control efficacy, are currently acceptable for organic agriculture. The objective of this study was to evaluate improved lower-risk, natural products, that are appropriate for use by organic growers, to provide enhanced weed management for organic vegetable growers. Postemergence (POST) treatments of Weed Zap, Manuka oil and Vinegar gave 48, 49 and 56% weed control, respectively, on June 30, 2016.  However, weed control with manuka oil, tank mixed with Weed Zap or Vinegar gave 79 and 86% weed control, respectively. This was a 30% improvement in weed control, compared to each product used alone. Finalsan gave 85% weed control.  Suppress gave 70 to 81% weed control while Pine Oil gave 66 to 68% weed control. By August 02, weed control was generally reduced, except for Manuka oil, tank mixed with Weed Zap or Vinegar and Suppress. Most treatments gave sweet corn yields that were not significantly different from the hand weeded control. Tomato yields were reduced except for Manuka oil, tank mixed with Weed Zap, and Suppress. Pepper yields were significantly reduced for all treatments, likely due to severe drought and significant late season weed competition. The best overall weed control was from applications of Manuka oil tank-mixed with Weed Zap or Horticultural Vinegar.  These combinations gave weed control that was significantly improved compared to either product used alone and gave a level of weed control that was comparable to the weed-free control. Manuka oil is the first natural product herbicide that has soil activity, is systemic and, when mixed with other approved products, enhances weed control activity. This research will improve weed management in organic farms by identifying specific organic weed management practices, appropriate for use by organic growers. This will increase productivity, significantly improve weed management, help growers to find solutions to the long standing issue of managing weeds in organic crop production while addressing the limitations of currently-approved products. 


MULCH AND BIOCHAR IMPACTS ON ORGANIC STRAWBERRY YIELD. S. K. Hogstad*, G. G. Gramig; North Dakota State University, Fargo, ND (68)


Perennial strawberries grown in organic systems are commonly mulched with hay/straw or plastic. Although hay/straw mulches add organic matter to the soil, they are unstable in windy conditions, harbor weed seeds, and may encourage pests. Plastic mulches efficiently suppress weeds; however, plastic does not biodegrade, thus presenting a disposal problem. Effective weed management is crucial for perennial strawberry production and the common mulching products pose weaknesses; therefore, introducing novel mulch materials would benefit producers. Diseases also pose a threat to strawberry production. Biochar soil amendment has been shown to increase resistance to some diseases and improve growth and yield of strawberry plants. Field trials were conducted during 2015 and 2016 at the NDSU Horticulture Research Farm in Absaraka, ND and at the Dickinson Research Extension Center in Dickinson, ND, to investigate the ability of two novel mulch materials (paper and hemp hurd) and pine-derived biochar to aid in perennial strawberry production. During early June 2015, Cavendish variety bare root strawberries were transplanted into prepared beds at both sites. The experiment was designed as a 2 (biochar vs. no biochar) x 4 (alfalfa hay, paper, hemp hurd, or no mulch) factorial arranged in a randomized complete block. Flower production, leaf number, and runner production were measured throughout the establishment year. Production year (2016) measurements consisted of fruit number and weight. Weed biomass and soil temperature were measured in both years of the experiment. Because weeds were removed during the establishment year, crop-weed competition did not occur during this year, therefore differences between mulch treatments were due to other factors. Leaf numbers were consistently affected by the mulch treatments across sites with paper mulched plots producing the greatest number (3.9) compared to bare ground (3.3), and hemp (3.3) plots; the fewest leaves were associated with those plants in hay mulched plots (2.6). At Absaraka, hay mulch was associated with the fewest number of flowers (3.6) compared to hemp mulch, no mulch, and paper mulch (5.0, 5.1, and 5.9 flowers per plant, respectively). Hemp mulched plots produced the most flowers at the Dickinson site (5.4), compared with paper (3.7), hay (2.9), or bare ground (3.2). In 2015, regardless of site or biochar application, no mulch was associated with the highest weed biomass (36.7 g m-2) compared with plots treated with hay, hemp, or paper mulch (5.1, 0.9, and 5.8 g m-2, respectively). During 2016, the production year, weeds were not removed. Therefore, treatment effects are the results of combined impacts of weed suppression (or lack thereof) and other effects caused by the various mulch materials. During 2016 and at both sites, hay mulched plots were associated with the greatest weed biomass whereas hemp mulched plots contained the least weed biomass compared with paper and no mulch plots. At Absaraka, greater strawberry weight was associated with hemp, no mulch, and paper compared to hay (4.7, 5.5, and 5.8 vs. 3.0 kg m-2, respectively). Mulch treatments had no significant effect on strawberry weight or number at the Dickinson site. Biochar had no effect on measures of strawberry yield at either site. Although the Absaraka site produced greater numbers of strawberries, per berry weight of strawberries harvested at Dickinson (7.59 g berry-1) was far greater than per berry weight at Absaraka (5.17 g berry-1). Plots mulched with hay contained greater soil N (175 kg ha-1) compared with those treated with hemp (46 kg ha-1), paper (54 kg ha-1), or bare ground (72 kg ha-1). Biochar amendment was associated with increased soil organic matter and pH at both sites. The novel mulch materials, paper and hemp hurd, were associated with greater yields at the Absaraka site and met or exceeded the ability of hay mulch to suppress weeds, especially during the production year. Hay mulch was associated with greater weed biomass in 2016 and greater soil N than the other mulch treatments; the increased weed biomass might be attributed to the hay mulch harboring weed seeds or increased soil N availability. This experiment demonstrated that hemp and paper mulch provide effective weed control for perennial strawberry production.

INTERACTION OF COMMON PURSLANE AND PALMER AMARANTH WITH TWO SWEETPOTATO CULTIVARS. S. Chaudhari*, K. M. Jennings, D. W. Monks; North Carolina State University, Raleigh, NC (69)


The growth habit of a crop cultivar can influence its competiveness with crops. Cultivar growth habit could influence the competitiveness of sweetpotato with weeds. The relative competitiveness of sweetpotato and weeds were determined by conducting replacement series experiments in the North Carolina State University Marye Anne Fox Science and Teaching Laboratory Greenhouse, Raleigh, NC. Sweetpotato cultivars included NC-10-275 (unreleased, drought tolerant) and Covington (most commonly grown cultivar in North Carolina). Weed species included a tall-growing (Palmer amaranth) and a low-growing (common purslane) weed. Sweetpotato cultivars were grown with Palmer amaranth or common purslane at densities of four plants per plot at five planting ratios of 100:0, 75:25, 50:50, 25:75, and 0:100. Relative yield (height and shoot dry weight) and aggressivity index of common purslane was lower than both sweetpotato cultivars. However, relative yield (height and shoot dry weight) and aggressivity index of Palmer amaranth was greater than Covington but lower than NC-10-275 . Reduction in common purslane shoot dry weight was greater when growing with NC-10-275  compared to Covington or grown alone. Palmer amaranth shoot dry weight was not reduced when grown with Covington; whereas, Palmer amaranth shoot dry weight was reduced with NC-10-275 . In competition with common purslane, shoot dry weight and root fresh weight of Covington was 20 and 26% lower than NC-10-275 , respectively. Whereas, Palmer amaranth competition reduced shoot dry weight and root fresh weight of Covington by 30 and 42% relative to NC-10-275 , respectively. This research indicates that both sweetpotato cultivars were more competitive than common purslane. In contrast, NC-10-275  was more competitive than Covington, with Palmer amaranth. In addition to drought tolerance, NC-10-275  also exhibited better weed competitiveness, which may result in its faster adoption when released for grower use.




The chemical control catalogue for chile pepper (herein “chile”) is lacking in POST-direct herbicides that can be applied near the time of crop thinning (9 to 10 weeks after seeding).  Previous studies determined that many weeds in chile were controlled with flumioxazin; however, this herbicide is not registered for use in chile in New Mexico.  The objective of this study was to evaluate POST-direct, hooded applications of flumioxazin for injury on chile.  To accomplish this objective, field studies were conducted in 2015 and 2016 at university research farms near Las Cruces, NM and Los Lunas, NM.  Soil at the Las Cruces site was silty-clay, 1.1% organic matter in 2015; clay, 1.2% organic matter in 2016.  At the Los Lunas site, soil was sandy-clay loam, 0.7% organic matter in 2015; sandy loam, 1.6% organic matter in 2016.  At both sites, chile was grown according to irrigation, soil and pest management practices typical for the specific region.  Treatments were: 1) flumioxazin (0.107 kg ai ha-1) at four weeks after crop thinning, 2) carfentrazone (0.035 kg ai ha-1) at 4 weeks after crop thinning, 3) flumioxazin (0.07 kg ai ha-1) at 4 and 6 weeks after crop thinning, 4) carfentrazone (0.035 kg ai ha-1) at 4 and 6 weeks after crop thinning, and 5) unsprayed control.  Carfentrazone is registered for use in chile and features the same mechanism of action as flumioxazin (Protoporphyrinogen Oxidase [PPO] Inhibitor).  All plots sprayed with flumioxazin and carfentrazone showed characteristic PPO inhibitor damage (speckling followed by chlorosis then necrosis) to some lower leaves on chile plants.  At Las Cruces, herbicide treatment did not influence chile yield in 2015 and 2016.  At Los Lunas, flumioxazin reduced yield of some chile cultivars (NM 6-4, Paprika, Sandia) in 2015, which was the year chile was grown on coarse-texture soil with 0.7% organic matter.  When chile was grown on coarse-texture soil with 1.6% organic matter (2016), flumioxazin did not cause yield reductions.  Reductions in chile yield were not observed for the carfentrazone treatments.  The results of this study suggest that a registration for POST-direct, hooded applications of flumioxazin in chile would need to be conditioned by soil type.  The alleged association between crop injury and organic matter in course-texture soil is currently being studied under greenhouse conditions.

FIELD BINDWEED (CONVOLVULUS ARVENSIS) RESPONSES TO PPI AND PRE HERBICIDES - A RESEARCH SUMMARY. L. M. Sosnoskie*1, B. Hanson2; 1University of California, Davis, CA, 2Univesrity of California, Davis, CA (71)


Field bindweed (Convolvulus arvensis L.), a deep-rooted and drought tolerant perennial, is a significant concern of the processing tomato industry in California. If allowed to compete with tomatoes during canopy establishment, field bindweed can significantly reduce both fruit number and quality. Furthermore, field bindweed vines can become physically entwined with tomato plants, which, in turn, can reduce harvest efficiency.  

Between 2013 and 2015, multiple field studies were conducted to evaluate the efficacy of pre-plant incorporated (PPI) and pre-emergence (PRE) herbicides on the suppression of field bindweed. All trials were conducted at the University of California, Davis, research farm (38 32’N, 121 47’W), where the soil is a fine, silty loam (Yolo series, 37% sand, 41% silt, 22% clay; 1.5-3% OM; pH 6.7-7.2). The fields used in this study were known to be heavily infested with field bindweed. Tomatoes were transplanted between April and June and were sprinkler-irrigated with 1 inch (2.5 cm) of water immediately after planting to facilitate crop establishment and activate soil applied herbicides. All herbicides were applied using a CO2-pressurized backpack sprayer equipped with three 8002VS flat-fan nozzles spaced 16-20 in (41.6-50.8 cm) apart and calibrated to deliver 20-30 GPA (187-281 L/ha). All herbicides were applied to the soil surface 1 day before transplanting; trifluralin, S-metolachlor, and sulfentrazone were mechanically incorporated immediately thereafter. Field bindweed cover (defined as the percent (%) of the plot area that was occupied by field bindweed) was assessed until tomato canopy closure began to occur.

Results indicate that trifluralin (as Treflan at 32 oz/A or 2.3 L/ha) applied PPI, rimsulfuron (as Matrix at 4 oz/A or 0.3 kg/ha) applied PRE, and sulfentrazone (as Zeus at 3.2, 4.5 and 6 oz/A or 0.2, 0.3 and 0.4 L/ha) applied PPI were effective at suppressing field bindweed for up to 4 weeks after transplanting (WAT). Across trials, field bindweed cover ranged from 11-76% in the untreated checks (mean = 51% cover). Cover in the S-metolachlor (as Dual Magnum at 27 oz/A or 2.0 L/ha) treatments (mean = 51% cover) did not differ, substantially, from the controls. Mean field bindweed vine cover in the trifluralin, rimsulfuron, and sulfentrazone treatments ranged from 4-35% cover. Mean cover, averaged over trials, was 16% for trifluralin, 10% for rimsulfuron, and between 4 and 17% for sulfentrazone, depending on rate. Results show that rifluralin, rimsulfuron, and sulfentrazone have some early-season activity against perennial bindweed vines, while S-metolachlor does not. Trifluralin, rimsulfuron, and S-metolachlor are all labeled for use in California processing tomatoes for the residual control of emerging weeds ( Sulfentrazone has/has had a supplemental label (as Zeus) allowing for its use in transplanted tomatoes for the suppression of yellow nutsedge. In addition to perennial bindweed suppression, rimsulfuron is effective against most nightshade species, pigweeds, and lambsquarters; trifluralin will control many annual grasses as well as some broadleaf weed species. S-metolachlor, while not effective against bindweed, can also suppress nutsedge and nightshades.


FIELD BINDWEED (CONVOLVULUS ARVENSIS) RESPONSES TO POST HERBICIDES - A RESEACH SUMMARY. L. M. Sosnoskie*1, B. Hanson2; 1University of California, Davis, CA, 2Univesrity of California, Davis, CA (72)


Field bindweed (Convolvulus arvensis L.) is a deep-rooted and drought tolerant perennial. Although bindweed seedlings are relatively easy to manage using physical and chemical control strategies, established plants with extensive root systems are tolerant of most management practices. Between 2013 and 2016, multiple trials were conducted at the University of California, Davis, to evaluate the efficacy of glyphosate (as Roundup Powermax at 1 and 2 qt/A or 2.3 and 4.6 L/ha), rimsulfuron (as Matrix at 2 oz/A or 0.14 kg/ha), halosulfuron (as Sandea at 2 oz/A or 0.14 kg/ha ), carfentrazone (as Shark at 2 oz/A or 0.14 L/ha), glufosinate (as Rely 280 at 3 pt/A or 3.5 L/ha), paraquat (as Gramoxone Inteon at 3 pt/A or 3.5 L/ha), and saflufenacil (as Treevix at 1 oz/A or 0.07 kg/ha) for the control of vigorously growing bindweed vines. All herbicides were applied post-emergence (POST) using a CO2-pressurized backpack sprayer equipped with three 8002VS flat-fan nozzles spaced 16-20 in (41-51 cm) apart and calibrated to deliver 30 GPA (281 L/ha). Adjuvants were used according to label recommendations. Control of field bindweed was rated for up to 6 weeks following treatment (WAT). Included in the suite of trials were studies to evaluate the diurnal and seasonal effects of herbicide applications on bindweed control.

Results from the diurnal timing trial indicated that herbicide, alone, had a significant effect on bindweed cover; the timing of herbicide applications and the interaction between herbicide and the time of day (sunrise, 2 hr after sunrise, mid-day, 2 hr before sunset, and sunset) when the herbicides were applied were not significant. Although the carfentrazone and the paraquat treatments worked rapidly (field bindweed cover was reduced by more than 90% at 1 WAT), the vines regrew vigorously; cover at 5 WAT was 42-45%, which was similar to what was observed for the untreated check (37%). Glyphosate was significantly better at reducing field bindweed cover at 5 WAT (2-5%) relative to the untreated check. Rimsulfuron did not reduce field bindweed cover, relative to the control, at any point in time. Bindweed cover in the untreated check and the rimsulfuron treatment decreased over time due to the development of powdery mildew, which resulted in leaf loss. 

With respect to the seasonal study, results show that herbicide applications made on 18 May, 2016, provided almost no control of field bindweed. Field bindweed cover increased (from 28-43% at 0 WAT to 57-78% at 6 WAT) for all herbicides with the exception of glyphosate (18-23% cover at 6 WAT). For the 30 June, 2016, herbicide applications, bindweed cover was reduced from 50-80% at 0 WAT to 4-38% at 6 WAT, including the untreated check; high temperatures, limited soil moisture, and a powdery mildew infestation helped facilitate vine senescence. That being said, vine cover was much more reduced in the glyphosate, glufosinate, saflufenacil, and paraquat treatments (4-8%) as compared to the check, rimsulfuron, and halosulfuron treatments (22-38%). The disparity in control between the APR-MAY and JUNE-JULY sprays dates is likely related to (1) the amount of aboveground biomass available at the time of treatment to capture the applied herbicides and (2) the strength of the rhizome as either a sink or source of carbohydrates. 


RESIDUAL EFFECTS OF PRE-PLANT HERBICIDES ON TRANSPLANTED TOMATOES. J. Angeles1, K. J. Hembree2, A. Shrestha*1; 1California State University, Fresno, CA, 2University of California Cooperative Extesnion, Fresno, CA (73)


Greenhouse studies were conducted in Fresno, CA in 2015 and 2016 to evaluate plant injury to simulated residues of some common pre-plant herbicides used in tomato production and other crops rotated with tomatoes. Above- and below-ground response of transplanted tomatoes to incremental doses of pre-plant herbicides trifluralin, s-metolachlor, and pendimethalin at simulated residual doses of 0, 0.03, 0.06, 0.12, 0.25, and 0.5 ppm were evaluated. Herbicide-free field soil was collected and placed in 11.4-l plastic pots after mixing in the different herbicide doses. One tomato seedling was transplanted in each pot. Plant height and leaflet numbers, chlorophyll concentration (SPAD) of leaves, and stomatal conductance were monitored weekly. At 45 days, the plants were clipped at the soil surface and the above- and below-ground parts were separated. The leaves were also separated and their total area was determined. The roots were thoroughly washed. Dry weights of all plant parts were recorded. Data were analyzed using ANOVA procedures and non-linear regression models. The doses required to reduce biomass by 10% (GR10) and 50% (GR50) were estimated. All the herbicides reduced plant biomass at the highest dose when compared to the non-treated control. Trifluralin caused greater reductions in above-ground biomass than pendimethalin and s-metolachlor with a GR10 and GR50 of 0.02 and 0.46 ppm, respectively. The GR10 of S-metolachlor and pendimethalin was 0.03 and 0.08 ppm, respectively for above-ground biomass. The GR50 for both these herbicides were >0.5 ppm. s-metolachlor caused the greatest reductions in root biomass with GR10 and GR50 of 0.004 and 0.22 ppm, respectively. The GR10 for trifluralin and pendimetalin was 0.008 and 0.04, respectively; whereas, the GR50 for both these herbicides were >0.5 ppm. Stomatal conductance was generally reduced at the higher doses of all herbicides compared to the untreated control. Leaf area was reduced by s-metolachlor more than the other herbicides. Although trifluralin caused greater reduction in above-ground biomass, s-metolachlor had the greatest overall potential to cause above- and below-ground injury. Pendimethalin was relatively safer than the other two herbicides. Therefore, residual concentrations of herbicides in the soil should be assessed before transplanting tomatoes in buried drip-irrigated fields in California.

BICYCLOPYRONE: MAJOR LEAGUE WEED CONTROL IN MINOR LEAGUE CROPS. C. L. Dunne*1, D. Bruns2, G. D. Vail3, T. Beckett3; 1Syngenta, Vero Beach, FL, 2Syngenta, Columbus, OH, 3Syngenta Crop Protection, Greensboro, NC (74)


Bicyclopyrone is a newly registered HPPD-inhibiting active ingredient for control of dicot and some grass weeds.  Bicyclopyrone is one of the four active ingredients in Acuron herbicide which was registered for sales in corn in 2015.  Syngenta is evaluating the potential for expanding bicyclopyrone use into minor/specialty crops where options for weed control are limited.  In 2016, University and Syngenta trials evaluated both PRE and POST bicyclopyrone applications for crop tolerance and weed control in various minor/specialty crops



MISSISSIPPI ROADSIDE RIGHTS-OF-WAY:  AN INVENTORY OF THE VEGETATION. J. D. Byrd, Jr.*1, V. L. Maddox1, D. G. Thompson2; 1Mississippi State University, Mississippi State, MS, 2Mississippi Department of Transportation, Jackson, MS (76)


The Weed Science Society Board of Directors revised the definition of weed in 2015 as any plant that causes negative economic or ecological impact, is detrimental to human or animal health, or grows where it isn’t wanted.  According to the 2011 American Association of State Highway and Transportation Officials (AASHTO) Guidelines for Vegetation Management, the positive attributes of roadside right-of-way vegetation are plants that promote driver safety, economical to establish and maintain, prevent soil erosion, environmentally friendly, promote positive public relations, do not expose liability, aesthetically pleasing, and contribute to transportation sustainability.  Three-hundred sixty-three species of plants in 225 genera and 72 families were identified and visual percent ground cover occupied by each was estimated in 2011.  Eight hundred 1.5 m2 plots on Mississippi Department of Transportation (MDOT) maintained highway rights-of-way were sampled.  Medians of divided lane roads were not included in the survey.  Native, perennial, warm-season vegetation dominates the highway rights-of-way in Mississippi.  USDA Plants Database ( revealed 77% of the species identified in the survey are native to Mississippi, 21% are introduced, and the remaining 2% are listed as both.  Based on lifecycle information from the same data source, 61.5% of plant species on Mississippi rights-of-way are perennial, 24.7% have an annual lifecycle, only 0.5% are biennial, and the 13.3% remaining are combinations of annual, biennial, and perennial. Based on various published taxonomic flower or seed production descriptions, 69% of the plants identified in this inventory grow during the warm-season, while 24% grow in the cool-season and the remaining 7% have a less definitive flower or seeding period. The plants observed in the greatest number of plots were those species intentionally seeded during right-of-way construction:  bermudagrass (Cynodon dactylon) in 390 plots, bahiagrass (Paspalum notatum) in 291 plots, Italian ryegrass (Lolium perenne ssp. multiflorum) in 223 plots, and tall fescue (Schedonorus arundinaceus), in 145 plots.  Since these four species are intentionally seeded during right-of-way construction, they cannot be considered weeds on roadside rights-of-way.  Any species not intentionally seeded on the right-of-way may be considered weedy.  Plants not intentionally seeded, but observed in most number of plots included southern crabgrass (Digitaria ciliaris) in 136 plots, little bluestem (Schizachyrium scoparium) in 99 plots, common lespedeza (Kummerowia striata) in 87 plots, cheat (Bromus secalinus) in 84 plots, buckhorn plantain (Plantago lanceolata) in 80 plots, rattail fescue (Vulpia myuros) in 75 plots, knotroot foxtail (Setaria parviflora) in 74 plots, large hop clover (Trifolium campestre) in 71 plots, broomsedge (Andropogon virginicus) in 67 plots, and vaseygrass (Paspalum urvillei) in 64 plots.  All species identified were also ranked by overall density.  This indicator was calculated as total percent visual cover summed over all 800 plots divided by 1200 m2, or the total area of all plots surveyed.  With this analysis, the most prevalent species across Mississippi highway rights-of-way were bermudagrass, bahiagrass, tall fescue, southern crabgrass, Italian ryegrass, little bluestem, centipedegrass (Eremochloa ophiuroides), common lespedeza, cheat, rattail fescue, Johnsongrass (Sorghum halepense), cogongrass (Imperata cylindrica), Virginia buttonweed (Diodia virginica), large hop clover, knotroot foxtail, and broomsedge.  Plants identified in the survey were also ranked by plot dominance, calculated as the quotient of the sum of percent visual cover in all plots divided by the number of plots infested.  While site dominance is partly a function of site suitability for a species, it is also an indicator of species fecundity, as well as interference with other plants.  Based on plot dominance analysis, only two intentionally seeded species ranked as top plants in the inventory, bahiagrass with 36% plot cover and bermudagrass with 33% plot cover.  Of the plants not intentionally seeded on rights-of-way, needlepod rush (Juncus scirpoides) ranked as a highly dominant species as it occupied 100% cover, but occurred in only a single plot. Eastern gamagrass (Tripsacum dactyloides) averaged 44% ground cover in the 4 plots infested.  Cogongrass occupied an average of 42% ground cover in the 17 plots it infested.  Mugwort (Artemisia vulgaris) occupied 40% ground cover in a single plot.  Centipedegrass occupied an average of 40% ground cover in the 35 plots in which it occurred.  Slender fimbry (Fimbristylis autumnalis) was more dominant than bermudagrass, but less than bahiagrass, at an average of 34% visual ground cover in the 3 plots infested.  Four species were each identified in a single plot and occupied an average of 30% ground cover in those plots: alligatorweed (Alternanthera philoxeroides), variableleaf sunflower (Helianthus heterophyllus), Samson’s snakeroot (Orbexilum pedunculatum), and pale dock (Rumex altissimus).  These data also demonstrate while Early Detection and Rapid Response (EDRR) of invasive plants sounds good in theory, the reality of this practice as a functional method to detect new weed invasions is not feasible.  This conclusion is based on the fact that while these specific plants are not necessarily invasive species, 93 plants identified in this survey were observed in only a single plot.  Of those 93 species, 22 occupied only 1% visual ground cover in plots.  Thus, the probability of early detection for a rapid response is extremely low, unless some other highly visible morphological characteristic exists in that species and is prominent when the survey is conducted.

TAXONOMIC IDENTITY AND CHARACTERIZATION OF AN INVASIVE LINARIA HYBRID. C. Miller1, S. E. Sing2, S. M. Ward*1; 1Colorado State University, Fort Collins, CO, 2US Forest Service, Bozeman, MT (77)


Gene flow between yellow toadflax (YT) and Dalmatian toadflax (DT) produces hybrid offspring that are highly fertile and potentially even more invasive that either parent species. Early generation (F1, F2 and BC1) hybrid toadflax (HT) plants are morphologically distinct from YT, DT and other Linaria taxa, and can form extensive stable populations through clonal spread and seedling recruitment. With HT populations now increasingly common throughout the Intermountain West, assignment of a formal taxonomic designation and associated identifying characteristics for these plants is needed.  We propose the designation Linaria x radersbergii for these hybrids, with associated morphological descriptors using growth form, leaf shape, leaf venation, flower color, petal shape, inflorescence structure, and seed shape as key identifying traits.  We quantified morphological identifiers in 24 YT, 22 DT, and 81 HT plants grown in a common greenhouse environment, and used these data to develop a dichotomous key that reliably distinguishes between YT, DT and HT.  Designation of HT as a separate taxon and availability of a user-friendly key as an identification tool will assist in early detection of hybrid toadflax populations in the field as an essential first step toward more effective management.



GREEN MILKWEED (ASCLEPIAS VIRIDIS): FRIEND OR FOE, DO WE REALLY KNOW? D. P. Russell*1, J. D. Byrd, Jr.2, N. H. Thorne1; 1Mississippi State University, Starkville, MS, 2Mississippi State University, Mississippi State, MS (78)


In an attempt to refute claims that herbicide applications indirectly caused monarch butterfly population decline by reducing the primary host of larvae development, green antelopehorn (Asclepias viridis) populations were treated with herbicides routinely used for vegetation management in rights-of-way and forages in 3 locations in Mississippi. Treatments were broken into groups to match available area for field evaluations. All treatments were replicated 4 times in a randomized complete block design and applied using a CO2 pressurized backpack sprayer that delivered 15 GPA. Response variables measured were visual estimates of herbicide injury, plant growth stage, plant height and stand counts.  Data were analyzed by analysis of variance and tested for significance by treatments, growth stage and interactions of treatment by growth stage. Responses presented here describe changes in stand counts, measured by plants/m2, from the initial treatment until the final evaluation. Means were separated by least square means.

Treatments in group 1 were applied in Oktibbeha county near Oktoc on May 5: Chaparral (aminopyralid+metsulfuron methyl) at 1.5 and 3.0 oz/A; Arsenal AC (imazapyr) at 1.0 and 2 pt/A; Remedy Ultra (triclopyr) at 2.5 and 5.0 pt/A; Graslan (picloram+2,4-D) at 1.3 and 2.7 pt/A; GrazonNext HL (aminopyralid+2,4-D) at 1.0 and 2.0 pt/A; Milestone (aminopyralid) at 3.5 and 7.0 fl oz/A; Vastlan (triclopyr) at 1 and 2 qt/A; Vista (fluroxypyr) at 11 and 22 fl oz/A. Although visual herbicide injury at 29 DAT did indicate significant differences by treatment, no differences were found among treatment, growth stage, or treatment by growth stage with regard to changes in stand counts from 0 to 120 DAT. Milkweed stand counts in all plots did decline over time, however none were more significant than the amount of decline in untreated check.

A second group of treatments were applied May 6 near Mayhew, MS: Cimarron Plus (metsulfuron+chlorsulfuron) at 0.6 and 1.2 oz/A; Derigo (foramsulfuron+iodosulfuron+thiencarbozone) at 3 and 6 oz/A; Escort (metsulfuron methyl) at 0.25 and 0.5 oz/A; Method (aminocyclopyrachlor) at 2.0 and 4.0 fl oz/A; Oust (sulfometuron methyl) at 0.5 and 1.0 oz/A; Pastora (metsulfuron methyl+nicosulfuron) at 0.75 and 1.5 oz/A; Perspective (aminocyclopyrachlor+chlorsulfuron) at 2.5 and 5 oz/A; Viewpoint (aminocyclopyrachlor+metsulfuron methyl+imazapyr) at 10 and 20 oz/A; and Velpar (hexazinone) at 1.5 and 3 pt/A. Analysis of 28 DAT visual injury responses indicated significant differences between herbicide treatments. Changes in stand counts across 119 DAT indicated significant reduction by growth stage and by the interaction of treatment by growth stage. The effect of growth stage on stand counts suggested the number of plants in the reproductive stage declined significantly more than plants in vegetative stage over 119 DAT. Effect of the interaction suggested vegetative green antelopehorn increased in number with each rate of Derigo and Escort at 0.5 oz. These gains in stand number however, were no different than the smallest stand decreases at the vegetative stage with each rate of Oust, each rate of Velpar, Cimarron Plus at 1.2 oz, untreated, Pastora at 0.75 oz and Perspective at 5 oz. Stands in each of these treatments had no more than a 1.12 plant/m2 decline by 119 DAT. Derigo at 3 and 6 oz/A were the only treatments causing more significant stand declines at the reproductive stage, decreasing an average of 4 and 3.37 plants/m2 respectively.

A third and final group of treatments were applied to green antelopehorn June 20, also near Oktoc in Oktibbeha county: Outrider (sulfosulfuron) at 0.65 and 1.3 oz/A; Roundup Powermax (glyphosate) at 1, 2, and 4 qt/A; Weedmaster (dicamba+2,4-D) at 0.67 and 1.3 pt/A; and Method (aminocyclopyrachlor) at 4, 8, and 12 fl oz/A. Stand counts were determined by the number of plants/m2 at each evaluation date. Changes in counts are shown as the difference between 0 and 74 DAT. Effect of treatment was the only level of significance at this location. Stand counts declined with all herbicide treatments, but declined the least with both rates of Outrider, each rate of Roundup Powermax, Weedmaster at 0.67 pt/A, and the untreated check. These treatments caused less plant decline than 8 oz/A Method, which declined an average of 2.87 plants/m2 by 74 DAT.

These preliminary evaluations confirm green antelopehorn is highly tolerant to many herbicides used for integrated vegetation management (IVM) on utility and highway rights-of-way. IVM practices that use these herbicides will protect monarch butterfly larvae habitat. These findings also confirm green antelopehorn management in pastures and hay fields will require diligence and persistence as no individual treatment provided acceptable control.





Exotic invasive weeds species pose a serious threat to forested and other landscapes in southern British Columbia. Of importance are scotch broom (Cytisus scoparius), gorse (Ulex europaeus), Hmalayan blackberry (Rubus armeniacus), English ivy (Hedera helix) and daphne surge (Daphne laureola). They were introduced as ornamentals in the last century or later and since then have invaded forests, thousands of hectares of urban lands, parks, right-of-ways, roadsides and are displacing/damaging the native species. Gorse is also associated with forest fires because its dried biomass with volatile oils and a  high fuel-load is highly combustible. Field experiments were carried out to control it by a chemical herbicide (triclopyr), a new formation of a bio-herbicide (Chondrostereum purpureum), a manual cutting method and uses of a mulch. The herbicide (480 gm/L) and the bio-herbicide formulation (with active mycelia and adjuvants to prolong shelf-life) were applied by a squeeze bottle (3ml/cut stem). The black mulch was a commercial plastic sheet, fitted to cover the entire cut stem surfaces devoid of light and small animal nests. Efficacy was measured by the degree of re-sprouting of the cut stems by which gorse propagates. Details are described in the poster. Results showed that the integrated approach with application of the herbicide, a new formulation of the bio-herbicide and mulching offered a significant control in re-sprouting behavior of the gorse. The new formulation of the bio-herbicide was patented in Canada and U.S.A. and now an improved formulation (Chontrol) is widely used for vegetation management by hydro, utility lines in Canada and U.S.A. Similarily, the two other bio-herbicides based on Fursarium tumidum and Phomposis species have been found to control scotch broom and Daphne surge respectively. 

Keywords: Chodrostereum purpreum


INTEGRATED MANAGEMENT OF BROMUS TECTORUM (CHEATGRASS) WITH SHEEP AND HERBICIDE. E. A. Lehnhoff*, L. J. Rew, J. Mangold; Montana State University, Bozeman, MT (80)


Control of cheatgrass can be problematic in a rangeland setting. In many parts of the sagebrush steppe, cheatgrass grows throughout the winter when native grasses are less active. This difference in growth phenology provides a window of opportunity to target the annual grass without impacting native grasses. However, in wet and cold regions of the sagebrush biome the growth of annual and perennial grasses is more simultaneous due to cold, dry winters followed by wet and warmer weather in April through June. Herbicides are frequently used to treat cheatgrass in range settings, but efficacy is variable in Montana. Targeted grazing is another approach that could be used. We evaluated the effect of herbicide alone, targeted intense grazing alone and a combination of both on cheatgrass and co-occurring vegetation. Herbicides included imazapic (0.42 kg ai ha-1), glyphosate (0.42 kg ai ha-1 + non-ionic surfactant, 0.1%v/v) and rimsulfuron (0.21 kg ai ha-1) applied in the fall alone and in combination with targeted spring grazing. The effect of spring glyphosate and a dual application of spring glyphosate and fall imazapic without grazing was also assessed. Sheep grazed for ~24 hours on each 5 m × 20 m plot in early May (2015-2016) for the grazing treatment. Plots were sampled the summer after herbicide application and two months after the second season grazing application. Grazing plus imazapic or rimsulfuron decreased cheatgrass cover but not seed production. Of the herbicide only treatments, the dual application of spring glyphosate and fall imazapic was the only treatment to reduce cheatgrass abundance, but this did not affect seed production. Bare ground increased in all grazing treatments. Grazing alone resulted in the most significant reduction in seed production, suggesting it may be the best approach for reducing seed return to the seedbank and consequently longer-term control of cheatgrass.  


USE OF HERBICIDES TO CONTROL WESTERN JUNIPER (JUNIPERUS OCCIDENTALIS) IN SAGEBRUSH COMMUNITY. G. M. Sbatella*1, S. Twelker2; 1University of Wyoming, Powell, WY, 2Oregon Department of Agriculture, Madras, OR (81)


In order to determine if herbicides can provide an effective way to control Western Juniper in sagebrush communities in the early stages of encroachment, field studies were initiated in 2013 near Prineville, Oregon. Fall and spring applications of the active ingredients picloram, hexazinone, aminocyclopyrachlor, triclopyr, imazapyr, and glyphosate were tested with spot and basal bark as applications methods. Mechanical removal was included as a treatment to verify the capability of Western Juniper to sprout after cutting.  Western juniper control with picloram applied as spot treatment was 96%, meanwhile when applied as basal bark control averaged 99%. The spot application of hexazinone resulted in 98% Western juniper control. The combination of aminocyclopyrachlor plus triclopyr when applied as a basal bark treatment, provided 57% control. Similarly, control was not satisfactory when tank mixing imazapyr with glyphosate and basal bark applied (30%).  Approximately 11% of the trees removed mechanically, regenerated foliage 24 months after cutting.





EPA’s Office of Pesticide Programs (OPP) is working to develop a new plant exposure estimation tool, Audrey III, which will incorporate refined methods for assessing exposure to plants in terrestrial and semi-aquatic environments. This model, which is a replacement for the current exposure plant model TerrPlant, may be used to address various protection goals, including habitat for animals, biodiversity of native habitats, plants of economic values, and species of special concern (e.g., endangered species). Audrey III will make better use of fate and transport data that are typically available for pesticides and will use the same crop scenarios (including soil and weather data) currently being used for Tier II surface water assessments. The Audrey III model will also integrate spray drift and runoff into a single exposure assessment.  OPP intends to develop Audrey III into a stand-alone Tier II model that utilizes existing algorithms used in the Pesticide in Water Calculator (PWC) for aquatic exposure assessments.

DIGITAL BOOK FOR WEED SCIENCE. B. A. Ackley*, A. I. Lamb; The Ohio State University, Columbus, OH (84)


Plant identification can be challenging and even intimidating for the inexperienced. Growers do not necessarily need to identify every weed in a field to be effective managers, but should be able to identify the major weeds that are important to their operations and goals. At first glance, learning how to identify weeds can seem like a daunting task given the number and diversity of species, but it is not as difficult as it may seem. Generally, there is a specific group of weeds that tends to dominate disturbed habitats within any native landscape. These digital books were created to help people better understand the nature of the weeds they are trying to control, and plant identification is a key component of that understanding. These digital books provides a new way to use an old tool - visualization - in the world of weed identification. Plant descriptions contained herein include key identification characteristics, photos of many species at different stages of maturity, and 360-degree movies for most species in the book.  These books are not meant to be a compendium of all weedy plants, but rather includes a number of the most common Midwestern U.S. and Central Europe weeds and the basic intellectual tools that are necessary to successfully identify plants.



Effective teaching involves the transfer of knowledge from the instructor to the student. This transfer though is most beneficial when the student can be a source of learning for the instructor, in order for the instructor to improve teaching methods for the course. Weed science, among the agronomic sciences, is not a course that can be taught in the classroom alone. Effective undergraduate learning in weed science requires a significant hands on component, especially for weed identification, sprayer calibration, herbicide injury and weed effects on crops. The Plant Protection Program at Northwest Missouri State University seeks to teach students how to critically think, especially after being able to correctly identify weeds and understand where to find information for their control. The program has received feedback from numerous area and regional employers who want students that can take a systems approach to make an effective weed management decision. This employer feedback has been especially helpful in guiding classroom instruction in the weed science, agricultural pesticides, and principles of spray application and technology courses at Northwest as they are continually improved to deliver improved student understanding of the weed sciences and be able to give them an advantage in the marketplace. While this development is far from complete, this ever changing work-in-progress will use 3, 5, and 10 year milestones to evaluate how these methods are working and make changes where necessary. 


DEVELOPMENT OF AN EDUCATIONAL MAPPING TOOL FOR DOCUMENTING AND RESEARCHING THE SPREAD OF HERBICIDE RESISTANT WEEDS IN THE US. A. Klodd*1, W. Curran1, D. Miller1, S. Crawford1, D. Lingenfelter1, A. S. Davis2; 1Pennsylvania State University, University Park, PA, 2USDA-ARS, Urbana, IL (86)


The spread of Palmer amaranth (Amaranthus palmeri) and waterhemp (Amaranthus tuberculatus), two competitive herbicide resistant pigweeds, is becoming an increased challenge for row crop production in many US states. As multiple resistant biotypes of these weeds continue to spread geographically, awareness of their locations may help producers prepare appropriate prevention and management strategies before infestations develop. Additionally, learning the geographic distribution and spread patterns of resistant pigweed populations could aid research efforts that aim to understand the causes and rate of spread. To gather information on the national distribution of Palmer amaranth and waterhemp resistance biotypes, an online mapping tool of all US states is currently being developed to crowdsource this data and make it easily accessible to stakeholders. The completed tool will enable voluntary data entry through an online platform, including GPS location, species, crop, and management practices for the location. The real-time public map displays the number of unique locations entered per county for each species, while all other data is accumulated in a non-public database for research use. Research data may be analyzed to correlate management variables to the spread of pigweed geographic range. The primary intended result of this tool is to create easy access to accurate and thorough distribution information to aid in decreasing the spread and development of herbicide resistant pigweed populations.


DEVELOPMENT OF TOOLS FOR IN-SERVICE TRAINING AND GROWER OUTREACH REGARDING RESISTANCE MANAGEMENT CONCEPTS. H. A. Sandler*1, L. G. McDermott2, K. M. Ghantous1; 1UMass Cranberry Station, East Wareham, MA, 2Cornell University, Ithaca, NY (87)


Selection and use of available pesticides, with varied modes of actions (MoA), must be correct and judicious to forestall or avoid resistance development. Growers currently receive management information from various sources (e.g., Extension, pest advisers), but the information delivered is not necessarily consistent and comprehensive. Northeastern Extension and agricultural industry personnel need education to properly provide pest management and resistance management (RM) advice to specialty crop growers. This initiative, funded by a NE-SARE Professional Development Program grant, is creating and coordinating a unified approach to deliver RM education to Northeastern producers. Four “train-the-trainer” webinars, augmented by a Moodle resource platform, have been produced and uploaded to YouTube. We produced a core module (slide presentation to be utilized in outreach workshops) that is available at: We are currently working on the production of an educational video for reinforcement of RM principles. Trained Extension personnel will participate in two Northeastern producer events to reinforce and exchange knowledge of RM.  We will distribute surveys to capture changes in growers’ knowledge and behavior after attending workshops where educators present RM information.

Our goal is that after participating in the multiple facets of this grant, Extension and agricultural industry personnel from Northeastern states develop crop-specific training modules and materials to transfer this knowledge to Northeast specialty crop growers. The full survey results from assessing the resistance management education and experience of educators and growers in the Northeast can be found at:

Selected results of the Pre-Webinar Series poll include:

Selected results from the Fungicide/Insecticide/Herbicide Webinar Series poll include:

We have been in contact with a small subset individuals to stay informed about workshops in their area and commodity.  We will use this short list of interested individuals to help us keep track of RM training sessions over the next year.  We will also engage this Short List to promote the use of the survey by educators. Twenty-eight (28) people, who registered for the webinar series, indicated that they are interested in obtaining a Certificate of Completion (COC), which requires attending at least 2 of the 4 webinars, conducting one-on-one or workshop education and participating in the verification portion of the grant.



TRASH TO TREASURE: AMARANTH RECONSIDERED AS A SOURCE OF NUTRITION AND ALTERNATE GRAIN PRODUCT. A. Taylor*, J. D. Byrd, Jr., Y. Zhang, S. Chang; Mississippi State University, Mississippi State, MS (89)


The USDA Plants Database ( lists 48 species of amaranth, 11 of which occur in Mississippi. Palmer amaranth (Amaranthus palmerii) is reported from 30 states.  It is also reported as the most troublesome weed of cotton in 7, peanut in 5, and soybean in 4 states within the Southern Weed Science Society region.  Resistance to herbicides is one characteristic contributing to this ranking.  Palmer amaranth could be a plant with the potential to become an important food source, rather than a detested weed.  It has the potential to provide an important source of nutrients, and as a hardy plant, could be easily cultivated.  Commercially produced Amaranthus grain has become more widely available in the U.S. The objective of this research was to compare the nutritional composition of glyphosate-resistant Palmer amaranth to commercially produced Amaranthus. Cultivated amaranth was acquired from a grocery store and glyphosate resistant amaranth was harvested from a field in Starkville, MS.  Both were finely ground to pass a 0.5 mm screen, then analyzed for nutrient content with methods approved by the Association of Official Analytical Chemists to determine the moisture, protein, lipid, ash, phenolic contents, and antioxidant capacity. The glyphosate-resistant amaranth contained significantly (p < 0.05) higher amount of lipid and ash but lower amount of protein than the commercially grown variety. Total phenolic content, total flavonoid content, DPPH-free radical scavenging property and oxygen radical absorbance capacity values in the glyphosate resistant amaranth were 77, 62, 499 and 157% higher than the values from commercial variety. These two varieties exhibited great differences not only in the contents but also in the types of individual phenolic acids present in free, extractable conjugated and bound forms. The glyphosate-resistant variety had 450% higher total free phenolic acids, and may be more beneficial for health. The present study offers new insight for the utilization of weeds.



Protoporphyrinogen oxidase (PPO) inhibitors are one of the few remaining postemergence weed control herbicide options for soybean growers of Mississippi. Resistance to PPO inhibiting herbicides has been recently documented in neighboring Arkansas and Tennessee. In addition, failure of PPO inhibitors in adequately controlling Palmer amaranth populations across the Mississippi Delta (a 17-county region in northwestern Mississippi encompassing 70% of the state’s row crop acreage) has been reported. It is not clear if the reduced performance of PPO inhibitors in Mississippi is due to resistance or to adverse environmental conditions and/or misapplications. Therefore, greenhouse studies were conducted to evaluate the role of non-biological parameters such as rainfastness, adjuvant, herbicide formulation, and nozzle type on the efficacy of PPO inhibitors. Simulated rainfall did not affect efficacy of fomesafen when applied at 0.5, 1, 2, or 4 hours after treatment of 10-cm tall Palmer amaranth plants. Reflex and Flexstar formulations applied with either nonionic surfactant (0.25 or 0.5% v/v) or crop oil concentrate (1 or 2% v/v) did not adversely affect performance of the herbicide. Further, nozzle type did not impact effectiveness of fomesafen on Palmer amaranth plants. Therefore, rainfastness, adjuvant, formulation, or nozzle type did not affect the activity of fomesafen under optimum application conditions in the greenhouse. 


DAY AND NIGHT APPLICATION OF 2,4-D CHOLINE SALT AND GLYPHOSATE: CONTROL OF GLYPHOSATE-RESISTANT CONYZA SUMATRENSIS. G. L. Gomes*1, C. A. Carbonari2, E. D. Velini2, U. R. Antuniassi2; 1Faculdade de Ciências Agronômicas / UNESP, Botucatu, Brazil, 2Universidade Estadual Paulista, Botucatu, Brazil (91)


The objective of this study was to evaluate the efficacy of 2,4-D (choline salt) and 2,4-D (choline salt) + glyphosate applied in the morning and evening on glyphosate resistant Conyza sumatrensis control. Four experiments were carried out in a greenhouse under a 2x2 factorial scheme (luminosity after application x formulation of 2,4-D). The applications were performed in two stages of plants (between 6 and 10 cm and 20 and 25 cm) and with two spray volumes (50 and 150 L ha-1). The 2,4-D choline salt at the dose of 975 g a.e. ha-1 and mixture of 2,4-D choline salt + glyphosate dimethylamine salt at the dose of 975 + 1025 g a.e. ha-1 were sprayed at 8 am or 8 pm. The plant visual injury evaluations were performed at 7, 21 and 35 days after application (DAA). The shoot dry biomass were determine at 35 DAA. The mixture of 2,4-D and glyphosate was more effective to control shorter plants (6 to 10 cm) when compared to 2,4-D in both application timings and spray volumes. For day applications to the larger plants, there was no significant difference between the formulations for both spray volumes. For night applications to larger plants, the herbicide 2,4-D + glyphosate was more effective than 2,4-D isolated for both spray volumes.

A TWO YEAR SUMMARY OF GLUFOSINATE EFFICACY USING DIFFERENT CARRIER VOLUMES AND NOZZLES. S. L. Taylor*1, P. A. Dotray2, J. Keeling1, R. Perkins3; 1Texas A&M AgriLife Research, Lubbock, TX, 2Texas Tech University, Lubbock, TX, 3Bayer CropScience, Lubbock, TX (92)


A TWO YEAR SUMMARY OF GLUFOSINATE EFFICACY USING DIFFERENT CARRIER VOLUMES AND NOZZLES. S.L. Taylor*1,2, P.A. Dotray1,2, J.W. Keeling2, W.R. Perkins3; 1Texas Tech University, 2Texas A&M AgriLife Research and Extension, 3Bayer CropScience, Idalou, TX.


Glufosinate-ammonium, 2,4-D Choline, and dicamba are critical components of two new weed management systems (Bollgard II XtendFlexTM and EnlistTM cotton) that can improve control of many problematic weeds including glyphosate-resistant Palmer amaranth (Amaranthus palmeri S. Wats.). The associated herbicide labels for use in these new cotton genetics will have several specific application requirements including nozzle type and carrier volume to reduce off target movement. Herbicide performance of potential future tank mix combinations may be greatly influenced by both carrier volume and nozzle type. The objective of this research was to examine herbicide efficacy of glufosinate, 2,4-D (amine), and dicamba (diglycolamine) applied alone and in tank-mix combinations when varying nozzle selection and carrier volume. The plots in both studies were 2 rows by 9 m and arranged in randomized complete block design with 4 replications. In the nozzle selection study, herbicide treatments were applied using three different spray nozzles delivering 140 L/ha. Nozzles were selected based on the following droplet sizes: medium droplet = 236-340 microns (Turbo TeeJet 11002 at 186 KPa), very coarse droplet (VC) = 404-502 microns (Air Induction XR TeeJet 11002 at 186 KPa), and ultra-coarse droplet (UC) = >655 microns (Turbo TeeJet Induction 110015 at 255 KPa). In the carrier volume study, herbicide treatments were applied at different carrier volumes (93, 140, and 187 L/ha) using TTI UC nozzles. Herbicide rates included glufosinate at 0.59 kg ai/ha, dicamba at 0.56 kg ai/ha, and 2,4-D at 1.06 kg ai/ha. In the 2015 nozzle selection study, glufosinate tank-mixed with 2,4-D or dicamba improved Palmer amaranth control over these herbicides when applied alone. When glufosinate was mixed with 2,4-D or dicamba, Palmer amaranth control using the ultra-coarse nozzle was as effective as current nozzles that produce medium to very coarse droplets. Glufosinate tank-mixed with 2,4-D or dicamba improved Palmer amaranth control over 2,4-D and dicamba when applied alone at 7 days after application (DAA) regardless of nozzle selection; however, at 21 DAA, less control was observed when glufosinate was mixed with dicamba using the VC and UC nozzles, and when glufosinate was mixed with 2,4-D using VC nozzles. In the 2015 carrier volume study, improved Palmer amaranth control was observed with increased carrier volume following glufosinate or 2,4-D alone or glufosinate + 2,4-D. However, carrier volume did not affect control following dicamba alone or glufosinate + dicamba in tank-mix. Improved Palmer amaranth control was observed when glufosinate was mixed with dicamba or 2,4-D  at 7 DAA regardless of carrier volume; however, at 21 DAA, reduced control was observed when glufosinate was mixed with dicamba using a carrier volume of 140 and 187 L/ha and when glufosinate was mixed with 2,4-D at all carrier volumes. The current XtendimaxTM with VaporGripTM label, the Engenia® label, and the Enlist DuoTM label all prohibit tank mixing with other herbicides; however, future labels may allow certain herbicide tank mix partners.

NON-AMS ADJUVANTS EFFECT ON DICAMBA+CLETHODIM TANK-MIXTURE ANTAGONISM IN CONTROL OF PALMER AMARANTH AND VOLUNTEER CORN. M. L. Bernards*1, B. G. Young2, G. Obear3, F. Sexton3; 1Western Illinois University, Macomb, IL, 2Purdue University, West Lafayette, IN, 3Exacto, Inc, Sharon, WI (93)


Dicamba antagonism of clethodim is an emerging issue that will be increasingly important as dicamba-resistant crop varieties are deployed to manage glyphosate-resistant weeds. Labels for dicamba formulations designed for dicamba-resistant soybeans (Glycine max) will not allow the use of ammonium sulfate (AMS) as part of the spray solution. The objective of this study was to determine whether adjuvants might overcome the dicamba-clethodim antagonism when tank-mixed with glyphosate. The study also investigated how novel nonionic surfactant drift reduction technology (NIS-DRT) and non-AMS water conditioners compare to the AMS + COC industry standard. A trial was conducted in Macomb, IL in a field planted with glyphosate-resistant corn (Zea mays) and forage sorghum (Sorghum bicolor) on 7 June 2016. A second trial was conducted in Winamac, IN in a field seeded with glyphosate-resistant corn on 19 May 2016. Glyphosate was tank-mixed with dicamba, clethodim, or dicamba + clethodim and applied on 30 June in IL and 19 June in IN with using TTI nozzles at a spray volume of 93 L ha-1. Five experimental adjuvants were tested and compared to an industry standard AMS + COC with each herbicide tank-mixture combination. Dicamba antagonized clethodim control of glyphosate-resistant corn at both locations.  Dicamba antagonized clethodim control of forage sorghum at the IL trial, and clethodim antagonized Palmer amaranth (Amaranthus palmeri) control in the IN trial.  Clethodim did not affect dicamba control of glyphosate-resistant waterhemp (Amaranthus tuberculatus var. rudis) present in the IL trial.   AMS + COC overcame or lessened the effects of herbicide antagonism on corn and Palmer amaranth and improved control. Experimental adjuvants performed similarly to AMS+COC at the IN site, but some were less effective controlling corn control at the IL site, potentially due to very dry conditions preceding the herbicide application. However, tank-mixtures with the experimental adjuvants controlled waterhemp and forage sorghum similarly to AMS+COC in IL. These results provide evidence that adjuvants can overcome dicamba-clethodim antagonism. Novel NIS-DRT combined with non-AMS water conditioners may provide growers with adjuvant options for new crop varieties where dicamba cannot be tank-mixed with AMS.


A NON-DESTRUCTIVE ASSAY FOR DETERMINING VIABILITY OF WEED SEEDS. J. Wood*, I. Marquez, B. J. Schutte; New Mexico State University, Las Cruces, NM (94)


Causal agents of mortality in weed seedbanks can be better understood with non-destructive assays for seed viability.  Such assays enable investigations on mechanisms of seed infection by pathogenic microorganisms.  Non-destructive assays for viability have been developed for weed seeds with water impermeable seed coats (physical dormancy).  In this study, we evaluate a non-destructive method for assessing viability of weed seeds with physiological dormancy.  Our method, which was modified from a published study, used a resazurin reagent that was made from resazurin and yeast.  In principle, changes in resazurin color caused by respiration in yeast correspond with differences in seed viability because nonviable seeds emit large amounts of solutes that are consumed by yeast.  To test this principle, we measured color change in resazurin solutions containing single seeds that were intact, mechanically damaged or subjected to conditions that accelerated aging.  Seeds were mechanically damaged by systematically slicing coats (1 incision seed-1).  Accelerated aging was accomplished by storing seeds for 80 d under 60% relative humidity, 45 C; conditions created, in part, with lithium chloride solutions in air-tight containers.  Weed species in this study were common lambsquarters, junglerice, Palmer amaranth and yellow foxtail.  Results indicated that intact, damaged and aged seeds of common lambsquarters and Palmer amaranth could not be distinguished with resazurin solution.  For junglerice and yellow foxtail, only mechanically damaged seeds caused resazurin solution to change from blue to pink after 3 hr of incubation.  This color change corresponded with reductions in absorbance at 600 nm (A600).  For yellow foxtail, A600 < 0.312 signified mechanically damaged seeds (false discovery rate for damage [FDRdamage] = 7.5%, N = 53; misclassification rate for damage [misclassifydamage] = 3.3%, N = 150).  Mechanically damaged junglerice seeds frequently produced resazurin solutions with A600 < 0.319 (FDRdamage = 20%, N = 15; misclassifydamage = 27.3%, N = 150).  These results suggest that resazurin solution can be used to identify mechanically damaged Poaceae seeds.  However, the resazurin solution, as evaluated in this study, cannot be used to non-destructively separate viable and nonviable weed seeds.

THE EFFECTS OF SEED SHATTERING DATE ON GERMINABILITY OF REDROOT PIGWEED (AMARANTHUS RETROFLEXUS) AND YELLOW FOXTAIL (SETARIA GLAUCA). S. C. Haring*1, M. L. Flessner1, W. J. Everman2, S. Mirsky3; 1Virginia Tech, Blacksburg, VA, 2North Carolina State University, Raleigh, NC, 3USDA Sustainable Agricultural Systems Lab, Beltsville, MD (95)


Annual weed species rely on seed as propagules for invading and persisting in agricultural fields. Investigation of seed shattering phenology and germinability can increase knowledge of how weeds make additions to and emerge from the soil seedbank. Field experiments in 2015 in Blacksburg, Virginia captured weekly seed shattering from 24 individuals each of redroot pigweed (Amaranthus retroflexus L.) and yellow foxtail (Setaria glauca (L.) Beauv.) in a soybean (Glycine max (L.) Merr.) field. An 11.5 cm diameter sample cup was secured to the ground at the base of each plant, and its contents were collected weekly. Collections continued from the first signs of weed seed shattering, through the first possible soybean harvest (November 1), until the end of a simulated three-week harvest delay. Weekly seed collections were counted and then subjected to a direct germination assay in a growth chamber. Data were analyzed using a generalized linear model with Poisson (log link) and binomial (logit link) distributions for seed shattering and germinability, respectively, with significance at P≤0.05. Redroot pigweed began shattering 15 weeks before harvest time, while yellow foxtail shattering first occurred six weeks before harvest time. Redroot pigweed shattering increased throughout the growing season, with this experiment capturing 84.7% of total shattered seed in the 15 weeks before harvest and 15.3% in the three weeks of the harvest delay. Yellow foxtail seed shattering decreased through the season, driven by 0% seed capture during the harvest delay. Redroot pigweed germinability was highest in the early weeks of the season, starting at 41.6% germination from seeds captured in the experiment’s first week and declining to 36.4% in the last week. Yellow foxtail germination had no relationship with seed shattering date and had an overall 55.2% rate. These results show differences in temporal patterns of dispersal biology across weed species, highlighting the value of species-sensitive management approaches. Understanding soil seedbank additions and emergence becomes more important as new harvest weed seed control technologies rely on weed seed retention and, therefore, a timely harvest. Future research must help develop improved methods for studying seed shattering, including developing methodology to relate weekly seed shattering to the total number of seeds produced by the plant. Additional future research must place the practical impact of these findings in the context of a production system using harvest weed seed controls.


POST-HARVEST SEED PRODUCTION POTENTIAL OF PALMER AMARANTH AND WATERHEMP IN SOUTHERN US: A NINE SITE-YEAR EXPERIMENT. V. Singh*1, P. A. Dotray2, L. M. Schwartz-Lazaro3, J. K. Norsworthy3, M. V. Bagavathiannan1; 1Texas A&M University, College Station, TX, 2Texas Tech University, Lubbock, TX, 3University of Arkansas, Fayetteville, AR (96)


Seed production by weeds recruiting after crop harvest can contribute significantly to seedbank size. Palmer amaranth and waterhemp are prolific seed producers and are known to emerge after crop harvest and produce seed prior to killing frost in the Southern US. A nine site-year field study was conducted across three locations (College Station and Lubbock, TX, and Fayetteville, AR) in three years (2014 to 2016) to determine the fecundity of Palmer amaranth and waterhemp plants emerging after crop harvest. All the three sites included Palmer amaranth in all the years, whereas waterhemp was studied only at two locations (College Station and Fayetteville) in 2014 and 2016, and at one location (College Station) in 2015. Seed production was determined on seedlings recruited at weekly intervals from late-summer until the first killing frost. At the termination of the experiment, seedlings pertaining to each cohort were harvested separately, dried, and thrashed to determine seed production on each cohort. Palmer amaranth and waterhemp exhibited high levels of plasticity in seed production, with greater fecundity in 2014 compared to 2015 and 2016. The average Palmer amaranth seed production/plant for the first cohort was 19510 (emergence at the 33rd Julian week, Aug 13-19), 266 (36th week) and 2 (36th week) in 2014, and 210, 167 and 175 (emergence during the 34th Julian week) in 2015, at College Station, Lubbock, and Fayetteville, respectively. Palmer amaranth produced mature seeds when seedlings emerged as late as the 41st week in College Station, 40th week in Lubbock, and 37th week in Fayetteville, in 2014 and 2015. Waterhemp (36th week) produced 824 seeds in College station and no seed in Fayetteville in 2014, whereas it produced 204 and 195 seeds respectively in College Station and Fayetteville in 2015 (34th week). Field data from 2016 is available only for College Station at this point. In 2016, Palmer amaranth and waterhemp produced 525 and 486 seeds respectively for the first cohort (emergence in 33rd and 32nd Julian week, respectively). Similar to previous years, no seed were produced when plants of both Palmer amaranth and waterhemp emerged after the 42nd Julian week.  Results demonstrate that Palmer amaranth and waterhemp seedlings that emerge after crop-harvest in the Southern US can add substantial amount of seed to the soil seedbank, though the level of seed addition can be variable across environments. Growers must implement management practices to target post-harvest recruits of these species to minimize seedbank addition.

A REPLACEMENT SERIES EXPERIMENT TO INVESTIGATE THE COMPETITIVENESS OF HYBRID TOADFLAX. S. M. Ward*1, S. E. Sing2; 1Colorado State University, Fort Collins, CO, 2US Forest Service, Bozeman, MT (97)


Hybrid toadflax (HT) populations from cross-pollination between invading yellow toadflax (YT) and Dalmatian toadflax (DT) are being reported at an increasing rate throughout the Intermountain West.  HT populations have the potential to out-compete and displace not only native vegetation but also the two parent toadflax species at sites of co-invasion, presenting additional challenges for weed managers. To determine how hybrid progeny might change the composition of invasive DT and YT populations, greenhouse-based replacement series experiments were conducted to measure the performance of HT grown in competition with YT and DT. HT plants were grown with YT in one series, and with DT in a second series, in ratios of 100:0, 80: 20, 60:40, 50:50, 40:60, 80:20, and 0:100.  Total above ground biomass was measured and the number of individual surviving plants counted for each taxon.  When these replacement series were established using transplanted seedlings, the proportion of HT in the final biomass and individual plant counts was not significantly different from the initial ratio for both YT and DT, indicating that HT plants persisted alongside the parent taxa but did not outperform them. However, for replacement series started from seed, HT comprised a greater proportion of the final biomass than the initial ratio, especially when initially planted at lower HT:DT and HT:YT ratios. More rapid seed germination and vigorous seedling establishment may enable HT to outcompete both YT and DT in the field.  Over time this could shift the composition of invasive toadflax populations towards HT, especially where disturbance favors the germination and establishment of HT from an existing soil seed bank.


CHARACTERIZATION OF FLOWERING TIME PATHWAYS IN CAMELINA SATIVA: A POTENTIAL WINTER COVER CROP FOR NORTHERN CLIMATES. J. V. Anderson*1, K. M. Dorn2, W. S. Chao1, D. P. Horvath1, M. Dogramaci1, M. Marks3, R. W. Gesch4, M. E. Foley5; 1USDA-ARS, Fargo, ND, 2Kansas State University, Manhattan, KS, 3University of Minnesota, St. Paul, MN, 4USDA-ARS, Morris, MN, 5USDA ARS, Fargo, ND (98)


Winter cultivars of camelina (Camelina sativa) are being evaluated as new oilseed cover crops for northern climates of the upper Midwest USA. Winter camelina grown as a cover crop during the corn/soybean fallow period can reduce soil erosion and nutrient leaching, suppress early season weed establishment, and provide early season nutrition for pollinators, while yielding a valuable oilseed feedstock for the production of advanced biofuels and bioproducts. We have identified a camelina genotype (‘Joelle’) with excellent winter hardiness, desirable yield, oil content, and disease resistance. However, an earlier maturing trait is desired for relay- and double-cropping systems in the upper Midwest, as it allows more optimal growing conditions and full development of a second crop. Here, we investigate the vegetative to reproductive growth transition in the shoot apical meristem of a summer ‘CO46’ and a winter ‘Joelle’ genotype of camelina and characterize several transcripts involved in flowering-time pathways. Transcript abundance associated with one of the three genes encoding FLOWERING LOCUS C (Csa20g015400), a transcription factor involved in floral repression, was 16 fold greater in Joelle compared to CO46 prior to vernalization. Abundance of this transcript decreased slightly in CO46 post-vernalization, compared to a significant decrease in Joelle. Abundance of transcripts mapping to the three chromosomes encoding MADS AFFECTING FLOWERING 2 (MAF2), another floral regulating transcription factor, were all greater in Joelle compared to CO46. MAF2 transcript specific to chromosome 18 (Csa18g038750) was preferentially expressed and most abundant in Joelle pre- and post-vernalization; whereas, changes in MAF2 expression were minimal in CO46. Understanding the genetic factors impacting early season maturity in this and other winter-hardy, weed-suppressing oilseed cover crops could lead to additional options for enhancing integrated pest management strategies for cropping systems in the upper Midwest.


GENETIC DIVERSTIY OF ECHINOCHLA SPP. IN KOREA INFERRED FROM NEW SIMPLE SEQUENCE REPEATS. J. Lee*1, I. Lee1, C. Kim1, K. Park2; 1National Institute of Agricultural Sciences, Wanju, South Korea, 2Chungnam National University, Daejeon, South Korea (99)


BARNYARDGRASS OR JUNGLERICE: USING KASP FOR ECHINOCHLOA SPECIES IDENTIFICATION. C. E. Rouse*1, D. Pettinga2, C. Oliveira3, T. A. Gaines2, N. R. Burgos1; 1University of Arkansas, Fayetteville, AR, 2Colorado State University, Fort Collins, CO, 3Universidade Federal de Pelotas, Pelotas, Brazil (100)


Echinochloa species are a global threat to low-land and up-land agriculture with a variety of species that impact crop production. Historically, barnyardgrass (E. crus-galli) was believed to be the primary species threatening crop production in the midsouth, USA. A generation of scientists dedicated significant resources to the characterization and management of weedy Echinochloa species. The common synopsis was that the species morphological traits intergrade significantly, which leads to confusion in species identification. The most confusion occurs with barnyardgrass and junglerice. Following reports from a USDA-led team of researchers on the characterization and identification of barnyardgrass and junglerice in the US mid-south, we sought to identify the species growing in rice production fields in Arkansas using taxonomic traits. This research  identified four species in rice fields - barnyardgrass (E. crus-galli), junglerice (E. colona), rough barnyardgrass (E. muricata), and coast cockspurgrass (E. walterii). Of these, junglerice is the most prevalent followed by barnyardgrass.  In many cases, proper identification required inspection of florets under a microscope, which would be impossible without the proper equipment and training. Even with a trained personnel, some judgement calls would need to be made occasionally as floret characteristics also intergrade to some extent. To achieve accurate species identification consistently, a high throughput, molecular identification method needs to be developed. Kompetitive Allele- Specific PCR (KASP), a quick, low-cost method for reliable SNP genotyping may be used to distinguish these species. Allele-specific PCR primers were designed to amplify the internal transcribed spacer (ITS2) of the ribosomal DNA for junglerice and barnyardgrass. This region is highly conserved within species and may be used to discriminate between species. Data from  this experiment will be used to validate the species identification using morphological  features, where there is ambiguity in taxonomic classification. Correct identification is relevant in the study of species evolution, response to management tactics, and adaptation.



Clones of Amaranthus palmeri, A. spinosus and seven authenticated Amaranthus palmeri x A. spinosus hybrids were established from axillary shoots and their growth rates and morphological traits.  Putative hybrids were collected from 2012 to 2014 from the field where they were originally discovered. Hybrids were confirmed by determining the presence of both alleles for intron 1 of EPSPS, and glyphosate and acetolactate synthase (ALS) inhibitor resistance which were established in local A. palmeri. Clones of A. palmeri had the highest growth rate and A. spinosus the lowest growth rate based on height, node counts, and dry weight. A. palmeri also had the greatest number of days to flowering and A. spinosus the fewest. Six of the hybrids had intermediary growth rates and days to flowering which were greater than A. spinosus.  The length of inflorescences and sex identity of hybrids also differed from A. spinosus.  The hybrids were either dioecious like A. palmeri or, if monoecious, had patterns unlike A. spinosus. Spine length and texture also varied in hybrids and some were without spines. Hybrid 16Ci was short compared to all others and had succulent leaves and stems, which easily separated from the plant body. Hybridization of glyphosate and ALS resistant A. palmeri with sensitive A. spinosus resulted in transfer of herbicide resistance into morphologically distinct types which differed from the parents. Repeated backcrossing of hybrids to A. spinosus may lead to introgression of new genes into the parental gene pool that could ultimately drive evolution of this species. 




Because herbicide effectiveness is thought to decrease as plants grow larger, spraying weeds very early in the growing season is a common recommendation for weed management.  However, many annual weeds germinate asynchronously, leading to wide variation in size within populations.  Also, annuals such as Conyza canadensis, known as marestail or horseweed, can germinate in autumn or spring in temperate North America, which further contributes to variation in the size of rosettes at the time of herbicide applications.  We tested the differences in glyphosate efficacy for smaller vs. larger rosettes of C. canadensis to determine whether larger rosettes are more tolerant of glyphosate than smaller ones.  We used seeds from each of three maternal plants that were presumed to be full-sibs due to predominant selfing in this species.  These maternal families from northeastern Ohio had previously been characterized as susceptible to 1x glyphosate [0.84 kg ae glyphosate/ha] by our group.  Plants were grown in small pots with standard potting soil in a greenhouse at Ohio State University for ~4 vs. 6 weeks.  For each maternal family, 40 seedlings (one per pot) were randomly assigned to one of 5 dosage treatments (0.0x, 0.125x, 0.25x, 1.0x or 4.0x), for a total of 600 plants.  We used the length of the longest leaf as an index of rosette size.  Half of the plants were measured and sprayed at ~4 weeks after seeds were planted, while the other half were measured and sprayed at 6 weeks after planting.  Survival and visual damage scores were recorded 21 days after spraying for each group.  ED90 values were calculated from dose response curves to determine the dose required for 90% damage based on visual scores.  Maximum leaf lengths of the 4 vs. 6 week plants averaged 2.0 cm vs. 2.6 cm, and percent increases in leaf length differed among families, averaging 19%, 27%, and 32% for Families 1, 2, and 3, respectively.  Despite the relatively short interval between age classes, i.e., two weeks, the older and larger plants were consistently more tolerant of glyphosate than younger and smaller ones.  For Families 1, 2, and 3, the early vs. late ED90 values were 0.9 vs. 2.1, 0.7 vs. 1.5, and 1.0 vs. 2.5, respectively (an ED90 value of 1.0 represents 1x; P<0.05 for each comparison).  Therefore, our results show that increases in the leaf lengths of young rosettes on the order of 19-32% are associated with greater tolerance of glyphosate.  We suggest that variation in plant size, even at early growth stages, is also likely to contribute to variation in the effectiveness of glyphosate applications under field conditions.  Conyza canadensis has repeatedly evolved strong resistance to glyphosate in the USA and elsewhere.  Prior to the evolution of resistance, greater tolerance of larger plants may encourage growers to use higher dosages of glyphosate to achieve adequate weed control.  Furthermore, it is possible that variation in glyphosate effectiveness based on plant size and age could contribute to the survival and persistence of weed genotypes with heritable levels of resistance.  


A NOVEL POTENTIAL OPTION TO CONTROL THE INVASIVE WEED KOCHIA SCOPARIA BY USING BIOCONTROL AGENTS. G. V. Reddy*1, G. Shrestha1, P. Jha2; 1Montana State University, Conrad, MT, 2Montana State University, Huntley, MT (103)


Kochia (Kochia scoparia L. Schrad), a broadleaf weed belonging to Chenopodiaceae family, is one of the most troublesome weeds infesting crop fields and rangelands across the US Great Plains. Traditionally, herbicides from Groups 2 (ALS-inhibitors), 4 (synthetic auxins), and 9 (glyphosate) have been used to manage this weed.. In the last decade, kochia has developed resistance to many of these contemporary herbicides, including evolution of multiple herbicide-resistant populations. Glyphosate-resistant kochia poses a serious threat to the rangeland and agronomic production systems in this region. Because of limited herbicide resources to control this weed, there is an urgent need to explore alternative options, such as the classical biological control (CBC) method. Plants from Chenopodiaceae family, in general, produce multiple secondary metabolic compounds which have anti-insect properties, resulting in very few insects living and feeding on them. Thus far, CBC to manage kochia invasions either in the USA or other parts of the world has not been attempted. Recently in Northern Japan, a few insects have been implicated to cause damage to this plant. Macdunnoughia confusa and Sarcopolia illoba (Lepidoptera) have been found to inflict considerable damage to K. scoparia plants. Because of the innate ‘resistance’ of chenopods in general and possibly in kochia, we propose here a strategy to attack kochia populations using these biocontrol agents, maintained under strict quarantine conditions. First, we propose to impose modest doses of an obligate biotrophic fungus Peronospora farinosa f. sp. spinaciae to lower the resistance capacity in kochia. The second phase of the strategy would be to counterattack the stressed kochia plants by applying larval populations of either one of the two, M. confusa and S. illoba, or both.

THE POTENTIAL USE OF SORGHUM BICOLOR (L.) MOENCH SHOOT EXTRACTS AS A BIO-HERBICIDE. H. Le thi1, O. Won1, Y. Park1, J. Hwang2, S. Park1, K. Park*1; 1Chungnam National University, Daejeon, South Korea, 2National Institute of Crop Science, Jeonju, South Korea (104)


The potential use of allelopathy in Sorghum bicolor (L.) Moench shoot extract for weed management

Kee Woong Park1*, Thi Hien Le1, Ok Jae Won1, Yun Ji Park1, Jae Bok Hwang2, Sang Un Park1

1Department of Crop Science, College of Agriculture and Life Science, Chungnam national University, Daejeon, 34134, Korea.

2National Institute of Crop Science, RDA, Jeonju 54875, Korea.

 This study was conducted to compare total phenolic contents of various cultivars of Sorghum bicolor L. Moench shoots (Donganme, Nampungchal, Sodamchal, Hwangumchal, and Gomadansusu) using different solvents (ethanol, chloroform, hexan, ethyl acetate, and methylene chloride) and examine their effect for weed control. Firstly, each sorghum sample was soaked and shaken in ethanol to form a solid-liquid mixture. After that, the solid residue was filtered out of the mixture to obtain a solution, which was divided into five volume-equal parts, and the solvent was completely evaporated. After the evaporation process, phenolic compounds were extracted from the remainder by dissolving it into different solutions of solvents (except ethanol) and distilled water (v/v, 1/1). These solutions were separated into two liquid phases, in which the water phase was removed. The remaining solution’s solvent was completely evaporated and dissolved into distilled water for quantitative analysis of total phenolic content using HPLC (high-performance liquid chromatography). Results showed that, among the cultivars, the highest total amount of phenolic compounds was extracted from the ‘Hwangumchal’ cultivar by using the solvent ‘ethyl acetate’. In order to assess allelopathic activities for potential weed management purposes, germination and foliar application tests were performed on weed species Abutilon avicennae, Digitaria sanguinalis, Amaranthus retroflexus, and Echinochloa crus-galli. Germination test results indicated that all sorghum extracts had an inhibitory effect on all four weed species. For foliar application, the extract from the ‘Hwangumchal’ sorghum cultivar obtained by ethyl acetate extraction was more effective than others. The ‘Hwangumchal’ cultivar extract was applied for evaluation in the field as a soil treatment. Results indicated that three times application every seven days after tillage can prevent the growth and development of weeds. In addition, using Hwangumchal’s extract at 1x concentration (1g/ml) in another field trial with foliar application, almost all weeds were controlled. In this work, we investigated the best extraction method for phenolic compounds from various sorghum cultivars, which is a promising method for the development of an environmentally friendly natural herbicide contributing to sustainable agriculture.

* This work was carried out with the support of "Cooperative Research Program for Agriculture Science & Technology Development (PJ011307012017)" Rural Development Administration, Republic of Korea.

GLYPHOSATE ABSORPTION AND TRANSLOCATION IN YOUNG 'GALA' APPLE TREES. I. C. Burke*, A. J. Raeder; Washington State University, Pullman, WA (105)


Postemergence (POST) directed applications of glyphosate are often applied in Washington apple orchards for weed management, particularly to control deep-rooted perennial weeds and weeds that escape a residual herbicide application. Scientists, agriculture professionals, and growers are concerned that POST-directed applications of glyphosate may have negative effects on apple trees are due to increased reports of herbicide injury in new high-density apple plantings suggesting glyphosate injury. Greenhouse and laboratory experiments were conducted to determine absorption of glyphosate following basal and leaf treatments, as well as if and how much translocation of glyphosate occurs following treatments of glyphosate applied basally compared to on a single leaf on a mid-tree branch. Analysis of 14C-glyphosate absorption applied to above graft basal (AGB), below graft basal (BGB) bark, and on the newest mature leaf (Foliar) on a mid-tree lateral branch indicate greater absorption when glyphosate is applied to basal bark compared to absorption by a foliar application. Observation of translocation from the AGB, BGB, and Foliar applications of 14C-glyphosate suggest that glyphosate translocates to the roots and is translocated to stump sprouts. The results suggest it may be possible to monitor stump sprouts in apple orchards for glyphosate residue after applications, or when injury is observed.


A GLYPHOSATE-RESISTANT PALMER AMARANTH (AMARANTHUS PALMERI) POPULATION CONFIRMED IN CALIFORNIA. A. Shrestha*1, K. M. Steinhauer1, M. To1, S. Budhathoki1, J. Angeles1, S. Rios2, B. Hanson3; 1California State University, Fresno, CA, 2University of California Cooperative Extesnion, Riverside, CA, 3Univesrity of California, Davis, CA (106)


The Weed Science Society of America recently ranked Palmer amaranth (Amaranthus palmeri) as the most troublesome weed in the U.S., based on a national survey. This ranking is largely due to confirmed and widespread glyphosate-resistant (GR) populations, primarily in Roundup Ready cropping systems, in 28 states. Although GR populations of this species were documented in Georgia as early as 2005, it had not been suspected in California until recently. Widespread glyphosate-escapes of Palmer amaranth were reported in various annual and perennial cropping systems beginning in 2012 in the Central Valley of California (CA). In 2013/14, 25 field collected populations were screened for glyphosate resistance in greenhouse studies, however, resistance was not observed in these studies. Subsequently, in 2015, Palmer amaranth plants were collected from a RR corn field in the Central Valley and grown to maturity in a greenhouse. Seeds produced from these plants were collected. In summer 2016, plants produced from these seeds were grown and tested for glyphosate resistance by comparing to a known GR population from Tennessee (TN) and a glyphosate-susceptible (GS) population from Fresno, CA. Plants at the 4- to 6-leaf stage were sprayed with glyphosate rates of 0, 0.42, 0.84, 1.68, 3.36, 6.72 kg ae ha-1 at a spray volume of 187 l ha-1 with CO2 backpack sprayer. Plants were periodically evaluated for mortality up to 28 days after treatment (DAT). At 28 DAT, the plants were clipped at the soil surface and the aboveground biomass was put in paper bags, dried in a forced-air oven at 60 C for 72 hours and dry weights were recorded. Treatments were replicated six times for each population and the experiment was repeated. About 60% of both the GR population from TN and the suspected GR population from CA survived up to the 6.72 kg ae ha-1 treatment; whereas none of the GS plants survived any of the treatments greater than 0.42 kg ae ha-1. However, the biomass of the suspected-resistant plants from CA and GR plants from TN was reduced by 50% at 0.84 kg ae ha-1 compared to the control treatment. Therefore, based on mortality the suspected-resistant plants from CA showed about 8-fold resistance to glyphosate. This is the first confirmed case of GR Palmer amaranth in California.



Several Amaranthus spp. around the world have developed resistance (and cross resistance) to various herbicide modes of action. Populations of A. tuberculatus and A. retroflexus in Mississippi have been suspected to be resistant to one or more acetolactate synthase (ALS) inhibiting herbicides. Whole plant dose-response experiments with multiple ALS inhibitors, ALS enzyme assays with pyrithiobac, and molecular sequence analysis of ALS gene constructs were conducted or are in progress to confirm and characterize the resistance profile and nature of mechanism in the A. tuberculatus and A. retroflexus populations. Both A. tuberculatus and A. retroflexus populations were resistant to imazethapyr (imidazolinone), pyrithiobac (pyrimidinyl thiobenzoate), and trifloxysulfuron (sulfonylurea) herbicides, surviving rates up to 16X the labeled rates. Their respective susceptible counterparts were controlled by 1X rates or less. DNA sequencing revealed the presence of a known resistance conferring point mutation, Trp574Leu. ALS resistance in Amaranthus spp. severely limits postemergence managing options for growers of Mississippi.

INVESTIGATIONS INTO SUSPECTED CLETHODIM-RESISTANT JOHNSONGRASS AND ITALIAN RYEGRASS FROM MISSISSIPPI. V. K. Nandula*1, G. Sharma2, T. Tseng3, J. Bond4; 1USDA-ARS, Stoneville, MS, 2Mississippi State University, Mississippi State, MS, 3Mississippi State University, Starkville, MS, 4Mississippi State University, Stoneville, MS (108)


Clethodim is a postemergence herbicide utilized for control of several annual and perennial (for example, johnsongrass) grass weeds in soybean and cotton. It is also used to manage grass weeds such as Italian ryegrass in spring preplant burndown operations. Several populations of johnsongrass and Italian ryegrass have been suspected to be resistant to clethodim during 2015-16 in Mississippi. Greenhouse experiments were conducted to evaluate response of these populations to a 1/2X labeled rate of clethodim followed by molecular analysis of putative resistant plants to search for/confirm known mutations of acetyl CoA carboxylase (ACCase), target site of clethodim, that would confer resistance to the herbicide. Several Italian ryegrass populations survived clethodim and some of these populations had one of the following two ACCase point mutations: I2041N (isoleucine to asparagine) and C2088R (cysteine to arginine). Allele specific PCR-assay detected the presence of isoleucine-asparagine substitution at nucleotide position 2041 in the ACCase gene of resistant johnsongrass populations.



Italian ryegrass (Lolium perenne ssp multiflorum) is a major weed of annual and perennial cropping systems of California. Survey of 118 populations from orchards, vineyards, crop fields, and roadsides across the Central Valley in 2005 revealed resistance to glyphosate in 54 populations. In 2015, we resampled the 118 Italian ryegrass populations by collecting seed from 50 plants in each population and testing seedlings from each population for resistance to glyphosate, glufosinate, sethoxydim, and paraquat.  Compared to 2005, the frequency of populations with glyphosate-resistant plants across the Central Valley increased significantly from 46% to 79% over the 10 years. Multiple herbicide resistance was confirmed in several populations. Preliminary greenhouse studies revealed that two glyphosate-resistant populations were not controlled by sethoxydim and paraquat at the labeled field rate of each herbicide. Eight populations contained individuals that survived glufosinate treatment at the recommended rate. To evaluate the level of resistance in the multiple-herbicide-resistant populations, dose-response experiments were conducted using eight doses of glyphosate, sethoxydim, and paraquat applied to 20 plants from each population at the 3- to 4-leaf stage. Resistant populations (Res1 and Res2) were treated with herbicides at doses ranging from 1/4X to 32X while the susceptible standard population was treated with doses ranging from 1/32X to 4X. Plant mortality was recorded 21 DAT. To calculate the lethal dose of these herbicides required to kill 50% of the plants (LD50), the mortality data were subjected to probit analysis in SAS using PROC PROBIT. Based on the LD50 values, the levels of resistance to glyphosate, sethoxydim, and paraquat were 45, 203, and 22.5-fold, respectively, for Res1 and 24, 147, and 4-fold, respectively, for Res2 compared to the susceptible standard population. This research confirms multiple herbicide-resistant Italian ryegrass populations in California. Our previous studies on the genetic basis of glyphosate resistance in Italian ryegrass exhibited a missense mutation at Pro106 codon as a likely mechanism of resistance to this herbicide. However, the mechanism of resistance to sethoxydim and paraquat in these populations remains to be investigated.

IDENTIFICATION OF CANDIDATE RESISTANCE GENES IN MULTIPLE HERBICIDE RESISTANT ECHINOCHLOA COLONA. A. A. Wright*1, R. Sasidharan2, M. Rodriguez2, D. Peterson3, V. K. Nandula4, J. Ray5, J. Bond1, D. Shaw3; 1Mississippi State University, Stoneville, MS, 2BASF, Research Triangle Park, NC, 3Mississippi State University, Mississippi State, MS, 4USDA-ARS, Stoneville, MS, 5USDA, Stoneville, MS (110)


                Non-target site herbicide resistance mechanisms are difficult to study due to the large number of candidate genes and the scarcity of sequence data for many weeds.  A biotype of junglerice (Echinochloa colona) with resistance to four herbicides, fenoxaprop-P-ethyl, imazamox, quinclorac, and propanil, each representing a different mechanism of action, was identified in Sunflower County, MS.  Resistance to fenoxaprop-P-ethyl and imazamox were a result of non-target site mechanisms.  RNA-seq technology was used to compare expression profiles of untreated resistant plants to untreated plants of a known sensitive biotype.  Three transcripts were identified as being significantly differentially expressed between the resistant and sensitive plants.  A kinase and glutathione-S-transferase were significantly upregulated in the resistant biotype compared to the sensitive, while an F-box protein was downregulated.  Additionally, a SNP analysis was performed on the cytochrome P450 family to identify nonsynonymous SNPs that might be relevant to resistance.  Twenty-seven cytochrome P450s were identified as having SNPs of interest.  Two of these had a premature stop codon in the sensitive biotype that was absent or occurred at a lower frequency in the resistant biotype.  These cytochrome P450s and the three differentially expressed transcripts represent a list of candidate genes for further study in this multiple herbicide resistant biotype of junglerice.  Additional studies examining the role of the products of these transcripts in herbicide resistance will further elucidate the non-target site resistance mechanisms present in this junglerice biotype.




A continuous fluorescent plate-based assay for 5-enolpyruvyl shikimate synthase was developed using the coupling system for continuous Pi detection method of Vazquez et al. (Anal. Biochem. (2003) 320:292). The assay is inexpensive, sensitive (< 0.1 nM Pi), quick (plates can be set up in 3-5 min with a liquid handling system and the assay itself takes 5-10 min), high throughput (run in a 96 or 386 well plate) and precise (standard errors are usually less than 5%). Kinetic parameters for recombinant maize EPSPS and a glyphosate-resistant variant purified from E. coli will be compared, along with experiments to distinguish mixtures of variants having differing glyphosate-sensitivity, and the measurement of EPSPS activity in crude plant extracts.

ITALIAN RYEGRASS FROM IREDELL COUNTY, NORTH CAROLINA IS RESISTANT TO GLUFOSINATE, ACCASE- AND ALS-INHIBITING HERBICIDES. W. T. Molin*1, V. K. Nandula2, A. A. Wright3; 1USDA, Stoneville, MS, 2USDA-ARS, Stoneville, MS, 3Mississippi State University, Stoneville, MS (112)


Italian ryegrass from Iredell County, NC, was reported to be resistant to sethoxydim herbicide. Seeds were collected from the suspect field in May 2016. Ryegrass plants were tested for resistance to herbicides commonly used in their control. In the first experiment, separate sets of plants were treated with 1X and 2X labeled rates of clethodim and sethoxydim, and 1X rates of quizalifop and fluazifop. These herbicides did not provide any control. In a second experiment, herbicides applied (n=18 in each group), all at 1X included clethodim, fenoxaprop, pinoxaden, glyphosate, paraquat, mesosulfuron, and glufosinate. Percent control was 23%, 6%, and 12% with clethodim, fenoxaprop, and pinoxaden, respectively and 100% control was achieved with glyphosate and paraquat. Control with mesosulfuron and glufosinate was variable, ranging from 0 to 100 % with no injury on 7 and 3 plants for mesosulfuron and glufosinate, respectively. In a third experiment, plants were treated with cyhalofop, pyroxsulam, and clethodim. Cyhalofop provided 0% control (n=18). Pyroxsulam provided 0 to 50 % control of a few plants, but over half of the plants had little to no injury (n=36). Clethodim provided no control on 83% of the plants (n=36). These results confirm resistance to the dims, fops, and den herbicides and these plants had ACCase point mutations leading to amino acid substitutions [I1781L (isoleucine to leucine), D2078G (aspartate to glycine), and C2088R (cysteine to arginine)] known to confer resistance. Plants surviving glufosinate application were found to have a point mutation in glutamine synthetase known to confer resistance. Difficulties were encountered in sequencing ALS from these plants. There was no mutation at the 574 loci and possible mutations at other loci could not be evaluated. These experiments confirm the presence of several new resistances in US Italian ryegrass populations.




Amaranthus palmeri (S. Wats.) rapidly evolved resistance to glyphosate through massive amplification and insertion of the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene across the genome. Increased EPSPS gene copy numbers resulted in higher titers of EPSPS enzyme, the target of glyphosate, and conferred resistance to glyphosate treatment. This resistance has spread to 25 states in 10 years.  To understand the genomic configuration and underlying mechanism of EPSPS gene copy number proliferation, a bacterial artificial chromosome (BAC) library from a highly resistant biotype was developed and used to sequence the local genomic landscape flanking the EPSPS gene. By sequencing overlapping BACs, a 399 kb sequence was generated, hereafter referred to as the “EPSPS cassette.”  The cassette includes: a single copy of EPSPS; several putative genes, dense clusters of tandem and inverted repeats, putative helitron sequences, and regulatory machinery. To compare genomic representation across the EPSPS cassette from resistant and sensitive biotypes, whole genome shotgun sequencing (WGS) and mapping of both biotypes (R and S) to the reference EPSPS cassette revealed no direct alignment to sequences from sensitive plants as indicated by the presence of gaps in the sequence.   WGS and mapping also revealed a high presence of single nucleotide polymorphisms (SNPs) in the sensitive plants relative to the cassette from resistant plants which showed extremely high sequence conservation. The observation of an abundance of SNPs and lack of repetitive sequence in the sensitive biotype suggests that these differences were due to assembly and amplification of the EPSPS cassette in the resistant plants.  EPSPS cassette copy numbers of 100 increased the genomic content by 6 % indicating that amplification of EPSPS appears to be a driver of evolution through genomic expansion and redistribution. The lack of homogeneity between the EPSPS cassette and the genome of sensitive plants may have resulted from repetitive transposon events that captured a diverse array of intervening sequences. The presence of putative helitron sequences in the cassette suggests a possible adaptive, replicative mechanism underlying amplification and distribution. 


SURVEY OF THE GENOMIC LANDSCAPE SURROUNDING THE EPSPS GENE IN GLYPHOSATE-RESISTANT AMARANTHUS PALMERI FROM GEOGRAPHICALLY DISTANT LOCATIONS. W. T. Molin*1, M. Jugulam2, M. J. VanGessel3, R. E. Hoagland4, W. B. McCloskey5; 1USDA, Stoneville, MS, 2Kansas State University, Manhattan, KS, 3University of Delaware, Georgetown, DE, 4USDA-ARS, Stoneville, MS, 5University of Arizona, Tucson, AZ (114)


Glyphosate resistant Amaranthus palmeri has spread to twenty-five states within the last ten years, making it one of the most prevalent and difficult to control weeds in the United States.  Resistance to glyphosate herbicide in this species is due to amplification and increased expression of the gene encoding the target site of glyphosate, 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS).  The DNA sequence containing the EPSPS gene and the sequences up and downstream of EPSPS, all of which are amplified, are called the EPSPS cassette. The current size of the EPSPS cassette stands at 297 kb, but considering that the ends of the cassette have not been reached, the actual complete sequence is unknown. To date, the EPSPS cassette has only been sequenced from one A. palmeri population from Mississippi. The present research compares EPSPS cassettes from a number of resistant and sensitive populations from geographically distinct locations within the U.S.  A PCR analysis using forty primer pairs specific to the cassette revealed that the resistant populations were very similar to each other, whereas many of the primers failed to generate a PCR product with DNA from the sensitive populations.  Selected regions of the EPSPS cassettes were sequenced in the resistant populations and were found to be nearly identical, indicating strong homology among the cassettes analyzed from the different A. palmeri populations.  Gene expression analysis showed that both EPSPS and another gene in the cassette, a reverse transcriptase, were elevated in all resistant populations tested relative to the sensitive populations.  Collectively, these data show that in terms of the EPSPS cassette, these resistant populations were very similar to each other and distinct from the sensitive population. These data support the conclusion that glyphosate resistance probably evolved once and then most likely spread rapidly across the U.S. 




Junglerice (Echinochloa colona) is a problematic weed in annual and perennial cropping systems in California. Moreover, in recent years, presence of glyphosate-resistant (GR) junglerice populations have compromised the effectiveness of glyphosate, a popular postemergence herbicide in orchards and vineyards. Hence, there is a need to identify other effective postemergence herbicides. It has been observed that the efficacy of postemergence herbicides often varies according to the microenvironment of orchards and vineyards, especially shade and soil moisture conditions. Therefore, a study was conducted in 2016 to assess the efficacy of glyphosate, glufosinate, and sethoxydim on potted pre-confirmed GR junglerice plants grown under two soil moisture regimes [100% field capacity (FC) and 50% FC)] and shade (Full Sun, 50% Shade, and 70% Shade) conditions. Label rates of the herbicides were applied at the 4- to 6-leaf stage of junglerice and the pots were immediately subjected to the abovementioned conditions for four weeks. Non-treated control weeds were also included in all shade and moisture regimes. Plant mortality was evaluated at 35 days after treatment and the plants were harvested, oven-dried, and the aboveground biomass and the number of seeds on each plant were recorded. The study was conducted twice and data were analyzed at a 0.05 level of significance. Plant mortality was not affected by soil moisture level but there was an interaction between the shade level and herbicide type. Sethoxydim and glufosinate provided similar control of the plants at all shade levels, whereas control with glyphosate increased as level of shade increased. Shade had no effect but moisture stress reduced the biomass of the plants and number of seeds produced. In the glyphosate-treated plants, both moisture stress and an increase in shade reduced the biomass and the number of seeds per plant. Therefore, sethoxydim and glufosinate provided good control of GR junglerice under both moisture stress and shade conditions tested.

GISH AND FISH MAPPING OF EPSPS COPIES IN INTERSPECIFIC HYBRIDS OF AMARANTHUS SPINOSUS AND AMARANTHUS PALMERI. M. Jugulam*1, S. Menzer1, D. Koo1, V. K. Nandula2, C. R. Thompson1, B. Friebe1, B. S. Gill1; 1Kansas State University, Manhattan, KS, 2USDA-ARS, Stoneville, MS (116)


Spiny amaranth (Amaranthus spinous) is a diploid (2n:34) monoecious weed widespread in many regions of the United States. Recently, the first case of glyphosate-resistant (GR) spiny amaranth was reported from Mississippi. This resistance was likely to have conferred as a result of hybridization with GR Palmer amaranth (Amaranthus palmeri, 2n:34), as the EPSPS sequence of GR spiny amaranth was identical to GR Palmer amaranth but different from glyphosate susceptible (GS) spiny amaranth. The objective of this investigation were: a) determine EPSPS copy number and expression in hybrids derived from a cross between A. spinosus x A. palmeri; b) map the physical location of EPSPS copies in the genome of hybrids using florescent in situ hybridization (FISH); and genomic in situ hybridization (GISH) analysis. Fresh leaf tissue from GR Palmer amaranth, GS spiny amaranth as well as the F1 hybrids was collected and genomic DNA was extracted. Root tips from these plants were also collected and prophase/metaphase mitotic spreads were prepared for FISH and GISH analysis. Genomic DNA was used to prepare probes for GISH, whereas, the probe for FISH analysis was prepared using EPSPS sequence of A. palmeri. The EPSPS expression correlated with the copy number in hybrids. GISH and FISH analysis displayed discriminated EPSPS gene signals throughout the genome of hybrid plants, similar to what was previously reported in GR Palmer amaranth. These results further support that the glyphosate resistance in spiny amaranth was introgressed via pollen mediated gene transfer from GR A. palmeri.




Knowledge of Palmer amaranth biology and physiology is essential for the development of effective weed management systems. The aim of this study was to investigate the response of Palmer amaranth gender to nutrient deficiency and light stress. Differential gender responses were observed for all growth, phenology, and photochemistry parameters measured. Female plants, for example, invested more in height, stem, and total dry weight whereas male plants invested greater in leaf area and leaf dry weight. The growth rate of females was higher than that of male Palmer amaranth plants although both followed similar declining trends as the experimental period progressed. Initiation of flowering of female plants occurred six to eight days earlier compared to male plants. Nitrogen, and to a certain extent phosphorous, were the most influential nutrients that affected growth and physiological parameters in both Palmer amaranth genders, particularly under high light intensity. Electron transport rate and chlorophyll content of female Palmer amaranth plants compared to male plants was lower at high light intensity in combination with nitrogen and phosphorous deficiencies. There is a potential to manipulate Palmer amaranth population structure by altering microenvironments at the field level.



Locoweeds (mostly Astragalus spp. and Oxytropis spp.) are legumes that contain swainsonine (SWA), an alkaloid that causes severe economic losses in the western U.S. through the livestock disease ‘locoism’. The fungal endophytes, Alternaria spp. section Undifilum, are primarily or completely responsible for SWA synthesis in locoweeds. To date, the locoweed-fungal endophyte complex seems physiologically asymptomatic, unlike in tall fescue where its endophyte can improve stress tolerance and enhance plant growth. However, previous studies in which the locoweed endophyte has been removed to investigate this symbiotic relationship were performed under greenhouse or tissue culture conditions. To explore the role of the fungal endophyte on locoweeds (Astragalus mollissimus var. mollissimus and Oxytropis sericea) under field conditions, plant growth parameters were measured in the common garden established in 2011 at the Montana Agricultural Experiment Station’s Post Farm near Bozeman MT. Plants were started by germinating seeds with (endophyte +, E+) and without (endophyte -, E-) seed coat, grown in a greenhouse, and transplanted as seedlings; endophyte presence/absence was confirmed using PCR. Growth parameters measured over a four-year period included transplant survival over winter, gas exchange, number of flowers and seeds, and seed germination rates. No endophyte effect for transplant survival was found although there was a species survival difference with 50% of O. sericea and no A. mollissimus plants surviving three years, regardless of endophyte status.  There was not an endophyte effect for plant photosynthesis or stomatal conductance in either of the locoweed species; however, there was a year effect for transpiration with O. sericea E+ plants having higher transpiration in year four only.  In addition, the presence of the endophyte did not affect fecundity of either species.  Thus far in this common garden study, there has been no apparent cost or benefit of the fungal endophyte on locoweed success.


EFFECT OF SALINITY ON CARDINAL TEMPERATURE OF MALVA SYLVESTRIS. O. Ansari1, J. Gherekhloo1, B. Kamkar1, F. Ghaderi Far1, P. T. Fernandez-Moreno2, R. De Prado*3; 1Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran, 2University of Cordoba, Cordoba, Spain, 3Department of Agricultural Chemistry and Edaphology, University of Cordoba, Cordoba, Spain (119)


Tall mallow (Malva sylvestris L.) is an important invasive weed in many crops in southwest of Iran which has proved troublesome for agricultural products and pastures. Seed germination is a complex biological process that is influenced by various environmental such as temperature, water potential, salinity, pH, light and genetic factors. This experiment was conducted to estimate cardinal temperatures of M. sylvestris seeds under salinity stress. Seeds were germinated at nine temperatures (5, 10, 15, 20, 25, 30, 35, 40 and 45 °C) and three NaCl solutions (0, 80 and 160 mM). Results showed that temperature significantly affected germination rate of tall mallow. Salinity stress significantly influenced on the germination rate in all temperatures. According to the segmented model fitted to germination rate, base temperature for 0, 80 and 160 mM were 1.83, 1.68 and 1.24 °C, optimum temperatures were 28.02, 28.05 and 20.63 °C and the maximum temperature were 43.46, 40.64 and 40.97 °C, respectively. These results could help implement a rational strategy in order to control and predict the spreading of tall mallow in saline areas.

Keywords: Cardinal temperature, Salinity stress, Tall mallow.


FITNESS COSTS AND MECHANISM OF ACETOLACTATE SYNTHASE-INHIBITING HERBICIDE RESISTANCE IN ANNUAL BLUEGRASS. T. Tseng*1, E. Santos2, V. K. Nandula3, E. E. Wilson2, G. Sharma2, J. D. McCurdy2; 1Mississippi State University, Starkville, MS, 2Mississippi State University, Mississippi State, MS, 3USDA-ARS, Stoneville, MS (120)


Annual bluegrass (Poa annua) is an annual weed that is particularly troublesome in managed turfgrass. It has traditionally been controlled with herbicides, including acetolactate synthase (ALS) inhibitors. However, resistance to these ALS inhibitors has been documented throughout the Southeastern United States since 2012, most recently in Mississippi. DNA sequencing was conducted on resistant annual bluegrass biotypes, two from Alabama (Lagoon and Ross Bridge) and one from Mississippi (Reunion) to determine if the mechanism of resistance was a target-site mutation. Additionally, plate assays were conducted on a susceptible and resistant annual bluegrass populations using the herbicide foramsulfuron to determine the best inoculation technique for rapid resistance screening of ALS-inhibitor resistant annual bluegrass, and to determine if resistance to ALS-inhibitor is associated with decreased fitness. The DNA sequencing results identified a Trp574 to Leu mutation in the ALS gene of the Lagoon biotype, which has been shown to confer resistance to ALS-inhibitors. The Ross Bridge biotype contained the same sequence as a wild type susceptible biotype.  This biotype could have non-target-site resistance causing different metabolism or translocation of the herbicide, which could confer ALS-inhibitor resistance. Measurement of fitness parameters among the three resistant and a susceptible biotype showed decreased fitness (lower biomass, and, shoot and root length) only in the resistant Ross Bridge biotype in comparison to the rest of the resistant and susceptible biotypes; thus, suggesting that ALS-inhibitor resistance is not strongly correlated with decreased fitness in annual bluegrass.

GERMINATION RESPONSE OF SEA BARLEY (HORDEUM MARINUM) TO TEMPERATURE. M. Taheri1, J. Gherekhloo1, A. Siahmarguee1, O. Ansari1, P. T. Fernandez-Moreno2, R. De Prado*3; 1Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran, 2University of Cordoba, Cordoba, Spain, 3Department of Agricultural Chemistry and Edaphology, University of Cordoba, Cordoba, Spain (121)


Sea barley (Hordeum marinum) is a winter annual weed of Gramineae family that grows in non-cropland and marginal land. A completely randomized design experiment was conducted to investigate the effect of different temperatures on germination and determine the cardinal temperatures of sea barley (Hordeum marinum), comprising temperatures of 3, 5, 10, 15, 20, 25, 30, 35, and 40 °C with 4 replicates. In order to quantify the response of germination rate of sea barley to temperature, first the changes in cumulative germination in response to temperature were quantified using 3 parameter logistic model and time to reach different percentiles was obtained. Then, three non-linear regression models including segmented, dented, and beta were implemented to quantify the response of germination rate of sea barley to temperature. The results demonstrated that temperature affects germination percentage as well as germination rate. When the applied models were compared with respect to parameters RMSE, CV, SE, and 1:1 line, the most proper model to assess cardinal temperatures was segmented model. For different percentiles and using segmented model, base, optimum, and ceiling temperatures fluctuated between 4.34-5.41, 27.11-29.06, 39.88-40.19°C, respectively, but there was no significant difference among the estimated temperatures in different percentiles


TRENDS IN RELATIVE TOXICITY OF HERBICIDE USE IN THE UNITED STATES, 1990 TO 2015. A. R. Kniss*; University of Wyoming, Laramie, WY (122)


DYNAMICS OF SULFENTRAZONE AND FLUMIOXAZIN APPLIED TO EUCALYPTUS HARVEST RESIDUES. C. A. Carbonari*, G. Gomes, E. D. Velini; Universidade Estadual Paulista, Botucatu, Brazil (123)


Minimum cultivation has become the major soil tillage system in eucalyptus plantations in Brazil, having as the main consequence, the maintenance of large amounts of harvest crop residues on soil surface affecting the dynamics and action of PRE herbicides. The objective of this research was to evaluate the dynamics of herbicides flumioxazin, and sulfentrazone applied on the eucalyptus harvest residue and its efficacy to control weeds. Two experiments were conducted to examine the effects of eucalyptus residue mass (15 and 40 t ha-1) on sulfentrazone and flumioxazim retention. Rainfall volumes were simulated at 5, 10, 20, 35, 50, and 100 mm. A 20 mm rainfall volume was simulated at 7 and 14 d after the first simulated event. The water passing through the residue was collected after each rainfall simulation. The concentration of each herbicide was measured by liquid chromatography and mass spectrometry and the release curves from residue to soil was determined. For both herbicides, the maximum amount released from residues were observed for 40-60 mm rainfall. The mass of eucalyptus residue affected the amount of herbicides recovered. The sulfentrazone was released 78 and 58%, and flumioxazim 57 and 75%, both respectively, to 15 and 40 t ha-1. The weed control (Spermacoce latifolia, Ipomoea grandifolia, Sida rhombifolia and Urochloa decumbens) was correlated with the amount of herbicide released from crop residues and reached the soil.



Widespread distribution of glyphosate-resistant weeds in soybean-growing areas across Mississippi has economically affected soybean planting and follow-up crop management operations. New multiple herbicide-resistant crop (including soybean) technologies with associated formulations will soon be commercialized. The objectives of this research were to determine the efficacy of new 2,4-D + glyphosate and dicamba formulations on herbicide resistant weeds, and to determine the impact of the new 2,4-D + glyphosate formulation on microbial communities in the soybean rhizosphere involved in nutrient cycling. New 2,4-D + glyphosate and dicamba formulations registered for use on 2,4-D and dicamba-resistant soybean, respectively, adequately controlled glyphosate resistant and susceptible pigweeds (Palmer amaranth and tall waterhemp) and common ragweed. The 2,4-D + glyphosate formulation did not significantly impact soil microbial activities linked to nutrient cycling in the soybean rhizosphere. These results indicate these new 2,4-D + glyphosate and dicamba formulations can be effective in controlling glyphosate resistant and other herbicide resistant weeds while not having adverse effects on the activities of beneficial soil microorganisms.

EFFECT OF AIR CO2 CONCENTRATION IN PHYTOREMEDIATION OF IMIDAZOLINONE HERBICIDE. L. A. Avila*, L. P. Souza; Universidade Federal de Pelotas, Pelotas, Brazil (125)


HERBICIDE RESISTANCE AND MANAGEMENT IN FLAXLEAF FLEABANE (CONYZA BONARIENSIS (L.) CRONQUIST)  FROM THE SOUTHEAST REGION OF CORDOBA, ARGENTINA. E. Bracamonte1, A. Leoni1, R. Tabasso1, P. Bellucini2, P. T. Fernandez-Moreno3, R. De Prado*4; 1Faculty of Agricultural Sciences, University of Cordoba, Cordoba, Argentina, 2INTA EEA Marcos Suarez, Cordoba, Argentina, 3University of Cordoba, Cordoba, Spain, 4Department of Agricultural Chemistry and Edaphology, University of Cordoba, Cordoba, Spain (126)


A research was developed with the main objective to establish efficient and comprehensive management strategies in flaxleaf fleabane (Conyza bonariensis (L.) Cronquist) from the agricultural region of southeastern Cordoba (Marcos Suarez), Argentina. The specific objectives were to determine the bio-ecological, agronomic dispersion, herbicide resistant causes, besides to evaluate the effectiveness control of sulfosate in tank-mix with different herbicides and doses: chlorsulfuron, metsulfuron, atrazine, diclosulam, sulfometuron + chlorimuron, flumioxazin (15 g / ha (chlorsulfuron + metsulfuron) + 1.5 L / ha sulfosate). According to the national and international literature consulted, the results can conclude that the agronomic practices and bio-ecological characteristics of flaxleaf fleabane favor their diffusion in this region. The best responses at 30, 60 and 90 days after treatment (DAT) were obtained with sulfonylureas in tank-mix with sulfosate, considering efficiency and cost of treatment. The use of herbicides in tank-mix with different modes of action allow an increase control to 95%, reducing pressure selection of resistant biotypes. The determination of useful water at 90 DAT (1 m deep), increased a 53% in the treated strip with herbicides. Currently, there are not many alternatives for efficient and economical chemical control of this weed, and it should consider other options for efficient control. Omission of chemical treatments in fallows, or leave weeds without herbicide treatment in an advanced phenological development, would enable the increase of soil seed bank with unwanted species. This situation increases the difficulty of control and the cost of the treatments, mainly in years with dry springs, where weeds consume water from the soil profile, hampering planting of the subsequent crop.

Keywords: Conyza bonariensis, glyphosate resistance, chemical control.


EFFECT OF MIXING 2,4-D AND SULFOSULFURON ON WILD MUSTARD CONTROL. S. Akhundi1, J. Gherekhloo1, N. Bagherani2, P. T. Fernandez-Moreno3, R. De Prado*4; 1Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran, 2Agricutural Research Center of Glestan, Gorgan, Iran, 3University of Cordoba, Cordoba, Spain, 4Department of Agricultural Chemistry and Edaphology, University of Cordoba, Cordoba, Spain (127)


In order to optimize the application of herbicides, fundamental approaches such as tank mixture are in spotlight. To investigate the effect of 2,4-D and sulfosulfuron on wild mustard weed, some factorial experiments based on completely randomized design with 3 replicates were conducted at the greenhouse of Gorgan University of Agricultural Sciences and Natural Resources. Herbicides were applied at 0, 0.1, 0.2, 0.4, 0.6, 0.8, 1, 2 X of recommended dose and tank mixture ratios of (0:100), (25:75), (50:50, (25:75), (100,0). Log-logistic function for dry weight of plants against differential doses of herbicides was fitted for each mixture and the dose required to inhibit 50% growth (GR50) was estimated, then, isobole curves were used to determine the effect of 2,4-D and sulfosulfuron mixtures. The results showed that the rates of 2,4-D and sulfosulfuron required for 50% reduction in wild mustard were 0.639 and 0.906  recommended dose of this herbicides, respectively. The results showed that increasing the rate of Sulfosulfuron in the mix led to higher GR50s, so adding Sulfosulfuron to 2,4-D herbicide reduces the inhibitory effect of the latter herbicide. The effect of Sulfosulfuron and 2,4-D mixture was additive. It may be deemed that increasing the share of 2,4-D in the mixture leads to more toxicity for wild mustard, rather than increasing that of Sulfosulfuron.

Keywords: Chemical control, Dose-response, Log-logistic function, Synergism, Wild mustard


IMPACT OF PALMER AMARANTH ON SOYBEAN PRODUCTIVITY AS INFLUENCED BY VARYING RATES OF METRIBUZIN AND SULFENTRAZONE. M. de Avellar*1, R. Werle2; 1University of Nebraska, Lincoln, Lincoln, NE, 2University of Nebraska, Lincoln, North Platte, NE (128)




Farmers typically use three applications of glyphosate to control weeds in no-till fallow.  Some are now experimenting with an unconventional modification to this widely-used approach.  This modified approach is based on an intentional delay in the time of the first spraying.  Farmers delay their first spraying because they want to rely on competition from winter annual grasses to suppress the growth of Russian thistle and eliminate the need for a third application.  Optimism for this kind of weed control program is tempered by concerns related to soil water storage.  The objective of this research was to evaluate effects of delayed control of downy brome and volunteer winter wheat on the plant-available water content of, and loss of water from, no-till fallow.  Treatments, applied to plots arranged in a randomized complete block design with four replications, were distinguished by the time of the initial glyphosate applicationThe initial early-season treatment was applied as soon as possible after emergence of downy brome and volunteer winter wheat.   Initial mid-season and late-season treatments were applied 4 and 6 weeks later, respectively.  The amount of plant-available water in the soil profile ranged from 71.8 to 153.7 mm in May and 16.5 to 80.9 mm in September.  Water loss was usually minimized in plots treated with the initial early-season treatment.  An exception to this trend occurred at a site where the density of downy brome and volunteer winter wheat was greater-than-average.  Abated water loss from the initial late-season treatment, at this site, may have been a consequence of reduced evaporation caused by a decrease in near-surface wind speed and deflection of solar radiation away from soil. Estimated impacts of water loss on grain yield of winter wheat, produced the year after fallow, range from 269 to 600 kg ha-1.

CASH COVER CROPS SUPPRESS SUMMER ANNUAL WEEDS. F. Forcella*1, R. Gesch1, D. Wyse2; 1USDA, Morris, MN, 2University of Minnesota, St Paul, MN (130)


COVER CROP SPECIES RESPONSE TO SINGLE ACTIVE INGREDIENT RESIDUAL HERBICIDES WITH SIMULATED HALF-LIFE DOSES. B. S. Heaton*1, M. L. Bernards1, R. Werle2; 1Western Illinois University, Macomb, IL, 2University of Nebraska, Lincoln, North Platte, NE (131)


Herbicide labels rarely contain specific rotation information for many of the species planted as cover crops.  In this study we use doses associated with three herbicide half-life times to estimate cover crop response at various potential establishment times relative to herbicide application time.  Eleven common cover crop species response to 12 corn and soybean herbicides were measured. The cover crops were red winter wheat (53 kg ha-1), cereal rye (65 kg ha-1), winter rapeseed (3 kg ha-1), red clover (7 kg ha-1), Austrian winter pea (58 kg ha-1), hairy vetch (9.7 kg ha-1), radish (6 kg ha-1), crimson clover (2.6 kg ha-1), annual ryegrass (1.2 kg ha-1), turnip (1.3 kg ha-1) and oats in 2016. The herbicides were applied at four doses (the first dose is the labeled rate), including: 2,4-D amine (1120, 280, 70, 17.5), atrazine (1120, 560, 280, 140), dicamba (1120, 280, 70, 17.5), isoxaflutole (48, 24, 12, 6), mesotrione (210, 105, 53, 26), chlorimuron-ethyl (17.5, 8.8, 4.4, 2.2), cloransulam methyl (35.3, 17.7, 8.8, 4.4), flumioxazin (107, 53.5, 26.8, 13.4), fomesafen (329, 165, 82, 41), pyroxasulfone (240, 120, 60, 30), sulfentrazone (420, 210, 105, and 53), and sulfentrazone + chlorimuron-ethyl (420+52.5, 210+26, 105+13, 53+6). The study was established in October 2013, June 2014, September 2015, and August 2016.  Visual evaluations of injury on a scale of 0 (no injury) to 100 (plant death) were made 3 and 5 weeks after planting. Cover crop response was not identical to a given herbicides across years. Crimson clover, red clover, radish, winter rape and turnip were most sensitive to injury from the herbicides evaluated; rye, ryegrass, winter pea, and hairy vetch showed an intermediate level of injury; and wheat and oats were the least likely to be injured.  Dose response curves will be presented for the various cover crop-herbicide combinations.




Horseweed (Conyza canadensis L. Cronquist) is problematic in no-till production, as seed will readily germinate on the soil surface. Additionally, herbicide resistant horseweed has made control of this weed even more difficult prompting new research into other techniques for control. Research was conducted to evaluate horseweed suppression from fall planted cover crops and compare suppression to fall applied residual herbicides.


This study was conducted in Blackstone, Virginia set up as a randomized complete block design with four replications. Treatments in this study consisted of four cover crop species: cereal rye (Secale cereale L.), forage radish (Raphanus sativus L.), hairy vetch (Vicia villosa Roth.), and crimson clover (Trifolium incarnatum L.), as well as two fall applied residual herbicides. Cover crop treatments included monocultures of each species, three two-way mixtures, each with cereal rye and one of the other species, and two three-way mixtures, each with cereal rye, forage radish, and either legume. Fall applied herbicides were metribuzin at 0.092 kg ai ha-1 and chlorimuron-ethyl at 0.015 kg ai ha-1 (Canopy®) and flumioxazin (Valor® SX) at 0.107 kg ai ha-1 + paraquat (Gramoxone® SL 2.0) at 0.7 kg ai ha-1. Adjuvants were included based on product label recommendations. A no cover crop control was also included. Cover crop treatments were drilled and herbicides were applied at 140 L ha-1 on October 20, 2015. The cover crop treatments were terminated by two sequential passes with a roller crimper two weeks apart with the initial pass on May 3, 2016. After the second pass, corn was planted at 61,775 seeds ha-1. Data collected included: horseweed counts taken in all plots from a 0.37m2 area in late March, visible horseweed suppression ratings taken on a 0 (no suppression) to 100 (complete suppression) scale 4, 6, and 8 weeks after termination (WAT), and horseweed biomass collected from a 0.09m2 area at harvest. Data were analyzed using JMP 12 Pro and subjected to ANOVA followed by means separation using Fisher’s Protected LSD and considered significant when p<0.05.


Horseweed counts in March indicated that hairy vetch and forage radish in monoculture, metribuzin + chlorimurion-methyl, and the nontreated check had higher horseweed populations with > 16 plants m-2 and all other treatments with < 8 plants m-2. Cover crop mixtures containing cereal rye, hairy vetch in monoculture, and flumioxazin + paraquat had better suppression of horseweed, starting at 70 to 90% suppression 4WAT and falling to 30 to 50% suppression 8 WAT as compared to the nontreated check. Forage radish and crimson clover in monoculture as well as the metribuzin + chlorimuron-methyl treatment performed poorly throughout starting with < 60% suppression 4WAT and falling to < 20% suppression 8WAT. Overall, cereal rye containing cover crops can suppress horseweed better than monocultures of crimson clover, forage radish, and hairy vetch. Flumioxazin + paraquat provides good horseweed control (50 to 90%) and was comparable to cereal rye containing mixtures. Future research is needed to corroborate these findings across multiple site-years and determine if suppression rates would be similar with herbicide resistant horseweed populations.


IMPROVING SELECTIVITY OF PHYSICAL WEED CONTROL:  NEW TRICKS FOR OLD DOGS? D. C. Brainard*, S. Hitchock Tilton; Michigan State University, East Lansing, MI (133)


In simplest terms, the “selectivity” of a weed management practice refers to its ability to kill weeds without damaging the crop.  Using the framework developed by Kurstjens et al. (2004), strategies for improving selectivity of physical weed control (PWC) tools include those that 1) improve their “selective ability” by reducing the variance or shifting the distribution of forces (e.g. uprooting, severing or burial) applied by those tools; and 2) improve their “selective potential” by increasing the mean or reducing the variance of crop tolerance to those forces.  Most work in PWC has focused on improving the selective ability of tools through adjustments in tool design, or recently by development of camera guidance systems and robotic weeders.  We hypothesize that several underutilized approaches including “tool stacking” (combining 2 or 3 tools in a single pass) and identification and exploitation of “cultivation tolerant” crop traits, may be useful for complementing these efforts. In field trials in sweet corn, snap bean and carrots, we evaluated the selectivity of three in-row PWC tools (finger, torsion and flextine weeders) used alone or in various stacked combinations.  A separate set of field trials was conducted to evaluate the tolerance of 6 carrot cultivars to PWC tools and partial burial.  Finger weeders had greater selectivity for most crop-weed combinations compared to either torsion or flextine weeders.  Although tool stacking generally increased weed mortality compared to single tools, it often also increased crop mortality, resulting in little or no improvement in selectivity.  Carrot cultivars varied in their tolerance to flextine cultivation and partial burial, presumably due to variation in early growth rates and root-shoot partitioning. These results suggest that 1) greater understanding of the mechanisms responsible for weed and crop mortality is needed before tool stacking can be effectively used to improve selectivity; and 2) identification and exploitation of cultivation tolerant traits in crops is a potentially valuable approach for improving the selectivity of PWC.    

DISTRIBUTION AND CONTROL OF GLYPHOSATE-RESISTANT WATERHEMP (AMARANTHUS TUBERCULATUS VAR. RUDIS) IN SOYBEAN (GLYCINE MAX) IN ONTARIO. M. G. Schryver*1, N. Soltani2, D. C. Hooker2, D. E. Robinson2, P. J. Tranel3, P. H. Sikkema2; 1University of Guelph, London, ON, 2University of Guelph, Ridgetown, ON, 3University of Illinois, Urbana, IL (134)


Glyphosate-resistant (GR) waterhemp (Amaranthus tuberculatus var. rudis) (WH) was first confirmed in Lambton County, Ontario in 2014. This small-seeded, summer annual, broadleaf weed has an extended emergence pattern, has high genetic diversity, is a prolific seed producer, and is very competitive. In Ontario, WH interference has been documented to reduce soybean yield by 73%. The focus of this research was to determine the distribution of GR WH in Ontario and to develop strategies for its control in soybean. Forty-eight WH seed samples were collected in the fall of 2015, and screened for resistance to: Group 9 (glyphosate), Group 5 (atrazine) and Group 2 (imazethapyr). Survey results conclude there are 40 sites with GR WH populations (82% of all samples) found in Essex, Chatham-Kent and Lambton counties. In addition, 100% of the samples surveyed were resistant to imazethapyr (Group 2) and 76% to atrazine (Group 5). At 84 days after application (DAA), pyroxasulfone/flumioxazin, pyroxasulfone/sulfentrazone and s-metolachlor/metribuzin provided 97, 92 and 87% GR WH control, respectively. At 84 DAA, in Liberty Link soybean, a sequential application of pyroxasulfone/flumioxazin, pyroxasulfone/sulfentrazone or s-metolachlor/metribuzin applied PRE followed glufosinate applied POST provided 98, 98, and 96% GR WH control, respectively. This research provides valuable information for growers by documenting the distribution of GR WH in Ontario and developing control programs in soybean.


ORGANIC WEED MANAGEMENT USING AIR-PROPELLED ABRASIVE GRIT MANAGEMENT. M. G. Carlson*1, S. Clay1, F. Frocella2, S. Wortman3; 1South Dakota State University, Brookings, SD, 2USDA-ARS, Morris, MN, 3University of Nebraska-Lincoln, Lincoln, NE (135)


Weeds are the number one problem in organic cropping systems. The use of air-propelled abrasive grits aimed at the crop row may provide weed control and an opportunity to simultaneously add slow-release fertilizers to the crop. Five grits, pelletized turkey litter (Sustane 8-2-4, Sustane 4-2-2), corn cob meal, crushed walnut shells (Agra-Grit), pelletized soybean meal (Phytaboost Plant Food 7-1-2) were added at 0, 1200 or 3600 mg to 1 g of silty clay loam soil at three application timings (1, 2, or 3 applications, with multiple applications 10 d apart starting at 0 d). The soil was maintained at 30% moisture under laboratory conditions. Sampling occurred at 0, 7, 14, 28, 56, 116, 142, 183 d after the initial grit application (DAA) to examine nitrogen release patterns. Soils were extracted with 1M KCL solution with extracts analyzed for NO3--N, and NH4+-N were quantified using a cadmium reduction method (ASTORIA-PACIFIC micro-segmented flow analyzer). NH4+-N release peaked at 14 d into the incubation with 230 mg N/g soil from the soybean meal grit after two applications. By the 112 d sampling, the NH4+-N levels were similar for all treatments. The NO3N levels were similar in all treatments to the untreated control until 14 d after application. For the three application treatment, the NO3-N mineralized in the soil treated with soybean meal and Sustane 8-2-4 after 14 d was described by the Mitscherlich Equation and by 183 DAA 556 ug NO3 was present in soil treated with soybean meal (r2 = 0.99 ) whereas with a total NO3 of 377 ug NO3 was quantified in the Sustane 8-2-4 (r2 = 0.74 ) treatment. Other grits and application treatments had a maximum of 170 ug of NO3 mineralized. These data indicate that, if chosen carefully and applied often, grits may serve a multiple purpose for weed control and help stimulate soil mineralization or be the supply NO3 to the crop.


EFFECT OF COMMON RAGWEED ON SOYBEAN GROWTH AND YIELD. E. Barnes*1, A. Jhala2, S. Knezevic1, P. H. Sikkema3, J. Lindquist4; 1University of Nebraska- Lincoln, Lincoln, NE, 2University of Nebraska-Lincoln, Lincoln, NE, 3University of Guelph, Ridgetown, ON, 4University of Nebraska - Lincoln, Lincoln, NE (136)


Common ragweed (Ambrosia artemisifolia L.) is an early emerging and competitive annual broadleaf weed species in soybean (Glycine max) production fields in much of the north central United States and eastern Canada. A field experiment was conducted in 2015 and 2016 at the University of Nebraska-Lincoln to assess common ragweed interference in soybean as affected by variable available soil water and common ragweed density. Three main plot irrigation treatments were established to achieve full, half, or zero replacement of predicted evapotranspiration (ET) using SoyWater ( triggered by 50% available soil water depletion. Subplot experimental treatments included common ragweed thinned to densities of 0, 2, 6, and, 12 plants m-1 row. Periodic destructive sampling of crop and weed leaf area index (LAI), above ground biomass, and yield were recorded. Because of adequate rainfall in 2015 and 2016, there was no significant effect of irrigation treatment. Yield loss varied by common ragweed density and year significantly. A model set was constructed using the rectangular hyperbolic yield loss model, leaf area ratio model, and model selection was performed using the corrected information-theoretic model comparison criterion (AICc). Soybean yield loss of 50 and 75% were predicted at common ragweed densities of 0.63 and 1.89 plants m-2 in 2015 and 3.08 and 9.23 plants m-2 in 2016, respectively. In 2015 the hyperbolic yield loss model with common ragweed LAI at the R6 soybean growth stage best described soybean yield loss. In 2016, the hyperbolic yield loss model with common ragweed density at harvest was the best fit model to describe soybean yield loss. When the data were pooled across years and modeled, the leaf area ratio model with relative leaf area at the soybean R6 growth stage best fit the multiyear data with model parameter estimates for I and A of 94.22 and 653.3, respectively. This model was a good fit to the data with root mean squared error and modeling efficiency coefficient of 194.64 and 88.52, respectively. The leaf area ratio model includes both the soybean and common ragweed leaf area and therefore accounts for more variation and has closer predictions among years.


EFFECTS OF INTERSEEDED COVER CROPS ON WEED SEED PREDATION IN CORN. C. Z. Youngerman*1, A. DiTommaso1, J. Losey1, W. Curran2, S. Mirsky3, M. Ryan1; 1Cornell University, Ithaca, NY, 2Pennsylvania State University, University Park, PA, 3USDA Sustainable Agricultural Systems Lab, Beltsville, MD (137)


Weed seed predation by invertebrates can be influenced by habitat quality. We
established an experiment in NY, MD and PA in 2016 to evaluate the effects of corn
planting density on the performance of interseeded cover crops and weed seed predation
in organic production. Corn was planted at three rates ranging from 25k-99k/ha and
interseeded with a cover crop polyculture consisting of cereal rye, annual ryegrass, hairy
vetch, and red clover at 66 kg seed/ha. Corn density treatments were arranged in a
randomized complete block design, and included a control treatment with no corn. Cover
crop biomass was sampled at 50 and 110 days after interseeding. Weed seed predation
was measured at 50, 80, 110 and 140 days after interseeding. Weed seed predation was
quantified using 25 seeds of Setaria faberi glued to seed arenas with and without
invertebrate exclosures. Preliminary results show that cover crop biomass at 110 days
after interseeding ranged from 0.7 to 419.8 g m -2  in NY, 0.2 to 163.6 g m -2  in MD, and 0.8
to 333.4 g m -2 in PA, and was negatively correlated with corn density. Weed seed
predation differed by site and sample date, and was lower on arenas with exclosures.
Grain yield reached its asymptote below the maximum planting
density in all three sites. Maximizing ecosystem services of interseeded cover crops
without a negative effect on grain yield may be achieved by planting at lower corn


COTTON AND PEANUT RESPONSE TO FLURIDONE. D. L. Teeter*1, T. A. Baughman1, P. A. Dotray2, C. D. Curtsinger1, R. W. Peterson1; 1Oklahoma State University, Ardmore, OK, 2Texas Tech University, Lubbock, TX (138)


Cotton and Peanut Response to Fluridone. D. L. Teeter*1, T. A. Baughman1, P. A. Dotray2, R. W. Peterson1; 1Oklahoma State University, Ardmore, OK, 2Texas Tech University, Lubbock, TX

Weed resistance has become an increasing issue in Oklahoma and Texas.  Renewed interest in fluridone can be correlated with the increasing population of glyphosate resistant Palmer amaranth (Amaranthus palmeri) in these crops.  Therefore, the objective of these studies were to evaluate cotton and peanut tolerance to different rates of fluridone applied preemergence alone and in combination with other herbicides in the Southern Great Plains.

Cotton was planted during the 2016 growing season at the Oklahoma State University Research Stations near Fort Cobb and Tipton and the Texas Agricultural Experiment Station near Lubbock. The trials were irrigated at Fort Cobb and Lubbock and rainfed at Tipton.  Fluridone was applied preemergence at 0.168 (1X) and 0.337 (2X) kg ai ha-1 alone and in combination with fluometuron at 0.84 (1X) and 1.68 (2X) kg ai ha-1.  Peanut trials were conducted during the 2015 and 2016 growing season near Fort Cobb.  Fluridone was applied preemergence at 0.168 (1X) and 0.337 (2X) kg ai ha-1 alone and in combination with flumioxazin at 0.107 kg ai ha-1 and metolachlor at 1.42 kg ai ha-1.  All treatments were applied with a CO2 backpack sprayer in 93.457 L ha-1.  The entire trial area for all studies was kept weed free and standard production practices were used throughout the growing season.  Cotton and peanuts were evaluated for visual injury, plant stand counts, cotton plant height, and yield.

Cotton injury evaluated at 2, 4, and 8 WAP was 10% or less except for an application of a 2X rate of fluridone + fluometuron at all 3 locations.  End of season injury was less than 5% at both Oklahoma locations.  Cotton stand counts and heights were not affected by the 1X rate of fluridone applied alone or in combination with fluometuron.  The 2X rate of fluridone alone reduced stand counts 2 WAP at Tipton but did not affect stands counts at Fort Cobb or Lubbock.  Fluridone + fluometuron applied at the 2X rate reduced cotton stand counts and plant height at both Oklahoma locations but did not affect cotton at Lubbock. Cotton yields were not affected by any treatment regardless of location.  Heavy rainfall shortly after planting in 2015, resulted in stand reductions greater than 15% when fluridone was applied at the 2X rate alone and in combination with flumioxazin and metolachlor.  This was evident even 10 WAP.  These same rainfall events caused visible peanut injury of at least 10% with all treatments except metolachlor applied alone PRE at 2 and 4 WAP. Peanut injury at 8 and 10 WAP was at least 20% with all 1X fluridone treatments and at least 35% with all 2X treatments.  Peanut yields were reduced compared to the untreated control with all fluridone PRE treatments.  Peanut stand reduction during the 2016 growing season were less than 5% except when fluridone at 1 or 2X rate was applied with Dual Magnum.  Visual peanut injury was less than 10% season long except with fluridone applied alone or in combination at the 2X rate 4 WAP.  This injury was 5% or less by late season.  Peanut yields were not affected by any treatment in 2016.  These trials would indicate that cotton has good tolerance to fluridone.  Fluridone could potentially provide another useful weed management tool in cotton.  Additional studies in peanut need to be conducted to determine if the injury observed in 2015 was likely more attributable to the heavy rainfall after planting considering the good tolerance observed in 2016.  




Terminated cover crop residue can create a mulch layer that has the ability to suppress summer annual weed emergence. The slower this cover crop degrades, the longer weed suppression is possible. Research was conducted to evaluate the rate of cover crop mulch degradation and how that correlates to cover crop biomass and quality metrics, such as carbon to nitrogen (C:N) ratios, as well as the effect of cover crop on cash crop yield.


Studies were conducted in Blacksburg and Blackstone, Virginia. This study was set up as a randomized complete block design with four replications. Treatments in this study consisted of four cover crop species: cereal rye (Secale cereale L.), forage radish (Raphanus sativus L.), hairy vetch (Vicia villosa Roth.), and crimson clover (Trifolium incarnatum L.), as well as two fall applied residual herbicides. Cover crop treatments included monocultures of each species, three two-way mixtures, each with cereal rye and one of the other species, and two three-way mixtures, each with cereal rye, forage radish, and either legume. A no cover crop control was also included. Cover crops were drilled on October 22 and October 20, 2015 and terminated on April 26 and May 3, 2016 using a roller crimper and glyphosate (Roundup PowerMAX®) at 1.26 kg ae ha-1 in Blacksburg and Blackstone, respectively. At termination, above ground biomass was taken from a 0.09m2 area. These samples were dried and analyzed for carbon and nitrogen content (Feed and Water Analysis Lab; University of Georgia). Quality metrics of the cover crop mixture treatments were determined by using the mass determination from the biomass samples to determine a weighted average of the components. Two weeks after termination, corn and soybeans were planted. Visible ratings were taken on a two-week basis, starting 4 weeks after termination (WAT), using a 0 (no residue cover) to 100 (complete residue cover) scale. Residue thickness was measured at each rating date. Corn and soybean yield data were also collected. Data was analyzed using JMP 12 Pro and subjected to ANOVA followed by means separation using Fisher’s Protected LSD and considered significant when p<0.05. Linear regressions were used to determine correlations between quantity and quality metrics and residue thickness or cover.


Blacksburg had higher biomass measurements ranging from 2,800 kg ha-1 to 11,900 kg ha-1 with Blackstone ranging from 3,200 kg ha-1 to 6,700 kg ha-1. C:N ratios ranged from 9 to 27 and 12 to 38 in Blacksburg and Blackstone, respectively. Treatments containing cereal rye had higher biomass and C:N ratio while hairy vetch and crimson clover had less biomass at each location by around 3,000 kg ha-1 and a decrease in C:N ratio of 10. No difference was found in yield of corn or soybeans, respectively. Using linear regression models to predict the relationship between initial cover crop metrics and residue thickness, higher initial biomass and C:N ratios resulted in thicker residue 8 WAT. C:N ratio was a better predictor of residue thickness than biomass; a C:N ratio of 25 would predict a residue thickness of 1.5 cm or 5 cm in Blackstone and Blacksburg, respectively 8WAT. Future research is needed to support these findings and determine the relationship between residue cover and thickness with summer annual weed suppression.


EVALUATING HERBICIDE TECHNOLOGIES IN OKLAHOMA SOYBEAN. C. D. Curtsinger*, T. A. Baughman, D. L. Teeter, R. W. Peterson; Oklahoma State University, Ardmore, OK (140)


This paper has been withdrawn.

NICOSULFURON AS A SUPPRESSANT IN A LIVING MULCH OF ANNUAL RYEGRASS (LOLIUM MULTIFLORUM LAM.) IN CORN (ZEA MAYS L.). T. B. Cholette*, D. E. Robinson, D. C. Hooker, P. H. Sikkema; University of Guelph, Ridgetown, ON (141)


Living mulches are seeded at the same time, or after establishment, of a cash-generating crop to reduce nitrate leaching, sequester nutrients, reduce erosion, and improve soil health.  However, annual ryegrass seeded at the same time as corn can compete for limited resources resulting in reduced grain yield.  It is hypothesized that using nicosulfuron at a fraction of its labeled rate could suppress annual ryegrass thereby reducing competition between the living mulch and the corn crop.  To investigate the hypothesis, annual ryegrass was seeded at the same time as corn at three sites in May 2016 near Ridgetown, ON.  Nicosulfuron was applied at seven rates (0.8, 1.6, 3.1, 6.3, 12.5, 25 and 50 g ai ha-1) at the 2-3 leaf stage or 4-5 leaf stage of the annual ryegrass.  Annual ryegrass control was assessed 1, 2, 4 and 8 weeks after application (WAA) and biomass was determined 4 WAA.  There was no difference in the annual ryegrass response when nicosulfuron was applied at the 2-3 or 4-5 leaf stage application timings.  Control of annual ryegrass ranged from 11 to 75% and from 10 to 96 % at 1 and 8 WAA, respectively, as the rate of nicosulfuron increased from 0.8 to 50 g ai ha-1.  Biomass levels ranged from 44 to 2 g m-2 as the rate of nicosulfuron increased from 0.8 to 50 g ai ha-1.  Corn yields were 15.4, 15.5, 15.6, 15.6, 15.7, 16.0, 16.1, 15.8 and 16.6 t ha-1 at 0, 0.8, 1.6, 3.1, 6.3, 12.5, 25 and 50 g ai ha-1 of nicosulfuron and in the control with no annual ryegrass, respectively.


RESIDUAL PIGWEED CONTROL WITH VLCFA HERBICIDES. M. M. Hay*, D. E. Peterson, D. E. Shoup; Kansas State University, Manhattan, KS (142)


Increased herbicide resistance in Palmer amaranth (Amaranthus palmeri) and waterhemp (Amaranthus rudis) across multiple herbicide sites of action (SOA) requires a change in management to facilitate weed control. Very long-chain fatty acid inhibitor (WSSA SOA 15) and microtubule inhibitor (WSSA SOA 3) herbicides have been largely used for residual grass control; it is often overlooked that these herbicides also can provide residual control of pigweed. Field experiments were established in 2015 and 2016 near Manhattan, Hutchinson, and Ottawa, Kansas to assess residual control of pigweed with SOA 3 and 15 herbicides. Acetochlor (non-encapsulated and microencapsulated), alachlor, dimethenamid-P, metolachlor, s-metolachlor, pendimethalin, and pyroxasulfone were applied at three different field use rates (high, mid, and low) based on labeled rate ranges for soybean. The experiment was a randomized complete block design with a factorial arrangement of herbicides and rates with four replications. All treatments were applied PRE in a non-crop scenario after the plot area was clean tilled with a field cultivator. The experiment was run one time in 2015 and four times in 2016 at two locations for a total of five site years of data. PRE applications were made June 1, 2015 near Manhattan. PRE applications in 2016 were made on April 12, 2016 at locations near Hutchinson and Ottawa; the second run of the experiment was applied on June 6, 2016 at locations near Hutchinson and Ottawa as well. Percent pigweed control was visually evaluated at 4 and 8 weeks after treatment (WAT). Analysis of fixed effects revealed no significance for three and two-way interactions of herbicide by rate by timing and herbicide by rate for each site at both 4 and 8 WAT; therefore, percent pigweed control was compared using means for each product across rates. At Manhattan pyroxasulfone, s-metolachlor, and dimethenamid-P resulted in the highest Palmer amaranth control at both 4 and 8WAT. At Hutchinson and Ottawa, pyroxasulfone, S-metolachlor, and non-encapsulated acetochlor resulted in the highest Palmer amaranth and waterhemp at both 4 and 8WAT. Pyroxasulfone was often the most effective herbicide; whereas, pendimethalin resulted in the least effective pigweed control at all sites and observation times. The high use rate across all herbicides resulted in superior control when compared to the low use rate across all herbicides at all sites and observation times. This research demonstrates the value of utilizing SOA 15 herbicides as part of integrated weed management and as an effective site of action for control of pigweed in various cropping systems. 


WEED COMMUNITIES SHIFT IN RESPONSE TO ORGANIC NO-TILL INTEGRATED WITH GRAZING. S. K. Hogstad*1, G. G. Gramig1, P. Carr2; 1North Dakota State University, Fargo, ND, 2Montana State University, Moccasin, MT (143)


No-till farming methods have gained popularity in conventional crop production systems in semi-arid regions were conservation of soil moisture is crucial. No-till farming is also associated with enhanced soil conservation. Organic producers, who often rely on tillage as the primary means of weed management, could benefit from these outcomes associated with no-till. Organic no-till methods that rely on roller-crimpled cover crop residue to suppress weeds have been successfully developed in states such as Iowa, Ohio, Pennsylvania, and New York. However, in the Northern Great Plains (NGP), developing these systems has been difficult due to shorter growing seasons that limit production of adequate amounts of weed-suppressive cover crop residue.  Consequently, we developed a hypothesis that incorporating livestock grazing into a no-till annual cropping system with cover crops might improve weed management. To test this hypothesis, a long-term study was conducted during 2013 to 2016 at the Dickinson Research Extension Center in Dickinson, ND to test continuous organic no-till crop production combined with periodic sheep grazing. The crop sequence followed in this experiment was hairy vetch (Vicia villosa) CC, winter wheat, CC cocktail, Proso millet, winter rye (Secale cereale) CC, navy bean (Phaseolus vulgaris), field pea. To encourage weed suppression in the no-till system, sheep (Ovis aries) were grazed pre and post-harvest of main crops and cover crops were retained on the surface as a mulch using a roller-crimper. This experiment was designed as a 2 [no-till (NT) vs. clean till (CT)] x 3 (field pea (Pisum sativum subsp. sativum), winter wheat (Triticum aestivum L. emend. Thell.), or Proso millet (Panicum miliaceum)) factorial arranged in a randomized complete block with 5 replications. Weeded micro-plots (1m2) were established within each whole plot (9.14 x 30.48m) yearly in order to assess yield loss due to weed competition. Weed biomass and density were assessed by destructively harvesting 2- ½ x 1m2 quadrats in each plot at peak biomass production, separating each weed and crop species. Analysis of variance (ANOVA) tests were performed to assess treatment (tillage system, crop, and year) effects on response variables (total weed density and total weed biomass). ANOVA tests were also conducted to assess tillage system and year effects on crop yield loss due to weed for each crop. Additionally, multivariate techniques were used to explore tillage system and crop effects on community weed species dynamics over time. ANOVA test results for treatment effects on total weed biomass and density both revealed three-way interactions between year, crop, and tillage system, but here we focus mainly on the tillage system effects. For plots planted to field pea in 2013, 2014, and 2015, weed biomass was greater for NT plots than CT plots (131.09 vs. 460.51, 110.25 vs. 29.97, and 206.74 vs. 78.7 g m-2, respectively). For plots planted to Proso millet in 2013 and 2014, weed biomass was greater for NT plots than CT plots (149.15 vs. 75.5 and 200.28 vs. 18.85 g m-2, respectively). For plots planted to wheat in 2014 and 2016, weed biomass was greater for NT plots than CT plots (110.75 vs. 6.52 and 18.64 vs. 1.79 g m-2, respectively). For all other combinations of crop and year, total weed biomass did not differ between tillage/grazing systems. Within field pea plots during 2014, weed density in NT plots was greater than that in CT plots (609.3 vs. 258.2 plants m-2). Within field pea plots during 2015, weed density in CT plots was greater than that in NT plots (448.2 vs. 210.7 plants m-2). Within Proso millet plots during 2014, weed density in NT plots was greater than that in CT plots (410.7 vs. 88.9 plants m-2). Within wheat plots 2016, weed density in NT plots was greater than that in CT plots (325.9 vs. 52.2 plants m-2). Other than these differences, weed density did not differ between tillage/grazing systems. For wheat, more yield was lost due to weeds in NT plots compared to CT plots (163 vs. to 325 kg ha-1). During 2014, field pea CT plots experienced greater yield loss to weeds than pea NT plots (8321 vs. 3770 kg ha-1). During 2015, NT pea plots suffered greater yield loss due to weeds than CT pea plots (22112 vs. 7382 kg ha-1). Except for 2015, CT Proso millet plots suffered greater loss due to weeds than NT millet plots (6559 g ha-1 vs. 0 g ha-1 during 2013, 4241 vs. 1135 g ha-1 during 2014, and 6388 vs 146 g ha-1 during 2016). But this result is somewhat misleading because most of the NT plots contained few crop plants, so without yield there is no yield loss. Multivariate analyses of weed species biomass and density demonstrated clear separations between four community types (NT+warm season crop, NT+cool season crop, CT+warm season crop, CT+cool season crop) in terms of weed species composition. In most instances, weed biomass and yield loss was greater for NT than for CT plots. Composition of the documented weeds was distinct depending on the combination of the tillage/grazing system (CT or NT) and type of crop grown (warm or cool season). Our results demonstrate that these two systems have different capacities for weed suppression, with CT generally providing greater suppression and, subsequently, increased crop yield. Developing no-till organic small grain production systems for the NGP region remains an elusive challenge

A NOVEL MECHANISM THAT CONFERS REDUCED GLYPHOSATE SENSITIVITY IN KOCHIA SCOPARIA. N. Soni*, K. Ravet, M. Fleming, S. J. Nissen, P. Westra, T. A. Gaines; Colorado State University, Fort Collins, CO (144)


Glyphosate has been very effective to control Kochia scoparia, which is one of the most troublesome annual weeds in agriculture fields. However, due to an increase in selection pressure in K. scoparia populations, several cases of evolved resistance to glyphosate have been reported. Glyphosate inhibits the enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS). Previous research reported one of the mechanisms for glyphosate resistance in K. scoparia is gene amplification of EPSPS. We identified two populations of K. scoparia (P1 and P8) that showed a reduction in glyphosate sensitivity without increased EPSPS gene copy number. Therefore, we hypothesized that P1 and P8 have evolved a different resistance mechanism. We conducted absorption, translocation, and metabolism experiments to compare P1 and P8 with known glyphosate-susceptible and resistant K. scoparia populations. The absorption and translocation experiments were conducted using [14C]-glyphosate on three plants per population at 6 different time points (6, 12, 24, 48, 96, and 192 h). Metabolism experiments aimed to quantify the glyphosate metabolite aminomethylphosphonic acid (AMPA) at 1, 3, 7, and 14 days after treatment. Results from these experiments showed that P8 had reduced glyphosate translocation compared to the susceptible and resistant (high EPSPS copy number) populations. Investigations into AMPA concentration and glyphosate metabolism are ongoing. Understanding the additional glyphosate resistance mechanism could lead to the development of markers for early detection of resistance in other K. scoparia populations.

METHODS TO ENHANCE GERMINATION OF THE RECALCITRANT GIANT RAGWEED SEED. N. T. Harre*, S. C. Weller, B. G. Young; Purdue University, West Lafayette, IN (145)


The continued biogeographical spread of herbicide-resistant (HR) weeds warrants timely methods aimed to screen putative HR populations in order to heighten grower awareness.  Giant ragweed populations resistant to ALS-inhibiting herbicides and/or glyphosate have been confirmed throughout much of the Midwest.  However, due to innate physical and chemical dormancy mechanisms of giant ragweed, the current standard of soil stratification is a particularly arduous process requiring several months before seed germination.

Giant ragweed seed was collected from identical field locations on September 28 (early collection) and October 28 (late collection) in 2014 and 2015.  Seeds were immediately germination tested following treatment with water, chemical, water + clipped, or chemical + clipped.  The chemical treatment consisted of ethephon (3mM) + gibberellic acid (1mM) + thiourea (2 mM).  The clipped treatment required excision of the “crown” region of the seed followed by 48 hr of aeration in an Erlenmeyer flask with either water or chemical solution.  Seeds were then evaluated for percent germination over the next 18 d.  The water + clipped and chemical + clipped treatment for both early- and late-collected seed each provided similar improvements over the water and chemical treatments alone (> 25% germination) in initial testing.  Following these experiments, seeds were placed in 4 C storage for two months.  During this period, a separate lot of seeds underwent a soil stratification process whereby they were buried in a moist mixture of 3:1 sand:soil.  Germination improved for all treatments following the cold storage period with the water + clipped treatment providing the greatest benefit for both early- and late-collected seeds (> 75%).  Soil stratification elicited the next highest germination percentage at greater than 40%.  A larger proportion of late-collected seed germinated compared to early-collected seed when exposed to the water or chemical treatments; however, these differences were eliminated by the soil stratification, water + clipped, or chemical + clipped treatments.  Compared to the standard soil stratification process, the water + clipped treatment improved maximum cumulative germination by nearly double, decreased the lag phase between planting and germination by 0.6 d, and increased the germination rate by almost two-fold according to Weibull function estimates. This work outlines a method providing significant germination enhancement of giant ragweed seed, foregoing the lengthy soil stratification method and enabling more timely confirmation of HR incidences.


TRANSCRIPTOME PROFILES OF QUINCLORAC-RESISTANT ECHINOCHLOA COLONA WITH RESISTANCE TO MULTIPLE HERBICIDES. C. E. Rouse*1, C. Saski2, A. Lawton-Rauh2, N. R. Burgos1; 1University of Arkansas, Fayetteville, AR, 2Clemson University, Clemson, SC (146)


Next-generation-sequencing (NGS) technology has paved the way into deeper understanding of weedy species, which were previously unattainable. The use of NGS has enabled the study of transcriptomes and its functional components through RNA sequencing. Transcriptomics focuses on the study and interpretation of gene expression under a specific set of conditions. The utilization of this technology in weed science is only just beginning. It will provide tremendous insight into our understanding of weed physiology, evolution, population genetics, and population dynamics. Junglerice (Echinochloa colona) is a problematic rice weed that infests both soybean and rice fields in the midsouth, USA. To date, resistance to common rice herbicides within 5 modes of action has dominated the landscape and caused weed management problems. From a state-wide resistance screening program, ECO-45 was selected for further investigation due to its multiple-resistance pattern to cyhalofop, glufosinate, propanil, and quinclorac. Independently, resistance to the three rice herbicides is common, but the coevolution of these resistance traits in this phenotype is of great interest. An experiment was conducted to identify the biochemical and physiological processes that endow resistance to quinclorac in ECO-45. The high resistance level (>32X) to this unique mode of action makes this population ideal material for RNA sequencing for the identification of biochemical pathways involved in resistance. Seedlings, 2- to 3-leaf, of ECO-45 and a susceptible standard (ECO-SS) were sprayed with quinclorac (560 g ha-1). Shoot tissues of treated and non-treated plants were harvested 24 hours later and frozen.  Following RNA extraction, RNA-sequencing was performed using paired-end reads on an Illumina-Hiseq platform. Assembly of the de novo transcriptome of ECO-45 and ECO-SS was conducted by CUGI using the Trinity package. Differential gene expression (DGE) of predetermined pairwise expression profiles was assessed using the edgeR package from Bioconductor. The de novo transcriptome was assembled from 76,414 transcripts, representing approximately 72% of the complete transcriptome based on BUSCO and the lineage embryophyta. Comparison of the nontreated resistant and susceptible populations indicated that 2.78% of the genes are constitutively upregulated in ECO-45 while about 0.5% are downregulated. Following quinclorac application, 7% (5,311) of transcripts were downregulated; less than 100 genes were upregulated. When compared with treated ECO-SS, the quinclorac-treated ECO-45 has a <0.5% decrease and/or increase in expression. The multiple-resistant and susceptible plants differed in the expression of 2,475 genes; some of which may be accumulated, fixed genes that contribute to multiple resistance. Further characterization of specific genes, or gene groups, of interest is ongoing with parallel experiments to characterize the biological pathways involved in resistance.



Germination Ecology of Two Australian Biotypes of Parthenium hysterophorus L.: Implications for Weed Invasion. Ali A. Bajwa*, Bhagirath S. Chauhan, Steve W. Adkins; The University of Queensland, Gatton, QLD, Australia.  

Ragweed parthenium is a highly invasive weed species in several countries including Australia. Laboratory experiments were conducted to evaluate the effect of temperature, light, salinity, pH and water stress on germination of two Australian biotypes (Clermont and Toogoolawah) of ragweed parthenium. Germination was improved by 49 and 20% under light as compared to dark conditions at constant and fluctuating temperatures, respectively. The two biotypes were able to germinate over a wide range of constant (8-35°C), as well as fluctuating day/night (15/5-35/25°C) temperatures. However, the germination percentage of the Clermont biotype was significantly higher (35-100%) across the range of temperatures as compared to the Toogoolawah biotype (0-97%). Maximum germination of Clermont (100%) and Toogoolawah (97%) were observed at constant temperatures from 14 to 23°C, and 23°C, respectively. Similarly, 100% of Clermont biotype and 99% of Toogoolawah biotype seeds germinated at the fluctuating day/night temperature regime of 25/15°C. Although salinity had negative effects on germination, both biotypes were able to germinate at 250 mM NaCl. The Clermont biotype gave 52% germination at 150 mM NaCl, and this was reduced to 26% at 200 mM NaCl. The Toogoolawah biotype gave less than 50% germination at concentrations beyond 100 mM NaCl. Water stress had moderate negative effects on germination with 52 and 37% of the Clermont and Toogoolawah seeds able to germinate at the lower osmotic potential of -0.6 MPa. Germination of the Clermont biotype was not affected by pH at all, whereas the germination of the Toogoolawah biotype was maximum (92%) in the control treatment (pH 6.4), followed by pH 6 (87%). In conclusion, ragweed parthenium has the ability to germinate under a wide range of environmental conditions. The Clermont biotype had a higher ability to germinate across all treatments when compared to the Toogoolawah biotype, which might be a contributing factor towards the high invasive ability of the former as compared to the latter biotype.




Grafting is a common horticultural technique used to impart desirable characteristics upon the scion. Conventional (CN) soybean (Glycine max) expressed increased glyphosate tolerance when grafted onto glyphosate-resistant (RR) soybean rootstocks. We examined this phenomenon in depth as a model for development of new knowledge, and technology to manage risks associated with herbicide drift. We examined the effects of grafted soybean growth stage, genotype, and temperature on the level of tolerance expressed, as well as shikimate accumulation in CN/RR, cp4-epsps mRNA transportation, and 14C-glyphosate translocation from scions to rootstocks. Glyphosate at 0.84 and 1.68 kg ae ha-1 was applied on the leaf. The effect of three soybean growth stages, combinations of six genotypes (3 CN and 3 RR) and 2 environments (28/22 ℃ day/night and 24/18 ℃) were determined. At 24 DAT, average injury of CN/RR did not differ when treated at the 3- and 6-leaf stages (28% and 17% reduction of injury compared to CN/CN, respectively for the 0.84 and 1.68 kg ha-1), but was higher than injury of 10-leaf stage plants. In genotype experiments, the scion had a greater effect on modulating tolerance than did the rootstock. CN/RR soybeans with SC352STS as scion were most tolerant, while those with SC5388STS as scion were less tolerant. Day/night temperatures of 28/22 °C or 24/18 °C did not affect tolerance of CN/RR plants.  However, under lower temperatures, more new leaf growth was observed. Shikimate accumulation in CN/RR was approximately 60% of that observed in CN/CN, and no cp4-epsps mRNA was detected in the CN scion. 14C-glyphosate activity in CN/RR treated leaflet was 82% of that in CN/CN, while activity in CN/RR root was 140% of that in CN/CN. The root of CN/RR plants contained 35% of the absorbed 14C-glyphosate, while the root of CN/CN plants contained 25%.

IMPACTS OF ENVIRONMENTAL AND BIOLOGICAL STRESSORS ON THE POPULATION DYNAMICS OF MULTIPLE HERBICIDE RESISTANT AVENA FATUA (L.). E. E. Burns*1, E. A. Lehnhoff2, W. E. Dyer1, F. D. Menalled1; 1Montana State University, Bozeman, MT, 2New Mexico State University, Las Cruces, NM (149)


Multiple herbicide resistant (MHR) weed populations pose significant agronomic and economic threats to agriculture and demand the development and implementation of ecologically-based tactics for sustainable management. We investigated the influence of nitrogen fertilizer rate and spring wheat (Triticum aestivum L.) seeding density on the demography of two MHR and one herbicide susceptible (HS) Avena fatua L. populations under two cropping systems (continuous cropping and crop-fallow rotation). To represent a wide range of environmental conditions, data were obtained under field conditions from three trials (2013-2015) near Bozeman, MT. A stochastic density-dependent population dynamics model was constructed using the demographic data to project A. fatua populations 20 years forward. To identify demographic processes with negative impacts on population growth that can be exploited in management tactics, elasticity analysis was used to quantify the proportional change in the A. fatua seedbank resulting from a proportional change in model vital rates. In the continuous T. aestivum and T. aestivum-fallow cropping systems, MHR seedbank densities were negatively impacted by increasing nitrogen fertilization rate and T. aestivum density, in which mean seedbank densities stabilized near zero by the fifth year of the projection. Overall, MHR seedbank densities were larger in the T. aestivum-fallow cropping system compared to the continuous T. aestivum cropping system. In both cropping systems, density-dependent A. fatua seed production was the most influential parameter impacting population growth rate. Overwinter seed survival was the second and third most influential parameter on MHR population growth rates across agronomic treatment combinations in the continuous T. aestivum and T. aestivum-fallow cropping systems, respectively. The short-term impact of ecologically-based weed management tactics can be seen through field experiments, but evaluations of their long-term consequences require the use of population dynamics models that allow for the range of outcomes based on variability in demographic data. Our results suggest that MHR is not necessarily an unsolvable problem as long as solutions are expanded beyond currently recommended herbicide-based approaches to weed management. Demographic models such as the one described here will aid in selecting ecologically-based weed management tactics such as manipulating resource availability and modifying crop competitive ability to reduce the spread and impact of MHR.


DICAMBA- AND GLYPHOSATE-RESISTANT GENES ARE NOT LINKED IN KOCHIA (KOCHIA SCOPARIA). J. Ou*1, P. W. Stahlman2, A. K. Fritz1, M. Jugulam1; 1Kansas State University, Manhattan, KS, 2Kansas State University, Hays, KS (150)


Kochia is one of the most troublesome weeds in the Great Plains of North America. Its infestation in productive lands can lead to significant losses in yield and quality of agricultural crops. Glyphosate and dicamba have been effective options to control kochia for decades. Due to extensive use of these herbicides, many kochia populations across the Great Plains have evolved resistance to glyphosate and/or dicamba. Especially, dicamba-resistant kochia populations are often also found to be glyphosate-resistant in Kansafs. However, the inheritance and linkage of dicamba and glyphosate resistance in kochia is unknown. In this study, reciprocal crosses were performed between dicamba- and glyphosate-resistant (DGR) and dicamba- and glyphosate-susceptible (DGS) kochia to produce F1 and F2 progeny. Two F1 and eight F2 progenies were screened with field rates of dicamba (560 g·ae ha-1) or glyphosate (840 g·ae ha-1), and two F2 progenies were screened with tank-mix of dicamba and glyphosate at field rates sequentailly. The two F1 progenies survived both dicamba and glyphosate treatments. Chi-square analyses of  F2 progenies  suggest that: a) both dicamba and glyphosate resistance in kochia are inherited via single dominant nuclear gene and b) dicamba- and glyphosate-resistant genes are not linked in kochia.


FIELD DISSIPATION OF S-METOLACHLOR IN ORGANIC AND MINERAL SOILS IN THE EVERGLADES AGRICULTURAL AREA OF SOUTH FLORIDA. J. V. Fernandez*1, D. C. Odero1, G. E. MacDonald2, J. Ferrell2, B. Sellers3, P. C. Wilson2; 1University of Florida, Belle Glade, FL, 2University of Florida, Gainesville, FL, 3University of Florida, Ona, FL (151)


Field Dissipation of S-metolachlor in Organic and Mineral Soils in the Everglades Agricultural Area of South Florida

S-metolachlor has been proposed for weed management in Florida sugarcane. However, there is no information on its persistence on organic and mineral soils used for sugarcane cultivation in south Florida. Therefore, understanding the dissipation rate and determining the half-life of S-metolachlor in these soils is important to formulate weed management programs in sugarcane. Field studies were conducted to determine dissipation of S-metolachlor applied preemergence on organic and mineral soils at 2,271 ai g/ha between 2013 and 2016. The organic soil was a Dania muck while the mineral soil was a Holopaw fine sand. S-metolachlor dissipated rapidly on mineral compared to organic soil. Dissipation of S-metolachlor in the organic soil was linear compared to exponential decay in the mineral soil. The half-life (DT50) of S-metolachlor in organic soil was 19 and 62 days in 2013 to 2014 and 2014 to 2015 sugarcane growing seasons, respectively. The DT50 was 12 and 24 days in 2014 to 2015 and 2015 to 2016 sugarcane growing seasons, respectively.  The DT50 of S-metolachlor in Florida sugarcane soils was similar to values ranging from 15 to 25 days previously reported in southern United States with the exception of 62 days observed on organic soil in one growing season. Further studies need to be conducted to relate the level of weed control to the DT50 of S-metolachlor in Florida sugarcane fields.

FIRST CASE OF MULTIPLE-RESISTANCE TO GLYPHOSATE AND PPO-INHIBITING HERBICIDES IN RIGID RYEGRASS (LOLIUM RIGIDUM L.) BIOTYPES FROM SPAIN. P. T. Fernandez-Moreno*1, A. M. Rojano-Delgado1, J. Menendez-Calle2, R. J. Smeda3, R. De Prado4; 1University of Cordoba, Cordoba, Spain, 2University of Huelva, Huelva, Spain, 3University of Missouri, Columbia, MO, 4Department of Agricultural Chemistry and Edaphology, University of Cordoba, Cordoba, Spain (152)


Worldwide, there are numerous biotypes of Lolium rigidum with evolved resistance to glyphosate. To improve control of weeds in olive groves in Spain, protoporphyrinogen oxidaxe (PPO)-inhibiting herbicides have been used. In 2015, seeds of a biotype from olive grove which had been treated with glyphosate 15 consecutive years, and 5 years with glyphosate+oxyfluorfen applications were collected. Seeds of a susceptible (S) biotype were collected from a nearby olive grove that had never received glyphosate or oxyfluorfen. Relative growth reduction (GR) and lethal (LD) doses were calculated at both 50% and 90% levels generating GR50, GR90, and LD50, LD90. The R-biotype exhibited a resistance index (RI) for glyphosate ranging from 14.0 (GR50) to 37.5 (GR90). A rate of glyphosate up to 26 L ha-1 is necessary to reach 90% control, rendering this biotype immune to field doses. Accumulation of shikimic acid determined that the S-biotype revealed levels 197-fold higher with respect to the R-biotype at 1000 µM glyphosate. Also, the R-biotype exhibited an RI with oxyfluorfen ranging from 20.1 (GR50) to 70.2 (GR90) with respect to the S-biotype. The accumulation of the photodynamic tetrapyrrole protoportphyrin IX (Proto IX) at 100 µM oxyfluorfen revealed that the S-biotype exhibited a 24.5-fold higher level compared to the R-biotype. These results indicate the expression of multiple-resistance mechanisms to glyphosate and PPO-inhibiting herbicides in L. rigidum. Fomesafen (Protox inhibitor) was applied to in the R-biotype, resulting in an RI of 8.4 (LD50) with respect to the S-biotype. These results demonstrate cross-resistance to multiple PPO-inhibiting herbicides. Research is underway to identify the mechanisms involved in PPO resistance. Hypothetically different mechanisms may be expressed to permit resistant to each herbicide mode of action. For example, non-target-site resistance may result in reduced translocation of glyphosate, and target-site resistance via a mutation in Protox may explain resistance to oxyfluorfen.




With increasing emphasis on improving the sustainability functions of agro-ecosystems, developing methods to enhance the feasibility of living mulch systems can contribute to these advancements. Adoption of living mulch systems is an excellent strategy for increasing diversity and resource use efficiency, and for preventing or reducing soil erosion through quick soil cover. Presence of living mulches is also an excellent deterrent to inter-row tillage during the season. However, adoption of living mulches is constrained by problems of excessive competition with the cash crop and unreliable weed control. The goal of this study is to assess the potential of reduced-rate herbicide applications in alleviating these drawbacks. It is hypothesized that such combinations of living mulches and herbicides will complement each other, thereby reducing both living mulch vigor and herbicide input without compromising weed control or crop yield. Owing to the numerous sustainability benefits of living mulch systems, herbicide applications are viewed as a tool to advance their feasibility. For such a living mulch-herbicide system to work, interactions between the crop, living mulch and weeds, and also the impact of the herbicide applications on these interactions, have to be carefully assessed. In 2014, a preliminary field trial was carried out at Freeville, NY, using sunnhemp (Crotalaria juncea L.) and sesbania (Sesbania sesban (L.) Merr.) as living mulches in fresh market tomato (Mountain Fresh F1). Metribuzin (two rates), rimsulfuron (two rates) and halosulfuron (one rate) were the herbicides used. No pre-emergent herbicides were used, and all the above herbicides were applied post-emergent. Each herbicide treatment consisted of applications of a single herbicide at a fixed rate. These five herbicide treatments were used along with a mowing treatment and a hand-weeded control. The trial was set up in a randomized complete block design with four replicates. Tomato was transplanted into 3.7 by 7.6 m plots at a row spacing of 122 cm and plant-to-plant spacing of 46 cm. Three rows of living mulch were present between two rows of tomato with 20 cm between living mulch rows and 40 cm between the living mulch and tomato row on either side. A similar trial was set up in 2015, but the mowing treatment was excluded and a fomesafen herbicide application, along with an untreated cover crop check and a weedy check were included. Each herbicide was classified as a ‘strong’ or ‘weak’ herbicide based on the extent of injury to the living mulch. Each herbicide treatment was a combination of two herbicide applications, each of a different herbicide. The 2015 trial was replicated in 2016. Data collected included living mulch and weed ground cover, density and aboveground biomass, and living mulch height. Tomato yield and tomato leaf-nutrient composition were also determined. In 2015, there was a strong positive correlation between tomato yield and living mulch biomass, but an opposite trend was observed in 2016. This difference may be due to 2015 being a very wet year and 2016 being a very dry year. Although irrigation was provided during 2016, competition for water likely affected results. Herbicide treatments reduced tomato yield losses by up to 71% in 2015 and 51% in 2016 compared with the untreated living mulch check. Surprisingly, there was no relationship between living mulch biomass and weed biomass in 2015 or 2016. In both years, up to 2.5 tons ha‑1 of dry matter was generated by the living mulch, with an average ground cover of up to 65% in 2015 and 85% in 2016. In 2016, weed biomass from all living mulch treatments (0.3 to 2.1 tons ha‑1) were much lower than from the weedy check (9 tons ha‑1). Relative to the weedy check, reduction in weed biomass in the untreated living mulch check was 77%, while the herbicide treatments reduced weed biomass by as much as 97%. In both 2015 and 2016, the two herbicide treatments with a first application of metribuzin did not reduce living mulch biomass, or ground cover, compared with the untreated living mulch check. Both these treatments also resulted in the lowest weed biomass in 2016. Our findings suggest that including low rates of herbicides (e.g. up to 75% and 81% reduced rates of metribuzin and rimsulfuron, respectively, in our trials) in living mulch systems is an effective approach that achieves sufficient weed control, without compromising living mulch biomass, soil cover or crop yield. 








LESSONS AND IMPRESSIONS FROM THE 2016 COMPETITION. D. A. Mortensen*1, M. Purcell-Miramontes2; 1Pennsylvania State University, University Park, PA, 2USDA-NIFA, Washington, DC (157)






In this presentation, a laboratory based method to determine the relative volatility of herbicide formulations will be described. An herbicide formulation is applied to a substrate in a closed dome system, the closed dome is placed into a temperature and humidity controlled chamber, and air is drawn through the closed dome for twenty four hours. The volatile analyte in the formulation is trapped on a piece of polyurethane foam (PUF) during this time period. The analyte is solvent extracted from the PUF and the extract is analyzed by liquid chromatography-mass spectrometry / mass spectrometry (LC-MS/MS). Details of the experimental setup and representative relative volatility data will be presented.  




Monsanto Company has developed formulations containing dicamba for use in the Roundup Ready® Xtend™ Crop System.  XtendiMax™ with VaporGrip™ technology is a dicamba standalone formulation based on the diglycolamine (DGA) dicamba salt. Roundup Xtend™ with VaporGrip™ technology is a premix formulation containing DGA dicamba and monoethanolamine (EA) glyphosate delivering a 2 to 1 ratio of glyphosate to dicamba.  Both formulations contain proprietary VaporGrip™ technology that reduces the potential of dicamba volatility compared to current commercial dicamba formulations. XtendiMax™ with VaporGrip™ technology and Roundup Xtend™ with VaporGrip™ technology show commercially acceptable physical/ chemical properties consistent with Roundup® agricultural herbicide formulations and are pending regulatory approval for in crop use.




A NEW S-METOLACHLOR PLUS DICAMBA PREMIX AS AN EFFECTIVE TOOL IN AN INTEGRATED WEED MANAGEMENT PROGRAM IN DICAMBA-TOLERANT SOYBEANS. R. Jain*1, B. Miller2, T. Trower2, A. J. Moses2, D. Porter2; 1Syngenta Crop Protection, Vero Beach, FL, 2Syngenta Crop Protection, Greensboro, NC (162)


A new S-metolachlor plus dicamba premix as an effective tool in an integrated weed management program in dicamba tolerant soybeans. Rakesh Jain*1, Brett R. Miller2, Timothy L. Trower3, Adrian J. Moses4, Donald J. Porter5, James C. Holloway6, 1Syngenta Crop Protection, Vero Beach, FL, 2Syngenta Crop Protection, Fargo, ND, 3Syngenta Crop Protection, Baraboo, WI, 4Syngenta Crop Protection, Gilbert, IA, 5Syngenta Crop Protection, Greensboro, NC, 6Syngenta Crop Protection, Jackson, TN.

A new low volatility premix formulation of S-metolachlor plus dicamba is under development by Syngenta Crop Protection for weed control in dicamba-tolerant soybeans and cotton.  The dual site-of-action herbicide is designed to deliver pre- and post-emergence activity as a burndown, pre-emergence or early post-emergence application. Field trials were conducted in 2015 and 2016 to evaluate weed control efficacy and crop safety of this new herbicide as part of an integrated weed management program in dicamba-tolerant soybeans.

The S-metolachlor plus dicamba formulation provides post-emergence control of many important weed species including horseweed, common and giant ragweed and common lambsquarters.  It also provides post-emergence and residual control of Amaranthus species and residual control of many annual grass weeds.  Successful and consistent weed control in dicamba-tolerant soybeans are targeted with programs that include an effective burndown, pre-emergence residuals and post-emergence herbicides with multiple, overlapping sites of action.  S-metolachlor plus dicamba will be an important herbicide tool as part of an integrated weed management program for dicamba-tolerant soybeans.



In June and July of 2016, the illegal application of dicamba to dicamba-tolerant cotton and/or soybean by a subset of producers in Missouri resulted in a significant number of incidences of off-target movement of dicamba.  Subsequently, many sensitive plants were injured, and questions regarding the causes of off-target dicamba movement began to emerge. Wind speed and air temperature data over the 2016-growing season were retrieved from weather stations in order to identify possible contributing factors. Historically, the average hourly wind speeds for June and July in southeast Missouri over the last 15 years have not exceeded the 16 kilometer per hour (kmh) threshold which the Environmental Protection Agency established as “high risk for off-target movement.”  In 2016, wind speeds were typical, and preliminary results indicate that wind speeds exceeded 16 kmh less than 1% of the time in June and July.  Under certain conditions, the new legal formulations of dicamba can be applied in wind speeds up to 24 kmh. In early 2015, weather stations in three geographically distinct regions of Missouri were equipped to monitor surface temperature inversions by measuring air temperatures at 3 heights: 46, 168, and 305 cm.  The temperature data for 2015 and 2016 were retrieved and analyzed to determine the possible impact of inversions.  Preliminary analysis of 2015 and 2016 data indicates that inversion formation was common in March, April, May, June, and July in southeast Missouri.  In June and July of 2016, 24 and 20 surface temperature inversions were identified, respectively.  These inversions typically started forming between 6:00 and 8:00 p.m. and lasted longer than 10 hours.  Inversions were typically associated with calm winds of less than 4.8 kmh. Missouri weather stations are equipped with anemometers at 305 cm. The 5-minute wind speeds at 168 cm, or the middle height of the monitored air-temperature inversions, were extrapolated using the log wind profile equation. Preliminary analysis of all the data generated at all 3 weather stations over both years indicated that temperature inversions correlated with low wind speeds greater than 90% of the time in May, June, and July, and greater than 75% of the time in March and April. Analysis of other indicators associated with temperature inversions continues. Preliminary insights from this weather analysis are currently being used to educate Missouri herbicide applicators in an effort to learn from 2016 in preparation for legal applications of dicamba in 2017.

MITIGATING OFF-TARGET APPLICATIONS IN THE FORM OF DRIFT AND TANK CONTAMINATION. D. B. Reynolds*1, G. Kruger2, Z. Carpenter1, T. Foster1; 1Mississippi State University, Mississippi State, MS, 2University of Nebraska, Lincoln, NE (164)


OFF-TARGET DICAMBA IN TENNESSEE: AN EXTENSION PERSPECTIVE. L. E. Steckel*; University of Tennessee, Jackson, TN (165)


There were an estimated 300,000 acres of Xtend cotton and soybean planted in Tennessee in 2016.   A number of growers of those Xtend crops elected to apply dicamba to manage weeds in-crop despite the fact that no label had yet been issued by the EPA.  The reason some growers used dicamba illegally in Xtend soybean was due to the quick development of PPO-resistance in Palmer amaranth that was already glyphosate-resistant.  In those cases they had two choices: disk up and replant or use dicamba off-label.  Unfortunately, many decided to use dicamba illegally.

This use of dicamba caused tens of thousands of acres of off-target drift injury to surrounding sensitive crops and broadleaf vegetation.  The Tennessee Department of Agriculture received 47 official dicamba drift complaints consisting of thousands of acres, primarily on soybean.  University of Tennessee Extension agents and specialists ran calls on many thousands of acres of dicamba injured crops and landscape vegetation.    

With no label for dicamba use in soybean or cotton, no training was conducted for applicators on best management practices and this showed.  Upon walking these fields and visiting with growers who did the drifting, it was apparent that many different formulations of dicamba were applied, often resulting in significant volatility drift. Moreover, nozzles that produce a large percentage of fines were commonly used to apply dicamba and boom heights were at times too high when applications were made.  In other cases, applications were made into inversion conditions in the evening. All of this resulted in off-target drift of dicamba moving vast distances from the point of application. 

Soybeans that were drifted on were at all different growth stages.  The ones that were still in the vegetative growth stages seemed to recover in a few weeks.  Soybean fields that were into flowering stages showed visual symptoms longer. In some cases, less fortunate fields that were drifted on multiple times - never did completely recover.

The ramifications of all this dicamba drift is still being assessed and probably will be on-going for years to come.  Many sensitive soybean fields that got drifted on and showed significant visual symptoms recovered by harvest time and farmers reported little or no yield loss.
Still other fields, particularly those drifted on multiple times within a six week window of time, were reported by growers to have lost 30 to 50% of their expected yield.  

The silver lining to all the dicamba issues in Tennessee is that educators are now working with a “teachable moment” and applicators are more motivated to follow the labels that are currently in hand.  Applicators in Tennessee clearly will need to do a better job of stewarding the auxin herbicide tolerant soybeans and cotton than was the case in 2016 or this will be a short lived technology here. 




In 2016, the majority of the cotton acreage in the southeastern portion of Missouri was planted with dicamba-tolerant (DT) varieties.  A limited number of DT soybean varieties were also planted throughout the state.  However, during the 2016 growing season, the Environmental Protection Agency had not approved any dicamba herbicide formulations for post-emergence application to DT cotton or soybean.  Although investigations are ongoing, some portion of growers made illegal applications of dicamba to their DT cotton and/or soybean, which resulted in off-target movement of dicamba to a variety of sensitive crops, including large acreages of non-DT soybean.  In southeastern Missouri alone, over 125 dicamba injury complaints were filed with the Missouri Department of Agriculture.  These injury complaints occurred on over 40,000 acres of soybean, 1,000 acres of cotton, 700 acres of peaches, 400 acres of purple hull peas, 200 acres of peanuts, 32 acres of watermelon, 9 acres of cantaloupe, 6 acres of alfalfa, 2 acres of tomatoes, and on numerous homeowner’s gardens, trees, and ornamental bushes.  Some of the primary factors that contributed to the off-site movement of dicamba will be discussed, as well as the impacts that this situation has had and will continue to have on Missouri agriculture.




Early detection and rapid response (EDRR) is recognized as the best approach to prevent the spread of isolated populations of invasive plants. However, extensive monitoring efforts have proven to be challenging for land managers due to reduced budgets, staff, and increased species of concern to monitor for EDRR. Habitat suitability models (HSMs) are one tool that can improve invasive plant detection. To aid in EDRR in Wisconsin, we developed 21 habitat suitability models (HSMs) for regulated invasive plants from known presence points from 2015 and earlier. We used an ensemble modeling approach that employed five statistical models (boosted regression tree, generalized linear model, multivariate adaptive regression splines, maximum entropy, and random forests) to determine the locations across the state in which the environmental, topographic and climatic conditions were suitable for a given species. Suitable habitat was determined on a binary cutoff basis for each of the five model approaches and georeferenced ensemble raster maps (spatial resolution of 250m) were created to depict the level of agreement across the five approaches. Prioritized lists of species were created within each of the 72 Wisconsin counties by listing the top 10 species that have suitable habitat for that area.  Species were considered a high priority if less than 10 points were present in the county.  Lists were summarized along with known location points and presented to stakeholders and citizen scientists in 2016 to encourage reporting new observations.  In 2016, 19,004 new occurrences were reported to our database in Wisconsin (increase of 33%) by 77 different stakeholders/reporters. Of these reports, 75% were of the 21 modeled species with 28% and 39% from the county priority or high priority lists, respectively. Results suggest that this approach was successful in improving reporting of priority species within a county. These observations will be utilized to improve existing models through an iterative approach that has been shown to be effective.  Resulting models will improve our understanding of the potential spread of regulated invasive plants in Wisconsin and what factors are drivers in suitable habitat.

EVALUATION OF KUDZU CONTROL OPTIONS. J. Omielan*1, D. Gumm2, M. Barrett1; 1University of Kentucky, Lexington, KY, 2Kentucky Transportation Cabinet, Jackson, KY (168)


Kudzu (Pueraria montana) is an invasive deciduous twining, trailing, mat-forming, woody leguminous vine that forms dense infestations along forest edges, rights-of-way, old homesteads, and stream banks.  It colonizes by vines rooting at nodes and spreads by seed dispersal.  The plants have extensive root systems with large tuberous roots which can be 3 to 10 feet deep. Kudzu can dominate a site to the exclusion of other vegetation.   Repeated herbicide applications along with other management measures are required to reduce the infestation.  Picloram is used for kudzu control in many states but has not been used extensively in KY in recent years. What are some of the other selective herbicide control options and how effective are they?

This study was initiated in June, 2014 to answer the questions asked above, by mowing a kudzu infested field near Beattyville KY.  Plots (9 m x 9 m) with 3 m alleys separating them were arranged in a 10 treatment randomized complete block design with 3 replications.  After kudzu regrowth, 9 herbicide treatments were applied at 337 L/ha on July 25, 2014 and two repeat treatments were applied on September 25.  These same treatments were applied in 2015 on July 23 and September 24.  Final assessments were taken in 2016.  The treatments included the following products (active ingredients):  Transline (clopyralid), Streamline (aminocyclopyrachlor + metsulfuron), Garlon 3A (triclopyr), Rodeo (glyphosate), Opensight (aminopyralid + metsulfuron), BK800 (2,4-D + 2,4-DP + dicamba), and Patron 170 (2,4-D + 2,4-DP).  Garlon 3A and Rodeo were applied again on two sets of plots.  All treatments included a non-ionic surfactant at 0.5% v/v.  Visual assessments of percent kudzu control and green vegetative cover (0-100%) were done 32 (8/26/2014), and 62 (9/25/2014) DAT (days after initial treatment) in 2014.  Visual assessments of percent green vegetative cover by kudzu, grasses, and other broadleaves, as well as percent bare ground were done 363 (7/23/2015), 392 (8/21/2015), 426 (9/24/2015), 689 (6/13/2016), and 760 (8/23/2016) DAT.

In 2014, all the treatments had kudzu control greater than 92% 32 DAT.  However by 62 DAT control with Patron 170 had declined to 72%.  Green vegetative cover 62 DAT ranged from 63 to 100% for most treatments except for Streamline with only 13% green cover.

In 2015, Patron 170 had 83% kudzu cover 363 DAT while the other treatments ranged from 28 to 4%.  After this year’s applications the kudzu cover was 67% with Patron 170, 8% with Transline and 0-3% for the other herbicide treatments 426 DAT.  At the end of the season (426 DAT), annual grasses had 77-93% cover in the Garlon 3A, Opensight, and BK 800 treatments.  Broadleaves had 73-77% cover in the two Rodeo treatments.  Streamline had the least green vegetative cover with 44% bare ground at the end of the 2015 season.

In 2916, Patron 170 had 70% kudzu cover 760 DAT while the other treatments ranged from 10 to 0%..  There are a number of herbicide options which are selective and effective in kudzu control.




FIELD AND MESOCOSM EVALUATIONS OF FUTURE AQUATIC HERBICIDE USE PATTERNS OF PROCELLACORTM. M. A. Heilman*1, M. D. Netherland2, B. E. Willis3, J. P. Beets4; 1SePRO Corporation, Carmel, IN, 2US Army Corps of Engineers, Gainesville, FL, 3SePRO Corporation, Whitakers, NC, 4University of Florida, Gainesville, FL (169)


PROCELLACOR™ is a novel reduced-risk herbicide technology under development for aquatic use and anticipated for USEPA approval in 2017.  PROCELLACOR (a.i. benzyl 4-amino-3-chloro-6-(4-chloro-2-fluoro-methoxyphenyl)-5-fluoropyridine-2-carboxylate) has unique, low-rate, short-exposure, systemic activity for selective control of major US submersed weeds including hydrilla (Hydrilla verticillata) and invasive watermilfoils such as Eurasian watermilfoil (Myriophyllum spicatum - EWM) and Eurasian X Northern (M. sibiricum) hybrids (HWM).  Relative to selectivity of control, PROCELLACOR has little to no effect on common US native submersed plants such as tapegrass (Vallisneria americana), common waterweed (Elodea canadensis), and pondweeds (Potamogeton spp.) as well as most common native emergent plants.  The new herbicide also has selective in-water and foliar activity for treatment of certain emergent/floating US invasive aquatic plants such as water hyacinth (Eichhornia crassipes), crested floating heart (Nymphoides cristata), alligatorweed (Alternanthera philoxeroides), and primrose (Ludwigia spp.).  To demonstrate selective control of mature target submersed weeds, multiple large-scale mesocosm trials (6,700 liter tanks) were conducted in 2016 and documented selective control of mature EWM, a 2,4-D tolerant HWM, and hydrilla with reduced or no impact to select native aquatic plants in the same trials.  Rates between 3 and 27 ppb were tested under 6-hour or 24-hour dilution half-lives, or a static exposure.  1 and 2-month biomass harvests showed a range of responses across the three target weeds with EWM showing highest sensitivity and a slightly reduced but still sensitive response by the HWM tested.  Hydrilla was less sensitive than either milfoil but effectively controlled by stronger rate/exposure scenarios tested.  A 2016 field demonstration implementing a small spot treatment of invasive watermilfoil in New Hampshire will also be reviewed.


EVALUATIONS OF PROCELLACOR EFFICACY AND SELECTIVITY FOR HYDRILLA CONTROL. R. J. Richardson*1, E. Haug1, M. A. Heilman2; 1North Carolina State University, Raleigh, NC, 2SePRO Corporation, Carmel, IN (170)


New herbicide chemistry is currently under development for aquatic weed management. 4-amino-3- chloro-6- (4-chloro- 2-fluoro- 3-methoxyphenyl)- 5-fluoro- pyridine-2- benzyl ester (common name pending) is identified as the active or in formulated forms for aquatic use as Procellacor™. Greenhouse, mesocosm, and field research at NC State University was conducted to evaluate the effect of Procellacor and an acid metabolite on numerous aquatic plant species including monoecious hydrilla [Hydrillaverticillata (L. f.) Royle]. In-water applications of Procellacor (as 300 gL -1 SC) and its acid metabolite (analytical grade material) were applied at rates of 0 to 81 µgL -1. Monoecious hydrilla was sensitive to both compounds with EC50 values ranging from 0.71 to 1.6 ug/L in greenhouse trials. Symptomology consisted of leaf pigmentation changes (purpling) and stunted growth, progressing to leaf curling, chlorotic/necrotic tissue and eventual plant death. Hydrilla stem tissue also became fragile to touch and broke easily at nodes as symptomology progressed. Field pond studies were also conducted to verify activity observed in small scale trials. Monoecious hydrilla was also sensitive to field treatments with high control observed. Overall, Procellacor appears to provide highly effective control of monoecious hydrilla.



Graminicides have had a tremendous impact in row crop agriculture over the last forty years, resulting in substantial reductions in the impact of grass weeds in crops such as cotton and soybeans. The selectivity provided by graminicides in many cropping systems is also highly desirable in many aquatic systems where native emergent vegetation provides many benefits. Invasive aquatic grasses such as torpedograss often displace native emergent vegetation and create difficult management scenarios. For many years, non-selective treatments of glyphosate and imazapyr have been the only options that provide meaningful invasive grass control. However, the lack of selectivity with both herbicides has resulted in considerable non-target damage to many desirable plant species. In 2015 and 2016, sethoxydim and fluazifop, respectively, received experimental use permits for treatment of emergent aquatic invasive grasses in Florida. Initial research verified selectivity in aquatics but has also indicated single applications provide insufficient control of key invasive grass species. To improve control, tank mixing graminicides with very low rates of glyphosate or imazapyr that would result in little to no non target damage has been proposed. However, little is known regarding graminicide interactions with either herbicide in aquatic settings. Antagonism between graminicides and ALS inhibitors has been well documented in agricultural settings and it would be useful to know if this is an issue in aquatics. In greenhouse studies, we examined torpedograss control with sethoxydim and fluazifop with and without reduced rates of imazapyr or glyphosate. We quantified reductions in above and below ground biomass at 60 days after treatment. Reduced rates of glyphosate or imazapyr did not generally improve torpedograss control when tank mixed with either sethoxydim or fluazifop. We also saw no evidence of antagonism between either graminicide with low rates of imazapyr and very limited evidence of antagonism for either graminicide with glyphosate. With glyphosate, evidence for antagonism was based more on the lack of a theoretical expected increase in control than in a significant decrease. Future studies should examine graminicide tank mixes with other aquatic labeled ALS inhibiting herbicides across a broader range of aquatic invasive grasses.    


BUFFELGRASS SUSCEPTIBILITY TO HERBICIDES IN GREENHOUSE EXPERIMENTS. W. B. McCloskey*1, D. Backer2; 1University of Arizona, Tucson, AZ, 2Saguaro National Park, Tucson, AZ (172)


Buffelgrass (Pennisetum ciliaris, L.; PESCI) is an invasive, C4 warm season perennial bunchgrass from Africa that was introduced into Southwestern USA in the late 1930s for use as a drought tolerant pasture grass. It is spreading across southern Arizona and threatens the Sonoran Desert ecosystem, including the region’s signature saguaro forests and associated wildlife habitat within Saguaro National Park and Coronado National Forest. The Sonoran Desert is characterized by low bimodal rainfall (12.6 in/yr.) with a summer monsoon and low plant density (25 to 35% canopy cover). Buffelgrass fills in canopy the gaps and produces dry biomass that is very flammable burning at 1,300-1600°F. Buffelgrass competes with native plants for resources, creates dense stands which inhibit native plant growth, and fuels fires in a community dominated by plants and animals (e.g., saguaros and desert tortoises) that are not adapted to fire. The objective of this project was to investigate buffelgrass susceptibility to herbicides using a greenhouse testing protocol. Buffelgrass seed was collected in Saguaro National Park and stored at room temperature for at least 4 months to overcome seed dormancy. Seeds were planted in pots, thinned to 1 plant per pot, fertilized, clipped ~5 cm above the soil when plants had 5 to 6 tillers and fertilized again. Plants were grown until they had 12 to 16 tillers; tillers number and leaf/shoot length per plant were measured prior to each treatment. Plants were sprayed with the tested herbicides using a CO2 pressurized (24 PSI) backpack sprayer equipped with a three nozzle boom that delivered 9.8 GPA using XR8001VS nozzles at 2.5 MPH. After the plants developed symptoms 3 to 4 weeks after spraying, shoot biomass was harvested by clipping ~5 cm above the soil. Fresh weight was measured immediately and dry weight was measured after the shoots were oven dried at 60°F for several days. Plants were returned to the greenhouse after the shoot biomass harvest and grown for about 3 more weeks to assess regrowth. Shoot biomass was harvested a second time and fresh and dry weight determined as above. Comparison of field experiments with glyphosate and imazapyr indicated that rates that killed plants in the greenhouse assays as determined by a lack of regrowth were about 10 time lower than rates required to kill plants in the natural environment. Thus, if a tested herbicide did not kill buffelgrass at its maximum labeled rate in the greenhouse assay, it was not considered promising for field tested. The herbicides glyphosate (the current herbicide of choice for field control efforts), imazapyr and nicosulfuron showed promise in the greenhouse assays while clethodim, fluazifop-p-butyl, sethoxydim, imazapic, metsulfuron methyl, sulfosulfuron, and triclopyr did not show sufficient activity to warrant field testing.


PALMER AMARANTH GROWTH IN SOUTHEASTERN SOUTH DAKOTA. S. Clay, B. M. Van De Stroet*; South Dakota State University, Brookings, SD (173)


Palmer amaranth (Amaranthus palmeri) is a native southern weed that has been extending its range northward.  In its southern range, Palmer is problematic due to fast growth rate, poor control once it reaches a 4 cm height, high seed production, and herbicide resistance to many different herbicide modes-of-action. It has recently been found in South Dakota, introduced as a seed contaminant of agricultural products.  There is little known about the basic biology of Palmer amaranth in South Dakota. Growth of Palmer amaranth was measured in Aurora, SD during the 2015 and 2016 growing seasons. Plants, started from seed in the greenhouse, were transplanted into the field at two week intervals at three consecutive timings when plants were at the one-leaf growth stage to simulate different germination flushes. Periodic measurements, with growing degree days calculated for each time, included height and diameter of plants and time to flower.  In late-August, plants were destroyed and biomass of female and male plants were obtained. Similar measurements were obtained for Palmer amaranth compared with cohorts of redroot pigweed (second planting) and waterhemp (third planting). Final growth and biomass of Palmer amaranth differed among planting dates. Redroot pigweed had more growth and biomass than Palmer amaranth whereas, waterhemp biomass was similar to Palmer within the planting dates.  The earliest Palmer amaranth cohort had slow growth for the first 3 weeks in the field, whereas the plants started one month later grew much more quickly. Growth of all three species for each cohort accelerated in late-June despite differences in accumulated GDD’s.  Palmer amaranth was shorter as the planting dates became later and had 66 and 76% less biomass than the first planting for the second and third planting, respectively.  At Corsica in 2016, soybean yield, as influenced by Palmer amaranth density, was quantified. As the number of Palmer plants per m2 increased, weight of individual Palmer plants and soybean yield decreased. A linear regression of total Palmer amaranth weight per m2 vs soybean yield had an r2 = 0.66 (p= 0.001). Soybean yield was reduced about 6% with each 100-gram/m2 increase of Palmer amaranth dry weight. 


GREENHOUSE SCREENING AND FIELD CHARACTERIZATION FOR DEVELOPING AUXIN AND GLYPHOSATE TOLERANT TOMATOES. G. Sharma*1, Z. Yue2, E. Avila dos Santos3, T. Tseng2; 1Mississippi State University, Mississippi State, MS, 2Mississippi State University, Starkville, MS, 3Universidade Federal De Santa Maria, Santa Maria, Brazil (174)


THE ROLE OF LATE-SEASON WEATHER EVENTS ON SEED SHATTERING OF REDROOT PIGWEED (AMARANTHUS RETROFLEXUS) AND COMMON RAGWEED (AMBROSIA ARTEMISIIFOLIA). S. C. Haring*1, M. L. Flessner1, W. J. Everman2, S. Mirsky3; 1Virginia Tech, Blacksburg, VA, 2North Carolina State University, Raleigh, NC, 3USDA Sustainable Agricultural Systems Lab, Beltsville, MD (175)


Seed shattering phenology influences how annual weed species use propagules to disperse through space and time. Many environmental factors, such as weather, affect when weeds shatter their seeds, therefore affecting biological dispersal patterns that are important for weed management. In 2016, a study was established in a soybean (Glycine max (L.) Merr.) field in Blacksburg, VA to investigate seed shattering phenology using 24 individuals each of redroot pigweed (Amaranthus retroflexus L.) and common ragweed (Ambrosia artemisiifolia L.). Plastic greenhouse trays lined with landscape fabric were fastened to the ground to cover 0.82m2 of soil surface at the base of each plant, and contents of the trays were collected weekly from the first signs of seed shattering, through the first possible soybean harvest (October 23), until the end of a simulated three-week harvest delay. Weather data were recorded by the Kentland Farm WeatherSTEM Unit. Principal components analysis was used to choose non-collinear weather variables that were related to seed shattering phenology in these two species. Significance of these variables was assessed using a generalized linear model with a Poisson distribution and log link, with a threshold of P≤0.05. Redroot pigweed began shattering six weeks before the first possible soybean harvest, while common ragweed began shattering three weeks before harvest. Seed shattered during the simulated harvest delay represented 51.8% and 66.1% of seed shattering compared to the whole-experiment total for redroot pigweed and common ragweed, respectively. Flagship weather variables chosen were weekly low temperature, total precipitation, and average wind speed. Each of these weather variables had a highly significant relationship with the total number of seeds shattered each week for both species. Colder weekly low temperatures were related to increased weed seed shattering, while higher average wind speed and precipitation were positively correlated with seed shattering for both species. These results highlight the importance of timely harvest, especially as weather conditions deteriorate into the winter season, when using harvest weed seed control technologies, which rely on weed seed retention at harvest time. Future research must better relate weekly seed shattering to total seed production. Furthermore, this study necessitates investigation of the mechanistic links between weather and seed shattering and how these results compare to other factors that regulate seed dispersal processes.




Weedy red rice (Oryza sativa L) is conspecific, aggressive weed that has been identified as a threat to global rice production. This weed has inherited high reproductive ability and high dormancy by outcrossing with modern rice cultivars and wild cultivars, respectively. Traits such as rapid growth, high tillering, enhanced ability to uptake fertilizers, asynchronous maturation, seed shattering, and long dormancy periods, makes weedy rice more competitive than cultivated rice. As weedy rice is more tolerant to stresses and has an elevated competitive ability than cultivated rice, we hypothesized that this species is more tolerant to herbicides and possesses weed suppressive ability. We evaluated 54 weedy rice accessions for tolerance to glyphosate at 1.12 kg/ha (1X rate). The same accessions were also evaluated for their ability to suppress a major weed in rice, barnyardgrass. Three of the accessions showed less than 40% herbicide injury while eight of them inhibited the growth of barnyardgrass by more than 50%. Accessions of weedy rice with glyphosate tolerance and weed suppressive traits were successfully identified. We will proceed in determining the molecular mechanisms associated with herbicide tolerance and weed suppressive ability, with the expectation of generating tools for rice breeding and crop improvement.





Evaluation of Post Emergence Herbicides for Goldenrod (Solidago spp.) Management in Wild blueberry Fields

Goldenrods (Solidago spp.) are creeping herbaceous perennials that reproduce through seeds and underground rhizomes and are among the most problematic weed species in wild blueberry production. Current management plans do not provide a profound control for goldenrod, therefore post emergence of the weed remain a serious problem in wild blueberry cropping system. Research trials were therefore conducted in commercial wild blueberry fields at Debert and Portapique, NS in 2016 to evaluate post emergence herbicides for goldenrod control. In the research trial, spot application of glyphosate, dicamba, dicamba plus diflufenzopyr, triclopyr, glufosinate, foramsulfuron, mesotrione, clopyralid, tribenuron methyl, flazasulfuron and bicyclopyrone were made to test these herbicides at floral bud and flowering stages. Preliminary results indicate that narrow leaved goldenrod were controlled 90 to 100% at floral bud stage by glufosinate and mesotrione. Bicyclopyrone and flazasulfuron reduced Canada goldenrod shoot density at least 95% at flowering stage, while glyphosate and mesotrione reduced both narrow leaved and Canada goldenrod shoot density up to 100% at these growth stages when compared to all other treatments.



CONFIRMATION AND MECHANISM OF RESISTANCE TO GLYPHOSATE IN ELEUSINE INDICA FROM BRAZIL. H. K. Takano*, R. S. Oliveira Jr, J. Constantin; Maringa State University, Maringa, Brazil (178)


THE EFFECT OF SAFENED SULFONLYUREA HERBICIDES ON ALS-SENSITIVE FIELD CORN HYBRIDS. O. W. Carter*1, E. P. Prostko1, J. W. Davis2; 1University of Georgia, Tifton, GA, 2University of Georgia, Griffing, GA (179)


Research was conducted in 2014 and 2015 to determine if acetolactate synthase (ALS) inhibitor herbicide formulations, that contain the crop safener isoxadifen, could be used on field corn hybrids with reported ALS sensitivity.  Small-plot field trials were conducted at the University of Georgia Ponder Research Farm located near Ty Ty, GA.   Two popular corn hybrids (DEKALB®  DKC 62-08 and DKC 64-69)  were treated 18 to 21 days after planting with nicosulfuron, nicosulfuron + rimsulfuron + isoxadifen, or  thiencarbazone + tembotrione + isoxadifen at 1X and 2X labeled rates.  No interaction was observed between herbicide treatment and field corn hybrid.  DKC 62-08 produced less above-ground biomass and was shorter in height than DKC 64-69; however, no difference in yield was observed.  Nicosulfuron had no effect on corn biomass, plant height or yield.  Only the 2X rate of tembotrione + thiencarbazone + isoxadifen reduced corn plant biomass by 19% at 14 days after treatment (DAT).    Nicosulfuron + rimsulfuron + isoxadifen and tembotrione + thiencarbazone + isoxadifen, at both 1X and 2X rates, reduced plant height by 5 to 9 % 26 DAT. However, only the 2X rates of these safened herbicides caused significant height reductions 61 DAT.  Additionally, yield losses of 4 to 7 % occurred with those treatments.  These data suggest that the herbicide safener isoxadifen does not provide complete protection against herbicide injury on ALS-sensitive field corn hybrids.  Field corn growers who are seeking alternatives to atrazine, glyphosate, or glufosinate need to weigh the risk of yield loss due to herbicide injury versus yield loss due to reduced weed control before making a decision on using these herbicide formulations on ALS-sensitive hybrids. 


A POOLED WHOLE-GENOME SEQUENCING APPROACH TO CHARACTERIZING ALS-INHIBITOR RESISTANCE IN MOUSE-EAR CRESS (ARABIDOPSIS THALIANA). R. S. Randhawa*1, M. L. Flessner1, J. H. Westwood1, C. W. Cahoon2, D. C. Haak1; 1Virginia Tech, Blacksburg, VA, 2Virginia Tech, Painter, VA (180)


A pooled whole-genome sequencing approach to characterizing ALS-inhibitor resistance in mouse ear cress (Arabidopsis thaliana L.). Ranjeet S Randhawa*, Michael L Flessner, David C Haak, James H Westwood; Virginia Polytechnic Institute and State University, Blacksburg, VA. 


Acetolactate synthase (ALS) inhibiting herbicides are among the most widely used chemical weed control measures. Frequent use and sole reliance on ALS inhibiting herbicides has eventually plagued their efficiency, resulting in herbicide resistance. This study was conducted to characterize the resistance mechanism of ALS inhibiting herbicide resistance in field-selected populations of mouse ear cress (Arabidopsis thaliana L.).

The two populations, Oakland Road (O) and Balderson’s farm (B) were collected from in Essex County, Virginia. Each population consisted of multiple putative resistant lines (OR & BR), collected from within a field with known history of commercial thifensulfuron control failures and putative susceptible lines (OS & BS), collected from close proximity outside the field. Plants were collected from the field and maintained in greenhouse conditions until seed harvest. Seeds were harvested from each plant separately and in the subsequent generation five plants were grown for every line within each population. Plants were sown in square trays (12 by 12 by 7cm) filled with potting mixture (Metro mix 360). Vernalisation treatment at 40 C for four days was given to accelerate germination and thereafter trays were maintained in growth chamber conditions; day temperature: 240C, night temperature: 190C, daylight: 12 hours. Seedlings were thinned to maintain five uniformly dispersed plants per tray. DNA was extracted from every plant using a cetyl-trimethylammonium bromide (C-TAB) based method. After DNA extraction, plants were treated with thifensulfuron (Harmony) at 15x (394 g ai ha-1) of labeled rate and 0.25% v v-1 NIS (Activator 90). Herbicide treatments were made using a spray chamber equipped with an 8001 EVS nozzle calibrated to deliver a spray volume of 140 L ha-1 at 172 kPa. Plants were returned to the growth chamber after herbicide application. Three weeks after herbicide treatment, plants were visibly evaluated and scored for level of resistance on a 0 (no injury) to 5 (all plants completely necrotic) scale. No fully susceptible lines were found, so lines were categorized into high resistance (HR) or low resistance (LR). DNA was pooled from multiple HR and LR lines from each location. Whole genome resequencing was done using Illumina sequencing technology to produce four different libraries: O-HR, O-LR, B-HR and B-LR. Genomes were aligned using BWA and thereafter GATK, to develop a consensus sequence and for SNP (single nucleotide polymorphism) calling. The results reveal a mutation in the ALS gene at Pro197 across all four pools (O-HR, O-LR, B-HR, B-LR) however, the substituted amino acid differs by population, O (Pro197Thr) and B (Pro197Phe).  Additionally, while the both B populations exhibited only a single mutation, the more resistant O-HR population exhibited additional mutations previously described in other systems, Trp574Leu and Asp376Glu, as well as two novel substitutions Asn554Gln and Val559Ile. These mutations occurred at varying frequency within the pools. From these data, we conclude that known target site mutations confer ALS resistance in mouse-ear cress and multiple mutations in the O population may be responsible for higher levels of resistance. Future research will focus on examining the impact of specific mutations on both overall resistance as well as cross-resistance, and on searching for SNPs outside of the ALS gene that may be associated with resistance.


EFFICACY OF AQUATHOL AND KFD-94-10 FOR CURLYLEAF PONDWEED (POTAMOGETON CRISPUS) CONTROL UNDER SIMULATED FALL CONDITIONS. M. F. Ortiz*1, J. Scarpin2, S. J. Nissen1, C. J. Gray3; 1Colorado State University, Fort Collins, CO, 2Universidade de Sao Paulo/ESALQ, Piracicaba, Brazil, 3UPI, Peyton, CO (181)


Invasions of non-native aquatic plants such as curlyleaf pondweed (Potamogeton crispus) (CLP) can have wide-ranging negative effects on whole lake ecosystems. Herbicide treatments have been shown to successfully control invasive aquatic plants during treatment years. Endothall and 2,4-D have been used in combination to control CLP for over 10 years. The objective of this project was to determine the efficacy of endothall (Aquathol® K) alone and endothall+2,4-D (Chinook®/KFD-94-10) for CLP control under simulated fall conditions. CLP plants from Washington were grown from turions in 50ml falcon tubes containing field soil, slow release fertilizer and fine, unwashed sand at the top. When the plants reached 10cm, they were treated with either endothall or endothall+2,4-D. Five-gallon mesocosms filled with 4 gallon of tap water were treated with one of the five treatments (non-treated, endothall 1.5ppm and 0.75ppm, or endothall+2,4-D 1.5+0.6ppm and 0.75ppm+0.3ppm, respectively). Three plants were exposed for 3, 6 or 12 hours to each treatment, triple rinsed in clean water and transferred to five-gallon mesocosms containing clean water. The plants were kept in growth chamber, at 14C with 12 hour day length. Visual control ratings were taken at 7, 14, 21 and 28 days after treatment. After 28 days all the turions were collected, rinsed with di-water and kept at 3C for 15 weeks. They were then planted and kept in the growth chamber under the same conditions previous described. The number of turions that resprout after 28 days was recorded. All the endothall+2,4-D treatments provided 100% CLP control, while treatments with only endothall did not. In addition, plants treated with endothall+2,4-D had more rapid symptom development than the ones treated with only endothall. The number of turions that resprouted was significantly lower when plants were treated with endothall+2,4-D.



Amaranthus tuberculatus (Moq.) J.D. Sauer is a problematic weed commonly found throughout the Midwestern United States. When not properly controlled A. tuberculatus can cause yield losses up to 74% and 56% in maize (Zea mays L.) and soybean [Glycine max (L.) Merr.], respectively. There are six herbicide sites of action that have documented cases of herbicide resistance in A. tuberculatus making it an important species of herbicide resistance research. The most recent case of herbicide resistance in A. tuberculatus was reported in 2011 when A. tuberculatus was confirmed to be resistant to p-hydroxyphenylpyruvate-dioxygenase (HPPD, EC inhibitor herbicides. Preliminary studies have identified one mechanism of resistance and described the inheritance of the herbicide resistance trait. There have also been initial attempts to identify important herbicide target site sequences within in the A. tuberculatus genome. To date, no studies have examined the transcriptomic expression response of HPPD-herbicide resistance in A. tuberculatus. Even with preliminary attempts to sequence the A. tuberculatus genome, the genomic resources of A. tuberculatus remains limited; therefore, we conducted an RNA-sequencing (RNA-seq) de novo transcriptome assembly of A. tuberculatus. We treated and mock-treated two A. tuberculatus populations (HPPD-herbicide resistant and susceptible) with mesotrione and collected leaf samples at three, six, twelve, and twenty-four hours after treatment (HAT). This de novo assembly was then used to measure transcript expression differences between genotypes, treatments and time points. Our results indicate that the response of HPPD-herbicide resistant and susceptible A. tuberculatus genotypes to mesotrione is very rapid and measureable as soon as three HAT. Furthermore, little overlap was found among the differentially expressed transcripts expressed by each genotype. We also identified the possibility of overlapping gene networks in response to other herbicides. The raw sequences, and assembled sequences with complete annotations will be made available for continued use by the weed science community. 




The water primrose complex (Ludwigia uruguayensis) has become one of the most serious problems in many Florida lakes over the past few years. Its rapid spread, coupled with the formation of dense mats and subsequent difficulty in control has become a great concern. Furthermore, variable morphology has been observed between populations and there is a lack of clear taxonomic and morphological characters to assist aquatic managers in field identification.  Therefore, the objectives of this study were to identify morphological characters to recognize taxonomic types of L. uruguayensis populations in Florida and to evaluate their response to commonly used herbicides. For the morphological study, plants were collected from five different lakes in Florida and grown in stock tanks under common garden conditions. Twelve vegetative and floral morphological parameters were quantified from these accessions as well as multiple field sites. Quantitative morphological characters were analyzed by ANOVA and Tukey’s HSD and qualitative morphological characters were analyzed using contingency tables and a chi-squared test. Results showed the presence of two clearly distinct species Ludwigia hexapetala and Ludwigia grandiflora in Florida and also the presence of intermediate types within L. grandiflora. A greenhouse bioassay was conducted on five accessions collected from five lakes in Florida to evaluate their response to the herbicides imazamox, triclopyr and glyphosate. Seven rates of each herbicide were compared with an untreated control. Shoot regrowth dry weight data at 70 days after treatment (DAT) was transformed to binomial data (alive vs dead). A two-parameter log-logistic model appropriate for binomial data was used to estimate the herbicide dose causing 50% mortality (LD50) for each accession. Results indicated there was differential herbicide sensitivity among Florida populations. These studies will assist aquatic managers both in taxonomic identification of target Ludwigia species and in proper herbicide selection for management.    





Some plant species respond to environmental stress with a form of genomic plasticity called “endoreduplication”.  Endoreduplication is the non-constitutive replication of the genome without cell division, which increases chromosome number (ploidy) and cell size.  But the degree which it is adaptive is poorly understood.  Increases in ploidy associated with this process may result in changes in cell size, metabolic processes and gene expression which may enhance the performance of plants; and thus, may be adaptive to stressful conditions.  For example, others have reported that endoreduplication was correlated with strong regrowth in response to simulated herbivory.  Sorghum halepense (Johnsongrass) is a highly aggressive agricultural pest and an invader of natural systems, but few mechanisms explain its widespread success.  A putative progenitor Sorghum bicolor has been found to endoreduplicate, but this has not been expressly examined in a stress tolerance framework.  We performed three experiments in which 40 accessions of Johnsongrass were exposed to stresses of herbicides, physical damage, and competition in order to assess the role of endoreduplication in stress tolerance.  Using flow cytometry, across experiments we found evidence for ploidy plasticity occurring in many of these accessions in response to different stresses.  Our study sheds light on a potentially important but poorly understood mechanism through which plants may cope with stress.



ABSORPTION AND TRANSLOCATION OF CLOPYRALID IN STRAWBERRY AND BLACK MEDIC. S. M. Sharpe*1, N. Boyd2, P. Dittmar1, R. Darnell1, G. E. MacDonald1, J. Ferrell1; 1University of Florida, Gainesville, FL, 2University of Florida, Balm, FL (185)


Black medic (Medicago lupulina L.) is a troublesome weed in Florida strawberries.  It emerges from the planting hole post-transplant to compete with the crop and impede harvest.  Clopyralid is the only available postemergence broadleaf control option available and strawberry producers report only suppression.  Two radiolabeled clopyralid experiments were conducted to increase understanding of clopyralid tolerance in strawberry and the lack of control in black medic.  The experimental design was a randomized complete block and the main factor was time after treatment.  Seven timings were selected: 0, 6, 12, 24, 48, 96 and 192 hours after treatment.  For each time point, the treated leaf was washed then the plant pressed and dried, sorted into parts and weighed, then a subsample was oxidized and the resultant carbon dioxide was captured and measured for radioactivity using liquid scintillation spectroscopy.  For strawberry, absorption reached a maximum of 82% (of the recovered radioactivity) and the time to near maximum absorption (90%) was 15 hours.  Translocation out of the treated leaf reached a maximum of 16.5% and took 52 hours to reach near maximum translocation (90%).  Translocation was primarily to dominant sinks.  For black medic, maximal absorption was 89% and reached near maximum (90%) at 2 hours.  Maximal translocation was 64% and reached near maximum (90%) by 38 hours.  Translocation was primarily to the treated stem.  Tolerance of clopyralid by strawberry appears to be in part due to limited translocation to the new growth while black medic may involve limited translocation to untreated, shielded stems.

INDAZIFLAM AND IMAZAPIC INTERCEPTION AND SORPTION BY DOWNY BROME (BROMUS TECTORUM), MEDUSAHEAD (TAENIATHERUM CAPUT-MEDUSAE), AND VENTENATA (VENTENATA DUBIA) THATCH . P. V. Da Silva*1, S. L. Clark2, D. J. Sebastian2, S. J. Nissen2; 1Universidade de Sao Paulo/ESALQ, Piracicaba, Brazil, 2Colorado State University, Fort Collins, CO (186)


Evaluating the interaction between herbicide and weed residues is necessary to determine herbicide availability.  An herbicide’s physicochemical properties can be used to predict how it will sorb to residues and determine ways to minimize herbicide interception and sorption. The objective of this research was to evaluate the interception, sorption, and desorption of imazapic and rimsulfuron using downy brome (Bromus tectorum), medusahead (Taeniatherum caput-medusae), and ventenata (Ventenata dubia). To determine sorption and desorption of imazapic on residues, Kd values were calculated across a range of herbicide concentrations. Imazapic adsorption was evaluated 24 hours after treating the residues with imazapic at each concetration plus 0.26 KBq 14C-imazapic. For desorption, the herbicide solution was removed from the 15 ml tubes and replaced with 8 ml of 0.02 M CaCl2 solution. The second experiment evaluated herbicide residue interception and rainoff using simulated rainfall at several intensities (3, 6, 12 and 20 mm). Dry residues of each winter annual grass were collected in the field, spread evenly on top of stainless steel screen, and then the screen was placed on top of a small glass pan. Pans were used to capture herbicide solutions during simulated rainfall events. Residues amounts were of 130 gm-2  and 520 gm-2. At 0.5 and 1 ppm there were no statistical difference between sorption of the three residue types. At 0.125 ppm imazapic, desorption was 69, 77, and 100% for ventenata, medusahead, and downy brome residue, respectively. For downy brome, imazapic interception was 62% and 84% for the low and high residue amounts, respectively. The residue quality and herbicide concentration influences imazapic adsorption and desorption, while  herbicide interception by the residue appears to be proportional to the residue amount. 


GENOTYPIC AND PHENOTYPIC DIVERSITY OF GLYPHOSATE RESISTANT GIANT RAGWEED (AMBROSIA TRIFIDA). J. C. Walker, III*1, T. Tseng1, D. B. Reynolds2, D. Shaw2; 1Mississippi State University, Starkville, MS, 2Mississippi State University, Mississippi State, MS (187)


CHARACTERIZATION OF ABIOTIC STRESS TOLERANT WEEDY RICE FOR IMPROVEMENT OF RICE. S. D. Stallworth*1, T. Tseng2; 1Mississippi State University, Mississippi State, MS, 2Mississippi State University, Starkville, MS (188)




Auxins are a class of small plant hormones that are involved in nearly every aspect of plant growth and development. Synthetic auxin herbicides are classified as such due to their auxin-like chemical structure and plant physiological response following application. The synthetic auxin herbicides 2,4-D and dicamba represent some of the first synthetic herbicides used for selective weed management in numerous settings.  Most recently, these herbicides have been used as components of herbicide resistance management strategies, including management of glyphosate-resistant horseweed (Conyza canadensis).

In 2015 and 2016, a field experiment was conducted at two field sites to investigate the influence of horseweed height on the efficacy of 2,4-D and dicamba. Twelve horseweed plants ranging from 5 to 30 cm in height were marked in each plot and heights were recorded at the time of herbicide application. Across years and locations, dicamba (280 g ae ha-1) controlled horseweed up to 24 cm in height, while 2,4-D (560 g ae ha-1) was more limited in efficacy and only resulted in control of horseweed that was 3 cm or less in height.

A greenhouse dose response experiment was designed to supplement the field research and evaluate differences in herbicide activity when applied to rosette-sized plants compared to 10 and 20 cm bolted horseweed plants under controlled environmental conditions. The rates necessary to reduce horseweed dry weight by 50% (GR50) and 90% (GR90) were calculated to determine relative herbicide efficacy. These values supported field observations that dicamba has a higher level of activity on horseweed at all heights compared to 2,4-D.

With the commercialization of dicamba-resistant crops and the future plans to commercialize 2,4-D-resistant crops, the role of these herbicides in managing herbicide-resistant weeds will be imperative. A better understanding is necessary to acknowledge and address the potential for cross-resistance among the synthetic auxin chemical families. Differential response of horseweed to 2,4-D and dicamba, especially relative to application rates, brings to question the physiological and biochemical aspects of the synthetic auxin mechanism of action. Are there differences in herbicide movement such as foliar absorption or translocation, metabolism, auxin receptor(s), or downstream effects of gene activation/deactivation? We feel these areas are important to further document the herbicide similarities or differences across chemical families that are grouped together within the synthetic auxin mechanism of action.


HYPERPECTRAL REFLECTANCE SPECTROSCOPY FOR MULTIPLE CROP AND WEED SPECIES DIFFERENTIATION. N. T. Basinger*, K. M. Jennings, D. W. Monks, E. L. Hestir, W. J. Everman, D. L. Jordan; North Carolina State University, Raleigh, NC (190)




Multispectral imaging has had limited success in weed/crop differentiation due to the utilization of large portions of the electromagnetic (EM) spectrum.  Utilization of hyperspectral reflectance data can allow for identification of more precise portions of the EM spectrum for utilization in multispectral sensors that will allow for improved accuracy of species differentiation. To identify wavelengths for differentiation, a field study was conducted to evaluate potential for differentiation of soybean (Glycine max), sweetpotato (Ipomea batatas), peanut (Arachis hypogaea), common ragweed (Ambrosia artimisiifolia), Palmer amaranth (Amaranthus palmeri), yellow nutsedge (Cyperus esculentus), large crabgrass (Digitaria sanguinalis).  Hyperspectral reflectance data of the crop canopy, was collected on each species using a handheld spectroradiometer at five collection dates over ten weeks. Data for each date were analyzed across all wavelengths to identify spectral reflectance bands where reflectance values differed between species. Early season differentiation was possible with sweetpotato and soybean, but not other species due to increased plant size.  At five and six weeks after planting, clear species differentiation was achieved in portions of the visible and near-infrared, regions of the EM spectrum. Preliminary results suggest that spectral differentiation of species occur mainly in the visible and near-infrared regions and is dependent on crop and weed growth stage and size



PALMER AMARANTH CONTROL AND TOLERANCE OF SWEETPOTATO (IPOMOEA BATATAS) TO FLUMIOXAZIN/PYROXASULFONE. S. C. Beam*1, K. M. Jennings2, D. W. Monks2, M. D. Waldschmidt2, N. T. Basinger2, M. B. Bertucci2, S. J. McGowen2; 1Virginia Tech, Blacksburg, VA, 2North Carolina State University, Raleigh, NC (191)


Studies were conducted at two locations in 2015 at the Horticultural Crops Research Station in Clinton, North Carolina to determine the response of sweetpotato and Palmer amaranth to a flumioxazin and pyroxasulfone premix applied PRE followed by simulated rainfall.  Herbicide treatments included flumioxazin/pyroxasulfone at 107 (47+60 g ai ha-1, respectively), 151 (66+85), 167 (73+94), and 280 (123+157) g ai ha-1.  A grower standard treatment of flumioxazin at 107 g ai ha-1 PREPLANT followed by S-metolachlor at 803 g ai ha-1 7 to 10 d after transplant (DAP) and a weed-free nontreated check were also included.  Simulated rainfall was applied to plots either one, two, or three times.  The timing of each rainfall event was at 0-2, 3-5, and 14 DAP, totaling approximately 1.9 cm at each timing.  Palmer amaranth control was >91% season long at both locations.  Sweetpotato injury was slow to develop and no injury was observed until 16 and 35 DAP at Location 1 and Location 2, respectively.  At Location 1 <6% injury to sweetpotato was observed across all treatments.  By 35 DAP at Location 1, sweetpotato injury was 12, 17, and 37% with flumioxazin/pyroxasulfone at 151, 167, and 280 g ai ha-1, respectively.  At Location 2, sweetpotato injury was <5% across all treatments.  Sweetpotato No. 1 storage root yield was reduced with 151 g ai ha-1 or above rate of flumioxazin/pyroxasulfone at Location 1 relative to the weed-free nontreated treatment (23,227 kg ha-1).  In contrast to these findings at Location 1, flumioxazin/pyroxasulfone did not reduce sweetpotato No. 1 yield at Location 2 relative to the weed-free nontreated check and yield ranged from 10,807 to 15,998 kg ha-1.  Flumioxazin/pyroxasulfone at 280 g ai ha-1 reduced sweetpotato marketable storage root yield at Location 1 but not at Location 2.  Flumioxazin/pyroxasulfone at 280 g ai ha-1 followed by a single rainfall event 0 to 2 DAP reduced No. 1 grade storage root length/diameter ratio (1.69 and 2.08 at Location 1 and Location 2, respectively) relative to the weed-free nontreated check (2.05 and 2.40 at Location 1 and Location 2, respectively).  Based on this research 107 g ai ha-1, was safe to sweetpotato and provided greater than 90% control of Palmer amaranth.  Rates above 107 g ai ha-1 has the potential to reduce yield and/or length/diameter ratio (shortening) of storage roots both of which are detrimental commercially to growers.



POTENTIAL CROP INJURY WITH EARLY POST APPLICATIONS IN XTENDFLEX COTTON. C. A. Samples*1, D. M. Dodds2, G. Kruger3, D. B. Reynolds1, J. T. Irby1, A. Catchot1, S. Davis1, M. T. Plumblee2, L. X. Franca2, B. R. Wilson1, J. T. Fowler Jr.4; 1Mississippi State University, Mississippi State, MS, 2Mississippi State University, Starkville, MS, 3University of Nebraska, Lincoln, NE, 4Monsanto Company, St. Louis, MO (192)


Due to the continued spread of glyphosate resistant Palmer amaranth (Amaranthus palmeri), technologies have been developed allowing growers to apply auxin-type herbicides post emergence. The XtendFlex® technology from Monsanto will allow growers to applyglypohsate, glufosinate, and dicamba over the top of cotton (Gossypium hirsutum L.).  Dicamba applied at 1.1 kg ae ha-1 provided up to 90 percent Palmer amaranth control. Dicamba tank mixed with glufosinate increased Palmer amaranth control over dicamba alone. Dicamba has also been observed to control other glyphosate resistant species 79 to 100 percent 14 days after application. As of 09 November 2016, the use of Xtendimax is labeled in XtendFlex® cotton and soybeans. However, currently no tank mix partners are allowed with Xtendimax. Since the development of glyhosate resistance, early POST applications with several modes of actions have become common.. However, the crop injury potential from these applications needs to be further examined.


Experiments were conducted in Starkville, MS at the R. R. Foil Plant Science Research Center and in Brooksville, MS at the Black Belt Branch Experiment Station. Plots consisted of 4-1 m spaced rows that where 12.2 m in length. Each plot was replicated four times. DP 1522 B2XF was planted in Starkville and Brooksville. Applications were made on 2-4 leaf cotton with a CO2-powered backpack sprayer calibrated to apply 140 L ha-1 @ 317 kpa while walking 4.8 kph. Treatments applied to DP 1522 B2XF included glyphosate @ 1.1 kg ae ha-1, glufosinate @ 0.6 kg ai ha-1, S-metolachlor @ 1.07 kg ai ha-1, dicamba (Engenia) @ 0.6 kg ae ha-1, dicamba (Clarity) @ 0.6 kg ae ha-1, and dicamba (MON 119096) @ 0.6 kg ae ha-1 either alone or in combination. Visual injury ratings were made 3, 7, 14, 21, and 28 days after applications. Other data collected included height at 1st bloom, nodes above white flower (NAWF) at 1st bloom, nodes above cracked boll (NACB) at the end of the season and, and lint yield. Data were analyzed using the PROC MIXED procedure in SAS version 9.4 and means were separated using Fisher’s protected LSD at p=0.05.


All six of the highest injury levels 3 days after application on DP 1522 B2XF were from treatments containing glufosinate and S-metolachlor in which visual injury ranged from 37-47 percent. The highest level of injury came from treatments containing dicamba (Engenia) + glyphosate + glufosinate + S-metolachlor. Similar to 3 days after application, five of the six treatments with the highest level of injury seven days after application contained glufosinate and S-metolachlor with injury levels ranging from 27-32 percent. At 14 days after application injury to DP 1522 B2XF had dissipated and ranged from 3-12 percent. At 21 Days after application, cotton injury had further dissipated and there were no significant differences observed amongst treatments. There were no significant differences in cotton height at first bloom with heights ranging from 61-69 cm. Similarly, there were no significant differences associated with NAWF or NACB with NAWF ranging from 6.8-7.2 NAWF and NACB ranging from 3.6 -4.5, respectively. This indicates that there were no signs of delayed maturity at first bloom or at the end of the year. Furthermore, there were no significant differences in lint yield at the end of the season with yields ranging from 1,904-2,119 kg lint ha-1.


INFLUENCE OF DROPLET SIZE ON LACTOFEN AND ACIFLUORFEN EFFECTIVENESS FOR PALMER AMARANTH CONTROL. L. X. Franca*1, D. M. Dodds1, G. R. Kruger2, T. Butts3, C. A. Samples4, M. T. Plumblee1, A. B. Denton4, B. R. Wilson4, S. Davis4; 1Mississippi State University, Starkville, MS, 2University of Nebraska, North Plate, NE, 3University of Nebraska - Lincoln, Lincoln, NE, 4Mississippi State University, Mississippi State, MS (193)


Influence of Droplet Size on Lactofen and Acifluorfen Effectiveness for Palmer amaranth control. L. X. Franca*1, D. M. Dodds1, G. R. Kruger2, T. Butts2, C. A. Samples1, M. T. Plumblee1, D. B. Denton1; 1Mississippi State University, Mississippi State, MS, 2University of Nebraska, Lincoln, NE.


Widespread occurrence of glyphosate and ALS-resistant Palmer amaranth has led to increased use of protoporthyrinogen oxidase (PPO) inhibiting herbicides. Lactofen and acifluorfen are non-systemic, PPO-inhibiting herbicides used to control several annual broadleaf species in soybeans, cotton, and peanuts. Concerns exist with regard to the dissemination Palmer amaranth populations resistant to PPO-inhibiting herbicides across the Midwestern and southern United States. Palmer amaranth populations resistant to fomesafen and lactofen have been reported in Arkansas, Tennessee, and Illinois. Therefore, efficacious and cost effective means of application are needed to maximize lactofen and acifluorfen effectiveness.

Experiments were conducted at Hood Farms in Dundee, MS, and the West Central Research and Extension Center in North Platte, NE to evaluate the influence of droplet size on lactofen and acifluorfen effectiveness for Palmer amaranth control. Lactofen was applied at 0.21 kg ai/ha + Crop Oil Concentrate (COC) at 1% v/v and acifluorfen at 0.42 kg ai/ha + Crop Oil Concentrate (COC) at 1% v/v using the following droplet sizes: 150 μm, 300 μm, 450 μm, 600 μm, 750 μm, and 900 μm. Prior to experiment initiation, droplet size spectra for each herbicide was characterized in a low speed wind tunnel at the Pesticide Application Technology Laboratory at University of Nebraska, North Platte, NE. Treatments were POST applied to 10 cm to 15 cm Palmer amaranth using a tractor mounted sprayer equipped with a CAPSTAN® AG Pulse Modulated Sprayer and Wilger® Precision Spray Technology Tips at 4.8 km per hour. Visual Palmer amaranth control was collected at 7, 14, 21, and 28 days after application. Fifteen plants per plot were tagged and used for dry biomass calculation at the end of the experiment. Data were subjected to analysis of variance and means were separated using Fischer’s Protected LSD at α=0.05.

Different droplet sizes of lactofen did not result in different Palmer amaranth control, regardless of rating period. Acifluorfen applied at 300 μm provided the greatest Palmer amaranth control at 14 days after application. In addition, Palmer amaranth control was greater with acifluorfen applied at 300 μm and 600 μm at 7, 21 and 28 days after application. Compared to 450 μm, acifluorfen applied at 300 μm provided a 30% increase in Palmer amaranth control, regardless of rating period. With exception of lactofen applied at 450 μm, all droplet sizes provided significant dry biomass reduction of Palmer amaranth. Acifluorfen applied with 300 μm droplet size resulted in significant reductions in Palmer amaranth biomass. These data suggest that the use of small or large droplet sizes does not affect lactofen effectiveness on 10 to 15 cm Palmer amaranth. Furthermore, in order to optimize Palmer amaranth control from acifluorfen, the use of 300 μm droplets is recommended. 




Chemical Programs for Annual Bluegrass Seedhead Suppression on Golf Greens

John R. Brewer, Sandeep S. Rana, and Shawn D. Askew

Annual bluegrass (Poa annua L.) seedhead suppression is an integral part of creeping bentgrass (Agrostis stolonifera L.) putting green management. Poa annua is a winter annual grass that emerges in fall and begins to produce seedheads primarily in the spring of the next year. This flush of seedheads can be aesthetically displeasing and can cause poor playability on putting greens. With the recent loss of mefluidide, ethephon is the most common method for seedhead suppression.  Unfortunately, ethephon can result in erratic and inconsistent seedhead suppression from year to year, which could be due to Poa annua biotypes, PGR application rate and timing, and seedhead evaluation methods. For example, an analysis of 195 observations from published reports across the United States showed ethephon suppressing seedheads an average of 56% with a standard deviation of 28%. These results suggest that about 70% of ethephon applications may suppress seedhead cover between 28 and 84%. We hypothesized that “early” PGR applications applied in advance of traditional spring applicaitons would result in more consistent seedhead suppression. At Virginia Tech from 2011 and 2012, two studies were conducted over multiple trial sites for seedhead suppression on putting greens in Blacksburg, VA, at the Virginia Tech Golf Course and Harrisonburg, VA, at Spotswood Country Club. Putting greens were ‘Penncross’ creeping bentgrass that were being overseeded with ‘L-93’.

Area under the progress curve (AUPC) was used to analyze creeping bentgrass and annual bluegrass injury and annual bluegrass seedhead cover, while the Gaussian function was used to calculate the maximum seedhead cover for the first study. Ethephon, methiozolin, and triadimefon did not injure creeping bentgrass in 2011 or 2012, while mefluidide injured creeping bentgrass 16% AUPC per day in 2011 and 21% AUPC per day in 2012. Annual bluegrass injury was pooled over both years. Ethephon and triadimefon caused slight to no injury to annual bluegrass, while mefluidide and methiozolin caused a maximum of 41% injury AUPC per day and 82% injury AUPC per day, respectively. NDVI showed similar trends to visual injury. The spring only program of ethephon and mefluidide contained a maximum of 72 and 76% annual bluegrass seedhead cover, respectively, while the early application programs contained 18 and 8% seedhead cover, respectively. For the second study, percent creeping bentgrass and annual bluegrasss injury, turf NDVI, and annual bluegrass seedhead cover was pooled across both locations. There was relatively no creeping bentgrass injury observed by any treatment. Mefluidide injured annual bluegrass 19%, while all other treatments caused less than 10% injury. At 3 weeks after spring treatment (WAST), the untreated check contained 69% seedheads, while the spring program of ethephon reduce seedhead cover to 31%. The spring program contained more seedhead cover than all other treatments. The March program of ethephon and spring program of mefluidide were similar, but lower than the spring program of ethephon and higher than the January and February programs of ethephon. The January and February programs of ethephon reduced seedhead cover the most at 3 WAST containing only 4 and 5% seedhead cover, respectively. 


HERBIDE PROGRAMS FOR RUBUS SP. CONTROL IN LOW-MAINTENANCE TURF. J. M. Craft*, J. R. Brewer, S. Askew; Virginia Tech, Blacksburg, VA (195)


Low-maintenance native turf areas have been increasingly adopted in out-of-play areas on the golf course to combat budget restraints. Native turf areas typically require less fertilization and less mowing however, this has led to unique weed problems with blackberry (Rubus spp.) being one of the most prominent broadleaf weeds to encroach. Blackberry is resistant to common 3-way herbicides used on golf courses for broadleaf weed control, but metsulfuron, fluroxypyr, triclopyr, and picloram have all been proven effective on blackberry species in pasture and native areas. Research was conducted in 2015 and 2016 at the Virginia Tech Golf Course in Blacksburg, VA to determine the effect of various herbicide combinations on Pennsylvania blackberry (Rubus pensilvanicus. Poir, RUPE) control. A tolerance study was initiated June 17, 2016 to evaluate hard-fine fescue (Festuca longifolia Thuill. 'Aurora Gold') response to herbicides treatments at the Glade Road Research Facility. Treatments were applied as follows: Turflon ester ultra at 1.12 kg ai ha-1, Spotlight at 0.526 kg ai ha-1, MSM Turf at 0.021 kg ai ha-1 and 0.042 kg ai ha-1, Turflon ester ultra at 1.12 kg ai ha-1 + MSM at 0.021 kg ai ha-1, Spotlight at 0.0526 kg ai ha-1 + MSM at 0.021 kg ai ha-1, Avenue South at 0.674 kg ai ha-1, T Zone at 1.4 kg ai ha-1, Speedzone at 1.54 kg ai ha-1, Solitaire 1.12 kg ai ha-1, Escalade II at 2.1 kg ai ha-1, Garlon P&D at 2.85 kg ai ha-1 Garlon P&D at 2.85 kg ai ha-1 + MSM at 0.021 kg ai ha-1, and an untreated check for comparison. All MSM Turf containing treatments received 0.25% v/v of NIS. Studies were arranged as randomized complete blocks with 3 replications. Data was analyzed in SAS 9.2 and treatment means for each response variable were separated using Fisher’s Protected LSD at the 5% level of significance.

Initial RUPE cover ranged from 20 to 90% and 58 to 81% in 2015 and 2016, respectively. At 6 WAIT, Spotlight, Spotlight + MSM Turf, Turflon+ MSM Turf, Turflon ester ultra, and Escalade II controlled RUPE ≥ 90%. AT 6 WAIT, T Zone, Speedzone, and Garlon P&D + MSM Turf controlled RUPE between 66 and 74%. All treatments controlled RUPE greater than 70% 8 WAIT, while speedzone, Avenue South, and Solitaire WSL controlled RUPE ≤ 50%. Turflon ester ultra + MSM Turf, Turflon ester ultra and Spotlight alone, and Spotlight + MSM Turf controlled RUPE ≥ 98% 12 WAIT, and these same treatments 11 months after 2015 treatments applications had the least RUPE shoots present. At 4 WAIT, only triclopyr containing treatments injured fine fescue greater than 20%. 

CHANGING THE ‘HACK AND SQUIRT’ PARADIGM FOR WOODY INVASIVE PLANT CONTROL. C. A. Lastinger*1, S. F. Enloe2; 1University of Florida, Lakeland, FL, 2University of Florida, Gainesville, FL (196)


Changing the ‘hack and squirt’ Paradigm

for Woody, Invasive Plant Control

Cody A. Lastinger and Stephen F. Enloe

University of Florida

               Hack and squirt is a commonly used approach for woody plant control in forestry, rights of ways, and natural areas.  The approach is highly selective as a series of hacks are generally made either continuously or semi-continuously around the trunk of a tree with a hatchet or machete and an herbicide solution is injected into each hack. Our goal was to determine if we could reduce the number of hacks on both single stem and multiple stem species to a single hack per stem at a height of 75 cm, reducing the time and energy to treat each and still achieve acceptable control. We compared aminopyralid and aminocyclopyrachlor (0.5 ml of 100 % v/v herbicide) injected into a single hack per stem on nine different invasive woody plant species. We compared these to both basal bark treatment with triclopyr ester (20% v/v) and cut stump treatment with triclopyr amine (50% v/v). Data collected included time to treat each individual plant, the amount of herbicide used, and percent canopy defoliation.  Species were treated in individual studies, and trees were blocked by size (diameter at breast height) with three size classes <4, 4 to8, 8 to 12 inches DBH. This presentation will focus on four species: Casuarina equisetifolia, Triadica sebifera, Bischofia javanica, and Schinus terebinthifolius, which were treated in December 2015 and January 2016. The cut stump and aminocyclopyrachlor hack and squirt treatments resulted in 100% defoliation across all four species and size classes 360 days after treatment. Aminopyralid was not different from either the aminocyclopyrachlor or cut stump treatments across all four species and size classes. Basal bark treatments provided 100% defoliation across all size classes on Triadica sebifera and Schinus terebinthifolius at 360 days after treatment. However, on Casuarina equisetifolia and Bischofia javanica, basal bark treatments resulted in less defoliation than either the aminocyclopyrachlor or cut stump treatments. On Bischofia javanica, basal bark treatment resulted in less defoliation in the 8 to 12 inch DBH size class than in the two smaller size classes. The studies will be continued through the second growing season following treatment to determine tree mortality. However, our current data suggests that this reduced hack and squirt approach may be a viable alternative to basal bark and cut stump treatments. 




Downy brome (Bromus tectorum L.) is a competitive winter annual grass species, and is considered one of the most problematic invasive species on rangeland.  Dalmatian toadflax (Linaria dalmatica L.) is an invasive perennial weed species found in dense populations in the western US.   Both of these species compete for moisture and can spread rapidly, outcompeting native grasses, forbs, and shrubs. The currently recommended herbicides (aminocyclopyrachlor, imazapic, picloram) for restoration of sites with invasive annual grasses and other biennial and perennial weeds have proven to provide inconsistent control or cause injury to desirable perennial species. Indaziflam, a new herbicide alternative for weed management in natural areas and open spaces, has been proven to provide long-term control of downy brome and other weed seedlings. A field trial was conducted to evaluate native species tolerance to indaziflam and other currently recommended herbicides used for downy brome (Bromus tectorum L.) and Dalmatian toadflax (Linaria dalmatica L.) control. A total of 11 herbicide treatments were applied at two separate locations.  For each native species, total counts were conducted across the entire plot area and analyzed as an increase or decrease compared to the non-treated control plots. Total species richness, downy brome control, and perennial grass response were also evaluated. Indaziflam treatments (73 and 102 g∙ai∙ha-1) increased native species richness and provided 95-100% downy brome control. Imazapic treatments provided limited downy brome control and failed to increase species richness in treated plots compared to non-treated plots.  Aminocyclopyrachlor and picloram treatments resulted in a significant reduction in species richness, with up to a 40% decrease compared to non-treated plots. This research provides necessary native species tolerance data for indaziflam and currently recommended herbicides.  These results suggest land managers should consider using indaziflam as an alternative herbicide treatment for restoring open spaces and natural areas severely impacted by downy brome and other invasive weed species. 

INFLUENCE OF GRAFTING ON THE CRITICAL PERIOD FOR WEED CONTROL IN WATERMELON. M. B. Bertucci*1, K. M. Jennings1, D. W. Monks1, D. L. Jordan1, F. J. Louws1, J. R. Schultheis2; 1North Carolina State University, Raleigh, NC, 2NC State University, Raleigh, NC (198)


Watermelon grafting is a cultural practice that allows growers to combine a rootstock having a beneficial trait (e.g., disease resistance, drought tolerance) with a high-quality scion that remains genetically unchanged. Grafting of watermelon has become a common practice in East Asia and in Europe, but it has not been implemented on a wide scale in the United States. Reported benefits include increased resistance to soilborne pathogens and an associated increase in yield. However, no research has investigated how grafting affects the critical period for weed control (CPWC) in watermelon. Thus, the objective of this study was to determine the influence of grafting on the CPWC in watermelon, using a mixed weed population of large crabgrass (Digitaria sanguinalis), common purslane (Portulaca oleracea), and yellow nutsedge (Cyperus esculentus).

Two field studies were conducted at the Horticultural Crops Research Station in Clinton, North Carolina in 2015 and 2016 to determine the critical period of weed control. ‘Exclamation’ a triploid watermelon was used as the scion in all grafting treatments. Grafting treatments included two Cucurbita maxima x Cucurbita moschata rootstocks ‘Carnivor’ and ‘Kazako’, as well as a non-grafted control (‘Exclamation’). Weed establishment and removal timings were 0, 2, 3, 4, 6, and 11 wk after watermelon transplanting (WAT). Marketable yield (fruit weighing >4.1 kg) and fruit count were measured over two harvests. A subsample of fruit from each plot were evaluated for hollow heart disorder.

Grafting treatment and timing of weed establishment and removal had a significant effect (p < 0.05) on marketable yield and fruit count. Neither grafting nor timing of weed establishment or removal had a significant effect on the incidence of hollow heart in watermelon fruit. Because watermelon is a high value per hectare crop, the CPWC was determined as the period when weeds must be controlled in order to achieve 100% weed-free yield. Results indicate weeds must be controlled from 0 to 32 d after transplant (DAT) to avoid loss in yield for all grafting treatments. Thus, grafting had no influence on the CPWC in watermelon.




The purpose of the areawide initiative is to develop, coordinate and implement superior strategies for pest control, strategies that incorporate integrating bio-intensive, environmentally sound and economical technologies over a region that is associated with the colonization and dispersal potential of a key pest or pest complex. AWPM projects should do all of the following: (1) target pests of significant economic or environmental importance , (2) coordinate and integrate existing pest control technologies (biological, cultural, physical, and chemical) over a region, and (3) involve multiple customers and stakeholders, and (4) develop cooperation and funding mechanisms that will maintain the areawide approach beyond the period of the research project.  The definition of a pest includes weeds, arthropod pests, and plant pathogens. Projects may focus on one important pest, or multiple pests at once (pest complexes).  Invasive plants and herbicide resistance weed issues can be good candidates for AWPM.



The California Delta is formed by the confluence of the Sacramento and San Joaquin Rivers, forming a large estuary which pre-settlement was wetland, but is now a series of diked islands used for agriculture that are below sea level, and relatively narrow waterways that flow to the San Francisco estuary.  A freshwater tidal estuary, the Delta is important for commercial and recreational navigation, water conveyance, as critical feeding and reproductive habitat for marine and freshwater fishes including endangered species, and for its ecosystem services.  Invasive aquatic plants such as waterhyacinth, Brazilian egeria, waterprimrose, and sponge plant have created a significant nuisance that threatens navigation as well as water conveyance for 25 million irrigated acres and drinking water for millions.  The Delta Region Areawide Aquatic Weed Project (“DRAAWP”), funded by the USDA-Agricultural Research Service, was initiated in 2014 to develop a new science-based integrated and adaptive weed management program.  USDA-ARS, working collaboratively with California State Parks Division of Boating and Waterways, NASA Ames Research Center, University of California-Davis, and others has developed a program of research, operations, assessment and outreach to address long-standing deficiencies of the aquatic weed management program.  DRAAWP is developing new techniques to detect, quantify and prioritize nuisance plant populations remotely, develop modeling approaches to predict plant population growth, and monitor the dispersal of plant propagules.  DRAAWP is improving the assessment of plant control operations, and identifying impacts of both the weeds and the techniques used to manage them on critical environmental factors.  DRAAWP is evaluating new biocontrol technologies, and testing new herbicides and adjuvants with a lower toxicological footprint.  Lastly, DRAAWP is improving interagency communication and collaboration, and expanding outreach to stakeholders and the general public.  While DRAAWP is the first Areawide project focused on aquatic weeds, this project fits well within the mission of the Areawide Program given the critical importance of the Delta for irrigation and domestic water conveyance, natural resource protection, and ecosystem services.

TAME MELALEUCA. P. Pratt*; USDA-ARS, Albany, CA (201)


TEAM LEAFY SPURGE - A LONG-TERM SUCCESS. R. G. Lym*; North Dakota State University, Fargo, ND (202)


TEAM Leafy Spurge – A Long-term Success.  Rodney G. Lym, North Dakota State University, Fargo, ND.

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.  Leafy spurge occupied over 1 million ha of the Little Missouri National Grassland (LMNG) in the 1990s and caused over $130 million in losses each year.  The LMNG covers a four-state region of North Dakota, Montana, South Dakota, and Wyoming and managing the weed in such a large and diverse area was a hopeless situation for most land managers prior to 2000.  In 1997, The Ecological Area-wide Management (TEAM) Leafy Spurge project was initiated to research and demonstrate IPM strategies to effectively manage leafy spurge in the LMNG.  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.  Control methods included chemical, biological, grazing, and seeding competitive species.  At the North Dakota site, leafy spurge was reduced from an average of 94 to 8 stems m‑2 5 yr after release of Aphthona spp. biological control agents and stem density remained at this low level in 2014.  As leafy spurge was successfully controlled in the LMNG, native species and diversity increased.  Controlling the invasive weed also helped the recovery of the endangered western prairie fringed orchid (Platantlgera praeclara Sheviak and Bowles) found in eastern North Dakota.  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.




Throughout the Great Basin and surrounding rangeland ecosystems invasion by winter-annual grasses, especially cheatgrass and/or medusahead, is a major factor detrimental to ecological function, forage production, and wildlife and wildlife habitat. Invasions by annual grasses promote frequent, dangerous and harmful fires. In response, ARS-personnel have developed a framework for planning and implementing Ecologically Based Invasive Pest Management (EBIPM) programs. Invasive and native plant communities are endlessly dynamic with multiple steady states. Implementing successful EBIPM requires a more consistent, systematic, and rigorous decision-making process. The EBIPM program and site specific management demonstrated and advanced during this areawide project was based on the integration of two decision making models currently being adopted on rangeland. The first is the “state-and-transition” model. State-and transition models describe stable vegetation composition and potential stable states within a given ecological site. Transitions are comprised of management strategies that propel succession from one state to another. State and transition models are being developed throughout the West for many rangeland types, and land management agencies are vigorously incorporating these models into the planning and decision-making process.




Areawide projects funded by USDA-ARS have several distinct characteristics: they focus on urgent issues, cover large spatial scales, integrate research and outreach, and address both human and technological dimensions of the problem. Multiple herbicide resistance in agricultural weeds has all of these aspects, and is thus more likely to respond to a coordinated areawide approach than through heavily siloed research. In 2015, an areawide project, ‘An integrated pest management approach to addressing the multiple herbicide-resistant weed epidemic in three major U.S. field crop production regions’, was formed with two social scientists  and 15 weed science investigators from the mid-Atlantic, south-central and north central regions. The project leverages its broad spatial extent and diversity of expertise to pursue three main activities at regional scales: 1) field studies of integrated weed management tactics, 2) improved understanding of the socioeconomic dimensions of the problem, and 3) outreach and stakeholder engagement through the web and social media as well as producer field days. One of the early products of the project is a landscape simulation model of the impact of cooperative weed management areas (CWMA) on herbicide resistance evolution. It demonstrates that both integrated weed management and CWMAs can slow the evolution of herbicide resistance, but that the largest reduction is achieved when diverse suites of weed management tactics are practiced in a coordinated way at large spatial scales.



When herbicide-resistant weeds are highly mobile across farms, delaying resistance becomes a common-pool 
resource (CPR) problem. In such situations, it is in the collective long-term interest of farmers to conserve an
herbicide's usefulness. Yet, each farmer has an individual short-run incentive to use the herbicide without
considering effects on resistance.

Economic factors are often at the forefront in determining what steps farmers might take to manage resistance.
Although economic factors provide important incentives for farmers, they are not the only motivator. The rapid
and widespread adoption of herbicide-tolerant crops reminds researchers that many ‘‘nonmonetary’’ factors are
also motivators. Examples include simplicity, convenience, flexibility, timing and time, crop safety, family and
worker health, water and wildlife quality, consistency of crop protection, yield loss, compatibility with conservation
tillage, clean fields, and land stewardship.

Two other interrelated socioeconomic phenomena that create a barrier to HRM adoption for individual farmers
are impatience and uncertainty. Farmers have less incentive to manage resistance to an herbicide if they
believe another new herbicide will soon become available to “solve” their problem. Ffarmers who are
overconfident about the availability of these new chemistries will be less inclined to adopt resistance
management practices. Managing resistance on an areawide basis is an additional challenge because if requires
collective action among growers. Fortunately, there is now a rich body of research on managing common
pool resources that can inform community-based approaches to resistance managements. Second, to
organize to prevent herbicide resistant weeds, farmers and other stakeholders do not have to start from
scratch. The multiple examples of community-based programs to control mobile insects and invasive weeds
illustrate that farmer groups—in collaboration with and assistance from the research and extension
communities—have organized effectively to overcome barriers to collective action problems. There is legal
and administrative precedent as well as institutional memory that could aid farmers in developing resistance
management programs based on programs they are already familiar with and which have a record of



COTTON AND PEANUT RESPONSES TO 2,4-D AND DICAMBA APPLIED PRE AND POST. S. Li*1, R. G. Leon2; 1Auburn University, Auburn, AL, 2University of Florida, Jay, FL (207)


As of Jan 17, 2017, Xtendimax with vaporgrip (Monsanto), Enlist duo (Dow agrosciences) and Engenia (BASF) have been registered by EPA in US cotton and soybean. These new technologies will bring better options for Alabama farmers to control resistant and problematic weeds, such as pigweed, morningglory, sicklepod, horseweed, cuttleaf evening primose and groundcherry, etc. Field trials and demonstrations conducted by Steve Li’s team haven shown 2,4-D and dicamba combined with glufosinate showed excellent growth suppression on very large pigweeds than current options. However, herbicide drift and off-target injury have been the greatest concern regarding using 2,4-D and dicamba in row crops. One specific risk farmers have to deal with is applying 2,4-D or dicamba very close to planting cotton to burndown existing weeds such as horseweed or marestail, then plant a wrong cotton variety that are not tolerant to 2,4-D or dicamba by error. This is likely to happen since only selected varieties in Deltapine and Phytogen product line are tolerant to these auxin herbicides. Moreover, if one used 2,4-D or dicamba to burndown existing weeds at planting, then crop stand is not acceptable, replanting variety with the same tolerance is required. If such tolerant variety is unavailable due to seed shortage, he may have to plant sensitive variety which may cause negative impact on crop growth. Therefore, experiment was conducted at Shorter AL, Fairhope AL and Jay FL to evaluate sensitive cotton responses to 2,4-D and dicamba residues in soil. Treatments included 2,4-D 1 pt/A and 2 pt/A applied 3-4 weeks before planting, 2,4-D 0.1 pt/A, 0.3 pt/A, 0.5 pt/A and 1 pt/A applied immediately after planting. All treatments were sprayed over soil surface and irrigated within 3 days of application.

Cotton stand at Fairhope was not affected by any of these treatments at 24 DAP, but in Shorter, 2,4-D 1pt/A applied at planting, dicamba 0.5 and 1 pt/A applied at planting reduced cotton stand as compared to NTC. Dicamba 1pt/A applied at planting reduced seedling height at Shorter 21 DAP. At 51 DAP, this treatment still reduced cotton height at Shorter when compared to NTC. Fairhope cotton height was not affected by herbicide treatments at 50 DAP. At the end of season, only dicamba 1 pt/A applied at planting reduced cotton yield at Shorter. No other treatment reduced cotton yield at Fairhope and Jay. The results of this study indicated high rates of dicamba have higher potential to injury cotton and cause yield reduction than 2,4-D, due to longer soil persistence. Therefore, more attention is needed after dicamba is applied to the soil immediately prior to or at planting to prevent cotton injury caused by planting error.  




EFFECT OF SIMULATED METRIBUZIN DRIFT ON COTTON AND SOYBEAN. T. B. Buck*1, D. Stephenson2, B. C. Woolam2; 1LSU AgCenter, Baton Rouge, LA, 2LSU AgCenter, Alexandria, LA (208)


Due to historical overlapping of cotton and soybean planting dates and subsequent applications of residual herbicides PRE in each crop for resistant weed management, there is a potential for off-target drift to emerged cotton or soybean.  Therefore, research was conducted at the LSU AgCenter Dean Lee Research and Extension Center near Alexandria, LA in 2016 to evaluate simulated early-season off-target drift of metribuzin on cotton and soybean.  Experimental design was an augmented factorial arrangement of metribuzin application timing and rate in a randomized complete block design with four replications.  Application timings were cotyledon, 2-, or 4-lf cotton or unifoliate, 2-, or 4-trifoliate soybean.  Cotton and soybean response was evaluated in separate experiments.  Application rates were 39, 78, or 157 g ai ha-1, which corresponds to 1/8, 1/4, and 1/2x, respectively, of the 1x rate of 314 g ai ha-1.  A nontreated check was included for comparison.  Visual evaluations of cotton and soybean injury were recorded 3, 7, 14, 28, and 42 d after each application.  Cotton and soybean heights were recorded 14, 28, and 42 d after each application.  Yields were collected at harvest with seed cotton yield adjusted to lint yield using a 40% turnout and soybean yield was adjusted to 15% prior to analysis.  Cotton and soybean heights and yields were converted to percent of the nontreated check prior to analysis.  Evaluation date was considered a repeated measure and included as a factor in the analysis. 

Averaged across rate, metribuzin injured cotyledon cotton 15% 3 d after treatment (DAT); however, injury increased to 80%, by 28 DAT.  Similarly metribuzin injured 2- and 4-lf cotton 11 and 24%, respectively, 3 DAT; however, injury increased to 65 and 47%, by 28 DAT.  Height following metribuzin application of 1/8x rate to cotton reduced height to 79 to 86% of the nontreated, regardless of application timing.  Height following metribuzin application of 1/4x and 1/2x rate reduced height to an average of 70% and 51% of the nontreated, respectively.  Averaged across metribuzin rate cotton yield was reduced to 37, 58, and 69% of the nontreated following the cotyledon, 2-, and 4-lf applications, respectively. 

Averaged across metribuzin rate, unifoliate soybean was injured 6% 3 DAT, but no injury was observed 42 DAT.  Metribuzin injured 2- and 4-trifoliate soybean 35 and 31%, respectively, 3 DAT, with injury decreasing to 3 to 10% 42 DAT.  Similarly, soybean injury decreased over time for all metribuzin rates with 15, 25, and 28% injury following the 1/8, 1/4, and 1/2x rates, respectively, 3 DAT; however, injury decreased to 1, 3, and 8% by 42 DAT.  Neither metribuzin application timing nor rate reduced soybean yield as a percent of the nontreated. 

Preliminary results indicate that early-season off-target movement of metribuzin can have negative implications on cotton and soybean production.  While both crops were injured in response to simulated drift of metribuzin, cotton growth and yield was more severely impacted.  Soybean visual injury was observed, but no reduction in yield was documented, which may be explained by soybean’s ability to compensate to negative early-season issues.  Research into this topic will continue in the future.


EVALUATION OF RESIDUAL HERBICIDES FOR INTERSEEDING COVER CROPS IN CORN. W. Curran*1, J. M. Wallace1, S. Mirsky2, M. Ryan3; 1Pennsylvania State University, University Park, PA, 2USDA Sustainable Agricultural Systems Lab, Beltsville, MD, 3Cornell University, Ithaca, NY (209)


In the Mid-Atlantic region, there is increasing interest in the use of relay-cropping strategies to establish cover crops in corn production systems.  Annual ryegrass and red clover cover crops consistently establish when interseeded at the V5 corn growth stage. However, this strategy may be limited by carryover injury to cover crops from residual herbicide programs. We conducted field experiments from 2013 to 2015 at Pennsylvania, Maryland and New York locations (10 total site-years) to evaluate the effect of common residual corn herbicides on interseeded red clover and annual ryegrass. We tested 22 herbicide treatments in at least two-site years and collected cover crop biomass in late-fall to evaluate herbicide carryover injury. Cover crop establishment and response to herbicide treatments was variable across study locations.  High levels of red clover and annual ryegrass biomass reduction were observed across herbicide treatments at the MD location, whereas negligible to moderate levels biomass reduction were observed at other locations. Among herbicides used for annual grass control, s-metolachlor, pyroxasulfone, pendimethalin and dimethenamid-P resulted in significant annual ryegrass biomass reduction relative to the untreated check, whereas annual ryegrass biomass in acetochlor treatments did not differ from the untreated check. The relative order of observed annual ryegrass biomass reduction among chloroacetamide herbicides was s-metolachlor > pyroxasulfone > dimethenamid-P > acetochlor.  Among herbicides used for broadleaf weed control, mesotrione resulted in significant red clover biomass reduction compared to the untreated check. Red clover biomass in saflufenacil, rimsulfuron and atrazine treatments did not differ from the untreated check.  This research provides preliminary evidence that annual ryegrass and red clover can be interseeded following use of several shorter-lived residual corn herbicides and also demonstrates that use of longer-lived residual herbicides likely preclude interseeding practices in corn production systems. Finally, our research demonstrates that the potential for carryover injury to interseeded cover crops can vary significantly across different soil and environmental conditions.



Recent survey by the Weed Science Society of America listed common waterhemp (Amaranthus rudis Sauer) among the top-five most problematic weeds in the United States. Use of premix-herbicides with multiple modes-of-action are recommended to delay the evolution of herbicide resistant weeds, such as Amaranthus sp. A premix of atrazine, bicyclopyrone, mesotrione, and S-metolachlor has recently been registered for PRE and early-POST applications in corn. Greenhouse and field dose-response studies were conducted in 2015 and 2016 to evaluate the response of common waterhemp to the premix applied PRE and POST. A four-parameter log-logistic function was used to determine the biologically effective doses (ED50 and ED90; premix doses required to control common waterhemp by 50 and 90%, respectively) using drc package in R. The ED90 values were estimated as ≤ 1,236 g ai ha-1 for the greenhouse PRE dose-response study; however, POST dose-response study conducted in greenhouse revealed that the ED90 values were 1,157 and 1,838 g ai ha-1 for 8 to 10 and 15 to 18 cm tall common waterhemp plants, respectively. Under field condition, PRE application of the premix at labeled rate (2,900 g ai ha-1) provided 98 and 93% control of common waterhemp at 14 and 35 days after treatment (DAT), respectively. The ED90 values for the POST dose-response study (in field) were 680 and 2,302 g ai ha-1 at 14 DAT for the 8 to 10 and 15 to 18 cm tall plants. The root mean square error (RMSE) values for the log-logistic functions were as small as 14.1, and the model efficiency coefficient (EF) values were ≥ 0.85 (close to 1.00), showing a good-fit for the predicted models. Regardless the application timing, no corn injury was observed at the labeled rate (2,900 g ai ha-1) of the premix; however, the injury was 7% when the premix was applied at 1.5× rate (4,330 g ai ha-1) to the 30-cm tall corn plant. Therefore, the new premix can be considered as an additional herbicide option for effective management of the problem weeds, such as common waterhemp in corn.

NEW PREMIX HERBICIDE FOR USE IN CORN. G. A. Elmore*; Monsanto, St. Louis, MO (211)


Upon receipt of regulatory approvals, Monsanto intends to introduce a premix of acetochlor with safener and mesotrione to be branded as Harness® MAX. Field trials were completed in 2016 to assess weed control and crop safety when applied pre-emergence and post-emergence to corn. Corn safety was excellent when applied pre-emergence or post-emergence to corn. Residual control of common weeds found in corn such as amaranths (Amaranthus sp.), lambsquarters (Chenopodium album), morningglories (Ipomoea sp.) and foxtails (Setaria sp.) was excellent. Once approved, the addition of Roundup® brand agricultural glyphosate herbicide will be recommended for improved control of emerged weeds. This product has been submitted to the United States EPA for registration and upon approval will be a valuable tool as part of a weed management program for corn.

This information is for educational purposes only and is not an offer for sale or distribution of Harness® MAX.

Harness® and Roundup® are registered trademarks of Monsanto Technology, LLC.

MINIMIZING RISK OF METRIBUZIN INJURY TO SOYBEANS IN WEED MANAGEMENT SYSTEMS. N. Rana*1, K. Kretzmer1, P. Feng2; 1Monsanto Company, Chesterfield, MO, 2Monsanto, St Louis, MO (212)


Glyphosate-resistant Amaranthus palmeri  was detected in the mid 2000’s and since then growers have relied upon Protoporphyrinogen Oxidase (PPO) herbicides for weed control in soybean and cotton. PPO-resistance in Amaranths was recently detected when applied pre and post-emergent. Metribuzin is a low-cost herbicide that provides an additional site of action to control glyphosate and PPO-resistant Palmer pigweed. With the heavy reliance upon PPO chemistry and glufosinate in soybean weed control systems, addition of metribuzin (162 to 280 g ai/ha) would boost the level of control of resistant Amaranthus species. Soybeans exhibit varietal sensitivity to metribuzin. Our research in molecular breeding led to the identification of a marker for metribuzin sensitivity. Laboratory assays indicate that combination of marker screen with a high throughput lab screen could potentially replace the greenhouse and field screens which produce inconsistent results stemming from variability in soil type and organic matter, rain amount and timing, and environmental conditions. Field experiments were conducted in 2014 and 2016 to validate the marker and lab high throughput assays. Results indicated that under normal field conditions genotypes selected by marker and lab screens showed little to no injury at 280 g ai/ha rate of metribuzin and furthermore, in 2016 no yield loss was observed in tolerant soybean germplasm in sandy soils and low organic matter. 


CAN WEEDS OVERTOPPING SOYBEAN OR ADZUKI BEANS BE MECHANICALLY PULLED TO REDUCE SEED INPUTS? M. Simard*1, R. E. Nurse2, E. R. Page2; 1Agriculture and Agri-Food Canada, Quebec, QC, 2Agriculture and Agri-Food Canada, Harrow, ON (213)


Herbicide-resistant weeds can seriously threaten profitability in crops where few alternative herbicides are available for their control.  In broadleaf crops, ragweed (Ambrosia spp.) and other broadleaved weeds resistant to one or multiple herbicides are an increasing concern. When these weeds reach a certain size, few options other than hand weeding will limit the production and dispersal of thousands of weed seeds carrying resistance genes. The objective of this project was to evaluate the efficacy of the Bourquin organic weed puller ® (a rotating series of wheels that grab and pull) at removing tall weeds before they shed seeds in soybean and adzuki bean. Trials were set-up in Canada at the AAFC research farms in Saint-Jean-sur-Richelieu, QC (2 years) and Harrow ON (1 year), on a loamy soil and a sandy soil respectively. The experimental design included crops of different potential heights (different soybean cultivars at one location or soybean and adzuki bean at Harrow), two weed species [lamb’s-quarters (Chenopodium album) (both locations) and common ragweed (Ambrosia artemisiifolia) or redroot pigweed (Amaranthus retroflexus) at Harrow] and two pulling dates. The set-up also included weedy and herbicide-treated control plots. Weeds overtopping the soybean canopy by at least 10 cm were tagged and characterised (height, stem diameter, stage, location across rows). Damage from the weed puller was rated as 1-pulled (desired effect), 2-cut, 3-folded, 4-peeled and 5-intact. The seed production of damaged and intact weeds was also noted. Less than 1/3 of ragweed or pigweed plants were pulled during any treatment combination. The highest pulling rates were observed for lamb’s-quarters at St-Jean (43%) but very few were pulled at Harrow (3.1% max). Pulling rates were not high enough to potentially control seed inputs from herbicide resistant populations.

EFFECT OF ACIFLUORFEN, CHLORIMURON, AND LACTOFEN APPLICATION TIMING ON SOYBEAN. D. Stephenson*1, B. C. Woolam1, T. B. Buck2; 1LSU AgCenter, Alexandria, LA, 2LSU AgCenter, Baton Rouge, LA (214)


Research was conducted at the LSU AgCenter Dean Lee Research and Extension Center near Alexandria, LA in 2015 and 2016 to access soybean injury and potential height and yield reductions following early-season herbicide application.  Experimental design was a factorial arrangement of treatments in a randomized complete block design with four replications.  Herbicides evaluated were acifluorfen at 280 g ai ha-1, chlorimuron at 12 g ai ha-1, lactofen at 218 g ai ha-1, and a nontreated.  Application timings included unifoliate, 1-trifoliate, or 2-trifoliate soybean.  Plots were maintained weed-free throughout the season with as-needed applications of glyphosate at 870 g ae ha-1 and with hand-weeding.  Visual evaluation of soybean injury, accessed on a 0 to 100 scale, were recorded 3, 7, 14, 21, 28, and 42 d after each application timing (DAT).  Soybean height was recorded 14, 28, and 42 DAT; however, only 2016 height data is presented due to a data collection error in 2015.  Yields were collected at harvest and adjusted to 15% moisture prior to analysis.  The repeated measure of evaluation date was included as a factor in the soybean injury and height analyses. 

Averaged across evaluation date, soybean injury was 26% following lactofen applied to unifoliate soybean, which was greater than acifluorfen or chlorimuron at all application timings.  Acifluorfen and chlorimuron injured soybean no more than 15 and 19%, respectively, at all application timings.  Regardless of herbicide, 45, 25, and 20% soybean injury was observed following the unifoliate, 1-, and 2-trifoliate application timings 3 DAT, with injury decreasing to 2 to 10% by 42 DAT.  Overall, injury following the unifoliate application timing was greatest.  Soybean height was reduced compared to the nontreated following chlorimuron when applied to 1-trifoliate soybean, regardless of evaluation date.  When averaged across application timing, both chlorimuron and lactofen reduced soybean height compared to the nontreated 42 DAT, but no differences were observed 14 and 28 DAT.  Regardless of herbicide, soybean height following the unifoliate application timing was less than the 1- and 2-trifoliate application timings 14, 28, and 42 DAT, mirroring visual injury observations.  Comparing soybean yield among treatnebts, yield following lactofen was less than acifluorfen when applied to unifoliate soybean and less than chlorimuron when applied to 2-trifoliate soybean.  When comparing treatments to the nontreated, yields were less than the nontreated following lactofen applied to unifoliate and 2-trifoliate soybean. 

Acifluorfen, chlorimuron, and lactofen were all injurious when applied to young soybean; however, lactofen was the most injurious overall.  When proper growing conditions are present following early-season herbicide application, soybean were capable of compensating for any visual injury and height reduction to yield similarly to the nontreated.  Although it will still be suggested to producers to utilize residual herbicide PRE and early-POST for glyphosate-resistant pigweed control, if a salvage herbicide application is needed, acifluorfen injured the soybean the least of the three evaluated.  Research will continue in 2017 to substantiate these observations.


SOYBEAN FLOWER AND POD RESPONSE TO DIPHENYL ETHER HERBICIDES. S. C. Beam*, M. L. Flessner, K. B. Pittman; Virginia Tech, Blacksburg, VA (215)


Protoporphorinogen oxidase (PPO) inhibiting herbicides (WSSA group 14) are commonly applied POST as rescue treatments in soybean production.  PPO inhibitors, especially the diphenyl ethers, are known to cause foliar injury such as bronzing to soybean.  It is not known if these herbicides applied at reproductive stages negatively impact flowers and developing pods.  A factorial field study was conducted in 2015 in Warsaw, VA and 2016 in Blacksburg, VA to determine the response of soybean flower/pods to diphenyl ether herbicides applied at multiple reproductive stages.  Factors were herbicide, lactofen (Cobra®) at 219 g ai ha-1, acifluorfen (Ultra Blazer®) at 420 g ai ha-1, and fomesafen (Flexstar®) at 395 g ai ha-1, and soybean growth stage at application (R1, R3, and R5).  Soybeans were planted on May 25, 2015 and June 2, 2016.  Treatments were arranged in a randomized complete block design with 4 replications and applied with a handheld spray boom calibrated to deliver 140 L ha-1.  At each application timing, eight plants in each plot were marked and the number of flowers or developing pods was counted.  One week after treatment (WAT) the flowers and pods of the same plants were counted again.  The plots were also rated for visible injury 1 WAT in 2015 using a 0 (no injury) to 100 (complete necrosis) scale.  Yield data were collected in both years and adjusted to 13.5% moisture.  Flower and pod count data were analyzed in JMP Pro 12 using Dunnett’s method (α= 0.05) comparing the difference between the initial flower/pod count and the count 1 WAT to that of the nontreated check.  Visible injury data were subjected to ANOVA and means separated using Fisher’s protected LSD (α= 0.05).  Yield data were analyzed using ANOVA and treatment means compared to that of the nontreated check using Dunnett’s method (α= 0.05).  There was no significant year by treatment interaction for flower/pod counts and yield, so data were pooled across years.  At all application timings, the difference in the number of flowers/pods between the initial treatment and 1 WAT was not different when compared to the nontreated check, indicating that herbicide treatment did not cause flower or pod abortion at differing levels than would occur without herbicide treatment (i.e. in the nontreated check).  In 2015, lactofen resulted in 43, 39, and 35% injury when applied at R1, R3, and R5, respectively.  Fomesafen resulted in 5% injury when applied at R1 and R5.  Acifluorfen resulted in 5, 6.3, and 5% injury when applied at R1, R3, and R5, respectively.  Yield ranged from 1974 to 2327 kg ha-1 with no differences between any treatment and the nontreated checks, indicating that visible injury did not result in a yield loss from any treatment.  Overall, soybean flower/pod development and yield are not negatively impacted by the application of diphenyl ether herbicides when applied at various reproductive growth stages despite visible foliar injury.  Of the three herbicides tested lactofen was the most injurious at all application timings. Future research may evaluate the effect of diphenyl ether herbicides on soybean flower and pod development when applied at different use rates.


EVALUATION OF LIBERTY LINK SOYBEAN WEED CONTROL PROGRAMS. R. W. Peterson*1, T. A. Baughman1, T. L. Grey2, D. L. Teeter1, C. D. Curtsinger1; 1Oklahoma State University, Ardmore, OK, 2University of Geogia, Tifton, GA (216)


Evaluation of Liberty Link Soybean Weed Control Programs. R. W. Peterson*1, T. A. Baughman1, T. L. Grey2, D. L. Teeter1; 1Oklahoma State University, Ardmore, OK, 2University of Georgia, Tifton, GA


Weed resistance is a growing problem in all-cropping systems therefore the use of preemergence herbicides as a foundation for weed management is crucial.  Soybean studies were conducted to evaluate the use of metribuzin in combination with other preemergence herbicides in Liberty-Link soybean system during the 2015 and 2016 growing season. The PRE herbicides applied alone or in various combinations included acetochlor, chlorimuron, dimethenamid, flumioxazin, fomesafen, imazethapyr, metolachlor, pendimethalin, saflufenacil, sulfentrazone, and thifensulfuron. All PRE herbicides were followed by Liberty applied twice at 22 fl oz/A.  Studies were conducted at the Wes Watkins Agricultural Research and Extension Center near Lane, OK; the Vegetable Research Station, near Bixby, OK; and in 2015 at the Southwest Georgia Research and Education Center near Plains, GA.  In the first year, heavy rainfall prior and after planting effected soybean stand establishment and weed control at both locations in Oklahoma. Trials at Bixby had to be replanted due to this excessive rainfall and stands were still not adequate to harvest. The second year rains in early season delayed planting at both locations.  However, unlike 2015 stands were good and no trial had to be replanted. The first study investigated premix herbicide combinations applied alone or with metribuzin PRE.  Soybean injury in 2015 at Bixby 2 WAP was at least 10% with flumioxazin + pyroxasulfone with and without chlorimuron applied alone PRE or with metribuzin. Palmer amaranth (AMAPA, Amaranthus palmeri) control was at least 99% with all treatments except metribuzin alone, and pyroxasulfone + saflufenacil with and without dimethenamid.  Soybean injury in 2016 was less than 5% 2 WAP for all treatments and no visible injury was observed 8 WAP.  Sulfentrazone + imazethapyr applied alone was the only treatment that did control AMAPA at least 99% 6 WAP.  Soybean yield was increased over the untreated control with all treatments applied at Bixby in 2016.  Control of tall waterhemp (AMATU, Amaranthus tuberculatus) and carpetweed (MOLVE, Mollugo verticillata) at Lane was 100% season long with all treatments applied in 2015. Late season control in 2016 of AMATU was at least 98% except with metolachlor + fomesafen PRE followed by 2 applications of Liberty POST.  The second study, conducted in both Oklahoma and Georgia, investigated individual preemergence herbicides applied alone or with metribuzin.  Soybean injury at Bixby was less than 10% 2 and 4 WAP for all treatments both years except metribuzin + fomesafen in 2015. Control of AMAPA was 100% with all treatments 2 WAP both years except pendimethalin applied alone in 2015. All metribuzin combinations followed by 2 POST applications of glufosinate controlled AMAPA 100% late season each year except metribuzin alone or in combination with pendimethalin in 2015.  Soybean injury was less than 10% 2 and 4 WAP at Lane except in 2015 with metribuzin applied in combination with flumioxazin or pyroxasulfone.  AMATU control was at least 95% 2 WAP with all treatments except metribuzin alone in 2015.  Soybean yield was increased over the untreated control with all treatments at both locations in Oklahoma. No soybean injury was observed with any treatment at Plains.  AMAPA control was 99% season long regardless of PRE herbicide applied.  Sicklepod (CASOB, Senna obtusifolia) and ivyleaf morningglory (IPOHE, Ipomoea hederacea) control was at least 97% season long except with fomesafen alone and pendimethalin + metribuzin PRE early season. When these treatments were followed by a POST application of glufosinate control was increase to 99%. All treatments increased yields with both Liberty-Link cultivars (5947LL and 7007LL) planted in Georgia.   Preemergence herbicide combinations can provide an excellent foundation for use in Liberty Link soybean systems.


BICYCLOPYRONE + BROMOXYNIL HERBICIDE:  INTRODUCING A NEW POSTEMERGENCE HERBICIDE FOR BROADLEAF WEED CONTROL IN CEREALS. S. M. Schraer*1, P. Forster2, D. Porter3, M. Saini3, T. Beckett3; 1Syngenta Crop Protection, Meridian, ID, 2Syngenta Crop Protection, Eaton, CO, 3Syngenta Crop Protection, Greensboro, NC (217)


Syngenta is introducing a new selective postemergence herbicide premix for the US market containing bicylopyrone + bromoxynil that provides broad spectrum broadleaf weed control in wheat and barley. The premix brand name is Talinor™ herbicide and contains two active ingredients with multiple modes of action, bicyclopyrone, a HPPD inhibitor (Site of Action Group 27), and bromoxynil, a PS II inhibitor (Site of Action Group 6). In field trial experiments conducted over multiple years, bicyclopyrone + bromoxynil at 212.5 to 283.3 g ai/ha combined with an additive (CoAct+™) at 64 to 80 g ai/ha provided excellent control of some of the more troublesome broadleaf weeds in cereals, such as Russian thistle, kochia, wild buckwheat, prickly lettuce and mayweed chamomile, including those populations that are resistant to ALS-inhibitor, synthetic auxin and glyphosate herbicides. Bicyclopyrone + bromoxynil has shown excellent crop safety to all tested varieties of spring wheat, durum, winter wheat and barley and can be applied from the 2-leaf stage to the pre-boot stage of the crop. Bicyclopyrone + bromoxynil can be tank mixed with graminicides such as pinoxaden (Axial® brands) for one-pass grass and broadleaf weed control. Syngenta received EPA registration approval of bicyclopyrone + bromoxynil in November of 2016. State registration approvals are in process.

TRIFLUDIMOXAZIN: A NEW PPO INHIBITOR THAT CONTROLS PPO RESISTANT WEED BIOTYPES. G. R. Armel*1, K. Hanzlik2, M. Witschel3, D. S. Hennigh1, S. Bowe1, A. Simon2, R. Liebl1, L. Mankin1; 1BASF Corporation, Research Triangle Park, NC, 2BASF Corporation, Limburgerhof, Germany, 3BASF Corporation, Ludwigshafen, Germany (218)


Trifludimoxazin [1,5-dimethyl-6-thioxo-3-(2,2,7-trifluoro-3,4-dihydro-3-oxo-4-prop-2-ynyl-2H-1,4-benzoxazin-6-yl)-1,3,5-triazinane-2,4-dione] is a new inhibitor of protoporphyrinogen IX oxidase (PPO or Protox).  This is the first PPO inhibitor containing a triazinone heterocycle.  Trifludimoxazin is very active when applied PRE or POST on dicot/broadleaf weeds including PPO resistant Amaranthus biotypes which are not controlled by currently registered PPO inhibitors like the diphenylether herbicides (e.g., fomesafen, lactofen, etc.), sulfentrazone, or flumioxazin.  Trifludimoxazin has also demonstrated activity on key monocot/grass weeds including Lolium spp.  The combination of trifludimoxazin plus saflufenacil improved the burndown and spectrum of weed control over solo trifludimoxazin and therefore will be a key mix partner along with other non-PPO inhibitor chemistries as part of a resistance management strategy.  Trifludimoxazin is expected to receive registration in key countries for use in multiple crops and total vegetation management by the middle part of the next decade.  Given its unique ability to control several resistant weed biotypes, trifludimoxazin will be an important tool for future PPO herbicide tolerant crops.

NOVEL PPO HERBICIDE TOLERANT TRAIT PROVIDES ROBUST CROP TOLERANCE TO MULTIPLE PPO HERBICIDES. R. Aponte1, L. Mankin*2, S. Tresch1, J. Lerchl1, M. Witschel3, T. Mietzner3, G. R. Armel2, R. Liebl4; 1BASF SE, Limburgerhof, Germany, 2BASF Corporation, Research Triangle Park, NC, 3BASF SE, Ludwigshafen, Germany, 4BASF Corporation, Raleigh, NC (219)


Protoporphyrinogen oxidase (PPO) inhibiting herbicides, or group E/14, are widely used to control weeds in a variety of crops primarily in preplant burndown, PRE and early POST applications. POST application usages are limiting due to poor selectivity. Genetically modified (GM) corn and soybean crops with tolerance towards PPO inhibiting herbicides were developed using a modified version of a plant PPO enzyme. Rational design using structural biology followed by in vitro screening of the designed PPO variants was used to select a tolerant PPO trait prior to in planta tolerance selection. Evaluation in both GM corn and soybean crops resulted in tolerance to all tested PPO inhibiting herbicides, including trifludimoxazine, saflufenacil, butafenacil, flumioxazin, carfentrazone, sulfentrazone, oxyfluorfen, lactofen, fomesafen and acifluorfen in PRE/POST applications. PPO herbicide tolerance represents a new mode of action in GM herbicide tolerant crops that will broaden the application timing and use rates of current and future PPO inhibiting herbicides.

NEXT GENERATION PPO HERBICIDES DELIVER BROAD-SPECTRUM WEED CONTROL INCLUDING GRASS AND PPO RESISTANT BIOTYPES. L. Parra1, T. Seiser1, D. S. Hennigh2, S. Bowe2, G. R. Armel2, L. Mankin3, R. Liebl*2; 1BASF SE, Limburgerhof, Germany, 2BASF Corporation, Research Triangle Park, NC, 3BASF Corp., Research Triangle Park, NC (220)


A striking feature of PPO herbicides is the large number of different chemical families, each with its unique set of structure-activity rules that can target this mode action. This combination of broad chemical diversity and multiple molecule design options has the potential deliver an almost limitless number of new active ingredients, yet only a handful of products have achieved commercial success. Part of the difficulty of exploiting PPO chemistry is the fact that, although it is relatively easy to identify chemistry with potent biological activity, it is much more difficult to find sufficient crop selectivity. The recent discovery of PPO herbicide tolerant crops as well as weed resistance to glyphosate has led to a resurgence in research at BASF to find new PPO herbicides with an expanded weed control spectrum.

The most promising PPO inhibiting chemistry discovered over the past 25 years can be broadly described as consisting of a heterocyclic ring attached to a phenyl ring. Of the many heterocyclic systems tested, the one having the greatest impact on biological activity is the 6-(trifluoromethyl)-1H-pyrimidine-2,4-dione – commonly referred to simply as uracil. In addition, pyridine and triazine heterocycles have generated potent biological activity. This chemistry has proven to be the most potent, broadest spectrum PPO chemistry tested to date. Weed control, including control of grasses, has been demonstrated at 25 g/ha in the field. While the increased use of PPO herbicides has increased the selection pressure for PPO resistant weeds and cross-resistance of PPO tolerant weeds to different chemical classes of PPO inhibitors is prevalent, it has been demonstrated that target site PPO resistant Amaranthus can be controlled by selected next generation PPO herbicides.

Without the need to address crop selectivity, PPO herbicide discovery can focus solely on maximizing efficacy. Next generation PPO herbicides will greatly expand the weed control spectrum over current PPO offers when paired with HT crops. Furthermore, the widely diverse chemistry that targets PPO mode of action suggests PPO can be a source of chemistry innovation well into the future.



In an effort to test both crop tolerance and residual herbaceous weed control, indaziflam and aminocyclopyrachlor were added to site preparation mixtures applied to a cutover forestry site in northern Mississippi. Seedlings were planted 4 months after treatment. Plots were evaluated at 6 MAT, 9 MAT, and 12 MAT for crop tolerance and herbaceous weed contol efficacy. Results indicate that bith loblolly amd longleaf were tolerant of the addition of indaziflam and aminocyclopyrachlor to the site prep treatments. Residual competition control varied by treatment

USE OF INDAZIFLAM FOR HERBACEOUS WEED CONTROL IN LONGLEAF PINE PLANTINGS. A. W. Ezell*, A. B. Self; Mississippi State University, Starkville, MS (222)


Herbaceous weed control is considered an essential component of stand establishment in the southern United States. Substantial work has been completed on loblolly pine due to its economic importance in this region. The relatively recent increased interest in establishing longleaf pine has created a need for more information on management options, especially as relates to artificial regenertion paractices. Since it is now a well established fact that competition control is the primary consideration in getting longleaf out of the grass stage, any new information on herbaceous weed control is highly desirable. New options are especially desirable since longleaf does not have the tolerance to some of the most effective herbicides used in loblolly management for this purpose. In 2015, a study involving eight treatments was established to evaluate the use of indaziflam applied over the top of recently planted containerized  longleaf pine seedlings. Treatments were evaluated at 30, 60, 90, 120, and 150 DAT. While forb control was adequate, grass pressure on the site was exceptional and overall control of the numerous species present was less than desirable. It is unlikely that most longleaf planting siteswill have such unusual grass competition. Results indicate that longleaf seedlings are tolerant of the over the top applications of indaziflam, and the material caould be useful in longleaf management.



There are an estimated 400 million ha of non-cropland in the US primarily designated as rangeland and pastureland, and there are over 300 invasive weeds found on these sites causing an estimated annual loss of $5 billion.  Among the most invasive and problematic weeds are Dalmatian toadflax, diffuse knapweed, downy brome, and musk thistle.  Currently, herbicides are the most common management strategy for broadleaf weeds and invasive winter annual grasses.  Indaziflam, a new herbicide for invasive plant management in non-crop areas, is a cellulose-biosynthesis inhibitor capable of providing residual invasive winter annual grass control up to 3 years after treatment (YAT).  A field experiment was conducted to determine if indaziflam tank-mix-treatments applied at two preemergence (PRE) timings provided longer residual Dalmatian toadflax and downy brome control than previously recommended herbicides (aminocyclopyrachlor, imazapic, picloram) applied without indaziflam.  Indaziflam tank-mix treatments provided increased Dalmatian toadflax (84 to 91%) and downy brome (89 to 94%) control 4 YAT compared to treatments excluding indaziflam.  Treatments without indaziflam controlled 50 to 68% of Dalmatian toadflax and <25% downy brome 4 YAT.  Based on these results, a greenhouse dose-response experiment was conducted with aminocyclopyrachlor, aminopyralid, and indaziflam to compare the preemergence control of nine invasive species commonly found in non-crop areas.  Averaged across species, aminocyclopyrachlor and aminopyralid GR50 values (herbicide concentration resulting in 50% reduction in plant biomass) were 29- and 52-times higher compared to indaziflam, respectively.  These data suggest that indaziflam could be used for long-term control of invasive species in non-crop areas, as a tank-mix partner with other foliar applied broadleaf herbicides. 

MANAGING VENTENATA DUBIA ALONG THE INVASION CURVE: FARMER, RANCHER AND LAND MANAGER PERSPECTIVES SHAPE FUTURE EDUCATION EFFORTS. T. Prather*1, J. M. Wallace2, P. Watson1, N. Norton3, K. Painter1; 1University of Idaho, Moscow, ID, 2Pennsylvania State University, University Park, PA, 3Palouse Land Trust, Moscow, ID (224)


The invasion process has been illustrated with a sigmoidal curve that includes a lag phase, a rapid increasing phase and then to a plateau where the species has invaded to its potential extent.  We have used the invasion curve conceptually to organize research approaches and it also should be relevant  as an approach to outreach education.  Should the topics covered be the same to all audiences?  Are people who are managing lands impacted by an invasive species interested in the same information as those people who are beyond the edge of the invasion front?    Ventenata dubia is an annual grass that has expanded throughout Oregon, Idaho and Washington.  Recently it has been found in Wyoming, Montana, Utah and Nevada.  How do we conduct outreach programs across an invasion front that is relevant to the participants? Secondarily, as management practices are developed, how do we create approaches to implementation of those management practices? In a series of extension workshops conducted using a technique called force field analysis, we explored what was important to the participants within the 3 phases of invasion.   We found that participants were most interested in identification, impacts and where the species might be found when they were beyond the invasion front.  Those people at the leading edge of the infestation were also interested in feasibility of eradication and control techniques.  People who were within the core of the infested area were interested in how to manage for the species and expressed varying degrees of acceptance for management strategies.  Through mailed surveys using the Dillman approach to survey, we identified current practices for management and were able to discover adoption or willingness to adopt, specific management techniques.  Understanding why some practices were more easily adopted than others helped shape our approach to teaching the management strategies.  Approaching outreach with respect to the invasion process should yield better outcomes for limiting the spread of invasive plants species and the conceptual model for the invasion process should be as fruitful for education as it has been for research.



Methiozolin is an isoxazoline herbicide that has been found promising to selectively control annual bluegrass in cool-season turf primarily on creeping bentgrass putting greens.  Roughstalk bluegrass is a troublesome weed in cool-season turf maintained at any cutting height and could be controlled by methiozolin.  Research was conducted for comparing various application regimes of methiozolin and other herbicides for long-term roughstalk bluegrass control in creeping bentgrass golf fairways.  Methiozolin-only treatments did not injure creeping bentgrass or reduce normalized difference vegetative index (NDVI) at either of two golf course locations on 20 evaluation dates over a 2.5-yr period.  2.5-yr average turf quality generally declined as roughstalk bluegrass control increased due to transient loss of turf cover.  At 1 yr after last treatment (YALT), methiozolin at 1500 g ha-1 applied four times in fall reduced roughstalk bluegrass cover 85%, which was equivalent to methiozolin at 1000 g ha-1 four times in fall but greater than low rates of methiozolin applied four times in spring or twice in fall and spring.    Amicarbazone, primisulfuron, and bispyribac-sodium alone either did not effectively reduce roughstalk bluegrass cover or did so at the expense of increased creeping bentgrass injury.  Results of this study suggest that methiozolin alone or tank-mixed with amicarbazone or primisulfuron is an effective long-term approach for selectively controlling roughstalk bluegrass in creeping bentgrass.




Cold air temperatures at the time of herbicide application are generally thought to decrease efficacy of systemic herbicides. Contact herbicides such as carfentrazone and sulfentrazone combined with systemic herbicides may provide an increased level of weed control when applied at cold air temperatures compared to products containing only systemic ones. Identical herbicide treatments were made at air temperatures of approximately 7 C and 18 C in four different trials. Control of ivyleaf speedwell (Veronica hederifolia L.), common chickweed (Stellaria media L.), henbit (Lamium amplexicaule L.), purple deadnettle (Lamium purpureum L.), and white clover (Trifolium repens L.) was evaluated. In general, warm temperature applications initially provided better weed control during the first week after treatment (WAT). By 2 to 3 WAT though, air temperature at the time of application generally did not affect overall weed control.  The herbicides evaluated generally provided similar weed control at approximately 7 WAT when applied at warm or cold temperatures. In study 1, at 56 days after treatment (DAT) regardless of air temperature at application, all tested herbicides provided 86% or greater control of ivyleaf speedwell, and 98% or greater control of henbit, with the exception of Trimec Classic, which did not provide acceptable control of henbit. Common chickweed control with combination treatments containing carfentrazone or sulfentrazone was similar at both temperature regimes, with control of 95% or greater, averaged across application air temperature. In study 2, after higher initial control with warm temperature treatments during the first WAT, Powerzone and Speedzone provided the highest level of control of ivyleaf speedwell and purple deadnettle at 35 DAT with no difference noted between air temperatures at application. Control of ivyleaf speedwell and purple deadnettle with Powerzone was 85 and 82%, respectively, averaged across temperature applications, while Speedzone controlled these two weed species 88 and 92%, respectively. Only for common chickweed control in trial 3 was there a significant interaction between temperature and herbicide treatment when evaluated 50 DAT. In that study, Speedzone and Trimec Classic gave greater control at warm compared to cold temperature application. Herbicides containing carfentrazone plus MCPP, dicamba, and an ester form of 2,4-D or MCPA provided the highest levels of control.


ARYLEX™ ACTIVE: A NEW, INNOVATIVE HERBICIDE FOR THE CONTROL OF BROADLEAF WEEDS IN TURFGRASS. V. F. Peterson*1, J. Breuninger2, A. L. Alexander3, D. Loughner4; 1Dow AgroSciences, Fort Collins, CO, 2Dow AgroSciences, Indianapolis, IN, 3Dow AgroSciences, Atlanta, GA, 4Dow AgroSciences, Lawrenceville, NJ (227)


Arylex is a new herbicide for postemergent weed control in turfgrass, cereals and other crops and registrations for use on wheat and other cereal crops has been obtained in the U.S. and other countries around the world. Arylex is an innovative low-dose synthetic auxin (HRAC group O) herbicide and the first member of the new arylpicolinate class of chemistry, designed to provide unique attributes compared to other growth regulator herbicides. Arylex unique binding affinity in the cell nucleus differentiates it from previous synthetic auxin herbicides:  Arylex demonstrates an affinity for the AFB5 auxin binding protein site of action in the cell nucleus of susceptible weeds.

Arylex provides consistent control of important broadleaf weeds in turf including common dandelion (Taraxacum officinale), narrow plantain (Plantago lanceolata), broadleaf plantain (Plantago major), common chickweed (Stellaria media), henbit (Lamium amplexicaule), and dollarweed (Hydrocotyle sibthorpioides). Trial work on both cool and warm season turf species including Kentucky bluegrass (Poa pratensis), perennial ryegrass (Lolium perenne) and tall fescue (Festuca arundinacea), bermudagrass (Cynodon dactylon), St. Augustinegrass (Stenotaphrum secundatum) and zoysiagrass (Zoysia japonica) has shown good turfgrass safety.

Arylex is effective at very low use rates of 10 g ae/ha and, due to its low vapor pressure, Arylex does not cause off-target damage to desirable broadleaf plantings through volatilization. Tree studies on many different species have shown that the Arylex can be used under the drip line without concern for off target injury.   Arylex rapidly degrades in soils and plant tissues. Field and laboratory studies with Arylex were conducted at Purdue University, West Lafayette, IN and Woods End Research Laboratory, Mt. Vernon, ME to determine its fate in grass clippings and compost.  It was determined that Arylex breaks down very quickly in turfgrass (DT50=1.5 days) and has no significant or lasting herbicidal activity in compost.  In November 2016, Dow AgroSciences submitted a request for registration to US EPA for Arylex containing formulations for use on turfgrass in both commercial and residential settings.

®™Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow

CONTROL OF TURFGRASS WEEDS WITH TWO NEW ARYLEXTM ACTIVE FORMULATIONS (GF-3566 AND GF-2687) IN COOL AND WARM SEASON TURFGRASS. V. F. Peterson*1, J. Breuninger2, A. L. Alexander3, D. Loughner4; 1Dow AgroSciences, Fort Collins, CO, 2Dow AgroSciences, Indianapolis, IN, 3Dow AgroSciences, Atlanta, GA, 4Dow AgroSciences, Lawrenceville, NJ (228)


GF-3566 is a systemic, postemergent herbicide composed of three proprietary active ingredients from Dow AgroSciences LLC for use on turfgrass. Two of the three active ingredients (Arylex and 2,4-D choline) are new to the turf market and the third component is fluroxypyr. The three actives are synthetic auxin herbicides which act through a synthetic auxin mechanism (HRAC group O, WSSA group 4) mode of action.  

GF-3566 provides quick activity and control of key problem weeds in cool season and bermudagrass turf. Upon US EPA registration, GF-3566 is expected to have a signal word of “Warning” rather than the “Danger” signal word attributed to many of the 2,4-D amine containing products.  The application rates will vary from 3.5 - 4.67 L/ha (3.5 - 4.0 pints/A) with use rates based on weeds and turfgrass species present. Positive attributes of GF-3566 include low odor and low volatility. GF-3566 is compatible with both low volume and traditional turfgrass application equipment, and mixes well in the tank with fertilizer and other products.

GF-2687 is also a systemic postemergent herbicide that controls both annual and perennial broadleaf weeds within southern turf stands.  GF-2687 is a 1:1 ratio of Arylex plus florasulam (HRAC group B, WSSA group 2) combining two distinct modes of action to help avoid and delay weed resistance. The application rate of GF-2687 is 50 g/ha (0.72 oz/A) and applications are rain fast after one hour. This low use rate provides effective weed control and is non-injurious across major warm and cool season turfgrass species. Turfgrass tolerance, even on herbicide sensitive St. Augustinegrass, has been demonstrated at temperatures above 32° C (90°F).  Upon US EPA registration, GF-2687 is expected to have a Caution signal word with no buffer zone or temperature restrictions. Coupling these features with one rate, safety across numerous turfgrass species, and effective performance on targeted weeds, GF-2687 will deliver maximum application flexibility for turfgrass managers.

Tree studies have shown that GF-3566 and GF-2687 can be used under tree drip lines without concern for off-target or root uptake injury.  Upon registration the expected use sites will include established turfgrass (commercial and residential), commercial sod farms, ornamental and sports turf, golf course fairways, aprons, roughs and tee boxes, campgrounds, parks, recreation areas, cemeteries, and unimproved turfgrass areas.

™Trademark of the Dow Chemical Company (“Dow”) or an affiliated company of Dow

PINOXADEN: A NEW HERBICIDE FOR TROPICAL SIGNALGRASS (UROCHLOA SUBQUADRIPARA) MANAGEMENT IN BERMUDAGRASS TURF. N. G. Young*1, R. G. Leon2, J. R. James3; 1Turfgrass Environmental Research Inc., Pompano Beach, FL, 2University of Florida, Jay, FL, 3Syngenta Crop Protection, Greensboro, NC (229)


Tropical signalgrass remains the most troublesome weed to control in bermudagrass turf during summer in Florida following deregistration of Monosodium methanearsonate (MSMA). New chemistries are needed to enable effective control during desirable periods for turfgrass managers. A multi-location field experiment was initiated during August, 2014 to evaluate pinoxaden (PXD) across six golf course locations in South Florida. The objectives were to (1) evaluate the stability of tropical signalgrass control from PXD across locations and compare to a commercial standard, (2) test weed control antagonism by cloquintocet (CQC) within a pre-mixed PXD formulation, and (3) assess bermudagrass injury from PXD and effect of the inclusion of CQC as a safener. Pinoxaden (0.14 kg ai ha-1) with and without CQC (0.035 kg ai ha-1) were compared to foramsulfuron + halosulfuron + thiencarbazone (FHT) (45 + 69 + 23 kg ai ha-1). Treatments were applied twice on a 14 d interval. Best linear unbiased predictions (BLUPs) were used to compute estimates of random treatment effects, while considering variance among random location effects. Location-specific inference with BLUP-based slices indicated no significant location by treatment effect, therefore, BLUPs for Tropical signalgrass control and bermudagrass injury were pooled across locations. At 13 weeks after initial treatment (WAIT), PXD, PXD+CQC, and FHT provided 89, 83, and 62 % control, respectively. Cloquintocet had no significant effect on control (p=0.5389) or bermudagrass injury 1 WAIT (p=0.6852) and with 8.5, 8.3, and 6.9 % injury for PXD, PXD+CQC, and FHT, respectively, safener inclusion appeared unnecessary. Pooled together, PXD treatments produced significantly higher control than FHT (p=0.0082). Findings suggest PXD represents a novel mode of action for control of Tropical signalgrass during summer in Florida, with excellent bermudagrass safety.

Nomenclature: bermudagrass (Cynodon dactylon (L) Pers. C. transvaalensis Burtt-Davy); cloquintocet; pinoxaden; tropical signalgrass (Urochloa subquadripara (Trin.) R. Webster)



SELECTIVE SUMMER GRASS WEED CONTROL IN DESERT TURF. K. Umeda*; University of Arizona, Phoenix, AZ (230)


A relatively new problem weed is occurring in the low desert turf of Arizona.  Panic liverseedgrass (Urochloa panicoides) was about 7.6 cm tall when mowed weekly in lesser maintained common bermudagrass turf, and maturing seedheads were present when initially treated on 02 June 2016 with postemergence herbicides.  At the Greenwood Cemetery in Phoenix, AZ, herbicide treatments were applied with a backpack CO2 sprayer to small plots and a sequential application was sprayed on 15 June.  A second experiment evaluating tank-mix combinations with mesotrione and topramezone was initiated on 16 June 2016. A sequential application was sprayed on 12 July followed by a third application on 04 August. In experiment 1 that compared several postemergence herbicides, topramezone at 25 g/ha demonstrated activity following the second application on the liverseedgrass.  Quinclorac and the pre-mix of quinclorac plus sulfentrazone plus 2,4-D plus dicamba and ALS-enzyme inhibiting metsulfuron and sulfosulfuron did not exhibit adequate acceptable activity against the mature liverseedgrass. In experiment 2, all treatments of mesotrione and topramezone demonstrated activity on liverseedgrass following the initial application. Within a week of the second and third applications, liverseedgrass control was approaching acceptable levels of better than 80%.  Mesotrione combined with metribuzin or simazine appeared to be more active among the treatments.  Nearly a month after the third application, mesotrione plus simazine and topramezone plus quinclorac exhibited liverseedgrass control at only 68 and 73% control, respectively.  Mesotrione at 180 g/ha and topramezone at 25 g/ha alone exhibited a bleaching effect on the grasses.  The combination with simazine or quinclorac caused less bleaching and more burning effect on the grasses. Overall, acceptable control of liverseedgrass was not achieved with multiple postemergence herbicide applications on the maturing weed.




This project was initiated in response to new ordinances proposed or adopted by some cities in southern California that limit the use products containing glyphosate on city-owned property. Seven products listed as organic (WeedZap 45%  clove oil, 45% cinnamon oil; AvengerAG 55% limonene; Suppress 32% capric acid, 47% caprilic acid; AXXE 40% ammonium nonanoate; FinalSan 22% free fatty acids and/or amine salts; WeedPharm 20% acetic acid; and Burnout II 8% clove oil, 24% citric acid), one classified as a biopesticide (Fiesta 26.52%  iron HEDTA) were included in the study as well as Finale (11.33% glufosinate-ammonium), Scythe (57.0% pelargonic acid, 3% related fatty acids) and Roundup Pro (48.7% glyphosate).  Herbicides were applied to plots with naturally occurring annual broadleaf weeds in a modified split pot design where the main treatment was the herbicide and a sub-treatment was the herbicide+0.5% Liberate surfactant (lecithin, methyl esters of fatty acids, alcohol ethoxylate). Results indicated that the tested organic and other herbicides are effective when applied multiple times and that activity is generally improved when the surfactant is added. However, the price of the material (2,5-32X more expensive than glyphosate for a single application) and the need for multiple applications may limit their use.




Aminocyclopyrachlor, flumioxazin, fluroxypyr, indaziflam, and metsulfuron-methyl (WSSA groups 4, 14, 4, 29, and 2, respectively) are herbicides used for weed control in turfgrass systems that have been associated with select cases of off-target injury to desirable plants. Their physicochemical properties suggest potential off-target transport, and subsequent injury, may be variably affected by edaphic conditions. Greenhouse research was conducted to elucidate the effects of soil organic matter content (SOMC) and soil volumetric water content (SVWC) on soil bioavailability of the aforementioned herbicides with the overarching goal of reducing off-target injury. Soil organic matter content was assessed at 0.5, 1.5, or 4.5% w/w via sphagnum peat amendment, while SVWC levels included 12, 25, or 40% v/v. Herbicides were syringe-applied over the soil surface of unique pots containing the bioindicator, mustard (Brassica juncea) for indaziflam or flumioxazin, and sunflower (Helianthus annuus) for aminocyclopyrachlor, metsulfuron-methyl, or fluroxypyr. As SVWC increased from 12 to 40%, injury caused by aminocyclopyrachlor, flumioxazin, fluroxypyr, indaziflam, and metsulfuron-methyl 21 days after treatment (DAT) increased 19, 87, 15, 84, 13%, respectively. Increasing SOMC from 0.5 to 4.5% reduced injury from aminocyclopyrachlor, flumioxazin, fluroxypyr, indaziflam, and metsulfuron-methyl 76, 49, 62, 29, and 86%, respectively, 21 DAT. Information from this research improves our understanding of the edaphic factors that affect herbicide transport, which can be used to create best management practices that minimize off-target injury.


THE GLOBAL HERBICIDE RESISTANCE ACTION COMMITTEE – INDUSTRY ENGAGEMENT AND COMMITMENT. M. A. Peterson*1, A. Cotie2, M. Horak3, A. Landes4, G. le Goupil5, T. Obrigawitch6, D. Refsell7, M. Bonnet8, S. Shinn9; 1Dow AgroSciences, West Lafayette, IN, 2Bayer Crop Science, Raleigh, NC, 3Monsanto, St. Louis, MO, 4BASF, Limburgerhof, Germany, 5Syngenta Crop Protection, Basel, Switzerland, 6DuPont Crop Protection, Wilmington, DE, 7Sumitomo Chemical, Walnut Creek, CA, 8Arysta LifeScience, Ougrée, Belgium, 9FMC, Philadelphia, PA (233)


The long term viability of weed management technologies has increasingly become an area of concern among farmers, researchers, industry, regulators, and the public in general.  The Global Herbicide Resistance Action Committee (GHRAC), an organization comprised of major companies associated with CropLife International, works to combat herbicide resistance and protect crop yields and quality worldwide.   The GHRAC companies bring unique knowledge and perspectives to the herbicide resistance discussion.  These companies have a long history of research and technical understanding of their herbicides along with extensive investment in development of new weed control technologies.  They also have in-depth knowledge of crop protection markets and farmer preferences along with working relationships with retailers who have influence on farmer decisions.  Companies work individually and through organizations such as CropLife to implement stewardship programs that ensure responsible use and long-term sustainability of crop protection tools.  Local and regional HRACs are active in various countries around the world and network with other stakeholders to help implement strategies and policies that result in effective, science-based resistance management strategies.  GHRAC works to aggregate, evaluate, and communicate herbicide resistance information to a range of stakeholders in support of local initiatives, often partnering with professional organizations to gain technical consensus.  GHRAC has recently launched a new website ( that contains information on site of action classification, guidelines for resistance testing, perspectives on monitoring, and other topics.  Additionally, GHRAC supports the International Survey of Herbicide Resistant Weeds (, a widely cited source of information on herbicide resistance.  GHRAC also sponsors working groups that assemble technical experts centered on specific sites of action or mechanisms of resistance.  These groups provide technical reviews and resistance management recommendations that help sustain the weed management tools which are critical to global food production.

ZERO TOLERANCE: REPLICATING A COMMUNITY-BASED HERBICIDE RESISTANCE MANAGEMENT MODEL FROM ARKANSAS. M. V. Bagavathiannan*1, J. K. Norsworthy2, T. Barber3, R. L. Nichols4, K. Smith5; 1Texas A&M University, College Station, TX, 2University of Arkansas, Fayetteville, AR, 3University of Arkansas, Little Rock, AR, 4Cotton Inc., Cary, NC, 5FMC Corporation, Groveton, TX (234)


Evolution of herbicide resistance in weeds is an emerging problem across the United States. In particular, multiple-herbicide-resistant Palmer amaranth is the major issue in row-crop production systems in the Southern US. Best management practices have been developed and recommended for tackling this issue. A key strategy for effective prevention or management of resistance is to reduce seedbank input from weed escapes and also minimize the opportunities for immigration of resistance alleles from the neighboring areas. A concern often expressed by many growers is that regardless of their efforts on resistance management in their fields, the outcomes are not always satisfactory because it is impacted by the actions of their neighbors; lack of sound resistance management practices in neighboring fields may lead to the inflow of resistance alleles and diminish the effectiveness of best management practices.  This is a typical example of how a common pool resource (in this case, weed susceptibility to a herbicide) exploited by some individuals, through a simplistic weed management approach driven by short-term economics, is affecting the entire community. To be very effective and sustainable, resistance management must occur at a community level such that all parties involved are engaging and benefiting from those practices. A pilot zero-tolerance program was initiated in Clay and Crittenden counties in Arkansas to completely eliminate Palmer amaranth in these counties through a community-level effort. This program brought together growers, crop consultants, industry participants, and extension personnel in achieving community-level management of this weed. This zero-tolerance program was a success story in the region and yielded great results within a short time in terms of reductions in Palmer amaranth seedbank size and weed management costs. Efforts are ongoing to replicate such a strategy in Texas where this species has already caused severe damages.

NEXT-GEN STUDENTS: A HANDS-ON APPROACH TO TEACHING MOLECULAR BIOLOGY AND GENOMICS FOR WEED SCIENCE. J. Westwood*1, H. Mehl2, D. C. Haak1; 1Virginia Tech, Blacksburg, VA, 2Virginia Tech, Suffolk, VA (235)


The discipline of weed science has an urgent need to integrate knowledge from molecular biology with principles of applied weed management. Understanding the genetic bases of weed growth, population biology, and evolution of herbicide resistance will provide new insights into weedy traits and inform strategies for weed control. At the same time, breakthroughs in sequencing technology have created a situation in which genomic scale data can be obtained with relative ease and a modest budget, making these approaches feasible for most weed research programs. However, a major constraint to their use is that graduate students in applied weed science typically lack previous training in molecular biology. To fill this gap at Virginia Tech we developed the course, “Molecular Biology for Applied Plant Sciences”. The target audience for this course is MS or PhD students in field-oriented programs in weed science or plant pathology. The course is one semester and consists of two lectures and one 3-hr laboratory per week. The goal is to provide students with the knowledge and experience to apply molecular/genomics tools to their own research, so the emphasis is on active learning. Lecture sessions provide some traditional instruction, but students are also asked to assimilate material outside of class, so that class time can be used for discussion and small-group activities. The laboratory section provides students with hands-on learning, and the semester is divided into two parts. The first guides students through essential skills of DNA isolation, PCR and cloning, but the emphasis is on aligning the work with student interests in weeds and plant pathogens, so activities include sequencing the Amaranthus acetolactate synthase gene and genotyping Fusarium isolates. The students also learn basic bioinformatics by analyzing data generated from Illumina sequencing projects that address questions related to population biology, gene expression, and genome reassembly. The second part of the semester allows students to apply their new molecular skills to their own research projects, and culminates with student presentations of findings. The outcome of the course is students who are substantially more informed about molecular/genomics concepts, who can discuss such concepts with molecular-oriented colleagues, and who can use these techniques to enhance their applied research projects. 




Focus stacking has increased the ability to visualize structures used in identification of weeds.  Fine detail of extremely small structures can now be seen clearly without the limitations imposed by shallow depth of focus.  Stigma structure is frequently employed in plant taxonomy, and as a character used in keys for identification. Small size, however, increases the difficulty in determining the characteristics of the stigma.  Photographic examples of sessile, simple, bifid, various knobs, trifid, multiple, feathery and miscellaneous stigmas are presented demonstrating the advantages of focus stacking for macro photography.


FENCELINE VEGETATION MANAGEMENT: A TEACHING MODULE FOR EXTENSION AGENTS. D. P. Russell*1, J. D. Byrd, Jr.2; 1Mississippi State University, Starkville, MS, 2Mississippi State University, Mississippi State, MS (237)


Fences have many functions. They have utility in their ability to define property boundaries, protect assets, provide safety measures, and reduce liability. Fences are not always affordable to build, and sometimes, even more expensive to maintain. Secondary succession is inevitable, thus vegetation management is necessary for fences’ long-term effectiveness. The challenge lies with multi-species control, which spans grasses, sedges, rushes, broadleaves, vines, and woody brush. Control measures vary from the most expensive and invasive heavy machinery, to herbicide applications, to simple, but slow and expensive mechanical removal using hand tools. Chemical weed control is one of the most versatile methods, but one with potentially high liability. Applicators must be ever aware of their environment and precise in their calibration, product choice, use rate, volume, and target. Dousing fences with herbicide material meant for vegetation may cause chronic degradation of even the most resilient metals. There is no silver bullet to control all vegetation. Tank mixes, and even various methods of weed control, may be necessary to keep plant succession at bay, but proper plant identification is essential.

ESTABLISHMENT OF A WEED SCIENCE GRADUATE PROGRAM AT THE AGRICULTURE AND FORESTRY UNIVERSITY, NEPAL. A. Shrestha*1, S. Sah2, S. Dhakal2, S. Marahatta2, V. R. Duwadi3, C. Bhattachan3, A. Thapa3; 1California State University, Fresno, CA, 2Agriculture and Forestry University, Rampur, Nepal, 3Winrock International, Lalitpur, Nepal (238)


For centuries weeds have been primarily managed with manual labor in Nepal. However, in recent years, migration of farm labor to other industries, including overseas employment, has required an increased use of herbicides. Unfortunately, there has been insufficient training in the safe and effective use of herbicides in Nepal, partly because the country has lacked academic programs and trained specialists in weed science. Rapid changes in weed management strategies and a lack of properly trained weed management personnel have led to a number of serious weed management issues, including herbicide-resistant weeds, in agricultural and non-agricultural sectors. Thus, poorly controlled weeds are now threatening agricultural productivity and native flora and fauna in the national parks and other non-agricultural areas of Nepal. To help address these problems, the newly established Agriculture and Forestry University (AFU) in Nepal envisioned developing a graduate major in weed science. However, lack of expertise in the development of such a curriculum was a significant issue. With the assistance of USAID-funded Asia Farmer-to-Farmer Program implemented by Winrock International and a faculty volunteer from California State University, Fresno, AFU faculty members worked jointly with personnel from these organizations and developed a graduate program in weed science in 2015. Curriculum and syllabi were developed for five specialized courses in weed science and a full-fledged graduate program was launched in 2016 at AFU. Although the program is housed within the Agronomy department at AFU, the courses cover weed management issues in other agricultural and non-agricultural systems as well. The university currently lacks trained faculty members and the necessary facilities for a full-fledged weed science program but AFU expects to put in more resources in the coming years to ensure the success of the newly established curriculum. It is expected that programs such as these meet the needs of developing sustainable weed management systems and responsible herbicide stewardship that is now the essence in ensuring global food security in the context of rapid urbanization, migration of labor from agriculture, increasing crop losses from weeds, increase in invasive weeds, and increase in reliance on herbicides.

SYMPOSIUM OVERVIEW AND GOALS. B. G. Young*; Purdue University, West Lafayette, IN (239)




The prolific and exclusive use of glyphosate in the preceding 20 years has shifted weed populations to those that are tolerant or resistant to glyphosate.  These weed shifts have made it very difficult for growers to control these problematic weed species across the United States.  To manage these glyphosate-resistant weeds, crop protection applications have changed from a glyphosate only program to a tank-mixture or pre-mixture that includes another mode of action.  Now with the deregulation of both the dicamba trait and the herbicide, this new technology brings another option to the weed control management system.  The perceived value of this technology in both cotton and soybean are apparent as growers are rapidly adopting this new trait in their cropping system.  With this demand brings another learning curve as we properly manage the entire process from the container to the final destination of the spray droplet. 

Over the last ten years, retailers and producers have learned how to effectivity manage the increasingly complex herbicide programs that at one time were very simple.  The addition of another herbicide or the use of premixtures has caused many to look at the optimization of the herbicides; this included proper nozzle selection, mixing order, application volume, and proper cleanout procedures.  This learning curve has set the foundation on how we currently are managing the proper application and will continue to build on the stewardship of the new dicamba technologies. 

Dicamba has been used for many years and we continue to optimize our application techniques to ensure a safe and effective result.  New product uses and innovation of the chemistry has resulted in new learning and training opportunities.  We continue to identify management practices such as proper nozzle selection, the use of drift reduction products, and the proper management of the buffer zones.  The use of adjuvants and effective tank cleanout procedures will be critical as the market share of the dicamba-tolerant crops continue to grow.      

Herbicide-resistant weeds continue to plague farmers across the U.S.  It’s imperative that the newest and best technology is used to mitigate the movement and introduction of hard to control weeds across the soybean growing regions, all while protecting the sensitive species and eliminating the concerns around off target movement.




Pesticide (herbicide) use in the U.S. is jointly and cooperatively regulated by the U.S. Environmental Protection Agency and pesticide state lead agencies, such as the Office of Indiana State Chemist (OISC). In most states the pesticide state lead agency has been granted “use primacy”, so the overwhelming majority of the pesticide compliance assistance and use enforcement activities, including education of pesticide applicators, fall to the states.

While off-target pesticide movement (drift) regulations, requirements, and mitigation measure may vary from state to state, there are common threads of each that are predominantly consistent, regardless of which state the pesticide use may occur. The underlying premise of most state and federal drift regulation focuses on compliance with the pesticide label use directions. In other words, “the label is the law”. This presentation will highlight some of the similarities, differences, measures, challenges, and procedures encountered by pesticide state lead agencies in attempting to regulate and mitigate drift.



Environmental fate and ecological risk assessments include the assessment of potential pesticide exposures and subsequent risks to plants inhabiting terrestrial and aquatic habitats. Currently, EFED uses the models TerrPlant, AgDRIFT, and PRZM-VVWM to estimate off-site runoff and spray drift exposures to plants inhabiting dry-land, semi-aquatic, and aquatic habitats adjacent to treatment sites.  The Agency relies upon required standardized toxicity tests and other published literature to evaluate the potential risks of the modeled environmental exposures to plants.  Based upon these tools and the pesticide use information, the Agency develops a risk assessment characterizing the potential risks to plants. The Agency will provide an overview of this process, the data and the models that are used, and provide insight into the considerations made when evaluating risks to terrestrial and aquatic plants.



When risks to terrestrial and/or aquatic plants are expected after a pesticide use, the Agency may consider additional data, refinements to the exposure, or additional lines of evidence to better characterize these risks.  Some of these considerations may include the comparison of the assessed chemical against other chemicals with the same or similar intended uses.  These comparisons allow the Agency to consider the relative risk of one chemical against another. Additionally, the Agency may further refine the assessment by considering: 1) the relationship of the traditional endpoints and approaches used in risk assessments with additional data and modeling tools; 2) increased resolution of the geospatial distributions of risks; and 3) consideration of the impact of reduced spray drift through the evaluation of data for drift reduction technology.  The Agency will discuss these topics, ongoing work regarding the development of a new plant exposure model, and recent developments in the areas of synergy and drift reduction technology.


THE MECHANICS OF DRIFT REDUCTION TECHNOLOGIES. J. Ferguson*; Northwest Missouri State University, Maryville, MO (244)


The nozzle has the greatest impact on the drift potential of a spray application. Reducing pesticide spray drift and maximizing herbicide efficacy are the paramount considerations when selecting technologies and operating parameters prior to making an application. It is well understood that the spray droplet size is the greatest factor that determines spray drift. Spray drift is defined by the US Environmental Protection Agency (EPA) as the “the physical movement of a pesticide through the air at the time of application or soon thereafter, to any site other than the one intended for application”. The growing concern of spray drift since 1997 has led to the adoption of nozzles with air-induction (AI) ports, pre-orifice chambers, and other design features that can increase droplet size to reduce spray drift. These design features can also allow for applications to be made in a wider range of environmental conditions. Many of these nozzle types use the Venturi process which introduces air into the liquid, forming droplets with air inclusions, which increases the spray droplet size. The design factors of AI nozzles are a significant component of what affects the atomization performance of these nozzles. The major design features and the reasoning behind development of major nozzle types will be discussed in the context of our new focus on spray drift. Further discussion will be aimed at the regulatory and research that underpinned a greater focus on spray drift and where how that shaped the technologies available to growers and applicators today. Optimal nozzle selection is the greatest factor that can result in spray drift reduction.




ASTM (American Society for Testing and Materials) standard E609 defines driftable fines as “the % volume of a spray droplet size distribution with a diameter less than 105 microns” and standard E1519 defines drift reduction agent as “a material used in liquid spray mixtures to reduce driftable fines”.It is well known that driftable fine can be reduced either by narrowing the droplet particle size distribution or shifting the distribution to a higher volume mean diameter.

It has been widely reported that the main physco-chemical parameters that affect droplet size distribution include dynamic surface tension, extensional viscosity. Information relating to the downward velocity of spray droplets is important to understand the risk of drift.

Conventional polymer drift control agents are function by increasing the extensional viscosity of the spray liquid, enabling it to resist disruption as it emerges from the spray nozzle, leading to an increase in the median droplet diameter of the spray droplets. It is clear when conventional polymer based DRT is added into the tank, the liquid spray remains as a coherent sheet farther down of the nozzle exit before breaking up into smaller droplets.   Oil emulsion based DRT products which are widely available in the market today do not significantly change the length of the coherent spray sheet, but have greater impact on the perforation of the sheet.

The current presentation tries to classify the various DRT products based on its chemistry and mechanism and to share an overview for their applications with agro chemicals.



Applying herbicides in mixtures has been a common practice for both soil- and foliar-active herbicides to generally broaden the spectrum of weed species controlled in a single application or improve the consistency of weed control.  Herbicide combinations are also a critical component of Best Management Practices to delay the evolution of herbicide-resistant weed biotypes or to manage existing herbicide-resistant weeds.  In fact, analysis of field data and modeling would support the practice of applying herbicide mixtures representing different site of action groups to reduce the selection pressure for herbicide resistance as being more effective than alternatives such as rotating herbicide sites of action annually.

One of the greatest challenges in applying herbicide mixtures, especially foliar-active herbicides, is the potential for an interaction between the individual herbicides on target and non-target plant species.  The three types of plant responses from an herbicide mixture includes antagonism, additive, and synergism in which the resulting plant efficacy is less, equal, or greater, respectively, than predicted by a reference model from the herbicides applied individually.  An overall decrease in herbicide efficacy from an antagonistic herbicide interaction may result in reduced weed control.  Herbicide synergism may result in excessive crop injury from a postemergence application of an herbicide mixture.  These interactions may be the product of chemical, biochemical, or physiological mechanisms associated with the herbicide chemistry, factors associated with the spray solution, or the physiological plant response to the individual herbicide mode(s) of action.

An abundance of research has been conducted on herbicide interactions over the past 50 years with several models proposed for the research methods and data analysis, drawing some comparisons to similar research pertaining to pharmaceuticals.  The most common plant response to herbicide mixtures has been additive which suggests independent herbicide activity, yet considered to be cooperative action on the plant.  This classification has typically been determined if the observed plant response for the mixture is neither greater nor less than predicted by a reference model.  Herbicide antagonism would be the second most common response which is a joint action of the herbicides resulting in less overall herbicide efficacy than predicted.  Herbicide synergism has been reported as the least common plant response to foliar herbicide combinations and results in greater overall herbicide efficacy than predicted.

Multiple reviews of the literature have described different facets of herbicide interactions depending on the objectives of the author(s), but generally have considered the experimental design and data analysis or focused more on herbicide synergism or antagonism.  Recent concerns in herbicide labeling and environmental stewardship have projected a greater emphasis on understanding the potential effect of herbicide mixtures on off-target plant species.  Risk assessment models incorporate the potential effect of individual herbicides and don’t account for the potential effect of herbicides combined in tank-mixture by the applicator if they result in an overall increase in herbicide efficacy.  Using Colby’s method as common reference model for classifying herbicide interactions, an additive or synergistic herbicide response could both result in greater herbicide efficacy than either herbicide applied alone.  Furthermore, even an antagonistic herbicide mixture could result in herbicide efficacy that is less than predicted, yet greater than each herbicide applied individually.  Thus, all three of these plant responses to herbicide mixtures may be of potential interest in assessing environmental impact.  The discrepancy in the literature for the research methods, experimental design, reference models, and classification of herbicide mixtures into the three categories of antagonism, additive, and synergism creates inconsistencies for interpreting the results.  Therefore, a review of the peer-review scientific literature in refereed journals was conducted to categorize research on foliar herbicide mixtures.  Documents that are not peer-reviewed or refereed such as patents or graduate student dissertations were not considered for this review.  Plant responses to herbicide mixtures that resulted in greater herbicide efficacy than either herbicide applied individually were the focus of the review.  This analysis will be presented in more detail to gain focus on the potential environmental impact of foliar herbicide mixtures and to derive any common trends and explanations for plant responses across herbicide active ingredients, herbicide chemical families, herbicide site of action groups, and target plant groups.




MEETING THE CHALLENGE: HOW DO WE MOVE FORWARD? M. Barrett*; University of Kentucky, Lexington, KY (248)




Time of day and temperature influence Palmer amaranth efficacy with glufosinate

Drake Copeland*

W.J. Everman

North Carolina State University

Raleigh, North Carolina


Time of glufosinate application has a large impact on weed control. Previous researchers have documented that both temperature and relative humidity also affect the activity of glufosinate. However, research is lacking on the role relative humidity has on time of day (TOD) effect of glufosinate efficacy on Palmer amaranth. Experiments were established to determine how relative humidity impacts the TOD effect of glufosinate at different temperature regimes.

Studies were conducted at the North Carolina State University Phytotron. Plants were grown in a growth chamber with 14 hour photoperiod ending at 9:30 pm light was set at 26/22 C with ambient relative humidity and transferred to a growth chamber 3 days prior to glufosinate application. Plants were transferred to growth chambers with 14 hour photoperiod ending at 9:30 pm set at 14, 26 or 34 C. Each temperature regime was split with two levels of relative humidity; 30 or 90%. A CO2 powered backpack sprayer, calibrated to deliver 140 L ha-1 was used to apply glufosinate at 160 g a.i. ha-1 to 8 cm tall plants at 2 and 10 pm. Treatments were arranged in a factorial arrangement and were replicated six times Percent control and plant heights were recorded both 4 and 7 days after treatments (DAT). Fresh shoot biomass was recorded 7 DAT.

Control of Palmer amaranth 4 DAT of glufosinate at the 2 pm application timing in 26C, 90%RH conditions (92%) resulted in significantly greater control than all other treatments. The TOD effect was observed for all treatments, with respect to control 4 DAT, with the exception of 26C, 30%RH condition where no difference in control was observed between 2 (24%) or 10 pm (20%) application timings. Plant height reductions 4 DAT were greater when glufosinate was applied in 26 and 34 C, 90% RH conditions compared to both 26 and 34C at 30% RH conditions (29 and 39% versus 14 and 11%, respectively). However, height reductions 4 DAT when glufosinate was applied in 14 C, 90% RH condition (15%) were similar to 14 C, 30% RH condition (9%). The time of day effect was observed for both 14C and 34C, regardless of relative humidity level, where control 7 DAT was greater when glufosinate was applied at 2 pm versus 10 pm. However, control 7 DAT was similar in 26C, 90% RH conditions when glufosinate was applied at 2 pm (99%) and 10 pm (93%). It may be possible that the TOD effect on glufosinate efficacy can be minimized if relative humidity is at an elevated level at a suitable temperature. This will be investigated in further experiments.


CONTROLLING PPO-RESISTANT PALMER AMARANTH USING PREEMERGENCE HERBICIDES. T. A. Reinhardt*, D. Copeland, W. J. Everman; North Carolina State University, Raleigh, NC (250)


Palmer amaranth (Amaranthus palmeri) is a troublesome weed for soybean growers in North Carolina. In effort to manage resistant or potentially resistant populations of weeds, soybean growers have been reconsidering residual preemergence herbicides. Several options are available from various companies, and while general efficacy evaluations are available for these herbicides, few studies have offered quantitative measurements comparing these products side by side. At two locations with similar soil type but with different levels of Palmer amaranth infestation, 17 herbicides, including 8 unique modes of action and 7 common premixes, were evaluated for crop injury and herbicide efficacy at 4, 6, and 8 weeks after planting. At the site with lower level of Palmer amaranth at 6 and 8 weeks after planting, all tested herbicides had control similar to weed-free plot except Prowl, Scepter, and Clarity. At the site with high level of Palmer amaranth, products containing a single mode of action resulted in higher number of plants and dry biomass than premix products. While this is only one year of data reporting currently, these results support the use of multiple mode of action products and will aid in grower decisions when comparing efficacy of different modes of action and combination products on Palmer amaranth in the future. 

PPO-RESISTANT PALMER AMARANTH: WHAT WE HAVE LEARNED AFTER ONE YEAR OF ON-FARM RESEARCH IN ARKANSAS. T. Barber*1, J. K. Norsworthy2, R. Scott3; 1University of Arkansas, Little Rock, AR, 2University of Arkansas, Fayetteville, AR, 3University of Arkansas-Cooperative Extension Service, Lonoke, AR (251)


Palmer amaranth exhibiting resistance to protoporphyrinogen oxidase inhibiting (PPO) herbicides was first identified in Arkansas in 2014. In 2015 increased state-wide sampling of Palmer amaranth populations revealed that resistance had quickly spread to 15 counties across the state, with 50% of Palmer amaranth populations in Northeast Arkansas testing positive for PPO resistance.   Due to the widespread increase in PPO resistance, on-farm locations for small plot research were identified prior to the 2016 growing season.  Trials were conducted in Gregory, Crawfordsville and Marion, Arkansas to determine the effect of common herbicides when applied both preemergence and postemergence on PPO-resistant populations.  Additionally studies were conducted to determine the most effective herbicide or herbicide combination for control of PPO-resistant Palmer amaranth in Roundup Ready, Liberty Link, Enlist and Xtend soybean technology systems.  For the first objective, bare soil plots that measured 1.9m by 3m were sprayed bare ground for preemergence evaluation and on 5 to 8cm Palmer amaranth for postemergence evaluation.  Plots were sprayed with a backpack sprayer calibrated to deliver 140 L/ha.  For a second objective, plots were arranged in a randomized complete block design with four replications.  Four rows of Roundup Ready, Liberty Link, Enlist or Xtend soybean were planted in a 3.86m by 9m plot. Twenty-six herbicide comparisons were applied preemergence to all four soybean technologies.  Preemergence herbicide programs were combined for analysis at 28 days after treatment (DAT) across all 10 trials.  Effect of postemergence programs were analyzed by technology and included 3 trials for Roundup Ready and Liberty Link technology and 2 trials each for Enlist and Xtend technologies.    Postemergence programs within each technology system were applied at 28 DAT and included: Roundup + Prefix for Roundup Ready; Liberty + Prefix (2 locations) and Liberty + Prefix followed by (fb) Liberty (1 location) for Liberty Link technology; Engenia (1 site) and Engenia fb Engenia (1 site) for Xtend technology; and Enlist Duo + Dual Magnum (2 locations) for Enlist technology.  Results from bare ground preemerge studies at 14 DAT indicate that the photosystem II inhibiting herbicides (group 7) such as atrazine and metribuzin provided the best PPO-resistant Palmer amaranth control (90%) at 14 DAT. Group 15 herbicides such as metolachlor and pyroxasulfone provided less control (68%) and treatments containing PPO herbicides such as flumioxazin only provided 50% control at 14 DAT.  Postemergence control of PPO-resistant Palmer amaranth was not greater than 60% with any PPO herbicide applied, but adequate (>90%) control was attained at 19 DAT with atrazine, diuron, paraquat and glufosinate.   When preemergence herbicides were combined in the program trials, an increase in overall control of PPO-resistant Palmer amaranth was achieved.  Combinations of pyroxasulfone + metribuzin or metolachlor + metribuzin provided >85% control at 28 DAT.  Postemergence programs in any technology were not found to be successful in controlling PPO-resistant Palmer amaranth if a robust preemerge program was not used encompassing 2 effective modes of action.  Liberty Link programs provided the highest level of PPO-resistant Palmer amaranth control (81%) followed by Enlist (79%), Xtend (75%) and Roundup systems (55%) when data were analyzed over all 26 preemergence treatments.  However, acceptable control can be achieved in Liberty Link, Enlist and Xtend technologies if a robust (multiple mode of action) preemergence program is utilized and effective postemergence herbicides are applied timely. 

A SURVEY OF BMP ADOPTION FOR RESISTANCE MANAGEMENT IN U.S. ROW CROPS. J. K. Norsworthy*1, M. Owen2, J. Gunsolus3, W. J. Everman4, D. E. Ervin5, G. Frisvold6, T. Hurley7, R. Jussaume8, S. Welcher9; 1University of Arkansas, Fayetteville, AR, 2Iowa State University, Ames, IA, 3University of Minnesota, St. Paul, MN, 4North Carolina State University, Raleigh, NC, 5Portland State University, Portland, OR, 6University of Arizona, Tucson, AZ, 7University of Minnesota, St Paul, MN, 8Michigan State University, East Lansing, MI, 9USDA, Beltsville, MD (252)


While most weed scientists readily agree on the strategies to mitigate the evolution of herbicide-resistant weeds, the level of understanding and adoption of these best management practices (BMPs) differs greatly among growers.  Overall, herbicide resistance in the US continues to increase at an alarming rate, with many weeds having evolved multiple resistances to four or more mechanisms of action, thus greatly limiting herbicide options.  In some row crops, producers have as few as one effective postemergence mechanism of action for weed control.  Adoption of BMPs must increase across the landscape if the precious herbicide resources that are still effective today are to be conserved for an extended period. 

Interviews with growers who participated in 10 focus groups in Iowa, Minnesota, Arkansas, and North Carolina in 2015, provided insights about farmer perceptions and management of herbicide-resistant weeds.  Subsequently, a national survey was constructed based on themes from the focus groups and administered in 2016 to measure the level of adoption of herbicide-resistance management strategies in US row crops.  One goal of this process was to identify important drivers, impediments, and perceptions influencing growers’ weed and herbicide-resistant management decisions as well as identify educational programs, incentives, and institutional innovations that could speed the adoption of BMPs for herbicide resistance management. 

Based on the focus groups and the survey, farmers continue to value simplicity and ease of operation, and maintain optimism that herbicide discovery will soon lead to new highly effective chemistries that will solve most of their current weed management challenges; albeit, growers in Northern states were generally more optimistic than those in Southern states.  Growers reported a high knowledge and awareness of herbicide resistance, with chemical control preferred over cultural and mechanical practices.  The development of herbicides was perceived as the solution to herbicide resistance, and most farmers felt that government should not be involved in herbicide resistance management.  However, farmers generally did recognize that weeds would continue to evolve resistance to new herbicides.  While community-based weed control has been practiced successfully in a few areas of the US, farmers were generally of the opinion that they would not directly speak to neighbors about their failure to control weeds.  Farmers did not individually take ownership of herbicide resistance, but rather thought it the fault of others.

Horseweed (marestail), Palmer amaranth, and waterhemp were the three most difficult-to-control weeds on US farms over the past two years.  Growers perceived weed pressure from these and other weeds to be greatest along field borders.  However, current federal regulations may create greater weed infestations near the field border because of extended herbicide buffers into the field in new herbicide-resistant genetically engineered crops.  A majority of growers surveyed (79%) had tried at some point to eliminate weeds on land boarding their farming operations.

Growers that are unaware of herbicide-resistant weeds on their farms were less likely to use a preemergence herbicide, herbicide mixtures, multiple herbicides, and altered planting dates than growers aware of multiple herbicide-resistant weeds.  Some of the BMPs not used by growers on any portion of their land include weed maps (78% of fields), inter-row cultivation (71% of fields), cover crops/mulches (56% of fields), and altered planting date (56% of fields).  The presence of a weed with multiple herbicide resistances vs the absence of any weed with resistance did not seem to affect the adoption of inter-row cultivation, tillage, crop rotation, use of postemergence and post-harvest herbicides, and full labeled herbicide rates.

Based on this survey, our focus groups, and other anecdotal evidence, it is our opinion that most growers are not lacking in awareness of herbicide-resistant weeds, and many are knowledgeable about strategies that can be used to mitigate the evolution of herbicide resistance.  However, they do not fully understand herbicide mechanisms of action, which at times makes herbicide resistance management challenging.  All individuals involved in education, including the popular press, must make an asserted effort to ensure that there is coherent messaging about herbicide-resistant weed management, and discussions among grower groups, academics, industry, and federal agencies must continue if a resolution of this problem is to be addressed in an effective manner.




How far is Argentina from managing herbicide resistant weeds compared to USA and Australia?


Weed resistance is the major problem that almost every farmer worldwide faces. Scientists are fighting a tremendous battle to stop it, with many resources, which go from the well-known chemical options to the most modern tools like cover crop or harvest weed seed bank management. In the whole frame of options, every country shows differences, depending on the possibilities they have to adopt one or more technologies. Communication among countries will be very helpful to increase knowledge, and therefore to contribute in reducing and managing cases.


Argentina´s crop area increased since RR® crop introduction in 1996 from 8 million to 31 million ha-1 by 2015. The USA has 130 mill ha-1 and Australia a total of cropland close to 25 mill ha-1. Cropping culture is not the same along these countries but weed resistance cases are common in both Argentina and USA summer crops, mainly waterhemp and palmer amaranth, among others. Australia's production is based on winter crops like wheat. Argentina is also a worldwide wheat supplier. A common weed, ryegrass, developed herbicide resistance in these two countries as well as in the USA's wheat production area. Australia is facing multiple resistant cases for this weed, and that is telling us that other countries will soon have the same issue if they rely just on herbicides.

Each country is developing many strategies to give a longer life to the available chemical options. The exchange of information among countries with common weed-like scenarios appears to be a good option to help in the delay of weed resistance.

The US is facing the problem with a huge multi-tasking force and on some occasions, the different States join forces thru cooperative field research and media awareness. Universities and the USDA-ARS are taking the lead in researching new strategies, where GMO´s, cover crops, and recently harvest weed seed management are studied.

Australia has changed its weed resistant status in the last twenty years, shifting what appeared to be an irreversible issue into a manageable one. Big scale research in farms between Universities and farmers lead them to develop many harvest seed strategies which gives an extremely valuable key tool for IWM preventing seed banks to grow year after year. In addition, they also provide growers with pot testing for multiple herbicide resistance in Ryegrass among other species, giving them the chance to know how many herbicides they can still rely on because of ryegrass multiple resistance.

As a relevant worldwide food supplier Argentina, is managing the issue with a reduced budget compared to the other two countries but still with a great commitment in Ag sustainability given the long-term no-till farming history that covers almost 90% of the cropland. A vast cover crop research plan is taking place with excellent results for summer crops as well as cultural practices related to weed emergency patterns, planting date, crop density and row spacing.

In order to look comparatively at the weed management and actions done by the cited countries, an easy to read scale was developed to provide with actual status information in various issues related to IWM.

IWM alternative tools to chemistry are fortunately increasing. Some of them, as cover crops, row spacing, and harvest weed seed management are the “new ones”, and the timing of the adoption of each technology differs in each of the countries analyzed. In addition, the industry is proactive in the development of new traits for herbicide crop tolerance, stacking more than one mode of action chemistry in soybeans, corn and cotton.

In order to categorize the main techniques suggested to manage weed resistance, a list with the main ones was put together in order to compare what situation is being adopted by each country.

The main idea of this information is not precisely to make a sort of country “challenge” but to provide rich information to other countries, or States within a country, to compare themselves to what others do, and what can be expected in the near future if one or more of these techniques are not yet being implemented.

Lack of budget appears to be one of the main reasons to adopt some of these technologies for Argentina, while different crop cultures can be delaying the implementation of others like harvest seed bank management, which was developed in Australia but is recently being tested for different weed seeds in USA.

In comparison, Australia has not yet lost glyphosate as an option because their main crops are not Glyphosate resistant (except for rapeseed) as US and Argentina's are, and therefore, they are making the effort to preserve that tool while Dims and Fops are their main problems.

Because of their similarities in weed resistance cases, these three countries were chosen rather than in how they manage them. Worldwide communication will be of great help to reduce the risk of this threatening issue increasing, and by trying to be ahead of it instead of following it.



Key words: herbicide resistance, cover crops, harvest weed seed bank, row spacing, crop density, communication. 


SOCIO-ECONOMIC FACTORS AFFECTING FARMER USE OF WEED BEST MANAGEMENT PRACTICES. G. Frisvold*1, D. E. Ervin2, W. J. Everman3, J. Gunsolus4, T. Hurley5, R. Jussaume6, J. K. Norsworthy7, M. Owen8, K. Dentzman6; 1University of Arizona, Tucson, AZ, 2Portland State University, Portland, OR, 3North Carolina State University, Raleigh, NC, 4University of Minnesota, St. Paul, MN, 5University of Minnesota, St Paul, MN, 6Michigan State University, East Lansing, MI, 7University of Arkansas, Fayetteville, AR, 8Iowa State University, Ames, IA (254)


Herbicides have been the predominant method for controlling weeds in U.S. crop production for more than half a 
century. Initially, as weeds developed resistance to one herbicide site of action due to repeated and wide spread 
use, a new site of action was discovered to address the herbicide resistance weed problem. More recently 
however, farmers have turned to herbicide tolerant crops that make it possible to use herbicides with a broader 
spectrum of control in crops where these herbicides could not have been used previously.  The emergence of 
glyphosate resistant weeds over the past decade reminds us that any herbicides or herbicide-tolerant crop is at 
best a temporary solution to the weed management problem. While weed scientists have promoted a more 
diverse set of weed management practices that include cultural and mechanical in addition to chemical tactics, 
farmer adoption has been low.
The objective of this research was to identify what factors are most strongly associated with a farmer’s use of a 
range of herbicide, mechanical and cultural weed management tactics. This objective was accomplished using 
2016 farmer survey data and multivariate regression analysis. Farmers from 28 predominately corn, cotton, and 
soybean producing states were surveyed. Reduced form regression equations were jointly estimated using a 
conditional mixed process model. Multiple model specifications with and without state level fixed effects were 
estimated to confirm the robustness of the results. The contribution of the research is the broader behavioral as 
well as economic perspective it takes to understand farmers’ weed management decisions when compared to 
previous literature. The benefit of taking this broader perspective is the opportunity to identify novel pathways 
for encouraging farmers to proactively manage herbicide resistance with more diverse management tactics.  
The weed management tactics explored include the use of inter-row cultivation, tillage, hand weeding, mulches, 
pre-emergence herbicides, post-emergence herbicides, post-harvest herbicides, crop rotation, crop planting 
population densities, planting dates, row widths, and weed maps. As one would expect from economic theory, 
our preliminary results show that risk and time preferences were significantly associated with a farmer’s decision 
to use alternative weed management tactics. Interestingly, we also found a consistent attenuating interaction 
between risk and time preferences in relation to weed management decisions. Farm operations with greater income 
were associated with significantly higher pre- and post-emergence herbicide use. Farmers that were more 
concerned that herbicide-resistant weeds can spread from neighbors’ fields used a greater diversity of management 
tactics. Farmers who were optimistic that new herbicides would soon be available were significantly less likely to 
use multiple herbicides or rotate herbicide sites of action, both of which reduce the risk of herbicide-resistant weeds 
emerging. Farmers who report that human and environmental health concerns were important to their weed 
management decisions were significantly less likely to use the full labeled herbicide application rate, which points 
to an interesting tradeoff between the risk of herbicide-resistant weeds and human and environmental health risks. 
Farmers who reported that convenience, flexibility and saving time were important considerations for their weed 
management decisions were significantly less likely to use multiple herbicides, full labeled herbicide application 
rates, herbicide site of action rotations, and crop rotations; all which reduce the risk of herbicide-resistant weeds.  
This result suggests these non-monetary factors are likely one of the more important drivers of herbicide-resistant 
weeds. Costs appeared to be an important consideration that discourages farmer use of post-harvest herbicide 


RINSKORTM ACTIVE, A NOVEL HERBICIDE ALTERNATIVE FOR GLOBAL WEED CONTROL IN RICE. M. Morell*1, R. K. Mann1, N. M. Carranza2, N. Dalla Valle3, D. Le4, H. Perry5, O. Shevchuk6, M. Yadav7; 1Dow AgroSciences LLC, Indianapolis, IN, 2Dow AgroSciences, Ibague, Colombia, 3Dow AgroSciences, Bologna, Italy, 4Dow AgroSciences, Ho Chi Minh, Vietnam, 5Dow AgroSciences LLC, Greenville, MS, 6Dow AgroSciences, Valbonne, France, 7Dow AgroSciences, Mumbai, India (255)


RinskorTM Active, a Novel Herbicide Alternative for Global Weed Control in Rice

RinskorTM active (Florpyrauxifen-benzyl) is the newest arylpicolinate herbicide from Dow AgroSciences with global utility in water-seeded, dry direct-seeded and transplanted rice, and utility in many other crops.  Data from field trials conducted since 2010 (> 1200 trials in major rice growing regions around the world) demonstrates that Rinskor provides a unique and broad-spectrum of control, including important grass, sedge, and broadleaf weed species in rice.  Most common broad spectrum use rate is 30 g ai ha-1, which depends on use pattern and target species.  When used at anticipated label instructions, rice shows excellent tolerance, and no impact on yield has been observed.  Key species controlled within defined use patterns include: Echinochloa crus-galli; E. colona; Urochloa plantaginea; U. platyphylla; Cyperus difformis; C. iria; C. rotundus; Abutilon theophrasti; Aeschynomene spp.; Amaranthus spp.; Alisma plantago-aquatica; Ambrosia spp.; Chenopodium album; Conyza spp.; Heteranthera spp.; Ludwigia spp.; Eclipta alba; Monochoria vaginalis; Sagittaria trifolia; Sesbania exaltata; Ammannia spp.; Commelina spp.; Murdannia nudiflora and Xanthium strumarium.  As compared to other auxin chemotypes, Rinskor demonstrates novel characteristics in terms low use rates (30 g ai ha-1 or lower), very low volatility, rapid degradation in soil, low persistence in the environment, favorable toxicology and ecotoxicology profiles, and differentiated receptor binding at the molecular level.  Rinskor has demonstrated a unique spectrum of activity and the ability to control ALS-, ACCase-, propanil-, and quinclorac target site-resistant grass, sedge and broadleaf species. Dow AgroSciences is developing different Rinskor based formulations, including straight concepts and ready to use pre-mixes. Initial registrations are expected in 2017 – 2018 time frame.

™Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow.

™Rinskor is not registered at the time of this presentation. The information presented is intended to provide technical information only and is not an offer for sale.


PROVISIA (TM) RICE SYSTEM - NEW TECHNOLOGY FOR CONTROL OF RED RICE AND OTHER GRASSES. C. D. Youmans*1, S. Tan2, A. Rhodes3, J. Guice4, J. Schultz5, D. Westberg2; 1BASF Crop., Dyersburg, TN, 2BASF Corp., RTP, NC, 3BASF Corp., Madison, MS, 4BASF Corp., Winnesboro, LA, 5BASF Corp., North Little Rock, AR (256)




One primary justification for studying invasive species is to reduce the negative impacts they impose on our diverse ecosystems.  Therefore, invasion ecologists have long sought to measure and quantify the ecological impacts of invasive plant species in an attempt to help in making management decisions.  Importantly two distinctly different methodologies have been utilized to quantify the ecological impacts of invaders, observational and removals studies.  Observational studies compare invaded sites with uninvaded sites that have never been invaded.  Alternatively, removal studies compare an invaded site to a managed site where the invader has been removed.  Unfortunately, it is unclear if these two differing methodologies result in similar interpretations of impact.  We performed a meta-analysis of 174 studies describing 547 impacts of 72 invaders.  We tested the effect of study methodology, invader cover, and removal period on both the direction and magnitude of impact.  Generalizing over all studies, we found utilizing observational comparisons showed no invader impact while removal comparisons showed a net negative impact.  However, when study ecosystem, invader life form, and impact type were entered into the analysis the two methodologies yielded similar results.  When only impact magnitude was considered (i.e., directionality ignored), again, we saw similar results between the two methodologies, suggesting the differences we saw were the result of impact directionality.  Additionally, impact magnitude also increased with increasing invader cover and increasing length of removal period (for removal studies).  We conclude that considering impact magnitude, not direction, is more important, however, it is unclear whether removal and observational studies can be used interchangeably.  


DIFFERING IMPACTS OF CO2 AND DROUGHT DUE TO COMPETITIVE INTERACTIONS BETWEEN ANNUAL AND PERENNIAL GRASS. L. J. Rew*1, C. Larson1, E. A. Lehnhoff2; 1Montana State University, Bozeman, MT, 2New Mexico State University, Las Cruces, NM (258)


Global climate change, including elevated atmospheric CO2 concentrations, increases in global surface temperatures and altered precipitation patterns have significant consequences for global plant communities. The invasive annual grass Bromus tectorum (cheatgrass), is expected to benefit from projected warmer and drier conditions, and elevated CO2 concentrations. We performed a replacement series experiment to determine whether warmer and drier conditions in conjunction with increased CO2 would increase B. tectorum’s competitiveness with an established native perennial grass, Pseudoroegneria spicata (bluebunch wheatgrass) in a controlled setting. The two grasses were sown in five density combinations, representing 0-1000 B. tectorum plants m-2. To be more representative of field conditions, P. spicata plants were established one month before sowing B. tectorum. The experiment was performed with two CO2 levels (400 and 800 ppm) and two water levels (representing local June precipitation and a reduction of 50%) within growth chambers set at 25-8 °C day-night temperatures. The experiment was conducted for ~10 weeks and replicated twice. Interestingly, when both species were grown in monoculture they responded positively to the elevated CO2 treatment. However, when grown in competition, the elevated CO2 increased P. spicata’s already significant suppressive effect on the B. tectorum individuals. Furthermore, P. spicata benefitted the most from the elevated CO2 when the available soil moisture was reduced. The results suggest that under elevated levels of CO2, B. tectorum will not be highly invasive and dominate in range settings with robust native grass cover within the northern region of the sagebrush-steppe.


A CHRONO-GEOGRAPHICAL ASSESSMENT OF GLYPHOSATE RESISTANCE IN CANADIAN POPULATIONS OF CONYZA CANADENSIS L.. E. R. Page*1, C. Grainger2, F. Tardif2, I. Rajcan2, M. Laforest3, R. E. Nurse1; 1Agriculture and Agri-Food Canada, Harrow, ON, 2University of Guelph, Guelph, ON, 3Agriculture and Agri-Food Canada, Saint-Jean-sur-Richelieu, ON (259)


In the decade since the introduction of herbicide tolerant (HT) crops, an increasing number of weed species have been identified with resistance to the widely utilized herbicide, glyphosate. In the USA, there are now 14 weed species with confirmed resistance to the non-selective herbicides utilized in these systems. Similarly in Canada, there are 5 weed species that exhibit glyphosate resistance (GR); two of which were documented in the last year alone. Conyza canadensis has developed GR in both countries and its capacity for long-distance dispersal raises the potential of cross-border movement of herbicide resistant traits. The objective of this research was to examine the origins of GR C. canadensis populations from SW Ontario and explore their mechanism(s) of resistance. New and historic populations of C. canadensis collected throughout the counties comprising the most SW portion of the province of Ontario, as well as from bordering states of the USA. Eight microsatellite markers were used to characterize the relatedness of these populations and the target site gene for glyphosate (EPSPS2) was also sequenced. Dose-response studies were carried out to ascertain or confirm the resistance levels of the various populations. Results from the microsatellite and dose response studies indicate that the majority of Canadian GR populations are distinct from the American populations tested and exhibit notably higher resistance. Sequencing of EPSPS2 confirmed that, while GR in American populations is mediated by non-target site mechanisms, the predominate mechanism of resistance in Canadian populations of C. canadensis is target site mediated. These results represent the first report of target site mediate resistance to glyphosate in C. canadensis and clearly expose geographically distinct mechanisms of resistance to a given active ingredient on a regional scale within a single highly mobile species.



We determined the variation in herbicide resistance phenotype dynamics for a single dominant allele mechanism for an outcrossing species that arrives in a field. The expectation would be rapid increase of resistance based on all previous models. The range of resistance evolution outcomes was assessed under different assumptions about the initial distribution of individuals (dense vs dispersed) at introduction of resistance, different relative fitness of the resistant (R) and susceptible (S) phenotypes and efficacy of the herbicide on the susceptible phenotype. Resistance evolution in a weed population would be extremely rare (<0.0001 probability) with an introduction of a single mutant seed into a 9,000 seed population even under strong selection of the herbicide (efficacy on S= 85% and R = 5%). We ran all of our simulation experiments starting with 14 heterozygote (R) and 86 homozygous recessive (S) seeds introduced into a field and reported the proportion of R after 20 generations. The proportion of seed with R phenotype in the population with no herbicide applied and no assumed fitness difference was random. With no difference in relative fitness other than dispersal potential the proportion of resistance in the population was higher in initially dispersed versus dense populations. Increasing seed production potential (fitness) of R increased the proportion of R in the population and more for initially dense populations than for dispersed populations. When herbicide efficacy on the susceptible population was decreased below 70% the proportion of R in the population became increasingly less predictable. The most surprising results from our simulation experiments was the variability in R success regardless of its relative fitness or the strength of herbicide selection.


GLYPHOSATE-RESISTANT AND -SUSCEPTIBLE JUNGLERICE (ECHINOCHLOA COLONA) BIOTYPE RESPONSES TO TEMPERATURE AND SHADE. L. M. Sosnoskie*1, B. Hanson2; 1University of California, Davis, CA, 2Univesrity of California, Davis, CA (261)


Glyphosate is the principal herbicide applied in high-value tree nut and stone fruit production systems in California. However, growers’ reliance on glyphosate has not come without consequences. Currently, resistance to glyphosate has been confirmed in seven weed species common to California’s perennial cropping systems including junglerice (Echinochloa colona (L.) Link), an annual, C4 grass native to Africa and tropical Asia. Members of the genus Echinochloa have been shown to exhibit morphological and phenological variability, which can occur in response to changing environmental factors, including: temperature, CO2 concentration, moisture stress, salinity, photoperiod, and light quantity. The evolution of herbicide resistance may also effect weed growth and development; researchers have reported fitness costs associated with herbicide resistance in some weed populations, as compared to their susceptible counterparts, although this phenomenon is not universal. Between 2014 and 2016, experiments were conducted at UC Davis and CSU Fresno to describe the effects of temperature and shade treatments on the germination and development of glyphosate resistant (A8, H5, SV2) and susceptible (A3, C6) junglerice populations.

Junglerice seed were scarified in concentrated sulfuric acid for 30 minutes; 50 seeds of each biotype were placed in Petri dishes containing 7 mL of 0.2% Captan fungicide solution. Dishes were incubated at temperatures of 15, 20, 25, 30, 35, and 40 C for 2 weeks and the germination recorded, daily. All treatment combinations were replicated three times and the study repeated twice. Results from regression analyses (3 parameter peak model) determined that the most and most rapid germination occurred at temperatures between 30 and 32 C for all accessions. Additional seedlings of each biotype were transferred to growth chambers programmed to constant temperatures between 20 and 40 C, where the plants were grown for seven weeks. At that time, specimens were destructively harvested and the aboveground biomass separated into distinct tissue classes: stems, leaves, and inflorescences. All treatment combinations were replicated three times and the study repeated twice. Results from regression analyses (3 parameter peak model) estimated that the maximum number of basal stems, leaves, and inflorescences occurred at temperatures of 27-28 C, 29-33 C, and 21-30 C, respectively.

In the summer of 2015, two to three seedlings (at the three tiller stage) of each biotype were transplanted into field plots (1 m wide by 15 m long) that were exposed to either full sunlight (0% shade) or 30% and 60% shade environments. The shade treatments were established by covering entire plots with black, plastic fabric of differing mesh size on PVC frames. Plant growth and development was monitored for four weeks after which each specimen was destructively harvested. With few exceptions, junglerice plants were largest when gown in full sunlight. In general, tissue number and biomass (stem, leaf, panicle) decreased as the amount of transmitted light decreased. For example, tiller number per plant averaged between 79 and 134 at 0% shade; at 30% shade, tiller number ranged from 62 to 88 per plant; at 60% shade, the mean number of tillers per plant did not exceed 61. Similar observances were made with respect to leaf number and inflorescence production.

Results from our studies show that junglerice populations collected from the Central Valley of California can develop under a range of temperatures and light environments. At the same time, the results did not demonstrate any clear and consistent differences between the glyphosate resistant and susceptible junglerice biotypes with respect to germination and growth. While this suggests that the resistant junglerice biotypes did not possess an inherent competitive advantage over the susceptible ones, neither were they negatively impacted by the trait in the absence of glyphosate.


DIFFERENTIAL TOLERANCE OF A GLYPHOSATE-RESISTANT AND A -SUSCEPTIBLE TYPE OF JUNGLERICE (ECHINOCHLOA COLONA) TO ENVIRONMENTAL STRESSES AND INTER-SPECIFIC COMPETITION. A. Shrestha*1, L. L. de Souza1, R. Cox1, P. Yang1, K. M. Steinhauer1, S. Budhathoki1, L. M. Sosnoskie2, B. Hanson3; 1California State University, Fresno, CA, 2University of California, Davis, CA, 3Univesrity of California, Davis, CA (262)


Junglerice (Echinochloa colona) is problematic in annual and perennial cropping systems in California and has become an even greater challenge due to the evolution of glyphosate resistance in many populations. Studies were conducted in 2015 and 2016 in Fresno, CA to compare responses of a glyphosate-susceptible (GS) and a glyphosate-resistant (GR) population of junglerice to several environmental parameters. Seed germination was tested under water potentials (Ψ) ranging from 0 to −5.56 MPa and salinity from 0 to 25 ds m-1. Growth of the plants was tested under salinity levels ranging from 0 to 25 ds m-1. The glyphosate sensitivity of GS and GR plants acclimated to day/night temperatures of 15°/10°, 25°/20°, and 35° C/30° C was evaluated following an application of 840 g ae ha-1 of glyphosate. A replacement series experiment was conducted to evaluate the competitive abilities of GS and GR plants grown at 0:100, 25:75, 50:50, 75:25, and 100:0 ratios. Germination of the GS and GR populations differed at all level of moisture and salinity stress compared to the control treatments. Germination was reduced by 50% at -1.5 and -2.3 MPa, and 8.5 and 12 ds m-1 in the GS and GR types, respectively. Similarly total aboveground biomass of the GS and GR biotypes were reduced by 50% at 9 and 12 ds m-1, respectively. In the temperature study, none of the glyphosate-treated GS plants survived at any of the temperature regimes tested. Among the GR plants, all the treated plants survived in the 25°/20° and 35° C/30° C temperature treatments but the plants died in the 15°/10° C treatment, whereas the untreated control plants survived in this temperature regime. In the replacement series experiment, the GR plants had approximately 30% more biomass than the GS plants when grown alone and, when grown in a 50:50 ratio, the GR plants had approximately 75% more biomass than the GS plants. The GR biotype evaluated in these experiments had a greater ability to germinate under drier and more saline conditions and also grow better under higher salinity concentrations compared to the GS biotype. The GR biotype also accumulated more biomass and outcompeted the GS biotype when grown together. Although resistant at warmer temperatures, the GR biotype did not survive the glyphosate treatment with preconditioned with colder temperatures.

MANAGING GLYPHOSATE-RESISTANT COMMON RAGWEED (AMBROSIA ARTEMISIIFOLIA L.): EFFECT OF GLYPHOSATE-PHENOXY TANK-MIXES ON GROWTH, FECUNDITY AND SEED VIABILITY . J. Bae*1, R. E. Nurse1, M. Simard2, E. R. Page1; 1Agriculture and Agri-Food Canada, Harrow, ON, 2Agriculture and Agri-Food Canada, Saint-Jean-sur-Richelieu, QC (263)


Common ragweed (Ambrosia artemisiifolia L.) is one of the most important weeds in the soybean producing areas of the United States and Canada.  Recently, glyphosate resistant (GR) biotypes have been reported in 15 States and one Canadian province.  Reducing the proliferation of GR common ragweed biotypes is complicated by the high fecundity and complex seed germination behavior exhibited by this species.  An experiment was conducted to evaluate the efficacy of late herbicide applications for reducing seed production, seed weight and seed viability of a GR common ragweed biotype.  Herbicide treatments included: water control; glyphosate; 2,4-D; dicamba; 2,4-D plus glyphosate and dicamba plus glyphosate.  Treatments were applied at the appearance of male flower buds (BBCH 51) or at the early female flowering stage (BBCH 61 to 63).  At BBCH51, 2,4-D or dicamba applied alone or in a tank-mix with glyphosate reduced seed production by an average of 80%.  Conversely, seed production following these same treatments applied at BBCH61 to 63 was not significantly different from when glyphosate was applied alone.  At this stage of development, all herbicide treatments reduced seed viability relative to the control; however, treatments containing 2,4-D or dicamba had significantly lower viability than when glyphosate was applied alone.  These results suggest that the application of tank-mixes containing 2,4-D or dicamba have the potential to limit seed production of GR common ragweed when applied on or before BBCH 51.  The development of new technologies that facilitate the in-crop application of tank mixes containing 2,4-D or dicamba may therefore be an effective option for limiting population establishment, seed bank replenishment and future spread of  glyphosate resistant alleles.

CONFIRMATION AND CONTROL OF GLYPHOSATE RESISTANCE IN WEEDY SUNFLOWER (HELIANTHUS ANNUUS) IN TEXAS ROW CROPS. V. Singh*1, L. Etheredge2, J. McGinty3, G. D. Morgan1, M. V. Bagavathiannan1; 1Texas A&M University, College Station, TX, 2Monsanto, Llano, TX, 3Texas A&M University, Corpus Christi, TX (264)


Weedy sunflower (Helianthus annuus) is a problematic weed in row crop production in Southern Texas. This weed is highly sensitive to glyphosate and has been effectively controlled by over-the-top application of glyphosate in glyphosate-resistant crops. Growers in Texas have recently reported field control failure of certain weedy sunflower accessions with label rates of glyphosate. A total of eleven putative resistant weedy sunflower accessions collected from Southern Texas were evaluated during spring 2016. The accessions were grown in a growth chamber at 30/26 C day/night temperature regime and sprayed with 1X and 4X rates (1X = 860 g ae ha-1) of glyphosate at the 3-leaf growth stage. Survival and growth reductions were documented 21 days after treatment (DAT). Additionally, field experiments were conducted at two locations (College Station and Granger, TX) during the 2016 growing season to evaluate the effectiveness of different tank-mix herbicide combinations to control naturally infesting glyphosate-resistant weedy sunflower accessions in glyphosate-resistant corn fields. The treatments included 0.5X to 4X rates of glyphosate, and tank-mix combinations of glyphosate with AMS, atrazine, prosulfuron, halosulfuron methyl, premix of diflufenzapyr+dicamba, and a premix of halosulfuron methyl+dicamba. All treatments along with non-treated check were replicated three times. Plant survival ratings were carried out at 21 DAT on a scale of 0 to 100%, where 0% represented no injury and 100% indicated complete plant death. Evaluations conducted in the growth chamber has revealed that three of the eleven populations were resistant to glyphosate for up to 4X rate, exhibiting about 60% injury. In the field study, tank-mix applications of glyphosate + halosulfuron methyl, glyphosate + prosulfuron, glyphosate + a premix of halosulfuron methyl and dicamba, or glyphosate + a premix combination of diflufenzopyr and dicamba provided 100% control of glyphosate-resistant populations at 28 DAT. Tank-mix applications of glyphosate + atrazine, and glyphosate + AMS were inferior to glyphosate applied at 4X in controlling the weedy sunflower accessions (56, 60 and 89% injury, respectively). This is the first report of glyphosate resistance in weedy sunflower. Experiments are ongoing to understand the mechanism of resistance in these accessions.



THE IMPACT OF FIELD DEMONSTRATION PROGRAMS IN CHANGING FARMER THINKING AND BEHAVIOR FOR WEED RESISTANCE MANAGEMENT. H. J. Strek*1, G. Chancrin2, D. Kerlen3, H. Naunheim3, M. Verbiest4, R. Beffa1; 1Bayer CropScience AG, Frankfurt, Germany, 2Bayer S.A.S., Lyon, France, 3Bayer CropScience AG, Langenfeld, Germany, 4Bayer CropScience NV, Diegem, Belgium (265)


Experience has shown that it is extremely difficult to convince farmers to adopt integrated weed management measures before they encounter weed resistance problems in their own fields.  One of our most successful programs at Bayer has been the use of “platform studies” in several countries.  Their intent is to demonstrate the value of using Integrated Weed Management (IWM) strategies to manage weeds over multiple years, especially in fields with previous resistance problems, and thereby influence farmers to adopt them.  The presentation will showcase our cooperative approach with countries in tackling this issue.  These studies are valued as demonstration platforms to attract farmers and dealers to the site and show them the effectiveness and economic value of integrated tactics.  These studies are supported by comprehensive analyses of field samples by the Weed Resistance Competence Center (WRCC) in Frankfurt to provide the initial resistance profile and to highlight structural changes in resistance over time under the different management programs.  Information showing the effectiveness of this approach with visitors to these field demonstration programs will be presented.

WEED MANAGEMENT IN LETTUCE: WHY HERBICIDE RESISTANT WEEDS ARE A NONISSUE. S. A. Fennimore*; University of California Davis, Salinas, CA (266)


Weed management in lettuce is a complex, integrated multi-tactic system, and herbicides are just one of many weed control tools used in lettuce. California’s seasonally dry weather and the ability to control soil moisture with irrigation allows for effective use of cultural and physical control practices like stale seedbeds and inter-row cultivation. There are layers of redundancy in the weed management system that include: field selection, sanitation, crop rotation, land preparation, stale seedbeds, herbicides, and physical weed control. Growers that carefully follow these practices are able to successfully control weeds and reduce weed seed in soil seedbanks.

Lettuce is nearly always grown on fields selected for low weed pressure so that weed control operations can be more efficient and economical. For example, perennial weeds like field bindweed are controlled during fallow periods with translocated herbicides to reduce the population to manageable levels. Growers often rely upon keeping vegetable fields and surrounding areas as weed-free as possible to prevent weeds from going to seed in and around the field. Some operations utilize “zero weed seed” philosophy and have successfully reduced weed pressure in subsequent vegetable crops by eliminating inputs to the weed seedbank. Other measures include the prevention of weed seed dispersal by cleaning all field equipment.  Lettuce is also grown in rotation with crops that have very effective weed control programs like celery and strawberry, which help to keep the field clean of weeds. The constantly changing conditions that occur as the field is rotated from crop to crop allow no one weed species to become predominant.

Direct-seeded vegetable crops require well-prepared seedbeds free of large clods, which facilitate precision planting, and allows rapid and uniform emergence of vegetable seedlings. Smooth seedbeds facilitate mechanical cultivation close to the crop row. Increasingly, growers are using automated guidance systems that improve the speed and accuracy of cultivation.  Preirrigation before final seedbed preparation stimulates a weed flush a few days after watering. As soon as the weeds have emerged and the field is dry enough to enter, shallow cultivation, flaming, or use of a nonselective herbicide such as glyphosate are used to remove the initial flush of weeds. Research has shown that this technique provides 15 to 50% weed control in crops like lettuce. The stale seedbed technique combined with herbicides, cultivation and hand weeding nearly always results in excellent weed control.

Vegetable growers make extensive use of physical weed control. Inter-row cultivation or shallow cultivation between the crop rows to control weeds is a very old but effective method of weed control that buries, cuts, or uproots weeds.  Hand weeding by workers with hoes is the last line in the defense of vegetable crops against weeds. Among the hoeing crew, human dexterity and depth perception allow careful weed removal from vegetable crops in the row and near the crop plant. Handweeding is also a very expensive method of weed control and can cost more than $378 ha-1 in conventional lettuce plantings; furthermore, this cost increases each year.

At time of lettuce seeding, soil active herbicides like pronamide are applied in 12.5 cm bands over the seedline leaving the rest of the area non-treated. There are few postemergence herbicides for lettuce and products like clethodim are seldom used. Given the diversity of the lettuce weed control program and extensive use of cultivation and hand weeding, the selection pressure of the herbicides on weeds is low.

Lack of a simple weed control program for vegetables is both a curse and a blessing. The curse comes from the need for so much hand weeding, which due to labor shortages and increasing age of the farmworkers may not be long-term sustainable. The blessing comes from the layers of effective tools built into the vegetable weed management system. The chance for development of herbicide resistant weeds is low for most vegetable crops. The technology for use of intelligent cultivators to remove weeds robotically from the intra-row space without herbicides is evolving; so there is reason for optimism that the development of herbicide resistant weeds in California vegetable fields will continue to remain low.

INFLUENCE OF WHEAT CROP PRODUCTION ON THE EFFICACY OF HARVEST WEED SEED CONTROL SYSTEMS. M. J. Walsh*1, J. Broster2, C. Aves3; 1University of Sydney, Narrabri, Australia, 2Charles Sturt University, Wagga Wagga, Australia, 3University of Melbourne, Dookie, Australia (267)


Influence of Wheat Crop Production on the Efficacy of Harvest Weed Seed Control Systems.

M. J. Walsh*1, J. Broster2, C. Aves3;

1University of Sydney, Narrabri, Australia, 2Charles Sturt University, Wagga Wagga, Australia, 3University of Melbourne, Dookie, Australia



Harvest weed seed control (HWSC) is an Australian innovation where systems have been developed specifically to target the weed seed bearing chaff fraction during crop harvest. Although necessitated by escalating frequencies of herbicide resistance in crop weeds, this approach to weed control was developed because of the opportunity to target weed seeds during crop harvest.  At crop maturity many annual weeds present retain high proportions of their total seed production at a height that ensures collection during harvest. However, the efficacy of HWSC does not always reflect the amount of seed retention. Specifically, for rigid ryegrass (Lolium rigidum) the retained seed may be present in the crop canopy at heights low enough to avoid collection during harvest. Therefore, the aim of this study was to examine the distribution of retained rigid ryegrass seed through the canopy of wheat (Triticum aestivum) crops at maturity. During the 2013 harvest period, rigid ryegrass and wheat plants were as collected at 5 heights (0, 10 20, 30, and 40cm) above the soil surface, within four 1.0m2 quadrats in 71 wheat fields at locations dispersed across the Australian wheat-belt. On average 75% of rigid ryegrass seed production was retained above a 10cm height. In the top one third yielding sites where the average grain yield was 5.3 t ha-1, 60% of seed was retained above 30cm. In contrast, in the bottom one third yielding sites where grain yields were 1.8 t ha-1, only 40% of seed production was retained above 30cm. Therefore, higher yielding, more competitive crops increased the average height of rigid ryegrass seed retention and consequently the potential efficacy of HWSC. Importantly, the competitive effects of higher yielding crops reduced seed production by 30% when compared with rigid ryegrass seed production on plants present in lower yielding wheat crops. Thus wheat crop competition had the dual effect of i) increasing susceptibility to HWSC and ii) reducing seed production of rigid ryegrass populations.



Efficacy of intra-row cultivation is often low and can be highly affected by multiple variables including cultivator speed, soil conditions, and weed size. Our objective was to determine if “stacking,” or using more than one cultivation tool per tractor pass, could result in an additive, or perhaps even synergistic increase in efficacy over a range of conditions. In 2016, we conducted two field experiments to determine the most effective of 14 tool combinations and sequences, using torsion weeders, finger weeders, and tine rakes. Cotyledon-staged condiment mustard was used as a surrogate weed and 2- to 5-leaf field corn was used as the test crop. Pre- and post-cultivation censuses were conducted in a 10 cm intra-row zone, and efficacy calculated as the percent difference between censuses. The most effective tool combination was later compared to each individual tool in three additional experiments in which we varied tractor speed (1.6, 4.8, 8.0, 11.2 km h-1), soil moisture (very dry, dry, moist, wet), and weed size (pre-emerged, cotyledon, 2-leaf, 4-leaf), respectively. The most effective configuration of tools was the torsion weeders followed by the finger weeders followed by the tine rake. The efficacy of this combination (88% in one trial, n = 4) was greater than was predicted by combining the efficacy of the three tools used individually, confirming a synergistic effect. Synergy was also observed in subsequent experiments as tractor speed, soil moisture, and weed size were varied. Unexpectedly, tractor speed had a minimal effect on cultivation efficacy. Soil moisture had a negative affect on efficacy of individual tools but less of an effect on the stacked combination. Increasing weed size generally had a negative effect on efficacy. Among all experiments, mean efficacy of the individual tools was 22% (n = 312), while mean efficacy of the stacked combination was 63% (n = 104), which is impressive given the often-suboptimal conditions. These results indicate that stacking intra-row cultivation tools may be used to increase efficacy over a range of conditions. Further testing, however, is required in a range of more sensitive crops as the aggressive settings used in our field corn test crop may have contributed to the observed effects.


FARMER PERSPECTIVES AND EXPECTATIONS: WHAT IS THOUGHT ABOUT HERBICIDE-RESISTANT WEED MANAGEMENT. M. D. Owen*1, W. J. Everman2, J. Gunsolus3, J. K. Norsworthy4, K. Dentzman5, G. Frisvold6, R. Jussaume5, T. Hurley3, S. Wechsler7; 1Iowa State University, Ames, IA, 2North Carolina State University, Raleigh, NC, 3University of Minnesota, St. Paul, MN, 4University of Arkansas, Fayetteville, AR, 5Michigan State University, East Lansing, MI, 6University of Arizonia, Tucson, AZ, 7USDA, Washington DC, MD (269)


The evolution of herbicide resistance in weeds has been a problem whenever and wherever herbicides are used but has become a major problem in row crop agriculture over the last two decades.  The problem was exacerbated by the way herbicide technologies have been used, particularly in crops with genetically engineered resistance to glyphosate.  Problems with evolved resistance to glyphosate, as well as other important herbicides, have been increasing at an increasing rate and approaches used by most farmers to manage these problems generally have not been effective.  Current farmer approaches typically include using more herbicides, applying them at higher rates and more often; these approaches will not resolve the herbicide resistance problems. Herbicide-resistant weed problems are not simple even though they have resulted from farmers focusing on simple, convenient and inexpensive control tactics.

Recent listening sessions and a survey initiated by a diverse group of scientist and funded by the United States Department of Agriculture (USDA AFRI grant 1002477) found that farmers differ regionally on how they view herbicide-resistant weed (HRW) problems and what they are willing to consider as options for management.  While all farmers, regardless of region, recognized the problem of herbicide resistance and were united in opposition to government interference with regard to regulatory approaches, farmers differed regionally with regard to their expectations of new herbicides and technological “fixes” to the problem.  Northern farmers felt that the industry was likely to develop new technologies while Southern farmers were skeptical.  Best management practices (BMP) were not regarded by most farmers as an effective approach to HRW management.  Indeed, many farmers felt “misuse” by farmers would result in the evolution in weed resistance to any new technologies.

Scientists involved in the AFRI project suggest that HRW are mobile across the landscape and thus represent a “common pool resource” problem.  Given this, individual farmer efforts are unlikely to result in successful and sustainable HRW management.  An approach that has demonstrated some success in managing common pool resource problems in agriculture is the establishment of community-based programs that involve farmer-leaders to address the problems across the landscape.  However, it is clear from farmer responses that this will be a difficult strategy to employ, given their reported unwillingness to communicate and act in coordination with neighbors.  Regardless, the approach involving farmer-organized and managed community-based HRW management programs are an important option to explore as a solution to the burgeoning problem with HRW evolution.  

 As “proof of concept”, three community-based HRW management programs have been proposed for Iowa; one program will address the unknown source for introduction of Amaranthus palmeri into a localized “community” in West-Central Iowa, another program will address the introduction of A. palmeri by the use of contaminated feed and forage in North-East Iowa dairy and cattle feeding communities, and a third program addressing the management of A. tuberculatus with multiple herbicide resistances in Story County, Iowa.  These community-based programs are under development in cooperation with the Iowa Department of Agriculture and Land Stewardship and the Iowa State University College of Agriculture and Land Stewardship.


THE ROLE OF FALL COVER CROPPING IN DIVERSIFYING WEED MANAGEMENT OF HORSEWEED IN CONSERVATION TILLAGE SYSTEMS. J. M. Wallace*1, W. Curran1, M. J. VanGessel2, D. A. Mortensen1, J. M. Bunchek1; 1Pennsylvania State University, University Park, PA, 2University of Delaware, Georgetown, DE (270)


Multi-tactic weed control strategies are needed to improve management of glyphosate resistant horseweed (Conyza canadensis [L.] Cronquist) in conservation tillage systems within the Northeastern United States. Current management recommendations include multiple herbicide sites of action in burndown programs and soil-applied residual herbicides to control later emerging horseweed cohorts. Integration of fall-planted cover crops has the potential to improve horseweed management through attenuation of germination cues, physical interference during the establishment phase, and through direct competition with emerged seedlings. Previous research has demonstrated that interactions among cover crop traits, growing season length and soil fertility can significantly impact the level winter annual weed suppression. Greater understanding of cover crop management practices are needed to optimize suppression of horseweed populations. Specifically, we are interested in cover cropping effects on horseweed populations at the time of typical burndown herbicide applications. We conducted field experiments to evaluate cover crop strategies for horseweed management in 2014-2015 and 2015-2016 at Penn State’s Russell E. Larson Agricultural Research Center (PSU-RELARC) in central PA and at University of Delaware’s Carvel Research and Education Center (UD-CREC) near Georgetown DE. Cover cropping treatments were evaluated following small grain production and were imposed as a RCBD with a split-plot and four replications. Main plots were cover crop treatments: no cover, cereal rye (134 kg ha-1), spring oats (134 kg ha-1), cereal rye + hairy vetch (67 + 22 kg ha-1), cereal rye + forage radish (67 + 6 kg ha-1), spring oats + hairy vetch (67 + 22 kg ha-1), and spring oats + forage radish (67 + 6 kg ha-1). Split-plots were fertility treatments: 0 or 67 kg N ac-1 using AMS. Cover crops were planted using a no-till grain drill on 19-cm row spacing following burndown and fertilizer applications in early September. Cover crops were terminated at the cereal rye boot stage (Zadok 45) using glyphosate + 2,4-D LVE (1.26 + 0.56 kg ha-1) and soybean was planted in 76-cm rows across the study. Prior to planting cover crops, locally-collected horseweed seed was distributed in permanently marked microplots (0.50 m2) at an average rate of 5,400 seeds m-2. Cover crop biomass (kg ha-1) and horseweed density and size were collected 10 weeks after planting (WAP) and at spring burndown. In 2015-16, two additional field studies were replicated at PSU-RELARC and UD-CREC using subsets of these cover crop treatments imposed as main-plots with split-plot evaluations of planting date (early: Sept 1-15 vs late: Oct 1-15), cover crop termination timing (boot vs heading stage of cereal rye), or herbicide programs (burndown only, burndown + soil-residual PRE, burndown + POST, burndown + PRE + POST). In these field studies, 44 kg N ha-1 was added at planting for early-planted treatments and as a top-dress application for late-planted treatments. Our results suggest that suppression of horseweed populations at the time of spring burndown application is strongly correlated to % cover and biomass accumulation of the cover crop measured in late fall. Population reductions exceeding 80% were observed when % cover was greater than 77% or when fall cover crop biomass was greater than 1,500 kg ha-1. Cereal rye was a common treatment across studies and years (n = 8), consistently reducing horseweed populations at spring burndown in comparison to the no cover treatment. Horseweed density was reduced from 57 to 99% in early planted treatments and 21 to 95% in late planted treatments. Nitrogen addition (0 vs 67 kg N ha-1) influenced the magnitude of population declines in early planted cereal rye in two out of three site years. In early planted treatments, cereal rye also decreased horseweed rosette size or height at the time of burndown applications.  Late-planted treatments did not consistently reduce horseweed size. We believe cover crop-weed competition may result in improved burndown efficacy as a result of reduced horseweed growth rates and/or vigor. Efficacy of the primary non-glyphosate burndown herbicides (dicamba, 2,4-D, saflufenacil) is dependent upon horseweed size, with greater efficacy occurring when horseweed rosettes are small. Future research will be conducted to determine if efficacy of burndown herbicides is negatively impacted by physical interference of cover crops.

NEIGHBOR AND COMMUNITY EFFECTS OF HERBICIDE RESISTANCE MANAGEMENT: A NATIONAL SURVEY OF FARM OPERATORS. D. E. Ervin*1, K. Dentzman2, W. J. Everman3, G. Frisvold4, J. Gunsolus5, R. Jussaume2, J. K. Norsworthy6, T. Hurley7, M. Owen8, S. Wechsler9; 1Portland State University, Portland, OR, 2Michigan State University, East Lansing, MI, 3North Carolina State University, Raleigh, NC, 4University of Arizona, Tucson, AZ, 5University of Minnesota, St. Paul, MN, 6University of Arkansas, Fayetteville, AR, 7University of Minnesota, St Paul, MN, 8Iowa State University, Ames, IA, 9U.S. Dept Agriculture, Washington, DC, DC (271)


Neighbor and Community Aspects of Herbicide Resistance Management: Insights from a National Survey

David Ervin, Elise Breshears, George Frisvold, Katherine Dentzman, Wesley Everman, Jeffrey Gunsolus, Terrance Hurley, Raymond Jussaume, Jason Norsworthy, Micheal Owen and Seth Wechsler

When herbicide-resistant weeds are mobile across farm boundaries, individual farmer actions are insufficient to effectively manage resistance.  A growing body of evidence indicates that weed mobility is more significant than previously thought.  Mobility can occur via pollen drift from herbicide-resistant weeds, seeds hitchhiking on machinery that travels between farms, counties, and states, movement by migratory birds and other animals, and even weed seeds floating down streams and rivers.  If herbicide resistance traits are mobile, the susceptibility of those weeds to herbicides becomes an open access resource shared by all operators in the affected community, i.e., a common pool resource.   In such cases, it is in the collective interest of farmers to delay resistance and to conserve the efficacy of an herbicide.  Yet, actions taken by individual farmers to conserve the usefulness of an herbicide cost both time and resources. Moreover, they are understandably minimized because farmers cannot be assured their neighbors will reciprocate.  Managing herbicide resistance, thus, becomes a community-wide problem – each farmer has an individual incentive to use the herbicide in the short run without considering the resultant effects on their neighbors in the long run.

A substantial body of theory and evidence has been devoted to finding approaches to manage and sustain common pool resources.  An early essay by Garrett Hardin in Science focused on the need for government or top-down regulation.  In contrast, the late Elinor Ostrom, 2009 Nobel Laureate in Economics, with colleagues around the world, argued that voluntary community-based approaches can be effective under certain conditions.  Their work documents the various requirements for privately led schemes to emerge and persist.  The following conditions must hold: 1) common pool resource users are aware of the effects of neighbors’ actions on their welfare, and 2) the users perceive a need for cooperation in controlling resource access.

In this presentation, we report multivariate statistical analyses of responses from the first national survey of farmers about their awareness of herbicide resistance and their perceived need for cooperative approaches with their neighbors.  Some recent survey data from Missouri indicate that farmers are willing to cooperate to control pests if simple local cooperative efforts are used rather than formal county-wide efforts.  This willingness is also consistent with the implementation of the Zero Tolerance herbicide-resistant Palmer amaranth (Amaranthus palmeri) control program in Clay County, Arkansas.  We add a national perspective to those results by examining the factors that are statistically associated with farmer awareness of interrelationships with their neighbors’ weed management as well as their reported receptivity to cooperative approaches across major crop production regions.  The findings give insights into which farmers are more likely to be first movers in such community-based approaches, and which are not.   



COVER CROPS FOR WEED SUPPRESSION IN KANSAS CROPPING SYSTEMS. A. Dille*, C. Ahlquist, D. E. Peterson; Kansas State University, Manhattan, KS (272)


Kansas’ farmers are demanding more information on how to include cover crops into their cropping systems to provide suppression of weeds, in addition to the other benefits provided by cover crops. Kansas’ cropping systems are very diverse and cover the west edge of the Corn Belt to the east edge of Central High Plains. Eastern Kansas commonly has row crops with short overwinter fallow periods, while western Kansas appears to be less intense with longer fallow periods.  No-tillage is a common practice for many fields.  This allows farmers in western Kansas to store more of the limited rainfall that occurs, from less than 450 mm in the west to more than 1150 mm in the southeast part of Kansas. This diversity of crops and cropping systems matches the diversity of key weed species of concern, with horseweed (Conyza canadensis) and waterhemp (Amaranthus tuberculatus) in the east, kochia (Kochia scoparia) throughout the west, and Palmer amaranth (Amaranthus palmeri) across the state, each with single or multiple herbicide-resistant populations. Many farmers across Kansas are experimenting with cover crops, leaving bare strips in order to assess the impact of cover crops on suppressing weeds in their fields. In general, to manage summer annuals such as Palmer amaranth and waterhemp, successful farmers established a cereal-based cover crop in early March and when terminated by end of May at the time of planting soybean, had significantly reduced weed biomass even if similar numbers of weed seedlings were present. These observations were substantiated in cover crop plots compared to no cover fallow plots in experiments at Hays and Colby, KS in 2016. At time of termination in late May, cereal-based cover crops reduced weed biomass by 97% compared to that in no cover fallow plots. If weed suppression with cover crops is to be successful, need to have fewer weed seedlings, and less biomass produced by time of cover crop termination. Other weed control practices need to be integrated with the use of cover crops, including residual herbicides, no-tillage production, and willingness for non-economic weed species to be managed in a different crop. In Kansas, problematic weed species are driving an interest in using cover crops in no-tillage cropping systems, especially in wheat stubble that is fallowed for several months before the next summer crop is planted. Substituting the expense of cover crop seeding and termination for one scheduled burndown chemical application appears to be an economically viable option for weed suppression.

COMMUNITY PARTICIPATION IN HERBICIDE RESISTANCE SURVEYING: A CASE STUDY IN CALIFORNIA RICE. W. B. Brim-DeForest*1, A. S. Godar2, A. J. Fischer2, K. Al-Khatib3; 1University of California, Yuba City, CA, 2University of California, Davis, Davis, CA, 3University of California Davis, Davis, CA (273)


The rice cropping system in California stretches over approximately 200,000 ha in the Sacramento Valley, and covers significant acreage in nine counties. It is primarily flooded, and there is little crop rotation, resulting in a weed management system that is dominated by herbicides. Further complicating weed management is the relatively few herbicide modes of action available with the majority of these herbicides belonging to the ALS-inhibitors. Herbicide resistance was first confirmed in CA rice in 1993 in smallflower umbrella sedge (Cyperus difformis L.) to an ALS-inhibitor, bensulfuron-methyl. As of 2016, resistance has been confirmed in nine species and to five modes of action, with several species resistant to multiple modes of action.

Since 2009, the University of California has provided a service to rice growers and Pest Control Advisers (PCAs), allowing them to submit seeds from weed species’ suspected to have herbicide resistance. Seed collections are made by growers or PCAs in the fall. The collected seeds are then treated to break dormancy (when appropriate). They are then grown in a greenhouse and subjected to a whole plant bioassay, screening with the field use rate of the recommended rice herbicides for that species. Growers and PCAs are then provided with a diagnosis of resistance and given recommendations of herbicides or modes of action to use for the following season. The number of species has grown over the years, from just two species when the program began, to seven species as of 2016.

We compiled seed submissions from 2012 to 2016 to gauge participation in the program. From 2012-2015, the submissions came from four or five of the nine rice-growing counties. In 2016, submissions came from eight of the nine rice-growing counties. The total number of samples submitted has been steadily increasing since the beginning of the program. In 2012, 23 samples from six species were submitted, and in 2016, the total number had iincreased to 117, also from six species. The increase may be due in part to increased extension efforts, but may also be due to spreading herbicide resistance. Smallflower umbrella sedge, sprangletop (Leptochloa fusca (L.) Kunth var. fascicularis (Lam.) N. Snow), and barnyardgrass (Echinochloa crus-galli (L.) Beauv.) submission numbers have been increasing since 2012, whereas ricefield bulrush (Schoenoplectus mucronatus (L.) Palla), early watergrass (E. oryzoides (Ard.) Fritsch) and late watergrass (E. oryzicola (Vasinger) Vasinger) submissions have remained relatively constant. Submittees were able to accurately identify resistance in the field in 100% of early watergrass samples, 96% of late watergrass samples, and 85% of barnyardgrass samples. Accuracy in identifying resistance in the sedges was also relatively high: 98% for smallflower umbrella sedge, and 73% for ricefield bulrush. Submittees were least accurate at identifying resistance in sprangletop, accurately identifying only 48% of submitted samples. This suggests that lack of control in sprangletop may be unrelated to herbicide resistance.


EVALUATION OF PRE- AND POST-EMERGENCE HERBICIDES FOR WEED CONTROL IN CASSAVA SYSTEMS. F. Ekeleme*1, A. Dixon2, S. Hauser3, G. Atser3, S. C. Weller4, H. Usman5, P. M. Olorunmaiye6, D. Korieocha7; 1International Institute of Tropical Agriculture, Ibadan, Germany, 2Internatiional Institute of Tropical Agriculture, Free Town, Sierra Leone, 3Internatiional Institute of Tropical Agriculture, Ibadan, Germany, 4Purdue University, West Lafayette, IN, 5University of Agriculture Makurdi, Makurdi, Germany, 6Federal University of Agriculture, Abeokuta, Germany, 7National Root Crops Research Institute, Umudike, Germany (274)


Cassava is an important root crop in sub-Saharan African where its cultivation is dominated by smallholder farmers. Weeds constitute a major impediment in cassava production. Although majority of farmers in Nigeria control weeds in cassava manually with simple tools such as hoes and machetes, the use of herbicides in weed control in cassava is becoming very important. Twelve pre- [sulfentrazone, prometryn + s-metolachlor, flumioxazin + pyroxasulfone, s-metolachlor + terbuthylazine, oxyfluorfen, aclonifen + isoxaflutole, indaziflam + isoxaflutole, diflufenican + flufenacet + flurtamone, s-metolachlor + atrazine, indaziflam + metribuzin, clomazone + pendimethalin] and four post- [lactofen, clethodim, trifloysulfuron-sodium, foramsulfuron-sodium + iodosulfuron-methly-sodium + thiencarbazone-methly, foramsulfuron + iodosulfuron-methly-sodium + isoxadifen-ethly) emergence herbicides with a hand weeded control without herbicides were evaluated in 2015. The trial was a split plot in randomized complete block design replicated 3 times in six locations covering the humid rainforest, derived and southern Guinea savanna agro-ecological zones in Nigeria.

Overall, pre-emergence herbicides had good (80-90%) to excellent (90 – 100%) control of Ageratum conyzoides, Calopogonium mucunoides, Centrosema pubescens, Chromolaena odorata, Corchorus tricularis, Desmodium scorpirus, Phyllanthus amarus, Solanum sp and Spermacoce ocymoides up to 8 weeks after treatment. Passiflora foetida and Ipomoea mauritiana were the most difficult weeds to control. Indaziflam + isoxaflutole, indaziflam + metribuzin, s-metolachlor + terbuthylazine, aclonifen + isoxaflutole and sulfentrazone provided > 90% control of these weeds up to 8 weeks after treatment.

Plots treated with prometryn + s-metolachlor, sulfentrazone, flumioxazin + pyroxasulfone, indaziflam + metribuzin and s-metolachlor + atrazine and received foramsulfuron-sodium + iodosulfuron-methly-sodium + thiencarbazone-methly as post-emergence had similar root yields [25.3 – 27.5 t/ha].

The results show that with appropriate herbicides, cassava root yield could be increased significantly above the national yields average of about 12 t/ha in Nigeria.






Environmental conditions in northwestern Wyoming are optimal for dry bean seed production. Weeds affect seed quality, therefore farmers try to reach harvest with clean fields in order to be certified. Late emerging weeds, such as Venice mallow (VM) interfere with harvest and affect quality. Field studies were conducted near Burlington, WY, to evaluate tank mixing lay-by treatments with post emergence applications to improve VM control late in the season. Pinto beans were planted at a population of 85,000 pl/a under furrow irrigation. EPTC (3 pt. /a) + dimethenamid-p (14 oz. /a) and EPTC (3 pt. /a) + ethalfluralin (2 pt. /a) were applied pre-plant incorporated (PPI) and followed by post emergence applications of imazamox (4 oz. /a) + bentazon (1.5 pt. /a) tank mixed with dimethenamid-p (7 and 14 oz. /a), and halosulfuron (0.66 oz. /a). Weed counts were recorded before post application, 15 days after treatment (DAT) and before harvest to determine treatment efficacy. Plots were inspected for seed certification previous to harvest. Venice mallow control with POST applications was determined by the combination of these treatments with the PPI treatment applied before planting. The majority of the treatments provided excellent Venice mallow control, with control levels ranging from 88 to 95%, for this reason a high percentage of plots were certified for seed production. Only when EPTC + dimethenamid-p were applied at PPI, and then followed by bentazon + imazamox + halosulfuron at POST, the percent of plots approved for certified seed was 37%.



Peanut production recommendations, based on long-standing research and grower experiences, discourage the use of cultivation for weed control.  Cultivation moves soil containing disease inoculum onto low-growing peanut plants increasing disease epidemics.  Weed management research has shown repeated cultivation with a tine weeder to be the focal point for cost-effective weed management in organic peanut.  During many organic peanut research trials, it was observed that disease epidemics were not problematic, which is inconsistent with conventional peanut production philosophy.  Structured research trials were conducted from 2012 through 2014 to determine if cultivation using a tine weeder affected disease incidence in organic peanut.  Treatments were a factorial arrangement of (a.) three levels of weed control, (b.) two levels of insect control, and (c.) three levels of disease control.  Weed control treatments were repeated cultivation with a tine weeder, weed-free using handweeding, and a non-cultivated (weedy) control.  Insect control treatments were two early-season applications of spinosad and a nontreated control.  Disease control treatments were bi-weekly applications of the conventional fungicide azoxystrobin, biweekly applications of copper plus sulfur, and a nontreated control.  The peanut cultivar GA-04S was planted each year of the study.  Compared to the non-cultivated control, cultivation with a tine weeder consistently reduced weed densities, but not enough to fully protect peanut yields from weed interference.  Spinosad applications provided no benefit.  Azoxystrobin controlled peanut diseases better than copper plus sulfur, but peanut yields did not respond to better disease control from the conventional fungicide.  There were no interactions among the main effects, indicating that intensive cultivation with a tine weeder does not increase disease epidemics and reduce peanut yield.  We speculate that ideal crop rotations to reduce disease inoculum and modern high-yielding peanut cultivars with improved disease tolerance are factors that allow the use of intensive cultivation with a tine weeder in organic peanut without increasing disease incidence.


MANAGING WEEDS IN INZEN SORGHUM:  A NEW TECHNOLOGY. C. R. Thompson*1, R. S. Currie2, P. W. Stahlman3; 1Kansas State University, Manhattan, KS, 2Kansas State University, Garden City, KS, 3Kansas State University, Hays, KS (277)


“Inzen” sorghum is the DuPont trade name assigned to sorghum hybrids containing a gene conferring resistance to the ALS inhibiting sulfonylurea grass herbicide nicosulfuron “Zest WDG”. The herbicide was registered for use in Inzen sorghum during 2016, thus this is new technology.  For the 2017 growing season, limited Inzen sorghum hybrids will be available.  This ALS resistant gene was transferred from shattercane (SORVU) through traditional breeding thus this sorghum is not a “GMO”.  Inzen sorghum hybrids are being developed by Advanta and Pioneer.  Experiments were established on Kansas State University Experiment Stations and Research Fields near Manhattan, Hutchinson, Garden City, Tribune, Hays, and Colby, KS to evaluate herbicide programs for Inzen sorghum that will manage annual grass and broadleaf weeds.  Inzen sorghum hybrid seeds, fluxofenim treated, were planted at all locations in 2014 and 2016.  In 2014, S-metolachlor & atrazine (1:1.292) at 2464 g ha-1 was applied to the soil surface post plant PRE emergence.  All post treatments were applied with nicosulfuron at 35 g ha-1, atrazine at 840 g ha-1, crop oil concentrate at 1% v/v, and spray grade ammonium sulfate at 2240 g ha-1.  This tank mix was POST applied alone or with pyrasulfotole & bromoxynil (1:5.65) at 235 g ha-1 , dicamba at 280 g ha-1,  2,4-D ester at 280 g ha-1 or with 2,4-D ester at 280 g ha-1 + metsulfuron at 2.1 g ha-1.  The POST applied tank mixes with pyrasulfotole & bromoxynil, dicamba, and 2,4-D ester at rates previously discussed were also used in a two pass system which followed soil applied S-metolachlor & atrazine at rates previous discussed. During 2016, S-metolachor & atrazine at 2464 g ha-1 was applied alone and applied to sorghum which was treated with the following POST applied treatments.  Nicosulfuron @ 25 g ha-1 + atrazine at 840 g ha-1 plus the adjuvant system discussed above.  A second and third treatment included the nicosulfuron + atrazine+ pyrasulfotole & bromoxynil at 234 g ha-1 or dicamba at 280 g ha-1.  The three previously discussed POST treatments were also applied to sorghum no treated with any PRE herbicides. Injury and weed control were evaluated visually.  No sorghum injury was observed from soil applied S-metolachlor & atrazine in either year.  When sorghum injury was rated within 7 days of the post applications, nicosulfuron caused sorghum chlorosis and rating ranged from 3 to 20% however chlorosis wasn’t evident 2 weeks after application. In 2014, Growth regulator herbicides caused typical to sever epinasty and tiller sprawling which declined over time to 0% at Colby, Hays, and Garden City. At Manhattan, Tribune, and Hutchinson when growth regulator tank mixes were applied to 12 to 15” sorghum, injury persisted at 4 to 17% 4 weeks after application. Similar injury was observed with dicamba tank mixes in 2016. The addition of COC and AMS likely increased sorghum response to treatments containing growth regulators. POST tank mixes with pyrasulfotole & bromoxynil caused leaf necrosis however, sorghum plants grew out of the injury over time.  This was generally observed at all locations in both years.  In some experiments, pyrasulfotole & bromoxynil antagonism control of certain annual grasses such as large crabgrass (DIGSA) The treatments containing POST nicosulfuron + atrazine + adjuvants controlled SORVU, conventional grain sorghum, giant foxtail (SETFA), green foxtail, (SETVI), barnyardgrass (ECHCG), witchgrass (PANCA) and volunteer wheat.  Annual grasses not adequately controlled with the nicosulfuron + atrazine treatment were DIGSA and stinkgrass (ERAME).  S-metolachlor & atrazine only provided very good control of all annual grasses if incorporated with rainfall except SORVU and volunteer wheat.  Two pass programs provided excellent control of all annual grasses evaluated.  S-metolachlor & atrazine provided excellent control of tumble pigweed (AMAAL) at Tribune and Hays and excellent Palmer amaranth (AMAPA) control at Manhattan and Hutchinson but inadequate AMAPA control at Garden City and Colby.  The two pass systems did provide 100% control of AMAPA at Garden City, Manhattan, and Hutchinson.  Post only treatments did not consistently control AMAPA or most annual grasses.  Nicosulfuron & atrazine alone provided only 65 to 80% control of AMAPA depending on location.  The addition of pyrasulfotole & bromoxynil provided 88 to 100% AMAPA control at Manhattan and Garden City but only 73 to 75% control at Colby and Hutchinson.  All treatments receiving a post applied herbicide provided better than 90% control of puncturevine (TRBTT).  Post treatments which included a growth regulator or pyrasulfotole & bromoxynil controlled velvetleaf (ABUTH) and hybrid sunflower (HELAN) 92 to 100%.  Two pass herbicide systems PRE followed by POST will be the most effective way to manage annual grass and broadleaf weeds in Inzen sorghum.



In 2016, Brake F16 and Brake FX were federally registered for preplant and preemergence applications in U.S. cotton. Each herbicide is a premix of the PDS-inhibitor fluridone with either the PPO-inhibitor fomesafen (Brake F16) or the PSII inhibitor fluometuron (Brake FX). PDS inhibiting herbicides are not currently used for weed control in cotton. Thus, the use of Brake herbicides may reduce selection pressure caused by repeated use of the same herbicide families. Brake F16 and Brake FX showed excellent cotton selectivity and control of annual grass and small seeded broadleaf weeds including Palmer amaranth (Amaranthus palmeri) across the cotton belt in 2016. Because of its longevity of control, herbicide programs that incorporate Brake as a foundational residual with a postemergence program, such as glufosinate plus s-metolachlor, could reduce the number of herbicide applications during the growing season.  Brake has also been very effective as a foundational residual in dicamba and 2,4-d systems.

PALMER AMARANTH (AMARANTHUS PALMERI) ADAPTATIONS TO CROPPING SYSTEMS: LOOKING BEYOND GLYPHOSATE-RESISTANCE. W. Bravo1, R. G. Leon*2, J. Ferrell1, M. Mulvaney2, W. Wood2; 1University of Florida, Gainesville, FL, 2University of Florida, Jay, FL (279)


Palmer amaranth (Amaranthus palmeri) adaptations to cropping systems: Looking beyond glyphosate-resistance. W. Bravo1 R.G. Leon*2, J.A. Ferrell1, M. Mulvaney2, and W. Wood2. 1University of Florida, Gainesville, FL 32611, 2University of Florida, Jay, FL 32565.


Palmer amaranth has become a very important weed in U.S. agriculture. Its rapid evolution to different herbicides, especially glyphosate, has played a major role in the success of this weed species. Although herbicide resistance evolution has been widely studied, adaptions in other traits that could favor weediness receive little attention. We hypothesized that despite high levels of gene flow Palmer amaranth populations have evolved life history traits to adapt to cropping systems. We compared morphological and growth traits of ten Palmer amaranth populations collected in Florida and Georgia from fields with different cropping histories. Palmer amaranth populations differed in multiple growth traits such as days to flowering, plant height, fresh and dry weight, and leaf and canopy shape. Glyphosate-resistant (GR) populations collected from cropping systems including GR crops exhibited higher values of adaptive traits such as height and biomass than glyphosate susceptible (GS) populations. Variation in growth traits was not explained by geographic separation between populations nor glyphosate resistance. Cropping system components such as crop rotation and crop canopy structure were associated with the differences observed among populations. Additionally, it was confirmed that nitrogen fertilization history influenced nitrogen use efficiency (NUE). Interestingly, GR populations exhibited higher NUE than GS. The results of the present study suggest that Palmer amaranth can quickly evolve life-history traits increasing its fitness in cropping systems, explaining its rapid spread throughout the U.S. Also, the results highlight how herbicide resistant populations of an obligate-outcrossing species can acquire genes that modify metabolic processes not directly associated to the herbicide resistance (HR) trait, but that could compensate for fitness penalties associated with the HR trait or even increase fitness.


A NEIGHBOUR'S LIGHT WILL STRESS YOU OUT. A. McKenzie-Gopsill1, S. Amirsadeghi2, C. J. Swanton*2; 1Agriculture and Agri-Food Canada, Charlottetown, PE, 2University of Guelph, Guelph, ON (280)


 Early season weed competition severely impacts yield potential. Prior to resource competition, neighbouring weeds compromise light quality resulting in dramatic alterations to growth and development with lasting effects on yield through as of yet unknown mechanisms. Using an experimental weedy system that eliminates direct competition for resources, we investigated early physiological responses of soybean to neighbouring weeds. An immediate impact of reduced light quality, a signal of neighbour proximity, is increased production of reactive oxygen species in soybean. Consequently, the induction of soybean antioxidant defence systems suggests that in addition to neighbour proximity, light quality is a signal of oxidative stress, which influences important processes of photosynthesis and carbon allocation with lasting impacts on biomass production.


PLANT COMPETITION AND THE CONCEPT OF AN ENERGY IMBALANCE. C. J. Swanton*1, E. R. Page2, A. McKenzie-Gopsill3; 1University of Guelph, Guelph, ON, 2Agriculture and Agri-Food Canada, Harrow, ON, 3Agriculture and Agri-Food Canada, Charlottetown, PE (281)


Plant competition is thought to be driven primarily by resource limitation.  Weeds compete with crops for light water and nutrients.  This has been a fundamental theory upon which we have based our teaching and research.  This theory of competition is still applicable but only under extreme limitations.  As a fundamental mechanism of competition, resource limitation does not explain how weed seedlings can alter yield potential at the earliest stages of crop development.  This presentation will explore how the presence of weed seedlings can alter cellular homeostasis by creating an energy imbalance. This imbalance of energy results in a cascade of molecular and physiological changes that results in a re-distribution of carbohydrates, a decline in photosynthesis and rate of leaf appearance.  This energy imbalance occurs at the seedling stage of crop development, well in advance of the onset of resource limitation. We propose that the definition of plant competition be expanded to include two distinct stages: 1. the creation of an energy imbalance that alters cellular homeostasis and 2.  as a result of this cellular energy imbalance, plants become more susceptible to direct competition for limited resources.


EFFECTS OF N FORM AND CROP DIVERSITY ON WEED-CROP COMPETITION. R. G. Smith*, N. Warren, E. Hobbie; University of New Hampshire, Durham, NH (282)


WEED SEED BANK DENSITY IN NO-TILL SYSTEM . M. A. Haidar*; American University of Beirut, Beirut, Lebanon (283)


Weed management is an important consideration in implementing new cropping systems. In Lebanon, farmer interest is increasing in adopting conservation agriculture (no-till) because it saves energy and reduces water and nutrients erosion.   However, no-till represents a major shift in production practices and is likely to produce new weed management challenges.  Thus, knowledge of soil seed banks of weeds in such system is becoming imperative in designing successful weed management strategies. The objective of this research was to assess the size of the weed seed bank in no-till fields. Soil samples were collected from established till and no-till fields at a depth of 0-5 cm. Transient and persistent weed seed banks were evaluated. Results suggest that the transient weed seed bank in no-till fields is bigger than in conventional tilled fields. In addition, the density of persistent weed seed bank in the no-till fields was almost seven times that in conventional tilled fields.  Results provide concrete evidence that the transient and persistent weed seed banks in no-till fields are larger than in till fields.

WEEDY RICE MANAGEMENT IN DIRECT SEEDED RICE SYSTEMS. V. Kumar*, O. Namuco, J. Lawas-Opeña, K. P. Valencia, T. Migo; International Rice Research Institute, Los Banos, Philippines (284)


TILLAGE AND COVER CROP EFFECTS ON SEED PERSISTENCE OF POWELL AMARANTH AND LARGE CRABGRASS. M. Frost*, D. C. Brainard, K. A. Renner, L. Tiemann; Michigan State University, East Lansing, MI (285)


Weed seedbank density and composition in intensive vegetable production systems may shift when tillage is reduced or cover crops are used. We hypothesized that reduced tillage and rye cover cropping would influence seed persistence because of greater exposure to fungal pathogens and less exposure to light.  To test this hypothesis, fungicide treated (captan, trifloxystrobin and metalaxyl) and untreated seeds of Powell amaranth and large crabgrass were buried in mesh bags between crop rows in a long term vegetable cropping system experiment with two tillage treatments (conventional tillage [CT] or strip tillage [ST]) and two cover crop treatments (none or rye).  Tillage and cover crop treatments were imposed on the same plots for six years in a sweet corn-snap bean-cucurbit rotation on sandy soils in SW Michigan.  Bags were exhumed after one, five, seven, nine, and eleven months and seeds were tested for viability using 2,3,5-triphenyl tetrazolium chloride.  Immediately prior to spring tillage in the CT no-cover crop plots, we exhumed a subset of weed seed bags in light and another set in the dark to determine if light exposure influenced weed seed persistence.  These bags were then reburied after tillage was complete and seed viability was evaluated after two months. Powell amaranth and large crabgrass seeds in ST had two to three times greater persistence than those buried in CT. Large crabgrass seeds had two-fold greater persistence under rye cover cropping compared to bare soil.  For large crabgrass, we found no evidence that differences in persistence were related to fungal pathogens or light exposure.  In contrast, light exposure appeared to be a major factor explaining reduced persistence of Powell amaranths seeds in CT compared to ST treatments.  These results demonstrate that reduced tillage and cover cropping practices aimed at improving soils may increase the persistence of seeds of important weed species.




Winter annual cover crops provide many benefits to growers, including weed suppression.  They can out-compete winter annual weeds while growing; residues persisting into the following cash crop can also suppress summer annual emergence, with the degree of suppression typically dependent on the amount of biomass produced.  Planting practices that maximize cover crop ground cover as early as possible may be more effective for managing winter annual weeds—these may include species selection, seeding rates, and also planting methods.  A field experiment was conducted in Lexington, KY, to determine the relative importance of these factors in their contribution to weed management prior to and in a soybean crop rotated with corn.    

Cover crops were seeded following corn harvest in October 2015 and 2016.  Ground cover produced by the cover crops was assessed over the winter through the use of overhead photos and the use of a light bar to measure percent light interception.  Weed density, weed biomass, and cover crop biomass was sampled on April 14, 2016; glyphosate was applied the following day.  Soybeans were planted on May 24, 2016, on 38 cm rows; weed density in the soybeans was measured one week later and at the end of the season. 

In the first year of the trial (2015-16), drilling seed resulted in 20% more cover crop biomass than broadcasting seed regardless of species or planting rate.  Due to an extremely dry fall in 2016, we expect an even greater impact of planting method on cover crop biomass in the spring of 2017.  Cover crop density was significantly lower in broadcast plots compared to drilled plots in late October 2016, indicating that establishment may have suffered in dry conditions.  At most sampling times in 2015-16, less light reached the soil surface in rye plots compared to wheat plots, with high seeding rates compared to low seeding rates, and in drilled plots compared to plots with broadcast seed.  In this first year, the high seeding rate of winter rye produced more than twice as much cover crop biomass as the low seeding rate of winter rye and the high rate of winter wheat, and more than four times as much biomass as the low rate of winter wheat.  All cover crop treatments reduced winter annual weed biomass relative to the no cover crop control, with the high rate of winter rye having lower winter annual weed biomass than the other treatments.  Density of early-emerging summer annuals, measured in mid-March and mid-April, was similar in all treatments.  All cover crop treatments reduced weed density one week after soybean planting relative to the no cover crop control.  Seeding rate had a larger influence than the other factors, regardless of the amount of residue produced.  Soybean yield, adjusted to 13% moisture, averaged 4.1 metric tons/ha (61 bushels/acre) and did not differ between treatments.



Soil solarization is an established weed management practice in arid and Mediterranean climates, but rarely used in cool northern regions.  We conducted field experiments over four site-years to test the hypothesis that two weeks of springtime solarization in Maine, USA would increase weed emergence, depleting the weed seedbank, and creating an improved stale seedbed when seedlings were killed by subsequent flaming.  We expected cultipacking to further increase weed emergence and resultant stale seedbed efficacy.  Contrary to expectations, two weeks of solarization reduced weed emergence in comparison to a control stale seedbed by 83% during treatment, and 78% after two weeks of observation following plastic removal and flaming.  Cultipacking did not affect weed emergence.  Maximum soil temperatures at 5 cm depth reached 47 C under solarization.  Un-flamed subplots established during one site-year indicated that solarization alone was as effective as solarization followed by flaming.  Based on grower interest, subsequent experiments examined the effects of two, four, and six weeks of solarization in field and hoophouse settings on soil microbiota, and compared the efficacy of solarization to occultation (using black plastic) for stale seedbed preparation.  Solarization in an open field did not affect plate counts of general bacteria, general fungi, Bacilli, or florescent pseudomonads during solarization of any duration, nor 5 days after plastic removal.  Hoophouse solarization negatively impacted florescent pseudomonad counts, but had no effect on other cultured taxa.  Overall, solarization decreased soil biological activity by 32% in the field and 45% in the hoophouse during treatment.  Biological activity rebounded somewhat in the field by 14 days after plastic removal, but remained suppressed in the hoophouse up to 28 days after plastic removal.  In both field and hoophouse experiments, concentrations of available nitrogen (nitrate and ammonia) were up to 4 times higher in solarized treatments than controls during and after treatment; other studies have found that solarization could benefit crop growth, but also potentially contribute to N-leaching.  Occultation and solarization were equally effective as stale seedbed preparation techniques when applied for seven weeks in April to May (both providing total control two weeks after plastic removal), but solarization was more effective than occultation when applied for two, four, or six weeks in June to July: overall 85% fewer weeds emerged following solarization as compared to occultation.  Soil biological activity, measured during this latter experiment, was not affected during treatment, but at 14 days after plastic removal was suppressed 18% following occultation and 43% following solarization in comparison with controls.  Overall, these results confirm that solarization is a very promising strategy for stale seedbed preparation in the Northeast.  The impacts of field solarization on beneficial microbiota do not appear severe, though more work exploring ramifications of the observed decreases in soil biological activity is recommended.  Occultation may impact microbiota less than solarization, but it is less consistently effective for stale seedbed preparation in our region.   


PASTEURIZATION OF MUSHROOM COMPOST REDUCES WEED SEED VIABILITY. K. M. Vollmer*, M. J. VanGessel; University of Delaware, Georgetown, DE (288)


Over one million tons of mushroom growing media, commonly referred to mushroom compost, are produced each year.  Following mushroom harvest, this compost is made available for use to both agriculture professionals and homeowners.  The potential to spread contaminated weed seed via mushroom compost has not been examined.  Composting has been shown to reduce weed seed germination; however, it requires high temperatures over an extended period of time to completely kill most weed seeds.  The process used to produce mushroom compost is unique in that the composting material undergoes two phases of intense heat prior to the mushroom production process, and a third phase immediately before the compost is removed from the growing houses.  Phase I involves mixing plant material and animal waste outdoors and forming compost beds (ricks).  The decaying organic matter heats the ricks, and piles are turned every two days for fourteen days.  Phase II compost production involves several days of high humidity and temperatures up to 60 C.  Phase III involves sterilizing the compost with steam after mushrooms have been harvested, but before the compost becomes available to consumers.

The objectives of this study were to examine the effectiveness of Phase II composting to reduce weed seed viability, and if various weed species responded differently.  Phase II was carried out either in beds of mushroom growing houses or using a tunnel system.  The temperature in the mushroom growing beds was raised to 60 C and then lowered to 38 C over 11 days, while relative humidity remained above 90%.  The tunnel system also raised the temperature to 60 C, but the temperature was lowered over 7 days.  Fifty seeds of annual ryegrass, hairy vetch, ivyleaf morningglory, Palmer amaranth, and velvetleaf were placed in two bag types, either mesh bags and Whirl-Paks and then inserted into mushroom compost.  Bags remained in place for 7 days or 13 for the bed and tunnel pasteurizations, respectively.  Bags were removed from the compost after Phase II pasteurization, and seeds tested or viability.  All seeds were subjected to pressure tests with forceps.  Seeds resisting slight pressure applied by forceps were considered viable.  Those seeds considered viable were placed on petri dishes containing germination paper, watered, and monitored for radicle emergence every 3 to 4 days for 4 weeks.  There were four replications per run.  Three runs were conducted using standard compost beds in the mushroom houses and two runs using the tunnel system for pasteurization.  Differences among weed species were analyzed as randomized complete block design separately for the compost beds and tunnel system.  Data were analyzed for analysis of variance using the mixed model in JMP Pro 12 and means separated using Student’s T test (α = 0.05).

Overall, weed seed viability was reduced for all species.  In the bed study a lower percentage of hairy vetch seeds failed the pressure test compared to other weeds. Percent germination for ivyleaf morningglory and velvetleaf was higher than other species.  In the tunnel study there were significant bag type by species interactions.  A higher percentage of hairy vetch and velvetleaf in mesh bags failed the pressure test compared to Palmer amaranth in mesh, hairy vetch in Whirl-Paks, and ivyleaf morningglory in Whirl-Paks.  More hairy vetch in Whirl-Paks and ivyleaf mornigglory in Whirl-Paks germinated compared to all other treatments.  Palmer amaranth did not germinate in either study.

This study shows that the Phase II composting process alone is enough to reduce the viability of weed seeds entering mushroom compost.  Additional studies are needed to determine how viability is affected in weed seeds that go through the entire mushroom production process.


TIME OF WILD OAT PANICLE CLIPPING ON SEED VIABILITY. K. Harker*1, B. D. Tidemann1, J. T. ODonovan1, C. J. Willenborg2, S. J. Shirtliffe2, E. N. Johnson2, L. A. Michielsen1, P. L. Reid1, E. A. Sroka1, J. A. Zuidhof1; 1Agriculture & Agri-Food Canada, Lacombe, AB, 2University of Saskatchewan, Saskatoon, SK (289)


Wild oat (Avena fatua L.) is one of the most problematic weed species in western Canada due to widespread populations, high frequencies of herbicide resistance and seed dormancy.  However, in crops such as wheat (Triticum aestivum L.) and especially in shorter crops such as lentil (Lens culinaris L.), wild oat extend their panicles above the crop canopy.  The first year of a two year panicle clipping and removal study in wheat and lentil was conducted in Lacombe, AB and Saskatoon, SK to determine when wild oat seeds become viable.  Panicle clipping for each crop began when the majority of panicles were visible above respective crop canopies and continued thereafter at weekly intervals.  Preliminary results indicate that while wild oat viability at the first panicle clipping time in lentil was near zero, viability at the first panicle clipping time in wheat was between 12 and 37%.  Distal awn angle with respect to the basal awn axis was negatively correlated with seed moisture content and positively correlated with seed viability and may be a useful indicator of seed viability at various stages of wild oat maturity.  Weed management techniques targeting the panicle must occur very soon after panicle emergence above the crop canopy; later treatment will add considerable viable seed to the seedbank.

IDENTIFYING POTENTIAL TARGET WEEDS FOR HARVEST WEED SEED CONTROL IN WESTERN CANADA. B. D. Tidemann*1, L. M. Hall2, K. Harker1, H. J. Beckie3, E. N. Johnson4, F. Stevenson5; 1Agriculture & Agri-Food Canada, Lacombe, AB, 2University of Alberta, Edmonton, AB, 3Agriculture & Agri-Food Canada, Saskatoon, SK, 4University of Saskatchewan, Saskatoon, SK, 5Private Consultant, Saskatoon, SK (290)


Identifying Potential Target Weeds for Harvest Weed Seed Control in Western Canada

B. D. Tidemann1*, Linda M. Hall1, K. Neil Harker2, Hugh J. Beckie3, Eric N. Johnson4, F. Craig Stevenson51University of Alberta, Edmonton, AB, 2Agriculture and Agri-Food Canada, Lacombe, AB, 3Agriculture and Agri-Food Canada, Saskatoon, SK, 4University of Saskatchewan, Saskatoon, SK, 5Private Consultant, Saskatoon, SK.


As chemical management options for weeds become increasingly limited due to the selection for herbicide resistance, investigation of non-chemical tools becomes necessary.  Harvest weed seed control (HWSC) is a paradigm of weed management that targets and destroys weed seeds that are otherwise dispersed by harvesters following threshing. While there is interest in Canada in the use of these methods, it is not known whether problem weeds in western Canada retain their seeds until harvest at a height suitable for collection. A study was conducted at three sites over 2 years to determine if retention and height criteria were met by wild oat, cleavers and volunteer canola. Wild oat consistently shed seeds early, but seed retention was variable, averaging 56% at the time of wheat swathing with continued losses until direct harvest of wheat and fababean.  The majority of retained seeds were >45 cm above ground level, suitable for collection. Cleavers seed retention was highly variable by site-year, but generally greater than wild oat.  The majority of seed was retained >15 cm above ground level and would be considered collectable.  Canola seed was highly retained on the plant, with >95% retention in most cases and nearly all seed retained >15 cm above the ground.  The suitability ranking of the species for management with HWSC was canola > cleavers > wild oat.  Efficacy of HWSC systems in western Canada will depend on the target species and site- and year-specific environmental conditions.

INTEGRATED HARRINGTON SEED DESTRUCTOR: HOW EFFECTIVE IS IT? L. M. Schwartz-Lazaro*1, J. K. Norsworthy1, M. J. Walsh2; 1University of Arkansas, Fayetteville, AR, 2University of Sydney, Narrabri, Australia (291)


Herbicide-resistant weeds are effecting every major cropping system today. Worldwide there are 47 herbicide-resistant weeds in soybean (Glycine max L. Merr.). Alternatives to herbicides are necessary to help combat herbicide-resistant weeds and to have sustainable farming practices. The integrated Harrington Seed Destructor (iHSD) has been developed to intercept and destroy weed seeds during crop harvest, but has never been tested in the United States or in soybean production. Thus, the objective was to determine the effectiveness of the iHSD on various weeds in a soybean cropping system and to discover the limitations, if any. Three experiments were run on a stationary iHSD: 1. Thirteen weed species were individually incorporated into a known amount of soybean chaff and run through the iHSD, 2. Varying belt RPM speeds were tested to determine the feeding rate effectiveness, and 3. Varying moisture levels of the soybean chaff were tested to determine any limitations on the ability of iHSD to process chaff material. For the first experiment, twelve of the thirteen weed species showed <1% survival rate when processed through the iHSD, including Palmer amaranth, morningglory species, and barnyardgrass. Common cocklebur had a 3% survival rate and was the only species that had >1% survival. The RPM and moisture experiments yielded <1% survival across all treatments for both Palmer amaranth and morningglory species; albeit, the iHSD did seem to collect more chaff as moisture content increased. Therefore, in soybean production the use of the iHSD can be highly effective for reducing weed seed inputs to the soil seedbank. Further research is needed on testing the iHSD in a combine at harvest.

BLACK GRASS (ALOPECURUS MYOSUROIDES HUDS.) RESISTANCE TO ALS- INHIBITORS: A CASE STUDY APPROACH TO STUDY CAUSES AND PREDICT WEED RESISTANCE TO HERBICIDES. J. Herrmann*1, R. Beffa2, H. Strek2, M. Hess2, B. Peters2, O. Richter1; 1TU Braunschweig, Braunschweig, Germany, 2Bayer AG, Frankfurt, Germany (292)


Herbicide resistance is an increasing thread for European farmers. However, little is known about the exchange of resistance genes between neighboring fields and the underlying field management and ecological factors. Therefore a case study project was initiated in Germany in 2010. The main goal was to study temporal and spatial evolution of resistance to ALS- and ACCase-inhibitors in black grass (Alopecurus myosuroides Huds.). The study includes 1225 fields for which seed samples were collected over a 6 year period. Samples were analyzed in the laboratory using SNP-analysis to detect target site mutations and by greenhouse biotests. Field management data of previous years was investigated through intensive farmer interviews to analyze the factors that are mainly contributing to the resistance evolution.

The study area contained fields with mostly low infestation of blackgrass after herbicide application by the farmer suggesting that blackgrass control was successful in the majority of the cases. Assessment of field survivors in the greenhouse revealed that over 83% of the samples showed resistance to ACCase-Inhibitors of the FOP/DEN-classes. Less than 32% showed resistance to mesosulfuron-methyl (ALS-Inhibitor). The degree to which resistance was pronounced and the pattern of the SNPs analyzed (2 ALS; 5 ACCase) varied from field to field and from year to year, suggesting that resistance develops locally on the individual field level. Fields with pronounced resistance were most often farmed with lower diversity of crops and less intensive tillage regimes. Furthermore, less use of delayed seeding was made. Surprisingly, the number of Modes of Action used seemed to have no significant effect on the resistance evolution to ALS inhibitors after 2-3 complete crop rotations. In addition, the effect of the herbicide use frequency and the use frequency of ALS- inhibitors was also less pronounced compared to the non-chemical weed management measures. However, similar management practices were not necessarily leading to the same resistance status within the small area assessed in this study. Deeper analyses showed that also particular soil types are correlated with the presence of ALS-resistant black grass populations.

An attempt to generate a prediction tool based on machine learning and a population simulation will be presented. Its prediction quality and application for practical agriculture will be discussed in the light of Integrated Weed Management.



While many tenure track positions gain national and international prominence via their research efforts, there is a possible view that the greatest true impact of a faculty member can be in their role as a classroom teacher.   The cumulative effect of dozens of students over a lifetime of courses eventually can lead to thousands of potential opportunities to improve the world by using sound principles of weed science.

This workshop focuses on teaching undergraduate weed science, with the goal of providing strategies to improve student learning.   Several topics will be covered, including presentations on perceptions of a new faculty member teaching undergraduate weed science for the first time, incorporating field scouting and developing weed management recommendations via experiential learning, how to successfully incorporate group projects into your undergraduate weed science class, novel pedagogy to instruct students on weed identification, and how to write exam and quiz questions to accurately assess student learning.

TEACHING WEED SCIENCE:  A NEW FACULTY PERSPECTIVE. E. Haramoto*; University of Kentucky, Lexington, KY (294)


The Integrated Weed Management at the University of Kentucky is a required course for students in the Horticulture and Plant Sciences Major.  Students learn about weed biology and ecology, different types of weed control, and how these control tactics are successfully integrated in different production systems.  The course has a laboratory, which uses hands-on experiments to reinforce concepts covered in lecture (fitness costs to herbicide resistance, weed-crop competition, and cover crop impacts on weed emergence).  Greenhouse-raised specimens are primarily used for weed identification, as the course is taught in the spring semester.  Field trips occur in April to area research farms and a golf course.

The course has specific objectives related to learning and understanding aspects of weed biology, ecology, and management.  It is also used to further develop key skills including critical thinking, information evaluation, writing, and oral presentation skills.  As a 400 level class, students are generally at the junior or senior level by the time they take this class.  Yet their skills related to information retrieval and evaluation is often lacking (e.g. papers are often submitted with only internet sources, students lack the skills needed to comprehend basic primary literature, design experiments, etc.).  Given the importance of these skills to our undergraduate population, these remain a focus through different assignments, presentation strategies, and other tools used in the course.  For example, students are repeatedly exposed to figures and tables from the primary literature in lectures.  Students are asked to explain the gist, then key features are highlighted using animations.  Slides are presented using a modified assertion-evidence structure—a simplified slide format focusing on key figures and graphics to highlight points instead of text.  Different assignments have students write to different audiences, and use and explain different sources of information.  Experiential learning in laboratories get students accustomed to conducting basic experiments, analyzing data, and communicating their findings.



Over two-thirds of the Agronomy majors at Kansas State University are enrolled in the Consulting and Production option out of six possible options, with graduating students returning to the farm, or becoming crop scouts, agronomists, or advisors to farmers. Weed Science is a fall-only junior level 3 cr hour course (2 hr of lecture and 2 hr of laboratory time each week) that all Agronomy majors are required to take and many students that are pursuing a minor in Agronomy are also enrolled. Enrollment numbers over the past five years has ranged from 68 to 88 students.

The Agronomy Learning Farm is a facility located within 3 miles of the Department of Agronomy building in Manhattan, KS. The Learning Farm has approximately 80 acres of cropland managed in larger tracts as a typical northeast Kansas cropping system, including a three-crop rotation sequence of winter wheat/fallow-grain sorghum-soybean as a no-till production field since 2001. This facility is a place where students, throughout their undergraduate career in Agronomy, can develop technical skills and intellectual competences during on-site experiences.

The final assignment in Weed Science is for a team of 2 to 4 students to develop a Weed Management Recommendation for each of three different field scenarios on the Agronomy Learning Farm. Each team is required to prepare a written summary of the best recommendation for the three fields, as well as to give an oral presentation in their lab section.

Prior to the final lab and student presentations, one lab period is used to review the purpose of field scouting, approaches on how to sample a field, and to review tools (paper- or computer-based) for documenting weed species, densities and distributions in the field, and then to travel to the three fields at the Agronomy Learning Farm where teams physically walk and scout the fields for weeds. Another lab is available for teams to review their scouting notes, and to search for a series of three to four possible weed control recommendations, and to select the best recommendation that they would fully develop and share to their lab section. Key elements of the assignment were to describe the scenario in their own words, show a map of weed species and sampling plan, best weed control recommendation, and specifics about cost per acre and for the entire field. Students were to also identify any environmental or economic restrictions that the field posed or would limit the implementation of their recommendation.

This particular assignment meets components of the five Agronomy Student Learning Outcomes: (1) Ability to think clearly and creatively and to apply critical thinking skills when evaluating information, (2) Learning, developing, and applying skills for the application of existing and emerging knowledge and technologies in Agronomy, (3) Competent application of scientific principles, quantitative skills, and other problem solving skills in Agronomy, (4) Knowledge and application of ethical practices and recognize the relationships between science and society within a diverse society, and (5) Develop competent oral and written skills to foster positive interaction and effective communication within a diverse team.



Weed identification is a central component of the weed science discipline and thus is a focus in many undergraduate weed science courses.  Traditionally, weed identification has been taught within the laboratory component of weed science undergraduate courses and has spanned from 6 to 15 lab-hours (2 to 8 weeks) per semester.  Various approaches have been used in these laboratory sessions to present and enhance student learning of this key facet of weed science.  These include powerpoint-aided lectures, lab manuals or weed guides to introduce students to specific plant morphological and anatomical terminology, and botanical classification.  Student-prepared weed collections and weed identification notebooks are also used.  Central to these courses is the use of greenhouse-grown and/or field-collected plant material. Various strategies to encourage and reinforce student learning of the material have been used including weekly on-line quizzes, weed walk quizzes, in-lab identification of recently collected or live plants, on-campus herbaria and weed garden visits, and seedbank projects.  During the last two decades new computer-based tools to assist faculty in teaching and strengthening student skills in weed identification have been developed. In general, these new technologies have not been widely adopted by weed science faculty.  Because of time constraints and often the large number of weeds that students are required to identify (40-100) in our traditional 3-4 credit courses, an emerging trend during the last decade is the development of separate 1-3 credit weed identification courses ranging from 7 to 14 weeks (averaging approximately 25 total hours).  Key components of these courses are the numerous weed walks and/or field trips taken especially when the course is offered during the fall semester.  Feedback from faculty teaching these more focused weed identification courses has been generally positive as has the level of student engagement and mastery of the material presented.  One concern is that such courses do require substantial resources for the limited number of credits and may not be sustainable under current budgetary constraints.  Regardless of whether weed identification is offered within a single comprehensive weed science course or as a stand-alone course, long-standing challenges related to the availability of sufficient resources (e.g. funding for field trips, teaching assistants, availability of live plant material) to adequately cover this important component of our weed science undergraduate curricula remain. 




One of the recurring themes in the teaching of undergraduate students is the challenge to impart the paramount skills of critical thinking, problem solving, and effective communication in both spoken and written forms. Professors often exam students through written exams that contain mostly trivia. One avenue to increase higher level thinking is to employ team projects on various subjects. From a conceptual standpoint, undergraduate weed science classes lend themselves well to a variety of potential topics for team projects. The workshop presentation will provide a forum to share ideas related to team-oriented weed science projects and their effectiveness in the pedagogy of weed science.



Many faculty have a good understanding of the subject matter they cover, and the teaching of undergraduate weed science (UWS) is often no exception.  They can share that knowledge with their students in a variety of ways, but sooner or later some type of formative or summative assessment is essential to determine if knowledge transfer from faculty to student has actually occurred. Writing, grading, and returning exams to students can be one of the most challenging aspects to teach UWS, especially for new faculty.  This workshop focuses on the essential question: How are tests useful? Formative and summative assessments can help instructors gauge student learning, provide methods to assess students and assign grades, provide feedback to students about their learning, and may contribute program information for assessment and/or accreditation.  In general, the types of possible exam questions include Multiple Choice, True/False, Matching, Completion or Short Answer/Essay.  Class size and other logistics can dictate or provide guidance to the types of questions that should be used.  Also, some subject matter, (i.e. weed ID) may lend itself to a specific format.  For example, one way to view drafting questions is to align the questions with learning objectives.  Learning objectives provide instructor & student with an overview of course; identifies concepts or skills students are expected to learn; helps students be aware of their learning responsibility; and establishes the expectations for your course.  Specific learning outcomes should be reasonable, measurable, and (ideally speaking) based on Bloom’s (or a similar) taxonomy.  This premise of a “question hierarchy” deals from a continuum from “simple” to “complex”, with one possible order for questions from low to high being: remember, understand, apply, analyze, evaluate, and create.  Each of these concepts will be discussed within the framework of the workshop, and various examples of “bad” and “good” exam questions will be shared and discussed.  Components of a “good” exam question include: linkage to course goals and objectives; encourages higher level thinking, but is appropriate for the level of the material; questions and responses are clear; and the focus is on concepts, not trivia.  The next idea in the workshop was that of using a test blueprint, to guide the faculty in preparing the exam.  Concepts important to a good test blueprint include: What will the test cover?  How will the material be distributed across the test?  How will the assessment grade/points be distributed and weighted?  How will the exam balance knowledge/recognition of higher order items (Bloom’s Taxonomy, Marzano’s or other method)?  Specific benefits of using a test blueprint include: A blueprint you use will help you visualize your test; “lower-order thinking” questions are easier to write and therefore may represent too much of your exam.  A blueprint will help you focus on higher order questions, and will help you distribute appropriate emphasis on important learning objectives.



Melaleuca quinquenervia (Cav.) Blake (melaleuca) is an invasive exotic tree of Australian origin that has formed dense monotypic stands in southern Florida. Its canopy-held woody capsule-cohorts prolifically shed (rain) seeds year around but their quality and quantity that directly aids to melaleuca’s further invasion potential has not been researched. This long-term, landscape-scale research investigated the quantity and quality of rained melaleuca seeds following the implementation of a classical biological control program. A series of 25 – 100 m2 permanent plots were established in melaleuca infested habitats where a suite of biological control agents (insects and a rust-fungus) were established and monitored for 10 - 14 years to elucidate melaleuca stand dynamics. Unfortunately, all plots except those in occasionally inundated habitats were eventually destroyed or altered within five years by fires or misapplications of herbicides. The plots in occasionally inundated habitat contained permanent litterfall and seed traps that captured fallen materials (dead or alive insect larvae and adults, melaleuca and non-melaleuca leaves, stems and seeds). The captured materials were collected on a monthly basis and processed and analyzed for quantity (larvae, damaged vs undamaged leaves, seeds) and quality (seed viability and germinability). The percentages of leaves damaged by biological control agents increased from 4% in 1999 to 80% during 2006 through 2011. Mean numbers of monthly seed rain during a calendar year was highest in October (104,371,813 seeds ha-1mo-1) and lowest in December (49,344,259 seeds ha-1 mo-1). Annual seed rain patterns period revealed three general configurations: 'normal' (first 5-years), 'spiked' (next 4-years) and 'flat' (last 5-years). This overall pattern closely matched the percentage of melaleuca leaf litter that was damaged by the biological control agents. The initial means of 12.8% viability and 10.8% germinability of seeds from 1997-98 decreased to 8.4% and 7.0%, respectively, by 2009-2010. Overall, biological control reduced both the quantity and quality of the rained melaleuca seeds which, in the long run, is expected to suppress seedling recruitment and invasion potential in southern Florida.  



Sorghum in known to produce the allelochemical sorgoleone. Production of sorgoleone is a dynamic process where plants produce these chemicals either by roots when they are still alive or by dead decaying matter and are known to have negative impact on weeds and following crops. There are concerns about sorghum affecting the following winter wheat crop when grown in rotation in North Carolina. Impact of sorgoleone on growth of wheat and various weed species was investigated under in-vitro conditions. Seeds of wheat (Shirley and USG3251) and four weed species, large crabgrass, Italian ryegrass, velvetleaf, and sicklepod were pre-germinated and then transferred to 20x100mm petri dishes treated with varying concentrations of sorgoleone. Sorgoleone was applied @ 0 (control), 25, 50, 100, 150, 200, and 300 µg ml-1. 10 days after placing seeds on the petri dishes, growth was measured in terms of shoot length. Significant sorgoleone treatment effects were observed for shoot growth when pooled over species. Shoot length was reduced at higher rates of sorgoleone compared to control treatments for all weed species. Wheat shoot length was not significantly affected by sorgoleone concentration. Velvetleaf shoot length was lower at all concentration compared to the non-treated control. At higher rates of sorgoleone, large crabgrass, Italian ryegrass, and sicklepod growth was reduced when compared to lower rates. Results suggests that sorgoleone has a negative impact on growth of weed species, however the wheat cultivars tested were not impacted.




Greenhouse and field experiments were conducted to determine the effects of an invert (water - in - oil) emulsion (IE) on dew period duration and dew delay, and host range of the fungus Colletotrichum coccodes (Strain NRRL 15547) for biocontrol of the weed, eastern black nightshade (Solanum ptycanthum; EBN).  Dew periods of 4, 8, or 12 h provided 10, 25, and 40% control, respectively, of EBN plants in the 2-to-5 leaf stage when C. coccodes spores were applied in water + Tween-80 surfactant (T-80) 12 days after inoculation.  However, a minimum of 16 h of dew was required to achieve ~ 95% plant mortality.  In contrast, at these same intervals of dew, 95, 100 and 100% mortality occurred, respectively, when spores were formulated in the IE.  Even in the absence of dew, 60% mortality and 70% plant dry weight reductions was achieved with the fungus/IE formulation.  Delaying dew by 2 h after inoculation did not significantly reduce weed control or plant dry weight when plants were inoculated with the fungus in T-80 or in the IE formulation.  However, when dew was delayed for 4, 8, or 12 h, only 60, 50, and 25% mortality occurred, respectively, of plants receiving the T-80 spore formulation.  In contrast, 95, 90, and 90% mortality occurred after the same dew delays of plants receiving the fungus/IE formulation.   Other Solanaceous weeds: hairy nightshade (S. sacchoides), American nightshade (S. americanum), black nightshade (S. nigrum), cutleaf nightshade (S. triflorum), tropical soda apple (S. viarum), and jimsonweed (Datura stramonium) were infected and killed at a significantly greater level by the fungus in the IE as compared to the T-80 formulation.  Field tests revealed that >90% EBN control and dry weight reductions occurred when plants were treated with the fungus/IE formulation. These results demonstrate that formulating C. coccodes spores in an invert emulsion greatly improves its bioherbicidal potential. Results also suggest that the invert emulsion formulation may promote the efficacy of certain pathogens that have been previously rejected for development as bioherbicides due to environmental and infectivity constraints.




In this day and age, we are often asked to think broadly, taking space and time into consideration when developing weed management approaches and areawide weed control; thus, precision agriculture seemingly goes in the opposite direction. Precision agriculture, also called site-specific agriculture, allows large fields to be managed as small ones. It typically utilizes geo-referencing of the crop and soil to improve production, but it can also be used to reduce the environmental impacts of herbicides and tillage. Weeds, and the methods used to control them, have economic and environmental impacts, and weed management inputs are traditionally applied uniformly to the whole field regardless of weed density and distribution. Precision Weed Management (PWM) applies “the right amount of inputs on the right weeds at the right time.” Ground, aerial, and satellite based sensor systems have all vastly improved in the last decade, and can now be used for weed detection, to compose weed maps, and to develop decision support tools to improve weed management strategies. Farm implementation systems already exists that simultaneously achieve weed detection and elimination, although they are not widely used yet. Site-specific weed management tools are also being developed for mechanical weed destruction, using inter-and intra-row hoeing, electricity, fire or lasers. In many ways, precision agriculture has advanced much faster than its applications to weed science. This symposium will provide up-to-date information on recent developments in PWM technologies, and provide insights as to how weed management might be improved by better incorporating precision agriculture approaches.




Geographic information systems afford users the ability to evaluate agricultural issues at local, county, state, national, and global levels. Also, they allow users to combine different layers of geographic information to help them develop strategic plans to solve problems. Furthermore, there is a growing interest in testing open source and no cost geographic information system software for weed surveys. In the southeastern United States, pigweeds (Amaranthus spp.) have become troublesome weeds in agricultural systems. To implement management strategies to control them, agriculturalists need information on areas affected by pigweeds. In this study, the open source software QGIS was used to develop a geographic information database showing the distribution of pigweeds at the county level in the southeastern United States. The maps focused on the following pigweeds: Palmer amaranth (Amaranthus palmeri S. Wats.), redroot pigweed (Amaranthus retroflexus L.), and tall waterhemp [Amaranthus tuberculatus Moq. Sauer]. Additionally, soil and crop data layers, and herbicide resistance information for the pigweeds were extracted from federal and state government databases and were added to the geographic information system database. Database queries were used to demonstrate applications of the geographic information system for precision agriculture applications at the county level, such as tallying the number of counties affected by the pigweeds, identifying locations of agricultural fields that may be affected by pigweed infestations, and determining soil chemical and physical properties that are associated with pigweed growth. This research demonstrates that open source and no cost software such as QGIS has strong potential as a decision support tool, with implications for precision weed management at the county level.



Undesirable plant species negatively impact agricultural crop production and other ecosystems and cause significant losses both economically and environmentally. Examples of losses include reduced crop yields, altered stream flow in riparian areas, increased frequency of fires in rangelands and forests, fewer habitats with high species diversity, and increased management for aesthetics in natural areas and production systems, respectively. For example, the services provided by the terrestrial systems in which undesirable plants have invaded or are established have yet to be completely quantified, but estimates are in the billions of dollars. A new electronic plant species identification program has been developed and is currently being tested for identifying selected plant and weed species found in Nebraska and fields of the Great Plains. A new identification process takes place through an acquired digital leaf image. The identification algorithm performs a classical shape analysis, but also concentrates on a very detailed leaf venation network features. Leaf species samples were supplied from plants grown in a growth chamber, greenhouse, and spring/summer/fall field specimens. Plants included various herbaceous species that are native and non-native (e.g., velvet leaf, pigweed, downy brome, phragmites, common reed, leafy spurge, cheat grass). Specimens are imaged using a high-resolution, color digital camera using a special portable back LED lighting panel. Development of the system included training and validation using a feature data-driven, fuzzy-logic classification scheme, with high success rates. The impact from the development of a real-time plant species identification system is to easily identify undesirable plants and weeds.  This could revolutionize and assist the way plant populations are studied by researchers, and monitored by crop and land managers.



Bruce D. Maxwell, Lisa J. Rew, Anton Bekkerman, Nicholas Silverman, Rob Payn, John Sheppard, Clemente Izurieta, Janette Rounds and Philip Davis

Crop production input decisions have become increasingly difficult in global market interdependencies have led to higher uncertainty of input costs, commodity prices, and price premiums, and there is increased spatial and temporal variation in response to inputs and climate variability. If producers had better knowledge of market prices, spatial variability in crop response, and weather conditions that drive crop response to inputs, they could more cost-effectively make profit-maximizing input quantity decisions. Understanding the drivers of variability in crop response and designing accompanying management strategies would hence allow increased resilience to economic or climatic perturbations or system stress. We have developed an on-farm precision experiment (OFPE) framework drawing on site-specific agriculture technologies to provide the best estimate of field-specific, site-specific profit-maximizing input application. Our test of the OFPE framework is to site-specifically optimize nitrogen fertilizer application rates in 12 dryland winter wheat fields on 4 farms in Montana. Simulation models indicated that consistent field-specific optimization results could be achieved in 6-8 crop years without climate prediction models. After one year of implementing the OFPE framework, we demonstrated that nitrogen rate experiments could be applied using a previous year yield stratification and standard variable rate fertilizer applicators. Empirical results based on three different optimization approaches (non-linear regression, Bayesian estimation and neural networks) and keeping constant climate year and economic market conditions show that producers can increase net returns by simply re-allocating resources (rather than increasing inputs). As additional data years from each field are added to the optimization models, profit-maximizing site-specific input amount and allocation recommendations will be based on probabilistic outcomes. In addition, mapping weeds at harvest with the site-specific Merja Mapper device could provide an efficient way to implement site-specific weed management and provide important weed information into the optimization of any input.




Precision weed management is an application of precision agriculture on weed management accounting for within-field variability of weed infestation and herbicide damage. Precision weed management in the entire field can be conducted with mapping of crop fields at different scales. Airborne remote sensing systems provide fairly high quality data for mapping weed and crop issues over the field. We have developed and used airborne systems for multispectral imaging using a number of imaging sensors (cameras) to determine crop injury from off-target drift of aerially applied glyphosate. However, these systems are limited in identifying weeds in the field.  Unmanned aerial vehicles (UAVs) provide a unique platform for remote sensing of crop field. They are efficient and more flexible than manned agricultural airplanes to acquire high-resolution images at both low altitude and low speed for capture. UAVs are more universal in their applicability than agricultural aircraft since the latter are used only in specific regions. We have developed and used UAV systems for RGB digital imaging to identify weeds in the field and determine crop injury from dicamba at different doses. This presentation will overview remote sensing technologies for weed management and focus on development and application of low-altitude remote sensing technology for precision weed management, especially the technologies on UAVs.



The Sacramento-San Joaquin River Delta (hereafter referred to simply as “the Delta”) can be viewed as an extensive agricultural landscape surrounded by urbanization, tidal freshwater wetlands, and major commercial waterways originating from California’s two primary river systems (Sacramento and the San Joaquin) that flow into San Francisco Bay.  Much of the Delta’s land cover is partitioned into discrete island tracts separated from open waters by man-made levees.  The Delta was once a great tidal marshland of peaty alluvial soils.  Pre-settlement vegetation consisted largely of native “tule” (bulrush) and reed marshes that were periodically submerged, with narrow patches of riparian forest on the natural levees along the major stream channels.  In the late 1800s, new and higher levees were built along the stream channels to protect the land from flooding, and the resulting complex of Delta island tracts were extensively drained, cleared, and planted to croplands.  Researchers at NASA's Ames Research Center, located about 40 miles southwest of the Delta, in collaboration with USDA ARS scientists, are using satellite imagery from the Landsat sensor to regularly detect the location and abundance of water hyacinth (and potentially other emergent aquatic plant species) in all Delta waterways and in wetlands throughout the San Francisco Bay Area (SFBA).  The archive of Landsat images extends back to the early 1980s, making long-term change studies of wetland habitats uniquely feasible. This satellite record of change shows a proliferation of high biomass cover associated with invasive aquatic weeds after 2010 in the Delta river courses.  Infestation by water hyacinth in these wetlands can crowd-out native plants and make pumping of river water onto the Island more difficult and expensive.  Aqautic weed control efforts by State agencies are being guided by these monthly satellite images to reduce costs and increase precision of herbicide and mechanical removal activities.



Landscape Level Weed Monitoring in the Florida Everglades Using Digital Aerial Sketch Mapping.

LeRoy Rodgers*, South Florida Water Management District, West Palm Beach, FL

Tony Pernas, National Park Service, East Ochopee, FL

Jed Redwine, National Park Service, Homestead, FL

Shea Bruscia, National Park Service, Palmetto Bay, FL

The South Florida Water Management District and the National Park Service are utilizing digital aerial sketch mapping (DASM) for regional invasive plant surveys in the Everglades Invasive Species Management Area.  This technique fulfills the practical need for more detailed geospatial information on priority invasive plants, and meets statutory requirements to conduct biennial surveys of exotic species within the Everglades Protection Area.  DASM is a remote sensing technique for observing ground conditions from low-flying aircraft and digitally mapping invasive plant infestations The DASM system is comprised of two networked touch-screen tablet computers connected to a GPS receiver.  We use GeoLink® SketchmapperTM mapping software, which utilizes a GPS signal to display the current location along with background imagery and other preloaded data on the computer screen.  The Everglades DASM program is intended to meet several monitoring objectives across the 1.8 million acre landscape including: 1) conducting region-wide assessments of the distribution and abundance of priority invasive tree and vine species, 2) evaluating small and large scale patterns of invasions, and to 3) provide natural resource managers with detailed data on infestation levels in planned treatment areas. Multiple monitoring designs are utilized to address each of these objectives. This presentation will provide an overview of the technology and monitoring methods utilized in the monitoring program. Long term trends in distribution and abundance for four priority plant species—Australian pine (Casuarina spp.), Brazilian pepper (Schinus terebinthifolius), melaleuca (Melaleuca quinquefolia), and Old World climbing fern (Lygodium microphyllum) will be presented as well as assessments of the efficacy of this tool for directing control efforts in remote wilderness areas.

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During the past decade, it has become possible to conduct on-farm, real-time assessments of crops and pests, such as weeds. Robot technology promises to reduce the amount of labor needed to effectuate weed assessment and weed control. As a consequence, true integrated weed management (IWM), which takes into account all relevant spatial and temporal scales, is within reach. However, even with advanced technology, several challenges remain. In terms of technology, occlusion of weeds by the crop and harsh environments present a challenge. In terms of socio-economics, growers are concerned that technology is replacing the human element of managing agriculture cropping systems. Finally, in terms of science, improved cross-disciplinary collaboration is needed between biologists, who know the most about agricultural systems, and engineers, who develop mechanical and automated solutions, in order to make the advances that are necessary to address critical global food needs and protection of the natural resource base. Examples of low-level, traditional, and precision IWM systems are discussed and research needs for a True IWM system presented.

FIELD BINDWEED SUPPRESSION IN PROCESSING TOMATOES WITH SUB-SURFACE TRIFLURALIN APPLICATIONS. L. M. Sosnoskie*1, B. Hanson2; 1University of California, Davis, CA, 2Univesrity of California, Davis, CA (310)


The successful control of deep-rooted perennials, such as field bindweed, is dependent upon herbicides reaching latent root and shoot buds. The majority of root/rhizome biomass for field bindweed is located within the top 2 feet (0.6 m) of the soil profile, although some vertical roots can reach depths of more than 10 feet (3.0 m). Trifluralin and other residual herbicides registered for use in processing tomatoes are usually incorporated into the top 2-3 inches (5.1-7.6 cm) of the soil profile. Because of their shallow placement, these herbicides may not suppress bindweed vines that are emerging from deeply buried rhizomes. In 2015 and 2016, we undertook a series of trials to describe how sub-surface layered (SSL, and defined as the deposition of a thin, concentrated, horizontal herbicide layer below the typically treated zone) applications of trifluralin (as Treflan at 32 oz/A or 2.3 L/ha) interacted with surface applied herbicides [(trifluralin, S-metolachlor (as Dual Magnum at 27 oz/A or 2.0 L/ha) and sulfentrazone (as Zeus at 3.2 oz/A or 0.2 L/ha)] with respect to field bindweed control. All trials were conducted at the University of California, Davis, research farm (38 32’N, 121 47’W), where the soil is a fine, silty loam (Yolo series, 37% sand, 41% silt, 22% clay; 1.5-3% OM; pH 6.7-7.2). The fields used in this study were known to be heavily infested with field bindweed. SSL applications of trifluralin were made using horizontal spray blades (each with a spray width of 6 inches or 15.2 cm) prior to transplanting. Trifluralin was applied as either a banded or a broadcast application; the application rig was calibrated to deliver 40 GPA (374 L/ha). A banded blade application received trifluralin only to the outer-most 6 inches (15.2 cm) of each bed (i.e. the bed shoulders) at a depth of 4-6 inches (10.2-15.2 cm); a broadcast application received trifluralin 4-6 inches (10.2-15.2 cm) deep across the entire width of the bed (38.4 inches or 1.0 m). Surface applied, mechanically incorporated herbicides, plus a non-treated check, were overlaid on top of the SSL treatments. All surface herbicides were applied using a CO2-pressurized backpack sprayer equipped with three 8002VS flat-fan nozzles (TeeJet Technologies, Wheaton, IL) spaced 16-20 inches apart (41.6-50.8 cm) and calibrated to deliver 20-30 GPA (187-281 L/ha). Tomatoes were transplanted within 24 hrs of the surface herbicide applications and were immediately irrigated with 1 inch (2.5 cm) of water to facilitate establishment. Field bindweed cover (defined as the percent (%) of the plot area that was occupied by field bindweed) and percent crop injury were assessed until tomato canopy closure began to occur.

Results from our 2015 trial indicated that field bindweed cover was significantly reduced when trifluralin was applied SSL in a broadcast pattern. When averaged over all surface herbicide treatments, bindweed cover in the broadcast-treated SSL plots was 7, 18, 36, and 12% at 1, 2, 3, and 4 weeks after tomato transplanting (WAT), respectively. Conversely, mean bindweed cover ranged from 10-11, 33-24, 49-50, and 26-31% at 1, 2, 3, and 4 WAT, respectively, in the banded SSL and non-treated plots. When averaged over all SSL treatments, bindweed cover was the greatest in the untreated check (16-66%) and the S-metolachlor treatment (10-47%); trifluralin and sulfentrazone were effective at suppressing field bindweed cover (5-34%), relative to the control plots. Crop injury was greatest when trifluralin was applied as a broadcast SSL application; when averaged over all surface herbicide treatments, crop injury in the broadcast-treated plots was 16, 29, 23, and 30% at 1, 2, 3, and 4 WAT, respectively. Crop injury for the banded SSL application and the non-treated control at 2, 3, and 4 WAT was 12 and 1%, 23 and 10%, 18 and 12%, and 22 and 12%, respectively. The extensive injury observed in this trial is likely because the transplants were relatively short and the root-balls could not be positioned below the SSL treated zone. Similar results were observed in the 2016 trial with respect to bindweed cover; cover in the broadcast SSL application ranged from 3-19% whereas cover in the banded and untreated check treatments ranged from 3-32%. Bindweed cover was significantly reduced when surface-applied, mechanically incorporated herbicides were applied; cover in the plots treated with surface-applied herbicides did not exceed 13%, regardless of the SSL treatment. Comparatively, bindweed cover in the untreated checks ranged from 4-66% (across all SSL treatments). Crop injury in the 2016 trial was typically <10%; this was attributed to that fact that the root balls of the transplants were successfully placed below the SSL zone. Although SSL applications of trifluralin appear to be effective at suppression bindweed in processing tomatoes, this strategy is not labeled for use in this crop. Crop injury can be significant when transplant roots are not positioned below the treated zones (as was observed in 2015). Carryover effects on rotation crops were not investigated in these trials and is a significant concern.


WEED MANAGEMENT IN ASPARAGUS WITH NEW HERBICIDES. B. H. Zandstra*, C. J. Phillippo; Michigan State University, East Lansing, MI (311)


Asparagus is a herbaceous perennial crop that is harvested for 6-8 weeks in spring and early summer.  Fields are productive for 12-15 years. PS II inhibitors have been the primary herbicides for many years, and their repeated use has resulted in development of resistance in some weed species.   Due to incomplete control, biennial and perennial weeds increase over time in asparagus fields.  Experiments were conducted in Michigan to test labeled and new residual herbicides for asparagus crop safety and weed control.


Residual herbicides were applied to the same plots for 4 years (2013-2016) on Spinks loamy sand with 86% sand.  The variety Millennium was planted in 2011.  Terbacil 1.12 kg/ha suppressed asparagus yields slightly over 4 years.  It controlled most annual weeds but was weak against Powell amaranth (Amaranthus powellii S. Wats).  A combination of diuron 1.8 kg/ha plus metribuzin 1.8 kg/ha provided good control of most annual weeds and caused no yield reduction.  Indaziflam 0.095 kg/ha caused some early scoring on asparagus spears but asparagus yield was not reduced in any year.  Indaziflam controlled common lambsquarters (Chenopodium album L.), field pansy (Viola rafinesquii Greene), hairy vetch (Vicia villosa Roth), Powell amaranth, and smallflower geranium (Geranium pusillum L.).  Clomazone 2.24 kg/ha did not reduce asparagus yield and controlled field sandbur (Cenchus incertus M.A. Curtis), common lambsquarters, and field pansy. It was weak against Powell amaranth, hairy vetch, and Russian thistle (Salsola iberica Sennen &Pau).  Rimsulfuron 0.07 kg/ha was safe on asparagus and provided good control of field pansy, hairy vetch, and Powell amaranth.  It was weak against common lambsquarters and Russian thistle.  Isoxaben 1.7 kg/ha plus S-metolachlor 2.1 kg/ha was safe on asparagus and provided good control of downy bromegrass (Bromus tectorum L.) and field pansy.  It was weak on hairy vetch, Powell amaranth, Russian thistle, and smallflower geranium.   Pyroxasulfone 0.3 kg/ha was safe on asparagus but did not provide sufficient weed control through the harvest season.  Bicyclopyrone 0.05 kg was safe on asparagus and controlled field sandbur, common lambsquarters, field pansy, hairy vetch, and Russian thistle.  It missed downy bromegrass, Powell amaranth, and smallflower geranium.  Mesotrione 0.27 kg/ha plus pendimethalin 2.1 kg/ha controlled downy bromegrass, common lambsquarters, field pansy, hairy vetch, and Powell amaranth.  It was weak on Russian thistle and smallflower geranium.


Powell amaranth was tolerant of preemergence treatments of diuron 2.24 kg/ha and terbacil 0.9 kg/ha.  Powell amaranth was controlled by preemergence treatments of metribuzin 1.12 kg/ha and mesotrione 0.27 kg/ha and postemergence treatments of halosulfuron


BICYCLOPYRONE IN VEGETABLE CROP WEED MANAGEMENT. C. J. Phillippo*, B. H. Zandstra; Michigan State University, East Lansing, MI (312)


Bicyclopyrone is a Group 27 (F2) HPPD inhibitor labeled for use on corn in the combination products Acuron® and Acuron Flexi®.  It is not currently registered as a single active ingredient.  Bicyclopyrone was applied to various vegetable crops for four years to determine crop tolerance and weed control efficacy.  The rates in most experiments were 0.037 and 0.05 kg/ha applied either pre- and post-transplant or pre- and postemergence.


Bicyclopyrone was safe on carrots (Daucus carota L.) at 0.037 kg/ha preemergence and early postemergence, but injured carrots at 0.05 kg/ha pre- and postemergence.  Addition of NIS 0.25% with bicyclopyrone increased carrot injury.  On muck soil there was minimal injury on onions (Allium cepa L.) when treated preemergence with bicyclopyrone at 0.037 and 0.05 kg/ha and a single postemergence application at 0.05 kg/ha.  Onions treated preemergence on mineral soil were severely injured by bicyclopyrone.  On mineral soil, it was safe on established chives (Allium schoenoprasum L.) pre- and postemergence, seeded chives preemergence, and green onion postemergence at 0.037 and 0.05 kg/ha, but results were mixed on green onion preemergence.    


Bicyclopyrone was safe on cole crops (Brassica oleracea L.) applied pretransplant at 0.037 and 0.05 kg/ha, but was often unsafe posttransplant and postemergence.  Bicyclopyrone did not injure banana pepper (Capsicum annuum L.) when applied postemergence at 0.037 kg/ha.  However, it was unsafe on banana pepper pre- or posttransplant, and caused major injury to bell pepper, cherry pepper, jalapeno pepper, and tomato (Solanum lycopersicum L.) both pretransplant and postemergence.  Bicyclopyrone was safe on pumpkin (Cucurbita pepo L.) winter squash (Cucurbita maxima L.), and cucumber (Cucumis sativus L.) preemergence at 0.037 kg/ha, but was not safe on winter squash at 0.05 kg/ha.  It was safe preemergence on asparagus (Asparagus officinalis L.) at 0.05 kg/ha, and safe on edamame (Glycine max (L.)Merr.), rhubarb (Rheum rhabarbarum L.), and sweet corn (Zea mays subsp. mays L.) at 0.037 and 0.05 kg/ha.  Bicyclopyrone injured celery (Apium graveolens L.) post-transplant at 0.037 kg/ha.


Bicyclopyrone was not safe on red beet (Beta vulgaris L.), sugar beet, swiss chard, and lettuce.  It was also not safe on basil (Ocimum basilicum L.), dill (Anethum graveolens L.), fennel (Foeniculum vulgare Mill.), parsley (Petroselinum crispum (Mill.) Fuss), or spearmint (Mentha spicatum L.).  It was safe on cilantro (Coriandrum sativum L.) preemergence at 0.037 and 0.05 kg/ha, but was not safe postemergence. 


Bicyclopyrone controlled barnyardgrass (Echinochloa crus-galli (L.) Beauv.), foxtails (Setaria spp.), and large crabgrass (Digitaria sanguinalis (L.) Scop) pre- and postemergence.  Fall panicum (Panicum dichotomiflorum Michx.) was controlled preemergence and witchgrass (Panicum capillare L.) was controlled postemergence.  Pre- and postemergence application controlled common ragweed (Ambrosia artemisiifolia L.), eastern black nightshade (Solanum ptycanthum Dun.), and redroot pigweed (Amaranthus retroflexus L.).  Bicyclopyrone also controlled common lambsquarters (Chenopodium album L.), field pansy (Viola rafinesquii Greene), horseweed (Conyza canadensis L. Scop.), prostrate knotweed (Polygonum aviculare L.), and wild radish (Raphanus raphanistrum L.) preemergence, and shepherdspurse (Capsella bursa-pastoris (L.) Medic.) postemergence.


WEED MANAGEMENT IN VEGETABLE CROPS WITH BICYCLOPYRONE. C. Hu*1, Y. Chen1, D. Bruns2, D. Doohan1; 1Ohio State University, Wooster, OH, 2Syngenta, Columbus, OH (313)


Bicyclopyrone is a new herbicide that has been registered for use in corn. Recent reports indicating tolerance in some vegetables make bicyclopyrone a promising candidate for weed control in vegetable production. Field trials were conducted from 2013 to 2016 to evaluate the response of selected vegetable crops to the herbicide. In 2013 and 2014, onion, carrot and dill showed tolerance to pre-emergence (PRE) application in muck soil while post-emergence (POST) application induced severe injury. Radish showed 18% and 29% injury respectively in 2013 and 2014 with PRE application. Post-directed applications were either completely safe or resulted only in slight injury. Further testing on carrot and onion in 2015 and 2016 confirmed results of the first two years. Tolerance of two onion varieties was evaluated in loam soil in 2015. Variety-dependent injury from 3 to 14% by PRE or POST-directed application at 50 g ai/ha was observed. Additional greenhouse experiments were conducted to determine the effect of soil type on the response of onion, carrot and leek.  Four PRE rates (12.5, 25, 50 and 100 g ai/ha) were tested.  Injury was not observed on vegetables in the muck soil; whereas, all vegetables were damaged when growing in a sand/Pro-MixTM blend at the rate of 50 g ai/ha. The control efficacy of PRE and POST bicyclopyrone application on hairy galinsoga, common purslane and prostrate pigweed was also determined. POST application at both 37.5 and 50 g ai/ha controlled hairy galinsoga and small common purslane plants. Efficacy was species- and stage-dependent. Efficacy of the PRE application was largely influenced by soil type. Control was better in sand than in muck soil for all three weeds. Our results provide further evidence that bicyclopyrone is a very promising PRE herbicide for the vegetable industry. 


RESPONSE OF VEGETABLE CROPS TO PREPLANT GLUFOSINATE APPLICATIONS. A. S. Leiva Soto*1, R. J. Edwards2, E. Chapman2, C. Hu1, D. Doohan1; 1Ohio State University, Wooster, OH, 2Department of Horticulture and Crop Science, The Ohio State University, Wooster, OH (314)


Response of Vegetable Crops to Preplant Glufosinate Applications. A. S. Leiva Soto, R. J. Edwards, E. Chapman, Hu C., C. Herms, D. Doohan; The Ohio State University, Wooster, OH.

Glufosinate-ammonium has shown to be an effective control for glyphosate-resistant horseweed (Conyza canadensis (L.) Cronq.), but the label requires a 70- to 180-day plant back interval for most vegetable crops. A greenhouse experiment was conducted at the Ohio Agricultural Research and Development Center in Wooster, OH in 2016 to evaluate the potential safety of glufosinate-ammonium for green bell pepper (Capsicum annuum) transplants when used at a shorter, and thus more practical, plant back interval. We were also interested to determine if soil characteristics like organic matter content had an impact on green bell pepper response. Prior to transplanting, different soil substrates were treated with glufosinate-ammonium. The herbicide was applied at X/2, X, 2X, 4X, 8X and 16X of the recommended field rate of 415 g ae ha-1, plus an untreated control. Three soil substrates were used (75:25 Linwood series muck soil:sand mixture (MS), Wooster series silt loam (SL), and 30:70 Wooster series silt loam:sand mixture (SLS)). The MS substrate had the highest level of organic matter (11.6%), followed by SL (1.9%) and SLS (0.1%). Herbicide doses were applied 24 hours before transplanting with a laboratory track-sprayer using a three nozzle hydraulic boom fitted with TTJ60-11002 nozzle tips. Nozzle spacing was 46 cm, liquid pressure was 276 kPa and boom travel speed was 6.5 km h-1 delivering 190 L ha-1. The experimental design was a randomized complete block with a factorial combination and 8 replications. Green bell pepper seedlings (ca. 14 cm tall) were transplanted into 1.72-L pots containing one of the three soils, 36 days after seeding. Crop injury was assessed visually using a 0-100 linear scale in which 0 indicated no injury and 100 indicated death of the crop. Crop injury and total plant height were measured 1, 2 and 3 weeks after transplanting (WAT), and a final dry weight of aboveground biomass was obtained. Final height data were converted to a proportional height increase (%) for analyses. Data were analyzed using Proc GLM in SAS (v. 9.3). Soil substrate impacted bell pepper injury, but only at the highest rates. Plants in the SLS substrate, which had the lowest organic matter content, showed significant injury at 8X and 16X, compared to very little or no injury for the other substrates at those same rates. A similar pattern was seen for final dry weight and height increase at the 16X rate, with SLS having the greatest impact. These data, along with that from several field trials, indicate little risk to green bell peppers transplanted 24 hours after glufosinate-ammonium application to silt loam and muck soils if the recommended rates are used, indicating that it can be used as an effective and safe burndown herbicide for weed control prior to transplanting green bell pepper.


DISSIPATION OF FOMESAFEN IN FLORIDA STRAWBERRY PRODUCTION. T. V. Reed*1, P. C. Wilson1, N. Boyd2; 1University of Florida, Gainesville, FL, 2University of Florida, Balm, FL (315)


Fomesafen is a protoporphyrinogen oxidase inhibitor that has the potential to be used as an alternative mechanism of action for preemergence nutsedge (Cyperus spp.) and broadleaf weed control in Florida production of small fruit and vegetables. The plasticulture system could decrease fomesafen dissipation and dissuade producers from using the herbicide for fear of injury to crops in subsequent growing seasons. Field experiments were conducted in Balm, FL in 2014-2015 and 2015-2016 growing seasons to investigate fomesafen persistence and movement in soil under Florida strawberry (Fragaria × ananassa Duch.) production system. Treatments included two rates of fomesafen at 0.42 and 0.84 kg ai ha-1, and a nontreated control. Fomesafen applications did not injure strawberry or decrease yields. Soil samples were taken from plots treated with fomesafen at 0.42 kg ai ha-1 throughout the growing season. Fomesafen concentration data for 0.0 to 0.1 m depth in soil was described using a three-parameter logistic function. The days required for 50% fomesafen dissipation were 37 and 47 for 2014-2015 and 2015-2016 growing seasons, respectively. Fomesafen was detected in the 0.0 to 0.1 m depth soil at 167 and 194 days after treatment in 2014-2015 and 2015-2016 growing seasons, respectively. Fomesafen concentration was less than 25 ppb on any sampling date for 0.1 to 0.2 m and 0.2 to 0.3 m depths. 

MINT TOLERANCE TO LINURON APPLIED AS A DORMANT AND EARLY POSTEMERGENCE TREATMENT. S. C. Weller*1, R. A. Boydston2, J. Colquhoun3, C. Mallory-Smith4, A. Hulting4, R. Wilson5; 1Purdue University, West Lafayette, IN, 2USDA-ARS, Prosser, WA, 3University of Wisconsin, Madison, WI, 4Oregon State University, Corvallis, OR, 5University California, Tulelake, CA (316)


A multi-state field trial was conducted in California, Indiana, Oregon, Washington, and Wisconsin to determine the tolerance of peppermint and Scotch spearmint to linuron. Field trials tested mint response to linuron applied at several rates, alone or in combination with other herbicides when applied preemegence to the soil at the dormant mint stage of growth, prior to mint emergence, at an early mint emergence stage or after the first cutting of the mint hay (in double cut mint). Results over all states showed linuron was safe on Scotch spearmint and peppermint when applied preemergence at 0.56 and 1.12 kg ai/ha alone. Linuron applied preemergence in tank mixes with other herbicides sometimes resulted in unacceptable injury to the mint depending on the location, herbicide combination and mint type. Injury was greater with linuron + sulfentrazone and linuron + flumioxazin at 2 locations but the mint recovered and hay and oil production were not reduced except in the IN experiments. Postemergence applications of linuron at 0.56 and 1.12 kg ai/ha injured mint to a greater extent than preemergence applications. In several cases, injury from the 0.56 kg ai/ha rate applied postemergence was minor and transient, however, injury at the 1.12 kg/ha rate applied postemergence was not acceptable at most locations. Injury from any of the linuron rates or application timings seldom resulted in significant hay or oil yield loss in the western states of CA, OR and WA but injury from postemergence application in IN and WI were not acceptable. Addition of crop oil concentrate to linuron applied postemergence tended to increase mint injury at some locations.


HERBICIDE TESTING IN DOUGLAS FIR NURSERIES. T. W. Miller*; Washington State University, Mount Vernon, WA (317)


Trials were conducted to determine the sensitivity of young Douglas fir (Pseudotsuga menziesii (Mirbel) Franco) seedlings to several herbicides.  Plots were established in May on newly-transplanted Douglas fir near Aurora, Oregon.  Herbicides were applied over-the-top of dormant seedlings four days after transplanting using a CO2-pressurized backpack sprayer equipped with a five-nozzle boom.  Postemergence applications were made June 15, 2015, using the same equipment described above.  Weed control and tree injury was estimated June 15, July 1, and September 9, 2015.  Three adjacent trees were dug in each plot January 20, 2016, and shoot length, shoot fresh weight, root fresh weight, and trunk caliper were measured.  Tree injury in June exceeded 40% (as compared to nontreated trees) with flazasulfuron (0.016 and 0.031 lb/a), saflufenacil (0.044 and 0.088 lb/a), oxyfluorfen + penoxulam (9 pt/a Pindar GT), and pyroxasulfone (0.067 lb/a).  Tree injury from these treatments and from triclopyr amine POST (1.13 and 1.88 lb/a) still exceeded 35% in July, while both rates of saflufenacil and triclopyr amine and oxyfluorfen + penoxulam (9 pt/a rate) exceeded 35% injury in September.  Other treatments did not differ from nontreated Douglas fir at the September evaluation.  September weed control exceeded 75% with all treatments except the two rates of saflufenacil (60 and 68% for low and high rates, respectively).  Douglas fir shoot length, shoot weight, and root weight in January, 2016 did not differ from nontreated Douglas fir trees, although saflufenacil at the high rate reduced trunk caliper.  Taken together, oxyfluorfen + penoxulam at 6 and 9 pt/a, and tested rates of flazasulfuron, triclopyr amine, and saflufenacil were injurious to Douglas fir seedlings.  Further testing of pyroxasulfone is warranted, while indaziflam, dithiopyr, isoxaben, and mesotrione appear to be safe for this use.

USE AND BENEFITS OF SIMAZINE IN FRUIT AND NUT CROPS THROUGH 2015. R. S. Fawcett*; Fawcett Consulting, Huxley, IA (318)


The US Environmental Protection Agency released its preliminary draft ecological assessment for the triazine herbicides for public comment in June, 2016.  This draft contains errors and incomplete information which if not corrected, would threaten to severely curtail a grower's ability to use simazine.  A Triazine Benefits Team was assembled by Syngenta to document benefits of the triazine herbicides.  The information reported here concentrates on the use of simazine in many fruit and nut crops.  Simazine provides residual control of many broadleaf and grass weeds.  It has been an important weed management tool in fruit and nut crops for over 50 years and is one of the lowest cost herbicide alternatives in these crops.  Independent third-party herbicide use survey data were analyzed for the 2013-15 period.  Only crops with simazine use on >10% of hectares grown are discussed.  Simazine was applied to an average 10.2% of apple hectares, 52.5% of caneberry hectares, 14.0% of grapefruit hectares, 11.5% of grape hectares, 22.7% of hazelnut hectares, 12.7% of orange hectares, 12.5% of peach hectares, 10.9% of pear hectares, and 12.3% of walnut hectares.  Average cost of simazine per base hectare was $24.49 for apples, $18.36 for caneberries, $38.57 for grapefruit, $22.19 for grapes, $27.28 for hazelnuts, $33.58 for oranges, $17.96 for peaches, $32.02 for pears, and $33.04 for walnuts.  These costs are markedly lower than those of some of the new herbicides that have entered the market in recent years.  In several crops (grapefruit, grapes, oranges and peaches), simazine was more cost effective than glyphosate, which was the active ingredient used on the most hectares in all these crops except except caneberries.  More caneberry hectares were treated with simazine than with any other herbicide.  Glyphosate is often applied more than once per season, ranging up to 3.5 times per year in oranges, while simazine is usually applied only once per season and provides good residual activity.  Glyphosate-resistant weeds are an increasing problem in fruit and nut crops.  Several new active ingredients have been recently registered.  Four are from the PPO inhibitors family of chemistry (carfentrazone ethyl, flumioxazin, pyraflufen ethyl, and saflufenacil), which already has an established product used in these crops (oxyfluorfen).  A new mode of action, inhibition of cell wall synthesis (indaziflam), is widely used in some crops.  Simazine is the only member of the WSSA Group 5 (photosystem II)  site of action products used on >10% of hectares in all crops in this analysis, except for oranges and grapefruit, which have one additional Group 5 product ( bromacil).  Simazine is needed for control of weed species having resistance to other modes of action. Simazine and other active ingredients with different modes of action are needed for use with or without glyphosate as part of sustainable resistance management programs.  The California Specialty Crops Council reports that simazine is used once every 2 or 3 years in rotation with other herbicides to manage herbicide resistance.

ACETYL-COA CARBOXYLASE OVEREXPRESSION IN HERBICIDE RESISTANT CRABGRASS (DIGITARIA SANGUINALIS). R. E. Nurse*1, K. Obeid2, E. R. Page1, M. Simard3, M. LaForest3; 1Agriculture and Agri-Food Canada, Harrow, ON, 2Ontario Ministry of Agriculture, Food and Rural Affairs, Harrow, ON, 3Agriculture and Agri-Food Canada, Saint-Jean-sur-Richelieu, QC (319)


Growers have to cope with increasing cases of herbicide resistant weeds.  The development of genetic tests is helping the identification of resistance for specific species and is leveraging years of research to identify causal mutations reported in the literature.  Whereas most of these studies describe target site mutations, an unknown number of cases exist in nature where this molecular mechanism is not involved.  The molecular descriptions of these cases are likely under-reported due to analytic challenges.  A crabgrass biotype (Digitaria sanguinalis) from Southern Ontario tested positive for resistance to Acetyl-CoA Carboxylase (ACCase) inhibitors (WSSA group 1) herbicides (up to 4x the labelled rate) although none of the target site mutations previously known to confer resistance were detected.  Our goal was to evaluate, using RNASeq, if any gene showed differential expression that could explain herbicide resistance.  Both RNASeq results and confirmation by Reverse-Transcriptase Quantitative PCR (QRT-PCR) indicated an increase in the level of expression of the target gene involved in the production of ACCase.  The number of transcrpts was 3.4 to 9.3 times higher in the resistant biotyupe compared to the susceptible population.  The high variability of ACCase transcript levels in the resistant plants could be indicitive of a genomic architecture promoting higher expression.  The QRT-PCR assay developed could serve as a diagnostic tool when ACCase inhibitor resistance is suspected. 

A COVER CROP MIXTURE FOR WEED AND STING NEMATODE MANAGEMENT. C. A. Chase*, S. B. Coplin; University of Florida, Gainesville, FL (320)


In utilizing cover crop monocultures for weed management the focus is often on maximizing cover crop biomass production. However, growers are increasingly interested in a broader range of agroecological services that can result from utilizing cover crop mixtures. To achieve mixtures in which each species is well represented, research is needed to determine the appropriate proportion for each component species. Of interest in this study, was a mixture for use in organic strawberry cropping systems and thus the cover crop species were selected based on reported resistance to sting nematode, Belonolaimus longicaudatus. In the summer of 2015, slender-leaf rattlebox (Crotalaria ochroleuca), hairy indigo (Indigofera hirsuta), sunn hemp (Crotalaria juncea), and American jointvetch (Aeschynomene americana) were evaluated in comparison with a weedy control. The seed proportions by weight were: 1:1:1:1, 1:2:1:2, 2:1:1:1, and 2:2:1:3, respectively. The mixtures were evaluated at the Plant Science Research and Education Unit in Citra, FL and at Rosie’s Organic Farm in Gainesville, FL. The objective of the study was to determine which mixture would provide a diverse but weed-suppressive canopy. By 10 weeks after planting (WAP) cover crop shoot biomass ranged from 8000 to 12000 kg/ha. Although sunn hemp seed proportion in the mixtures comprised only 12 to 25% of the seed mix, the sunn hemp shoot biomass produced ranged from 46 to 73% in Citra and 80 to 91% in Gainesville. Weed biomass with mixtures was very low in Citra by 10 WAP (< 1000 kg/ha) but was not significantly different from the weedy control. In Gainesville, weed biomass ranged from 4000 to 9000 kg/ha with no significant difference among treatments. The dominance of ‘Tropic Sun’ sunn hemp in mixtures regardless of seed proportion appears to have inhibited establishment of slower growing and/or shorter species in the mix. Future research will utilize ‘AU Golden’, a shorter stature sunn hemp variety.    



Fall-seeded cover crops offer many benefits to crop production, including weed suppression in subsequent direct-seeded summer annual crops.  A roller-crimper can be used to terminate cover crop growth prior to planting; however, little is known about managing cover crop residues for direct-seeded snap bean production.  Our objectives were to: 1) quantify the effectiveness of roller-crimper-based cover crop control methods on rye and vetch cover crops, and 2) determine snap bean and weed response to the cover crop control methods.  We conducted field experiments in two primary snap bean production regions of the US, namely, Illinois and Washington.  In three cover crop treatments (vetch, rye, and vetch+rye), four cover crop control methods were tested, including: 1) roller-crimped once, 2) roller-crimped twice, 3) roller-crimped + burndown herbicide, and 4) roller-crimped + burndown herbicide + residual herbicide + handweeding.  In order for roller-crimping to be effective, cover crops needed to be well into their reproductive stages, which resulted in a large amount of cover crop biomass (>8,500 kg ha-1) at snap bean planting.   Heavy residues of rye complicated snap bean planting; however, earlier cover crop termination resulted in incomplete vetch control, which later became a weed in snap bean.  Roller-crimped rye and vetch suppressed final weed biomass; however, snap bean yields often were reduced relative to the bare soil control.  Challenges to using roller-crimped rye and vetch cover crops in no-till snap bean center on striking a balance among: 1) obtaining weed-suppressive levels of cover crop biomass, 2) avoiding excessive levels of cover crop biomass detrimental to snap bean, and 3) obtaining complete termination of the cover crop.  Growers electing to not use synthetic herbicides face additional challenges related to weed escapes in the crop.


PREEMERGENCE HERBICIDES IN COVER CROPS DURING THE FALLOW PERIOD FOR WEED CONTROL IN LEAFY BRASSICA CROPS. P. J. Dittmar*1, N. Boyd2; 1University of Florida, Gainesville, FL, 2University of Florida, Balm, FL (322)


Florida vegetable growers plant cover crops during the fallow period to suppress weeds, control nematodes, and improve soil structure. The application of preemergence herbicides during the summer fallow period can decrease weed populations in the fall planted vegetable crop. Cover crops have different canopy structures that influence light penetration to the soil surface. Field experiments were planted in 2016 to evaluate s-metolachlor applied in cover crops for weed control in fall planted bok choy. Treatments were sorghum sudangrass with or without s-metolachlor, sunn hemp with or without s-metolachlor, cowpea with or without s-metolachlor, two applications of glyphosate, and nontreated fallow period. Early weed control in the cover crop was not different between the treatments. At 4 wk after planting the bok choy, two applications of glyphosate during the fallow period had the lowest number of nutsedge compared to the other treatments. Sorghum sudangrass with s-metolachlor had greater control of nutsedge in the bok choy compared to sorghum sudangrass alone. No differences were observed between treatments for grass and broadleaf weed populations in bok choy. The use of s-metolachlor during the summer cover crop is dependent on the canopy structure of the cover crop and the types of weeds that are in the field.


EXPLORING THE POTENTIAL FOR A REGULATORY CHANGE TO ENCOURAGE DIVERSITY IN HERBICIDE USE. S. B. Powles1, T. A. Gaines*2; 1University of Western Australia, Perth, Australia, 2Colorado State University, Fort Collins, CO (323)


An over-reliance on herbicides in several important grain and cotton producing regions of the world has led to the widespread evolution of herbicide resistant weed populations. Of particular concern are weed populations that exhibit simultaneous resistance to multiple herbicides (MHR). Too often, herbicides are the only tool used for weed control. We term this quasi-addiction to herbicides as Herbicide Only Syndrome (HOS). Growers and their advisers focus on herbicide technology, unaware of or ignoring basic evolutionary principles or the necessary diversity provided by other methods of weed control. Diversity in weed control practices disrupts resistance evolution. Significant challenges exist to implementing diversity, including how to address information so that producers choose to alter existing behaviors (HOS) and take calculated risks by attempting new and more complex strategies. Herbicide resistance management in the long-term will require creativity at many sectors, including roles for growers, industry, researchers, consultants, retailers, and regulators. There can be creativity in herbicide registration and regulation, as exemplified by the recent EPA program that encourages herbicide registrants to register products in minor crops. We propose one idea for a regulatory incentive to enable herbicide registrants in jurisdictions like the U.S. to receive an extended data exclusivity period in exchange for not developing one new herbicide in multiple crops used together in rotation, or for implementing stewardship practices such as robust mixtures or limitations on application frequency. This incentive would provide a mechanism to register herbicides in ways that help to ensure herbicide longevity. Approaches based only on market or financial incentives have contributed to the current situation of widespread MHR. Our suggestion for regulatory creativity is one way to provide both financial and biological benefits to the registering company and to the overall stakeholder community by incentivizing good resistance management.

A BIOECONOMIC ANALYSIS OF TRIAZINE HERBICIDE USE IN U.S. CORN AND GRAIN SORGHUM. D. C. Bridges*; Abraham Baldwin Agricultural College, Tifton, GA (324)


WEED SCIENCE IN CHINA: OPPORTUNITIES AND CHALLENGES. L. Jiang, Z. Li*; China Agricultural University, Beijing, Peoples Republic (325)


Rapid industrialization in China has been draining the labor forces from agricultural production for decades. As a result, Chinese farmers have to inevitably rely on herbicides to managing weeds to maintain profitable. Currently, the usage of herbicides in China surpasses insecticides and fungicides, becoming the leading pesticide. Consequently, herbicide misuse and overuse bring great challenges on crop safety and result in rapid development of herbicide tolerance in weeds. Wise use of herbicide resistant (HR) crops could effectively address these issues. However, Chinese farmers have no access to biotech HR crops because of the transgenic nature. Genome editing biotechnologies are capable of generating non-GM HR traits; notably, the first genome-edited crop, SU canola resistant to sulfonylurea herbicides, was approved to be non-GM, and planted for the first time in human history in the US in 2015. This event indicated genome-editing biotechnologies could confer essentially all crops non-GM HR traits. Researchers at China Agricultural University committed and succeeded in generating no-GM HR plants using the state-of-the-art base-editing biotechnology, thus opening a new era of weed control in China.


THE U.S. EPA'S HERBICIDE RESISTANCE MANAGEMENT APPROACH. B. J. Chism*1, J. Becker2, A. Jones2; 1US Environmental Protection Agency, Point of Rocks, MD, 2US Environmental Protection Agency, Washington, DC (326)


The EPA's Office of Pesticide Programs in consultation with USDA, grower groups, Resistance Action Committees, and WSSA has released guidance for registrants concerning herbicide resistance management.  This will provide growers and other herbicide users with detailed information and recommendations to slow the development and spread of herbicide resistant weeds.  The Agency has created two pesticide registration notices one on guidance for herbicide resistance management labeling, education, training, and strewardship and a second on guidance for pesticide registrants on pesticide resistance management labeling.  During the registration review process and the registration of herbicides on herbicide resistant crops the Agency has started to recommend that registrants incorporate resistance management into their herbicide labels and educational materials.   The Agency expects that in the longer term, registrants will routinely incorporate resistantce management elements on all herbicide labels. 

FIELD-EVOLVED RESISTANCE OF DOWNY BROME (BROMUS TECTORUM) TO IMAZAMOX IN CEREAL PRODUCTION. P. Jha*1, V. Kumar1, A. J2, S. Leland1; 1Montana State University, Huntley, MT, 2Montana State University-Bozeman, Huntley, MT (327)


Downy brome (Bromus tectorum L.) is an invasive winter annual grass weed in crop, range, and pasture lands across the Western US, including Montana. During summer 2016, a downy brome population with putative resistance (R) to imazamox (Beyond®), an acetolactate synthase (ALS) inhibitor, was collected from a winter wheat (ClearfieldÒ) field, near Hammond, MT, where imazamox has been used to control downy brome over >5 yr. The objectives were to confirm and characterize the level of imazamox resistance in R downy brome population relative to a susceptible (S) population, and investigate the underlying mechanism of resistance. The S downy brome population was collected from the research farm at the Montana State University Southern Agricultural Research Center, near Huntley, MT. Whole-plant dose–response experiments indicated that the R population had approximately 98-fold level of resistance relative to the S population on the basis of percent control ratings (I50 values). On the basis of shoot dry weight response (GR50 values), the R downy brome exhibited resistance index (R/S) of 121-fold. A pre-treatment of R downy brome with malathion (cytochrome P450 inhibitor) did not alter the resistance phenotype for imazamox, most likely ruling out the possibility of a non-target site resistance mechanism in this population. The sequence analysis of ALS gene in R plants exhibited a single-point mutation from G to A, conferring a change of the amino acid serine to asparagine at codon 653. Therefore, we propose that a Ser653 to Asn substitution in the ALS gene confers high levels of resistance to imazamox in the R downy brome population. This is the first report on the evolution of imazamox-resistant downy brome identified in Montana, USA, and first confirmation of this target site (ALS gene) mutation (Ser653 to Asn) as a mechanism of ALS resistance in this weed species. 





Waterhemp is a problematic annual weed species in the Midwest, and has evolved resistance to one or more of six groups of herbicides i.e. synthetic auxins, 5-enolypyruvyl-shikimate-3-phosphate synthase (EPSPS), protoporphyrinogen oxidase (PPO), acetolactate synthase (ALS), photosystem II (PSII), and 4-hydroxyphenyl-pyruvate-dioxygenase (HPPD) inhibiting herbicides. In 2014, a grower in north central Missouri reported increasing difficulty in managing a waterhemp population with numerous herbicides, including 2,4-D. To characterize herbicide resistance, dose-response studies were conducted and confirmed five-way resistance to the synthetic auxins, EPSPS, PPO, ALS, and PSII inhibitors. Molecular basis for resistance was studied by performing DNA sequencing. DNA sequencing confirmed the presence of a previously characterized point mutation in the ALS gene, which results in the TRP-574-Leu amino acid change, and is associated with resistance to ALS-inhibiting herbicides. The PP2XL gene sequencing confirmed the codon deletion mutation that corresponds to ∆G210 and is known to confer resistance to PPO-inhibiting herbicides.  The previously characterized point mutations associated with resistance to PSII and EPSPS inhibiting herbicides were not detected in the psbA or EPSPS genes of this waterhemp population, respectively. Further molecular investigations are underway to characterize the mechanism of resistance to synthetic auxins, PSII- and EPSPS-inhibiting herbicides.

CHARACTERIZATION OF GLYPHOSATE-RESISTANT RUSSIAN-THISTLE (SALSOLA TRAGUS L.) POPULATIONS IN MONTANA AND PACIFIC NORTHWEST. V. Kumar*1, P. Jha2, J. F. Spring3, A. J2, V. K. Nandula4, K. N. Reddy4, D. Lyon3, I. C. Burke3; 1Montana State University, Huntley, MT, 2Montana State University-Bozeman, Huntley, MT, 3Washington State University, Pullman, WA, 4USDA-ARS, Stoneville, MS (330)


Glyphosate-resistant (GR) weeds are an increasing management concern for growers in the no-till cereal-based production systems of the northwestern United States. During summer/fall of 2015, Russian thistle control failures with glyphosate were reported from chemical fallow fields in Choteau County, MT (MT-R) and Columbia County, Washington (WA-R). To confirm and characterize the levels of resistance in these GR populations relative to known glyphosate-susceptible (GS) populations (MT-S and WA-S from MT and WA, respectively), whole-plant glyphosate dose-response and shikimate accumulation assays were conducted. To understand the mechanism of resistance, the EPSPS (5-enolpyruvylshikimate-3-phosphate synthase) gene was analyzed for target-site mutations (PCR and sequencing) and increase in gene copy numbers (qPCR assay). On the basis of shoot dry weight response (GR50 values), the MT-R population showed 4.5-fold and 5.9-fold resistance to glyphosate relative to the MT-S population under greenhouse and outdoor conditions, respectively. The WA-R population had 3.0- to 5.0-fold resistance relative to the WA-S accession in greenhouse experiments, and 1.9- to 7.5-fold resistance in multi-site field experiments. The MT-S population accumulated approximately 4- and 9-times more shikimate than the MT-R and WA-R populations, respectively, 10 d after treatment with 1260 g ae ha-1 of glyphosate. Partial sequencing of the EPSPS gene revealed no mutations at the Thr102 or Pro106 codon in those GR populations. Additionally, no difference in the EPSPS genomic copy number was observed between GR and GS populations. Further investigations on transcript expression of the EPSPS gene and [14C]-glyphosate uptake and translocation of GR vs. GS populations are under progress. This is the first global report on field-evolved GR Russian thistle identified in Montana and Washington. Growers should adopt diversified weed control tools including alternative, effective sites-of-action herbicides to prevent further spread of GR or evolution of multiple HR Russian thistle populations in this region.       


GLYPHOSATE RESISTANT ECHINOCHLOA SPP. FROM TENNESSEE AND MISSISSIPPI – MOLECULAR ANALYSIS. V. K. Nandula*1, D. A. Giacomini2, J. Ray3, J. Bond4, L. E. Steckel5, P. J. Tranel2; 1USDA-ARS, Stoneville, MS, 2University of Illinois, Urbana, IL, 3USDA, Stoneville, MS, 4Mississippi State University, Stoneville, MS, 5University of Tennessee, Jackson, TN (331)


Echinochloa spp., including barnyardgrass (E. crus-galli) and junglerice (E. colona), are some of the worst weeds in the world causing devastating economic damage to growers and other land managers. In the midsouthern U.S., E. crus-galli is a particular problem in row crops including cotton, rice, and soybean. During the 2015-16 growing seasons, several E. crus-galli populations in Tennessee and Mississippi survived labeled rates of glyphosate. Greenhouse and laboratory studies were conducted to evaluate responses of these populations to a 1X labeled rate of glyphosate, followed by a glyphosate dose response experiment, on progeny of putative resistant plants. Prospective resistant plants were analyzed for the presence of one or more known point mutations on the enolpyruvyl shikimate-3-phosphate synthase (EPSPS) gene. DNA sequencing confirmed a P106S (proline to serine) mutation (CCA → TCA) in at least one resistant EPSPS allele in some of the Mississippi accessions, but not in the Tennessee accessions. Further research is underway to delineate the number of copies/alleles of EPSPS on which the P106S mutation occurs in the Mississippi E. crus-galli accessions.

RNA-SEQ ANALYSIS OF AMARANTHUS PALMERI TRANSCRIPTOMIC RESPONSE TO GLUFOSINATE. R. A. Salas*1, C. Saski2, R. E. Noorai2, A. Lawton-Rauh2, S. Srivastava1, R. L. Nichols3, N. R. Burgos1; 1University of Arkansas, Fayetteville, AR, 2Clemson University, Clemson, SC, 3Cotton Inc., Cary, NC (332)


Amaranthus palmeri is an aggressive, prolific weed that has become one of the most economically damaging weeds in the United States. Widespread occurrence of glyphosate-resistant A. palmeri prompted the use of alternative herbicides such as glufosinate to help control herbicide-resistant weeds in tolerant crops. Background variation in response to herbicide exists because of genetic diversity in weedy populations and field use rates are set to effect a reliable level of control. However, under suboptimal conditions, some naturally tolerant individuals may survive, providing incremental progression toward higher level of tolerance of the population.   A study was conducted to analyze the transcriptome of A. palmeri for differential gene expression between sensitive and tolerant plants in response to glufosinate. Leaf tissues from glufosinate-treated and nontreated seedlings were harvested 24 h after treatment for RNA-Seq analysis. Global gene expression was measured using Illumina reads from nontreated and treated tolerant (T) and susceptible (S) plants. A reference cDNA transcriptome consisting of 72,794 contigs was assembled, with 65,282 sequences assigned with putative annotations.  Sequences of glufosinate target gene GS2 from the transcriptome assembly did not contain polymorphisms unique to the T plants. Expression profiles revealed differential response to glufosinate in T and S plants. Glufosinate treatment in T plants triggered the expression of genes related to xenobiotic detoxification, ABA biosynthesis, stress response, stress signaling, structural stabilization, growth and senescence. Some genes associated with carbohydrate transport were repressed in T plants. On the other hand, glufosinate treatment in S plants induced the expression of genes associated with lipid biosynthesis, protein degradation, flavonoid biosynthesis, and stress signaling. Genes associated with photosynthesis were repressed in both T and S plants. Five hundred sixty-seven genes were differentially expressed between treated T and S plants. Genes that potentially enable tolerance to glufosinate included ABC transporter, glutathione S-transferase (GST), NAC transcription factor, nitronate monooxygenase (NMO), chitin elicitor receptor kinase (CERK1), heat shock protein 83, ethylene transcription factor, heat stress transcription factor, NADH-ubiquinone oxidoreductase, ABA 8-hydroxylase, and two cytochrome P450 genes (CYP72A, CYP94A1). Collectively, the level of induction of these genes endowed only 2-fold tolerance to glufosinate. The induction of genes that are related to stress response signaling, detoxification process, and transport of substances is a universal response to phytotoxic xenobiotics to enhance the plant’s ability to alleviate lethal effects. The cumulative small-effects of multiple genes could get fixed in a population that is subjected to a persistent stress factor such as herbicide application and lead to nontarget-site resistance.  


TRANSCRIPTOME PROFILES OF CYTOCHROME P450S IN MULTIPLE-RESISTANT ECHINOCHLOA COLONA IN RESPONSE TO PROPANIL. N. R. Burgos*1, S. Srivastava1, C. E. Rouse1, R. E. Noorai2, A. Lawton-Rauh2, C. Saski2; 1University of Arkansas, Fayetteville, AR, 2Clemson University, Clemson, SC (333)


Transcriptome Profile of Cytochrome P450s in Multiple-resistant Echinochloa colona in Response to Propanil and other Rice Herbicides

N.R. Burgos1, R. Noorai2, C.E. Rouse1, A.L. Rauh2, L. Fan3, J. Qiu3, C. Saski2

1Dept. of Crop, Soil, and Environmental Sciences, University of Arkansas, Fayetteville, AR, USA

2 Dept. of Genetics and Biochemistry, Clemson University, Clemson, SC, USA

3College of agriculture and biotechnology, Zhejiang University, Hangzhou, China


Mechanisms that endow resistance to herbicides fall into two broad categories: target site (TS) or nontarget site (NTS).  Target-site mechanisms are generally straightforward as many herbicides bind to a specific target, which are usually proteins that perform critical functions for plant growth and development. The majority of documented resistance mechanisms belong to this category.  Nontarget-site resistance mechanisms pertain to processes that either prevent, or reduce the amount of, herbicide reaching the target; detoxify the herbicide molecule; or mitigate the lethal toxic effects of the herbicide. Common examples of these are reduced herbicide absorption/translocation and increased herbicide detoxification. These processes involve many genes; thus, understanding NTSR is difficult. Cytochrome P450s (cytP450) are responsible for many herbicide detoxification processes in plants.  Multiple herbicide resistance is evolving among populations of junglerice (E. colona) and barnyardgrass (E. crus-galli) in the US-midsouth. A RNA-seq experiment using E. colona (ECO-45) with high resistance to propanil and quinclorac and low resistance to cyhalofop and glufosinate was conducted. ECO-45 and a susceptible standard (ECO-SS) were treated with the recommended dose of each herbicide and shoot tissues were harvested 24 hours later for transcriptome generation using paired-read ends in an Illumina-Hiseq platform. Nontreated plants were used as controls. The de novo transcriptome was assembled at CUGI using the Trinity package. Differential gene expression of predetermined pairwise expression profiles was assessed using the Bioconductor package from edgeR. The total number of differentially expressed genes (DEG) was 76,414. Only 7.5% of these were responsive to propanil in ECO-45 relative to the nontreated check. There were 15 cytP450 DEG transcripts in ECO-45 treated with propanil. Four of these were unique to propanil, 3 were common between propanil and quinclorac, 1 was common between propanil and glufosinate, and 3 were common between propanil, quinclorac, and glufosinate. There were 52 DEGs unique to glyfosinate and 23 DEGs unique to cyhalofop. These will be compared to the corresponding treatments with the susceptible standard to identify which genes are more highly expressed in resistant plants than in susceptible ones without herbicide application and which ones are more highly induced in resistant plants than in susceptible ones in response to herbicide treatment.



Susana Gonzalez1, Satoshi Iwakami2, Veonika Brabetz1, Todd A. Gaines1,2,4, Gudrun Lange5, Frank Maiwald3, Mark-Christoph Ott3, Heping Han1, Roberto Busi1, Qin Yu1, Stephen B. Powles1, and Roland Beffa2.

1Australian Herbicide Resistance Initiative (AHRI), School of Plant Biology, University of Western Australia, Australia; 2Bayer CropScience, Weed Resistance Research, Frankfurt am Main, Germany; 3Bayer CropScience, Bioinformatics Monheim, Monheim am Rhein, Germany; Colorado State University, Fort Collins (CO), United States; 5Bayer CropScience, Computing Science, Frankfurt am Main, Germany.

Weed-herbicide-resistance can cause significant crop losses worldwide. Weed herbicide detoxification, a major resistance mechanism (EMR), can confer resistance to a broad spectrum of chemical classes representing one or several modes of action.  Molecular elements involved in herbicide detoxification are still poorly characterized and understood.  An RNA-Seq transcriptome analysis was used to identify genes conferring EMR in a population (R) of a major global weed (Lolium rigidum), in which herbicide-resistance to diclofop-methyl was experimentally evolved through recurrent selection from a susceptible (S) progenitor population. This population showed also resistance to chlosulfuron. Transcriptomic-level gene-expression was measured using Illumina 100 bp reads. Among contigs overexpressed in the resistant plants, several, including CytP450s, GSTs, and GTs, were validated using a forward genetics approach and showed co-segregation between their over-expression and the resistant phenotypes in the F2 population. Genes from Cyp72 and Cyp81 families were further characterized in transgenic rice calli for they ability to detoxify diclofop-methyl and other herbicides including chlorsulfuron. Structure activity was initiated  on a range of herbicides representing several chemical classes. In addition first data on protein modelling and herbicide docking in the active site of one Cyp81 will be presented.  Not all overexpressed CytP450 genes co-segregating with the resistance phenotype were found to be able to detoxify diclofop-methyl and chlorsulfuron. In addition not all chemicals from a given chemical class (e.g. Fops or SUs) can be detoxified by a given CytP450. Structure-activity relationships will be discussed.  

USING THE GENOME OF KOCHIA SCOPARIA TO INFORM CROP IMPROVEMENT RESEARCH. P. Westra*, T. A. Gaines, F. E. Dayan; Colorado State University, Fort Collins, CO (335)


LACK OF EFFECT OF GLYPHOSATE ON MINERAL NUTRITION, AMINO ACID CONTENT, AND YIELD IN GLYPHOSATE-RESISTANT SOYBEAN AND CORN. S. O. Duke*1, K. N. Reddy2, A. M. Rimando1, J. V. Cizdziel3, M. M. Williams4, J. E. Maul5; 1USDA, ARS, Oxford, MS, 2USDA-ARS, Stoneville, MS, 3University of Mississippi, Oxford, MS, 4USDA, ARS, Urbana, IL, 5USDA, ARS, Maryland, MD (336)



Some investigators have claimed the glyphosate adversely affects mineral nutrition in glyphosate-resistant (GR) crops.  In a field study in Stoneville, Mississippi, the effects of glyphosate on mineral nutrition of glyphosate-resistant soybean and maize was conducted in 2013 and 2014, using unsprayed, non-isogenic cultivars of non-GR soybean and maize for comparison. Maize and soybean were sprayed with 0.87 kg ae/ha glyphosate at 5 and 7 weeks after planting (WAP) and 3 and 6 WAP, respectively. The studies were conducted on both a field that had a history of glyphosate use for several years and a field with no history of glyphosate use.  All plots were maintained weed free throughout the experiment by hoeing, as needed.  Leaf samples of maize and soybean were taken at 11 and 10 WAP, respectively, and seed samples were harvested at seed maturity for elemental analysis by inductively coupled plasma mass spectrometry.  Yield of all treatment plots was determined.  Free and protein amino acid analysis was conducted on soybean seed. Glyphosate and aminomethylphosphonic acid (AMPA) content of seed of soybean and maize were determined.  Although we found some statistically significant effects (both decreases and increases) for some of the minerals, there were no consistent effects between years, treatments, or plant tissues or for specific minerals for either soybean or maize.  These apparently random effects were at the frequency expected with a 95% confidence analysis.  There were no significant effects on amino acids in soybean.   Likewise, yields were not affected by glyphosate treatment, presence of the GR transgene, or field history.   Glyphosate and AMPA were found in the seed of soybean, but not in maize seed.  Our results indicate no adverse effects of glyphosate, the glyphosate transgene, or soil with a glyphosate use history on mineral content or yield of GR crops. 


A DEPSIPEPTIDE FROM THE PATHOGENIC FUNGI BURKHOLDERIA SP. A396 TARGETS PLANT HISTONE DEACETYLASES. F. E. Dayan*1, D. Owens2, C. Carbonari3, G. Giovanna3, R. Asolkar4, L. Boddy4; 1Colorado State University, Fort Collins, CO, 2University of Hawaii, Honolulu, HI, 3Sao Paulo State University, Botucatu, Brazil, 4Marrone BioInnovations, Davis, CA (337)


MBI-010 MW 540, a 16-membered cyclic depsipeptide bridged by a 15-membered macrocyclic disulfide, has been isolated by Marrone BioInnovations from one of their in-house microbial extracts of Burkholderia sp. A396.  The herbicidal activity of MBI-010 MW 540 was discovered through a bioactivity-guided isolation of the microbial broth.  It causes necrosis of the treated plants similar to that observed with compounds that inhibits glutamine synthetase (GS).  However, MBI-010 MR540 does not inhibit GS activity.  We discovered that this natural phytotoxin inhibits histone deacetylase (HDAC). Histone acetylation and deacetylation by histone acetylases and deacetylases regulates epigenetic transcriptional activation and silencing in eukaryotes. These regulatory partner enzymes are an important class of global transcriptional regulators that play crucial roles in plant development, defense, and adaptation.  Inhibition of HDAC has lethal consequences in plants. Reduction of the disulfide bridge of MBI-010 MW 540 liberates a long sulfhydryl side chain that extends in the cavity of HDAC and binds reversibly to the catalytic domain and renders the enzyme inactive.

SEED PRODUCTION AND RETENTION OF AMARANTHUS PALMERI AND ECHINOCHLOA CRUS-GALLI IN SOYBEAN AT HARVEST. L. M. Schwartz-Lazaro*, J. K. Green, J. K. Norsworthy; University of Arkansas, Fayetteville, AR (338)


Today, herbicide resistance is a global phenomenon. Two of the most prominent weeds in soybean (Glycine max L. Merr) production in the midsouthern United States are Palmer amaranth (Amaranthus palmeri S. Watson) and barnyardgrass (Echinochloa crus-galli (L.) Beauv). Typically, when harvesting occurs the weed seed has already either shattered or has been pulled through the combine. Thus, the weed seeds are being redistributed on the soil surface causing further spread as well as increasing the soil seedbank. However, there is little research on how much seed is retained on different weed species at harvest time. Thus, the objective of this study was to determine the percentage of total Palmer amaranth and barnyardgrass seed production that was retained on the plant at and after soybean maturity. In 2015 and 2016, the weed species were transplanted two weeks after soybean planting. At the onset of inflorescence, four flats were placed underneath the targeted weeds and seed shatter was assessed weekly until one month after soybean maturity. Furthermore, additional plants were collected weekly to determine biomass and seed production throughout the growing season. Total seed production over time showed a similar trend between years, but was significantly different between years for only Palmer amaranth. Seed retention was not significantly different between years for either weed species. Palmer amaranth and barnyardgrass retained 93 and 32% of their seed one month after soybean maturity, respectively. This research indicates that if there are escaped weeds at the time of harvest, barnyardgrass has already shattered most of its seeds and a more proactive approach needs to be taken earlier in the season. Additionally, Palmer amaranth will not lose most of its seeds prior to a timely soybean harvest. Furthermore, this makes Palmer amaranth an excellent candidate for harvest weed seed control in the future.



Palmer amaranth is a major problematic weed in most crops, particularly in southern US. Future management strategies will rely on an improved understanding of weed biology and ecology. A series of research projects were conducted to study the biological, phenological, and physiological attributes along with the demography and population dynamics of Palmer amaranth. More particularly, the demographics of Palmer amaranth, at field scale, using life table and cluster analysis were investigated. In addition, the performance of the weed under wide-row and drill-seeded soybean cropping systems at different emergence dates, interrow distances, and soybean densities was examined. Experiments under controlled growing conditions were employed to study the response of female and male Palmer amaranth plants to nutrient deficiency and light stress. The occurrence of Palmer amaranth, at eastern Arkansas field margins and adjacent drainage ditches, in relation to soil properties, at large-scale experiments, was investigated. Key points of the research described above highlight a) the importance of light interception in regulating, quantitatively and qualitatively, Palmer amaranth population and flowering initiation; b) the dominance of male plants at high Palmer amaranth population density; c) the significance of emergence date on Palmer amaranth seed production through greater biomass production early in growing season; d) the role of interrow distance on high Palmer amaranth performance 0 and 1 weeks after crop emergence. The dioecious nature and the differential response of Palmer amaranth gender to abiotic stress can be used for the development of new research approaches and long-term Palmer amaranth control methods. Nitrogen (N) deficiency is an important factor that affects the performance of both genders, especially female plants under high light intensities. The growth of weeds at increasing rates of N is species dependent, and Palmer amaranth thrived under N enriched environments in eastern Arkansas field margins and adjacent ditches. High soil bulk density and low organic matter were important physicochemical soil parameters affecting Palmer amaranth occurrence. Implications of this research are related with the quantitative and qualitative manipulation of Palmer amaranth population.

POPULATION STRUCTURE OF WEEDY RICE IN JAPAN. T. Imaizumi*; National Agriculture and Food Research Organization, Tsukuba, Japan (340)


Weedy red rice was occasionally found in rice fields of Japan until the 1970's. Weedy rice was effectively managed and became negligible because mechanical transplanting and pre-emergent herbicides became widespread. Weedy rice, however, reappears in recent years. Shifting from transplanted to direct-seeded rice has been considered the main cause of the emergence of weedy rice. Few studies have been conducted to investigate a relationship between the shifting to direct-seeded rice and the emergence of weedy rice. In addition, knowledge of its genetic relationships among populations in Japan is still limited. In this study, methods of planting rice (transplanting or direct seeding) in fields infested with weedy rice were obtained by interviews with farmers. I also revealed population structure of weedy rice using whole genome re-sequencing and restriction-site associated DNA-sequencing. There was no specific relationship between methods of planting rice and emergence of weedy rice, and actually, rice has been produced using only transplanting system in most of the fields infested with weedy rice. As for the population structure, the weedy rice populations occurring in Japan were divided into three major groups. The three weedy rice major groups were not closely related to cultivated rice variety widely grown in Japan.


POPULATION DYNAMICS OF ADAPTIVE EVOLUTION TO HERBICIDE STRESS IN AMARANTHUS PALMERI. A. Lawton-Rauh*1, J. D. Burton2, N. R. Burgos3, R. L. Nichols4, A. O. Disharoon1, K. E. Beard1; 1Clemson University, Clemson, SC, 2North Carolina State University, Raleigh, NC, 3University of Arkansas, Fayetteville, AR, 4Cotton Inc., Cary, NC (341)




Waterhemp (Amaranthus tuberculatus) and Palmer amaranth (A. palmeri) are two of the most problematic weeds in the U.S. These weeds are particularly adept at evolving herbicide resistance and multiple resistance, in part because of their dioecious nature. Little is known about the molecular basis of gender determination in these species; previous information, however, indicates gender is under genetic control with males being the heterogametic sex, although there are no obvious sex chromosomes. We utilized a restriction-site-associated DNA sequencing (RAD-seq) approach to identify gender-specific markers and to begin to explore the molecular basis of dioecy in the species. Approximately 200 each of male and female waterhemp plants were used to make barcoded RAD-seq libraries, which were then sequenced on the Illumina platform. Approximately one million, unique, 64-base-pair sequences (tags) were recovered that appeared at least 10 times in the dataset. Applying arbitrary criteria of appearing at least 500 times in one sex and not more than twice in the other, 22 male-specific and 0 female-specific tags were obtained. Permutation analysis also was applied to identify gender-biased tags. Results from this analysis (e.g., more male-biased than female-biased tags) supported the previous conclusion that males are the heterogametic sex. Interestingly, however, numerous female-specific tags were identified, although they appeared in only about one-fifth of the females. This observation prompted us to speculate that a cryptic (non-functional) male locus may exist in some female plants. Candidate male-specific tags were selected and used to develop PCR-based markers. Evaluation of these markers across several waterhemp populations demonstrated their male specificity. Male-specific tags were mapped to transcripts (using a previously obtained waterhemp transcriptome), which were then used in gene ontology (GO) term analysis. Five of these transcripts were associated with pollen germination. A similar approach used for waterhemp is now being applied to Palmer amaranth. Ultimately, a better understanding of dioecy in these two species could lead to a novel weed control approach, in which a gene drive is used to manipulate gender ratios. 




Testing for underlying fitness effects related to glyphosate resistance can be confounded by variable genetic backgrounds in weed populations. To avoid this problem, we used transgenic Arabidopsis thaliana to study phenotypic effects of over-producing EPSPS, a resistance mechanism found in at least seven weed species. We engineered a binary vector expressing a native EPSPS gene from Arabidopsis under control of the CaMV35S promoter (denoted as OX, for overexpression) and an empty vector (denoted EV). We produced six OX and seven EV independent, homozygous T3 lines for each construct. Here, we report results from a glyphosate dose-response experiment, a gene expression experiment, and two greenhouse fitness experiments. OX lines were more resistant to glyphosate and had ED50 values that were ~7- to 23-times greater than those for EV lines (dose-response models from the drc package in R). Quantitative real-time PCR was used to estimate gene expression of EPSPS relative to the native Actin7 gene. OX lines with enhanced glyphosate resistance had ~24- to 66-fold greater EPSPS expression than EV or wild-type controls, which were similar to each other. Results from these experiments showed consistent patterns in levels of glyphosate resistance among the OX, EV, and wild-type lines, and enhanced resistance was positively correlated with levels of EPSPS gene expression across vegetative and flowering stages of development. In the absence of glyphosate, fitness experiments showed that two of the OX lines produced significantly more seeds per plant than wild-type or EV lines, while the other OX lines were not significantly different from the wild-type. Fecundity of the EV lines was similar to or less than that of wild-type lines. Other traits measured included: longest leaf length of rosettes, number of fruits per plant and seeds per fruit, and flowering time. Based on results from the EV lines, there appeared to be a fitness cost related to the insertion of the binary vector in some cases.  However, we suggest that over-production of EPSPS compensated for this cost.  Our results are consistent with the hypothesis that over-production of EPSPS in Arabidopsis does not have a fitness cost and may have a fitness benefit.


INDUCTION OF BIOCHEMICAL AND MOLECULAR SEED DEFENSES BY A SEED DECAY PATHOGEN IN DORMANT WILD OAT AND WHEAT CARYOPSES. E. Fuerst*1, M. S. James1, A. T. Pollard1, P. A. Okubara2; 1Washington State University, Pullman, WA, 2USDA-ARS, Washington State University, Pullman, WA (344)


E. Patrick Fuerst, Matthew S. James, Anne T. Pollard, Patricia A. Okubara, G.N.M. Kumar, and Craig F. Morris.

Dormant weed seeds possess several mechanisms of defense against pathogens but the biochemical defenses are relatively unknown. We previously reported that the seed decay fungus Fusarium avenaceum isolate ‘F.a. 1’, induces ≥ 2-fold induction of the plant defense enzyme, polyphenol oxidase (PPO), in wild oat (Avena fatua) caryopses. We have now also observed that F.a. 1 induced defense enzyme activities of peroxidase, exochitinase, and glutathione S-transferase in wild oat caryopses but reduced oxalate oxidase activity. We observed a dramatic apparent increase in NADPH oxidase activity that was insensitive to NADPH concentration; superoxide is measured in this assay and we propose that an alternate superoxide-producing system was involved. In dormant wheat caryopses, we observed induction of exochitinase but inhibition of peroxidase and oxalate oxidase. Thus, defense enzyme activities can either be induced or inhibited by this pathogen. Preliminary real-time PCR results indicate that induction occurs, in part, at the level of transcription for PPO, chitinase, and NADPH oxidase mRNA (cDNA) in wild oat and wheat in response to F.a.1 challenge. Peroxidase transcripts were induced in wheat but not in wild oat. The ability of F.a. 1 to cause seed decay and induce defense enzymes was also evaluated in soil, both in caryopses and whole seeds of wild oat.  F.a. 1 caused faster caryopsis decay at 25C than at 15C and also caused significant induction of PPO, exochitinase, and peroxidase at certain time points at 25C and 15C. In a preliminary study, whole seeds were incubated in soil, removed and dissected after 2, 4, 6 or 8 weeks, and hulls and caryopses were assayed separately. F.a. 1 induced PPO, exochitinase, and peroxidase in the hulls at each time point but there was little or no enzyme induction in caryopses. The reduced enzyme response in caryopses is not entirely surprising considering the caryopsis was protected by the hull during incubation. We hypothesize that these biochemical and molecular defense responses contribute to the longevity of dormant wild oat and other weed seeds.  




In Argentina around 90% of soybeans are produced under a no-till cropping system. Though initially very effective, glyphosate resistant weed populations heve become an important problem in many no-till fields. Conyza summatrensis which infested around 10 MM ha in 2015-16 season have becomes in one of the key weeds in Argentina due to increasingly high levels of glyphosate resistance, with few effective alternative herbicide modes of action. As Conyza continues expanding, new technologies are needed to achieve effective controls in soybeans. The introduction of Enlist E3TM soybean technology (glufosinate-glyphosate-and 2,4-D tolerant) and Enlist Herbicide (2,4-D choline salt) will provide an alternative. Eleven field trials were conducted in 2014, 2015 and 2016 seasons in Pergamino, Argentina, to evaluate herbicide programs utilizing 2,4-D choline plus glyphosate in Enlist E3TM soybean targeting the glyphosate-resistant biotypes of Conyza summatrensis. The program approaches included preemergence (PRE) treatments of glyphosate plus: chlorimuron + 2,4-D, diclosulam + 2,4-D and diclosulam + Arylex; followed by 2,4-D choline + glyphosate in postemergence (POST); was also included in POST a sequential application of glufosinate followed by 2,4-D choline + glyphosate named double knock-down strategy; finally a program using glyphosate as unique POST herbicide representing the current standards. PRE treatments were applied with Conyza of 10 cm height. Visual percent control evaluations were made 60 days after PRE. Results: Programs that received 2,4-D choline + glyphosate in POST provided high controls. Diclosulam + Arylex (93%), the double knock-down strategy (97%), diclosulam + 2,4-D (85%) and chlorimuron + 2,4-D (81%). The program using glyphosate alone in POST provided 53% of control. These results indicate that the utilization of 2,4-D choline and glufosinate in POST Enlist E3TM  soybean provide an effective tool capable of controlling glyphosate-resistant Conyza, and offering sustainable programs to manage weeds in soybeans.

TMEnlist is trademark of the Dow Chemical Company ("Dow") or an affiliated company of Dow.

Enlist E3TM soybeans are being jointly developed by MS Technologies and Dow AgroSciences

60% OF ORGANIC FARMERS IN THE EASTERN CORNBELT BELIEVE THAT WEEDS CAN BE CONTROLLED THROUGH SOIL BALANCING: DOES THE EVIDENCE MATCH THE APPEAL? C. Herms*1, S. Culman2, M. Kleinhenz2, V. Chaganti2, D. Doohan2; 1Ohio State University/OARDC, Wooster, OH, 2Ohio State University, Wooster, OH (346)




USE OF UNMANNED AERIAL SYSTEMS (UAS) FOR PRECISION WEED DETECTION AND MANAGEMENT IN ROW CROPS: PROGRESS MADE AT TAMU. A. Rana*1, M. Lonesome2, S. C. Popescu2, D. Cope2, J. Valasek2, M. Bishop2, S. Yeyin3, A. Thomasson3, M. V. Bagavathiannan2; 1Virginia Tech, Virginia Beach, VA, 2Texas A&M University, College Station, TX, 3TAMU, College station, TX (348)


QUANTITATIVE ASSESSMENT OF SPRAY DEPOSITION AND CANOPY PENETRATION WITH FLUORESCENT TRACERS. J. A. Gillilan1, M. Ledebuhr2, G. K. Dahl3, R. Edwards4, S. Wedryk5, J. J. Skelton*6; 1WinField Solutions, Springfield, TN, 2Application Insight, LLC, Lansing, MI, 3Winfield, River Falls, WI, 4WinField Solutions, Eagan, MN, 5WinField Solutions, Shoreview, MN, 6WinField Solutions, Franklin, TN (349)


Title: “Quantitative assessment of spray deposition and canopy penetration with fluorescent tracers”

As new dicamba-tolerant crops and technologies are introduced, there is a concern over maintaining herbicide performance and reducing the likelihood of drift.  The use of spray nozzles with a droplet spectrum of “Very Coarse” to “Ultra Coarse,” (as defined by ASABE S572.1) like TTI nozzles, can reduce drift but may also affect canopy penetration and herbicide efficacy by reducing the number of smaller sized droplets.  Another means of mitigating drift is by using drift reduction products such as InterLock and StrikeLock.  The combination of drift reduction products and nozzles is effective at decreasing driftable droplets, but the impact on canopy penetration and herbicide performance is less understood.  The objective of this study is to determine if the drift reduction products, InterLock and StrikeLock, affect spray deposition and canopy penetration of a tank-mixture of dicamba and glyphosate in soybean.  In 2016, field trials were conducted in Tennessee and Minnesota using a fluorescent tracer to quantify the area of spray coverage, number of droplets, and the average droplet size in the upper, middle, and lower levels within the soybean canopy. Mixtures of glyphosate and dicamba with fluorescent tracer and two commercial drift reduction products, InterLock and StrikeLock, were sprayed at 18 gal/A (140 l/ha) using a backpack sprayer in Tennessee and a commercial sprayer in Minnesota, both equipped with TTI nozzles. Sampling cards were positioned within the canopy at three levels, upper (top of the canopy), middle (18-20” from ground), and lower (2-5” from ground) to capture the spray solution. The number of droplet hits, percent area covered by the spray solution, and average droplet size on both sides of the cards were quantified using ImageJ analysis, and the volumetric deposition was determined by rinsing the herbicide from the cards. There were no significant differences between the herbicides alone treatment and the drift reduction products in the area of spray coverage, number of droplets, or average droplet size throughout all three levels of the soybean canopy.  The average size of droplets did decrease further in the soybean canopy with all treatments indicating that a range of droplet sizes are required to achieve maximum canopy penetration.  The results from this study show that the drift reduction products, InterLock and StrikeLock, can be included in tank-mixtures of dicamba and glyphosate when utilizing dicamba-tolerant crops and technologies to reduce drift while maintaining canopy penetration and spray deposition.

TRACTOR SPEED AND BOOM HEIGHT EFFECTS ON SPRAY COVERAGE. E. P. Prostko*, G. C. Rains; University of Georgia, Tifton, GA (350)


Weed science research trials are typically conducted using hand-held, CO2-powered, back-pack sprayers and walking speeds of 3.5 MPH.   However, many commercial farm herbicide applications are made using modern, self-propelled, large boomed (80’+), and fast moving tractors (> 10 MPH).  Occasionally, there are differences between the performance of weed control programs in research plots and on-farm.  The general concerns with today’s commercial farm applications are that the tractors are moving too fast and that the spray booms are set too high above the target. 

Therefore, the objective of this research was to evaluate the influence of tractor speed (8.5 and 13.0 MPH) and boom height (40” and 60”) on spray coverage (%) and droplet size (VMD50).  In March 2016, a commercial John Deere 4630 sprayer (80’ boom, 20” nozzle spacing) was calibrated to deliver 15 GPA using air induction nozzles (AI11004VS and AI11006VS) and operated at 45 PSI.  Thirty Kromekote cards (2” X 3”), spaced 7’ X 10’ apart, were placed under the spray boom.  Water + dye were sprayed over the cards using the various boom heights and tractor speeds.  The cards were analyzed using Dropletscan (WRK of Arkansas, LLC).  There was no difference in spray coverage between tractor speeds or boom heights (P>0.45). VMD50 increased with tractor speed from 418 microns (8.5 MPH) to 443 microns (13.0 MPH).  However, the increase in VMD50 may be more related to nozzle size than tractor speed since a larger nozzle was required to obtain 15 GPA with the same pressure at 13 MPH.  Boom height had no effect on VMD50 (P>0.31).   

In an additional test, three nozzle systems were evaluated for their effects on spray coverage and VMD50.  System 1 including the following parameters: AI11004VS; 45 PSI; 8.5 MPH; 40” boom height; and 15 GPA.  System 2 included the following parameters: AI11006VS; 45 PSI, 13.0 MPH; 40” boom height; and 15 GPA.  System 3 included the following parameters: TADF05-D; 38 PSI; 40” boom height; and 15 GPA.  There was no difference in spray coverage between the 3 systems (P>0.41).  VMD50 for System 1 was lower (418 microns) when compared to System 2 (446 microns) or System 3 (450 microns).


NOZZLE ORIENTATION, PRESSURE, AND NOZZLE FLOW RATE EFFECTS ON SPRAY COVERAGE ON ARTIFICIAL COLLECTORS. J. Ferguson*1, C. C. ODonnell2, A. J. Hewitt2; 1Northwest Missouri State University, Maryville, MO, 2The University of Queensland, Gatton, Australia (351)


Spray applications are most effective when they cover the greatest per unit area, improving target pest control. In order to optimize spray applications, nozzle companies have developed new designs that seek to provide the greatest and most uniform coverage per target unit area. While dual fan nozzles have been examined against single fan nozzles in several studies, there has not been a comprehensive comparison of multiple nominal flow rate and multiple dual fan nozzle types. This study sought to examine pressure, droplet size classification, and nozzle arrangement effects on droplet number density on horizontal artificial collectors using a fixed application rate. The relationship between coverage and nozzle type was significant (P <0.001) as was the relationship between coverage and pressure (P< 0.001). The 207 kPa pressure resulted in the highest coverage for every nozzle type except the alternating TADFs (ATADF)s. The GAT 11003 resulted in the highest coverage overall with 39.6% at the 207 kPa pressure, followed by the TADF 11005 and TADF 11003 at 38.6% and 38.3% coverage respectively. The effect of pressure was significant for the droplet number density (P < 0.001) as was the effect on droplet number density from nozzle type (P< 0.001). The 414 kPa pressure resulted in the highest droplet number density for all nozzle types except the AITTJ 11003 and the MDD 11004. The GAT 11003 and GAT 11004 produced the highest overall droplet number densities with 73.0 and 72.6 droplets cm2 at the 414 kPa pressure. The GAT 11003 had the greatest droplet number density at every pressure. Nozzle arrangement has a significant effect on spray coverage with asymmetric dual fan nozzles, and it would be recommended to alternate these nozzles on a spray boom to increase coverage especially at higher application speeds. Results from this study show that an applicator can select a coarser droplet size classification without observable loss in coverage, while greatly reducing the drift potential of the application.


INTRODUCING STRIKELOCKTM; A NOVEL ADJUVANT SYSTEM. G. K. Dahl*1, R. Edwards2, J. A. Gillilan3, A. Clark1, E. P. Spandl4, J. V. Gednalske1; 1Winfield, River Falls, WI, 2WinField Solutions, Eagan, MN, 3WinField Solutions, Springfield, TN, 4Winfield, St. Paul, MN (352)


StrikeLock® is a novel MSO-HSOC adjuvant from Winfield United that optimizes performance of hydrophobic herbicides with the additional benefit of drift control and droplet deposition. MSO-HSOC adjuvants are classified as containing 25-50% w/w surfactant with a minimum of 50% w/w oil. MSO-HSOC’s have shown excellent compatibility with glyphosate while providing equivalent performance to other oils. US field trials supported that StrikeLock® had equal or better efficacy to other MSO-HSOC products, while maintaining glyphosate compatibility. Drift performance testing revealed a decrease in fine droplet production comparable to other commercial drift reduction agents. StrikeLock® will be available in the marketplace in 2017.






Monsanto Company has developed formulations containing dicamba for use in the Roundup Ready® Xtend™ Crop System.  XtendiMax™ with VaporGrip™ technology is a dicamba standalone formulation based on the diglycolamine (DGA) dicamba salt. Roundup Xtend™ with VaporGrip™ technology is a premix formulation containing DGA dicamba and monoethanolamine (EA) glyphosate delivering a 2 to 1 ratio of glyphosate to dicamba.  Both formulations contain proprietary VaporGrip™ technology that reduces the potential of dicamba volatility compared to current commercial dicamba formulations. VaporGrip technology works by preventing the formation of the volatile species in the formulation. Although volatility is a small contributor to potential off-target movement, this often remains a concern from growers and applicators as a legacy from use of the dimethylamine (DMA) salt launched in the 1960s. The DGA salt of dicamba consistently shows low volatility potential, and this can be reduced further by using VaporGrip™ technology. Spray drift and tank contamination are the main contributors to potential off-target movement.  These can be decreased significantly through appropriate application practices and proper tank clean out.  Application requirements for on-target applications will appear on approved herbicide product labels.

SIMULATED SPRAY TANK-CONTAMINATION WITH 2,4-D AND DICAMBA COMBINATIONS ON GLYPHOSATE- AND DICAMBA-RESISTANT SOYBEAN. M. L. Moretti*1, J. M. Young2, W. G. Johnson2, A. G. Hager3, S. P. Conley4, K. W. Bradley5, L. E. Steckel6, D. B. Reynolds7, J. K. Norsworthy8, G. R. Kruger9, B. G. Young2; 1Oregon State University, Corvallis, OR, 2Purdue University, West Lafayette, IN, 3University of Illinois, Urbana, IL, 4University of Wisconsin, Madison, WI, 5University of Missouri, Columbia, MO, 6University of Tennessee, Jackson, TN, 7Mississippi State University, Mississippi State, MS, 8University of Arkansas, Fayetteville, AR, 9University of Nebraska, North Plate, NE (354)


The release of auxinic herbicide-resistant soybean varieties in the USA market is expected to increase the use of dicamba and 2,4-D herbicides. The increase in use of these herbicides could be associated with greater off-target herbicide exposure by spray drift or spray tank contamination. Additionally, it is unknown how dicamba-resistant soybean would respond to dicamba applications with 2,4-D as a tank contaminant. The objectives of this research were to:1) evaluate whether the addition of dicamba at field use rate would affect dicamba-resistant soybean response to 2,4-D, and 2) characterize glyphosate-resistant soybean response to 2,4-D or dicamba. Experiments were conducted in several states of the Midwest region during 2016. Soybean plants were treated at initial vegetative (V2) or reproductive (R1) stages. The effective herbicide doses (ED) causing yield loss were calculated. Glyphosate-resistant soybean was more sensitive to dicamba than 2,4-D. Dicamba rates of 73 ± 17 g ae ha-1 caused 50% yield loss as compared with 564 ± 104 g ae ha-1 of 2,4-D. Response to herbicide was not dependent on soybean growth stage at the time of exposure. In the dicamba-resistant variety, soybean yield was significantly affected by 2,4-D applied as a tank contaminant with a ED50 of 545 ± 59 g ae ha-1. Response was not affected by plant development stage or the addition of dicamba at full rate. Based on these data, dicamba-resistant soybean response to 2,4-D is not influenced by the addition of dicamba at the field use rate.