Information on the use of hyperspectral reflectance data to discriminate soybean (Glycine max L.) varieties from weeds is limited. Discriminant techniques developed could be useful for targeted management programs where there is a mixture of crops or weeds. Research was conducted to determine the feasibility of using leaf hyperspectral reflectance data to differentiate four soybean varieties from three weeds commonly found in the lower Mississippi Delta.  The following soybean varieties containing the Liberty Link (LL) gene were evaluated in this study: ‘4928LL’, ‘5160LL’, ‘5460LL’, and ‘5960LL’.  The three weeds were Palmer amaranth (Amaranthus palmeri S. Wats.), redroot pigweed (Amaranthus retroflexus L.), and velvetleaf (Abutilon theophrasti Medik.).  On July 10, 2013, leaf hyperspectral reflectance data were collected on plants growing in a greenhouse located at Stoneville, Mississippi.  Data were obtained with a contact probe attached to a spectroradiometer (spectral range, 350-2500 nm).  The reflectance data were aggregated to 165 ten-nanometer bands covering the visible to shortwave infrared region (400-2350 nm) of the electromagnetic spectrum.  A leave-one-out cross validation (LOOCV) procedure incorporating a correlated adjusted t-score to rank the importance of the spectral bands and Fisher’s linear discriminant analysis were used for binary classification (1 variety versus 1 weed) of soybean varieties and weeds.  Typical leaf reflectance properties observed for the soybean varieties and weeds included an increase in reflectance within the green region (500-600 nm) of the optical spectrum and the highest reflectance occurring in the near infrared (760-1300 nm) region of the light spectrum.  Differences in spectral reflectance properties between soybean varieties and weeds occurred in the visible (400-680 nm), near infrared (760-1300 nm), and shortwave infrared (1300-2350 nm) regions of the spectrum.  The results of the LOOCV classifications indicated that two to eight spectral bands were needed as input into the classifier to distinguish soybean varieties from the weeds.  The classification accuracy rate was high and ranged from 98 to 100% for the binary classifications (1 variety versus 1 weed).  Red edge bands (680-750 nm) were identified as important variables to enter into the classifier for discrimination of soybean varieties from redroot pigweed.  Green spectral bands (500-600 nm) were ranked as the most influential variables for input into the classifier to distinguish the soybean variety 5160LL from velvetleaf.  Combinations of spectral bands encompassing two or more regions of the light spectrum were used in the classifier to separate the remaining soybean varieties from weeds. The findings suggest that spectral bands selected for soybean-weed discrimination are dependent on soybean variety and that hyperspectral data could be used in a decision support tool for soybean-weed discrimination. 

To limit yield loses caused by weed interference, weed management decisions must be made early in the growing season. Volunteer canola can be a significant weed in soybean that may warrant additional herbicides to manage, however, decision support tools to assist with prudent management of this weed in soybean are lacking. In an additive design study to develop economic thresholds for volunteer canola in soybean, early-season ground cover measurements were obtained to determine the relationship between incremental early-season ground cover in response to increasing densities of volunteer canola and soybean yield loss. When significant, linear regression was adequate for predicting yield loss in soybean from early-season incremental ground cover caused by interference with volunteer canola. No clear differences in regression parameters between narrow and wide row spacing, years and locations were observed which suggests the potential for a universal yield loss model for volunteer canola in soybean using digital image analysis. This method shows promise as a potential decision support tool for predicting the impact of volunteer canola interference on soybean yield. Further refinement of this method is necessary to optimize the developmental stage at which the images are taken as this influenced the slope of the relationship.

A Saskatchewan, Canada study examined hybridization between two mustard (Brassica juncea and B. carinata) crops that were either adjacent to a glyphosate-resistant canola (B. napus) crop or separated by a 5-m strip. Overall, field hybridization levels, detected with glyphosate resistance and species-specific AFLP markers, were low: 0.024% and up to 400 m in the adjacent B. juncea field and 0.013% (up to 350 m) in the separated field, and 0.005% (up to 150 m) in the adjacent B. carinata field and 0.002% (up to 65 m) in the separated field. Based on fitness information under controlled conditions, the fertility of hybrid plants is expected to be low.

The University of Kentucky has conducted field trials examining overall crop tolerance and weed control of a new GMO soybean trait developed from a collaboration between MS Technologies and Bayer CropScience, Balance™ GT.  These soybeans are tolerant to glyphosate and isoxaflutole, an HPPD-inhibiting herbicide.  By incorporating HPPD tolerance, we now have additional options for controlling resistant and problematic weeds in soybean production. Treatments included isoxaflutole at varying rates with and without other herbicides both preemergence and at V2 in 2012.  Weed species evaluated were common lambsquarters (Chenopodium album), smooth pigweed (Amaranthus hybridus) and morning glory (Ipomoea spp).  All treatments provided 99% control of weed species evaluated and no crop injury was observed.  For 2013, weed species evaluated were smooth pigweed, morning glory and giant foxtail (Setaria faberi). Treatments were similar to those in 2012 but included higher rates of isoxaflutole both preemergence and at V2. All treatments achieved 99% weed control of all species though there was some early crop injury observed in 2013.    sara.lawson@uky.edu

Separate field trials were conducted in 2012 and 2013 near Columbia and Moberly, Missouri to determine the response of FG72 soybeans to various HPPD-inhibiting herbicides, and to evaluate weed control programs for use in these systems. Treatments in the FG72 tolerance experiment included isoxaflutole, tembotrione, mesotrione, or topramezone at a standard (1X) and twice the normal use rate (2X). Treatments were applied preemergence (PRE) to soybeans and at the V3 and R1 stages of soybean growth. Visual crop injury and soybean height and fresh weight reduction were taken 7, 14, and 28 days after application (DAA). Based on visible injury ratings and percent soybean biomass and height reduction 7 and 28 DAA, HPPD-inhibiting herbicides applied to soybean at the V3 stage of growth were more injurious than either PRE or R1 stage applications, and tembotrione generally resulted in higher visible injury and soybean biomass and height reduction than either isoxaflutole, mesotrione or topramezone.  In the weed management experiments, all PRE followed by (fb) postemergence (POST) herbicide programs resulted in 74 to 98% control of glyphosate-resistant waterhemp 28DAA while 2-pass POST programs resulted in 28 to 78% control, and 1-pass POST programs provided only 18 to 28% control of this species. Similar results were observed at the Columbia site with giant foxtail, common cocklebur, and ivyleaf morningglory Results from these experiments indicate that FG72 soybeans exhibit acceptable tolerance to isoxaflutole, mesotrione, and topramezone, and that the incorporation of HPPD-inhibiting herbicides will provide a novel mechanism of action in soybean to aide in the management of certain resistant and susceptible weed biotypes.

Emergence of grasses such as browntop millet, Digitaria spp. and junglerice late in the season, has become a problem in glyphosate-resistant (GR) soybean production. In the southern US, soybean is harvested beginning in August. The time between harvest in August and frost (October-November) provides a favorable environment for these grasses to emerge, establish, and replenish seedbank. A 3-yr field study was conducted during 2011 to 2013 at Stoneville, MS to determine efficacy of in-crop and post-harvest herbicides on late-season grasses and on yield in twin-row GR soybean. Experiment was conducted in a split-plot arrangement of treatments in a randomized complete block design with fall herbicides (with and without pendimethalin @1.12 kg ai/ha and paraquat @0.84 kg ai/ha) as main plots and in-crop herbicides as subplots with four replications. The six in-crop herbicide programs were: glyphosate applied early POST (EPOST) at 0.84 kg ae/ha followed by (fb) glyphosate late POST (LPOST) at 0.84 kg/ha with and without pyroxasulfone PRE applied at 0.18 kg ai/ha; pyroxasulfone PRE fb glyphosate at 0.84 kg/ha LPOST or glyphosate at 0.84 kg/ha + S-metolachlor at 1.68 kg ai/ha EPOST; pyroxasulfone PRE fb S-metolachlor at 1.12 kg/ha + fomesafen at 0.27 kg ai/ha EPOST fb clethodim at 0.14 kg ai/ha, and a no-herbicide control. Browntop millet, Digitaria spp. and junglerice densities at 2 weeks after LPOST, grass weed dry biomass at harvest, and soybean yields were similar regardless of post-harvest herbicides in all three years. At 2 weeks after LPOST, browntop millet, Digitaria spp. and junglerice densities were greatly reduced in all five in-crop herbicide treatments compared with no herbicide plot in all three years. Grass weed dry biomass in no-herbicide plots was 3,346, 6,136 and 6,916 kg/ha in 2011, 2012, and 2013, respectively and the five herbicide treatments reduced grass weed dry biomass by at least 86, 84, and 100% in 2011, 2012, and 2013, respectively. Soybean yields were similar in all three years regardless of post-harvest herbicide applications. Soybean yields were higher with all five in-crop herbicide treatments compared with no herbicide control in all three years. These results indicate that browntop millet, Digitaria spp. and junglerice infestations could be reduced with pyroxasulfone-based in-crop herbicide programs in twin-row GR soybean.

The resistance to glufosinate of two lines —genetically modified (GM-Wh) and unmodified (UM-Wh)— of Triticum aestivum has been studied. The line GM-Wh, in which the bar gene was introduced to increase its resistance to glufosinate, presented a high resistance to glufosinate with an ED₅₀ value of 478.59 g ai ha^-1 versus 32.65 g ai ha^-1 for line UM-Wh. The  glutamine synthetase (GS) activity was investigated in both lines, with line GM-Wh achieving a resistance factor of 12.51 with respect to  line UM-Wh. Metabolism studies showed, at 48 h after herbicide treatment (300 g ai ha^-1), an 83.4% conversion of the herbicide (66.5% in N-acetyl-glufosinate metabolite) in GM-Wh, while in UM-Wh, the conversion of the herbicide was about 40% (0% to N-acetyl-glufosinate metabolite). Also, by this method, we were able to corroborate a higher and faster penetration of glufosinate in line UM-Wh than in line GM-Wh.

These results suggest that the metabolism of glufosinate by the bar gene is a key resistance mechanism  in line GM-Wh, that explains such high levels of herbicide tolerated by the plant, together with other mechanisms due to unmodified pathway, absorption and loss of glufosinate affinity for its target site.

Herbicide-resistant weed problems differ considerably from region to region.  At present herbicide-resistance problems in North America, Brazil, and Argentina are dominated by the dramatic increase of glyphosate-resistant weeds in Roundup Ready Crops.  In much of the developing world ALS inhibitor resistant weeds of rice present the greatest problems.  Thirty years ago Europe’s herbicide-resistant weed problems were dominated by triazine resistant weeds in corn, however today the focus has shifted to grassy weeds in cereals.  Target site resistance to ACCase and ALS inhibitors is widespread in Alopecurus myosuroides, Avena fatua, Apera spica-venti, and Lolium multiflorum, however the greatest concern is non-target site resistance particularly in Alopecurus myosuroides.  Multiple resistance in Alopecurus myosuroides is very common and it is easy Europe’s most serious herbicide-resistant weed.  ALS inhbititor resistance is also widespread in Papaver rhoeas and Stellaria media.  Echinochloa sp. in rice with resistance to ACCase inhibitors, ALS inhibitors, propanil, and quinclorac present problems in Italy, Greece and Turkey. The European countries reporting the most cases of herbicide resistance are France (35), Spain (33), Germany (32), Italy (29), and the United Kingdom (27).  Glyphosate resistance has been identified in Lolium and Conyza species, primarily in orchards in Spain (5 sp.), Greece (3 sp.), Italy (3 sp) and one species in each of France, Poland, Portugal, and the Czech Republic.  While strong research programs on herbicide-resistance are found in Poland, the Czech Republic, and Serbia, there are few reports of herbicide-resistant weeds from other eastern European countries, despite widespread herbicide use and large grain growing regions.  Reports of herbicide-resistant weeds in Russia and the Ukraine have been received however they have not been sufficiently documented.  Part of the aim of this poster is to solicit help in finding contacts in Eastern Europe that can provide data on herbicide-resistant weeds.  Data on herbicide-resistance of weeds in Europe is posted at http://www.weedscience.org, please contact the author if you can help find additional contacts.

Glyphosate herbicide has been used for a long period of time to control a wide range of weeds. In Europe, where the main perennial crops are olive, citrus and vineyards, the use of glyphosate has represented the main chemical tool for controlling weeds. Unfortunately, overreliance on glyphosate as sole weed control tool has led to the evolution of some resistant biotypes. Currently, there are worldwide biotypes of 25 species reported as being glyphosate-resistant. 20% (5 species) of these confirmed cases are found in Europe. Confirmed glyphosate-resistant biotypes correspond to Conyza and Lolium genus: C. bonariensis (Spain, Greece, and Portugal), C. canadensis (Spain, Czech Republic, Poland, Italy, and Greece), C. sumatrensis (Spain, and Greece), L. multiflorum (Spain), and L. rigidum (France, Spain and Italy). Information about the resistance indexes can be found in databases. Nonetheless, some species that are suspected to become glyphosate-resistant and need further confirmation (accepted paper) are C. sumatrensis from Portugal, Italy and France, and Lolium perenne from Douro region in Portugal. Integrated weed management in line with EC Sustainability Directive 128/2009/EC should be adopted on plots where herbicide resistance is suspected in order to minimize and delay the evolution of additional resistance.

A field experiment was conducted near Middleville, MI to evaluate the effectiveness of several herbicide programs on the control of multiple-resistant (glyphosate-/ALS-resistant) Palmer amaranth in corn.  The herbicide programs evaluated were: a) one-pass total early-postemergence (EPOST) programs, b) two-pass preemergence (PRE) followed by postemergence (POST) herbicide programs, and c) a two-pass EPOST followed by POST applications of glufosinate.  PRE applications were made shortly after planting, and EPOST and POST applications were made when Palmer amaranth was approximately 8 cm tall.  Evaluations for weed control were made throughout the growing season from 21 days after planting (DAP) through corn harvest (110 DAP).  Palmer amaranth sub-samples were harvested from each plot for biomass 60 DAP.  The herbicide program that provided the greatest percentage of multiple-resistant Palmer amaranth control was s-metolachlor plus atrazine (1.4 plus 1.8 kg ha^-1) (PRE) followed by mesotrione plus atrazine (105 plus 675 g ha^-1) (POST), 94%.  Of the 10 PRE fb. POST programs evaluated, four provided similar results to this treatment.  These programs generally consisted of a minimum of three-effective herbicide sites of action.  Control of Palmer amaranth was generally greater if two-effective herbicide sites of action were applied POST.  Of the three EPOST programs evaluated two provided 80% or greater control of Palmer amaranth at harvest.  One of these one-pass programs provided similar Palmer amaranth control to the s-metolachlor plus atrazine (PRE) followed by mesotrione plus atrazine (POST) program.  Again full-rates of herbicides with at least three effective sites of action were needed.  Multiple applications of glufosinate also provided greater than 80% control of Palmer amaranth at harvest, but timing was critical.  For effective management of multiple-resistant Palmer amaranth PRE herbicide applications should include atrazine in combination with a seedling shoot inhibitor and POST applications need to contain at least two modes of action with foliar activity as well as have some residual component for season-long control.  While this research did show that acceptable levels of Palmer amaranth control can be achieved in a one-pass program, the recommended approach for Palmer amaranth management would be a PRE followed by POST program.    

Management of Glyphosate-Resistant Palmer Amaranth in Cotton Using Cover Crops and Herbicides
Matthew S. Wiggins
Robert M. Hayes
Lawrence E. Steckel
University of Tennessee
Jackson, TN.

Abstract

Glyphosate-resistant (GR) weeds continue to be the most problematic weeds to control in most cropping systems in the Mid-South region of the United States.  There are now no less than ten GR weed species in the Mid-South and no less than six confirmed species GR species in Tennessee. Of these, Palmer amaranth (Amaranthus palmeri S. Wats) is the most difficult of to control.  Successful management schemes for controlling GR weeds include the use of PRE-emergence (PRE) herbicides, overlaying residual chemistries, making timely applications of POST-emergence (POST) herbicides and integrating cultural control methods. Unfortunately, rainfall to activate PRE’s and residual herbicides can be sporadic at best in Tennessee.  Therefore, timely applications of POST herbicides are essential for many producers to grow a profitable crop.  This heavy reliance on POST herbicide applications increases selection pressure and the possibility of herbicide resistance.  Integrating cultural control methods, such as cover crops, is a viable option available for area producers to reduce selection pressure and gain early season weed control.  Unfortunately, research on integrating herbicides with a cover crop system is limited.  Therefore, this trial was conducted to evaluate the effectiveness of integrating high residue cover crops in to a glyphosate and glufosinate based weed control system in cotton.  A study was conducted during the 2013 growing season to investigate Palmer amaranth control in a no-till cotton system where treatments of cover crops and POST herbicides applications were applied.  The cover crops evaluated were crimson clover (Trifolium incarnatum L.), hairy vetch (Vicia vilosa L.), winter wheat (Triticum aestivum), and cereal rye (Secale cereal L.).  Seeding rates were 16.8 kg hectare^-1, 22.4 kg hectare^-1, 67.2 kg hectare^-1, and 67.2 kg hectare^-1 of viable seed for crimson clover, hairy vetch, winter wheat and cereal rye, respectively.  Cover crops were established in the autumn of the previous year using a no-till drill and were terminated approximately three weeks prior to estimated cotton planting date.  Prior to chemical termination of cover crops, biomass yields were obtained by clipping a 0.1 m² quadrat above the ground.  The POST herbicide applications were applied when Palmer amaranth reached a height of 10-15 centimeters, which was approximately 15 days after cotton planting date.  Herbicide treatments included glufosinate (595 g ai/ha), glyphosate (1544 g ae/ha), and an untreated control.  A sequential herbicide application was made 14 DAA, as this is a common production practice to control larger Palmer amaranth.  Weed control was assessed starting 7days after application (DAA) and continued until 28 DAA.  Weed density and cotton yield data were also assessed in this trial.  Experimental design was a randomized complete block design with four replications and a factorial arrangement of treatments.  Factors evaluated were cover crop specie and herbicide treatment.  Means were separated using Fisher’s Protected LSD at P ≤ 0.05.  Results indicate that winter wheat, cereal rye, and hairy vetch accumulated the greatest amount of biomass, which directly added to early season weed control.  Palmer amaranth control was increased throughout the assessment periods when integrating cover crops and POST herbicides, when compared to the untreated control.  Cover crop specie also had an effect on cotton yield.  However, there were no differences among treatments when assessing weed densities.  In summary, these results indicate that using high residue cover crops can offer some benefits in a no-till cotton system, including effective early season weed control of Palmer amaranth.  However, timely applications of POST herbicides are essential for the season long control of this prolific pest. 

Pending regulatory approvals, Bollgard II^® XtendFlex^TM Cotton is anticipated to be available to growers as early as the 2015 growing season.  This technology will be a three-way herbicide tolerance stack in cotton with tolerance to dicamba, glyphosate, and glufosinate when applied preplant, at-plant, preemergence, and postemergence.  The proposed dicamba application window will be full season, which is similar to the current glyphosate application window, and the current glufosinate application window will remain through early bloom.  This technology will improve control of many troublesome annual and perennial weeds on the Texas High Plains, including glyphosate-resistant Palmer amaranth (Amaranthus palmeri S. Wats.).  The objective of this research was to examine weed management “systems” in Bollgard II^® XtendFlex^TM Cotton.  Weed management treatments included systems with and without trifluralin (0.84 kg ai/ha) preplant incorporated; acetochlor (1.26 kg ai/ha, Warrant Herbicide), acetochlor plus MON 119096 (0.56 kg ae/ha, an experimental low-volatility formulation of dicamba), or no herbicide applied preemergence (PRE); and glufosinate (0.66 kg ai/ha), glufosinate plus MON 119096, Mon 76832 (1.68 kg ae/ha, an experimental low-volatility premix formulation of dicamba plus glyphosate), glyphosate (1.27 kg ae/ha), or glyphosate plus acetochlor applied early-postemergence (EPOST), mid-postemergence (MPOST), and/or late-postemergence (LPOST).  Trials were conducted at two locations on the Texas Southern High Plains.  One location was at the Texas Tech Research facility near New Deal.  The soil type was a Pullman clay loam.  Plots, four rows by 9.1 m replicated 4 times, were arranged in a randomized complete block in a sub-surface drip irrigation field that previously was in corn monoculture since 1998.  This location contained a dense population of Texas millet (Urochloa texana Buckl.) and a sparse population of glyphosate-susceptible Palmer amaranth. The second location was at the Texas A&M Glover Research Farm near Lubbock with limited furrow-irrigation capabilities.  The soil type near Lubbock was an Acuff loam.  Dense populations of Palmer amaranth and devil’s-claw (Proboscidea louisianica P. Mill.) were present at this location. Plot sizes were described previously.  At the New Deal location, late-season control of Texas millet and Palmer amaranth was at least 95% in the following herbicide systems:  trifluralin followed by (fb) acetochlor PRE fb MON 76832 MPOST; trifluralin fb MON 76832 MPOST fb glyphosate plus acetochlor LPOST; and trifluralin fb glufosinate plus MON 119096 MPOST and LPOST.  At the Lubbock location, late-season control of Palmer amaranth and devil’s-claw was at least 95% following acetochlor plus MON 119096 PRE fb MON 76832 EPOST; acetochlor PRE fb MON 76832 EPOST and LPOST; trifluralin fb acetochlor PRE fb MON 76832 MPOST; and trifluralin fb glufosinate plus MON 119096 MPOST and LPOST.  In summary, several effective weed management systems were identified in Bollgard II^® XtendFlex^TM cotton in both an irrigated and dryland environment.  Trifluralin and acetochlor were effective “foundations” for control of Palmer amaranth, Texas millet, and devil’s-claw, which reduced weed emergence and crop competition with less reliance on postemergence herbicides.

Cotton Response and Palmer Amaranth (Amaranthus palmeri) Control following Pyrasulfotole plus Bromoxynil Applied Postemergence-directed. T. S. Morris*^1,2, P. A. Dotray^1,2,3, J. W. Keeling³, R. Perkins⁴; ¹Texas Tech University, Lubbock, TX, ²Texas A&M AgriLife Research, Lubbock, TX, ³Texas A&M AgriLife Extension, Lubbock, TX, ⁴Bayer CropScience, Idalou, TX.

A premix combination of pyrasulfotole plus bromoxynil (Huskie™) may be applied postemergence in sorghum (Sorghum bicolor L. Moench), wheat (Triticum aestivum L.), and barley (Hordeum vulgare L.) for control of many weeds including Palmer amaranth (Amaranthus palmeri S. Wats.) and other Amaranthus species, kochia (Kochia scoparia L.), Russian thistle (Salsola tragus L.), prickly lettuce (Lactuca serriola L.), and several ALS and glyphosate resistant weed biotypes.  The objective of this research was to evaluate cotton response (leaf necrosis and stunting) and Palmer amaranth control when pyrasulfotole plus bromoxynil was applied postemergence-directed (PDIR) with and without prometryn at different hooded sprayer heights and application timings. Field trials were conducted at two sites in 2013 in Lubbock County, Texas. Postemergence-directed (PDIR) applications were made using a CO₂-pressurized 4-row Redball hooded sprayer. Applications were made at both locations using a standard PDIR sprayer setting, where the hoods run as close to the ground as possible. At the New Deal location, an additional PDIR setting was used where the hoods were raised 10 cm about the soil. Herbicide treatments included pyrasulfotole plus bromoxynil (0.26 kg ai ha^-1) alone or in combination with prometryn (0.90 kg ai ha^-1). Ammonium sulfate was added to all treatments at 1.12 kg ha^-1. Palmer amaranth control and cotton injury were observed 4 days after treatment (DAT) following the early application timing. No differences were observed between the pyrasulfotole plus bromoxynil alone and pyrasulfotole plus bromoxynil and prometryn treatments regardless of PDIR timing and hooded sprayer height. At Lubbock, Palmer amaranth was controlled at least 93% following all treatments when evaluated at 7 DAT, but this control declined at 14 DAT. Crop injury was observed with the early PDIR treatments, but not from the mid or late PDIR treatments. At New Deal, cotton injury at 4, 7, and 14 DAT following the early, raised (10 cm) PDIR application was 23, 34, and 55% respectively.  No other treatment caused greater than 15% injury at any timing. Cotton lint yield ranged from 1,542 to 2,103 kg ha^-1 and were not adversely affected by the standard PDIR treatment at any application timing. Cotton yield was reduced 22% following the early, raised PDIR application.

Glyphosate resistant (GR) Canada fleabane (Conyza canadensis) is an extremely problematic weed in no-tillage farming operations.  A total of six field trials were conducted over a two-year (2012 and 2013) period in Ontario to determine the level of GR Canada fleabane control with a two-pass weed control program of a soil applied residual herbicide followed by 2,4-D choline/glyphosate DMA (Enlist Duo®) applied POST in no-till corn.  Among residual herbicide treatments evaluated, s-metolachlor (1600 g ai haˉ¹) + flumetsulam (50 g ai haˉ¹) + clopyralid (135 g ai ha¯¹) provided the most consistent (95-99%) control across all sites 8 weeks after application (WAA).  S-metolachlor/atrazine (1800 g ai haˉ¹) did not provide effective GR Canada fleabane control (21-86%) 8 WAA.  The PP residual herbicides followed by 2,4-D choline/glyphosate DMA (1720 g ae ha¯¹)  POST provided 97-100% control.  Glyphosate (900 g ae ha¯¹) applied PP followed by 2,4-D choline/glyphosate DMA POST provided  80-93% control 8 WAA.  The application of 2,4-D choline/glyphosate DMA POST following any PP residual herbicide resulted in 97% or greater control of GR Canada fleabane.  Results from this research demonstrate that residual herbicides applied PP followed by 2,4-D choline/glyphosate DMA POST provides excellent control of GR Canada fleabane, and also incorporates different modes of action thereby limiting the development of resistant weeds. 

Traditional breeding technology is currently being used to develop grain sorghum germplasm that will be tolerant to acetolactate synthase (ALS)-inhibiting herbicides. This technology (INZEN) has the potential to improve sorghum production by allowing for the postemergence control of many weeds, including traditionally hard-to-control grasses. However, grain sorghum and shattercane can interbreed and introduced traits such as herbicide resistance could contribute to the invasiveness of the weedy relative. Moreover, ALS-resistance in shattercane populations has been reported, indicating that over-reliance on ALS-chemistry may also select for resistant biotypes. The objective of this research is to develop a simulation model according to the weed’s life cycle and parameter values based on our research and the literature to assess management options to mitigate risks of ALS resistance evolution in shattercane populations in the USA sorghum production areas. The core structure of the model will be based on: i) weed demography, ii) genetics and inheritance of the resistance trait, and iii) crop and weed management strategies. The simulation model will be implemented using R programming language. The value of this work will be in identifying how much of a change in the risk of evolved resistance occurs with each added management tactic and which tactics (e.g., crop rotation, herbicide rotation, tillage) result in the greatest reduction in that risk. It is expected that the risk of resistance evolution will decline with increasing cropping system complexity (more practices than continuous production of ALS-resistant sorghum). The ultimate goal of this research is to develop recommendations on best practices for grain sorghum production to manage weeds and maintain the utility and value of herbicide-tolerant grain sorghum.

Cereal leaf diseases are a major concern across northern U.S. spring wheat areas. Recent higher grain commodity prices have increased the return on fungicide investment. Growers commonly include a fungicide with herbicide applications for grass weed control. Applying fungicide at this timing provides effective weed and pathogen control and reduces the potential and impact of later pathogen infections while avoiding a second pass to apply fungicides only. The crop response of herbicide plus fungicide tank mixes in cereals has not been thoroughly studied in North America. Three trials were conducted both in 2012 and 2013 in Montana, North Dakota, and South Dakota to examine crop response to an oil dispersion formulation containing pyroxsulam, florasulam, and fluroxypyr (GoldSky®) alone and when tank mixed with the phenoxy herbicide 2,4-D (ethylhexyl ester) and various fungicides.  Fungicides evaluated included propiconazole (PropiMax®), pyraclostrobin (Headline®), and a formulated blend of propiconazole and trifloxystrobin (Stratego®).  Observed injury with GoldSky alone never exceeded 6% averaged across locations and years and injury with 2,4-D ester never exceeded 3.5%.  Injury with individual fungicide-only treatments never exceeded 0.9% across all evaluation intervals. Greatest injury was observed with tank mixes of GoldSky® + 2,4-D ester that included each of the fungicide products.  Generally, injury with tank mix treatments was roughly equal to the sum of the injury observed with the individual components.  Mean injury with GoldSky® and 2,4-D ester combinations ranged from 5 to 10% up to 28 days after application, but ranged as high as 25% for individual plot ratings across those same intervals.  Observed injury did not appear to effect spring wheat yields.  Spring wheat yields where combinations of GoldSky with 2,4-D, fungicides, or 2,4-D plus fungicides applied were equal or greater than yields from nontreated.  GoldSky tank mixes yielded as much as 10% greater than the nontreated.

Imidazolinone (IMI)-resistant crops are insensitive to herbicides that inhibit the enzyme acetolactate synthase (ALS) through processes that involve the target site (enzyme mutation or overexpression) or processes unrelated to the target (reduced herbicide penetration, reduced translocation, or increased herbicide metabolism). The objective of this work was to evaluate the mechanism by which different wheat cultivars develop resistance to Imazamox herbicide. The IMI-resistant wheat cultivars (line 1, line 2, line 3, line 4, and line 5) which have been commercialised in Chile were compared to a sensitive cultivar (line S) using several approaches ranging from in vitro to field experiments. The variables evaluated included the dose-response to the herbicide, ALS enzymatic activity, leaf retention of Imazamox, photosynthetic activity, and chlorophyll content. The Imazamox dose, expressed as a gram of active ingredient per hectare (g ai ha^-1) that reduced the wheat fresh mass by 50% (ED₅₀), ranged from 151.0 for line 5 to 1.6 for line 6. The herbicide concentrations that inhibited ALS enzyme activity by 50% (I₅₀) were correlated with the ED₅₀, suggesting that the Imazamox resistance could be due to a mutation in the ALS enzyme. However, the finding that IMI-resistant wheat cultivars recovered their photosynthetic activity with time and the fact that  line 5 plants showed increased chlorophyll content over time suggest that other herbicide resistance mechanisms might be involved in the differential tolerance to Imazamox in these wheat cultivars.

Uncontrolled kochia plants following mechanical harvest of wheat could potentially regrow and produce significant amount of seeds for infestation in the following year. To prevent further spread of glyphosate-resistant (Gly-R) kochia in the Northern Great Plains, it is critical to develop postharvest weed management strategies aimed at preventing weed seed bank replenishment. Field experiments were conducted at the Montana State University Southern Agricultural Research Center, Huntley, MT, in 2012 and 2013, to evaluate the effect of various POST herbicides on late-season control, fecundity, and progeny fitness of kochia in postharvest wheat stubble. A randomized complete block design with four replications was used.  Herbicides were applied using handheld boom sprayer calibrated to deliver 94 L ha^-1 at 276 kPa. All treatments were applied 2 to 3 wk following harvest of wheat, with regrowth and flower initiation of uncontrolled kochia plants. Kochia late-season control with paraquat + atrazine (0.84 + 0.56 kg ha^-1), paraquat + linuron (0.84 + 0.84 kg ha^-1), and paraquat + metribuzin (0.84 + 0.84 kg ha^-1) was 100% at 28 d after treatment (DAT), and did not differ from paraquat (0.84 kg ha^-1), dicamba + glyphosate (0.56 + 1.26 kg ha^-1), saflufenacil + atrazine (0.05 + 0.56 kg ha^-1), and saflufenacil + 2,4-D (0.05 + 0.56 kg ha^-1). Late-season control with glufosinate (0.59 kg ha^-1), tembotrione + atrazine (0.09 + 0.56 kg ha^-1), and topramezone + atrazine (0.02 + 0.56) was at least 91% 28 DAT. Dicamba (0.56 kg ha^-1) alone or dicamba + 2, 4-D (0.560 + 0.560 kg ha^-1) provided ineffective kochia control (≤ 55%) 28 DAT. Consistent with percent control, kochia biomass reduction with paraquat + atrazine, paraquat + linuron, and paraquat + metribuzin treatments was highest (≥ 70% of nontreated check), and did not differ from glufosinate and saflufenacil + atrazine. The least biomass reduction was observed (13 to 40%) with dicamba, dicamba + 2, 4-D, and diflufenzopyr + dicamba + 2, 4-D (0.056 + 0.140 + 0.56 kg ha^-1). Although kochia control was inadequate, a late-season application of dicamba alone or with 2, 4-D, atrazine, and diflufenzopyr + 2, 4-D reduced kochia seed production by 32 to 77 % compared with the nontreated plants. All other late-season POST herbicide treatments prevented kochia seed production. Viability of seeds produced by kochia plants treated with dicamba + atrazine was 8% lower compared with the seed viability of dicamba, dicamba + 2, 4-D, or diflufenzopyr + dicamba + 2, 4-D treated plants. Results from this research indicate that a late-season application of paraquat, paraquat + atrazine, paraquat + metribuzin, paraquat + linuron, glufosinate, saflufenacil + atrazine, saflufenacil + 2, 4-D, tembotrione + atrazine, and topramezone + atrazine can effectively control kochia postharvest in wheat stubble. Furthermore, these late-season herbicides as an alternative to glyphosate could potentially reduce seed bank replenishment and further spread of Gly-R kochia.  

Winter annual grass weeds are a major concern in the production of winter cereals in the Pacific Northwest region of the United States. Many winter annual grass herbicides used in winter wheat are not labeled for use in barley. Previous wheat field research and barley greenhouse research indicated that pyroxasulfone and flufenacet/metribuzin may be safe to use on barley that is seeded over 2.5 cm deep and application is made after seed is germinated. Winter barley varietal tolerance to flufenacet was evaluated in the field using conventional tillage in Idaho. Three varieties of winter barley were planted in Moscow (rainfed) and Kimberly (irrigated) fall 2010. Flufenacet/metribuzin and flufenacet were applied to the soil before barley emergence. Rates used were 0.5, 1, and 1.5 times the use rate of flufenacet/ metribuzin. Flufenacet was applied at equivalent rates compared to the flufenacet portion of flufenacet/metribuzin. Yield was lower with all flufenacet/metribuzin and flufenacet treatments compared to the untreated check at Moscow, but yield at Kimberly was lower than the check with the 1.5 use rates only. Test weight, plumps and thins were not different among flufenacet/metribuzin or flufenacet rates and the untreated check at either location. All varieties responded similarly to herbicide treatments, although yield and quality was different among varieties. Yield was highest with Eight-twelve and lowest with Charles at Moscow. At Kimberly, Endeavor was highest and Eight twelve was lowest. Seeding depth and application timing was investigated in a second experiment. Eight-Twelve winter barley was seeded October 11, 2012 at 1.25 and 5 cm on the University of Idaho Parker Farm east of Moscow. The soil was dry and powdery at the time of seeding. Rainfall (1cm) one day later moistened soil about 2.5 cm from the surface and the shallow seeded barley began to germinate within days. Barley seeded deep did not germinate until after additional rain events 3 days later and emerged 7 days later than the shallower seeded barley. Rainfall also caused some collapse of the soil in the rows and some seeds were 6.5 cm below the surface. Pyroxasulfone and flufenacet/metribuzin herbicides were applied October 14 and 21. Barley was not germinated on October 14. On October 21, the shallow seeded barley had 1 cm roots and the deep seeded barley was just beginning to germinate. Fall emergence and stand throughout the season was reduced and variable with the deep compared to the shallow seeded barley, even in the non-herbicide treated plots. Barley grain yield was 4909 and 3892 kg/ha, plump kernels were 82 and 75%, and thin kernels were 4 and 6% with shallow seeded barley compared to deep seeded barley, respectively, averaged over application time and herbicide treatment. Due to the variability of the deep seeding, data was analyzed for the shallow depth. Grain yield was lower with flufenacet/metribuzin (4278 kg/ha) compared to the untreated check (5709 kg/ha), but pyroxasulfone (4738 kg/ha) was not statistically different from either treatment averaged over application time. Test weight, plump and thin kernels were not different among treatment. Application timing did not have an effect on any measured variables at either depth.

North Carolina growers produced Sorghum on 100,000 acres in year 2013. This acreage is expected to increase in the future due to an assured market, grower enthusiasm, low production cost, drought tolerance and a lowered risk when compared to corn, especially on sandy soils. Since sorghum is an old crop with renewed interest, this is the first time it has been grown on a large scale in North Carolina. This crop may be a good fit in the overall cropping system of the state. However, limited information on production and weed management is available in the state. Weed control is an important aspect of profitable crop production which has a bearing on the success of a new crop, and in determining its fit in a cropping system. In order to address the issues of successful weed management under the given environment and cropping system, studies were conducted in 2012 and 2013 at the Upper Coastal Plain Research Station (Rocky Mount, NC) and at the Central Crops Research Station (Clayton, NC). The objective was to evaluate the growth and yield response of sorghum to different rates of 2,4-D amine (100, 217 and 333 g ai.ha^-1) and one rate of Dicamba (280 g ai.ha^-1) applied post-emergence beyond the recommended growth stage (15-20 cm tall), at 25, 35, 46, 56, 66, and 74 cm height. Significant reduction in yield was observed with later applications of both 2, 4-D and dicamba compared to earlier applications. No difference in yield reduction was observed across the different rates of 2,4D-amine. Yield reduction was significantly more important for dicamba compared to 2,4-D amine. Significant yield reduction was observed when growth regulators were applied beyond 50cm tall sorghum.

Field and greenhouse studies were conducted to examine if the organophosphate insecticide, disulfoton, could be used as safener to reduce clomazone injury to canola from a PRE application. In a greenhouse study with a Cecil sandy loam soil, clomazone was applied PRE at 115, 230, 350, and 460 g ai/ha with and without disulfoton applied at 825 g ai/ha.  Clomazone injury increased with rate to 75% 28 DAT. Disulfoton decreased clomazone injury by about 20% at each rate examined and clomazone injury when applied with disulfoton was not higher than 40%.  Field trials were conducted in 2013 near Athens and Tifton, GA. Clomazone was applied PRE at 150, 300, 460, and 616 g ai/ha of clomazone with and without disulfoton applied at 275 g ai/ha.  At the Athens location (Cecil sandly loam soil, 0.9% OM)28 DAT, clomazone injury increased with rate to a maximum of 38% visual injury. When clomazone was applied with disulfoton, clomazone injury was not above 5%. At the Tifton location (Tifton loamy sand, 0.5% OM) 30 DAT, clomazone injury increased with rate to a maximum of 89%. Unlike the Athens location, disulfoton did not reduce clomazone injury at any rate.  There seems to be a soil environment interaction that influences the disulfoton’s ability to reduce clomazone injury to canola.

Pre-harvest seed losses in canola can be substantial and are caused by pod-drop and pod-shatter.  Pod-shatter refers to the dehiscence of seeds from the silique, while the middle lamella (replum + funiculus) and pedicel remain attached to the mother plant.  In contrast, pod-drop refers the abscission of undehisced siliques at the pedicel.  Little information is available on the relative contribution of each phenomenon to total pre-harvest seed losses.  The objectives of this study were to i) evaluate the contribution of pod-drop and pod-shatter to pre-harvest losses and ii) determine whether that relationship is similar between breeding-types among a group of eight canola genotypes with a diverse genetic background.  Catch trays were used to collect total (pod-drop + pod-shatter) pre-harvest seed losses in canola.  Results from correlation analysis showed that pod-drop and pod-shatter were largely independent and that increased seed size in hybrids did not contribute to increased pod-drop.  Interestingly, pod-shatter was linked primarily to genotype while pod-drop was influenced more by the environment.  When significant differences were observed, average pod-drop was greater in the open-pollinated than in the hybrid cultivars used in this experiment.  Further investigations on pod-drop and pod-shatter in canola are necessary to develop genotypes with reduced harvest losses to increase revenue and reduce volunteer canola populations.

Sugarcane weed control programs in Florida generally consist of combinations of early and late postemergence herbicide weed control programs. Triazine herbicides atrazine, metribuzin, and ametryn are the foundation of these programs applied in combination with mesotrione, trifloxysulfuron, asulam, halosulfuron, and 2,4-D. Field studies were conducted near Belle Glade, FL in 2013 to determine the efficacy of different herbicide programs for early and late postemergence weed control in sugarcane. Predominant weed species were yellow nutsedge, fall panicum, and broadleaf weeds. Broadleaf weeds were mainly common lambsquarters and spiny amaranth. At 8 weeks after treatment (WAT) prior to the late postemergence treatment application, the early postemergence combination of metribuzin (1.05 kg/ha) + atrazine (4.5 kg/ha) + halosulfuron (0.84 kg/ha) provided the highest level of control of yellow nutsedge (88%), fall panicum (71%), and broadleaf weeds (90%). The late postemergence combination of asulam (3.74 kg/ha) + trifloxysulfuron (0.0158 kg/ha) and mesotrione (0.105 kg/ha) + atrazine (0.56 kg/ha) + asulam (3.74 kg/ha) + trifloxysulfuron (0.0158 kg/ha) provided the highest level of fall panicum and broadleaf weeds 6 WAT. These late postemergence programs provided 79 to 81% control of fall panicum and 84 % control of broadleaf weeds. Appropriate timing of application of these herbicide combinations is critical for efficacious weed control in sugarcane.

Field trials were conducted in 2011-2012 and 2012-2013 at Tifton, Georgia to evaluate the effects of previously applied residual herbicides on seeded autumn-planted energy beet (industrial sugar beet) growth and root production.  Prior to planting beet, herbicides were applied to bare soil at times when they would be used in a preceding crop.  Sulfentrazone (0.28 kg/ha), atrazine (2.8 kg/ha), metribuzin (0.42 kg/ha), linuron (0.84 kg/ha), and flumioxazin (0.10 kg/ha) were applied in June; pyrithiobac (60 g/ha), fomesafen (0.56 kg/ha), imazapic (70 g/ha), diclosulam (26 g/ha), and nicosulfuron (35 g/ha) were applied in early July; diuron (1.34 kg/ha), prometryn (1.34 kg/ha), chlorimuron (9 g/ha), and 2,4-DB (0.28 kg/ha) were applied in August.  Beet was seeded into lightly tilled soil (~5 cm depth) in early Oct of each autumn in 2011 and 2012.  At 90 days after planting (DAP), most injury was from residual herbicides that traditionally have greater than 10 month beet rotational restrictions.  Imazapic, sulfentrazone, diclosulam, and trifloxysulfuron beet injury ranged from 20 to 99% in both years of the experiment.  Fomesafen, mesotrione, flumioxazin, nicosulfuron, and pyrithiobac injured beet 10 to 55%.  Atrazine, metribuzin, linuron, diuron, prometryn, and 2,4-DB injured beet less than 20% at 90 DAP.  Overall stand reductions occurred with herbicides that caused significant injury and these same herbicides also reduced yield.  Beet was harvested in May of each season for root biomass.  Sulfentrazone, imazapic, diclosulam, and chlorimuron reduced yield to less than 50% of the non-treated control.  In contrast, atrazine and metribuzin did not cause stand or yield reductions, and was attributed to rapid dissipation for this soil type, a Tift sandy loam.  This research suggests that further studies need to evaluate the potential for herbicide carryover to beet in Southeastern US energy beet production due to differences in soil types and the temperate climate regime.

Field trials were conducted at the Saginaw Valley Research and Extension Center near Richville, MI in 2013 to evaluate the effects of desiccation and yield with three black bean varieties. Type II black bean varieties: ‘Zorro’, ‘Eclipse’, and ‘B10244’ were planted at two different dates, June 13 and June 26, for diverse growing conditions. Three desiccation treatments: 1) paraquat (0.56 kg ha^-1) + non-ionic surfactant (0.25% v/v), 2) glyphosate (0.84 kg a.e. ha^-1) + ammonium sulfate (2% w/w), 3) saflufenacil (0.05 kg ha^-1) + methylated seed oil (1% v/v) + ammonium sulfate (2% w/w) were compared to an untreated control for each variety. Desiccation treatments were applied at two different timings for each planting date: a) 50% of pods were yellow (early) and b) 80% of pods were yellow (normal). The early timing was to evaluate differences in desiccation treatments and many times there are areas in a field that may be at this stage when a desiccation treatment is made. Black bean desiccation was assessed at 3, 7, and 14 days after treatment (DAT) and yield direct harvested. A herbicide by variety interaction was observed in the first planting for the early application timing. Paraquat provided greatest desiccation (>96%) for ‘Eclipse’ and ‘B10244’, 3 DAT. At 3 DAT, black bean desiccation with glyphosate was similar to the untreated for all varieties. By 7 DAT, all herbicide treatments were greater than the natural dry down of their untreated counterpart. Saflufenacil provided the greatest dry bean desiccation for both application timings 3 DAT for the second planting date. By 7 DAT, differences between herbicide and varieties were observed. Overall yield was lower for ‘Eclipse’ for the first planting date and yields were lower for ‘Zorro’ and ‘B10244’ when paraquat and saflufenacil were applied early in the first planting. This may be due to the rapid desiccation observed that stopped the continued development of these beans. Yields were also lower for early applications of paraquat and saflufenacil in the second planting. ‘Zorro’ also yielded slightly behind ‘Eclipse’ and ‘B10244’ for the early application at the later planting, which may  be partially explained by the slight difference in maturity between ‘Eclipse’ and ‘Zorro’. Overall differences in desiccation and yield were observed between the varieties. This research will be conducted again in 2014 to further evaluate these varieties.  

Field studies were conducted in 2009 and 2010 at the Huron Research Station, Exeter, Ontario and the University of
Guelph Ridgetown Campus, Ridgetown, Ontario to determine the tolerance of four cultivars of cranberry bean (‘Etna’, ‘Hooter’, ‘SVM Taylor’, and ‘Capri’) and four cultivars of kidney bean (‘Red Hawk’, ‘Pink Panther’, ‘Calmont’, and ‘Majesty’) to linuron applied preemergence at 1125 and 2250 g ai ha^-1. One week after emergence (WAE), linuron applied PRE caused 0.4 to 1.2% injury in ‘Etna’, ‘Hooter’, ‘SVM Tayler’, and ‘Capri’ cranberry bean and 3.1 to 3.6% injury in ‘Red Hawk’, ‘Pink Panther’, ‘Calmont’, and ‘Majesty’ kidney bean. At 2 and 4 WAE, there was no significant difference in injury among the dry bean cultivars. Contrast comparing injury due to linuron in cranberry vs kidney bean cultivars indicated 2.3, 1.7, and 1.2% greater injury in kidney bean compared to cranberry bean at 1, 2, and 4 WAE, respectively. Linuron PRE cause slightly greater injury in kidney bean compared to cranberry bean but crop injury was minimal with no adverse effect on plant height, shoot dry weight, seed moisture content, and yield under the environments evaluated. Based on this research, linuron applied PRE at the proposed rate of 1125 g ai ha^-1 can be safely used in cranberry and kidney beans in Ontario.

PEANUT CULTIVAR RESPONSE TO PYROXASULFONE APPLIED PREEMERGENCE

P.M. Eure

E.P. Prostko

Department of Crop & Soil Sciences

The University of Georgia

Tifton, GA 31793-5737

ABSTRACT

Pyroxasulfone, previously known as KIH-485, is a residual herbicide that provides control of several annual grasses and broadleaf weeds.  This herbicide is currently registered for use in field corn and soybean and is being developed for use in wheat and sunflower.  Very little is known concerning peanut cultivar tolerance to PRE application. Therefore, field trials were conducted to evaluate peanut cultivar response to pyroxasulfone applied PRE.

An experiment was conducted in 2012 and 2013 at the UGA Ponder Research Farm on a Tifton loamy sand with 93% sand, 2% silt, 4% clay, 1% organic matter, and pH 6.0.  Treatments were arranged in a split-plot design with whole plots consisting of three peanut cultivars (`Georgia-06G`, `TifGuard`, and `Georgia Greener`) and sub-plots consisting of three pyroxasulfone rates (0, 120, or 240 g ai/ha).  Treatments were replicated four times and plot area maintained weed-free.  Plant population, visual estimates of peanut stunting, and peanut yield (adjusted to 10% moisture) were recorded.  All data were subjected to ANOVA and means separated using Fisher’s Protected LSD Test (P≤0.05) when appropriate.

Significantly more stunting occurred during 2012 than in 2013.  Peanut stunting 10 days after planting (DAP) during 2012 and 2013 ranged from 38 to 55% and 3 to 11%, respectively. During 2012, greater injury at 10 DAP was observed in `Tifguard` following 120 g ai/ha of pyroxasulfone applied PRE than in `Georgia-06G`.  `Georgia Greener` was injured more than `Tifguard` following 240 g ai/ha of pyroxasulfone applied PRE.  Greater injury during 2012 is most likely due to heavy rainfall at peanut emergence.  By 120 DAP, peanut had recovered substantially from stunting caused by PRE applications of pyroxasulfone with no cultivar interactions.  Peanut stunting at this time ranged from 6 to 8%.  Peanut yield was influenced by pyroxasulfone rate when applied PRE.  Peanut yield was 7,140 kg/ha in treatments that did not include pyroxasulfone.  Treatments that included pyroxasulfone applied at 120 g ai/ha yielded similar to treatments without pyroxasulfone.  Pyroxasulfone applied at 240 g ai/ha reduced yield to 6,750 kg/ha (7%).  Although peanut yield was not reduced following a full field rate (120 g ai/ha) of pyroxasulfone applied PRE, early season stunting and less than a 2x safety margin is concerning. Future research must be conducted to understand the influence of soil type and rainfall/irrigation on peanut injury from PRE applied pyroxasulfone.

Common pokeweed (Phytolacca
americana) is a perennial broadleaf weed with a large persistent taproot
that is also capable of abundant seed production. It has become a frequent
problem in agronomic crops in Pennsylvania. Traditionally, tillage was used to
manage pokeweed; however, the wide-spread adoption of no-till and a decline in
the use of soil residual herbicides in soybean may have allowed pokeweed
populations to increase in recent years.

Glyphosate is a commonly used herbicide in agricultural systems.
In other Penn State research, glyphosate proved to be a key ingredient for the
control of common pokeweed, especially in soybean. In order to examine
glyphosate efficacy more closely, four individual experiments were conducted in
2012 and 2013 in central Pennsylvania in fields infested with common
pokeweed.  The experiments focused on nozzle
selection, herbicide rate, carrier volume, and application timing.

In most experiments, individual common pokeweed plants were treated
with glyphosate at 0.87 kg ae/ha using air induction nozzles at 187 L/ha in
mid-June. However, in the nozzle study, air induction nozzles were compared to
standard flat fan nozzles.  For the rate
study, glyphosate was applied at 0.87, 1.27, and 1.73 kg/ha and for the volume
study, 93, 187, and 374 L/ha were compared. Visual control ratings and pokeweed
biomass were collected at both 12 and 44 weeks after application (WAA). The
results showed that control was similar for the two nozzles, there was a trend
for better control with the higher rates, and a trend for reduced control as
volume increased at both 12 and 44 WAA.

For the application timing study, individual common pokeweed
plants were treated every two to four weeks from mid-May to late August. For
each application timing, treated and untreated plants were collected 8 WAA.
Regrowth was also assessed the following spring. Applications before mid-June
provided less than 70% control. In mid-June, pokeweed plants were 1.2 meters
tall; after mid-June, pokeweed plants averaged 1.5 meters tall. Any application
at or after mid-June provided at least 93% control at 8 WAA and at least 80%
the following spring. The results from these experiments showed little
advantage to increasing glyphosate rate or altering nozzle selection or carrier
volume to improve common pokeweed control. 
Late spring application timings proved less effective than summer-time
treatments; glyphosate should be applied after mid June in central
Pennsylvania. Primary author’s e-mail: pokeweed@psu.edu

Experiments were conducted in 2012 and 2013 at Dundee and Robinsonville, MS to determine the impact of spray tip and herbicide program on glyphosate-resistant Palmer amaranth control.  Applications were initiated with Palmer amaranth was 10 to 15 cm in height.  Applications were made with a CO2 powered backpack sprayer with 324 kPa pressure and an application volume of 140 L/ha.  Treatments utilized in these experiments included:  dicamba at 0.6 kg ai/ha; glufosinate at 0.6 kg ai/ha; dicamba + glufosinate at 0.6 kg ai/ha each; dicamba + glufosinate at 0.3 kg ai/ha each; and glyphosate + dicamba at 0.75 kg ae/ha and 0.6 kg ai/ha, respectively.  All herbicide treatments were applied using the following spray tips:  Extended Range Flat Fan, Greenleaf Asummetric Dual Fan, Extended Range Air Induction, and Turbo Teejet Induction.  All tips utilized in these studies delivered 0.06 liters per minuteat 276 kPa.  At application, water sensitive spray cards were place ni each plot to determine percent coverage from each spray solution.  Experiments were conducted using a factorial arrangement of treatments in a randomized complete block design with four replications.  Data were subjected to analysis of variance and means were seperated using Fisher's Protected LSD at p = 0.05.

Two weeks after application, dicamba + glufosinate at 0.6 kg ai/ha provided greater than 80% reduction in total Palmer amaranth plants compared to the untreated check.  Glufosinate alone, glyphosate + dicamba, dicamba + glufosinate at 0.3 kg ai/ha, and dicamba alone provided 70, 56, 61, and 46% reduction in total plants per square meter, respectively, two weeks after treatment.  Dicamba + glufosinate at 0.6 kg ai/ha significantly reduced plant heights compared to all other treatments.  Visual estimates of control indicated tthat dicamba + glufosinate at 0.6 kg ai/ha provided 90% control two weeks after application.  Similar control was observed following application of glufosinate alone and glyphosate + dicamba two weeks after application.  Four weeks after treatment, dicamba + glufosinate at 0.6 kg ai/ha reduced the total number of plants per square meter and plant heights approximately 80% compared to the untreated check.  In addition, glyphosate + dicamba reduced the total number of plants by 60%.  Visual estimates of weed control and reduction in above ground biomass were similar in that dicamba + glufosinate at 0.6 kg ai/ha and glyphosate + dicamba each provided greater than 50 to 80% reductions compared to the untreated check.

Spray tip did not impact herbicide efficacy; however, tip selection did affect coverage.  Spray card data revealed that Extended Range Flat Fan had significantly higher percent coverage than other tips.  The Greenleaf Asymmetric Dual Fan, Extended Range Air Induction, and the Turbo Teejet Induction tips were all significantly different and provided 62, 52, and 34% coverage, respectively.  Herbicide programs did not significantly affect the coverage from a given spray tip.

The Turbo Teejet Induction tip produced the largest spray droplets, regardless of herbicide.  Less than 10% of the total droplets produced were less than 450 microns in size.  Depending on herbicide, 40 t0 60% of the total droplets produced by the Turbo Teejet Induction spray tip were greater than 730 microns in size.  However, approximately 50% of the total droplets produced by an Extended Range Flat Fan tip were less than 200 microns in size.

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

Annual production systems commonly rely on a number of primary and secondary tillage activities to prepare the soil for cash crops.  Resulting from these activities are potential detrimental effects on soil health, increased production costs, and threats to the long-term success of agricultural producers.  Weed pressure is commonly ranked as the number one cost for organic producers.  Additionally, the primary weed management tool for organic producers is the use of cultivation equipment to reduce weed pressure and seed production.  All of these activities invert/churn/disrupt soil and thus simultaneously bury and uncover weed seeds in the seedbank.  An increasing number of organic producers are looking to incorporate reduced tillage practices into their production systems in the maritime Pacific Northwest.  Reducing and/or eliminating tillage forces the need for an alternative weed management, such as using overwintering cover crops to create a mulch from the residue. Recent developments in other regions of the United States have identified the potential for an organically approved reduced tillage system relying on mechanical termination of the cover crop.  Transfer of this technology will require adjustments in this system so that it is adapted to the Pacific Northwest climate and production systems to maintain the economic competitiveness of producers within the parameters of this regions marketplace. Trials have been performed since 2009 in this locale and we will report findings from these trials.  

Glyphosate-resistant (GR) populations of Conyza spp. are problematic in orchards and vineyards of California, particularly in the San Joaquin Valley (SJV).  Alternative pre-(PRE) and post-emergence (POST) herbicides are being evaluated in greenhouse and field studies as potential immediate short-term measures to control these populations.  PRE herbicides being evaluated include flumioxazin, rimsulfuron, penoxsulam+oxyfluorfen, and indaziflam.  POST herbicides include glufosinate, saflufenacil, and paraquat.  The usage patterns, costs, and environmental impact (EI) of the above herbicide treatments were analyzed and calculated.  The usage pattern showed that the total amount of active ingredient of glyphosate applied in SJV orchards and wine grape vineyards increased by about 60% from 2005 to 2011.  However, the use of glufosinate has also increased since 2007, which was the year the GR Conyza was first reported.  In terms of costs, some of the alternative treatments were comparable or less expensive than existing recommendations.  However, the total EI ha^-1 of alternative herbicide treatments was greater than that of glyphosate-based treatments.

Weed management in organic vineyards is a challenge because of the lack of cost-effective, reliable, and organically-acceptable herbicides.  In the current context, weed management methods also need to be environment-friendly with low pollution and carbon dioxide (CO₂) emissions.  This study compared CO₂ emissions (in kilograms carbon equivalent) from various weed control methods in organic vineyards as a part of a study that compared the efficacy and economics of these methods.  The weed control methods included mechanical (tree and vine cultivator, and a plow), steam, and an organic herbicide.  These were also compared with a standard conventional method (one application each of a PRE and POST herbicide followed by mechanical cultivations) in San Joaquin Valley (SJV), California vineyards.  Only equivalent carbon emission (CE) occurring during the implementation of the above weed control practices in the vineyards were considered in the analysis.  Actual estimates of time required to implement the various treatments were taken from the field study and some estimates were taken from USDA cost studies.  The mechanical weed control methods were more effective, economic, and had lower CE values than the steam and organic herbicide treatments.  The conventional weed control method had the same level of CE as the organic herbicide treatment.  Between the two mechanical weed control methods, the tree and vine cultivator had lower CE than the plow.  In areas with strict air quality and other environmental regulations, such as the SJV, this type of analysis may have important implications.

Heavy rye cover crop influences weed control and melon production.  A. S. Culpepper, P. Eure, L. Sosnoskie, E. Prostko; University of Georgia, Tifton, GA.

The Montreal Protocol and the United States' (U.S.) Clean Air Act classified methyl bromide (MB) as a Class I ozone depleting substance in 1990 and called for its gradual removal from the market.  The phase out of MB was completed on December 31, 2005, although the use of MB was allowed to continue for preplant fumigation in some cropping systems upon approval by the U.S. EPA through a Critical Use Exemption (CUE) Process.  Georgia growers were able to successfully obtain MB from 2006-2013; however, January 1, 2014 will signify a new era without MB.

A watermelon study comparing MB to four alternative systems for weed control and yield was conducted during 2012 and 2013.  The MB system followed standard practices wherein the fumigant was injected (broadcast rate 240 lb/A; applied in row only) at the bottom of raised beds (32" wide, 8" tall) while covering with a virtually impermeable mulch.  Alternative systems included a smaller low density polyethylene mulch bed (17" wide; 2" tall; beds 6' apart) plus the following: 1) no herbicide and no rye cover crop (control), 2) a rye cover crop without herbicides, 3) an herbicide program without a rye cover crop, and 4) an herbicide program with a cover crop. The modified bed size was intended to help improve environmental and economic sustainability by reducing the need for mulch and fumigation; the area was not infested with nematodes.  In December of each year, land preparation, MB injection, mulch installation, rye seeding (90 lb/A), and part of the herbicide system was implemented.  For the herbicide system, an application of Sandea (0.75 oz/A) + Sinbar (4 oz/A) + Reflex (1 pt/A) was made only under the mulch when laid.  In the following March just before transplanting watermelon, 6 to 8 foot tall rye was rolled and glyphosate was broadcast over the trial area.  At this time, the rest of the herbicide system was implemented including a broadcast application of Sinbar (4 oz/A) + Reflex (1 pt/A) applied over the mulch and bare soil (area previously not treated); irrigation was used to remove all herbicides from the mulch.  Additionally, this herbicide mixture was applied between the rows of the MB standard.

Glyphosate-sensitive Palmer amaranth, yellow nutsedge, and annual grass densities of 88,015, 44,805, and 62,350 plants/A, respectively, were recorded in the no herbicide and no rye cover crop control (small bed mulch only). The addition of only the rye cover between the mulch reduced populations to 30,350, 5945, and 2030 plants/A, respectively.  When using the herbicide program instead of the rye, the herbicide program was more effective on Palmer amaranth (7380 plants/A), less effective on nutsedge (8845 plants/A), and similarly effective on annual grasses (1740 plants/A).  Greater weed control was achieved when the rye cover was combined with the herbicide program; Palmer amaranth and nutsedge densities ranged from 2465 to 2900 plants/A with only 435 annual grass plants/A.  When compared to MB, the rye cover plus herbicide program provided similar control for Palmer amaranth and annual grasses but was less effective on nutsedge (290 plants/A).

Weed control and soil temperatures influenced crop yield.  Watermelon fruit numbers were similar with MB and the rye cover plus herbicide program (5075 to 5510 fruit/A); while fruit weights were greater with the MB system (95,120 vs 79,605 lbs/A).  Yields from other programs were at least 35% lower than with MB. Fruit weights were likely greater with MB compared to the rye cover plus herbicide program because soil temperatures during early season were 5 to 15 F warmer in the raised wide beds.  Although alternative systems produced less fruit weight, an economic analysis will be conducted to determine net returns as the MB system is a far more expensive system.

Organic cropping systems are required under the
National Organic Program regulations to include cover crops.  Cover crops offer ecological services that
include pest suppression.  Sunn hemp (Crotalaria juncea) is currently the most
widely used cover crop in organic strawberry in Florida and provides off-season
suppression of weeds and sting nematodes (Belonolaimus
longicaudatus).  We propose that
organic strawberry cropping systems in the southeastern US can be more
resilient with greater cover crop diversity. 
To this end, we compared sunn hemp at a seeding rate of 44.8 kg/ha with
hairy indigo (Indigofera hirsuta), jointvetch
(Aeschynomene americana), and
short-flower rattlebox (Crotalaria
breviflora), each with a seeding rate of 22.4 kg/ha, for their utility in
suppressing weeds and sting nematodes during the off-season.  The study was conducted in two locations in
Florida: on-farm in Plant City and on-station in Citra with planting dates of
July 18 and July 30, 2013, respectively. 
The experimental design was a randomized complete block with the four
cover crop treatments and a weedy control treatment replicated four times.  Nine weeks after planting (WAP) just prior to
termination sunn hemp was the tallest cover crop by at least 49 cm at Plant
City and 53 cm at Citra and had the largest amount of dry shoot biomass at both
locations (9584 kg/ha and 6811 kg/ha, respectively). At Plant City, hairy
indigo and jointvetch produced an intermediate amount of biomass, whereas at
Citra the biomass of the three alternative species was not significantly
different.  At 3 WAP the sunn hemp canopies
were most effective at suppressing photosynthetically active radiation (PAR) penetration.  However, by 6 WAP only short-flower rattlebox
had more than 12% PAR penetrating its canopy at Plant City and at Citra only
sunn hemp and hairy indigo had slightly less than 25 % PAR penetration.  At Plant City, broadleaf weed biomass was suppressed
with hairy indigo and jointvetch as effectively as with sunn hemp.  However, at Citra, all the cover crops were equally
effective at suppressing broadleaf weed biomass.  Grass and sedge biomass at Plant City and
sedge biomass at Citra were not significantly lower with the cover crops than
with the weedy control.  However, grass
biomass was effectively suppressed to an equivalent extent by the four cover
crops in Citra.  Neither location
appeared to harbor sting nematodes as none was observed in soil sampled before
planting and after termination of the cover crops.   

Demand for organic food is increasing as public sentiment toward synthetic herbicides is growing more negative. While demand for organic food has grown, weed management remains the most significant agronomic problem associated with organic crop production. Natural weed control alternatives that are currently approved for organic agriculture are mostly nonselective essential oils used as postemergence, burn-down products. Their low efficacy requires multiple applications of high volumes to achieve good weed control. They lack systemic activity and have a nonspecific mode of action. There is a need for new natural weed control products. This research evaluated improved biological and lower-risk herbicides that are appropriate for use by organic growers to provide enhanced weed management in organic crop production. These included manuka oil and Opportune (MBI-005). Natural triketones present in manuka oil have the same molecular target as some commercial synthetic herbicides. Opportune is a new organic bioherbicide based on thaxtomin, a phytotoxin derived from Streptomyces scabies. The objective of this research was to make available organically-acceptable products from novel biological sources to control weeds in organic crop production by developing efficacy and crop safety data for these products. Field experiments were conducted at the Simcoe Research Station, Simcoe, Ontario, in 2013. Plots were arranged in a randomized complete block design with 4 replications. Plot size was 1.5m X 15m. Herbicides were applied at 1000 L ha-1 with CO2-pressurized back-pack sprayer @ 240 k pa. Manuka oil demonstrated soil activity and when mixed with other essential oils, enhanced their activity. Opportune also showed that it has soil activity but, when mixed with other essential oils, did not enhance their activity. More research into the pre-activity of manuka oil and Opportune on other weeds is needed to further explore the bioactivity and selectivity of these natural herbicides. The synergy associated with tank-mix applications of manuka oil with currently approved essential oils and acetic acid was demonstrated. Weed control with manuka oil, tank mixed with Green Match EX, Weed Zap or acetic acid generally ranged from 90 to 95% control. Synergy with manuka oil resulted in a 20 to 25% improvement in weed control, compared to each product used alone. This synergy has the potential to significantly improve weed management and will help growers to find solutions to the long standing issue of managing weeds in organic crop production.

Meadowfoam (Limnanthes alba Hartw. ex Benth.) seed meal (MSM), a by-product after oil extraction, has a plant defensive compound known as glucosinolate (glucolimnanthin). Activated MSM, produced by adding freshly ground myrosinase-active meadowfoam seeds to MSM, facilitates myrosinase-mediated formation of glucosinolate-derived degradation products with herbicidal activity. These products inhibited lettuce emergence by 58% and growth by 72% compared to the control. Glucolimnanthin was converted to 3-methoxybenzyl isothiocyanate (“isothiocyanate”) and 3-methoxyphenylacetonitrile (“nitrile”). Methoxyphenylacetic acid (MPAA), a previously unknown metabolite of glucolimnanthin, was detected from soil amended with MSM and activated MSM. Its identity was confirmed by LC-UV and high resolution LC-MS/MS comparisons with a standard of MPAA. Isothiocyanate inhibited lettuce germination about six and 13 times more effectively than MPAA and nitrile, respectively. Similarly, isothiocyanate provided the greatest inhibition of radicle length followed by MPAA, and nitrile, respectively. Results of the study suggest that MSM has potential uses as a pre-emergence bioherbicide.

Sweet potato is an important crop for both processing and fresh market growers in Oklahoma.  Prior to 2011 few acres of sweet potato were reported, but during the past three years commercial production has increased to nearly 1,000 acres for fresh market and processing. The objectives of this study were to determine crop safety and effectiveness of different preemergence herbicides for control of weed species on a commercial site.  Six different herbicides or commercial mixes of herbicides (S-metolachlor, flumioxazin, flumioxazin + pyroxasulfone, fomesafen, S-metolachlor + fomesafen, and linuron) were used alone and in combination for a total of 14 treatments plus non-treated and weeded checks.  Plots were replicated four times in a RBD, each plot consisting of four rows of sweet potatoes on 36” row centers 20’ in length.  Pre and post-transplant treatment applications were made on 6/12/13 with a tractor-mounted PTO driven pump sprayer (cone tank, 12’ wide boom with seven Tee Jet DG 11004 nozzles) at a spray volume of 25 gpa at 38 psi.  Following pre-transplant treatment applications the study area was transplanted with ‘Beauregard’ sweet potato slips using a commercial transplanter and crew (approximately 20 slips for each 20’ long plot).  Post-transplant treatments were applied the same day as transplanting except for the second application (4 weeks after transplanting) of S-metolachlor for the flumioxazin + S-metolachlor post-transplant + S-metolachlor 4 WAT treatment which was applied on 7/10/13 using a CO₂ hand boom sprayer with a six foot wide boom, again at a rate of 25 gpa.  Plant counts on 6/19 did not vary between treatments and ranged from 9 to 15 plants per plot.  Crop injury and weed counts did not vary on either day that ratings were recorded for any of the treatments, weeded or non-treated checks.  Initial ratings ranged from 8.8 to 26.3% injury while second ratings ranged from zero to nearly nine percent.  Numbers of weeds per plot did not vary for either date (7/10 and 7/25) for either weed species (Amaranthus palmeri and Mollugo verticillata) (Table 1).  On 7/10 the number of Amaranthus palmeri ranged from zero to 0.8 and Mollugo verticillata ranged from zero to 0.3 plants per plot.  Weed counts on 7/25 ranged from zero to 4.3 for Amaranthus palmeri and from zero to 9.0 for Mollugo verticillata.  Yield for treatments, weeded, and non-treated checks did not vary for any of the categories (U.S. # 1’s, canners, jumbos, culls, total marketable, %U.S. # 1’s).  Total marketable yield ranged from 21,408 kg/hectare for the weeded check to 59,573 kg/hectare for fomesafen pre-transplant at 280.5 grams/hectare.  Although no differences were observed there are trends that the authors would like to point out.  First, the weeded check had lower yields than any of the treatments.  Second, fomesafen pre-transplant at 280.5 grams/hectare yielded well overall and would appear to have potential for future work.  The authors would further conclude that there were stand problems in many plots with the highest percent stand at approximately at 75% the remainder averaging approximately 59%.  The plot variability in stands may account for the lack of differences recorded in the study.

Liquid Carbon Dioxide for Selective Weed Control in Established Turfgrass Systems.                                                                D. J. Mahoney*, M. D. Jeffries, and T. W. Gannon; North Carolina State University, Raleigh, NC.

In recent years, increasing pressure from environmental groups and human health advocates has driven laws and regulations aimed to reduce synthetic pesticide use in select public and private areas. Further, since turfgrass systems may be located near ecologically sensitive areas, control strategies need to be identified that reduce synthetic herbicide use . Biological, cultural, and mechanical weed control methods are currently used to varying extent in agronomic systems; however, many of these techniques are not viable in established turfgrass systems. The application of liquid carbon dioxide (LCD) causes a rapid freezing in/on treated plant tissue, which may result in cell membrane destruction and reduce plant survivability. Field and greenhouse experiments were conducted to evaluate LCD for selective weed control in established turfgrass systems. Liquid carbon dioxide was applied with a handheld prototype that was modified over time to reduce the amount of LCD required for weed control. Initially, applications were made through a 0.6 cm disc nozzle with output exposed to atmospheric conditions. The prototype was
modified with the addition of a flat fan XR8002E or XR8004E nozzle and an uninsulated cone to reduce output. Final modification included a full cone nozzle with an insulated cone. Plant response to varying LCD amounts and exposure duration was evaluated and compared to an industry standard postemergence synthetic herbicide. Common annual and perennial turfgrass weed control was visually estimated on a 0-100% scale (0 = no injury; 100 = complete plant death) for the following species: common chickweed (Stellaria media (L.) Vill.), corn speedwell (Veronica arvensis L.), goosegrass (Eleusine indica (L.) Gaertn.), large crabgrass (Digitaria sanguinalis (L.) Scop.), smooth crabgrass (Digitaria ischaemum (Schreb.) Schreb. ex Muhl.), Virginia buttonweed (Diodia virginiana L.), and white clover (Trifolium repens L.). Further, turfgrass tolerance was determined with visual injury estimations on a 0-100% scale (0 = no injury; 100 = complete plant death) on the following species: hybrid bermudagrass (‘Tifway 419’), Kentucky bluegrass (‘Unique’), tall fescue (‘Confederate’), and zoysiagrass (‘El Toro’). Treatments including a nontreated control were arranged in a randomized complete block design for all experiments. The final modification allowed for lower output (0.5 kg LCD min^-1) when compared to the initial prototype (3 kg LCD min^-1) and the uninsulated cone fit with either flat fan XR8004 (2 kg LCD min^-1) or XR8002 (1 kg LCD min^-1) nozzle without compromising weed control. In general, weed control increased as LCD mass per treatment increased. Averaged over annual and perennial weed species, LCD provided 38%
greater control of annual species compared to perennials, which may be in part to underground reproductive structures. Further, LCD exposure time affected control, as output was equal (30 kg m^-2) for XR8002 (30 sec) and XR8004 (15 sec) treatments; however white clover, Virginia buttonweed, and large crabgrass control was superior (18, 14, 15% greater, respectively) from the longer LCD exposure duration. The final model allowed for adequate weed control with less output; however, the data indicate plant maturity affects control. Large crabgrass control in 1-2 and 3-4 leaf stages (> 90%) was greater than in the 1-2 tiller stage (< 70%). Turfgrass injury at 7 DAT was unacceptable (> 30%) on all species, but declined to 0% by 28 DAT; however, Kentucky bluegrass coverage was significantly reduced compared to other evaluated species 28 DAT. These data suggest LCD may offer a viable alternative for weed control where synthetic herbicides are not desired.

Author contact: djmahone@ncsu.edu

Screening for Tolerance to Asulam in St. Augustinegrass and to Fluazifop-P-butyl in Zoysiagrass Germplasm. R.G. Leon*¹, J.B. Unruh¹, and K.E. Kenworthy²; ¹University of Florida, Jay, FL 32565, ²University of Florida, Gainesville, FL 32611.

POST grass weed control in St. Augustinegrass and zoysiagrass is a challenge due to limited number of selective herbicides available. Asulam and fluazifop-P-butyl can provide POST control of grass weed species in St. Augustinegrass and zoysiagrass, respectively. However, these warm-season turfgrass species have only partial tolerance to those herbicides, so turfgrass injury can reach unacceptable levels in case of overdose or in the presence of other stresses. We screened 20 St. Augustinegrass and 80 zoysiagrass (Z. japonica) breeding lines for tolerance to Asulam (2,340 g ai ha^-1) and fluazifop-P-butyl (88 g ai ha^-1), respectively. Injury in St. Augustinegrass ranged from 0 to 33% at 2 weeds after treatment (WAT). Injury was characterized by chlorosis and stunted growth. Several breeding lines showed unacceptable injury for more than 8 WAT for recovery. 'Capitva', 'Floratam', 'Palmetto' showed 13, 17 and 20% injury, respectively 2 WAT, while 6 breeding lines showed significantly less injury (0-5% injury). Injury in zoysiagrass breeding lines ranged from 0 to 30%, and symptoms included chlorosis, leaves turning purple, and stunting. More than 80% of the screened lines showed less injury than 'Empire' (23% injury) and 47% of the lines showed less injury than 'JaMur' (13% injury). The results of the present study highlight the value of incorporating screening for herbicide tolerance as part of turfgrass breeding programs to develop new cultivars with increased tolerance to herbicides will reduce the risk of turfgrass injury and could allow the use of higher rates to ensure grass weed control.

In Puerto Rico, pastures used for dairy cattle and hay production as well as wetlands are threatened by the invasive perennial shrub catclaw mimosa (Mimosa pigra L.).  Catclaw mimosa is not grazed by cattle and forms impenetrable thickets that reduce available grazing areas.  Moreover, its presence often makes it difficult for grass harvesting in hay production.  Although catclaw mimosa is widespread throughout the island and can colonize many habitats, lowland humid areas in the north, west and east are observed to be preferred by this weed.  Both farm owners and wetland managers have limited resources for implementing management methods for weed control.  However if suitable habitats for catclaw mimosa growth are identified, they can establish priorities and implement management methods that prevent the invasion of catclaw mimosa, or enable the development of an early detection rapid response plan to address the problem at the onset.  An island-wide prioritization analysis was performed using GIS along with ground-truth surveys.  Layers of wetlands, land cover, hydrography, and flood areas were ranked and combined to create a model that identified high, low and no suitable habitat classes for catclaw mimosa growth.  Then, a total of 708 random points were visited aided with a hand-held GPS unit to validate the accuracy of the model.  At each point visited the presence (1) or absence (0) of catclaw mimosa was recorded.  Using Chi-square analysis in SAS, the three predicted classes (high, low and no habitat) were analyzed to determine their association with the actual presence/absence data.  Results showed that 73% of the time, catclaw mimosa was found at high suitable habitat.  These areas were mainly located in flood plains and lowland areas.  Catclaw mimosa was found 52% of the time growing in low suitable habitat.  These areas were mostly located in areas far from the river bank in upper elevations.  As expected, areas identified by the model as no habitat had catclaw mimosa being observed only 16% of the time.  The total acreage at each class was 29,630, 405,061 and 459,764 hectares for high, low and no habitat respectively.  After having these areas clearly identified, farmers and wetland managers may allocate resources to suitable habitats and establish priorities according to their importance for catclaw mimosa growth.

The invasive catclaw mimosa (Mimosa pigra) is rapidly spreading, invading many beef, dairy and hay farms in Puerto Rico. The presence of this invasive species diminishes forage quality and causes injury to cattle and humans because of its thorny stem and leaves. This study evaluates practical control options for this weed. The experiment was conducted from May 2012 to January 2013. The site was a dairy pasture with a natural infestation of catclaw mimosa. Three systemic herbicides were evaluated using foliar and cut stump applications. The selected shrubs were from 1.82m to 2.44m in height. The herbicide treatments were glyphosate (480g/L), metsulfuron (272g/454g of formulation) and amynopyralid + 2,4-D (49g/L+400g/L). For foliar applications, the rate for glyphosate was 5 and 8% soln., aminopyralid + 2,4-D was 1 and 2% soln., and for metsulfuron was at 0.060g/L and 0.18g/L. Each treatment was applied to a single catclaw mimosa shrub as a spot treatment by using a backpack sprayer. For the cut stump technique, a rate of 50 and 100% soln. was used for glyphosate, 2 and 10% soln. for aminopyralid + 2,4-D, and for metsulfuron  the same rate as for the foliar application. Herbicides were applied to the cut surface immediately after the cut was made. A non-ionic surfactant at 0.25% vol/vol were used for all treatments. Weed control efficacy was evaluated up to 44 weeks after treatments applications (WAA). Results indicated that catclaw mimosa was susceptible to all treatments, with 100% control by week 44. The first symptoms of defoliation were observed 3 weeks after the application. Grasses were affected by glyphosate up to 11 WAA; then  recovered. Excellent (>89%) control of catclaw mimosa was recorded for all herbicides used with the cut stump application. A second trial was conducted by using the same herbicides but at lower rates  in foliar applications. The area for this trial had relatively tall shrubs; most of them taller than 2.44m. Treatments were glyphosate at rates of 2.5 and 5% soln., aminopyralid + 2,4-D at 0.5, and 1% soln. and metsulfuron at 0.029 and 0.060g/L. At 9 WAA all individual treatments caused defoliation and dry branches in at least 90% of the shrubs. However, many of the shrubs regrew by week 36 after application, except those subjected to metsulfuron at 0.060g/L. The latter treatment showed 100% control of the shrubs.

Field studies were conducted near Lexington, Kentucky in 2011-2013 to evaluate the effects of synthetic auxin herbicides on clover, soybean, and tobacco following application to an established orchardgrass pasture.  Treatments evaluated included aminopyralid at 88 or 122 g ai ha^-1, aminocyclopyrachlor at 70 or 105 g ai ha^-1, formulated premixture of picloram + 2,4-D at 226 + 840 g ai ha^-1, and premixture of triclopyr + fluroxypyr at 840 + 280 g ai ha^-1 plus an untreated control.  Herbicide treatments were applied May 3, 2011 and red clover var. 'Kenland' and white clover var. 'unknown' was no-tilled planted into the treated area on September 1, 2011, approximately 120 days after herbicide application (DAA).  Initially red clover injury was observed 156 DAA with aminopyralid at 122 g ai ha^-1 (3% visual injury), aminocyclopyrachlor at 70 and 105  g ai ha^-1 (6% and 17%, respectively), and slight injury (1%) with the premixture of picloram + 2,4-D.  However, visual injury was not observed 223 and 314 DAA with these four treatments. Visual injury was not observed on red clover with the lower rate of aminopyralid at 88 g ai ha^-1 or with the premixture of triclopyr + fluroxypyr.  No injury was observed on white clover for each of the three evaluation dates.  In spring 2013, approximately 2 years after herbicides were applied, a portion of the experimental area was mold board plowed and disked twice before planting soybean and tobacco.  No visual injury from herbicide soil residues was observed throughout the growing season when soybean was planted on June 4, 2013.  In addition, these synthetic auxin herbicide treatments did not reduce soybean yields.  After tillage preparation tobacco was also transplanted on June 5, 2013 within the treated areas.  No visual injury was observed on tobacco within the first 4 weeks after transplanting for any of the six herbicide treatments.  However, at 6 weeks after tobacco tranplanting visual injury on tobacco leaves was observed with aminopyralid, aminocyclopyrachlor, and with the premixture of picloram + 2,4-D treatments.  Prior to tobacco harvest visual injury was 22% and 25% with aminopyralid at 88 or 122 g ai ha^-1, respectively; 5% and 10% with aminocyclopyrachlor at 70 and 105  g ai ha^-1, respectively; and 28% with the premixture of picloram + 2,4-D.  No visual injury was observed with the premixture of triclopyr + fluroxypyr.  No significant differences in leaf fresh weight yield were observed with tobacco.  These results suggested that red clover could be sensitive when planted in the fall following applications of aminopyralid, aminocyclopyrachlor, or picloram + 2,4-D, whereas, soybean was not affected when planted 2 years after treatment following periods of adequate rainfall.  However, tobacco transplanted within 2 years after treatment could be injured from soil residues of aminopyralid, aminocyclopyrachlor, or picloram + 2,4-D.

Switchgrass (Panicum virgatum L.) is a perennial grass used for soil conservation, livestock forage systems, wildlife habitat programs and, more recently, as a feedstock for biofuel production. Despite its many positive attributes, switchgrass can be very difficult to establish due to weed pressure. Atrazine can be used to control weeds in switchgrass but applications cannot be safely made until switchgrass has between 3 and 4 leaves. Unfortunately, this application timing can be too late to prevent weed competition. This study examines the effect of switchgrass seedling growth stage and herbicide rate on switchgrass sensitivity to atrazine. The objective of our experiment was to determine whether the field observations of switchgrass sensitivity to atrazine could be replicated in the greenhouse environment.  ‘Alamo’ switchgrass plants were established in the greenhouse and were sprayed with atrazine (2.24 kg a.i. ha^-1 or 4.48 kg a.i. ha^-1) at the 1, 2, or 4 true leaf stage. All atrazine treatments contained crop oil concentrate at 1% v/v. Data collected two weeks after treatment included: Percent herbicide injury, plus fresh weights and dry weights. These were compared to an untreated control. There was a significant atrazine rate by leaf stage interaction. Plants treated at the 1 true leaf were most sensitive to atrazine herbicide injury; while plants treated at the 4 true leaf stage were least sensitive. Across all leaf stages atrazine at 4.48 a.i. ha^-1 injured plants more than 2.24 kg a.i. ha^-1 of atrazine. These results are consistent with the field observations and support delaying atrazine application until switchgrass has at least 4 true leaves. On-going studies are examining the rate of atrazine metabolism in switchgrass at these leaf stages.

Invasive species introduced for horticultural purposes often have complex origins typified by multiple introductions of species, cultivars, and genotypes, and interspecific and intraspecific hybridizations in introduced ranges. We inferred the origins of the invasive French broom complex in California by characterizing the genetic diversity and population structure of invasive and horticultural brooms and of Genista monspessulana from its native Mediterranean range using 12 nuclear microsatellite markers. Bayesian analyses showed that some invasives assigned to a group containing G. canariensis, G. stenopetala, and ornamental sweet broom, and the remaining invasives assigned to a group containing G. monspessulana from Sardinia and Corsica. Admixture between the groups was detected. Multiple introductions, escapes from cultivation, and inter-taxon hybridizations likely contribute to the invasive success of French broom in California and have important implications for management.

Winter creeper is a nonnative invasive plant that was introduced from Asia in 1907 as an ornamental plant.  It is commonly planted as an ornamental, and because of ornamental planting and bird-dispersed seeds it has become prominent as a ground cover in disturbed forest areas and poorly managed landscapes.  Winter creeper is very competitive, in part, because it retains its leaves year round, in some environments.  A previous study demonstrated that application of foliar herbicides can selectively control winter creeper, after other desirable species have dropped their leaves.  Do late season applications result in greater control than early season applications?

This study was initiated in January, 2013 at the University of Kentucky Arboretum to answer the question asked above.  Herbicide treatments were applied with a single tipped CO₂ sprayer until the leaf surface of the entire plot (0.9 m x 0.9 m) was wet.  The early winter treatments were applied on January 9, 2013 while the late winter/early spring treatments were applied March 23. Visual data were collected on plots for percent winter creeper foliar cover (0-100%) at 133 (5/22/2013), 259 (9/25/2013), and 370 (1/14/2014) DAT (days after treatment) using the January application as the start date.  The assessments were 60, 186, and 297 DAT for the March application.

The treatments included the following products (active ingredients):  Finale (glufosinate), Garlon 4 Ultra (triclopyr), and Roundup Pro (glyphosate) by themselves as well as combinations with Roundup Pro.  All treatments included a non-ionic surfactant at 0.5% v/v.  Time of application did not have an effect on winter creeper control at any of the assessment dates.  The best control was with the treatments containing Garlon 4 (0 to 7% foliar cover).  Winter creeper regrowth in the Finale treated plots resulted in an increase in foliar cover from 133 to 370 DAT.  However, the foliar cover decreased in the plots treated with Roundup alone from 133 to 370 DAT.

The Eurasian vines pale swallow-wort (Vincetoxicum rossicum) (PSW) and black swallow-wort (V. nigrum) (BSW) are invasive perennials that have infested natural areas in the northeastern United States and southern Canada.   A biological control program is being developed, though it is unclear how these perennial plants might respond to potential biological control agents as they experience little herbivore damage in North America.  We are evaluating the effect of multiple seasons of artificial defoliation and clipping at different frequencies on the survival, growth, and reproduction of mature PSW and BSW plants grown under field conditions in Ithaca, NY.  Root crowns of PSW and BSW were transplanted into a common garden in a 3-way factorial structure within a completely randomized experimental design with 5 replicates that included: [1] two target species (PSW, BSW), [2] eight damage treatments: 50% defoliation (all new leaves cut in half widthwise plus stem tips cut) or 100% defoliation once (July) or twice (June & July) each season; clipping stems 8 cm above soil level once (June), twice (June & July) or four times (May, June, July, Aug.) each season, and an undamaged control, and [3] year (repeated measures on above-ground [non-biomass] data or independently collected biomass samples after 1, 2, 4 & 6 seasons of damage).  No plants died from damage over the past four years, and stem number increased from 5 (both species 2009) to 13 (BSW) or 17 (PSW) stems/plant in 2012.  Plants clipped 4x per season had a lower root dry mass than other damage treatments; otherwise root mass increased over time, from 19 g (2009 average) to 65 g (2012).  BSW root mass (27 g on average) was less than PSW root mass (42 g).  Viable seed per BSW plant was less for plants clipped 2x or 4x per season than undamaged control plants; PSW also showed a similar but non-significant trend.  Pale and black swallow-wort display a high tolerance to above-ground tissue loss, whether by artificial defoliation or clipping, in high-light environments without plant competition.  Four clippings per season was the only type of damage that consistently reduced biomass and reproductive output.  The continued annual increase in root dry mass and stem number calls into question the potential efficacy of a defoliating insect against field populations of swallow-worts.

Invasive plant species can have ecosystem level impacts when they alter ecosystem processes such as fire regimes.  Bromus tectorum (cheatgrass) has been found to form a positive feedback with fire in some areas of the sagebrush biome of Western North America by increasing fire frequency and size, which in turn further increases abundance of the grass post-fire.  However, this response is not consistent across the sagebrush steppe.  Here we ask whether a positive feedback forms between B. tectorum and fire in an intact sagebrush steppe community on the Upper Snake River Plain, Idaho, which is in the northeastern portion of the sagebrush biome.  We compared B. tectorum abundance across unburned sites and sites within a chronosequence of fires that occurred between one and 15 years prior to sampling.  Bromus tectorum cover was the same in the burned and unburned plots, and negatively associated with litter cover.  Therefore, we found no evidence for a positive feedback between B. tectorum and fire in the northeastern region of the sagebrush biome.  Climate variables between sagebrush steppe sites that have been reported to have positive B. tectorum response to fire and those that have not were also compared.  We conclude that a positive feedback between B. tectorum and fire is unlikely to occur at sites that have high spring precipitation and low winter temperatures.  However, it is possible that as a result of climate change B. tectorum’s role as a negatively transformative invasive species could extend to the entire sagebrush biome.

Annually, Cooperative Extension specialists at The Pennsylvania State University update “The Penn State Agronomy Guide” – a crop management reference for famers and agricultural service providers. Prior to editing, industry representatives provide current information about their respective herbicide label revisions and any new products. In addition, herbicide prices have been obtained from 1998 to the present. Each year, several pesticide dealers throughout the state provide us with their seasonal herbicide price lists. The prices for each herbicide are averaged and used by University specialists and extension educators for the sole purpose of comparing the costs of various herbicide programs (i.e., one-pass compared to sequential applications or total post) when consulting with a grower about various program options.  They are not intended as a direct comparison to prices quoted by specific retailers and are not meant for publication in newsletters or otherwise broadcast. While compiling these documents, herbicide product and price trends have been detected. The total number of corn and soybean herbicide entries and premixed products in “The Penn State Agronomy Guide” has increased over the past 20 years. In 1993, 39 corn herbicides were listed, by 1998, it increased to 72 entries, and in 2013, 109 entries are listed. (These same types of trends can be traced for herbicides used in other commodities too.) Over the same time period, corn premixes increased from 12 products to 46. In 1993, 44 soybean herbicides were listed and 62 and 60 entries in1998 and 2013, respectively. 15, 19, and 17 soybean premixes were listed in the respective years. Many of these premixes are useful since they combine commonly used active ingredients and multiple modes of action in a convenient and economical product. However, others may simply be different active ingredient ratios or formulations of already existing products. Often, new trade names are associated with additional products or premixes sometimes causing confusion or the misunderstanding that they are indeed new herbicide modes of action. Or conversely, some products use a similar trade name yet have different formulations, contain different active ingredients at different ratios, and are
used at different rates or in different settings. All of these factors make it challenging when making recommendations and explaining the differences to farmers and cooperators. However, the recent inclusion of herbicide group numbers on product labels and in production guides has helped with education about herbicide mode of action and resistance management issues. Herbicide prices have varied over the past 15 years depending on the product. In general, products such as 2,4-D ester, Accent, Classic, Dual II Magnum, FirstRate, Lumax, and Permit have gradually increased in cost over the years. Products like Assure II, Liberty, metribuzin, Pursuit, and Select have shown price decreases. While other herbicides such as atrazine, Bicep II Magnum, Canopy DF, Clarity, Harness Xtra, Prowl, and Reflex had rather volatile price fluctuations over short timeframes within the 15 year period. Glyphosate-containing herbicide prices have been very unstable ever since the expiration of the United States patent for Roundup (glyphosate) in September 2000. With more competition from generic products, glyphosate prices have widely varied over the past decade. For example, in 2003, Roundup WeatherMax (4.5 lb ae/gal) cost $60/gallon while generic glyphosate (3 lb ae/gal) products averaged $27/gallon. By 2007, Roundup averaged $46/gallon but increased to nearly $80 in 2009 and by 2013 decreased to $33/gallon. The same trend was observed with the generic glyphosate products. In 2007, they were about $15/gallon, $35 in 2009, and about $16/gallon in 2013. The reasons for these glyphosate price fluctuations vary; some suggest more acres of corn and soybean, some blame added global demand, while others say it is related to various events in Asia and other complex reasons throughout the industry. Other noticeable trends within the past couple decades include: the proliferation of generic/off-patent herbicides that try to mimic Bicep, Harness, Guardsman, Prowl, Cimarron, Harmony, Crossbow, Canopy, Select, Accent, Permit, Resolve, Steadfast, Reflex, Gramoxone, and other products; more spray tank adjuvant products;
an increase in no-till acres and cover crop usage; an emphasis on spray drift management; and the lack of new herbicide modes of action. Also, there is a correlation between the dominance of herbicide resistant crops, namely Roundup Ready, and the use of soil-applied residual herbicides, especially in soybean systems. By the late-1990s and into the early-2000s, soil-applied herbicides were neglected in lieu of perceived simplified herbicide programs.  However with the increasing prevalence of herbicide resistant weed species, there has been a revived use of PRE soybean herbicides to incorporate additional modes of action to manage resistant weed problems.

Currently, natural products used in organic agriculture for crop growth and weed management have been shown to be less effective than comparable conventional methods (pesticides and fertilizers). The objectives of this research were to (a) determine the promotive effects of various organic emulsifiers (sugar bubble, natural detergent, loess sulfur, brown rice vinegar, and powder soap) on lettuce, Chinese cabbage, radish, cucumber, and barley, to (b) investigate whether the increase in crop growth by the emulsifiers is related to photosynthetic efficiency (quantum yield), chlorophyll and carotenoid contents, and to (c) evaluate the herbicidal effects of the organic emulsifiers on common lambsquaters (Chenopodium album), curled dock (Rumex crispus L.), dandelion (Taraxacum officinale), and barnyardgrass (Echinochloa crus-galli). Plant height and shoot fresh weight in the radish, Chinese cabbage, and lettuce were increased up to 15-51% by sugar bubble, 11-49% by brown rice vinegar, and 8-48% by natural detergent at 1, 3, 5, and 10% concentrations in the greenhouse. The plant height and shoot fresh weight did not increase in powder soap and loess sulfur treatments. Plant height and shoot fresh weight in cucumber and barley did not increase in the emulsifier treatments. The increase in crop growth by the emulsifiers was not related to photosynthetic efficiency (quantum yield), chlorophyll and carotenoid contents. Germination rate, shoot and root lengths in cucumber and barley were 100% inhibited by brown rice vinegar, powder soap, and loess sulfur at 3% and 5% concentrations in Petri dish bioassays. Shoot and root lengths in barley and cucumber were also 100% inhibited by brown rice vinegar at 3% and 10% concentrations, respectively, and loess sulfur at 10% and 5%, respectively in soil experiments. Shoot and root lengths in common lambsquarters, curled dock, and dandelion were 100% inhibited by 3% concentrations of all emulsifiers tested (sugar bubble, brown rice vinegar, powder soap, and loess sulfur) in Petri dish bioassays. In greenhouse study, curled dock was 28-30% and 47-100% controlled by foliar applications of brown rice vinegar and loess sulfur, respectively, at 3, 5, and 10% concentrations, and dandelion was 46-55% controlled by loess sulfur at 5% and 10% concentrations. The results of this study suggest that the organic emulsifiers tested can be used to increase crop growth and provide in-row weed control for transplanted vegetable crops.

The management of herbicide resistant or invasive weeds that escape treatment can be particularly challenging. Producing crops that are ensiled could be a management option allowing a reduction of the seed input of these problem weeds as any harvested seed will potentially be killed during silage fermentation and rumen digestion. However, few studies have evaluated the survival of weed seeds in silage. This study aimed at evaluating the viability of seven weed species in experimental mini-silos of corn. The species tested included weeds for which glyphosate-resistant biotypes have been reported in Canada (Ambriosia artemisiifolia, Conyza canadensis, Kochia scoparia) or the USA (Amarantus retroflexus), an invasive weed regulated in Canada (Eriochloa villosa) and two species of weeds expected to present low (Echinochloa crus-galli) or high (Abutilon theophrasti) survival in silage. Nylon mesh bags containing one hundred seeds of either weed species were inserted at random locations in mini-silos filled with compacted silage corn (1200 kPa pressure) and stored for one, three and six months. The experiment included five mini-silos per storage time. The permeability of the seed coat of the species was also evaluated to determine if it was related with survival. A single month in corn silage lowered the viability of all weed species by ca. 95%, except A. theophrasti whose viability was not significantly reduced. Leaving the seeds for three months further reduced the viability of all species to an average of 0.39% with only A. theophrasti and C. canadensis showing some viability. After six months no seed of any species was viable. Seed viability was unrelated to seed coat permeability. Ensiling for six months could be used to kill harvested weed seeds of herbicide resistant or invasive weeds. Further evaluations in commercial farm silos could be done to support results.

The use of cover crops in the United States has been on the rise over the past several years, yet it is unclear how these organic amendments, with varying C:N ratios, influence weed dynamics, specifically weed seed mortality. A collaborative experiment among states in the North Eastern region of the US began in 2012 with the objective of determining the extent to which cover crops affect weed seed mortality over time. It was hypothesized that cover crops with relatively low C:N ratios, such as leguminous cover crops would enhance seed mortality through increased microbial activity (seed decay) and germination stimulation due to increase nitrate availability (fatal germination). In Michigan, the cover crop treatments assessed were cereal rye ‘Wheeler’, medium red clover ‘Marathon’, and no cover and the weed species studied were velvetleaf, common lambsquarters, and giant foxtail.  Seeds of each species were buried with sand in mesh bags in cover crop plots in the fall at a depth of 15 cm, exposing seeds to any root leachates during the fall and winter months. Immediately prior to cover crop incorporation in the spring, all bags were retrieved. One set was analyzed for seed viability, while a high rate of the cover crop (fresh, chopped shoot and root material) was added to the other bags (equivalent to 6.2 g of dry biomass per bag, which is 22 times higher than the other states added). Enough bags were buried to allow for six removal times at 0, 1, 2, 4, 6, and 12 months after cover crop incorporation (MAI), with 4 replications. At each removal time seeds were separated from the sand and organic debris and counted. Viability of seeds recovered was determined using a combination of germination and tetrazolium chloride testing. Data are presented for all removal timings from 2012, and from the 0-4 MAI pull timings from 2013. In both years weed seed viability was highest when bags were pulled at the time of cover crop incorporation (0 MAI). Overwinter seed mortality ranging from 4-46% depending on the species and year. In 2013 the overwinter mortality of giant foxtail seed was very high, at 72%. In both years, seed mortality increased with storage time across all covers for each of the weed species. Weed seeds of all species buried in red clover plots in 2012 had greater mortality when compared to rye, when combined across removal times. Furthermore, rye (with a high C:N ratio) increased persistence of giant foxtail and velvetleaf seed  compared with the no cover treatment. In 2013, the same trend has occurred for common lambsquarters for the 0, 1, 2, and 4 MAI pull times, with seed mortality being highest in clover (53%), followed by no cover (33%) and rye (22%). Though the cover crop rates examined in this study were higher than estimated for a cover crop planting in Michigan, our data suggests that a cover crop with a high C:N ratio (such as rye) could enhance weed seed survival, when compared with no cover crop or a cover with a low C:N ratio (such as clover). 

Giant ragweed (Ambrosia trifida) has become an increasingly important weed of arable land in many parts
of North America because of the development of resistance to Group 2 and 9
herbicides (i.e., ALS/AHAS inhibitors and glyphosate, respectively). This has
led to an increase in the number of suspected cases of resistance that are
submitted for testing, as well as an increased emphasis on examining the
molecular mechanisms conferring resistance. Testing for resistance in giant
ragweed can be a lengthy process as germination is delayed by a physiological
dormancy of the embryo and an inhibitory influence of the embryo covering
structures. The objective of this research was to develop a protocol for alleviating
dormancy and stimulating germination in seeds of giant ragweed in as short a
time period as possible. We compared several physical (i.e., complete embryo
excision or a partial removal of the involucral hull) and chemical (i.e.,
gibberellic acid or potassium nitrate) methods for stimulating germination, as
well as a range of cold stratification periods (i.e., up to 8 months). Results
indicate that the complete excision of the embryo was the most effective means
for overcoming dormancy, providing 96% germination with no cold stratification.
The remaining physical and chemical seed treatments were not significantly
different from the untreated control. The results of this study demonstrate
that excising the embryo can overcome the seed dormancy imposed by the embryo
covering structures, which can significantly reduce the time required to
produce ragweed seedlings for resistance testing or other experimental
purposes.

A simple, user-friendly decision-support software is being developed for guiding growers, consultants, and other weed management practitioners on the integrated management of Palmer amaranth (Amaranthus palmeri S. Wats) in the midsouthern US row-crop (cotton, corn, and soybean) production systems. The Palmer amaranth management model (PAM) is based on RIM (ryegrass integrated management) a decision-support system developed by the Australian Herbicide Resistance Initiative, which has been popular in the Australian southern grainbelt. The PAM software can be used in four simple steps: 1) define field, 2) build strategy, 3) compare outputs, and 4) export results. The ‘define field’ module allows the user to input parameter values for average crop yields, prices, key weed management options (both chemical and non-chemical) specific to the chosen field, as well as costs incurred, and control efficacy on Palmer amaranth. Additional management information can be specified in the ‘more options’ and ‘more prices’ sections. The user is expected to provide parameter values only for the key components that are unique to the represented field, whereas key crop and weed values are pre-determined based on published literature and expert opinion. The ‘build strategy’ section is used to customize a weed management strategy for a 10-yr period, by choosing from a list of pre-existing management options deemed applicable to the system. Several control options, which are not available by default in the model, can also be defined by the user. A number of strategies can be customized and saved for subsequent comparison in the ‘compare outputs’ module. In the ‘export results’ section, the user can download these outputs in a number of formats. The calculations are carried out in a separate module hidden from the visual interface, but can be accessed by unlocking the model. The Microsoft® Visual Basic® for Applications framework provides the model with a software-like appearance and facilitates navigation among different modules. The user can seek assistance by clicking the ‘help’ button provided in each page. A user-guide is also being developed to assist the users with this tool.

Palmer amaranth (Amaranthus palmeri) was first identified in Michigan in 2010. This non-Michigan native pigweed species was confirmed to be resistant to glyphosate- and ALS-inhibiting herbicides at a field site in southwest Michigan. In 2012 and 2013, a field experiment was conducted at the Michigan State University Crop and Soil Sciences Research Farm in East Lansing, MI to compare seed mortality of Palmer amaranth with that of the native pigweed, Powell amaranth (Amaranthus powellii).   Mature seeds from Palmer amaranth and Powell amaranth plants were collected and cleaned in the fall of 2011 and 2012.  One-hundred seeds of each species were mixed with 100 g of an air dried Capac loam soil and sealed into separate 10x10 cm mesh bags. These bags were double contained in another mesh bag to prevent seed loss.  Seed bags were buried in the soil at depths of 0, 2.5, and 10 cm in November of 2011 and 2012.  Mesh bags were collected 1, 6, and 12 months after burial (MAB).  Palmer amaranth and Powell amaranth seeds were sieved and intact seeds were counted.  Intact seeds were germinated in petri dishes containing 3 ml deionized water on #1 filter paper in the dark at 20 C for 1 week and counted to determine non-dormant viable seed.  Seeds that did not germinate were subjected to tetrazolium chloride (TZ) testing to determine seed viability.  Seeds that tested positive were considered viable.  Percent seed mortality was determined by subtracting the germinated and viable seeds from the 100 initial seeds in each mesh bag.  Seed mortality in 2012 from Palmer amaranth and Powell amaranth 12 MAB was 90 and 70%, respectively; mortality at 12 MAB was 32% and 50% greater than mortality at the 1 month retrieval time for Palmer amaranth and Powell amaranth, respectively.  Palmer amaranth seed mortality was 20 to 38% greater than Powell amaranth depending on retrieval time.  In 2013, mortality across species at 12 MAB was 53%, which was 22 and 25% greater than the 1 and 6 month retrieval time, respectively.  Rainfall in 2012 was 3 times greater than rainfall in 2013 from burial until the one month retrieval time, which may have contributed to the increased seed mortality observed in 2012.  In 2013, the main effect of species was also significant with 9% greater Palmer amaranth seed mortality compared to Powell amaranth.  Burial depth did not influence seed mortality except at the 6 month retrieval time in 2012 when there was 17 to 21% greater mortality of seeds buried at 2.5 and 10 cm compared to seed placed on the soil surface. Our research indicates that eliminating additional Palmer amaranth seed rain for just a single season will decrease viable seed in the soil seedbank by more than 50%.  

Soil disturbances can facilitate reductions in weed seedbank density by providing light cues that modify the response of buried seeds to environmental factors for germination (i.e., appropriate temperature and sufficient soil moisture).  Based on literature indicating that light-induced germination is negatively affected by water scarcity immediately following light exposure, we hypothesized that, for weed species featuring photoblastic seeds, disturbance-induced reductions in seedbank density increase as the time period between soil disturbance and irrigation decreases.  To test this hypothesis, we established artificial seedbanks at a university research farm near Las Cruces, NM.  Weed species in this study included two species for which germination is considered to be stimulated by light (junglerice and Palmer amaranth) and one species for which germination is thought to occur independent of light (yellow foxtail).  Treatments included undisturbed controls and soil disturbances 10, 3, or 0 days prior to irrigation, with each soil disturbance-irrigation treatment applied twice during a single growing season.  Results indicated that soil disturbances reduced seedbank densities of Palmer amaranth and yellow foxtail, but did not affect seedbank density of junglerice.  For Palmer amaranth, soil disturbances 10 days prior to irrigation reduced 1-yr seedbank persistence by 70% compared to undisturbed controls, whereas soil disturbances 0 and 3 days prior to irrigation reduced 1-yr seedbank persistence by 89%.  For yellow foxtail, seedbank reductions relative to undisturbed controls were greatest when soil was disturbed 10 days prior to irrigation.  Increased knowledge of the species-specific interactions between soil disturbance, irrigation timing and seedbank persistence can guide the development of weed seedbank reduction strategies that utilize existing technologies for crop production.

EFFECT OF LIGHT INTENSITY ON GROWTH, MORPHOLOGY, AND SIZE HIERARCHY OF REDROOT PIGWEED (Amaranthus retroflexus L.).  R. Gaire and M.K. Upadhyaya; University of British Columbia, Vancouver, BC.

Size hierarchy, inequality in the frequency distribution of plant size in a population, influences competitive interactions and plant fitness within a population. Knowledge of effects of environmental factors on size hierarchy is therefore important to understand their effects on competitive interactions and the persistence of weedy species. A field experiment was conducted at the University of British Columbia to evaluate the effect of light intensity on growth, morphology and size hierarchy of redroot pigweed (Amaranthus retroflexus L.). Pigweed plants were grown under four light intensities (400, 600, 1,000 and 1,800; µE m⁻² s⁻¹) using 3, 2, 1 and 0 (control) layers of charcoal fibreglass mesh screen respectively. These treatments represent approximately 22%, 33%, 55% and 100% of full sunlight on a clear day. A randomized complete block design with four replications (1 m x 1 m plots; 100 plants/plot) per treatment was used. Effects of light intensity on plant growth parameters (n = 10) and the size hierarchy for plant height and aboveground biomass (85 plants) were monitored. Lorenz curves were plotted and Gini’s coefficients, a measure of size hierarchy, were calculated; a higher Gini’s coefficient indicates a higher size inequality within a population.

The results showed significantly greater plant height, aboveground biomass, inflorescence length, inflorescence biomass, branch number and branch length at 100%, compared to 33% and 22%, sunlight treatment. Plants grown under 100% sunlight had 91% greater inflorescence biomass compared to those grown under 22% sunlight. The size hierarchy for plant height significantly increased with decreasing light intensity. Gini’s coefficient was 17.6 in the 22% sunlight treatment but only 5.6 in the 100% sunlight treatment (Expt. 2), indicating a 67% lower  size inequality at higher light intensity. Size hierarchy of the aboveground plant biomass was not affected. There was no consistent and/or significant difference in either growth parameters or the size hierarchy of plant height between 100% and 55% sunlight treatments.

This study characterizes effects of light intensity on growth and morphology of pigweed and shows a strong influence of this environmental factor on size hierarchy. The effect on hierarchy suggests a differential influence of light intensity on competitiveness and potentially the fitness of individual plants within a population. Since light treatments were applied to relatively uniform populations, this effect could possibly be due to genetic variability in A. retroflexus population.

IMPACT OF PLANT DENSITY ON SIZE HIERARCHY OF COMMON LAMBSQUARTERS (Chenopodium album L.). L. Ma and M.K. Upadhyaya; University of British Columbia.

Plant fitness is related to its class in size hierarchy, which refers to the frequency distribution of individual plant sizes in a population. Field experiments were conducted in the summer of 2013 to study the effect of lambsquarters (Chenopodium album L.) density on its size hierarchy. Individual plants were grown in sandy loam soil in plastic cones (410 ml) to eliminate competition for soil resources. The cones were spaced to achieve three density treatments [D₁ (18 m^-2), D₂ (32 m^-2) and D₃ (74 m^-2)].  A randomized complete block design with three replications of 60 plants each was used and the experiment was repeated. Effects of plant density on lambsquarters growth parameters and size hierarchy were monitored periodically for around 30 days. Lorenz curves were plotted and Gini’s coefficient was calculated to assess the effect of density on size hierarchy. Red: farred (R/FR) ratio of the light reflected from the neighboring plants at different densities was measured by positioning the sensor horizontally. Results showed a decrease in R/FR ratio with increasing density, presumably due to a greater reflection of the reflected far-red light from neighboring plants. R/FR ratio in D₃ was 8.4% to 22.4% lower compared to that in D₁ in the Expt. 1 and 10.3% to 25% lower in the Expt. 2.  Plant height increased with the increasing plant density in both experiments (α = 0.1); the magnitude of the increase was 5.6% and 9.2% in Expts. 1 and 2, respectively. Plant density did not influence size hierarchy (Gini coefficient) and had no consistent influence on relationships between plant biomass and plant height or plant biomass and stem diameter.  These results suggest that in the absence of competition for soil-borne resources, plant density influences plant height presumably due to its effect on the R/FR ratio of the light reflected from neighbours. There was, however, no effect on plant size hierarchy for up to 30 days.

Comparative Growth of Henbit (Lamium amplexicaule) Based on Emergence Date.  B. C. Woolam*, D. O. Stephenson, IV, and R. L. Landry; Louisiana State University Agricultural Center, Alexandria, LA.

Research was conducted in 2012 and 2013 at the Louisiana State University Dean Lee Research and Extension Center near Alexandria, LA, to compare growth characteristics and growth pattern changes in henbit (Lamium amplexicaule) that emerged in October and November.  Cotyledon henbit seedlings that emerged in early-October and -November were transplanted on raised beds in the field.  Individual plants constituted a single experimental unit.  Plants were arranged as a factorial in a completely randomized experimental design.  Factors included emergence dates (previously described) and harvest intervals of 2, 3, 4, 6, 8, 10, and 12 wk after emergence (WAE).  Twelve plants were harvested for destructive measurement at each interval.  Values of total aboveground plant weight, leaf area ratio (LAR), specific leaf area (stem leaf ratio (SLR), net assimilation rate (NAR), and relative growth rate (RGR) were calculated on a per-plant basis at each harvest interval.  All data were subjected to ANOVA with means separated with Tukey’s HSD at alpha 0.05.

Total aboveground plant weight for henbit that emerged in October and November was similar 2 through 6 WAE (3 to 47 mg); however, aboveground plant weight of October-emerged henbit was approximately 600 to 1,000% greater than November-emerged henbit 8 to 12 WAE.  Leaf area ratio and SLA were greater for October-emerged henbit 2 and 3 WAE, but no differences were observed from 4 to 12 WAE.  Stem leaf ratio at 2 WAE was 3.21 and 0.32 for October- and November-emerged henbit, respectively, but little to no differences in SLR was observed between emergence dates at all other harvest intervals.  Net assimilation rates for both emergence dates were similar initially; however, NAR of October-emerged henbit was greater than November-emerged henbit 3 to 4 and 6 to 8 WAE.  In contrast, NAR was greater for November-emerged henbit 10 to 12 WAE.

Henbit is often difficult to control with herbicide applications in the spring, which is historically attributed to overall plant size at application.  Total aboveground plant weight indicates that October-emerged henbit may mimic the size of difficult-to-control henbit in Louisiana producer fields at time of spring herbicide application.  Although LAR, SLA, and SLR were greater initially for October-emerged henbit, the similarity for these variables for October- and November-emerged henbit 4 to 12 WAE does not explain the differences in total aboveground plant weight 8 to 12 WAE.  However, the increase in NAR, which is a measure of photosynthetic efficiency of leaves, 6 to 8 WAE for October-emerged henbit compared to November emergence may be the reason for greater total aboveground plant weight.  Experiments will be repeated to substantiate results.

Abstract:  In an attempt to evaluate the allelopathic potential of horseweed (Conyza canadensis) to inhibit the growth of seedling corn and soybeans, a greenhouse study utilizing several sources of horseweed extract was conducted.  Five seeds each of either corn or soybean was planted in greenhouse media in 10 cm diameter pots.  Horseweed extract was applied to the containers through one of four treatments:  incorporation of (4 grams/pot) of chopped, dried plant material; applying 150 ml of aqueous extract made by soaking 10 grams chopped, dried shoot material/150 ml water for 24 hours; applying 150 ml of aqueous extract made by soaking 10 grams/ of chopped, dried root material/150 ml for 24 hours; applying 150 ml of leachate collected from a container growing a mature horseweed plant.  The control containers were planted with the seeds but received no horseweed extract.  After 8 weeks, aqueous root extracts reduced corn germination to 55%, but did not affect growth of surviving plants negatively.  In pots with fewer than five plants, corn height, root length and plant dry weights were higher than controls, possibly due to less competition. Soybeans receiving aqueous shoot extracts had the lowest germination rate (65%), although root extracts also tended to reduce germination from untreated plants.  The aqueous shoot extracts also significantly reduced soybean height, and tended to reduce soybean root length.  Soybean plant dry weights were not significantly affected by the horseweed extracts. Confirmation horseweed allelopathy is inconclusive from this study, although germination inhibition appears likely, and soybeans may be more sensitive to the horseweed extracts than corn.

The evolution of herbicide resistance in major weed species of California rice, including Cyperus difformis L. (smallflower umbrellasedge) and Echinochloa phyllopogon (Stapf) Koss (late watergrass), has necessitated the search for management options that utilize cultural controls. In order to effectively apply these cultural controls (such as intermittent irrigation or stale seedbed), it is necessary to be able to better predict the dynamics of weed germination and emergence under a variety of tillage and irrigation methods. Recently developed laboratory models of germination and emergence for C. difformis and E. phyllopogon have accurately predicted timing of germination and emergence using soil moisture and temperature (hydro- and thermal-time models) in controlled environments. The long-term goal is to be able to utilize these models to predict weed emergence in the field, and thus, assessments were begun in 2013 to determine the models’ validity under field conditions. Two locations known to have large seedbanks with susceptible populations of each species were selected. Beginning from the initial irrigation event, daily counts of emerged C. difformis and E. phyllopogon seedlings were conducted under two irrigation treatments: continuously flooded (water maintained at approximately 10 cm above the soil), and flushed (flush irrigated when the top layer of soil became dry). Plants were counted until no new individuals emerged (45 days for smallflower umbrellasedge, and 40 days for E. phyllopogon).  Volumetric water content (m³/m³) and air and soil temperature (°C) were recorded continuously for the duration of the counts. Field data were compared to the laboratory-generated data. Using laboratory-determined averaged base temperature (T_b) for two biotypes of susceptible California C. difformis (18.39°C), and laboratory-determined base temperature for the susceptible biotype HR for E. phyllopogon (9.03 °C), emergence percentage was expressed in growing degree-days (GDD in °C d). C. difformis in the flushed treatment initiated emergence between 103 (±6) (GDD ± S.E.) and 113 (±6) GDD, whereas under the continuously flooded irrigation, emergence was initiated much earlier, between 63 (±2) and 73 (±2) GDD (both p = 0.0037). The average total number of plants (per 25 cm²) that emerged from the flushed treatment was 25 (±3) (average ± S.E.), significantly less (p = 0.0014) than the number that emerged under a continuous flood: 315 (±36) per 25 cm². E. phyllopogon initiated emergence between 96 (±3) and 109 (±3) GDD in the flushed treatments and between 104 (±2) and 117 (±2) GDD in the continuously flooded treatment (no differences between flushed and continuously treatments, p = 0.1069 and p = 0.1134, respectively, which is consistent with the ability of E. phyllopogon to germinate under both aerobic and anoxic conditions. The average total number of plants that emerged (per 25 cm²) under flush irrigation was 24 (±3), which was no different (p = 0.3549) from the average total number that emerged from the continuously flooded treatment: 36 (±10) per 25 cm². Since an emergence model has not yet been developed for C. difformis, observed emergence was compared with predicted germination curves for C. difformis using the thermal time model with laboratory-generated parameters, G= [log t_g – (log θ_T(50) – log (T– T_b))] / σ_θT (under the assumption that T_b for germination and emergence are equal). For C. difformis, thermal time for emergence was assumed to be thermal time to germination plus a constant number of GDD (assuming all fractions of the population emerged from the same soil depth). Observed emergence was compared with predicted emergence curves for E. phyllopogon. The predicted emergence curves were generated using laboratory-generated parameters for germination curves in GDD (°C d), which were then added to the GDD’s for growth to 4.5 cm above the soil surface (seed depth was assumed to be normally distributed). There are differences between the predicted data generated in the laboratory and observed emergence in the field. Reasons for the differences remain to be further evaluated and could result from soil moisture effects upon germination or growth to emergence, as well as inaccurate estimates of seed depth (non-normal distribution), dormancy status of the seed, or start of hydrothermal accrual. 

Simulation models have been shown to be useful in providing guidelines for practical management allowing exploration of a broad set of scenarios. However, many of those models are not spatial, missing the patchy nature of weeds and their dispersal dynamics. We have designed a spatial-temporal model based on experimental data. Our main goals were to use the model to 1) assess the spatial-temporal metapopulation dynamics of Johnsongrass (S. halepense), 2) assess the effect of initial conditions (plant density, proportion of field infested, and aggregation pattern) and dispersal (natural and mechanical) on Johnsongrass dynamics, and 3) use the model to compare control strategies (non-herbicide treatment, rimsulfuron treatment applied uniformly, and site-specific herbicide treatment) to optimize Jonhsongrass management in two agronomic systems (with tillage, and no-till). The model was validated with independent field data. Simulations over seven years indicated that rimsulfuron helped to increase crop yields significantly in infested areas every year, but it was not enough to decrease the infestation of the following year (after each treatment year) in most scenarios. The no-till system was more profitable than the tillage system to control Johnsongrass when rimsulfuron was applied, due to the higher intraspecific competition that resulted in increased herbicide efficacy. The total net returns, in current currency, during the seven years with a site-specific treatment were always higher than with a uniform herbicide application, assuming weed detection and application errors of 20% with the site-specific strategy. Based on the economic injury level, husbandry costs, herbicide costs, and grain sale price, the model facilitated optimization of Johnsongrass management for a range of scenarios both in the short and in the long term.

Crops with novel traits for abiotic stress resistance are being developed and field tested but there are no standard effective methods to compare weedy or invasive potential of GM and conventional crops apriori. Population matrix modeling is an established method to project changes in population growth rates in response to different environments. To evaluate their usefulness for novel crops, we established common gardens experiments at 5 research stations across Canada in 3 disturbance regimes (agricultural to natural area) and at two densities using Brassica napus, Camelina sativa, Triticum aestivum, and Kochia scoparia. Using field data from two site years and reported seed persistence, we derived life cycle graphs depicting important life stages.  Life table response experiments allow us to determine critical life stages by decomposing the variability of the population growth rate (lambda, λ) and determine the effects of experimental treatments. Despite high fecundity, a lack of seed dormancy in the crop plants resulted in low overwintering survival rate. The λ values of a species varied with the level of disturbance and with environment. Population matrix modeling will provide a framework by which we can assess the weedy or invasive potential of novel crops.

Since the discovery of the mechanism of glyphosate resistance via EPSPS gene amplification in Palmer amaranth, a critical follow-up question has been “How does the EPSPS gene move around the genome?”  To answer this question, a number of groups have been working to define the length of the “amplicon” or the piece of DNA that is being duplicated.  Building off of EPSPS fosmid sequences published out of a Mississippi lab last year, the research reported here presents a novel technique of using 454 sequence data to manually extend the amplicon out and then confirm the extensions using molecular laboratory analyses.  This process resulted in a 38.6 kb amplicon with interesting repeat elements flanking the entire sequence.  Work is now being done to use additional genomic data sets with deeper coverage to confirm the ends of the amplicon, find these repeats in other glyphosate resistant biotypes, and potentially associate the repeats with a regulatory element, like a transposon.

The Asteraceae genus Artemisia is represented in North America by about 60 species, of which 8 or 9 have been introduced.  Fifteen annual/biennial and perennial species are considered to variously impact agricultural production in arable fields, pastures and rangeland.  A significant feature of the seed biology in some species is the production of a slimy mucilage envelope (pellicle) when cypselas (fruits) are wetted.  Mucilage coatings consist primarily of a skeleton of cellulose fibres in a pectinous matrix, and are likely perform two basic functions including facilitating germination (enabling or inhibiting under suboptimal conditions) and diaspore dispersal (enabling or inhibiting the impact of water, wind or animal vectors) with complex, even opposite, advantages in different conditions.  Of the Fifteen weedy species examined: mucilage cells were detected in the pericarp of all but A. douglasiana, A. filifolia and A. tridentata; mucilaginous cells were observed in A. abrotanum, A. absinthium, A. stelleriana and A. vulgaris, but only a small pellicle was produced; moderate to large pellicles were observed in A. annua, A. biennis, A. campestris, A. cana, A. dracunculus, A. frigida, A. ludoviciana, and A. scoparia.

A 2010 survey of weed escapes in Washington State mint and potato fields, and a subsequent dose-response study, identified 25 redroot pigweed (Amaranthus retroflexus) and 8 common lambsquarters (Chenopodium album) populations resistant to the heavily used photosystem II inhibitor herbicides metribuzin and terbacil. Most reported photosystem II inhibitor resistance is due to target site insensitivity from mutation of the chloroplast psbA gene encoding the D1 protein of photosystem II – most commonly a serine for glycine substitution at amino acid residue 264 (Ser₂₆₄Gly). A cleaved amplified polymorphic sequence (CAPS) analysis was used to confirm the presence/absence of Ser₂₆₄Gly mutation in these resistant populations, and for 22 susceptible redroot pigweed and 13 susceptible common lambsquarters populations collected and identified in the same dose-response screening. The majority of resistant populations had the Ser₂₆₄Gly mutation in all individuals tested, indicating it is the most likely mechanism of resistance. Populations identified as susceptible in dose-response screening did not have the mutation. Five populations identified as resistant in dose-response screening did not have the Ser₂₆₄Gly mutation in a majority of individuals tested, indicating other resistance mechanisms in these populations. These five populations generally exhibited a lower level of resistance in dose-response studies than observed for those with the Ser₂₆₄Gly mutation.

Glyphosate-resistant weeds are an increasing problem in perennial cropping systems in the Central Valley of California.  We assessed the geographical distribution of glyphosate resistance in horseweed (Conyza canadensis) and hairy fleabane (C. bonariensis) in 77 orchards and vineyards and inferred evolutionary origins and patterns of resistance spread using microsatellite markers.  Resistant horseweed occurred at high frequencies only in the southern valley, but resistant fleabane occurred at high frequencies throughout the valley although it exhibited greater phenotypic plasticity in resistance response than horseweed.  Frequencies of resistant individuals were positively correlated with the size of Ground Water Protection Areas (GWPAs) within counties.  Bayesian population genetic analyses revealed multiple independent origins of resistance in both species and showed that resistant horseweed genotypes underwent expansion for many years before being detected.  Interspecific hybridization was detected.  The lower selfing rate and greater genotypic diversity in fleabane relative to horseweed indicates greater evolutionary potential over shorter time periods. 

Seed was collected in July and August, 2012 from a population of Palmer amaranth, Amaranthus Palmerii, in Buckeye, AZ in western Maricopa County suspected of being resistant to glyphosate due to control failures. For comparison, seed was also collected from two known glyphosate susceptible Palmer amaranth populations, one at the University Of Arizona Maricopa Agricultural Center (MAC) and the other in a riparian area near Sahuarita, AZ along the Santa Cruz River. These initial seed collections were screened for resistance to both glyphosate and pyrithiobac. In collaboration with Pest Control Advisors, seed was collected in additional locations in Maricopa County in the summer of 2013 in response to glyphosate control failures. In all experiments, seeds of each biotype were planted in 4 inch pots, plants were grown to about the 4 leaf growth stage in a greenhouse and then sprayed with various rates of glyphosate and pyrithiobac-Na using a CO₂ pressurized sprayer and flat fan nozzles (XR8001) calibrated to deliver 112 L/ha at 183 kPa. In the first experiment, the Buckeye biotype showed little response to slight stunting at glyphosate rates of 0.42, 0.84, 1.68 and 3.36 kg ae/ha. In contrast, the Maricopa biotype was killed by rates of 0.42 and 0.84 kg ae glyphosate/ha. In the second experiment, the phytotoxic responses to increasing glyphosate rates from 0.01 to 0.4 kg ae/ha, 14 days after treatment (DAT) were 3.5 to 9.9 for the Maricopa biotype (0 to 10 scale with 10 representing death). In contrast, the phytotoxic responses to increasing glyphosate rates from 3 to 10 kg ae/ha 14 DAT were 3.5 to 6.6 for the Buckeye biotype. The Buckeye plants were severely stunted and chlorotic for a period of two weeks after treatment but eventually recovered, resumed growth and began flowering in the greenhouse. Additional dose response experiments showed that the original suspected glyphosate resistant Buckeye population was about 100 fold more tolerant of glyphosate than susceptible populations in Maricopa and Sahuarita, AZ. In addition, Palmer amaranth plants in other locations many kilometers from the field where resistant seeds were first collected are highly resistant to glyphosate. To make matters worse for alfalfa and cotton producers, dose-response experiments showed that the Palmer amaranth populations that were highly resistant to glyphosate were also about 10 times more tolerant of pyrithiobac-Na than susceptible populations in Maricopa and Sahuarita, AZ. Palmer amaranth is native to the desert southwest and is ubiquitous following summer monsoon rainfall with many plants growing along roadsides, in drainage ditches and other low lying areas not associated with agricultural fields. Plants growing in these areas could become reservoirs of the herbicide resistance traits; thus there is a significant risk that the herbicide resistance traits will spread to other agricultural areas in Arizona. 

Summer annual forage crops can be an important source of livestock feed in emergency situations when flooding or drought compromises corn silage and alfalfa crops. We tested for resource partitioning and facilitation in summer annual forage crops grown mid-summer in the northeastern United States. Four species with different statures and nitrogen acquisition traits: 1) sorghum sudangrass (Sorghum bicolor x S. sudanense, grass, tall); 2) pearl millet (Pennisetum glaucum, grass, short); 3) sunn hemp (Crotolaria juncea, legume, tall); and 4) cowpea (Vigna unguiculata, legume, short) were seeded at multiple rates in mono- and bicultures and in all possible combinations of 3 and 4 species mixtures. A portion of the treatments, including monocultures and the 3 and 4 species polycultures, were compared in a separate complementary experiment that was conducted at three different field sites that varied in planting date, climate, and soil type. Low-input conditions were simulated with a reduced seeding rate and by applying 40 kg/ha of total nitrogen in the form of either poultry litter (5-4-3) or mineral fertilizer (10-20-20) prior to seeding crops. Although this rate was potentially more nitrogen than would typically be applied prior to legume crops, it represents less than half of the recommended rate for sorghum sudangrass. Crop and weed biomass were sampled by clipping vegetation in 0.5 m² quadrats at approximately 50 days after planting. The dominant weed species present across experiments were Panicum capillare, Setaria spp., Amaranthus retroflexus, and Ambrosia artemisiifolia. Weed biomass in the main experiment ranged from 9 g/m² in the 4 species mixture to 200 g/m² in the low seeding rate biculture treatment of millet and cowpea. When averaged across all seeding rates, weed biomass in the legume biculture (sunn hemp and cowpea) treatment was 130 g/m², whereas weed biomass in the grass biculture (millet and sorghum sudangrass) treatment was only 29 g/m². The biculture treatment that produced the greatest crop biomass (sorghum sudangrass and sunn hemp) had a relatively low average weed biomass of 41 g/m². Preliminary analysis in the complementary experiment shows that on average, weed biomass was greater in monocultures (21 g/m²) than polycultures (8 g/m²), with the exception of the millet (6 g/m²). Overall, the short legume crop, cowpea, was the least weed suppressive, most likely due to less efficient use of sunlight and soil nitrogen. Other the other hand, the mixture of sorghum sudangrass, millet, and sunn hemp was one of the most weed suppressive, likely due to greater use of available resources. Results suggest that summer annual forage crop mixtures can enhance weed suppression, increase resource use efficiency, and provide greater quality forage at yields similar to the best yielding monocultures.          

Bromus tectorum (downy brome) is an invasive winter annual grass species, widespread throughout the winter wheat production regions of the Pacific Northwest (PNW). Study objectives were to identify how plant development differs among downy brome accessions from the PNW small grain production region and establish if distribution of development traits are spatially significant. Ninety-five downy brome accessions were collected from within the small grain production area of the Pacific Northwest during 2010 and 2011. To reduce maternal effects due to environment, all accessions were planted in the greenhouse in early 2012 and allowed to complete one life cycle. In November of 2012, accessions were then transplanted as seedlings into a common garden located near Central Ferry, WA. Phenotypic measurements with an emphasis on plant development stages were recorded weekly until flowering. Environmental readings were recorded by an onsite weather station for the duration of the experiment. The initiation of culm production and onset of inflorescence differed by up to three wks among accessions. The spatial distribution of late and early flowering accessions indicates positive spatial autocorrelation at distances less than 100 km and negative spatial autocorrelation at scales between 150 and 225 km. The distribution of early and late flowering accessions is directionally significant with early flowering accessions predominantly found in the western portion of the PNW small grain production region, while later flowering accessions were found in the eastern portion. The western portion of the small grain production region is characterized by higher summer temperatures and decreased summer precipitation. Projected changes in climate include increased temperatures throughout the year and decreased summer precipitation. Future climate scenarios may favor range expansion of early flowering biotypes to the east of the PNW small grain production region.

The most inexpensive, and practical option to control noxious weeds is with herbicide. However the effect on non-target native vegetation is not often considered. Burke Park is a small area (40 acres) of sagebrush steppe located within Bozeman city limits. It contains approximately 270 plant species, including small populations of seven state listed noxious weeds. In recent years weed control via herbicide has been occasionally undertaken. The goal of our project was to determine if herbicide control of noxious weeds has reduced native plant species diversity. We compared two surveys of seven 50 m transects each containing 15 permanently marked 0.5 m² plots. The first survey was conducted in July 2004 prior to any known herbicide application, and was repeated in July 2013. In 2013, four of the seven transects had been treated with herbicide, leaving three no-treatment control transects.

Noxious weeds totaled 1.5% of the total cover in 2004, and 0.8% of the total cover in 2013. We found a general decline in plant species diversity across all transects in the Park (y=-3.33x+32.3; F_1,10=10.8, p=0.01), but a greater decline in species richness in transects sprayed with herbicide (y=-11.1x+32.3; F_1,8=3.5, p=0.1). Native forbs had declined in treated plots, while the non-native perennial grass Kentucky Bluegrass (Poa pratensis) increased from 15 to 20% cover in all plots.

Increased use of the park, related to a 27% population increase over the last decade, likely contributed to the overall decline in native species diversity. However, a portion of the loss in plant species richness can be attributed to herbicide spraying. Therefore to preserve plant species diversity in natural city parks, land managers should minimize damage to the native flora by monitoring changes to small noxious weed populations, and applying herbicide only if these populations are found to be increasing. Careful spot spraying or wipe-on applications should be employed to reduce collateral damage to native species. Our study suggests that current practices may do more harm than good to plant diversity and the aesthetics of a city park.

Corresponding author: lrew@montana.edu

Kochia (Kochia scoparia (L.) Schrad.) is a problem weed in the Great Plains of North America. Understanding the seedling emergence patterns of kochia has direct implications for effective management of the weed, especially with the increasing occurrence of herbicide-resistant kochia in this region. A field study was initiated at the Montana State University Southern Agricultural Research Center near Huntley, MT, in spring of 2013, to characterize the seedling emergence of nine kochia accessions from Northern and Central Great Plains. Kochia accessions from North Dakota (ND), Garden city, KS (GC), Colby, KS (Cb), Manhattan, KS (Mn), Hays, KS (Hy), Huntley, MT (Hn), Las Lunas, NM (LL), Idaho (Id), and Artell, OK (At) were included. The study was established in a randomized complete block design with six replications. Sixty seeds of each accession were planted on the soil surface inside open-ended cylindrical PVC rings (30-cm dia) on March 15, 2013. Seedling emergence of each accession was recorded weekly from April 1 through September 30 (cessation of emergence of all kochia accessions in the field). Cumulative emergence was calculated as a percent of the initial seed bank or as a percent of the total emergence during the season. A 3-parameter log-logistic regression model was used to fit the cumulative emergence data. Cumulative growing degree day (cGDD T_base 0 C, starting April 1) was a good predictor of emergence of kochia accessions. Highest total cumulative emergence (as percent of initial seed bank) was observed for ND and Hy accessions, whereas Mn accession exhibited the least total emergence. Among all accessions, Mn accession emerged early, with significantly lower cGDD required for 10% (145, April 26), 50% (286, May 9), and 90% (564, May 26) of the total emergence during the growing season. ND and Cb accessions showed similar emergence patterns, and emerged over a longer duration with higher cGDDs (avg. 895, June 16) required for 90% of the total in-season emergence compared with other accessions. Validation of our model developed for predicting kochia emergence in U.S. Great Plains is needed. Forecasting seedling emergence patterns will help producers make proactive decisions for managing herbicide-resistant kochia seed bank in this region.

Roadsides along highways and major roads in southern Québec have been planted Trifolium cultivars, together with cold-season salt-tolerant turf grass mix. However, the clovers struggle to establish near the pavement edges. Ambrosia artemisiifolia has frequently occupied the empty areas and formed a dense linear population. The species is not only a noxious agricultural weed, but also the most prevalent allergenic weeds. Roadside topsoil contains heavy metals at concentrations toxic to plants. The way plants deal with metal stress may determine their success of establishment near roadside edges of highways and major roads. Hence, the study aims to investigate germination and early seedling behaviors of the study species (Ambrosia artemisiifolia, Lotus corniculatus, Coronilla varia, and Trifolium arvense) subjected to a range of heavy metal levels. All metals did not affect the final germination percentage (TG) of A. artemisiifolia over 2 weeks. However, Ni (≥ 100 ppm), Cu (≥ 50 ppm), and Cd (≥ 5 ppm) inhibited TG of C. varia. For L. corniculatus, the significant reductions in TG were caused by Pb (≥ 200 ppm), Cu (≥ 50 ppm), and Cd (≥ 5 ppm). TG of T. arvense was negatively influenced by all metal treatments (i.e. ≥ 100 ppm of Zn; ≥ 50 ppm of Pb, Ni, Cu; and ≥ 5 ppm of Cd). Germination rate (T₅₀ = time required to reach 50 % final germination) was also measured. Except for Cu treatment, there was no significant change in T₅₀ for A. artemisiifolia by the treatments. As compared to other test species, the degree to increase in T₅₀ was the lowest in A. artetesiifolia. With exception in case of Cd for C. varia and Zn and Pb for L. corniculatus, T₅₀ of C. varia, L. corniculatus, and T. arvense was significantly delayed by the heavy metal treatments. Low levels of Pb and Ni promoted the germination rate of A. artemisiifolia, suggesting its adaptation to contaminated environments. The aboveground growths of L. corniculatus and T. arvense were not inhibited by 50 % up to 100 ppm Pb, and ragweed growth was not decreased by 50 % up to 10 ppm Cd. Except for those, the other metal additions greatly hindered the aboveground growths of all test species. The inhibitory effects on the belowground growth were greater than on the aboveground. Ragweed had higher seedling survival rates under all metals. In terms of survival, L. corniculatus and C. varia were susceptible to Ni and Cu, while T. arvense was sensitive to all metals except for Pb. Although the metal stresses inhibited its growth, maintaining great germination capacity and low mortality rates under all metals can afford A. artemisiifolia a competitive advantage over T. arvense that had low germination ability and high mortality rates under all metals. Furthermore, L. corniculatus and C. varia can be potential ground cover candidates particularly for Zn and Pb contaminated roadsides as evidenced by great germination capacity and high seedling survival rates under those metals. Due to the ban on herbicide application for roadside weed control and adverse effect of frequent roadside mowing practices on ground covers, new roadside vegetation management favorable for interspecific competition must be developed. The present research project will outline the potential mechanisms that may drive the ragweed dominance along roadside edges. It can provide appropriate roadside vegetation and soil management practices for controlling ragweed.

Purple nutsedge (Cyperus rotundus L., PNS) and yellow nutsedge (C. esculentus L., YNS) are common weed species in the Southern United States. Previous research has shown that these perennial nutsedges serve as good hosts for the
southern root-knot nematode (Meloidogyne incognita, SRKN), a serious sedentary root endoparasite. Infection by SRKN increases YNS and PNS resource allocation towards tubers, which in turn harbor SRKN, protecting the nematodes from fumigant nematicides and deleterious environmental conditions. In June 2012, during a routine tomato bioassay of tubers to confirm no SRKN infection of YNS and PNS, prominent galling was observed on PNS roots but was absent on the standard host of SRKN, ‘Rutgers’ tomato.  This observation was unexpected, because neither PNS nor YNS exhibit readily-apparent galling and tomato is heavily galled when parasitized by SRKN, the target nematode of the bioassay.  Furthermore, NaOCl extraction of roots recovered eggs from PNS but not tomato. Subsequent dissection of PNS root galls revealed small mature Meloidogyne females with egg masses that were primarily contained inside the root tissue.  Further morphological observation revealed second stage juveniles (J2) with relatively long, thin tails and females with perineal patterns somewhat resembling those characteristic of M. naasi and different from M.incognita. A greenhouse study was conducted to compare the susceptibility of PNS and ‘Rutgers’ tomato to SRKN and the undetermined Meloidogyne species (hereafter referred to as ‘nutsedge root-knot nematode’, NSRKN).  Results showed PNS to be a host of both NSRKN and SRKN, whereas tomato was a host for SRKN only.  In addition, PNS biomass and tuber production, photosynthesis, and stomatal conductance were not affected by either Meloidogyne species compared to a control.  Three additional experiments were conducted to determine the NSRKN host status of alfalfa, chile pepper, corn, cotton, onion, sorghum, tomato, barley, oats, perennial ryegrass, wheat, winter rye, bentgrass, YNS, and PNS after inoculation with 2,000 NSRKN eggs and harvest at 700 to 800 cumulative heat units above 10 C.  Roots of each plant species were individually macerated in a 1.0% NaOCl solution in a blender.  Galling was observed and eggs were recovered from YNS, PNS, barley, oats, perennial ryegrass, wheat, and bentgrass.  From previous reports, the cool-season grasses as well as alfalfa and sorghum are hosts for M. naasi.  In a separate study, DNA was extracted from 56 NSRKN single J2 from multiple infested nutsedge sources.  After direct sequencing of an approximately 550 bp DNA fragment amplified using a primer set that targeted a locus between the mitochondrial cytochrome oxidase subunit II gene (COII) and the 16S rRNA gene, all J2 showed high similarity to each other,
but only 90% similarity to M. graminicola (closest BLAST hit) and even less similarity to M. naasi in a search of data bases containing Meloidogyne mitochondrial DNA sequences.  None of these results appear consistent with data previously reported for M. naasi.  Further investigation is needed to identify and characterize this Meloidogyne species, determine the pathogenicity of NSRKN to these grain crops, and understand the relationship between NSRKN and YNS, in particular, considering the geographic distribution of YNS relative to the grain production regions of the US and Canada.

Imperata cylindrica threatens food security and biodiversity on a global scale. Considered a noxious weed in 73 countries to date, this invasive pest plant species is well suited to displace food crops, forested areas, and endemic plant species in natural areas. With its traits for competitive success and adaptation to a wide range of water regimes, soil types and significant herbicide resistance, this C4 grass species is likely to thrive and invade more land as the earth is faced with weather extremes associated with climate change.

We have formed multiple international partnerships in order to obtain international samples of Cogongrass for sequencing with the goal of creating a comprehensive global genetic profile of this invasive plant. The overarching goal of this work is to expedite the development of biological controls for this herbicide-resistant species.

Restriction enzyme-assisted, reduced representation genotyping by sequencing is a cost-effective means for genetic profiling studies of magnitude. This method produces thousands of sequence-based genetic markers that can be tracked to specific sites in a reference genome for verification and accuracy. We have employed close relative, Sorghum bicolor (L.) Moench, as a proxy reference genome and have produced over 10,000 SNP (single nucleotide polymorphism) markers for 1050 Cogongrass accessions to date. Integrating GIS-associated data with this sequencing strategy, this approach has produced a sequence-based population genetic profile of this species with unprecedented resolution, a significant step in the overarching goal of controlling the spread of and reclaiming lands invaded by Cogongrass.

Palmer amaranth (Amaranthus palmeri) is one of the most aggressive broadleaf weeds in many cropping systems in the US. Availability of extensive genetic variability coupled with intense herbicide selection resulted in evolution of Palmer amaranth resistance to multiple herbicides with different modes of action including hydroxyphenylpyruvate dioxygenase (HPPD)-inhibitors such as mesotrione. The objective of this study was to investigate the mechanism of resistance to mesotrione in Palmer amaranth. Uptake and translocation of ¹⁴C-mesotrione were investigated in a HPPD-inhibitor-resistant Palmer amaranth population from Kansas (KSII) using a HPPD-inhibitor-susceptible population from Missouri (Azlin) as a control. Stock solution containing mixture of ¹⁴C- labelled (3.3kBq) and unlabeled mesotrione was applied on a fully expanded fourth youngest leaf of 10-12 cm tall plants (6 replications).  Total applied radioactivity was measured separately in leaf rinsate, treated leaf, above and below treated leaf, and roots 2, 4, 8, 24, 48 and 72 hours after treatment (HAT) by oxidative combustion of samples and using a scintillation analyzer. The results suggest no significant difference in ¹⁴C-mesotrione uptake or translocation between HPPD-inhibitor-resistant or-susceptible Palmer amaranth 2, 4, 8, and 24 HAT. Experiments are in progress to determine the metabolism of mesotrione and expression of HPPD gene in KSII and Aazlin Palmer amaranth. Understanding the mechanism of HPPD-inhibitor resistance is valuable to design weed management strategies to prevent the spread of resistance and also delay evolution of such resistance in new Palmer amaranth populations.

Glyphosate resistant Amaranthus palmeri is one of the worst weeds in row crop agriculture.  Resistance to glyphosate in this weed is a consequence of amplification of 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), the target enzyme of glyphosate.  Recent studies have shown that the EPSPS amplicon is at least thirty kilobases (kb).  The actual size of the amplicon and mechanism of amplification are unknown.  To gain a better understanding of EPSPS amplification, a bacterial artificial chromosome (BAC) library was constructed from genomic DNA of glyphosate resistant A. palmeri.  The library, consisting of 36,864 clones, provides 10x coverage of the A. palmeri genome.  Screening the library with an EPSPS specific probe revealed 680 clones containing the EPSPS.  To identify clones for sequencing, 192 clones were fingerprinted.  Of these, 186 assembled to a large contig about 200 kb in size, indicating that the EPSPS amplicon is very large and complex.  From this group five BACs were selected for end sequencing.  BAC end sequencing revealed that each clone had one end that anchored to the known 30 kb region of the EPSPS amplicon.  Some of these aligned outside of the probe, indicating that the EPSPS may be repeated within the amplicon.  Additionally, the other end of the five BACs aligned to sequence known from 454 sequencing to be highly amplified.  Sequencing of these five BACs should help elucidate more of the amplicon and will provide the basis for further studies in which the entire amplicon and the mechanism of amplification can be determined.

Amplification of the EPSPS gene was determined as a resistance mechanism in glyphosate-resistant (GR) populations of Palmer amaranth (Amaranthus palmeri) from New Mexico (NM). However, it should also be determined if other mechanisms of resistance occur in these GR populations.  Therefore, the objective of this study was to investigate glyphosate sequestration as a potential additional mechanism of resistance in those populations. In vivo shikimate accumulation assays with and without the addition of glycine were conducted in this study. The addition of different concentrations of glycine in wells of microtiter plates with excised leaf tissues of GR plants increased the shikimate concentrations compared with wells without glycine. The accumulation of shikimate was dependent on the level of resistance in the GR Palmer amaranth plants, previously determined to be correlated with the number of EPSPS copies. The precision of this assay was also tested with horseweed (Conyza canadensis) plants from California, previously confirmed to be GR due to glyphosate sequestration.  The assay also supported that the resistance mechanism in horseweed was indeed glyphosate sequestration.  Our results suggest that the mechanism of glyphosate resistance in Palmer amaranth populations from NM is both EPSPS amplification and glyphosate sequestration. The adjusted in vivo shikimate accumulation assay in this study seems to be a promising method for rapid detection of glyphosate sequestration as a mechanism of resistance in GR plants.

The herbicide glyphosate is one of the most commonly used herbicides in eucalypt forests in Brazil. However intoxication occurs commonly in plants due to herbicide drift and deposition on leaves. Different behaviors of eucalyptus clonal hybrids to glyphosate have been observed in the field. This study aimed to analyze metabolic changes in seedlings of three Eucalyptus clonal hybrids (clonal hybrid 1 - E. urophylla x E. platiphylla, clonal hybrid 2 - E. urophylla, clonal hybrid 3 - E. urophylla x E. grandis), submitted to glyphosate application. The treatments consisted of glyphosate application at 7.2, 18, 36, 72, 180, 360 and 720 g a.e. ha^{- 1}, and a control without application. Leaves of plants at 2, 7, 14 and 21 days after application (DAA) were sampled for shikimic acid level quantification. Shikimic acid was extracted from dried ground samples and quantified by LC-MS/MS. Shikimic acid levels in plants were greatly affected by sampling time and the highest amount of the compound occurred at 7 and 14 DAA. The shikimic acid levels behavior varied according to clonal hybrid, independent of glyphosate application.

The glyphosate used in sugarcane in Brazil as a ripener and to control sugarcane ratoon for replanting. This study aimed to evaluate the metabolic changes of sugarcane (variety SP801842) treated with glyphosate. The treatments consisted of application at 7.2, 18, 36, 72, 180, 360 and 720 a.e. g ha^-1, and a control without application. The levels of shikimic acid and the three aromatic amino acids (phenylalanine, tyrosine and tryptophan) in sugarcane cultivated in a greenhouse were evaluated. Sugarcane leaves at 2, 7, 14 and 21 days after application (DAA) were sampled. The shikimic acid and amino acids were extracted from dried ground samples and quantified by LC-MS/MS. High levels of shikimic acid were found in plants that received glyphosate application at rate from 180 g ha^-1 at 2 DAA until 21 DAA, in comparison to the control. The largest accumulation of shikimic acid occurred at 2 DAA. The plants presented reduced levels of tryptophan from 7 DAA at rates from 72 g ha^-1. Tyrosine levels were reduced in plants at 7 and 14 DAA even at the glyphosate rate lowest. Phenylalanine levels were reduced in plants from 14 DAA at rates at least 72 g ha^-1.

The auxin signaling F-box protein 5 (AFB5) has been linked to differential sensing and response to auxin-like compounds. Arabidopsis thaliana (ARBTH) mutants deficient in AFB5 function are tolerant to the commercial herbicides picloram and clopyralid and the experimental herbicide DAS534 but lack tolerance to 2,4-D, dicamba and fluroxypyr in agar-based root growth assays. The mutant ARBTH line afb5-1 showed tolerance to foliar applications of picloram but not 2,4-D. The differential response of these mutants to different chemical classes of auxin herbicides shows a clear distinction in the molecular recognition of these auxinic herbicides. Understanding the response of afb5-1 relative to wild type (WT) ARBTH with respect to structurally diverse synthetic auxin herbicides may help identify unique chemical structure-to-target receptor correlations. The response of WT and afb5-1 ARBTH to foliar applications of a diverse set of auxinic herbicides was assessed. Dry weights of the treated plants were measured to calculate 50% growth reduction (GR₅₀) values. The GR₅₀ values for the WT and afb5-1 were compared to determine tolerance.  As anticipated based on previous research, afb5-1 showed tolerance to the commercial herbicides picloram and clopyralid as well as the experimental herbicide DAS534, but showed no tolerance to 2,4-D. Tolerance was also noted with applications of the commercial herbicides aminopyralid and aminocyclopyrachlor and a new herbicide under development, Arylex^TM active (halauxifen methyl). afb5-1 did not show any tolerance to triclopyr, but did show low levels of tolerance to fluroxypyr and dicamba. Indole-3-acetic acid, 1-naphthylacetic acid and quinclorac did not provide enough growth reduction in foliar applications to determine any differential tolerance for afb5-1.

Palmer amaranth plants from seeds collected in 2000 in Washington Co., MS (suspected to be susceptible to glyphosate), were examined as a population and as individual plants and found to exhibit varying levels of tolerance or resistance to glyphosate.  Whole-plant spraying of glyphosate (0.84 kg ha^-1) to the population revealed that approximately 40% of this population was resistant to glyphosate, with an LD₅₀ of 0.75 kg ha^-1.  This set of plants displayed varying degrees of resistance 14 DAT.  Initial tests using leaf disc bioassays on 10 individual plants selected randomly from the population, allowed characterization of glyphosate resistance using both visual ratings of injury and quantitative measurement via chlorophyll content analysis.  After initial bioassays and spray application, five plants with a range of tolerance to glyphosate were selected for cloning so that further studies could be accomplished on these individuals.  Q-PCR analysis of these clones showed that resistance was not associated with elevated EPSPS gene copy number.  Shikimate levels were lower in the resistant and higher in the susceptible clones which correlated with varying degrees of resistance demonstrated in bioassays and spray application of glyphosate of these clones.  Results demonstrate that individuals in a population can vary widely with respect to herbicide resistance and suggest that uptake, translocation, sequestration, metabolism or altered target site may contribute to the resistance expressed in some individuals of this population. 

Horseweed (Conyza canadensis) is a winter or summer annual weed native to North America of importance in no-tillage crop production systems. A biotype of this weed was reported as being glyphosate-resistant, and its resistance mechanism was attributed to two non-target mechanisms. With the aim of studying if gene amplification was involved in the resistance mechanism, molecular studies were carried out. Results indicated that both resistant and susceptible biotypes have the same EPSPS gene copy number, suggesting that gene amplification is not involved in the resistance mechanism of C. canadensis biotype from Spain.

Glyphosate is a non-selective herbicide used for controlling weeds in cultivated areas including glyphosate-resistant (GR) crops and non-cultivated areas. Transformed GR wheat developed by genetic engineering was rejected by the wheat marketplace. As a consequence, a mutagenesis breeding effort was initiated using spring wheat cv. Macon, Louise, and Hollis to select for glyphosate tolerance. The objective of this study was to investigate the segregation of gene(s) associated with a resistance trait to glyphosate on these cultivars. The mutant line Macon 14-8-16-1, Louise-ORI, and Hollis 9-14-5-3 were used in this study. Mutants were backcrossed to their wild types to create a F1 generation and were then self-fertilized to yield F2 progenies. The F2 plants were applied with glyphosate at a rate of 0.42 kg/ha at 3-5 leaf stage. At 28 days after herbicide application, plants were rated for stunting of growth and scored for susceptible or resistant phenotype. A chi-square (χ²) test was performed in segregation analysis at significance level of 0.05 (χ² <3.84). It was determined that gene(s) involving in glyphosate resistance in Macon 14-8-16-1, Louise-ORI, and Hollis 9-14-5-3 segregated as a single recessive gene, a single dominant gene, and more than 2 genes (quantitative trait), respectively. The result indicates that the mutations in the cultivars conferring increased glyphosate tolerance may confer different degrees of resistance to glyphosate as resistance gene(s) were transmitted dissimilarly.  

Reliance of glyphosate in glyphosate-resistant (GR) cropping systems has created strong selection pressure resulting in weed resistance to this herbicide. Kochia is a competitive summer annual weed, well adapted to the US Great Plains and has recently evolved resistance to glyphosate by gene amplification of 5-enolpyruvyl shikimate 3-phosphate synthase (EPSPS), the target-site of glyphosate. The overall goal of this research was to understand the genetic basis and inheritance of GR trait in kochia. Homozygous resistant (R) and susceptible (S) parental lines were identified. Using these parents, reciprocal crosses were conducted to produce F₁ progeny. As expected for a nuclear encoded EPSPS gene, F₁ plants from both crosses survived various doses of glyphosate application. However, F₁ plants showed intermediate shikimate accumulation and EPSPS gene copy number (relative to ALS gene) compared to parents. F₂ progeny were produced upon self-pollination of F₁ plants. In response to 840 g ae ha^-1 glyphosate, F₂ plants (n=115) segregated into 3R:1S implying a Mendelian monogenic segregation of glyphosate resistance in kochia. However, in F₂ dose-response, phenotype response and EPSPS gene copy number varied among resistant individuals, suggesting a correlation between the level of resistance and relative EPSPS gene copy number. These results demonstrate that the glyphosate-resistance in kochia segregates in monogenic fashion and inherited as a semi-dominant trait. The monogenic inheritance of glyphosate resistance will facilitate evolution and spread of this resistance in new kochia populations. 

Glyphosate has been a popular herbicide for weed management in annual, perennial cropping systems and non-crop areas for more than a decade.  Heavy reliance on a single mode of action can increase the risk of weed species evolving resistance to the herbicide. Glyphosate-resistant (GR) populations of Palmer amaranth have been confirmed throughout the southeast United States since 2005. Since 2012, growers in California’s San Joaquin Valley (SJV) have observed poor control of Palmer amaranth in glyphosate-tolerant corn (Zea mays L.) and cotton (Gossypium hirsutum L.). Palmer Amaranth (Amaranthus palmeri) is one of the most problematic weeds because of its competitive ability, C4 photosynthesis, high water use efficiency and drought tolerance, rapid growth rate, and prolific seed production. However, it is not known if these are cases of GR populations or application of glyphosate at more tolerant stages of the weed. Glyphosate screenings at rates ranging from 0 to 3360 g ae ha^-1 were conducted on natural populations of Palmer amaranth at various growth stages in the field in 2013.  However, all the plants were controlled with the labeled rate of glyphosate in these studies. Therefore, Palmer amaranth seeds from 23 annual and biannual cropping systems from different locations of the SJV were collected for evaluation of glyphosate resistance. To date, two SJV populations have been evaluated against a known GR and a glyphosate-susceptible (GS) population from New Mexico. The experimental design was a 4 by 9 factorial randomized complete block with four replications.  The 4 populations and the 9 herbicide doses were the factors. Glyphosate treatments were administrated at the 5- to 8- leaf stage at  0.5x, 1x, 1.5x, 2x, 2.5x, 3x, 3.5x, and 4x rates with a control, where 1x= 1260 g ae ha^-1 (labeled rate). The study was repeated. Both the SJV populations had 100% mortality at the 1260 g ae ha^-1 rate of glyphosate in both studies and therefore deemed to be GS.  However there was a significant difference (P< 0.05) between the two studies in the biomass. When the light intensity and day length were increased in the chamber in the second study, some of the plants from one of the SJV population took a longer time to die and regrew at the1.5x and 2.5x rate of glyphosate. Additional field studies are also being conducted to evaluate the effect of growth stage of the plants in tolerance to glyphosate.  Collectively, these studies will provide information on whether the reported lack of control in the SJV Palmer amaranth populations are cases of GR populations or  due to tolerance to glyphosate at later growth stages and environmental conditions during glyphosate application. 

fEchinochloa crus-galli (L.) Beauv. is one of the worst weeds of rice, and severe infestations can greatly reduce yield.  Several herbicides with different mechanisms of action have been used, often repeatedly, to control E. crus-galli in rice, which has led to resistance to multiple herbicides in this weed.  An E. crus-galli biotype, MS1, suspected of resistance to several herbicides labeled for rice, was collected from a field in Sunflower County, Mississippi.  Initial screens revealed resistance to imazamox, penoxsulam, bispyribac sodium, fenoxaprop-P, propanil, and quinclorac.  An earlier study revealed that MS1, unlike other E. crus-galli biotypes resistant to acetolactate synthase (ALS) inhibitors, did not have an altered ALS gene, suggesting a non-target-site mechanism of resistance.  Dose response studies were performed in which MS1 and a susceptible biotype were treated with increasing doses of imazomox in the presence and absence of malathion.  Malathion reduced resistance of MS1 to imazamox, implicating at least one cytochrome P450 in the resistance mechanism.  However, the presence of malathion did not affect resistance to fenoxaprop-P, indicating separate mechanisms for imazamox and fenoxaprop-P resistance.  Dose response studies are ongoing to determine the level of resistance of MS1 to these herbicides.  To address this non-target-site resistance, a RNA seq study is underway to examine imazamox treated and untreated MS1 and a susceptible biotype.  The goal of the RNA seq study is to identify genes that may be involved in resistance.  The above research will improve understanding of non-target-site resistance mechanisms and multiple herbicide resistance in weeds such as E. crus-galli.

Extensive and repeated use of herbicides creates selection pressure resulting in evolution of herbicide resistance in weed populations. Kochia (Kochia scoparia) is a problem weed in several cropping systems in the US Great Plains and has been historically prone to evolve resistance to several herbicides. We recently characterized resistance to atrazine, chlorsulfuron, and glyphosate in a kochia biotype from Garden City (GC), Kansas. The objective of this study was to investigate target-site and/or non-target-site-based mechanisms determining resistance to above herbicides in GC biotype. Genomic DNA was isolated from GC and susceptible (to above herbicides) kochia.  Gene specific primers, were used to amplify psbA (encodes D1 protein of PSII), acetolactate synthase (ALS), and 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) genes, the target sites of atrazine, chlorsulfuron and glyphosate, respectively. The PCR amplified fragments were purified and sequenced. Furthermore, the  EPSPS gene copy number relative to ALS (reference gene) was also determined using quantitative PCR. The nucleotide sequence analysis revealed no known mutations in the ALS gene in our GC kochia biotype, indicating a possible non-target- site-based resistance to chlorsulfuron. However, a single point mutation involving substitution of serine (AGT) with glycine (GGT) at position 264 of the psbA gene was found in GC kochia for atrazine resistance. EPSPS gene sequence showed no proline 106 mutation leading to glyphosate resistance in GC kochia. Nevertheless, increased copy number of EPSPS gene (up to 12 copies) relative to ALS was observed. These results demonstrate evolution of both target-site and non-target-site-based multiple herbicide resistance in GC kochia biotype. Development of weed resistance to multiple herbicides is a serious threat to agriculture because of limited herbicide rotation options for weed control.

The continuous use of glyphosate during the last 15 years as the solely chemical weed control method in woody Mediterranean crops, mainly olive and vineyards, has led to the selection of glyphosate-resistant Lolium spp populations in the Iberian Peninsula. As a management strategy, farmers are starting to use oxyfluorfen within rotating MOA or tank mixtures strategies to control these populations. This increases the risk of herbicide multiple resistance in these glyphosate-resistant weed biotypes. A previously characterized glyphosate-resistant biotype of Italian ryegrass (Lolium perenne L. spp. multiflorum (Lam.) Husnot) showing resistance to the herbicide oxyfluorfen displayed significant differences in terms of leaf surface characteristics, compared to the susceptible biotype. Microroughness, contact angle, herbicide retention and % of leaf area coverage studies were carried out to characterize leaf surfaces of both oxyfluorfen-resistant (R) and –susceptible (S) biotypes. Leaf surface differences between Italian ryegrass biotypes were mainly related to surface microroughness. Microroughness studies showed that although adaxial surfaces of both biotypes shared similar characteristics, differences on the abaxial ones were quite significant. Abaxial microroughness values accounted for 19.7 degrees for the R biotype, a value about 50% lower than values obtained for the susceptible one (33.8 degrees). Differences in interaction between the spraying solution and abaxial surfaces were observed as well, with contact angles accounting for 40.4 degrees (S) and 29.6 (R) degrees. These differences were not translated to other parameters studied such as total herbicide retention or % of leaf area coverage. These biotype-specific differences in abaxial leaf surface characteristics may be a putative source of oxyfluorfen resistance in the glyphosate-resistant Italian ryegrass biotype studied.

As of January 13, 2014, 25 weed species have been documented to be resistant to glyphosate worldwide (weedscience.com), including giant ragweed (Ambrosia trifida L.). Glyphosate resistant (GR) giant ragweed has been reported in 10 states in the United States (Ohio, Arkansas, Indiana, Kansas, Minnesota, Tennessee, Iowa, Mississippi, Nebraska, and Wisconsin, in chronological order of occurrence) and Canada (Ontario) (weedscience.org). In 2009, a giant ragweed population, suspected of being resistant to glyphosate, was identified in a soybean field in Tunica County, Mississippi. The resistance level of this population was characterized and the resistance mechanism determined. Glyphosate dose response experiments resulted in GR₅₀ values of 0.52 and 0.34 kg ae ha^-1 glyphosate for the GR and a susceptible (GS) population, respectively, indicating a 2-fold level of resistance. The absorption pattern of ¹⁴C-glyphosate in the GR and GS populations over a course of 168 h after treatment (HAT) was similar. The amount of ¹⁴C-glyphosate that translocated out of the treated leaves of GR and GS plants was similar up to 24 HAT. Thereafter, the GS population translocated significantly more ¹⁴C-glyphosate away from the treated leaf (71% and 76% of absorbed at 48 and 96 HAT, respectively) than the GR population (44% and 66% of absorbed at 48 and 96 HAT, respectively). Sequence analysis of 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), the target site of glyphosate, transcript from GR and GS plants revealed no mutation at the Pro₁₀₆ site. Thus, glyphosate resistance in the giant ragweed population from Mississippi is due to reduced translocation of glyphosate.

Volunteer wheat plant samples were sent to Oregon State University in spring 2013 with a request to test for glyphosate resistance.  The wheat plants survived a glyphosate application and were not showing any injury symptoms.  The samples initially were tested using AgraStrip® RUR Strip Test Seed & Leaf which indicate the presence of the CP4 EPSPS protein present in Roundup Ready® crops.  All volunteer wheat samples tested positive for the trait while control wheat plants were negative.  DNA was extracted from the volunteer wheat plants, positive (Roundup Ready Agrostis stolonifera) and negative controls, and tested for the presence of transgenic material. The volunteer wheat samples and the positive control tested positive for the presence of CP4 gene, CaMV 35S (promoter), nos 3’ (terminator), and rice actin 1 gene (promoter), while the negative control did not. Molecular markers were used in an attempt to determine the wheat cultivar.  The samples were not from one cultivar but are of mixed genetic backgrounds.  USDA-APHIS confirmed that the volunteer wheat was Roundup Ready and that the event in the wheat was MON 71800. Roundup Ready wheat was never deregulated; therefore, an USDA-APHIS investigation into the incident was initiated but a final report has not been released.

Auxinic herbicides such as 2,4-D and dicamba have been in use for several decades for selective control of broadleaf weeds. Evolution of cross-resistance to different classes of auxinic herbicides has been reported in several weed species. We conducted dose-response studies to investigate cross-resistance to 2,4-D (phenoxy) or dicamba (benzoic acid) in recently evolved auxinic herbicide-resistant broadleaf weed species, viz; 2,4-D-resistant waterhemp (Amaranthus tuberculatus) from Nebraska and wild radish (Raphanus raphanitrum) from Australia, and dicamba-resistant kochia (Kochia scoparia) from Kansas. Plants of all species were grown in individual pots in a greenhouse and were treated with 0, 125, 250, 500, 1000, and 1500 g ae ha^-1 of 2,4-D amine and dicamba when they were 10-12 cm tall (4 to 10 plants per treatment). Aboveground dry biomass, mortality, and visual injury were recorded 4 weeks after herbicide treatment. Analysis of above data suggests that both waterhemp and wild radish biotypes resistant to 2,4-D (survived 1500 g ae ha^-1) had reduced sensitivity to dicamba (survived up to 1000 g ae ha^-1 of dicamba). Kochia is known to have natural tolerance to 2,4-D, however, the dicamba-resistant biotype was less sensitive to 2,4-D compared to the susceptible biotype (67 and 80% injury with 1500 g ae ha-¹, respectively). Overall these results indicate the presence of low to medium level of cross-resistance to 2,4-D or dicamba in these auxinic herbicide-resistant weeds. Knowledge of cross-resistance patterns in weeds helps formulate effective weed management strategies and reduce selection for evolution of such resistance, especially with future introduction of dicama- and 2,4-D-resistanct crop technologies for commercial use.

Aminocyclopyrachlor is a synthetic auxin herbicide which is currently registered for use in non-crop systems to control shrub and broadleaf weed species. Absorption and translocation of aminocyclopyrachlor in quacking aspen (Populus tremuloides Michx.) was evaluated over a three-month period. The third youngest leaf on aspen seedling was spotted with 15 µL radiolabeled DPX-MAT28 (3.3 kBq). Plants were harvested at 0.25, 1, 7, 30, 60 and 90 days after treatment (DAT) and divided into separated parts: meristem, treated leaf, above treated leaf, below treated leaf, secondary shoot and root(s). Soil was also collected at each harvest interval. All partitioned parts were dried, weighed, ground, sub-sampled, oxidized and then quantified for radioactivity using a liquid scintillation counter. Herbicide absorption was 39.34% of applied material at 0.25 DAT and increased to 57.99% at 60 DAT. Absorption did not differ significantly from 1 to 90 DAT. Translocation of radiolabeled herbicide from treated leaf was 16.02% and 33.81% at 0.25 and 7 DAT, respectively. Herbicide translocation didn’t differ from 1 to 90 DAT. Applied radioactivity translocated in meristem was significantly increased between 30 and 90 DAT, from 1.37 to 6.72%. Most radiolabel herbicide (21.99%) stayed in treated leaf and 14.37% of applied herbicide translocated to the parts above treated leaf by 90 DAT. Limited radioactivity was recovered in parts below the treated leaf and soil during the 3 months study period.

Field studies comparing the dissipation and mobility of pyroxasulfone and s-metolachlor were conducted in sunflowers in 2009 and 2010. In 2009 there was minimal phytotoxicity on sunflowers by the herbicides, but in 2010 significant sunflower injury was observed in plots treated with pyroxasulfone and sulfentrazone but not with s-metolachlor and sulfentrazone. In 2009 all of the herbicides remained in the top 7.5 cm of the soil, whereas in 2010 all of the herbicides leached after a heavy rainfall.  Sulfentrazone had moved further down in the soil profile compared to pyroxasulfone or s-metolachlor which resulted in the herbicides being stratified in the soil profile, with pyroxasulfone or s-metolachlor above sulfentrazone. Sunflower variety trials conducted in 2011 with pyroxasulfone alone at rates up to 600 g ai/ha showed minimal sunflower injury. So it appeared there was some type of interaction between pyroxasulfone and sulfentrazone. Greenhouse studies were conducted to evaluate the interaction of pyroxasulfone and sulfentrazone when stratified in the soil profile, and how they impact sunflower injury.  The emerging roots and shoots were exposed to different combinations of soil treated with pyroxasulfone, s-metolachlor, alone or in combination. Pyroxasulfone, s-metolachlor or sulfentrazone alone did not injury sunflowers.  However sunflowers were severely injured when pyroxasulfone was present in the shoot zone and sulfentrazone was in the root zone, a situation similar to what was observed in the field.  Field and greenhouse data suggest that when pyroxasulfone is stratified above sulfentrazone in the soil profile there is potential for increased sunflower injury, compared to either herbicide alone.

Worldwide, agriculture accounts for the greatest portion of land with the U.S. having 45% of its land used for agricultural purposes.  In addition, agriculture is estimated to contribute greatly to the output of two of the main greenhouse gases suspected of contributing most largely to climate change with methane and nitrous oxide contributing 37 and 59 percent to emissions, respectively. These large percentages are suspected to partially be due to the fact that only one-third of nitrogen applied to cropping systems is actually utilized by the system while the additional two-thirds are lost to the environment.  With different agricultural practices contributing differently to these greenhouse gas emissions, finding how different practices contribute to greenhouse gas emissions will help in the recommendation of best management practices for minimal gas emission contributions by agriculture in the southeastern U.S.  Field studies were conducted in 2013 at the Center for Agricultural Farming Systems at the Cherry Research Farm in Goldsboro, NC.  Long-term plots of conventional no-till, conventional-tillage, conventional crop-hay, organic tillage, organic minimal tillage, and organic crop-hay systems were all used with subplot treatments of weedy and weed-free to measure the flux of the greenhouse gases CO₂, CH₄, and N₂O, 24 to 48 hours after ~1.25 cm or more of rainfall following USDA-ARS GRACEnet Project Protocols. Much greater differences were observed between different systems than between subplots.  Minimal differences could likely be attributed to low weed densities in the organic system treatments.

Fomesafen effectively controls glyphosate-resistant Palmer Amaranth when applied PPI and PRE in cotton. However, cotton tolerance and its field dissipation have not been sufficiently studied in the Southeast. Therefore, the objective of this research was to study cotton response to various rates of fomesafen, and to evaluate its field dissipation in two locations of Georgia (Athens, Tifton). Greenhouse bioassays indicated fomesafen reduced cotton height and dry weight with increasing rate in the Athens and Tifton soil but not in the Plains soil. At the Athens location, fomesafen did not affect cotton height from 10 to 70 DAT. At the Tifton location, fomesafen did affect cotton height as cotton treated with fomesafen was shorter at the two highest rates 29, 42 and 57 DAT. In Plains, there was no trend between fomesafen rate and cotton height. Fomesafen applied at rates greater than 1120 g ai/ha may reduce cotton stand. Although fomesafen has the potential to reduce cotton height and stand count, cotton yield at Athens and Plains were not affected by fomesafen applied in this study. However at the Tifton location, the two highest rates decreased cotton yield.  Lab study indicated that fomesafen dissipation varied significantly between locations: residue lasted over 120 days in Athens but was not detectable 28 days after treatment in Tifton. Half-life (DT₅₀) of 280 g ai/ha rate were 47 and 6 days for Athens and Tifton, respectively. DT₅₀ for 560 g ai/ha rate were 34 and 4.2 days, respectively, for Athens and Tifton. Rainfall may have affected fomesafen degradation in Athens but not in Tifton.

In Spain, biotypes of the species C. bonariensis, C. canadensis and C. sumatrensis have been reported as being glyphosate-resistant. With the aim of elucidating the efficacy of amitrol on glyphosate-resistant and -susceptible C. bonariensis biotypes, dose-response assays were performed under greenhouse conditions. Dose-response assays included seven doses and an untreated control per herbicide/biotype. Results showed a GR₅₀ (herbicide required to produce a diminution of fresh weight by 50%) of 159.8 g ae ha^-1 and 42.6 g ae ha^-1 for resistant and susceptible biotypes, respectively using glyphosate. On the contrary, using amitrol, GR₅₀ values were 134.4 g ai ha^-1 and 122.4 g ai ha^-1. From the above results, we can assume that the chemical control of glyphosate-resistant weeds would include rotation of molecules such as amitrol. Field assays corroborated those results.

Canola is the major oilseed crop grown in western Canada.  Canola has a high potential for seed shatter before and during harvest which causes loss of revenue and future weed problems.  An on-farm survey was conducted to determine harvest losses in four regions in western Canada and relate these to agronomic, harvest management, and environmental factors.  Over 300 fields were surveyed over three years and regional average yield losses within years ranged from 4.0 to 8.4%.  Factors that are commonly thought to contribute to harvest losses in canola including choice of variety and combine type were not identified as important contributors to on-farm harvest losses.  A number of other factors, however, contributed to harvest losses and the results showed that harvest management begins at the time of planting canola. Increased plant densities and increased yield reduced proportional harvest losses. Fungicide applications at the time of flowering lowered average harvest losses by about 1%. Harvest management such as early windrowing and in particular reduced combine ground speed lowered harvest losses, while higher average maximum daily wind speeds between the time of windrowing and combining contributed to greater harvest losses.  Significant differences among producers were detected over the three years of the study.  In two regions, producers with the highest harvest losses lost about 7% more yield on average than those with the lowest harvest losses.  This confirmed the significance of management factors to harvest losses in canola and that significant reductions in harvest losses and weed seedbank additions are possible through improved crop and harvest management.

While demand continues to grow and prices for organic grains have remained double those of conventional grains, few growers in the dryland region of eastern Washington produce organic grain. Growers have cited soil fertility and weed control constraints as the main factors preventing conversion. To address these concerns, soil fertility and weed pressure effects on yield were examined in the winter wheat (WW) crop of three organic cropping systems: 1) three-year alfalfa–WW–spring barley, 2) WW–winter pea (green manure), and 3) WW–spring wheat–winter peas (hay). Fertility is supplied primarily by green manure in the first and second systems (alfalfa and winter pea, respectively) whereas the third system relies on animal (poultry) manure. Yields were significantly higher in system 3 than in systems 1 and 2, and were not different from those achieved in the conventional system. Inorganic soil nitrogen (N) was significantly higher in system 3 than in system 2, but was not different from system 1. Weed pressure was highest in system 1 and was the main factor in its poor yield performance. Dryland organic systems utilizing animal manure not only perform better than those using green manure for fertility, but also can produce yields competitive with those of conventional systems. Additionally, maintaining good soil fertility can serve as a weed management tool in organic systems.

Marabu (Dichrostachys cinerea L. Wight & Arn.) is a thorny, acacia-like, fast-growing woody bush which invades fields, wasteland, road sides and other disturbed areas. This gregarious species has become a very aggressive invasive weed in Cuba, where no native predators or pathogens are found. It often encroaches in fallows, overgrazed areas and mismanaged veld. Marabu is a very difficult weed to eliminate because of its active suckering, and is liable to produce dense thickets quite impenetrable on account of the density and the abundance of long, stiff, sharp thorns. In the Trinidad Valley (An UNESCO-protected area in Cuba Central), it forms veritable forests in areas where sugarcane growing has been discontinued. Physical management by cutting and burning of the plants is not a very efficient control method, since the seeds survive in the soil, and the growth is very fast. Therefore, chemical methods via the use of herbicides are often necessary to eradicate this weed. A preliminary study using readily available preemergence herbicides such as diuron and metribuzin has been carried out in order to elucidate the best treatments rendering maximum and persistent weed control with minimum herbicide rate and environmental stress. The effect of two herbicide treatments (diuron and metribuzin) at five different herbicide rates (1/8, 1/4, half, full and double of the recommended rates) were tested under laboratory-controlled conditions. Pregerminated seeds were planted in batches previously treated with herbicides, and mortality and shoot fresh weight was recorded 28 days after treatment. The process was cycled four times in order to test both effectiveness and herbicide persistence. Dose-response assays showed that metribuzin results in terms of both mortality and reduction in fresh weight were just fair at full herbicide rates of higher, with an average persistence of only 28 days. Diuron treatments resulted much more effective, displaying good weed control even at 1/4 rates during the first 28 days. This effectiveness lasted up to 84 days at full and double herbicide rates. As a preliminary conclusion, diuron preemergence treatments seem the best, effective and persistent option to control marabu in sugar cane-infested areas of the Trinidad Valley.

Common buckthorn (Rhamnus cathartica) was recently listed as a prohibited noxious weed in the Alberta Weed Control Act and as such, it must be destroyed when found. Common buckthorn grows throughout the City of Edmonton’s natural areas in various densities and terrains but a limited amount of information is available regarding effective removal strategies. In August 2011, a one hectare area infested with common buckthorn was selected and common buckthorn trees were treated with a ready-to-use triclopyr product (Garlon^TM RTU) using a selective basal bark application. For each plant diameter at breast height (dbh) was measured and the number of stems recorded. In September 2012, the tree health of 471 trees in a 2500 m² subplot was visually assessed. For each tree it was recorded whether or not signs of re-growth (green leaves) were visible. When no signs of re-growth were visible, trees were considered as successfully controlled. 95% of treated single-stem trees were successfully controlled but only 60% of multi-stem trees. The high success rate on single-stem plants confirms the expected product efficacy on common buckthorn. The reduced treatment efficacy on multi-stem trees is most likely due to inefficient product application. The results suggest that for a successful treatment with Garlon^TM RTU every single stem of a multi-stem tree requires treatment. Common buckthorn tends to start branching almost at the base and the stems tend to overlap and grow close together which makes a treatment of every single stem of multi-stem trees difficult. The dbh had no effect on treatment efficacy. The evaluation also showed that 25% of common buckthorn trees were missed by the applicators due to due difficulties in the identification due to the presence of similar native species, indicating a need for better identification training. The initial results show that Garlon^TM RTU applied as basal bark treatment can be considered an efficient treatment option against common buckthorn under Edmonton’s growing conditions but further research is needed to confirm good efficacy on multi-stem trees.  

A healthy, active soybean root system is of central importance in achieving a high soybean yield. Previous studies on soybeans indicate that light quality (i.e. low Red:Far Red [R:FR]) can reduce root biomass. To date, there has not been detailed exploration into the effects of low R:FR light reflected from above ground neighbouring weeds on soybean root morphology, nodulation, or the physiological and molecular mechanisms involved with the observed reduction in biomass. Lab studies were initiated to test the hypothesis that FR light reflected from above ground neighbouring weeds would reduce root biomass, including nodulation, and trigger an increase in hydrogen peroxide. Soybean root surface area and volume were reduced by the presence of above ground weeds at the first and second trifoliate stages of soybean growth. The number of root nodules were reduced as early as the unifoliate stage. Accompanying this reduction in nodule number was a decline in root flavonoid content, and an increase in root hydrogen peroxide levels; indicating a clear reduction in cellular antioxidant activity. The results from this study provide further evidence in support of the importance of early season weed control in soybeans.

Neighbouring weeds have previously been shown to induce the shade avoidance response in crop plants leading to yield losses and the development of the critical period. This response is initiated by phytochrome due to changes in the ratio of red/far-red light. This low R/FR signal has been shown to induce oxidative stress in plants. We investigated this response in the early stages of maize and soybean development with the goal to compare and contrast this response in both a monocot and dicot system. We hypothesized that signs of oxidative stress and associated morphological changes would be detected upon emergence of maize and soybean in the presence of above-ground neighbouring weeds. Differences in morphology were detected in both maize and soybean upon emergence therefore we measured free radical accumulation upon emergence in both systems. The enzymes responsible for scavenging of free radicals were investigated using qt-PCR and enzyme activity assays in both systems. We compare and contrast the responses of both a monocot and dicot to neighbouring weeds and discuss how the response to R/FR might be conserved across diverse taxa.

Diverse cropping systems with different input levels and cropping diversities (rotations) can alter weed community dynamics (weed abundance and crop-weed competition). Organic systems with diverse crop rotations believed to have a greater heterogeneity in soil resources with the potential to tolerate competition from weeds greater than the conventional systems. However, direct evaluation of crop-weed competition among organic and conventional systems under wide range of crop diversities is limited. Therefore, a study was carried out within a long-term (18 years) cropping systems study at Scott, Saskatchewan to study crop-weed competition. The main experiment consists of two input levels; Reduced (RED) and organic (ORG), and three crop diversity levels; low (LOW), diversified annual grains (DAG), and diversified annual perennials (DAP). A micro-plot study was carried out within the main experiment with four weed control treatments applied to the wheat phase of all RED and ORG rotations. The treatments were 1.weed free treatment, 2. weedy treatment, 3. standard weed control, and 4. pseudo weed (tame oat) seeded at 1:1 ratio with the crop. Within organic crop rotations, weed density was high in DAP system while in reduced systems (conventional) it was high in DAG rotations. There was no difference in weed biomass between ORG and RED systems. Overall, DAP system had low weed biomass compared to the LOW diversity rotation. Organic systems had low grain yields in all weed control treatments including under weed-free conditions indicating that weeds are not the major yield limiting factor in these systems. There was no difference between organic and reduced systems for yield loss due to natural weed competition or due to pseudo weed competition. Given the low productivity in ORG systems, the similar yield loss as RED systems suggests that ORG systems probably able to tolerate weed competition better than RED systems. However, the results of this study did not provide evidence of better crop tolerance with increasing diversity of crops.

Soybeans (Glycine max) have become a popular crop choice for producers in Manitoba as the number of seeded hectares has grown from 40 500 ha in 2005 to 232 700 ha in 2011. Volunteer canola (Brassica napus) is a competitive, common weed in these cropping systems and specifically glyphosate resistant volunteer canola poses a potentially significant management issue for soybean producers.  In 2012 and 2013, six field experiments were established across southern Manitoba as a RCBD with four replicates. Three experiments were seeded with a narrow row spacing of 25 cm, and three experiments were seeded with a wide row spacing of 75 cm. In an additive design, eight volunteer canola densities (0, 10, 20, 40, 80, 160, 320, and 640 plants m^-2) were broadcast and incorporated at the time of seeding the soybean crop. The measurements collected included soybean heights, densities, leaf area, light interception, biomass, number of branches, harvested yield and volunteer canola seed return. Preliminary results indicate the yield loss in soybean caused by volunteer canola can be significant (up to 85%) and that even low densities of volunteer canola can cause significant yield losses in soybean.  The effect of row spacing on the ability of soybean to compete with volunteer canola was relatively small.  Competition and row spacing altered some of the soybean morphological characteristics that contributed to reduced yield.  Action thresholds for managing volunteer canola in soybean will be developed from these studies.  

Field pea (Pisum sativum L.) is an important grain legume in Western Canada. Growers can, however, be reluctant to include pulse crops in their rotation because they are poor competitors with weeds. Developing more competitive field pea cultivars is important to mitigate weed competition. The identification of competitive cultivars and the traits conferring competitive ability should lead to the development of more competitive field pea cultivars. The objectives of this research were to evaluate the ability of semi-leafless field pea cultivars to suppress and withstand weed competition as well as to identify traits that may confer competitive ability in field pea. Field experiments were conducted in 2012 and 2013 at Floral and Saskatoon, Saskatchewan and St. Albert, Alberta. Fourteen semi-leafless field pea cultivars with divergent pedigree, vine length, seed size, and market classes were seeded at a target density of 75 plants m^-2 under weedy and weed-free conditions in a split block design. Imidazolinone-tolerant wheat (c.v. CDC Imagine) and canola (c.v. 45H73) were planted as pseudo weeds at a target density range of 20-25 plants m^-2 each in the weedy plots. Variables measured were leaf area index, plant height, pea biomass, weed biomass, days to full crop canopy closure, pea yield, and weed seed production. Data were subjected to ANOVA using the mixed model procedure in SAS. The site years in Saskatchewan and Alberta could be combined, therefore Alberta and Saskatchewan are comprised of two and three site years, respectively. Field pea biomass and yield were only significant among competition treatments in Alberta. The the weed-free competition treatment produced 23% and 64% more biomass and yield, respectively, than the weedy competition treatment field pea yield. At Saskatchewan, 37% and 36% more field pea biomass and yield, respectively, were produced by the weed-free competition treatment. CDC Striker and CDC Dakota produced the greatest pea biomass, regardless of competition treatment and were significantly different from Reward, which produced the lowest pea biomass at Saskatchewan. However, CDC Dakota was among the best for producing pea yield whether competition was absent or present, CDC Striker was intermediate for pea yield, and Reward was significantly different with the lowest pea yield. The cultivars in both provinces did not differ in their weed suppressive ability (reduction of pseudo weed biomass and seed production); this was non-significant. No Significant correlations were observed among traits that may confer competitive ability in either province. cory.jacob@usask.ca

Cultivated plants are known to readily hybridize with their wild relatives, forming invasive populations that can become weedier than their parental phenotypes. With global climate change, increasingly variable precipitation may create new advantages for weeds in agricultural habitats. To assess the relative ability of new populations to grow and invade a new location, we compared the demography of wild radish (Raphanus raphanistrum) and crop-wild hybrid radish (Raphanus raphanistrum x Raphanus sativus) populations across a soil moisture gradient. Field populations of wild radish and F1 hybrid radish were established in 2012 and received one of four watering treatments over the 2012-13 field seasons. Weekly population censuses assessed the number of seedlings emerging, their rate of survival and eventual fecundity. Hybrid populations had higher λ than wild populations but λ did not differ across precipitation treatments. Fecundity represented the greatest contributions to λ and was the most elastic demographic parameter relative to other life history stages. Predicting the likelihood that a weedy genotype will successfully invade requires an understanding of its λ and compositional demographic transition rates relative to its competitors. This study better informs selective weed control by isolating the most effective life-history stage ‘choke point’ to suppress population growth. 

Kernel number (KN) per unit area is the main yield component in maize. Although potential KN is fairly stable, any stress occurring during the silking period will reduce yield. Little is known, however, of the effects of early stresses such as weed competition, drought, or intraspecific competition on subsequent reproductive processes that drive potential (ear and floret initiation) and actual yield (silking, anthesis to silking interval-ASI- and, kernel set). This study was conducted to determine the effect/s of early stress on reproductive performance and yield. We hypothesize that the underlying reproductive mechanisms driving final yield may be common among stresses. The effects of early stress on i) ear and floret formation, ii) anthesis-to-silking interval (ASI), fertilized florets (kernels set) and final yield were investigated in 2012 and 2013 in two maize isolines that differ in their tolerance to drought stress in two field locations. Stresses consisted on weeds competition, drought stress and three levels of intraspecific competition imposed before canopy closure (12-14 leaf tips). Grain yield decreased with early stresses at both locations. Reductions in yield were larger for the drought and the intraspecific competition treatments. Lower KN was explained by both increases in ASI, lower kernel set and reductions in floret number.  In both locations the drought tolerant genotype (DT) exhibited lower yield reductions when compared with the non-drought tolerant (NDT) genotype while potential yield did not differ. Differences in yield between DT and NDT were largely explained by their inherent reproductive performance.

Parasitic flowering plants, present in numerous families, are one of the most destructive agricultural pests and have major impact on crop yields throughout the world. Being dependent on finding a host plant for growth, parasitic plants penetrate and invade their host using specialized organs called haustoria. These tissues establish vascular connections with the host, which enable the parasite to steal nutrients and water. The underlying molecular and developmental basis of parasitism by plants is largely unknown. In order to investigate the process of parasitism, we have used RNAs from different stages, i.e. seed, seedling, vegetative strand, prehaustoria, haustoria, and flowers, to de-novo assemble and annotate the transcriptome of the obligate plant stem parasite Cuscuta pentagona (dodder). Subsequently, the assembled transcriptome was used to dissect transcriptional dynamics during dodder development and parasitism, and identified key gene categories involved in the process of plant parasitism. Host plant infection is accompanied with increased expression of genes underlying transport and transporter categories, and associated decreased expression of photosynthetic genes in the dodder infective stages compared to normal stem. We also observed increased expression of gene categories involved in response to stress and stimuli, and genes encoding enzymes involved in cell wall modifications. In addition, genes relating to biosynthesis, transport and response of phytohormones, such as auxin, gibberellins and strigolactone, were differentially expressed in the dodder infective stages compared to stem and seedlings. This analysis sheds light on the transcriptional changes that accompany parasitism by plants and will aid in identifying potential gene targets for use in controlling infestation of crops by parasitic weeds.

Most non-native species designated as naturalized or invasive have broad ecological amplitude, in that they are observed over a wide range of abiotic and biotic conditions.  This provides a gradient of environmental suitability which corresponds positively with population growth rate and increases in density and spatial extent for the non-native species we have studied. However, establishment and survival at a site depends on seed availability as well as the suitability of the environment. Vehicles are known to disperse seeds, and roadsides provide relatively disturbed conditions.  To assess the role different abiotic and biotic drivers have on plant establishment, survival and productivity we studied populations in proximity to roads (disturbed sites with seed rain opportunities).

Specifically, we studied Dalmatian toadflax (Linaria dalmatica) populations in close proximity to roads, along an elevation gradient in the Greater Yellowstone Ecosystem (GYE) for four years.  Elevation influenced Dalmatian toadflax’s probability of occurrence and was hump shaped with more suitable sites in the middle of the gradient (1800 m).  Dalmatian toadflax plant density and number of germinable seeds also increased along the probability of occurrence gradient. However, once established, Dalmatian toadflax cover was more driven by biotic variables, having a negative response to plant community metrics of species richness and cover, particularly perennial species cover.  These data, and more collected by our group, show that establishment, invasiveness and community impact differs within species across abiotic and biotic gradients. Nonetheless, management of non-native species is currently focused on species rather than specific populations, which we propose leads to inefficient use of limited funding for management. We suggest that management efficiency would be improved by concentrating on populations that are most invasive and where non-target management impacts would be minimized.

Invasion by exotic plants and climate change are major environmental changes that may threaten the sustainability of global ecosystems. Exotic plant species invade approximately 700,000 ha of US wildlife habitat annually, resulting in an annual economic cost that exceed $34 billion, and degrade habitat biodiversity. Similarly, the anticipated increase in average global temperature not only challenges the survival of many species but also accelerates the loss of stored carbon (C) from soils through oxidation. Since, soils store more carbon (1500 GT) than the atmosphere (500 GT) and the standing biomass (600 GT) combined, factors that affect the fate of the soil C can have a substantial feedback on the global carbon cycle, and thus on climate warming. Plant invasion and climate change are predicted to interact catastrophically, with climate change facilitating a massive range expansion of many exotic species by the turn of this century. However, remarkably less studied are the potential of plant invasions to feedback climate change by regulating the accrual, composition, and stability of soil organic matter (SOM) in invaded ecosystems.

 We hypothesized that soil carbon (C) sequestration, as an ecosystem property, would be strongly influenced by invasive plants capable of depositing disproportionately high quantities of chemically distinct litter that disrupt ecosystem processes. We studied the impact of invasion of two noxious non-native species- Polygonum cuspidatum (Japanese knotweed) that produces recalcitrant litter, and Pueraria lobata (kudzu) that produces labile litter, on the quantity, molecular composition, and stability of C in the soils they invade. The molecular identities of C in soils as well as the degradation stage of the SOM were assessed using a biomarker approach using gas chromatography mass-spectrometry that determine the source of biomolecules (plant or microbes). Stability of the SOM was assessed through oxidation with hydrogen peroxide that could mimic the biological degradations, followed by stable isotope analyses.

Compared to the adjacent non-invaded old-field, knotweed invaded old-field soils exhibited a 26% increase in C. This increase in soil C was partly explained by the selective preservation of plant polymers derived from lignin, cuticular matrix and suberin of knotweed, and fungal lipids (ergosterol) in invaded soils.  Despite receiving 22% higher litter input, kudzu invaded Pinus-stands exhibited 28% decrease in soil C compared to the adjacent non-invaded Pinus soils. This decrease of soil C in invaded soils was accompanied by a two-fold decrease in Pinus-derived plant polymers, a three-fold decrease in ergosterol content, and six-fold increase in muramic acid that represent bacterial biomass. This indicate that invasion of kudzu into Pinus forest accelerate the oxidation of native soil C by facilitating microbial priming.  Interestingly, the stability of soil C exhibited an opposite trend- compared to their respective adjacent non-invaded soils the proportion of C that was resistant to oxidation was 21% lower in knotweed invaded soils and 50% higher in kudzu invaded soils. The higher stability of SOM in kudzu invaded soils could be attributed to the bridging of organic C to soil mineral surfaces by the humified nitrogenous compounds. Calculations based on the spread of kudzu in U.S. and the observed C loss from invaded soils, we estimate that kudzu invasion results in a loss of 4.8 x 10⁶ Mg C yr^-1, which equates to the C sequestered annually by 5.9 M ha of the U.S. forests. Thus annually, each hectare of kudzu invasion releases C sequestered by 2 ha of U.S. forests, while knotweed invasion results in the accrual of soil C that is more prone to oxidation.

Our study brings forth an understudied yet debilitating ecosystem impact of exotic plants- their influence on C storage in invaded ecosystems. More importantly, our results highlight the capacity of invasive plants to feedback to climate change by destabilizing native soil C stocks. Considering that future warmer climates could result in rapid northward range expansion of both the study species, with kudzu spreading to southern New England and knotweed expanding into northern Canada, our results signifies the potential for substantial feedback of these invasive species to climate warming. From a soil C management perspective, our results indicate that environments that promote microbial priming of SOM could enhance the long-term storage of soil C.

The evolution of herbicide resistance in weed populations is contingent on genetic variation, selection, and gene flow. Additive genetic variation for resistance to glyphosate has been documented in one of the most problematic weed species in the southeastern United States, the common morning glory (Ipomoea purpurea), suggesting that resistance could evolve to higher levels in this species. As part of a larger project to determine the impact of gene flow on resistance evolution in this species, we assessed temporal and spatial variation in the level of glyphosate resistance as well as genetic differentiation among populations collected from the southeast and midwest US. We performed a replicated greenhouse resistance screen utilizing 44 populations collected from the field in 2012, 29 of which were initially collected in 2003. In this talk, we will present data showing spatial and temporal heterogeneity in the level of resistance in I. purpurea, and will interpret this data along with estimates of historical gene flow and the mating system to provide an integrated view of the potential for continued resistance evolution in this weedy plant species. 

Our integrated research and extension project aims to lower barriers to establishment of diversified biofuel grassland agroecosystems that produce both biomass and other ecosystem services, such as pollinator habitat. Establishment of biofuel grasslands is often difficult, unpredictable, and vulnerable to interference and invasion by weeds. We explored the use of a variety of ‘nurse species’ that might affect soils, prior to grassland establishment, so as to promote growth of native perennial species. We also assessed such effects in perennial weeds that might be present before or during establishment of desirable species. We grew replicated nurse- and invasive-species plots for three years of soil conditioning, and added nitrogen fertility inputs to subplots, as might be used by growers seeking high biomass yields. In greenhouse experiments assessing seedling growth in response to soils from replicated plots, we found little evidence of plant-soil feedbacks that would tend to promote native over invasives, or vice versa. These results contrast with several similar studies of grasslands, but there is little published work on such feedbacks affecting perennials in soils used for row-crop agriculture. We found that nitrogen inputs during the soil-conditioning phase did interact with species-specific responses to soil conditioning, suggesting that such inputs could alter the community composition of biofuel grasslands during the establishment phase and potentially thereafter, with potential implications for the maintenance of desirable native plant diversity in such grasslands.  

Our NIFA supported research project will provide insight into important biological processes that drive weed and crop growth in agroecosystems, including the transformation, cycling, and uptake of soil nutrients by weeds, crops, and their microbial symbionts. Our research will shed light on the mechanisms underlying crop-soil feedbacks and will expand upon recent work showing that these feedbacks can alter weed-crop competitive interactions. Our overall goal is to test how soil resource pools, crop and weed species-specific abilities to partition soil resources, and mutualistic plant-microbe associations interact to affect weed-crop competition in controlled environments and in field conditions. We will accomplish our goal through the following objectives: (1) Quantify the effects of crop and soil management practices on organic and inorganic nitrogen pools and weed-crop competition in a long-term cropping systems experiment; (2) Quantify soil nitrogen partitioning among crops and functionally diverse weeds using in-situ 15N labeling in a long-term cropping systems experiment; (3) Assess the roles of trait diversity, mycorrhizal fungi and other rhizosphere microorganisms, and soil nitrogen pool diversity in crop and weed resource acquisition and weed-crop competition in controlled environments; and (4) Assess weed-crop competition along an experimental crop-derived input diversity gradient. Completion of these objectives will advance understanding of the ecological processes related to integrated weed management in cropping systems and of the linkages among crop and soil management, crop diversity, and weed problems.

Most herbicide-resistant weed biotypes are the result of single mutations in genes encoding target site enzymes, and many show little, if any, reduction in fitness as compared to the wildtypes.  Therefore, predictions about the evolution, spread, and management of HR biotypes are biased towards this scenario.  National weed management programs are now confronted with the far more complex and economically costly problem of multiple herbicide-resistant (MHR) weed biotypes.  We have identified biotypes of Avena fatua (wild oat) that are cross-resistant to at least four different herbicide modes of action, conferred by enhanced metabolism as mediated by cytochrome P450 enzymes.  There is no evidence that they evolved under reduced herbicide use rates, which is usually cited as the primary selection environment for metabolic resistance.  Understanding the genetic basis and population dynamics of these phenotypes will lead to better predictions of resistance frequency change and spread under systems dominated by transgenic crops with one or more resistance genes.

Our overall hypothesis is that MHR resistance is mediated by a combination of constitutive over-expression and inducible expression of one or more cytochrome P450 isozymes.  Our preliminary evidence also shows some fitness differences that we predict will influence its frequency and spread through populations.

The specific objectives of this grant (2012-2015) are to:  1) Investigate the resistance spectrum, metabolism patterns, molecular biology, and genetics of resistance in the A. fatua MHR biotype;  2)  Compare the impacts of environmental and biological stressors on the demography, ecological fitness, and primary physiology in A. fatua MHR and susceptible (S) biotypes;  3)  Refine a simulation model to assess herbicide resistance phenotype frequency dynamics and spread of MHR using the A. fatua data and relationships determined in Objectives 1 and 2; and 4)  Develop, test, and deliver a transformative, research-based Extension program to educate stakeholders on preventing and managing HR biotypes.

Progress has been made on the first two objectives, as follows:  1) resistance has been confirmed to members of five different herbicide families (ALS inhibitors, ACCase inhibitors, the VLCFA elongation inhibitor triallate, the ROS generator paraquat, and difenzoquat); characterization of herbicide metabolism patterns is underway using mass spectrometry; enzyme assays and western blots demonstrate subtle changes in oxidative stress response pathways; constitutive and inducible (by herbicide treatment) expression of a cytochrome P450 mRNA was shown in MHR plants; reciprocal crosses between homozygous MHR and susceptible plants are underway; 2) small differences in ecological fitness between MHR and susceptible plants have been shown in greenhouse experiments, but no overall trends are apparent; similar field experiments are underway; comparisons of volatile emission spectra between MHR and susceptible plants are underway.

Jointhead arthraxon [Arthraxon hispidus(Thunb.) Makino], also referred to as small carpetgrass, is a native of Asia. Jointhead
arthraxon is a low-growing grass with ovate leaf blades, hairs along the margins of the leaf blades, and the cordate bases of
the leaves encircle the stem. The flowers are borne on digitate spikes. This summer annual grass prefers sunny, wet habitats.  It can be a weed in turfgrass and other areas.    Little information is available on the control of this weed.  Greenhouse trials were
conducted to evaluate commonly-used preemergence and postemergence herbicides in turfgrass for control of jointhead
arthraxon.  Pendimethalin at 2.24 kg ai/ha, prodiamine at 0.84 kg/ha, mesotrione at 0.28 kg/ha, oxadiazon at 2.24 kg/ha, dithiopyr at 0.56 kg/ha, siduron at 6.7 kg/ha, indaziflam at 0.067 kg/ha, and DCPA at 11.1 kg/ha all gave 80% or greater preemergence control of jointhead arthraxon.  Topramezone at 0.05 kg/ha and quinclorac at 0.84 kg/ha provided lower control.  In
postemergence trials, single applications of fenoxaprop at 0.13 kg/ha and fluazifop at 0.1 kg/ha and two applications of mesotrione at 0.28 kg/ha, topramezone at 0.05 kg/ha, and MSMA at 2.24 kg/ha all gave 70% or greater control of jointhead arthraxon.  Dithiopyr at 0.56 kg/ha, indaziflam at 0.067 kg/ha, and quinclorac at 0.84 kg/ha provided overall lower postemergence control.

Topramezone, marketed by BASF as Pylex, is a new herbicide for bermudagrass control in cool-season turf.  Similar to mesotrione (Tenacity®), topremazone is an HPPD-inhibiting herbicide that controls many grassy and broadleaf weeds and is safe to many cool-season turfgrasses.  Topramezone can control crabgrass, goosegrass, and white clover with a single application and controls bermudagrass greater than mesotrione.  A field trial was conducted to determine efficacy of topramezone alone or in combination with triclopyr (Turflon® Ester) or quinclorac (Drive XLR8®) to control bermudagrass in cool-season turfgrass, and to compare topremazone-containing treatments with the industry standard for bermudagrass control in cool-season turf i.e. fenoxaprop (Acclaim® Extra) plus triclopyr (Turflon® Ester).  The study was initiated on July 21, 2012 at the Virginia Tech Turfgrass Research Center (TRC) in Blacksburg, VA.  The study site consisted of a ‘Kelly’ Kentucky bluegrass lawn infested 70-80% by a natural bermudagrass population and was maintained at 7.6-cm height.  All treatments consisted of three applications applied at three-week intervals.  Topramezone was applied twice at 37 g ai ha^-1 followed by (fb) a third application at 25 g ai ha^-1.  Three treatments contained topramezone at the aforementioned rates, one with topramezone alone, one with triclopyr at 1120 g ai ha^-1 tank mixed with each topramezone application, and one with quinclorac at 420 g ai ha^-1 tank mixed with each topramezone application.  Fenoxaprop at 530 g ai ha^-1 + triclopyr was applied at the same rates three times.  Mesotrione was applied twice at 210 g ai ha^-1 + triclopyr and fb mesotrione at 140 g ai ha^-1 + triclopyr.  All topramezone or mesotrione treatments included a methylated seed oil adjuvant at 0.5% v/v.  A non-treated check was included for comparison.  At 57 days after initial treatment (DAIT), topramezone + triclopyr controlled bermudagrass 94% and significantly better than topramezone + quinclorac, fenoxaprop + triclopyr, and mesotrione + triclopyr.  Topramezone applied alone controlled bermudagrass 85%, 57 DAIT, and equivalent to topramezone + triclopyr, topramezone + quinclorac, or mesotrione + triclopyr.  Topramezone + triclopyr was the only treatment that controlled bermudagrass and had statistically less bermudagrass cover than the untreated check on June 30, 2013 at 300 DAIT.  Topramezone caused white symptoms on bermudagrass resulting in over 30% of plot areas exhibiting white tissue in late summer and fall while treatments were applied.  When triclopyr was mixed with topramezone, white tissue symptoms were almost eliminated.  Kentucky bluegrass was not injured at any timing in this study.  Results of this study indicate that topremazone is a promising herbicide for bermudagrass control in cool-season turfgrasses.  Moreover, addition of triclopyr with topremazone would not only enhance the bermudagrass control but will also maintain aesthetic beauty of lawn by reduce whitening symptoms. 

Topramezone is an HPPD-inhibiting herbicide registered for use in turf in June 2013 by BASF Corporation under the trade name Pylex™.  In previously non-replicated studies, topramezone controlled mature goosegrass at rates much lower than the label indicates required for goosegrass, crabgrass, and bermudagrass control.  The objective of this study was to determine if goosegrass and smooth crabgrass can be controlled with lower rates of topramezone with and without triclopyr to potentially be investigated as a grassy weed control herbicide in bermudagrass turf.  Two field trials were conducted in June 2013 in Blacksburg, VA at the Turfgrass Research Center (TRC) as randomized complete block experimental designs with a two-by-two factorial treatment design.  One site was a zoysiagrass lawn infested with approximately 30-40% multi-tiller goosegrass and 15-30% smooth crabgrass per plot and maintained at a 5 cm mowing height.  The other site was a fallow area with no desirable turfgrass species and an average of 11-28% multi-tiller goosegrass and 25-60% smooth crabgrass per plot, maintained at a 1.5 cm mowing height.  Herbicide treatments for both studies included topramezone applied twice, three weeks apart, at 6.14 and 12.3 g ae haâ�»¹ alone and with the addition of triclopyr at 140 g ae haâ�»¹.  Each treatment contained a methylated seed oil surfactant at 0.5% v/v, and an untreated check was included for comparison.  Topramezone rate was insignificant so data were pooled.  Goosegrass cover was reduced by 86% by topramezone plus triclopyr and 69% by topramezone alone in the zoysiagrass lawn and 100% in the fallow site with all treatments, 10 weeks after initial treatment (WAIT).  A trial by triclopyr interaction noted at 8 and 10 WAIT for smooth crabgrass and goosegrass was likely due to triclopyr suppressing recovery of these weeds in the dense zoysiagrass where spray coverage was not as efficient as in the fallow site which contained no turfgrass competition.  No treatment significantly reduced smooth crabgrass cover in the zoysiagrass lawn.  In the fallow site, topramezone plus triclopyr reduced smooth crabgrass cover by 76%, 10 WAIT, and significantly better than topramezone alone (18%).  These data suggest that two applications of topramezone at 6.14 g ae haâ�»¹ controls multi-tiller goosegrass, the addition of triclopyr may suppress regrowth in areas of dense turf, and topramezone rates higher than 12.3 g ae haâ�»¹ are likely needed to effectively control smooth crabgrass as indicated by the Pylex™ label.          

As the current economic turn down affects golf budgets, more scrutiny is placed on managed turf areas to reduce fertility and mowing costs.  Nonmow areas, or secondary roughs, are a cost effective and visually appealing approach to maintaining out-of-play areas on the golf course.  Fine fescues are typically used for these areas because they are shorter than other grasses and tend to allow golfers to find and advance errant shots.  A unique set of weeds exist in nonmow situations and weed control programs are lacking.  Some fine fescues have demonstrated tolerance to glyphosate in past research, and glyphosate would be a valuable tool for controlling various perennial grass weeds in nonmow areas.  More information is needed to determine which fine fescue varieties are more tolerant to glyphosate and how glyphosate rates affect visual quality and seedhead production of fine fescues.  The objective of this study was to evaluate glyphosate at 0.6, 0.8, and 1.4 kg ai ha^-1 for effects on visual quality, NDVI, and seedhead production of 56 fine fescue varieties. 

Glyphosate was applied at 0.6, 0.8, and 1.4 kg ai ha^-1 with an 18 inch wide sprayer on May 16, 2011 and June 26, 2013.  The 56 fine fescue varieties were comprised of 1 sheep fescue, 3 slender creeping fescues, 12 hard fescues, 13 chewings fescues, and 27 strong creeping fescues.  All plots were mowed approximately 5 weeks prior to treatment and not mowed again for the duration of the study.  In 2011, glyphosate injured fine fescue most at 1 month after treatment.  At this timing, 22, 9, and 2 varieties maintained acceptable quality when treated with 0.6, 0.8, and 1.4 kg ai ha^-1 glyphosate, respectively.  Of the 22 varieties that maintained acceptable quality 1 month after 0.6 kg ai ha^-1 glyphosate, 12 were hard fescues, 8 were strong creeping, 1 was a slender creeping, and 1 was a sheep fescue.  The following 7 hard fescue and 1 sheep fescue varieties maintained acceptable quality 1 month after 0.8 kg ai ha^-1 glyphosate: SPM, Pick HF#2, Berkshire, Quatro, IS-FL 28, Scaldis, SRX 3K, Oxford, and Heron.  Only Quatro sheep fescue and Oxford hard fescue maintained acceptable quality 1 month after glyphosate at 1.4 kg ai ha^-1.  Fine fescues were injured most at 2 weeks after initial treatment (WAIT) in 2013.  At this timing, 26, 20 and 15 varieties maintained acceptable quality when treated with 0.6, 0.8, and 1.4 kg ai ha^-1 glyphosate, respectively.  Of the 26 varieties that maintained acceptable quality at 2 weeks after 0.6 kg ai ha^-1, 12 were hard fescues, 1 was slender creeping, 13 were strong creeping and 1 was sheep fescue.   Of the 26 varieties that maintained acceptable quality at 2 weeks after 0.8 kg ai ha^-1, 11 were hard fescues, 7 were strong creeping, 1 was slender creeping and 1 was sheep fescue.  The following 10 hard, 1 slender, 3 strong creeping  and 1 sheep fescue varieties maintained acceptable quality 2 weeks after 1.4 kg ai ha^-1: Predator, SPM, A0163Rel, Jasper II, Pick HF#2, Berkshire, Quatro, IS-FRR30, IS-FL 28, SR 3000, SRX 3K, SRX 55R, Oxford, Heron and Chariot.  At approximately 6 WAIT, nearly all varieties had recovered fully, and rate effects were no longer distinguishable.  

Creeping bentgrass (CBG) (Agrostis stolonifera) is the most widely used cool-season turfgrass species on golf course fairways and tees in the United States, but it is tolerant to few postemergence herbicides. Pinoxaden is a pro-herbicide that is metabolized to an inhibitor of acetyl-CoA carboxylase. It is registered for selective control of Lolium spp. in fine-leaf Festuca spp. and Poa annua in the United Kingdom; however, it is not labeled for use on CBG. Previous experiments demonstrated that the safeners cloquintocet-mexyl (cloquintocet), fenchlorazole-ethyl (fenchlorazole) and mefenpyr-diethyl (mefenpyr) applied at 450 g ha^-1 increased CBG tolerance to pinoxaden at 90 g ha^-1. Data describing CBG tolerance to pinoxaden with lower safener rates and control of Lolium perenne and Poa trivialis with these safeners are warranted.

Greenhouse experiments were conducted in 2012 and 2013 at the University of Tennessee to evaluate CBG tolerance to pinoxaden applied with various rates of cloquintocet, mefenpyr or fenchlorazole. Pinoxaden (90 g ha^-1) was applied to mature ‘Penncross’ CBG alone or in combination with cloquintocet at 450, 225, 90, 68, 45, 23 and 0 g ha^-1. All treatments were applied with NIS at 0.25% v/v. Treatments were applied with a water carrier at 221 L ha^-1 using a spray chamber to mature CBG maintained at a 1.3 cm height in 6-cm cone-tainers filled with a peat moss, perlite, and vermiculite growing medium. Plants were maintained in a greenhouse under ambient light and fertilized every 10 days with 10 kg N ha^-1 using a complete (20-20-20) fertilizer. Treatments were in arranged in a completely randomized design with four replications and repeated in time. Injury was evaluated visually on a 0 (no injury) to 100% (complete kill) scale. CBG clipping yield was also measured 21 DAT.

When effects of all three safeners were pooled, application at between 90 and 450 g ha^-1 reduced CBG visual injury from 21% (pinoxaden alone) to < 10% at 14 DAT. Safeners increased clipping yield from 50 mg per cone-tainer (pinoxaden alone) to > 90 mg per cone-tainer when applied at ≥ 68 g ha^-1. The safener mefenpyr was more efficacious in reducing CBG injury than cloquintocet or fenchlorazole.  

Additional greenhouse experiments evaluated weed control with pinoxaden (90 g ha^-1) in combination with cloquintocet, mefenpyr or fenchlorazole at 68 or 225 g ha^-1. Treatments were applied to 30-by-14 cm flats filled with Sequatchie silt-loam soil containing rows of CBG, Lolium perenne and Poa trivialis. Flats were fertilized with 25 kg N ha^-1 from a complete (20-20-20) fertilizer 2 days prior to treatment. Treatments were applied in the same manner described above. CBG injury and weed control were evaluated visually on a 0 to 100% scale at 14 DAT.

In the first experimental run, pinoxaden provided 55% Lolium perenne control when applied alone; control was not affected by safener application. Poa trivialis control from pinoxaden was reduced by application of mefenpyr (68 and 225 g ha^-1), cloquintocet (225 g ha^-1) and fenchlorazole (225 g ha^-1). However, these treatments also reduced CBG injury from 29% (pinoxaden alone) to ≤ 6%, thereby increasing the selectivity of pinoxaden for Poa trivialis. In the second experimental run, all treatments (regardless of safener) provided 100% control of Poa trivialis, Lolium perenne and CBG.

Treatments for the first and second experimental runs were applied in June and December, respectively. The cause of this extreme variation in pinoxaden efficacy is unknown, but warrants further investigation. Field research is also warranted to evaluate these pinoxaden-safener combinations on CBG injury and weed control.

Fate of Arsenic in a Managed Turfgrass System Following MSMA Applications.                                                                         D. J. Mahoney*, M. D. Jeffries, M. L. Polizzotto, and T. W. Gannon; North Carolina State University, Raleigh, NC.

In 2006, the Environmental Protection Agency (EPA) proposed a phase-out of organic arsenical herbicides including monosodium
methylarsonate (MSMA). MSMA has commonly been used as postemergence herbicide in cotton and turfgrass since the 1960s. The phase-out was enacted because of groundwater contamination concerns due to the the addition of arsenic (As) from MSMA applications. Public pressure hastened the phase-out before thorough experimentation was conducted; however, MSMA use is currently allowed and will continue until the review conducted by the National Academy of Sciences is completed. Previous field research has shown As concentrations in MSMA-treated turfgrass clippings may be significantly greater than nontreated turfgrass for up to 8 wk after treatment (WAT). To further investigate, greenhouse experiments (Method Road Greenhouse; Raleigh, NC, USA) were conducted to evaluate the effect of clipping management (clippings returned or collected) on As cycling in MSMA-treated turfgrass lysimeters (schedule 40 PVC; 10 cm diameter by 30 cm length). Further, the effect of clipping management on total As content of the system was determined. Arsenic was quantified in clippings, vegetation, soil, and porewater following a MSMA application at 4.5 kg ai ha^-1. Unique lysimeters were used for sampling each week over the experimental duration with mowing events occurring twice per week. Clippings were harvested over 8 wk after MSMA application with destructive sampling occurring at 2, 4, and 8 WAT to measure As concentrations at various soil depths. Samples collected included: clippings, above-ground vegetation, and soil from 0-5 cm, 5-15 cm, and 15-30 cm depths. EPA protocol 3050B was used to determine total As concentrations in plant, foliage, and soil. Leachate was continuously collected over the experimental period and total As was determined. Porewater sampling (5 and 15 cm) occurred at 0, 3, 7, 14, 28, and 56 d after treatment to determine As speciation using ion chromatography-inductively coupled plasma-mass spectrometry (IC-ICP-MS). The experiment was arranged in a randomized complete block design with four replicates and a nontreated control to measure background As. In general, As concentrations decreased over time. Further, differences between management practices were not detected in plant foliage or
soil; however, As concentrations fluctuated in plant foliage and soil over time. Over all evaluation dates, increased soil As concentrations were detected at 0-5 cm (2.2 mg kg^-1), while 5-15 and 15-30 cm depths increased 0.2 and 0.1 mg kg^-1, respectively. Increased soil As concentrations were greatest at 4 WAT (1.2 mg kg^-1) compared to 2 WAT (0.4 mg kg^-1) and 8 WAT (0.9 mg kg^-1). These data suggest As concentrations fluctuate over time following a MSMA application. Similar trends were detected in clippings over time, with highest As concentrations at 1 WAT (181mg kg^-1) and decreasing over time. Interestingly, As concentrations increased from 5 WAT (11.9 mg kg^-1) to 8 WAT (16.2 mg kg^-1), which may partially explain the decline in soil As concentrations from 4 to 8 WAT. Throughout the research, As leachate concentrations (< 8 µg L^-1) never exceeded the EPA’s maximum As contamination limit of 10 µg L^-1. Of the total As detected from treated lysimeters at 3 and 7 DAT, MSMA (58% and 65%, respectively) was greatest, followed by dimethylarsinic acid (DMA) (23% and 13%, respectively), As(V) (10% and 10%,
respectively) and As(III) (9% and 12%, respectively). However, data at 14 DAT suggest As speciation transforms over time, as As(V) (44%) was greatest, followed by MSMA (27%), DMA (17%), and As(III) (12%). This is important, as mammalian toxicity of these As species ranks As(III) > As(V) > MSMA ≈ DMA. Results suggest low potential downward mobility of As following a MSMA application. Further, As concentrations in turfgrass and soil fluctuated over time, suggesting As is cycled through the system. Future research is needed to elucidate the effects of additional management practices and plant interactions on As cycling and transformations following MSMA applications.

Author contact: djmahone@ncsu.edu

WSSA Lesson Modules for Herbicide Resistance Management in Turfgrass. R.G. Leon*¹, D. Shaw², J.T. Brosnan³, J.S. McElroy⁴, S.D. Askew⁵. ¹University of Florida, Jay, FL 32565, ²Mississippi State University, Mississippi State, MS 39762,³University of Tennessee, Knoxville, TN 37996, ⁴Auburn University, Auburn, AL 36849, ⁵Virginia Tech, Blacksburg, VA 24061.

The evolution of herbicide resistant (HR) weed species has seriously impacted row crop production in the United States for more than three decades, and it has reduced the number of herbicide alternatives that producers have for effective weed control. The WSSA Education Committee developed online training modules to help producers understand and manage HR weed species in row crops. Recently, cases of HR weed species have been reported in turfgrass systems. For example, populations of annual bluegrass (Poa annua) with resistance to simazine (Photosystem II inhibitor), glyphosate (EPSPS-inhibitor), prodiamine (mitosis-inhibitor), and several ALS-inhibitors have been confirmed in golf courses in different states. Due to the increasing number of HR cases in turfgrass systems, the WSSA Education Committee developed online training modules specifically for turfgrass professionals (e.g. golf course superintendents, sod producers, landscaping specialists). The turfgrass training modules were based on the row crop modules, but modifications were implemented to provide specific examples of HR weed species in turfgrass systems. Additionally, HR management strategies took into consideration the reduced number mechanical control options (e.g. tillage and cultivation), cultural practices (e.g. crop rotation) and mechanisms of action available for herbicide rotation in turfgrass systems in comparison with row crop systems. It is expected that these new training modules will raise awareness about the risk of HR weed species among turfgrass professionals and help them design and implement weed management strategies that delay and mitigate HR issues in turfgrass systems.

The Evolution (or Revolution) of Weed Regulation in Canada

Weeds have been a problem in Canada ever since the origin of crop production. The losses caused by weeds are believed to be greater than the combined losses produced by animal diseases, plant diseases and insect pests. In response, the Canadian Food Inspection Agency (CFIA) has developed an Invasive Plant Program. The objective of the program is to prevent or limit the introduction or spread of invasive plants that threaten Canada’s plant resource base, economy, environment or society.  As of October 2013, the CFIA regulates nineteen invasive plants as pests under the Plant Protection Act, including jointed goatgrass, mile-a-minute weed, Paterson’s curse, and cuscuta. Additional weeds and response plans will be evaluated as the program evolves. The CFIA’s Invasive Plant Program is an evolving program which began in earnest with the publication of the Invasive Alien Species Strategy for Canada and is led by the CFIA’s Invasive Alien Species and Domestic Programs section. More recently, approaches to weed regulation have experienced a paradigm shift evolving from a reactive to a proactive approach that considers weeds that are not yet in Canada.

APHIS authority, regulations and policy are always under review, but currently APHIS is undergoing reorganization beyond our normal ongoing process for updating programs for weeds.  The newly reorganized Cross Functional Workgroup for weeds is refining our internal process for identifying, tracking, prioritizing, and decision-making on weeds of potential concern to the U.S. We intend to clarify and streamline this process, which relies on information from NAPPRA (Not Allowed import Pending Pest Risk Assessment) datasheets and weed risk assessments to identify high risk species for regulatory action. The process also engages other APHIS groups such as the New Pest Advisory Group an dthe NAPPRA program for program decision-making. Development and use of risk management documents will be discussed. The above listed processes relate to ongoing APHIS programs.  A new program is developing due to EPA\'s recently promulgated final rule regarding biomass for renewable fuels made from Arundo donax or Pennisetum purpureum. This regulation includes review processes by USDA regarding plans for Best Management Practices and Risk Mitigation.  APHIS is currently discussing with EPA and USDA sister agencies how this process will be structured, and which USDA agencies will be included.

Value Assessment of Pesticides at the Pest Management Regulatory Agency.  M. P. Downs*; Pest Management Regulatory Agency, Health Canada, Ottawa, ON.

Prior to being registered for use in Canada, pesticides must undergo a thorough scientific evaluation to ensure that when used as directed, they do not pose unacceptable risks to human health or the environment, and that they have acceptable value.  The purpose of the value assessment is to evaluate the pesticide’s contribution to pest management and includes a consideration of elements related to performance and benefits.  Performance considerations relate to efficacy and crop safety to both host and rotational crops.  Benefits may relate to health, safety and environmental aspects, as well as social and economic impacts.  The final determination of acceptable value is made using a weight of evidence approach, in consideration of the various contributors to value.

Value Assessment: Guidance for Registrants and Applicants.  M. P. Downs*; Pest Management Regulatory Agency, Health Canada, Ottawa, ON.

In September 2013, the Pest Management Regulatory Agency (PMRA) published a new regulatory directive, DIR 2013-03: Value Assessment of Pest Control Products.  The directive outlines the approach to, and components of value assessment, and the types of information that may be used to support this assessment.  These information types include: experimental data, use history information, scientific rationales, published literature and benefits information.  To assist applicants, the PMRA has developed guidance to aid in the preparation of the value information package.  In addition to the regulatory directive, other documents include: a use history information template and mock up, data summary templates, and a value summary template and mock ups.  Additional documents with specific guidance related to certain types of products (e.g. agricultural pesticides, antimicrobials, personal insect repellents) will be published in the future.

Previous research has demonstrated the R:S ratio in dose response studies may be affected by experimental methods. A greenhouse experiment was conducted to determine the effect of harvest time on the R:S ratio of triazine-resistant and -susceptible common lambsquarters (Chenopodium album). Greenhouse grown common lambsquarters plants were treated at the 6 to 10 true leaf stage with atrazine applied at 0, 0.1, 0.5, 1.0, 2.0, or 5.0 kg ai ha-1 plus crop oil concentrate at 1% v/v. Plants were harvested at 14 days after treatment (DAT), 30 DAT, 60 DAT, and at maturity. Three-or four-parameter log-logistic models were used to quantify the response of common lambsquarters biotypes to atrazine for each harvest time. Visual control of the resistant biotype never exceeded 15%.The dose resulting in 50% dry weight reduction (ED50) was significantly lower for the susceptible biotype at all harvest times (P=0.003). The estimated R:S ratio for plants harvested at 14 DAT, 30 DAT, 60 DAT, and maturity was 38.9, 50.7, 56.7, and 13.4, respectively. The results of this study show harvest time can significantly affect the R:S ratio.

Studies were conducted to evaluate absorption, translocation and metabolism of ¹⁴C glyphosate by silvery threadmoss (Bryum argenteum Hedw.).  No previous studies have herbicide absorption in bryophytes.  Bryophytes have no true vascular system and many of them lack protections such as cuticle wax and trichomes.  These protections provide herbicide tolerance to some higher plants.  Glyphosate does not control silvery threadmoss, but the mechanism of glyphosate tolerance is not known for this species.

Silvery threadmoss colonies were collected from putting greens and stored dry for several weeks until bentgrass stolons died.  Pure moss colonies cut into 3 x 12 mm plugs.  Experiments were arranged as randomized complete block split-split plot designs with three replications.  Main plots consisted of a 2 by 6 factorial treatment arrangement with two surfactant treatments and six harvest timings.  Moss colonies were harvested at 12, 24, 48, 72, 96 and 192 hours after treatment.  Subplots consisted of four sections of the moss colony, 3 mm by 3 mm each, to test for spatial movement of herbicide through the moss colony.  Radiolabeled glyphosate (glyphosate [phosphonomethyl-¹⁴C], Figure 1) was diluted in sterile water and applied as one 3-ml drop of solution containing 38.4 kBq glyphosate with 1% v/v non-ionic surfactant (Helena Chemical Co., Collierville, TN) on the left side of a 3 x 12 mm colony approximately 1 mm from each edge.  Experiments were conducted at ambient temperature in the laboratory with supplemental lighting provided by one 8-bulb Sun System Tek Light (Sunlight Supply, Inc. Vancouver WA) set to provide a 12 hour photoperiod.

Plugs were harvested by cutting each into four equal 3 mm by 3 mm sections.  Each section was vortexed 10 s in 3 ml sterile deionized (DI) water, followed by 30 s in 3 ml methanol to strip the cuticle and any embedded herbicide.  The remaining plant tissue was divided further into shoot and rhizoid parts and each part was placed in a combustocone (Fisher Scientific, Pittsburg, PA) for biological oxidation.  Samples were dried at 70°C, weighed, and burned in a Biological Oxidizer OX500 (R. J. Harvey Instrument Corporation, Tappan, NY) for a 2-minute oxidation cycle.  Samples were counted on a LS 6500 multipurpose scintillation counter (Beckman Coulter Inc, Indianapolis, IN) to determine total recovered radioactivity.  Data were converted to percent of applied ¹⁴C and subjected to ANOVA in SAS 9.2 (SAS Institute, Inc. Cary, NC) with sums of squares partitioned to reflect a factorial spit-split plot treatment structure and trial effects. Means were separated using Fisher’s Protected LSD at p=0.05. 

Foliar applied ¹⁴C glyphosate was quickly absorbed into moss shoots and rhizoids, reaching equilibrium within the plant by 24 hours after treatment (HAT).  Total ¹⁴C recovery from all parts and sections was 70-88% 24 HAT but decreased significantly with time, to 40 to 55% recovered at 48 HAT and only 35% recovered by 192 HAT.  The water wash had the most significant decrease in total recovered radioactivity over time; however, no complimentary increase was observed inside moss tissues or the methanol wash over time.  Thus, ¹⁴C glyphosate was lost, presumably to the capillary water in the moss colony, where it is possible for microorganisms to degrade ¹⁴C glyphosate rapidly into ¹⁴CO₂.

Evolutionary Dynamics of Glyphosate-Resistant and Sensitive Populations of Palmer amaranth in  North Carolina A. L. Lawton-Rauh¹, K. E. Beard¹, J. D. Burton²*, R. L. Nichols³, K. Lay¹, D. Jordan², A. C. York²; ¹Clemson University, Clemson, SC, ²North Carolina State University, Raleigh, NC, ³Cotton Incorporated, Cary, NC.

The genetic origins and population dynamics of glyphosate-resistant Palmer amaranth (Amaranthus palmeri) in North Carolina, USA were investigated using gene sequences of non-target genes not involved in glyphosate resistance as determined by 454 transcriptome comparisons.  Best fit models of population structure and genetic history indicate there was more than one, independent origin of glyphosate resistance in the North Carolina populations.  Correlation analyses of quantitative real-time polymerase chain reaction (PCR) counts of EPSPS gene copy number versus shikimate acid response showed that independently-derived glyphosate-resistant populations had similar mechanisms of glyphosate resistance within and between stratified, randomly replicated glyphosate resistant and sensitive populations.  There is a statistically significant association between copy number and resistance level, within the independently-derived populations.  Four out of five identified independent populations are significantly associated with a glyphosate resistant phenotype. Together, these results suggest that elevated gene copy number is the primary mechanism underlying documented glyphosate-resistant A. palmeri in North Carolina, and the best fit models suggest that the origin and proliferation of glyphosate-resistant genotypes have been independently-derived  in genetically distinct populations.

Giant ragweed (Ambrosia trifida) biotypes have recently
evolved two mechanisms of resistance to the herbicide glyphosate, yet
biological differences between resistant and susceptible biotypes are not well
understood. The goal of this study was to determine if there were measureable
differences in growth, reproduction, and germination among two
glyphosate-resistant (rapid necrosis), two glyphosate-resistant (no-response),
and three glyphosate-susceptible biotypes. 
Growth trials were conducted in a greenhouse, and the germination
trials were conducted under controlled conditions in an incubator at Harrow, ON..  There were no measurable differences in
growth characteristics between biotypes during the seedling stage. The
reproductive ratio suggested that susceptible biotypes invested more resources
into seed production.  Germination trials
confirmed that susceptible seeds had higher germination rates than resistant
biotypes. Although a biological fitness penalty was observed
during germination trials, the overall ecological fitness penalty is probably
negligible, based on the ability of resistant giant ragweed biotypes to thrive
under current management practises. 

Giant ragweed is one of the most competitive annual weeds in corn and soybean production across the eastern Corn Belt in the United States. The use of glyphosate (commercial name: Roundup) and glyphosate-ready crop systems were effective in managing giant ragweed populations for several years.  However, in the last decade, glyphosate-resistant giant ragweed have been reported in the eastern cornbelt and Canada resulting in a huge problem to farmers and requiring use of additional preemergence and postemergence for acceptable control in order to avoid yield loss. The research reported here has the goal of identify the genes responsible for conferring glyphosate resistance. Both glyphosate-resistant and glyphosate-sensitive biotypes of giant ragweed were studied using a RNA-seq experiment. Total mRNA was extracted from leaf disks of untreated and glyphosate treated leaves over a time-course of 0 to 6 hours after herbicide application and the transcriptome of sensitive and resistant giant ragweed biotypes were compared. We have identified a list of genes that were differentially expressed between the two biotypes as the first step in eventually identifying genes responsible for the glyphosate resistance observed.

Glyphosate-resistant (GR) kochia was identified in Warner county in southern Alberta in 2011 in a chemical fallow field. To determine the distribution and frequency of GR kochia, a randomized stratified survey of more than 300 locations (one population per location) in southern Alberta was conducted in the fall of 2012. Mature plants were collected, seed separated, and F1 seedlings screened by spraying with glyphosate at 900 g ae ha^-1 under greenhouse conditions. Screening confirmed 13 GR kochia sites: seven in Warner county, five in Vulcan county, and one in Taber county. The frequency of GR individuals in a population ranged from 0.3 to 98%. In addition to these sites, 9 sites from Alberta and 10 from southwestern Saskatchewan were confirmed from samples submitted by growers. GR kochia were identified in arid areas where chemical fallow occurs in rotation. Because of wind dispersal, kochia is an imminent threat to growers who use chemical fallow or grow glyphosate resistant corn, sugar beets or canola. Economic and agronomic impact of this GR weed is compounded because of multiple resistance to ALS inhibiting herbicides. 

After 12 years of commercialization, the herbicide-resistant Clearfield rice is planted in at least 50% of rice acreage in Arkansas, USA.  In 2013, 43% of total rice acreage in the USA was in Arkansas. Weedy rice samples were collected from 26 commercial fields in 2010, the majority of which had been planted with Clearfield rice some years.  These weedy plants escaped the weed control program used in 2010. We aimed to determine the level of herbicide resistance among weedy types in these fields.  We also aimed to determine the population structure of herbicide-resistant weedy types and detect any major changes in weedy traits of these populations relative to historical populations.  Panicles from representative plants of each weedy type were harvested; seeds were planted in single rows in 2011, in three replications, and tested for resistance to imazethapyr.  Only three of the fields sampled had <10% resistant weedy rice offsprings.  The rest had at least 20% resistant offsprings. These resistant weedy rice were 97-199 cm tall, which were taller than accessions collected years earlier between 2002 and 2003. The initiation of flowering among these resistant plants had also shifted from 78-128 d from planting relative to the older accessions (56-126 d). Whereas the majority (71%) of the older accessions were strawhull types, 54% of the contemporary resistant accessions were blackhulls and only 30% were strawhulls. Structure analysis showed that resistant weedy rice carry a large portion of the cultivated rice genome, whereas the old, herbicide-sensitive blackhull and strawhull weedy rice do not harbor any portion of the cultivated rice genome, except on rare occasions, at negligible proportions.  Principal component analysis placed US rice cultivars, sensitive blackhull weedy rice, and sensitive strawhull weedy rice in separate clusters. The resistant, contemporary weedy rice formed a loose cluster in between the rice cultivars and the two clusters of sensitive weedy rice. Thus, the herbicide-resistant weedy rice were all outcrosses with Clearfield rice, formed a distinct population relative to the old weedy rice accessions, and showed a slightly different morphological, phenological, and seed dormancy profile overall than the old weedy rice accessions.

Detoxification of 2,4-D in Resistant Wild Radish (Raphanus raphanistrum)

Danica E. Goggin, Stephen B. Powles*; University of Western Australia, Perth, Australia

Wild radish is the most economically damaging crop weed in southern Australian agriculture. The auxinic herbicide 2,4-D and the ALS-inhibiting herbicides have long been used to control wild radish, especially in cereal crops. Consequently, multiple resistance to 2,4-D and ALS inhibitors is widespread in wild radish in south-western Australia. Until now, there have been few studies on the mechanistic basis of 2,4-D resistance in wild radish. In this study, the mechanism of resistance has been investigated using ¹⁴C-labelled 2,4-D acid. Although leaf uptake of the herbicide is almost total, the labelled 2,4-D does not move out of the treated leaf in the resistant biotype. In contrast, ¹⁴C-2,4-D is rapidly translocated to the shoot and untreated leaves in a control susceptible biotype. Thin-layer chromatography of treated plant extracts has revealed that the resistant biotype converts approximately 40% of applied ¹⁴C-2,4-D to at least three different metabolites, one of which, based on its behaviour under acid and base hydrolysis, appears to be a phenolic glycoside of a ring-hydroxylated 2,4-D derivative. Mass spectrometry will be used to further characterise the 2,4-D metabolites produced by the resistant wild radish biotype. The fact that only 40% of the applied 2,4-D is metabolised but essentially 0% is transported out of the treated leaf suggests that at least two resistance mechanisms exist in the resistant wild radish biotype. Experiments are underway to determine if parent 2,4-D is sequestered (e.g. in the vacuoles or apoplast) in the resistant plants. Given the likely introduction of transgenic 2,4-D- and dicamba-resistant crops, increased emphasis on mechanisms of auxin resistance and their potential to arise in weed species is required.

*stephen.powles@uwa.edu.au

Plants must mount specific and coordinated defense responses to survive under adverse growing conditions in the field.  Previous studies in our laboratory have indicated that herbicide safeners induce the expression of glutathione S-transferases (GSTs) that detoxify chloroacetamide herbicides mainly in the outer two cell layers of cereal crop-seedling coleoptiles, and that safeners appear to be tapping into an unidentified, pre-existing signaling pathway for detoxification of environmental toxins, herbicides, or other xenobiotics.  A new theory resulting from our proteomic research is that safeners may be triggering an oxidized lipid-mediated signaling pathway, which subsequently leads to the dramatic up-regulation of tissue- or cell-specific GST expression.  Therefore, our current hypothesis is that the coleoptile not only provides structural protection for the newly-developing leaves enclosed within, but in addition the outer cell layers are biochemically equipped to detoxify herbicides, which prevents injury to the leaves via safener-regulated transcriptional activation of plant defense gene expression.  The overall goal of our current research is to couple laser-capture microdissection for isolation of epidermal and sub-epidermal cells with RNA-seq at three time points to provide insights into cell-specific expression patterns involved with safener-regulated detoxification mechanisms within the seedling coleoptile.  Biochemical and molecular studies have been conducted using a safener-responsive cereal crop (grain sorghum; S. bicolor), which has a fully-sequenced genome, is diploid, and is thus an ideal model system for investigating inducible detoxification systems in cereals. This new approach has yielded valuable molecular information towards revealing novel aspects of safener-responsive signaling pathways pertaining to oxidized lipid-mediated signaling, and in the identification of new candidate defense genes and detoxification proteins.  These discoveries will allow for new hypotheses to be generated and questions to be answered in future research for a more complete understanding of herbicide safener mechanism of action in cereal crops.

Wild oat is a serious weed of many cropping systems across the Northern Great Plains of North America, and several wild oat biotypes with resistance to one or more herbicides have been described.  Here, we characterize two biotypes with multiple herbicide resistance (MHR) to members of five different mechanism of action families:  acetyl-CoA carboxylase (ACCase) inhibitors, acetolactate synthase (ALS) inhibitors, the carbamothioate herbicide triallate, the membrane disruptor paraquat, and the growth inhibitor difenzoquat.  Greenhouse dose response experiments showed that the MHR3 and MHR4 biotypes were 6.9- and 8.0-fold more resistant to triallate than susceptible biotypes, and were 1.8- and 1.5-fold more resistant to paraquat, respectively.  DNA sequencing revealed that MHR biotypes did not contain point mutations known to confer resistance to ALS or ACCase inhibitors.  Pre-treatment of MHR plants with the cytochrome P450 inhibitor malathion partially reversed the resistance phenotype for flucarbazone (both biotypes), imazamethabenz (MHR4), difenzoquat (MHR4), and pinoxaden (MHR3), but not for tralkoxydim, fenoxaprop-P, or triallate.  To examine the potential for P450-mediated herbicide metabolism in more detail, PCR was used to amplify a 956-bp wild oat cDNA termed AfCYP81L, with a deduced amino acid sequence that shared 93% identity with the L. rigidum CYP81B1, and contained four P450 conserved domains.  Northern blots and qPCR assays showed that MHR4 plants contained constitutively elevated levels of the cognate mRNA before herbicide treatment, and that the mRNA was induced to higher levels 24 h after treatment with imazamethabenz.  Northern hybridizations also showed that malathion pre-treatment caused a further induction of AfCYP81L expression levels beyond those induced by herbicide alone.  These results indicate that enhanced herbicide metabolism may be involved in resistance to some herbicides, and demonstrate for the first time that a specific CYP gene is constitutively and inducibly regulated in any MHR weedy biotype.

Weed control failures due to herbicide resistance are an increasing and worldwide problem significantly impacting crop yields.  Metabolism-based herbicide resistance (MBHR) in weeds is not well characterized at the genetic level.  An RNA-Seq transcriptome analysis was used to find candidate genes conferring MBHR in a population (R) of the major global weed Lolium rigidum.  A reference cDNA transcriptome of 19,623 contigs was assembled and annotated.  Global gene expression was measured using Illumina 100 bp reads from untreated control, adjuvant-only control, and diclofop-methyl treatment of R and susceptible (S).  Due to the established importance of cytochrome P450 (CytP450), glutathione transferase (GST), and glucosyltransferase (GT) genes in MBHR, 11 contigs with these annotations and 17 additional contigs related to metabolism or signal transduction were selected for further analysis, all having constitutive expression differences between untreated R and untreated S.  In a forward genetics validation experiment, nine contigs had constitutively higher expression in R individuals from a segregating F₂ population, including 3 CytP450, one nitronate monooxygenase (NMO), 3 GST, and 1 GT.  Cluster analysis using these nine contigs differentiated F₂-R from F₂-S individuals.  In a physiological validation experiment where 2,4-D pre-treatment induced diclofop-methyl protection in S individuals due to increased metabolism, seven of the nine genetically-validated contigs were significantly induced.  Four contigs (2 CytP450, NMO, and GT) were consistently highly expressed in nine field-evolved MBHR L. rigidum populations.  These four genes were strongly associated with the resistance phenotype and are major candidates for having a critical role in conferring MBHR.

Metabolomics is a rapidly emerging field that is aimed at a comprehensive identification and quantitation of low-molecular weight metabolites (metabolome) present in any living systems. Unlike genes that are subjected to epigenetic regulations and proteins that are influenced by post translational modifications, by directly measuring the metabolic state of a cell that closely influences the phenotype, metabolomics offers an unprecedentedly powerful approach for molecular phenotyping. Lethality of most systemic herbicides could mainly be attributed to their disruption of essential metabolic pathways in plants, hence the metabolomic approach presents a unique opportunity not only to gain detailed understanding on the mode of action of herbicides and natural compounds, but also to outline the possible cellular-level metabolism that confers tolerance/resistance to some weedy biotypes.

We used a targeted-metabolomics approach to study the metabolic responses of glyphosate-tolerant Ipomea purpurea, and glyphosate-resistant and susceptible biotypes of Palmer amaranth. Plants were subjected to different doses of glyphosate, and the ensuing changes in both carbon and nitrogen metabolism was captured at multiple time points using gas and liquid chromatography-tandem mass spectrometry, followed by data processing and multivariate statistical approaches.

Application of 0.75x glyphosate (recommended dosage=0.84 ai/ha; 1x) caused a 17 fold increase in shikimic acid concentration in susceptible A. palmeri biotypes within 24 hours after treatment (HAT), indicating a rapid disruption of shikimate pathway. This was further reflected in the amino acid profiles of susceptible biotypes; at 24HAT, compared to the water-sprayed control, the concentration of aromatic amino acids (Tyr, Phe, Trp) decreased, whereas the level of Asn, Gln, Ile, Leu and Pro increased in glyphosate-sprayed susceptible biotypes. The blockage of shikimate pathway by glyphosate could increase the C flow through EMP pathway and the TCA cycle, which in turn would upregulate the biosynthesis of other amino acids. Interestingly, even though the glyphosate treatment resulted in a 11fold increase in shikimate accumulation in resistant biotypes at 24HAT, their amino acid profile was similar to that of the control, indicating a less physiological response of resistant biotypes to glyphosate treatment.  At 72HAT, compared to their respective water-sprayed control, the shikimate accumulation in the glyphosate-treated susceptible biotypes increased by 24 fold, while the shikimate concentration in resistant biotypes decreased to 5 fold. However, the amino acid profile of the glyphosate-treated resistant biotypes remained similar to those observed at 24HAT, indicating a disconnect between the accumulation of shikimate and the amino acid biosynthesis in resistant biotypes of A. palmeri.

The growth of I. purpurea was not affected at 1x and 2x glyphosate doses and the plants showed stunting and yellowing beyond 4x concentration. However, the shikimate accumulation was observed at all glyphosate concentration (1x, 2x, 4x, and 8x), which was 20 times higher than that of the water-sprayed control, and was less sensitive to increasing glyphosate concentration. At 72HAT the concentration of aromatic amino acids showed a liner increase with increase in glyphosate concentration, with higher accumulation of Phe, Tyr and Trp occurring at 8x dosage. Given that both Phe and Tyr were below the detection limit in water-sprayed control plants, the observed accumulation of aromatic amino acid could reflect a down-regulation of protein synthesis or an up-regulation of proteolytic activities at higher concentrations of glyphosate.  This accumulation of aromatic amino acids despite an increase shikimate concentration highlights a disconnect between glyphosate response of I. purpurea and the interruption amino acid metabolism. Unlike the N metabolism the C metabolism of I. purpurea responded inversely to glyphosate concentration, with the sugars (sucrose, mannose and tagatose) increasing at lower concentrations and decreasing at higher concentration of glyphosate. The sugar alcohols and inorganic acids steadily increased with increase in glyphosate concentration indicating an osmotic stress, which mirrored the visual wilting symptoms at 8x dosage. Though the level of tissue phosphoric acid of I. purpurea at lower dosage of glyphosate was similar to that of the control, beyond 2x there was a 10 fold increase phosphoric acid content indicating that the tolerance mechanism exhibited by this species could be highly energy demanding.  Overall our results indicate that targeted metabolomics approach is a powerful tool in probing the cellular physiology and metabolic pathways, which could provide real-time insight into the physiological mechanisms that regulate herbicide tolerance/resistance in weedy biotypes. 

Mechanism of Propanil Resistance in Cyperus difformis L. 

Pedroso, R.M; Alarcón-Reverte, Rocio; Fischer, A.J.

Herbicide-resistance in Cyperus difformis L., a major weed of rice, is widespread worldwide but has thus far only been reported for acetolactase synthase-inhibiting herbicides. Faced with the ensuing reduced control options, rice growers in California have come to rely on the contact herbicide propanil (3,4-dichloropropionanilide) for control of ALS-resistant C. difformis populations. Nonetheless, growers have recently experienced poor control with any of the available propanil formulations, suggesting resistance to this photosystem II-inhibiting herbicide may have evolved in C. difformis populations. The objectives of this study were to (a) confirm resistance to propanil in C. difformis lines using whole-plant dose-response experiments and establish resistance levels, (b) evaluate response to propanil in combination with the insecticide carbaryl (a known propanil synergist) in order to test for metabolic resistance, (c) assess the response of propanil-resistant lines to various other PSII-inhibiting herbicides, such as diuron and metribuzin, , and (d) examine whether or not mutations at the photosystem II thylakoid-membrane-bound D1 protein could be involved in conferring resistance to propanil. A C. difformis line derived from populations collected in rice fields of California’s Sacramento Valley was confirmed resistant to propanil with an R/S ratio (fresh-weight biomass) of 13.8. This is the first case of propanil resistance outside the Poaceae family and the first time C. difformis exhibits resistance to an herbicide mechanism of action other than ALS inhibition. Carbaryl - a known propanil synergist due to its role as substrate for the propanil-degrading enzyme aryl acylamidase – slightly increased propanil toxicity in R plants but synergized propanil against S plants to a much greater extent, resulting in an R/S ratio of 23.6 when carbaryl was present. Such results suggest enhanced degradation of the herbicide molecule is not playing a major role in C. difformis resistance to propanil. By means of whole-plant dose-response experiments, R plants were shown to be cross-resistant to the PSII-inhibitors bromoxynil, diuron and metribuzin, whereas all lines were susceptible to atrazine. Although R/S values for such herbicides could not be calculated from our data, R plants sprayed with the herbicides bromoxynil and metribuzin at full rates (1x) had in average 3.14 and 9.11 times more fresh aboveground biomass than S plants per pot, respectively, as measured 15 days after spraying. Moreover, despite the fact that R plants sprayed with diuron at 1x had only 1.85 times more biomass than S plants in the same treatment, the former when treated with diuron at 0.25x (a more discriminant rate) had in average 20.7 times more biomass than S plants per pot. Following such results, we amplified the herbicide-binding region of the chloroplast psbA gene of propanil-R and -S plants using PCR. Sequence analysis of the R line exhibited a substitution from valine to isoleucine at position 219 of the D1 protein encoded by the psbA gene, thus suggesting a partial loss of affinity between propanil and its binding site could be playing a role in C. difformis resistance to propanil. Such mutation (Val₂₁₉Ile) has been reported to confer resistance to metribuzin and diuron in Poa annua populations. To our knowledge this is the first report of a higher plant exhibiting resistance to propanil due to a psbA mutation, for all previous cases were attributed to enhanced propanil degradation by aryl acylamidases. Ongoing research is aimed at elucidating whether or not propanil degradation by aryl acylamidases play a secondary role in C. difformis resistance to propanil by means of in-vivo propanil conversion to metabolites. The loss of propanil to control this important weed of rice underscores the fragility of herbicide-based weed control in monoculture rice. Integrated weed management approaches to decrease herbicide selection pressure are needed to mitigate the evolution of multiple-herbicide resistance in C. difformis of California rice.

Palmer amaranth is an economically important weed that has developed resistance to glyphosate via an unknown mechanism involving  amplification of EPSPS gene. While sensitive biotypes usually contain 1-2 copies of EPSPS per haploid genome, resistant palmer plants may contain up to 100-200 copies. Unlike most cases of genomic amplification, a very large fragment of genome (>25 kb) containing EPSPS gene and its flanking sequences is amplified via a mechanism that poorly understood and copies are spread around the genome. In an effort to better understand molecular events that led to the rise of glyphosate resistance , we have discovered that the number of copies of EPSPS gene can significantly vary within clonal progeny of a given plant, indicating somatic instability of the amplified locus within palmer genome. Moreover, glyphosate resistance is not always correlating well with the number of copies, suggesting that other mechanisms might also  involved. We have been exploring different ideas on why glyphosate resistance can't be fully predicted by EPSPS copy number, as well as how these loci proliferate and are maintained in the genome. Molecular aspects of the amplified locus gene structure and its protein products will be discussed. 

Concerns over the safe use of pesticides for lawn and garden care have led to widespread policy reform in Canada including the restriction of cosmetic pesticide use at the municipal and provincial levels in some provinces. Different pesticide reduction policies have been adopted all with the goal of protecting public health. At the extremes are, for example, voluntary reductions in chemical pesticide use in Calgary, Alberta as opposed to a province-wide cosmetic pesticide ban in Ontario. Our research explores the processes underlying the formation of divergent pesticide reduction approaches and the resulting public responses. This multi-phase project includes the views of decision-makers (n=26), from pesticide advisory committees, and residents (n=1088) in Calgary and Halifax. Findings from interviews with policy makers indicate that scientific uncertainty was used to legitimize opposing ‘protectionary’ and ‘precautionary’ policy narratives of the chemical industry in Calgary and the anti-pesticide coalition in Halifax, respectively. Surveys and follow-up interviews with residents reveal that, although there is a general divide about the appropriateness of pesticide bans, home owners are more concerned with balancing perceived aesthetic and health risks in order to ‘get along’ in the neighbourhood context. Additionally, residents generally agree with the reduction of non-essential pesticide use and are open to alternatives to chemical pesticides to assist in lawn maintenance. This indicates that municipal policy-making about pesticides must be sensitive to the complexities inherent in the yard as a socially contested space. We conclude that the success of environmental health management at any level may depend on our understandings of the “social” at the local level.

An overview of the Cosmetic Pesticides Ban in Ontario, adoption of herbicide alternatives and current weed control problems without solutions.

Canada has a history of pesticide reduction on turf beginning in the 1980’s.  This was accomplished through integrated pest management programs, plant health care programs, pesticide by-laws and pesticide bans.   In 1991, the pivotal pesticide by-law in Hudson, Quebec was enacted and was the first time that a municipal by-law banned the use of pesticides on privately owned land.  This municipal by-law paved the way for the provincial pesticide ban legislation in Quebec in 2003 and Ontario in 2008.   In Ontario there is a new class of pesticide ingredients (Class 11) for cosmetic uses under the ban.  This class is mainly bio-pesticides and naturally occurring pesticides.  These are the only pesticide ingredients for use on turf throughout the province.  There are exemptions for golf course turf, specialty turf,  plants that are poisonous to the touch and sod production.  Class 11 pesticides are less efficacious, require repeat applications and are expensive.  Due to these factors, there has been a slow adoption of these products by homeowners and the lawn care industry.  Currently, there is a need for an effective pre and post-emergence crabgrass control product and more efficacious post-emergence broadleaf herbicides, especially for weeds such as Trifolium repens, Plantago major, Viola papilionacea , Glechoma hederacea and Euphorbia supine. 

Exploring Alternative Weed Mangement in Turfgrass Systems in Ontario

C. Siva, F. J. Tardif, E. M. Lyons and K. S. Jordan,  University of Guelph, Guelph, ON N1G 2W1

In April of 2009 the province of Ontario, Canada passed a cosmetic pesticide ban restricting the use of conventional pesticides on various turfgrass systems, including home lawns and municipal athletic fields. This led to the development of various alternative, low-risk options for weed management within the province. This study compared various alternative options for both pre-renovation and post-establishment broadleaf weed management over a 2-year period. Results indicated that of the available alternative products only one, chelated iron (sold as Fiesta herbicide), was comparable to the conventional 3-way herbicide traditionally applied to turf. Results also indicated that renovating a lawn with established Kentucky bluegrass sod also reduced weed invasion significantly and kept weeds to below 5% over the course of the study. The results of this study suggest that there may be alternative options to conventional pesticides for the management of broadleaf weeds in established turfgrass systems.

Starting in 2011, schools and daycare centers across the state of New York were banned from using conventional pesticides on playing fields, lawns, and playgrounds. The NYS Child Safe Playing Fields Law was enacted to minimize pesticide exposure to children and teenagers. The law restricts the use of pesticides to minimal risk ingredients that include clove oil, lemongrass oil, cinnamon oil, and other compounds listed under FIFRA 25(b). http://www.epa.gov/oppbppd1/biopesticides/regtools/25b_list.htm. In 2012 and 2013, we evaluated three organic herbicides, one thermal weeding device, and two reduced risk herbicides for their effectiveness in controlling weeds in turfgrass plots. These preliminary evaluations indicate that a certain level of weed management of a heavily infested turf area can be attained. However, conventional notions of adequate broadleaf weed control in athletic turf would seem to be beyond the reach of the currently permitted sprayable herbicides. One of the more promising tools for some level of acceptable weed control is with the chelated iron products (FeHEDTA). Although these are not currently permitted under the NYS law, they may be applied if the proper waiver is obtained.  To attain maximum coverage and efficacy, these herbicides appear to require a relatively high volume of water as a carrier. This may be an additional limitation for practical applications other than spot treatments. The propane flamer provided the greatest level of total weed control, but the inherent problems with burning dry weeds at a facility with children nearby would make this a limited option in most cases. More research is being conducted on combining some of the better products to determine if additive levels of control are possible.

In recent years increasing pesticide bans and restriction have affected turfgrass management.  For instance, in 1996, the city of San Francisco, CA, banned the use of pesticides on city and public property.  In 2004 pesticide buffer zones for protection of salmon and steelhead habitat were established throughout Washington, Oregon and California.  In 2009 Connecticut implemented pesticide bans on all school grounds and day care centers.  As of 2010 Quebec, Ontario and New Brunswick have placed restrictions on the cosmetic use of synthetic pesticides as a result of health and environmental concerns.  Considering pesticide restriction such as these, the turfgrass industry as a whole is in need of pesticide alternative control practices and strategies.  The objective of this presentation is to 1) review the herbicide alterative, or organic, weed control options available within the field of turfgrass management, and then 2) review recent and current research pertaining to the development of novel organic weed control methods.  First, the review of herbicide alternative weed control methods will highlight the efficacy of mustard seed meal (sinalbin), citric acid, garlic, vinegar (acetic acid), Borax (sodium borate), corn gluten meal, soy bean meal and steam.  This review will include information pertaining to activity, application rates and frequency, type of vegetation controlled and percent control of the various herbicide alternative methods.  Next, recent and current research pertaining to the development and practical application of new organic weed control methods, particularly the application of deciduous leaf mulch and the use of rhizosphere bacterium will be discussed.  Finally, this presentation will conclude with a progress report pertaining to the efficacy of deciduous leaf mulch and rhizosphere bacterium application as an herbicide alternative weed control options within the field of turfgrass management. 

Classical biological control has a long history of success for the management of introduced weed species in non-crop and range systems.  Efforts to develop bioherbicide approaches for weed management have been less successful.  Major factors limiting success have been cost and requirements for specific environmental conditions for successful infection leading to inconsistent performance under field conditions.  Turfgrass systems offer opportunities for overcoming these two development hurdles.  Interest in organic approaches to lawn care continues to increase and the amount of money consumers are willing to spend on organic options is much greater than is possible in most cropping systems.  Additionally, turfgrass is an intensively managed system where fertility, mowing, and irrigation can be managed, thus providing the opportunity to manage the environment to improve success of biological control agents.  For these reasons, many fungal and bacterial pathogens have been evaluated for potential use in turfgrass systems.  The monoculture of grasses has led to research on broad-host range pathogens, such as Sclerotinia sclerotiorum, Sclerotinia minor, Pseudomonas syringae pv. tagetes, and Phoma macrostoma, for broadleaf weed control in turf.  Narrow host range pathogens for the control of Poa annua, Digitaria sanguinalis, and Cyperus esculentus in turfgrass have also been evaluated.  Recently this area of research has been stimulated by regulatory restrictions on the use of synthetic herbicides for weed control in lawns.  

Since the introduction of 2,4-D in the 1940s turf managers have relied on herbicides to keep lawns free of plants other than the desired perennial grasses. When developing grass seed mixtures for lawns, seed companies have selected species and varieties for characteristics such as rapid establishment, abundant seed production, wide adaptation, and desirable color. The resulting mixes frequently lack the ability to maintain a sufficiently thick turf to exclude weeds over the long term, particularly when the soil or environmental conditions are less than optimal. Significant variation exists in the ability of turfgrass species and cultivars to persist as weed-free turf over the long term. Ten turfgrass species were evaluated in a five-year study under low input conditions on poor soil at the University of Rhode Island. Hard fescue (Festuca ovina complex) performed best with an overall quality score of 6.9 on a 1-9 scale, significantly higher than other entries. The plots averaged 92% cover in years 2-5 and scored 7.8 for crabgrass suppression where a score of 9 indicates no crabgrass present. Tall fescue, red fescue, colonial bentgrass, and crested hairgrass (Koeleria macrantha) formed a second group with overall quality scores of 5.4 to 5.7. Tall fescue, red fescue, and colonial bentgrass averaged 80 to 82 percent cover in years 2-5, and had better cover than hard fescue in year 1. Crabgrass suppression scores were similar to hard fescue. Perennial ryegrass gave the best cover 6 weeks after establishment but declined rapidly, averaging only 20% cover in year 5.  In trials on good soil with maintenance as recommended for lawns weed intrusion scores in established plots of Kentucky bluegrass ranged from 2.3 to 8.0 with a score of 9.0 indicating no weeds; on the poor soil Kentucky bluegrass was completely dominated by weeds. Weed suppression in established plots of creeping red fescue varied from 2.5 to 9.0 under lawn conditions. On good soil Chewings fescue out-performed both hard fescue and creeping red fescue, averaging 89% cover over five years; averages were 79% and 67% for hard and red fescues, respectively. The top chewings fescue cultivar had 87% cover in April following September seeding, exceeded 95% cover in years 2-5, and allowed minimal weed intrusion. The top hard fescue cultivar was slower to establish, with only 60% cover in April of year 1, but exceeded 90% cover in years 2-5 and completely excluded all weeds. These results show that turfgrasses can successfully out-compete weeds, but it is necessary to select varieties and species for long-term competitive ability and suitability to the soil and expected inputs.

The processes through which plants can recognize kin and alter competition strategies to increase overall fitness at the family level are currently being investigated, and results are varied and controversial. Due to the fact that autogamy and passive seed dispersal are common in the life cycles of many annual weeds, it was hypothesized that kin recognition may play an important role in annual weed population dynamics. This hypothesis was tested using four families from one (geographic) population of wild oats (Avena fatua L.) and four families from two (geographic) populations of cow cockle (Vaccaria hispanica L.). Twelve replications of kin vs. kin and stranger vs. stranger treatments were planted in a greenhouse in a randomized complete block. Each population was treated as a separate experiment. A 3:1 sand-to-topsoil soil mixture was used, and limited fertility was supplied to assure adequate competition. Data was collected relative to internode length, plant height, leaf area, shoot biomass, and root biomass. Mixed model ANOVA was carried out using SAS, and the analysis on these variables showed no significant difference (P > 0.05) between the kin vs. kin treatments and the stranger vs. stranger treatments in any of the families of either species. mel072@mail.usask.ca

Competition of Red Fescue (Festuca rubra L.) in Wild Blueberry
Sunil Kant Sikoriya1, Derek Lynch1, Nathan Boyd2
1Department of Plant and Animal Sciences, Faculty of Agriculture, Dalhousie University, PO Box 550, Truro, NS, B2N5E3,
2Gulf Coast Research and Education Center, University of Florida, 14625 C.R. 672, Wimauma, FL, 33598
Competition occurs when the available resources do not fulfill the combined demands of neighboring organisms in a community. Red fescue (Festuca rubra L.) is a common, sod forming grass that spreads via seeds and rhizomes. Its recent spread into agricultural fields has made it an emerging weed, especially in wild blueberry fields in Nova Scotia. A 2-year (2012-2013) field study was conducted to determine the effects of weed (Red fescue) removal at different times on wild blueberry growth and yield. Results showed hand weed removal at the end of June and July of the crop sprout year significantly reduces red fescue density per square meter, by almost 45% in the subsequent crop year. However, wild blueberry’s stem height, density, biomass, floral bud, number of flowers and yield were not significantly different between weed removal treatments, both during sprout and crop years. If red fescue can be managed during June and July of the sprout year for a few years, then it may be brought under control in wild blueberry field.
Key words: Competition, red fescue, wild blueberry, weed removal, yield, sprout year and crop year

Canola is the main oilseed crop produced in western Canada.  Based on seeded acreage, canola is currently the most abundant crop grown in Manitoba.  Volunteer canola, derived mainly from canola harvest losses, has become a significant agricultural weed in many fields throughout western Canada.  Seedbank persistence and seed return of volunteer canola, along with genetically-engineered herbicide-resistance, create difficulties managing this weed.  Based on seeded acreage, soybean is currently the third most abundant crop grown in Manitoba.  Populations of glyphosate-resistant volunteer canola can limit options for herbicide management within glyphosate-resistant soybean, creating a need for an integrated management approach.  The integration of mechanical, cultural and chemical weed management methods were evaluated based on their efficacy for minimizing seed production of volunteer canola while minimizing yield losses in soybean.  Soybean row spacing (7.5”, 15.0”, and 30.0”), seeding rate, and inter-row management (tillage or seeding cereals between soybean rows) were evaluated in Carman, Manitoba in 2013.  Soybean seeded at 15.0” row spacing was the ideal, resulting in low volunteer canola seed return (294 kg∙ha^-1) and high soybean yield (2055 kg∙ha^-1).  Increasing narrow-row soybean seeding rate from 70 kg∙ha^-1 to 140 kg∙ha^-1 did not have an effect on volunteer canola seed return, but did however increase soybean yield.  Inter-row tillage in soybean seeded at 30.0” row spacing resulted in the lowest volunteer canola seed return (106 kg∙ha^-1) while maintaining a high soybean yield (2154 kg∙ha^-1).  Spring-seeding wheat or fall rye between 30.0” soybean rows decreased volunteer canola seed return, but also decreased soybean yield.  The in-crop application of glyphosate to half of each plot resulted in termination of inter-row cereals.  This eliminated many of the differences among treatments.

Studies comparing the crop agronomic response to no-till under organic crop management are lacking. The objective of the study was to compare the effect of organic rotational no-till and two organic tilled systems on the basis of mulch biomass quantity, soil chemical properties, weed control, and subsequent crop productivity. A two-year field study was conducted three times in Carman, Manitoba, Canada. Three green manure management systems were tested, in a randomized complete block design. A barley/hairy vetch green manure was grown in the first year of the study and terminated by rolling (No-Till), rolling and tillage (Roll+Till), or haying and tillage (Hay+Till). Flax was seeded the following year. Amount of barley/hairy vetch mulch produced by late-fall of the green manure year varied among sites and ranged between 7.9 and 10.8 Mg ha^-1. In the following spring, flax was no-till seeded into 6.7, 7.7, and 4.2 Mg ha^-1 of mulch at site A, B, and C, respectively. There was an overall trend towards lower levels of soil nitrate-N in No-Till, although it did not influence total plant nitrogen uptake. At two of three sites, organic flax yields were significantly higher in No-Till than in the two tillage treatments. There was no penalty on flax yield for haying the green manure in mid-summer instead of incorporating it into the soil by tillage, across all three sites. Success of flax crop grown in an organic rotational no-till system in Southern Manitoba depended on environmental conditions, mulch biomass production (> 6.7 Mg ha^-1), and weed species present. The use of a barley/hairy vetch green manure mulch in an organic rotational no-till system eliminated the need for tillage for a period of 1.5 to 2 years, under certain conditions.

Canada is the largest lentil (Lens culinaris L.) exporting nation. Desiccating lentil with desiccants/harvest aids can dry down lentil evenly and quickly, and control late-growing green weeds, which enhances lentil harvesting efficiency and early harvesting. Since the harvest aids are applied at a late growth stage, high herbicide residue in seeds may cause commercial issues with marketing lentil. Application timing of harvest aids is critical for producers. Improper application timing may reduce yield and thousand seed weight, but increase herbicide residue in seeds. Therefore, the objective of the harvest aids application timing (% seed moisture) trial was to evaluate the responses of lentil to different herbicide application timings at Saskatoon and Scott, Saskatchewan, over 2 years (2012 and 2013). For this trial, glyphosate (900 g a.e. ha^-1), saflufenacil (50 g a.i. ha^-1), and the combination of glyphosate plus saflufenacil (900 g a.e. ha^-1 and 36 g a.i. ha^-1) were applied when seed moisture content was 60%, 50%, 40%, 30% and 20%. Significant relationships between evaluated variables and application timing on the basis of seed moisture content were detected. Also, this trial indicated that early application timing (60% application seed moisture) could result in adverse reductions in lentil yield and thousand seed weight. Glyphosate residue in seeds was less than 4 mg kg^-1 when glyphosate was applied alone at 30% and 20% average seed moisture. Glyphosate residue decreased when adding saflufenacil to glyphosate. Saflufenacil residue consistently increased with earlier application timing of the harvest aids. Plant moisture content was evaluated at 7, 14 and 21 days after each treatment application. Compared to the untreated control, application of the harvest aids at 40% and 30% average seed moisture provided better crop desiccation. tiz626@mail.usask.ca  

Cover crops improve soil aggregation and nutrient availability; many however, are not grown because herbicide residues applied in previous seasons may negatively impact them.   Our research aim is to find how nitrogen availability are affected by various spring and fall cover crops grown after application of three different herbicides. Hypotheses are (1) herbicide residues will decrease cover crops ability to increase soil aggregate stability and nitrogen scavenging by roots and (2) herbicide retention is modulated by the ability of the cover crop to improve soil structure. Treatments were set in a randomized split plot factor. Herbicides treatments were saflufenacil/dimethenamid-p at 735 and 1470 g ai ha^-1, a tank mixture of s-metolachlor/benoxacor/ atrazine (2880 and 5760 g ai ha^-1) with mesotrione (140 and 280 g ai ha^-1), and imazethapyr (100 and 200 g ai ha^-1). Spring cover crops were spring wheat (Triticum aestivum), buckwheat (Fagopyrum esculentum), sorghum-sudangrass (Sorghum bicolor spp. drummondii) and annual rye (Lolium multiflorum). Fall cover crops in contrast were oilseed radish (Raphanus sativus), and fall oats (Avena sativa). Root organic nitrogen was not significant in spring cover crop stands whereas oilseed radish showed lower values under labeled rates of imazethapyr and fall oats shower greater values under double-labeled rates of the same herbicide. Root biomass values were not significant under any treatment. Heavier roots are likely a response to compensate for poor number of stands and above ground biomass injury. This may influence storage of organic nitrogen in the fall.

 

Glyphosate resistant Canada fleabane (GRCF) was confirmed in Ontario from seed collections made in the fall of 2010. The repeated use of glyphosate on Roundup Ready (RR) crops has contributed to the selection of the resistant biotypes. An integrated approach that uses multiple modes of action is one component of an overall strategy to address glyphosate resistant weeds. Single versus sequential applications of glyphosate/2,4-D choline (Enlist Duo) and a two-pass weed control programs using preplant (PP) residual herbicides followed by post-emergence (POST) applied Enlist Duo have been evaluated.  The single applications of Enlist Duo (1720 g ai ha¯¹) provided 69-86% control of the GRCF while the sequential applications increased control to 92-100%.  Three applications of Enlist Duo did not provide an increase in control over two applications 8 weeks after the application (WAA).  The PP residual herbicide that provided the most consistent control (95-99%) of GRCF 8 WAA was s-metolachlor (1600 g ai haˉ¹) + flumetsulam (50 g ai haˉ¹) + clopyralid (135 g ai ha¯¹).  The PP residual herbicides followed by Enlist Duo (1720 g ai ha¯¹) POST provided 97-100% control.  Results from this research will help farmers implement the most efficacious herbicide program thereby maximizing GRCF control, corn yield and net returns.  

Pre-seeding and post-harvest control of Kochia scoparia for management of glyphosate resistance.  Low, Ryan. H., Agricultural, Food and Nutritional Sciences, University of Alberta, Edmonton.

In 2012 glyphosate-resistant (GR) kochia populations were confirmed in chemical fallow fields in southern Alberta. Pre-seeding and post harvest trials were conduced on susceptible kochia to evaluate the effectiveness of commercially available herbicides to supplement or replacement glyphosate. In 6 pre-seeding trials conducted in 2011 and 2012, 2,4-D ester, pyrasulfotole/bromoxynil, dicamba, gluphosinate ammonium, diflufenzopyr/dicamba, diquat and bromoxynil/2,4-D were less effective than glyphosate alone; carfentrazone-ethyl and saflufenacil provided similar control; and fluroxypyr/MCPA ester enhanced control when applied after kochia emergence and before wheat seeding. In 4 post harvest trials eight herbicides, pyrasulfotole/bromoxynil, dicamba, saflufenacil, carfentrazone-ethyl, fluroxypyr/MCPA ester, glufosinate ammonium, diquat, and diflufenzopyr/dicamba were applied at two different intervals after the planted crop was harvested to determine if an additional spray timing would enhance kochia seed production and viability.

The prevalence of group 2 resistant broadleaved weeds threatens successful lentil production on the Canadian Great Plains. The objective of this study was to develop an integrated weed management strategy combining physical, cultural and chemical weed control methods for lentil producers dealing with group 2 resistant wild mustard. The study was conducted for 3 years between 2011 and 2013 at 2 locations at Saskatoon and Scott, Saskatchewan. It was a randomized two way factorial with weed control method and seeding rate as the main effects. Weed control treatments tested consisted of a control treated with a glyphosate burnoff, saflufenacil (Heat ™) herbicide, rotary hoeing, half rate metribuzin (Sencor ™) herbicide, a fully integrated treatment, and a full herbicide treatment. Three seeding rates representing 1, 2, and 4 times the recommended seeding rate were tested (130, 260, and 520 plants m^-2). Increasing seeding rate consistently lowered mustard biomass and increased crop yields in 4 of 5 site years. The full herbicide treatment provided the greatest reduction in mustard biomass followed by the integrated treatment. The integrated treatment relied more on increased seeding rate to reduce mustard biomass, and at the highest seeding rate it was able to provide equivalent yield to the full herbicide system. The results of this study show that an integrated system utilizing an increased seeding rate can control resistant weeds and maintain yields to a similar level as a strategy that relies only on herbicides for weed control. The study also suggests that farmers should consider increasing the seeding rate of extra small red lentils in order to maximize weed control, increase yields, and improve economic returns.

Pyroxasulfone, a new group 15 Very Long Chain Fatty Acid Elongase (VLCFAE) inhibitor, in combination with sulfentrazone, a group 14 Protoporphyrinogen Oxidase (PPO) inhibitor, may be useful for control of ALS inhibitor resistant false cleavers (Galium spurium) (hereafter referred to as cleavers), and wild oat (Avena fatua) in pea crops. Field studies were conducted at 4 sites in 2011, and two in 2012 to assess potential herbicide interactions. Analysis of observed and expected means using the Colby Method indicated no interactions (antagonism or synergy) between pyroxasulfone and sulfentrazone as quantified by cleavers and wild oat biomass reduction.  However, weed control varied between sites and years, suggesting edaphic factors may play a role in efficacy of these soil applied herbicides. Greenhouse studies were conducted to further investigate interactions and soil organic matter effects. They also indicated additivity of pyroxasulfone and sulfentrazone on wild oat, barley and canola biomass. Under greenhouse conditions, pyroxasulfone and sulfentrazone tended to have lower efficacy on plant biomass in higher organic matter soils as had been demonstrated previously in field studies.  Prediction of field efficacy of two soil applied herbicides using data from simplified greenhouse trials is difficult due to the interactions of variable soil moisture, soil organic matter and soil structure in the field that can affect herbicide availability. Pyroxasulfone and sulfentrazone co-application, while not synergistic, broadens the weed spectrum controlled and will reduce the selection for herbicide resistant weeds.

blaturnu@ualberta.ca

Seeds have physical, chemical, and biological defense mechanisms to defend their food reserves against decay organisms.  We recently hypothesized that seeds also possess biochemical defenses based on ≥ 2-fold induction of the plant defense enzyme, polyphenol oxidase (PPO), by Fusarium fungi that cause wild oat (Avena fatua) seed decay.  PPO activity was readily washed (leached) from caryopses exposed to Fusarium avenaceum isolate ‘F.a. 1’ indicating that the enzyme was released from the caryopsis surface.  Results strongly suggest that a latent PPO enzyme is proteolytically activated. Preliminary real-time PCR results suggest that PPO transcripts (cDNA) accumulated in response to F.a.1 challenge, showing an apparent “on-off” switch. Preliminary results further suggest that the plant defense enzymes peroxidase, chitinase, and oxalate oxidase are also induced, which implies that a complex seed defense mechanism.  We hypothesize that these biochemical defenses and molecular responses contribute to the longevity of dormant weed seeds. 

Imperata cylindrica (Cogongrass) has invaded more than 1.5 million acres in the southern US, and current control measures of herbicide application and tillage do not adequately control this noxious weed. Cogongrass demonstrates extraordinary adaptability to a range of soil types, rainfall regimes, and temperature conditions and is also a host for Imperata Yellow Mottle Virus, a pathogen of maize which could be a significant threat to domestic and global food security. Development of biological controls for Cogongrass as part of an integrated pest management strategy may help control the spread of this highly invasive weed. To this end, we have established a multi-disciplinary, multi-national team to collect samples of Cogongrass from around the world to create a comprehensive global genetic profile for this species. This data is being used to correlate US Cogongrass genotypes to genotypes from the native range to aid in the identification of host-specific biological controls.  More than 1000 Cogongrass samples, 550 from across the Southeastern US and 450 from International sites, have been collected and genetic profiling performed using a high throughput genotyping-by-sequencing approach. Data from over 3200 SNP markers was integrated with GIS-associated data to produce a population genetic profile of unprecedented resolution which identified several international regions for biological control exploration. 

A growing body of evidence indicates that contemporary evolution, including that shaped by hybridization, can be important for the success of invasive species. Yet, the effects of hybridization and rapid evolution are rarely taken into account when biological control projects are designed against these invaders. We will evaluate the consequences of hybridization between two distinct populations of a biological control agent on the efficacy and safety of biological control. We focus on the tansy ragwort (Jacobaea vulgaris) and ragwort flea beetle (Longitarsus jacobaeae) system, in which introduced Swiss and Italian populations of the control agent have hybridized in the field. We will conduct field surveys in NE Montana followed by molecular analyses to evaluate the extent of hybridization in natural populations. The performance of hybrid and parental populations will be quantified in common garden experiments, and demographic models of weed and biological control agent will be developed to predict efficacy. In addition, the host range of hybrids will be assessed to evaluate risk of non-target effects. The results of this project will enable us to provide specific recommendations about whether biological control of ragwort in cold climatic zones in North America should be based on releasing hybrids. However, our broader goal is to increase the success rates of programs by promoting evolutionary thinking in biological control. Based on our findings, we will develop recommendations on how to assess the potential positive and negative consequences of accidental or deliberate intra-specific hybridization in biological control agents prior to their release into a novel environment.

Scotch broom (Cytisus scoparius) is a non-native, invasive shrub of major concern in Douglas-fir forests of the Pacific Northwest capable of causing long-term changes in soil ecological processes, resource supply, and forest community structure and composition. Relatively little is known about links between management practices and invasion, impacts on soil properties, and whether these impacts are mitigated following broom removal. Following are objectives of a new 5-year research program supported by NIFA. (1) Identify relative contributions of soil disturbance, altered soil and light environments, and seed bank dynamics to Scotch broom invasion. (2) Determine effects of Scotch broom on soil chemical and physical properties, resource supply, and plant community structure and composition. (3) Assess potential recovery of soil properties and native plant communities over time after Scotch broom removal. A combination of manipulative and observational studies will be conducted at three existing research sites that differ in soil texture and nutrient pools. For objective (1), we will compare five-year development of Scotch broom and planted Douglas-fir among combinations of logging debris removal, soil disturbance, and herbicide treatments. For objective (2), soil properties and plant community characteristics will be compared between Scotch-broom-invaded and non-invaded areas at two sites. For objective (3), areas will be established at one site in which Scotch broom was removed 1, 4, and 10 years previously to evaluate potential soil P depletion, altered soil physical properties, and allelopathic effects. The new research assesses a broad variety of ecological processes related to integrated pest management of Scotch broom and then uses links between forestry practices and Scotch broom invasion to design strategies that will prevent future invasions, control existing infestations, and mitigate associated impacts.

Less than 10 years after glyphosate-resistant soybean cultivars debuted, glyphosate-resistant weeds began proliferating. Among the most problematic of these is Amaranthus tuberculatus (waterhemp) in the midwestern U.S. Many such populations have been reported in Illinois production fields, beginning in 2006. From an experimental perspective, each of these populations can be considered a unique resistance event, harboring information on all the factors (e.g. biological, environmental, management) that contributed to its occurrence. We have compiled extensive, landscape-scale data on glyphosate-resistance frequency, field-management history and environmental characteristics for over 100 such events in central Illinois. Classification and regression tree analysis of these data indicated that historical diversity in herbicide mode of action and glyphosate rate in a given field were both linked to variation in the proportion of glyphosate resistance in A. tuberculatus seeds collected in 2010. Resistance levels were over five times greater in fields in which herbicide programs contained, on average, less than 3.5 different herbicide MOA (mean proportion resistant seeds = 0.089), compared to those in which 3.5 or more MOA were used (mean proportion resistant seeds = 0.016). The prevalance in glyphosate resistance in A. tuberculatus seeds followed a unimodal distribution, in which fields experiencing low or very high mean rates of glyphosate application over the 7 years of historical management data had lower proportions of resistant seed (0.043 and 0.095, respectively), compared to those fields receiving between 1.1 and 1.5 times the labeled rate of glyphosate (mean proportion resistant seeds = 0.24). Diversifying weed management practices appears to help delay the onset of glyphosate resistance for this important weed species in grain production fields in the midwest U.S.

Oak regeneration in Eastern deciduous forests is dependent on increases in light to the forest understory, which is often accomplished by harvesting or fire.  Unfortunately, these disturbances may also promote invasion by non-native invasive plants (NNIS).  The purpose of this study is to define forest management that allows for oak regeneration but deters growth of NNIS.  We evaluated germination, survival, and growth of three planted NNIS (Ailanthus altissima, Alliaria petiolata, and Microstegium vimineum) as well as existing populations of NNIS in 56 sites that varied in terms of management regime (control, single burn, repeat burn, diameter limit cut (DLC), and shelterwood), local topography (northeastern or southwestern slopes), and physiographic region (Allegheny Plateau or Ridge and Valley) in West Virginia, Ohio, and Virginia.  Secondly, we determined the spread rate of each of the three NNIS using eight seed traps and vegetation plots placed along a 20 m transect for A. petiolata and M. vimineum, and seed traps and plots placed every 5 m along a 100 m transect for A. altissima.  Thirdly, we grew these NNIS and Quercus rubra in growth chambers under eight light levels and corresponding light quality (red:far red) ratios, which represented forest light conditions under different management regimes.  Height and leaf number were determined, and biochemical indicators of growth and stress were measured, including the polyamines putrescine and spermidine and the amino acid proline.  Our results from these separate objectives were then used to calculate an Invasive Potential Value (IPV) for each combined management and environment type (20 total).  IPV was calculated using vulnerabiltiy to invasion data (likelihood of germination, survival, and growth) multiplied by the averaged spread rate (1.72 m/yr), and one minus the lowest light level showing NNIS growth (180 umolm^-2 s^-1 or 9% PAR).  All four shelterwood types had among the highest IPVs, followed by all four DLC types.  Northeastern slopes within the shelterwoods and DLC types had the largest IPVs.  These results indicate that management resulting in light levels below 10% PAR may help prevent invasion but still enable oak regeneration.  We are in the process of running stand growth and yield models (Forest Vegetation Simulator) using our IPVs as a weighted NNIS cost in order to evaluate if such harvesting limitations are commercially viable.

Cultural and mechanical weed management practices are underused in many cropping systems, particularly for herbicide-resistant weed management. This may be due, in part, to a lack of knowledge on the impact of non-herbicide management practices on herbicide-resistant weed development. Modeling is currently the most common approach for comparing the impact of weed control practices on herbicide-resistant weed evolution. Nearly all modelers recognize the importance of validating assumptions and results of predictive models through field research, yet there is an alarming lack of field studies that quantify the impact of non-herbicide weed management practices on the evolution of herbicide-resistant weed populations. We propose conducting field studies to quantify the impact of tillage and diverse crop rotations on the development of herbicide resistance in a summer annual weed species with relatively short soil life. We will establish a kochia (Kochia scoparia) population throughout our study site with a known proportion of ALS-herbicide susceptible (S) and resistant (R) individuals, and monitor the proportion of R:S as well as total weed density in response to tillage intensity, crop rotation, and herbicide use. Based on the results of this study, we will develop biological and economic models that will aid in developing herbicide-resistant weed management recommendations that go beyond herbicide use patterns. By determining the efficacy and economic impacts of non-herbicide practices on development of herbicide resistance, we hope to decrease the reliance on herbicides, thereby reducing the evolution and spread of new herbicide-resistant weed biotypes.

Pixxaro™ is a new herbicide being developed by Dow AgroSciences for post-emergence broadleaf weed control in Canadian cereal crops.  Pixxaro herbicide is a premix formulation of Arylex™ Active (halauxifen-methyl) + fluroxypyr-meptyl co-packed with MCPA ester and will have a typical recommended use rate of 5 + 77 + 350 g ae/ha, respectively.  Performance of Pixxaro was evaluated in field trials conducted in Canada between 2010 and 2013.  Pixxaro was very safe to spring wheat, winter wheat, durum wheat and spring barley, and provided excellent control (>90%) of many hard-to-kill broadleaf weeds, including Canada fleabane (Conyza canadensis), chickweed (Stellaria media), cleavers (Galium aparine), hemp-nettle (Galeopsis tetrahit), common lambsquarters  (Chenopodium album), kochia (Kochia scoparia), common ragweed (Ambrosia artemisiifolia), redroot pigweed (Amaranthus retroflexus), roundleaf mallow (Malva pusilla), stork’s-bill (Erodium cicutarium), wild buckwheat (Polygonum convolvulus), and volunteer alfalfa (Medicago sativa).  Due to its complete auxinic mode of action, Pixxaro will provide control of all major resistant weed biotypes found in Canadian cereal crops, including Group 2 resistant cleavers, chickweed, hemp-nettle, lamb’s-quarters, and redroot pigweed, as well as Group 2 + 9 resistant Canada fleabane, kochia and common ragweed.  Pixxaro offers broad flexibility to rotate to cereal, pulse and oilseed crops the season after application.  In addition to providing exceptional performance when applied across a wide range of crop and weed growth stages, Pixxaro offers Canadian cereal growers many unique benefits including low use rate, short rainfast interval, excellent compatibility with all graminicides, and versatility to be applied by ground or air.

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

Paradigm™ is a new herbicide being developed by Dow AgroSciences for post-emergence broadleaf weed control in Western Canadian cereal crops.  Paradigm contains the new arylpicolinate, Arylex™ Active (halauxifen-methyl), a Group 4 mode of action, and florasulam, a Group 2 mode of action herbicide. The typical recommended use rate will be 5 + 5 g ae/ha or 25 g product/ha.  Small plot field research trials were conducted in Western Canada between 2010 and 2013 to evaluate its performance.  Paradigm was applied to spring cereals including wheat, durum wheat, and spring barley from the one leaf to flag leaf stage and was found to be safe to all crops. In addition to providing excellent control of a wide range of annual broadleaf weeds, Paradigm also had good activity on key perennial weeds such as Canada thistle (Cirsium arvense), dandelion (Taraxacum officinale), and perennial sowthistle (Sonchus arvensis).  Additional tank-mix options include Curtail M (clopyralid + MCPA ester) and MCPA ester for expanded broadleaf weed control, or Simplicity (pyroxsulam) for grass weed control.  The inclusion of Arylex in Paradigm provides control of all major resistant weed biotypes found in Western Canadian cereal crops, including Group 2 resistant cleavers (Galium aparine), chickweed (Stellaria media), hemp-nettle (Galeopsis tetrahit), lambsquarters (Chenopodium album), and redroot pigweed (Amaranthus retroflexus).  In fields without resistant weed biotypes, Paradigm offers robust multi-mode of action resistance management due to the wide overlap of weed spectra controlled individually by florasulam and Arylex.  Paradigm provides broad flexibility to rotate to cereal, pulse and oilseed crops the season after application.  Other attributes of Paradigm include low use rate, short rainfast interval, excellent performance under adverse environmental conditions, and versatility to apply to a wide range of crop and weed growth stages.

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

Two experiments were conducted in Saskatchewan, Alberta, and Manitoba, Canada in 2012 and 2013.  In Experiment 1, studies were conducted at 6 site-years to evaluate different pre- and post-emergence herbicides for control of Japanese and downy brome (Bromus japonicus and Bromus tectorum, respectively) in winter wheat (Triticum aestivum).  Treatments included: untreated check, pyroxsulam applied POST in fall and spring at 15 g ai ha^-1, flucarbazone-sodium (DG and SC formulations applied POST in fall and spring at 30 g ai ha^-1), thiencarbazone-methyl applied POST in fall and spring at 5 g ai ha^-1, flumioxazin applied PRE at 88 g ai ha^-1, pyroxsulfone applied PRE at 112 and 150 g ai ha^-1, and a pyroxasulfone-flumioxazin tank-mix applied PRE at respective rates of 112 and 88 g ai ha^-1.  The POST treatments generally resulted in higher levels of crop injury than the PRE treatments with fall applications typically resulting in higher injury than spring applications.  When combined over locations, most treatments provided >90% control of Japanese brome as determined by visual control ratings and biomass reduction.  The only exception was flumioxazin that provided suppression of Japanese brome.  Pyroxsulam was the only POST treatment that provided >75% control of downy brome, with other treatments providing 50 to 70% control.  Flumioxazin PRE provided inconsistent suppression of downy brome.  Treatments that included pyroxasulfone resulted in >90% consistent control of downy brome over the 6 site-years. In Experiment 2, trials were conducted at 9 site-years to investigate the interaction of seed rate and pre- and post-emergence herbicides for controlling wild oat (Avena fatua) and cleavers (Galium spp.) in winter wheat.  Treatments included a factorial combination of seed rate (150 and 450 seeds m^-2) and herbicide (untreated, pyroxasulfone applied PRE- at 100, 150, 200, and 250 g ai ha^-1, pyroxsulam applied POST in the spring at 15 g ai ha^-1, and a tank-mix of pinoxaden and fluroxypyr and MCPA applied POST in spring at respective rates of 60, 105, and 560 g ai ha^-1).  Increasing seed rate resulted in higher plant densities, and reduced grass and broadleaf weed biomass by approximately 50%.  All herbicides provided control of wild oat and cleavers; however, densities were low to moderate at most site-years.  Higher seed rates resulted in significantly higher winter wheat yields.  Herbicides applied to low seed rates resulted in lower seed yields than untreated yields at higher seed rates indicating that herbicides were unable to compensate for low plant densities.  At high seeding rates, herbicides did not improve winter wheat yield.  Pyroxasulfone application did not result in significant crop injury or reduce winter wheat plant stand at any of the 15 site-years. Pyroxasulfone provided excellent consistent control of Japanese and downy brome and reduced density and biomass of wild oat and cleavers; however, herbicides to control spring germinated weeds are not required if winter wheat plant densities of > 250 plants m^-2 are achieved.  

The joint action of a herbicide mixture analysed with the Additive Dose Model(ADM) and the efficacy of the mixture with three adjuvants, a methylated seed oil (MSO), a Latex-sticker (LSA) and a acidifier surfactant blend (ASB) on oilseed rape and barley was assessed in a field experiment.

 The logarithmic sprayer yielded 150 l ha^-1 with a halving distance of the rate at 8 m. The sprayed strip of 1.5 m width was replicated twice. The assessment of effect was visual assessment, height measurement and analysis of images taken from 30 m with a hexacopter. The herbicides and their mixture efficacies were evaluated by comparing ED-levels and compare them by ADM.

The mixture ED₅₀ 25 Days After Treatment (DAT) in oilseed rape  was 10 times higher than for one of the herbicides applied alone. The difference at ED₉₀  was approximately 4 times. The plant height of oilseed rape 40DAT resulted in an  ED₅₀ somewhat higher than one of the herbicides applied alone. The same applies at the ED₉₀ level.  The use of the ADM showed clear antagonism at the ED₉₀ and ED₅₀ Level.

A MSO adjuvant was at all assessing times causing the most severe symptoms and highest efficacy. The MSO yielded 4.5 fold higher efficacy in oilseed rape and in barely 2 times higher efficacy in barley compared to no adjuvant. The difference between ED₅₀- for the MSO and the second best adjuvant LSA in oilseed rape increased over time. In barley, however, the difference between the MSO and LSA ED₅₀ decreased over time, indicating that potency of MSO and LSA approached each other. The ASB adjuvant ED₅₀ was not different from spraying with no adjuvant at any assessing time and crops. The adjuvant dose–response results indicate, that fast herbicide activity equals a high efficacy over time. 

The research of joint action of mixtures and adjuvants efficacy assessment in the field can be inexpensively done with logarithmic sprayers. And last but not least the ED levels can be assess depending on the objectives of the experiment, e.g-for tolerance of crops ED₁₀ and/or control of weeds ED₉₀.

The Provisia™ Rice System, a new non-GM herbicide tolerant system under development by BASF, will complement the Clearfield^® rice system, providing growers with another effective weed control technology and a new tool for resistance management. The system will be a combination of Provisia herbicide with Provisia rice.   Provisia herbicide is a postemergence graminicide which controls volunteer Clearfield rice (Oryza sativa L.), conventional rice types, red rice, weedy rice, and other common annual and perennial grasses, including barnyardgrass (Echinochloa crus-galli L). It is not an ALS herbicide, and thus, provides another mode of action to combat ALS-resistant grasses. In field trials, Provisia rice exhibited excellent tolerance to single and sequential herbicide applications. Optimum control of red rice and other grass species was obtained with sequential applications. Provisia herbicide can be tank-mixed with many common rice herbicides to provide broad spectrum control of broadleaf and grass weeds. Current research is focused on optimization of performance and weed control systems that mitigate the potential for the development of herbicide resistant weeds. BASF is working with multiple seed partners to bring the Provisia™ Rice System to the market in the latter part of this decade.

Bicyclopyrone is a new selective herbicide for weed control in field corn, seed corn, popcorn and sweet corn. The bicyclopyrone mode of action is inhibition of HPPD (4-hydroxyphenyl-pyruvate dioxygenase) enzyme which ultimately causes the destruction of chlorophyll followed by death in sensitive plants. Upon registration, SYN-A197 will be the first bicyclopyrone containing product launched with anticipated first commercial application in the 2015 growing season. SYN-A197 is a multiple mode-of-action herbicide premix that provides preemergence and postemergence grass and broadleaf weed control. Field trials were conducted to evaluate SYN-A197 for weed control and crop tolerance compared to commercial standards. Results show that SYN-A197 very effectively controls many difficult weeds and provides improved residual control and consistency compared to the commercial standards. 

Postemergence control of grass weeds in sorghum has been a high-priority objective for weed scientists for many years.  Up to now, this effort has been hampered by inadequate herbicide selectivity to the sorghum crop.  Inzen™ is a new herbicide tolerance trait for sorghum that delivers crop safety to a number of ALS herbicides that have good postemergence activity on grass weeds. Inzen™ is a non-GMO trait introduced into sorghum from wild, herbicide-tolerant shattercane using natural breeding techniques.  In this case, the exchange of genetic information between a cultivated crop and its wild, weedy relative resulted in the development of a valuable weed management tool for sorghum producers.  However, the potential reverse movement of the trait from the crop to non-target weeds would not be desirable.  Two-way movement of the Inzen™ trait between cultivated sorghum and its weedy relative shattercane (both sorghum bicolor) via pollen-mediated gene-flow has been well-studied and the trait has been shown to move within this species.  Pollen-mediated gene flow across species lines to other sorghum relatives, such as johnsongrass (sorghum halepense), has also been studied and a significantly lower potential for genetic exchange has been found.  Efforts are underway to better understand and minimize the potential of pollen-mediated gene flow from cultivated sorghum containing the Inzen™ trait to its weedy relatives.  Learnings are being applied towards the development and implementation of Best Management Practices (BMPs) sorghum growers will be required to adopt prior to planting sorghum containing the Inzen™ trait.  DuPont Crop Protection has licensed the Inzen™ trait to sorghum seed companies and several have announced the commercial introduction of hybrid sorghum lines carrying the Inzen™ trait as soon as 2015-16.  Pending regulatory approval, DuPont Crop Protection will introduce new postemergence grass control solutions in sorghum that were not possible prior to the introduction of the Inzen™ trait.  Successful implementation of the Inzen™ BMPs will help ensure value to sorghum producers who plant sorghum containing the trait.

The DuPont™ Inzen™ herbicide-tolerance trait is not registered for sale or use. No sale, offer for sale, or use of this product is permitted prior to issuance of the required governmental approvals. Products with the Inzen™ trait are not yet available for sale or use. Products, benefits and concepts described are subject to full regulatory approval and field testing.The DuPont Oval Logo, DuPont™, The miracles of science™ and Inzen™ are trademarks or registered trademarks of DuPont or its affiliates. Copyright © 2013 E.I. du Pont de Nemours and Company. All Rights Reserved. 12/13 

Enhanced Weed Management Solutions with MGI Herbicide-Tolerant Soybeans. Rakesh Jain*¹, Dain E. Bruns², James C. Holloway³, Thomas H. Beckett⁴, Brian L. Wilkinson⁵, Brian Erdahl⁶; ¹Syngenta, Vero Beach, FL, ²Syngenta, Marysville, OH, ³Syngenta, Jackson, TN, ⁴Syngenta, Greensboro, NC, ⁵Syngenta, Nevada, IA, ⁶Syngenta, Clinton, IL.

Field trials were conducted in 2012 and 2013 to evaluate mesotrione-based weed control programs in MGI herbicide-tolerant soybeans stacked with glyphosate tolerance.  These multiple mode-of-action herbicide tolerant soybeans enable the use of mesotrione and isoxaflutole pre- and post-emergence in addition to glyphosate and glufosinate-ammonium post-emergence.

Several mesotrione-based herbicide programs provided control of key weed species, including glyphosate resistant populations.  The most successful and consistent weed control was achieved with two-pass programs that included pre-emergence residual herbicides and multiple, overlapping modes of action.  These programs were designed to align with HRAC principles of weed resistance management. The use of these chemically diverse and novel programs will offer effective, safe and sustainable weed management options for soybean growers. rakesh.jain@syngenta.com

Field trials were conducted over a three-year period (2011-2013) at different locations in Southwestern Ontario, Canada to compare various two-pass weed management strategies in glyphosate-resistant soybean for crop injury, weed control, soybean yield, and profit margin. There was minimal injury (2% or less) with most treatments evaluated but chlorimuron + flumioxazin (PRE) and V-10233 (PRE) caused as much as 4 and 7% visible injury in soybean, respectively. At 8 weeks after glyphosate applied LPOST, glyphosate (EPOST) provided 79, 73, 81, 84, 72, and 80% control of ABUTH, AMARE, AMBEL, CHEAL, ECHCG, and SETVI, respectively. Glyphosate (LPOST) provided 87, 98, 88, 92, 91, and 95% control of ABUTH, AMARE, AMBEL, CHEAL, ECHCG, and SETVI, respectively. The sequential application of glyphosate (EPOST fb LPOST) provided 98-100% control of weeds evaluated. The sequential application of preemergence herbicide fb glyphosate (LPOST) provided 96-100 control of ABUTH, AMARE, AMBEL, CHEAL, ECHCG, and SETVI. All herbicide programs evaluated provided equivalent yield as the weed-free control. All herbicide programs evaluated provided greater profit margin than the weedy control. Glyphosate (LPOST), imazethapyr + metribuzin (PRE) fb glyphosate (LPOST), s-metolachlor + flumetsulam (PRE) fb glyphosate (LPOST), and chlorimuron (PRE) fb glyphosate (LPOST) reduced profit margin as much $152.86 compared to the weed free control. However, glyphosate (EPOST), glyphosate (EPOST) fb glyphosate (LPOST), imazethapyr/saflufenacil (PRE) fb glyphosate (LPOST), saflufenacil/DMTA-P (PRE) fb glyphosate (LPOST), s-metolachlor + flumetsulam + metribuzin (PRE) fb glyphosate (LPOST), chlorimuron + flumioxazin (PRE) fb glyphosate (LPOST), s-metolachlor + metribuzin (PRE) fb glyphosate (LPOST), and flumioxazin (PRE) fb glyphosate (LPOST) herbicide programs provided profit margins equivalent to the weed free control. Based on this study, the most efficacious and profitable weed management programs in glyphosate-resistant soybean are a sequential application of glyphosate or a two-pass program of a preemergence residual herbicide followed by glyphosate LPOST. The two-pass programs have glyphosate stewardship benefits.

Glufosinate Rate and Application Timing for Control of Johnsongrass (Sorghum halepense) in Glufosinate-Resistant Soybean (Glycine max).  R. L. Landry*, D. O. Stephenson, IV, and B. C. Woolam; Louisiana State University Agricultural Center, Alexandria, LA.

Experiments were conducted at the LSU AgCenter Dean Lee Research and Extension Center near Alexandria, LA in 2011, 2012, and 2013.  These experiments assessed glufosinate rate and timing for control of johnsongrass in glufosinate-resistant soybean.  Experiments were a 3x2x2 factorial arranged in a randomized complete block with four replications.  Factors consist of: (1) 0.5, 0.6, or 0.7 kg ai ha^-1 of glufosinate applied to 46-cm johnsongrass at the first application; (2) sequential application of 0.5 or 0.6 kg ha^-1 of glufosinate; (3) sequential application timings of 3 or 4 wk after the initial application (WAIT).  Johnsongrass control and heights (converted to percent of nontreated), and soybean yield were collected.

Glufosinate applied 4 WAIT controlled johnsongrass 83%, but glufosinate applied 3 WAIT provided only 76% control 28 d after treatment (DAT).  At harvest, johnsongrass control was increased following initial application of 0.7 kg ha^-1 (77%) compared with 0.5 kg ha^-1 (64%).  Delaying the sequential application from 3 to 4 WAIT increased johnsongrass control 13% at harvest (78% vs. 65%).  Following the sequential application rate of 0.5 and 0.6 kg ha^-1, johnsongrass heights were reduced 48% and 37% of the nontreated control, respectively, 28 DAT.  Furthermore, a 13% reduction in johnsongrass height was observed after delaying the sequential application to 4 WAIT (36%) rather than 3 WAIT (49%) 28 DAT.  Sequential application of glufosinate at 0.6 kg ha^-1 reduced johnsongrass heights as a percent of the nontreated control 15% percent more than 0.5 kg ha^-1at harvest.  Moreover, delaying the sequential timing from 3 to 4 WAIT decreased johnsongrass heights 76 and 63% of the nontreated control, respectively, at harvest.  Soybean treated with 0.5, 0.6, and 0.7 kg ha^-1 of glufosinate at the initial application yielded 2400, 2600, and 2670 kg ha^-1, respectively; however yield differences were only observed between the 0.5 and 0.7 kg ha^-1 glufosinate rates.  When applying sequential glufosinate applications, soybean yield was increased following 0.6 kg ha^-1 rather than 0.5 kg ha^-1.

Johnsongrass control was maximized following an initial application of 0.7 kg ha^-1 as the first application to 46-cm johnsongrass followed by a sequential glufosinate application 4 WAIT.  Soybean yields were increased when 0.7 kg ha^-1 of glufosinate was applied as the initial application.  Furthermore, soybean yields were increased when applying 0.6 kg ha^-1 glufosinate as the sequential application.  These data indicate that glufosinate applications are a viable tool for management of johnsongrass in glufosinate-resistant soybean.  Research will be repeated in 2014 to substantiate these results.

An encapsulated formulation of acetochlor has been registered recently for Pre-Plant, PRE, and POST application in soybean. Information is not available about sequential application of acetochlor for weed control and crop safety in soybean. Field experiments were conducted at Clay Center, NE in 2012 and Clay Center and Waverly, NE in 2013 to evaluate weed control efficacy and crop safety of encapsulated acetochlor applied Pre-Plant, PRE and POST in a split application in a tank mix with glyphosate in glyphosate-resistant soybean. Results suggested that acetochlor applied alone or in tank mix with fomesafen, flumioxazin, or sulfentrzone plus chlorimuron provided 99% control of common waterhemp, green foxtail, and velvetleaf at 15 days after planting (DAP); however, control reduced to ≤ 40% at 100 DAP. Acetochlor tank mixed with glyphosate applied PRE followed by early- or late-POST resulted in ≥ 90% control of common waterhemp and green foxtail, reduced weed density ≤ 2 plants m^-2, and weed biomass ≤ 12 g m^-2. In fact, these treatments were comparable with acetochlor applied sequentially three times (pre-plant or PRE followed by early and late-POST) as well as with weed free plots for achieving higher weed control, reducing weed density and biomass, and securing higher soybean yields. Acetochlor tank mixed with glyphosate applied pre-plant or PRE followed by early and late-POST at 1.68 kg ai ha^-1 resulted in season long weed control; however, these treatments were off label because it exceeds a cumulative application restriction of 3.37 kg ai ha^-1 per season. It is concluded that an encapsulated acetochlor can be a good option for soybean growers if applied sequentially (PRE followed by POST) in a tank mix with glyphosate. More research is required to evaluate efficacy of encapsulated acetochlor applied in a tank mix with PRE and POST soybean herbicides.

Roundup Ready® crops, which allow growers to use the broad-spectrum herbicide glyphosate, represent one of the most rapidly adopted weed management technologies in recent history, currently accounting for 93% of the acreage in soybean in the U.S. However, intensive selection pressure has led to the evolution of glyphosate-resistant weeds, which brings the need to incorporate herbicides with alternative modes of action as a strategy for weed resistance management. Metribuzin, a photosystem II inhibiting herbicide that controls some broad-leaf and narrow-leaf weeds in pre- and post-emergence, is a complementary mode of action that can be used in the Roundup Ready® soybean system. Here, we investigated the interactions between metribuzin and other herbicides used in the Roundup Ready® soybean system and determined if herbicide tank-mixtures can result in enhanced weed control.

Effect of Pyroxasulfone Application Rate and Timing on Soybean (Glycine max) Growth and Yield.  D. O. Stephenson, IV*¹, J. L. Griffin², B. C. Woolam¹, R. L. Landry¹, and M. Hardwick²; ¹Louisiana State University Agricultural Center, Alexandria, LA; ²Louisiana State University Agricultural Center, Baton Rouge, LA.

Research was conducted at the Louisiana State University Dean Lee Research and Extension Center near Alexandria, LA in 2011, 2012, and 2013 and the Louisiana State University, Central Research Station, Ben Hur Research Farm in Baton Rouge, LA in 2012 and 2013 to investigate the effect of pyroxasulfone on soybean growth and yield.  Pyroxasulfone was applied PRE and POST to V3 (three visible trifoliate) at 0.06, 0.12, 0.18, 0.24, and 0.3 kg ai ha^-1.  Glyphosate (0.86 kg ae ha^-1) was co-applied with all pyroxasulfone treatments.  Data collected included visual soybean injury 7, 14, and 28 d after treatment, soybean plant density 21 d after PRE application, soybean plant heights 28 and 42 d after PRE treatment and 7 and 14 d after POST treatment, and soybean grain yield.  Soybean was maintained weed-free during the growing season with as needed applications of glyphosate.  Prior to analysis, soybean plant density, heights, and grain yield were converted to a percentage of the nontreated control.

Averaged across application timing, 9% injury was observed following pyroxasulfone at 0.3 kg ha^-1 which only differed from 0.06 kg ha^-1 (6% injury) 7 d after treatment.  All other rates did not differ 7 d after treatment.  A similar trend was observed 14 d after treatment with 3, 4, 6, 6, and 7% injury observed following 0.06, 0.12, 0.18, 0.24, and 0.3 kg ha^-1, respectively.  No differences among pyroxasulfone rates were observed 28 d after treatment.  Averaged across pyroxasulfone rate, soybean injury was greater following the POST application timing (15%) than the PRE (1%) 7 d after treatment.  However, soybean injury 14 d after the PRE and POST application timings were 6 and 4%, respectively, with PRE causing greater injury.  A slight difference for soybean injury was observed 28 d after the PRE and POST application timing with 0 and 1% injury, respectively.  Soybean plant density, heights, and grain yield were not influenced by pyroxasulfone application rate or timing ranging from 89-96%, 94-97%, 94-96%, and 96-98% of the nontreated control, respectively.  Data indicates that visual injury increases slightly with increasing pyroxasulfone rate and POST applications are more injurious than PRE applications regardless of rate.  However, regardless of pyroxasulfone rate or timing, soybean growth and yield was not negatively impacted.

Clusterbean (Cyamopsis tetragonoloba) is an important cash crop of north-west India. It is an annual legume crop raised in arid and semi-arid regions with good drought tolerance. India produces 80% of world clusterbean from 2.3 m ha area, but with <0.5 t/ha productivity. Weeds are major constraints in realizing the yield potential of improved varieties as they can cause 30-98% yield losses. Imidazolinone herbicides though effective against weeds, their soil persistence affects mustard crop (Brassica juncea) raised in succession. Field studies were carried out at CCS HAU Hisar, India during 2012 and 2013 using imazethapyr 10% SL (WeedBlock) at 50, 62.5, 75 and 100 g/ha applied 3 or 4 weeks after sowing (WAS) and compared with pendimethalin (30% EC and 38.7 % CS) 1.0 kg/ha, tank mix of pendimethalin 500 g + imazethapyr 50 g/ha, readymix of pendimethalin + imazethapyr 32% EC (Valor),  readymix of imazethapyr + imazamox 70% WG (Odyssey) 70 g/ha and imazethapyr 100 g/ha alone applied pre-emergence (PRE), weedy and weed free check. Clusterbean variety HG 365 and HG 563 were planted on 24 July 2012 and 22 June 2013, respectively in a plot size of 10 x 2.5 m with three replications arranged in a RBD design. Trianthema portulacastrum, Cyperus rotundus, Echinochloa colona, and Eragrostis sp were major infesting weeds. Mustard was planted after clusterbean harvest in November. Highest weed control efficiency (WCE) was recorded with imazethapyr 100 g/ha PRE which was similar to its tank mix with pendimethalin (50 + 500 g) or readymix (Valor).  POE application of imazethapyr (100 g/ha) was less effective than its PRE application and also caused crop injury. Delaying in spraying from 3 to 4 wk further decreased WCE. Due to more rains in 2013, pendimethalin PRE and imazethapyr POE at lower rates were not effective. There were no significant differences in the WCE of both formulations of pendimethalin. Imazethapyr (100 g/ha) resulted in 30-70% injury to succeeding mustard crop compared to 15-25 when applied PRE. Imazethapyr applied as readymix (Odyssey) or Valor and tank mix with pendimethalin were safe to mustard crop with less than 10% crop injury. Lower rates of imazethapyr resulted in 5-20% crop injury. No mustard injury was recorded during 2013-14 as the flooding of field due to excessive rains might have leached imazethapyr.

Cotton Tolerance and Weed Control by Acetochlor/S-Metolachlor and Pyrithiobac Tank Mixes. C. W. Cahoon*, A. C. York, D. L. Jordan, and W. J. Everman; North Carolina State University, Raleigh, NC

Few residual herbicides can be applied over-the-top of cotton without the potential for significant injury.  Recently, topical applications of s-metolachlor (2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide) and encapsulated acetochlor (acetochlor) (2-chloro-N-(ethoxymethyl)-N-(2-ethyl-6-methylphenyl)acetamide) have increased in popularity.  These herbicides have demonstrated the ability to provide adequate preemergence control of GR Palmer amaranth with little to some injury noted.  Furthermore, the addition of a tank mix partner, especially pyrithiobac (2-chloro-6-[(4,6-dimethoxy-2-pyrimidinyl)thio]benzoic acid), was originally thought to increase necrosis caused by s-metolachlor and acetochlor  on cotton.  The objective of this study was to determine if pyrithiobac enhances necrosis caused by s-metolachlor and acetochlor on cotton.  Furthermore, researchers also wanted to compare Palmer amaranth (Amaranthus palmeri ) control by acetochlor/ s-metolachlor plus pyrithiobac tank mixes in both glyphosate (N-(phosphonomethyl)glycine) - and glufosinate (2-amino-4-(hydroxymethylphosphinyl)butanoic acid)-based systems.

Glyphosate-based System.  The experiment was conducted in 2011 at two separate fields on the Central Crops Research Station near Clayton, NC (North CCRS and South CCRS) and on a private farm near Mount Olive (MO), NC.  In 2012, research was repeated at North CCRS and MO.  Design of the experiment was a randomized complete block replicated four times.  Dimensions of plots were four rows by 9 m long, with a row spacing of 97 cm.  Postemergence (POST) residual herbicide treatments included pyrithiobac sodium applied at 0, 48, and 85 g ai ha^-1 alone or in combination with encapsulated acetochlor at 1260 g ai ha^-1 or s-metolachlor at 1067 g ai ha^-1. In addition, a non-treated control was included in the experiment.  All residual herbicides were applied 16 to 25 days after planting (DAP) or POST 1.  The potassium salt of glyphosate was applied at 866 g ae ha^-1 alone or in combination with residual herbicides at POST 1.  Additionally, glyphosate was applied 29 to 56 DAP (POST 2) and 39 to 65 DAP (POST 3) at 866 g ae ha^-1

Glufosinate-based System.  In 2011, the experiment was conducted at two separate fields on the Central Crops Research Station near Clayton, NC (North CCRS and South CCRS) and on a private farm near Mount Olive (MO), NC.  In 2012, research was repeated at North CCRS, MO, and on a private farm near Micro, NC.  The experimental design and plot size was identical to those used in the glyphosate-based system.  Using a treatment structure identical to the glyphosate-based system, residual herbicides were applied 16 to 22 DAP (POST 1) in the glufosinate-based system.  Applied in combination with residual herbicides POST 1, all plots except the non-treated control received glufosinate-ammonium at 543 g ae ha^-1.  In addition, 543 g ae ^ha-1 of glufosinate was applied 29 to 56 DAP (POST 2) and 43 to 65 DAP (POST 3).  At POST 1, POST 2, and POST 3, cotton was approximately at the 1- to 2-leaf, 5- to 10-leaf, and 8- to 12-leaf stage, respectively. 

Data collection and statistical analysis.  Data for cotton necrosis, chlorosis, and growth reduction was collected at 7 days after (DA) POST 1, 14 DA POST 1, POST 2, POST 3, and 105 to 120 DAP (late season).  Weed control ratings were performed 7 DA POST 1, 14 DA POST 1, POST 2, POST 3, and late season.  Data for cotton necrosis, chlorosis, growth reduction, weed control, and yield were subjected to analysis of variance using the PROC MIXED procedure of SAS (version 9.2).  Herbicide treatments were a fixed factor, whereas locations and replications were treated as random.  Means were separated using Fisher’s Protected LSD at p < 0.05.

Results and Discussion.  Necrosis was greatest 7 days after POST 1 in both glyphosate- and glufosinate-based systems.  In the glufosinate-based system, glufosinate alone caused 5% necrosis.  Necrosis was increased 3 and 4% when pyrithiobac was applied at 48 and 85 g ai ha^-1, respectively.  The addition of s-metolachlor and acetochlor to glufosinate also increased necrosis observed (19 to 23%). Furthermore, necrosis caused by acetochlor plus pyrithiobac (20%) was equivalent to acetochlor alone (19%).  However, the addition of pyrithiobac to s-metolachlor did increase injury.  Compared to s-metolachlor alone (23%), pyrithiobac in combination with s-metolachlor increased necrosis 3 to 4%. 

As expected, glyphosate alone produced the least amount of necrosis (1%).  The addition of residual herbicides, however, did increase necrosis.  S-metolachlor, acetochlor, and pyrithiobac alone increased necrosis 13, 11, and 2%, respectively.  Furthermore, s-metolachlor plus pyrithiobac (16 to 18%) was more injurious than s-metolachlor alone (14%).  However, the addition of pyrithiobac to acetochlor did not increase necrosis. 

In general, glufosinate-based systems were more effective for control of Palmer amaranth, mostly due to the presences of GR Palmer amaranth at research sites.  However, the addition of residual herbicides had varying effects depending on the primary POST product used (glufosinate or glyphosate).  In glufosinate-based systems, glufosinate alone controlled 86% of Palmer amaranth at POST 3.  The addition of a single residual herbicide increased control of the weed (91 to 93%).  However, the greatest control was achieved by combinations of residual herbicides (95 to 96%).  In the glyphosate-based system, glyphosate alone provided 73% control of Palmer amaranth.  Contrary to results when glufosinate was used POST, s-metolachlor and acetochlor in combination with glyphosate provided no benefit in control of Palmer amaranth (71%).  However, when pyrithiobac was tank mixed with glyphosate, control improved 15 to 16%.  Furthermore, combinations of s-metolachlor /acetochlor with pyrithiobac (88 to 91%) provided equivalent control of Palmer amaranth to pyrithiobac alone (86 to 87%).  Cotton lint yield followed a trend comparable to Palmer amaranth control.  

 In conclusion, it appears pyrithiobac can enhance injury of cotton by s-metolachlor.  In both glufosinate- and glyphosate-based systems, necrosis caused by s-metolachlor plus pyrithiobac was greater than s-metolachlor alone.  However, the increase in necrosis was very slight (2 to 4%).  Contrarily, the addition of pyrithiobac to acetochlor did not increase necrosis.  A typical effect of pyrithiobac on cotton is growth reduction.  General field observations found that cotton sprayed with pyrithiobac was often shorter and had less leaf area compared to cotton not receiving pyrithiobac POST.  Therefore, it is possible that plants with reduced leaf area would appear to have a greater percentage of necrosis.  Furthermore, plants not sprayed with pyrithiobac are quicker to recover from foliar burn caused by POST herbicides.  This is the likely explanation for why necrosis caused by glufosinate plus pyrithiobac was greater than glufosinate alone.  From a weed control stand point, residual herbicides provided an advantage in both POST herbicide systems.  However, in the glufosinate-based program, adequate control of Palmer amaranth was achieved by glufosinate plus s-metolachlor /acetochlor (92 to 93%).  In the glyphosate-based system, the addition of s-metolachlor or acetochlor to glyphosate provided no benefit in control of the weed.  In contrast, pyrithiobac added to glyphosate increased Palmer amaranth control 15 to 16%.  Likewise, where glyphosate was applied POST, lint yield was greatest in plots that received pyrithiobac alone compared to s-metolachlor or acetochlor alone.  Thus, pyrithiobac emerged as a critical weed control component in the glyphosate-based program.  In the glufosinate-based system, lint yield was equivalent in plot receiving s-metolachlor or acetochlor alone or pyrithiobac plus s-metolachlor /acetochlor. Because there was only a minimal benefit to Palmer amaranth control and no yield advantage, pyrithiobac seems less crucial in glufosinate-based herbicide programs compared to s-metolachlor and acetochlor.  cwcahoon@ncsu.edu

Natural pines pose one of the rgeatest challenges to site preparation on forestry sites in the South. While current site preparation mixtures do an excellent job of controlling the unwanted hardwoods on sites to be planted with loblolly pine, land managers are often faced with many thousands of natural pine seedlings per acre at the time of planting. These trees will compete with the planted seedlings and significantly reduce growth of the crop trees. This situation often requires expensive  corrective action after the pines are planted. A total of seven treatments were applied to an area with both hardwoods and naturally occuring loblolly pines. The pines ranged in size from one foot to six feet in height. Initial stems were recorded by species and height class, and these measurements were repeated one year after treatment. Results will be presented on the efficacy ofthe variuos mixtures for controlling both the principal species of hardwood present and the natural pines.

ClearView^TM Brush Herbicide (Aminopyralid + Metsulfuron-methyl + Triclopyr BEE) for Foliar Control of Black Spruce (Picea mariana) on Rights-of-Way, Industrial Areas, and Non-Crop Areas.  D.D. Hare*, R.F. Degenhardt, L.T. Juras, and A.W. MacRae.  Dow AgroSciences Canada LLC, Calgary, AB, Canada.

ClearView^TM Brush Herbicide is a newly registered herbicide being developed by Dow AgroSciences for foliar post-emergence control of Black spruce (Picea mariana) in Canadian non-crop areas.  ClearView Brush Herbicide contains three active ingredients, including: the Group 4 mode of action pyridine-carboxylic acids aminopyralid and triclopyr, plus the Group 2 sulfonylurea metsulfuron-methyl.  Performance of ClearView Brush Herbicide was evaluated in field trials conducted in Canada between 2010 and 2013. ClearView Brush Herbicide was applied at 0.4% V/V triclopyr + 230 g PR/ha ClearView^TM, and Tordon^TM 101 was applied at 1.0% V/V, as directed spray applications in 1000 L/ha water application volume.  ClearView Brush Herbicide provided excellent control of hard-to-kill black spruce trees (89% average control), versus commercial standard Tordon 101 (89% average control), evaluated one to two years after treatment. Additionally, ClearView Brush Herbicide provided excellent control of Trembling aspen (Populus tremuloides) (100% average control), and Balsam poplar (Populus balsamifera) (100 % average control), evaluated one year after treatment.  ClearView Brush Herbicide offers industrial vegetation managers flexibility to utilize a new multiple mode of action product to control hard-to-kill woody and tree species present on rights-of-way, industrial areas and non-crop areas in Canada. In addition to exceptional field performance, ClearView Brush Herbicide offers many unique benefits including: a reduced risk active (Aminopyralid), a product safe to wildlife and livestock, excellent user safety profile, and versatility to apply by ground or air.

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

The purpose of this trial was to screen Streamline (aminocyclopyrachlor (39.5%) and metsulfuron (12.6%)) and Viewpoint (aminocyclopyrachlor (22.8%), metsulfuron (7.3%), and imazapyr (31.6)) mixed with reduced rates of Krenite (fosamine) for
control of selective brush species.  Test species were:  oak (Quercus stellata, alba, rubra, falcata, velutina), winged elm (Ulmus
alata), and all (the above plus tupelo (Nyssa sylvatica), blueberry (Vaccinium spp), black hickory (Carya texana), persimmon (Diospyros virginiana), hawthorn (Crataegus spp), and green ash (Fraxinus pennsylvanica).

Herbicides were applied on 21-Sep-12 and visually evaluated on 1-Nov-13 (1-YAT).  Test treatments were:  (1) MAT28+Escort+Krenite+NIS (7.52+2+96+1%), (2) MAT28+Escort+Krenite+NIS (7.52+2+128+1%), (3) MAT28+Escort+Krenite+NIS (7.52+2+192+1%), (4) MAT28+Escort+Krenite+Arsenal PowerLine+NIS (5.94+1.58+96+8.26+1%), (5) MAT28+Escort+Krenite+Arsenal PowerLine +NIS (5.94+1.58+128++8.26+1%), (6)
MAT28+Escort+Krenite+Arsenal PowerLine +NIS (5.94+1.58+192+8.26+1%, (7) Milestone+Arsenal PowerLine+Accord XRT II+NIS (7+16+128+1%, (8) MAT28+Escort+Accord XRT II+NIS (7.52+2+128+1%, (9) MAT29+Escort+Arsenal PowerLine, Accord XRT II+NIS (5.94+1.58+8.26+128+1%), and (10) untreated check.  The rates for all treatments are expressed in
ounces of product/acre.  The NIS was Induce.  Escort was formulated as Escort XP; MAT28 as 50% SG; Milestone as 2SL; Arsenal PowerLine as 2SL; Accord XRT II as SL5.4; Krenite as SL4.

Test plots were established between row middles of one year old loblolly pine seedlings planted in a clearcut near Broken Bow (McCurtain County) OK.  Herbicides were applied using a backpack CO₂ aerial simulator to treatment plots 12-ft by 120-ft. 

Treatments were analyzed according to a randomized complete block design.  The treatment variable was percent
control.  At least 10 rootstocks of oak, winged elm, and all species were monitored in each treatment plot in each of 3 blocks.

Oak control ranged from 17% (check) to 80% (MAT28+Escort+Krenite+Arsenal AC+NIS 5.94+1.58+8.26+128+1%).  The least herbicidal control was 47% and achieved with Milestone+Arsenal Powerline+Accord+NIS (7+16+128+1%).  This is a range for herbicide treatments of 33%.  Statistical differences were detected between treated and untreated treatments.  Treatments 2, 5 and 8 were similar and better than other herbicide treatments that were all similar. 

Elm control ranged from 7% (check) to 95% (MAT28+Escort+Krenite+NIS 7.52+2+128+1%).  For herbicide treatments, the least control was recorded at 57% for (Milestone+Arsenal PowerLine+Accord XRT II+NIS 7+16+128+1%)
providing a range for herbicide treatments of 38%.  Significantly less control was observed for the Milestone+Arsenal Powerline+Accord+NIS (7+16+128+1%) treatment than other herbicide treatments.  Statistical differences were detected between treated and untreated treatments. 

When all woody species in plots were evaluated, control ranged from 6% (check) to 97% (MAT28+Escort+Krenite+NIS (7.52+2+128+1%).  Statistical differences were detected between treated and untreated treatments only. 

MAT28+Escort+Krenite+NIS (7.52+2+128+1%) provided numerically best control of elm, oak and all species. 

Directed spray applications are neede in areas where aerial or other forms of broadcast applications cannot be used. A total of seven tank mixtures were applied to understory hardwoods to test the efficacy of Mat-28 applied in combinations with metsulfuron and imazapyr. Principal hardwood species on the site were red oaks, post oak, persimmon, and red maple. All stems in plots were recored by species and heights prior to application and again at one and two years after treatment. Results will be presented on the efficacy of the various treatments for controlling the hardwoods o nthe site.

The purpose of this screening trial was to assess aminocyclopyrachlor and metsulfuron without and with imazapyr sprayed to wet as individual plant treatments.  Test rootstocks of unwanted red oaks (Quercus falcata, nigra, phellos) and yaupon (Ilex
vomitoria) were growing along the border of a loblolly pine stand near Moscow (Polk County) in East Texas.

Herbicides were applied on 17-Sep-12 and visually evaluated on 19-Sep-13 (1-YAT).  Test treatments were:  (1) MAT28+Escort+NIS (124+32+.5%), (2) MAT28+Escort+NIS (225+61+.5%), (3) MAT28+Escort+NIS (404+108+.5%), (4) MAT28+Escort+Imazapyr+NIS (87.2+23+79.3+.5%, (5) MAT28+Escort+Imazapyr+NIS (180+48+159+.5%), (6) MAT28+Escort+Imazapyr+NIS (346+92+320+.5%), (7) MAT28SL+Garlon 3A (.5%+.667%+.5%), (8) Capstone+Arsenal
PowerLine+Accord XRT II (5%+.5%+6%), and (9) untreated check.  The rates for all MAT28, Escort without/with
imazapyr are expressed in grams of material/100 liters.  The NIS was Induce.  Escort was formulated as Escort XP; imazapyr
as 75% WG; Arsenal PowerLine as 2 SL; MAT28 as 50% SG except for treatment 7 which was a 2 SL.

Treatment plots were approximately 30-ft by 120-ft. At least 10 rootstocks of red oaks and yaupon were treated and monitored in each plot.  Herbicides were applied on 17-Sep-12 using a backpack CO₂ sprayer, a single 8002VS nozzle and 20 PSI. Trees were measured for total height at the onset of the study and again for live height 1-YAT.  Values were used to compute percent control. Treatments were assigned according to a randomized complete block with three blocks.

Red oak control ranged from -15% (check) to 90% (Capstone+Arsenal PowerLine+Accord XRT II).  The Capstone treatment was
similar to MAT28+Escort+Imazapyr (346+92+320) and both better than other treatments.  Treatments MAT28+Escort+NIS
(225+61+.5), MAT28+Escort+ Imazapyr+NIS (87.2+23+79.3+.5%), MAT28+Escort+Imazapyr+NIS (180+48+159+.5%), and MAT28+Escort+Imazapyr+NIS (346+92+320+.5%) were similar and better than treatments MAT28+Escort+NIS (124+32+.5%), MAT28SL+Garlon 3A (.5%+.667%+.5%) and the untreated check.

Yaupon control ranged from-9% (check) to 79% (Capstone +Arsenal PowerLine+Accord XRT II).  The Capstone treatment provided best control.  Treatments MAT28+Escort+Imazapyr+NIS (346+92+320+.5%) and MAT28SL+Garlon 3A (.5%+.667%+.5%) exhibited intermediate control that was better than MAT28+Escort+NIS (225+61+.5), MAT28+Escort+NIS
(404+108+.5%), MAT28+Escort+Imazapyr+NIS (87.2+23+79.3+.5%), and MAT28+Escort+Imazapyr+NIS(180+48+159+.5%).  Least control was observed for MAT28+Escort+NIS (124+32+.5%) and the check.  Numerically, the Capstone treatment provided 2X the efficacy of the next best treatment.

The purpose of this screening trial was to assess aminocyclopyrachlor and metsulfuron mixed with imazapry and/or glyphosate for the control of unwanted trumpet creeper (Campsis radicans), greenbriar (Smilax glauca, rotundifolia), and Japanese honeysuckle (Lonicera japonica) vines growing on fences near Corrigan (Polk County) in East Texas. 

Test treatments (oz prod/ac) were:  (1) MAT28+Escort+NIS (7.5+2+1%), (2) MAT28+Escort+Arsenal+NIS (5.76+1.53+16+1%), (3) MAT28+Escort+Roundup +NIS (5.76+2+128+1%), (4) MAT28+Escort+Arsenal+Roundup+NIS
(5.76+1.53+16+128+1%), (5) MAT28+Escort +MSO (5.76+1.53+1%), (6) MAT28+Escort+Arsenal+MSO
(5.76+1.53+16+1%), (7) Surmount 2%+.5%MSO and (8) untreated check. The NIS was Induce and the MSO was by Helena.   

Treatment plots were 10-ft by 30-ft and clearly defined by completely severing vines between plots approximately 45 days before treatment.  Plots were visually blocked based on vine biomass-low, medium, and high.

Herbicides in a total volume of 20 gpa were applied on September 7, 2012 using a backpack CO₂ sprayer supporting a single Teejet XP Boomjet 10L. Treatments were randomly assigned to each of 3 blocks.  Visual evaluations for percent control were conducted on October 8, 2003, 1 YAT.  

Control of Japanese honeysuckle ranged from a low of 57% (Surmount) to a high of 89% (MAT28+Escort+MSO).  Control with
MAT28+Escort+MSO was best and different from Surmount which was different from the check.  Control by most treatments was 70-80%, perhaps due to the pair of herbicides-MAT28 and Escort, common to most treatments.

Greenbriar control was difficult with a low of 40% by (Surmount) to a high of 50% by both MAT28+Escort+Arsenal+Roundup
and MAT28+Escort+MSO.  Similar control was observed for all herbicide treatments which were better and different from
the check.

Control of trumpet creeper was statistically similar for all test treatments, including the untreated check.  Perhaps two items
contributed to this.  An examination of the GLD of five rootstocks in each plot revealed rep 1 rootstocks were significantly larger than those in reps 2 and 3.  Furthermore, evaluation day biomass on check plots was estimated to be 3X of that on application day.  Together, these suggest visual blocking (level=high) of trumpet creeper biomass on the fence failed.  That is coverage by the 20gpa application was probably inadequate, resulting in minimum control.

Numerically, MAT28+Escort+MSO control among all treatments was best for Japanese honeysuckle and green briar and intermediate for trumpet creeper.

Incorporation of a legume, such as red clover (Trifolium pratense), into grass pasture systems is advantageous for many reasons. However, susceptibility of red clover to herbicides commonly used in these systems limits its use; the University of Kentucky pasture weed management guide states that “In grass pastures interseeded with clover or other forage legumes, selective herbicide options are not available”. Since 2,4-D has long been a standard herbicide for pasture weed management, a 2,4-D tolerant red clover would expand the weed management options for interseeded pastures. Sufficient variability in red clover tolerance to 2,4-D was identified to suggest a 2,4-D tolerant red clover could be selected for. A Florida red clover line with improved 2,4-D tolerance was crossed to 2,4-D susceptible Kenland and the resulting population was field selected for 2,4-D tolerance (2006-2013). To assess progress towards 2,4-D tolerance, plants were grown in the greenhouse from seed collected after the 2010, 2011 and 2012 selections and treated with 0.0, 0.5, 1.0, 1.5, or 2.0 kg/ha of 2,4-D. Plant fresh weights and visual injury at two weeks post-treatment were compared to the similarly treated parent lines. Based on fresh weight reductions and injury ratings, the 2010 and 2011 lines had 2,4-D tolerance similar to the Florida parent. Thus, while our cross to the 2,4-D tolerant Florida line increased 2,4-D tolerance compared to Kenland, little additional gain had been made in 2,4-D tolerance beyond that of the Florida line, despite numerous rounds of selection for 2,4-D tolerance. In a second experiment, plants grown from 2012 seed had similar fresh weight reductions to plants grown from 2011 and 2010 seed following 2,4-D application. However, 2,4-D caused significantly less visual injury to plants grown from the 2012 seed than those grown from the 2010 and 2011 seed. The suggests that continued improvement in red clover 2,4-D tolerance may be possible. Ongoing work consists of additional selection for 2,4-D tolerance and examining the potential roles of altered 2,4-D absorption, translocation and metabolism in the increased 2,4-D tolerance.

Common milkweed (Asclepias syriaca L.), as the name implies, is a weed, and it can substantially lower corn yields.  Milkweed is also a host plant for several aphid species.  Aphid honeydew can be an important source of nutrition for beneficial insects in corn cropping systems including parasitoids, predators, and pollinators.  Weed scientists and entomologists usually work in separate spheres of plant protection and often may not view pests from the same perspective.  Here we present collaborative work between researchers in these two plant protection sub-disciplines with the aim of balancing the losses to corn yield due to weed competition with the benefits due to facilitation of beneficial insects. In turn, this provides a path for integrating this new balance into the decision-making process for milkweed control.  We build on the widely used decision-making concept in entomology of the ‘Economic Injury Level’ (EIL), which is defined as the level of damage to a crop that is equal in value to the cost of suppressive measures.  In other words, EIL = C/VD where, C= the cost of control, V= the value of the commodity, and D= damage or yield lost per unit pest density.  The EIL of milkweed infesting a corn crop can thus be easily determined from existing yield loss/weed density data and can be updated as commodity and control costs change. However, milkweed can also have beneficial impacts on pest management in corn systems by harboring aphids that are a food source for parasitoids such as the polyphagous wasps, Trichogramma spp. These tiny parasitoids lay their eggs in insect egg masses such as those of the European corn borer (ECB) (Ostrinia nubilalis Hübner), a major pest of corn.  Our data show that providing a food source such as aphids can increase the severity of parasitism to ECB eggs as well as increase the duration that eggs are parasitized relative to Trichogramma provided only plant leaves as a food source.  For example, our calculated EIL for milkweed when no ECB eggs are present is 1.6 stems/m², however, the EIL increases to 8.6 stems/m² when 1.5 ECB egg masses per plant are present. Thus, the presence of milkweed in a corn crop can provide a valuable system benefit that needs to be incorporated into the overall control decision-making process for this aggressive weed.  A broader accounting of costs and benefits and modified EIL can lead to more profitable decisions for single farm and/or fields.  If enough growers adopt a broader view such as presented here, we might be able to avoid or delay larger scale problems facing current cropping systems.

A tremendous amount of useful information exists on the demographic or spread dynamics of several important invasive species. Though these studies have furthered the wealth of knowledge of undesirable plant species, there has been no attempt to integrate the data from diverse studies into a meaningful framework to help understand invasions through the entire process of establishment to spread.  Additionally, the landscape matrix in which invasions manifest are typically assumed to be homogeneous and all equally susceptible to invasion, which is certainly not the case in reality. Realistic modeling of invasion dynamics must consider demographic rates, spread dynamics, and landscape heterogeneity and should be parameterized with empirical data.

We created the Invasive Dispersal & Establishment Risk model (InvDER) as a spatially explicit stochastic simulation model that characterizes the invasion process across a heterogeneous landscape at annual time steps.  By integrating geographic and land-use data, species demographic characteristics, species-specific dispersal kernels, and landscape-specific establishment probabilities this model is capable of more accurately characterizing the relative risk of establishment and spread of an invasive species.  The InvDER model is capable of both explaining past invasions using historical introduction accounts (i.e., hindcasting), but can also be used to simulate future invasions over any timeframe (i.e., forecasting). Currently the model is being used to describe the invasion of Miscanthus sinensis from the initial point and time of introduction and forecasted into the future.

            By manipulating each parameter (e.g., establishment probability, dispersal characteristics) within the model it is possible to run sensitivity analyses to better understand critical parameters required for successful invasion across a landscape.  Additionally, this model can identify critical threshold values within parameters that determine whether invasion will be successful.

            InvDER model results will lead to a more holistic understanding of the invasion process.  By better understanding the most critical components of invasion, land managers will be better able to discourage the establishment and success of invasive species across heterogeneous landscapes.

Herbicide resistance is a prime issue confronting the sustainability of row-crop production systems in the midsouthern United States. In particular, resistant Palmer amaranth (Amaranthus palmeri S. Wats) has been causing severe economic damages to cotton, corn, and soybean growers in this region. Best management practices have been developed and recommended for preventing and managing resistance in this species. However, successful adoption requires adequately educating growers, consultants, and other practitioners on the benefits of adopting and the penalties of not adopting certain management practices. There is a critical need for simple, user-friendly decision-support tools for demonstrating the value of best management practices and their impact on long-term weed population dynamics and economic outcomes. The Palmer amaranth management model (PAM), a Microsoft Excel® based tool, is being developed for this purpose, by adapting RIM (ryegrass integrated management), a decision-support system developed by the Australian Herbicide Resistance Initiative. The RIM model is being modified with the biological and economic parameters pertinent to Palmer amaranth in midsouthern cotton, corn, and soybean production systems. The key feature of this decision-support tool is that the users can build weed management programs and crop production practices that reflect their own operations (10-yr term). Users can define crop rotations, method of soil preparation, planting dates, herbicide options (pre-and post- emergence), and harvest weed seed control options, among others, that are specific to their system. Furthermore, the model allows for a direct comparison of user-built strategies for their impact on Palmer amaranth seedbank dynamics and on gross margins. This aspect of the model is critical, as long-term economic returns have been demonstrated to contribute to changing growers’ perceptions and subsequent adoption of practices.  For instance, the practitioner can evaluate how investing in a specific harvest weed seed control strategy can be beneficial over the long-run. Overall, it will be an excellent tool that will help weed managers make informed decisions regarding the integrated management of Palmer amaranth. 

First- and second-year seedbank emergence of 23 summer annual weed species common to U.S. corn production systems was studied. Field experiments were conducted between 1996 and 1999 at the Iowa State University Johnson Farm in Story County, Iowa. In the fall of 1996 and again in 1997, 1,000 seeds for most species were planted in plastic crates. Seedling emergence was counted weekly for a 2-yr period following seed burial (starting in early spring). Soil temperature and moisture at 2 cm depth were estimated using STM² software. The Weibull function was fit to cumulative emergence (%) on cumulative thermal time (TT), hydrothermal time (HTT), and day of year (DOY). To identify optimum base temperature (T_base) and base matric potential (ψ_base) for calculating TT or HTT, T_base and ψ_base values ranging from 2 to 17 C and −33 to −1,500 kPa, respectively, were evaluated for each species. The search for the optimal model for each species was based on the Akaike’s Information Criterion (AIC), whereas an extra penalty cost was added to HTT models. Overall, TT was a better descriptor of summer annual weed emergence than HTT. Based on the AIC criterion, for 17 species, the best fit of the model occurred using T_base ranging from 2 to 15 C with four species also responding to ψ_base = −750 kPa. For six species, a simple model using DOY resulted in the best fit. The AIC approach was a powerful tool for selecting adequate base threshold values and models to predict emergence of different weed species based on observational field studies. Adding penalty costs to AIC calculation allowed us to compare TT and HTT when both models behaved similarly. The results of this research provide robust information on the prediction of the time of summer annual weed emergence, which can be used to schedule weed and crop management.

The need to balance food production with conservation of biodiversity and ecosystem functions in agriculture has led to an interest among scientists, consumers, and producers in reducing the use of off-farm synthetic inputs. Thus, agroecologists have been called for further development of ecologically-based management practices, such as cover crops, which can enhance nutrient cycling through biological fixation and manage weed populations through competitive exclusion. One limitation to the implementation of cover crops is that they do not provide a direct source of revenue for producers. Integrating livestock grazing for cover crop termination could provide alternative sources of revenue in the form of grazing leases as well as food (meat) and fiber (wool, leather) production. We conducted a two year study investigating the effects of integrating sheep grazing for cover crop termination on plant community structure, weed pressure, and crop yield in an organically managed diversified vegetable market garden. In the 2012 growing season, we seeded six 10 m × 15 m plots with a cover crop of buckwheat, beet, sweetclover, and pea following a completely randomized design. We allowed the cover crop to grow to anthesis at which time it was terminated by either tractor mowing or sheep grazing. In 2013 we planted spinach, kohlrabi, and lettuce into each of these plots following a split-plot design. Metrics for plant community structure include plant biomass, plant density, species richness and Simpson's diversity index. These metrics and a multivariate analysis indicated that plant communities converged to a similar structure following cover crop termination, regardless of the approach used to terminate the cover crop. Furthermore, we found that weed density at emergence (p = 0.445), total weed biomass at anthesis (p = 0.241) and cash crop yield (p = 0.511) did not differ between grazed and mowed plots in the subsequent growing season. These results suggest that mowing and grazing represent similar ecological filters for the plant diversity of agroecosystems. Moreover, our results suggest that producers integrating sheep grazing should not experience declines in cash crop yields.

Strip tillage (ST) has several potential benefits in vegetable cropping systems compared to conventional full-width tillage (CT) including soil erosion protection, improved moisture retention, and reductions in fuel and labor costs.  However, adoption of ST has been constrained in part by concerns about its impacts on weeds.  In 2009 and 2010, two separate field trials (Trial 1 and Trial 2) were established in adjacent fields on sandy soils in SW Michigan to evaluate the long-term effects of tillage (CT vs ST), cover crops (none, rye or rye-vetch), and weed management intensity (high [HWM] or low [LWM]) on crop quality, yield and profitability in a rotational sequence of sweet corn, snap beans and winter squash.  Weeds were managed with a combination of herbicides, cultivation (CT only) and handweeding that reflected either standard grower practice, or reduced rates of herbicide application and no additional handweeding.  The germinable seedbank of summer annual weeds was estimated using a greenhouse emergence assay from soil samples taken in the spring of 2013. Profitability of each system under a range of assumptions was calculated based on experimental yields, combined with estimates of costs of production and prices for each crop.  Summer annual weed species that were sufficiently abundant in both trials to obtain meaningful seedbank data included Powell amaranth (AMAPO), common lambsquarters (CHEAL), large crabgrass (DIGSA) and carpetweed (MOLVE).  Compared to CT, ST resulted in an increase in the seedbank density of DIGSA, but had no effect on the AMAPO seedbank. For CHEAL, the effects of tillage were not detected under HWM.  Under LWM, ST resulted in higher CHEAL seedbank density compared to CT in Trial 1, but lower seedbank density in Trial 2.  Tillage had little or no effect on profitability of sweet corn or snap bean production.  For winter squash, ST resulted in higher profits in Trial 1 due primarily to a reduction in fruit rot, but lower profits in Trial 2, due to poor control of weeds—particularly DIGSA—in the absence of cultivation.   Compared to HWM, LWM resulted in an increase in total seebank density and a reduction in cumulative estimated profitability due to yield reductions from weed escapes, particularly in sweet corn and winter squash.  

In addition to the direct effects of resource competition, weeds can also impact crops by their effects on disease risk.  Identifying which weeds and other non-crop host species act as reservoirs for disease can improve and inform integrated pest management.  Accurate measurement of the basic processes that determine the effects of weeds on disease risk requires a basic understanding of these processes and plant pathology methodologies that often need to altered to be used in weed species.  The objective of this research is to determine the effects of weeds on the risk of disease caused by Wheat streak mosaic virus (WSMV), a mite-transmitted Potyvirus that infects cereal crops around the world.  Examples are given that emphasize the accurate measurement of susceptibility in non-crop plant species.  Previously, susceptibility of weeds and crops was estimated using mechanical inoculation of the virus, followed by enzyme-linked immunosorbent assay (ELISA) where a threshold of twice the optical density (OD) of uninfected wheat (2xWt) was used to identify infected plants.  The accuracy of the 2xWt threshold was compared to a species-specific (SS) thresholds based on the mean and variance in OD values in virus-free plants in six weed species. Purified WSMV was added to healthy tissue to create known virus-positive samples.  The SS thresholds had greater than 95% accuracy. The 2xWt threshold had much lower accuracy and in some cases incorrectly classified all virus-positive samples. In a separate experiment, infection rates in five grass species were compared following mite and mechanical inoculation. The relative susceptibility among species differed between inoculation methods. These results demonstrate that previous methods used to estimate the susceptibility of non-crop grasses to WSMV are not accurate. Accurate estimates can be obtained using mite-inoculation and improved methods for setting the viral detection thresholds in ELISA.

In strip tillage (ST), tillage is limited to strips where the crop will be planted and the rest of the soil remains undisturbed.  This contributes to soil conservation and improved soil quality in the untilled zone.  Weed management in ST vegetables is a challenge since inter-row cultivation is not an option and there are often few labeled herbicides for vegetables.  Greater information on the mechanisms by which tillage and cover crops influence weed population dynamics should be helpful for designing weed-suppressive reduced-tillage systems.  This research seeks to understand how Powell amaranth (Amaranthus powellii) emergence varies in ST cabbage (Brassica oleracea var. capitata) with and without cover crops and to evaluate the potential role of fungal pathogens, nitrogen and soil moisture in mediating cover crop and tillage effects on emergence.  Fully-factorial field trials were established in 2010, 2011, and 2012 with tillage (ST vs. CT), cover crop (oat (Avena sativa) or none) and crop competition (cabbage or no cabbage).  Powell amaranth seeds were sown both in the crop row (IR) and between rows (BR) immediately following tillage and again 9-13 days after tillage (DAT) at the time of cabbage transplanting (only data from seeds planted immediately after tillage are presented here).  In 2011 and 2012, three subplot treatments were included to elucidate mechanisms responsible for regulating emergence:  two rates of additional N (2011 only), two moisture levels (supplemental irrigation or plastic tent exclosures), and untreated vs fungicide-coated seeds.  Emerged seedlings were counted and pulled daily.  Soil temperature, moisture, and inorganic nitrogen content were assessed in all years.  In most cases, ST resulted in lower emergence than CT.  Emergence IR was consistently reduced in ST compared to CT.  BR emergence was also lower in ST than in CT in two of the three years (2010 and 2011), though only with oats in one of those years (2011).  The subplot treatments did not mediate this tillage effect in either zone, suggesting that neither fungal pathogens, nitrogen immobilization, nor soil moisture were responsible for this reduction.  In 2012, BR emergence was greater in ST than in CT in all subplot treatments except that in which water was withheld—suggesting that, contrary to expectations, CT may have offered moisture conservation benefits in this year.  In three of the four zone-by-year combinations examined, emergence following oats residue was increased by fungicide seed treatments.   Oats suppressed emergence of untreated seeds IR in 2012 and BR in 2011, but emergence of fungicide-treated seeds was similar with and without oat residue.  In 2011, IR emergence of fungicide-treated seeds was higher with oats residue than without, but emergence of untreated seeds was similar with and without oats.  These observations suggest that fungal pathogens may have played a role in reducing emergence in oat residue in these zone and years.  When water was withheld, oats also increased emergence IR in 2011, suggesting that oat residue may also have retained soil moisture in the driest conditions.   Emergence was not increased by nitrogen additions in either zone.

A better understanding of kochia (Kochia scoparia) seed dynamics is necessary for long term management of this increasingly troublesome weed.  The objectives of this research were to evaluate maternal environmental effects on kochia growth in the field and document its variability in dormancy and viability of seed produced within a single kochia plant in the greenhouse and field.  Field experiments were conducted in 2012 and 2013 at the Kansas State Agricultural Research Center in Hays, KS.  Two kochia seed populations (cropland and non-cropland) from Hays, KS were planted with and without five different crop canopies , in a split plot RCBD, to mimic a typical environment in which kochia is found in the Great Plains.  Different canopies included corn, soybean, grain sorghum, wheat stubble, and kochia plants.  Plant heights of kochia were taken weekly for the duration of the experiment.   A greenhouse experiment was conducted with the same two kochia seed populations from Hays, KS.  Kochia plants were grown and limited to self-pollination in 2012 and 2013.  For both field and greenhouse experiments initial flowering date was recorded and plants were harvested when seed was mature and divided into three equal parts (top, middle and bottom).  Seeds were removed from each section and a germination assessment was conducted with two treatments (off-plant and cold).  Subsets of approximately 50 seeds per plant section per petri dish with 10 mL water were placed in a growth chamber with 12 h light: 12 h dark at a temperature of 20:10 C and germination counts were taken for six weeks.  A viability assessment was then conducted two to three months following the germination assessment to test the viability of seeds remaining in the petri dishes.  For field grown kochia in 2012, there was a significant two-way interaction of crop canopy and presence of canopy on observed kochia plant heights at the end of the growing season.  Germination percentages from field grown kochia ranged between 77 and 100% and there are interactions with presence and absence of crop canopy and kochia biotype on percent germination.  Regardless of the year greenhouse grown kochia seed that came from the bottom third of the plant had greater germination percentages than the middle and top sections.  There was a maternal environmental effect on kochia seed characteristics with implications on future seedbank life.

Maternal environments may significantly impact embryo development, potentially altering the ability of offspring to colonize or reproduce within newly invaded or altered home environments. Here, we explored the consequences of manipulating summer, soil-moisture conditions (control rain, no rain, double rain) over two growing seasons for the life history and reproduction of two subsequent generations (F1, F2) of Raphanus raphanistrum, an agricultural weed. Offspring produced in relatively dry maternal environments were significantly smaller (reduced seed biomass, smaller size at reproduction) and less fecund regardless  of the environment in which offspring were grown. In contrast, increasingly moist maternal environments produced larger, more fecund offspring, especially when grown in novel environments. Our work reveals how weediness is not only a product of the population genetics of colonists and environmental characteristics of the invaded environment but may be also heavily influenced by the environmental characteristics of the source population.

Germination and Growth of Three Weed Species in Response to the Addition of Vinasse and Biochar to the Soil.  N. Soni¹, R.G. Leon*¹, J.E. Erickson², J.A. Ferrell², and Maria Silveira³. ¹University of Florida, Jay, FL 32565, ²University of Florida, Gainesville, FL 3261, ³University of Florida, Ona, FL 33865.

Vinasse and biochar are by-products of bioenergy production that can be incorporated into the soil to contribute to nutrient cycling and improve soil quality, but little is known about their effect on weed communities. The objectives of the present study were to determine the effects of vinasse and biochar on the germination and growth of palmer amaranth (Amaranthus palmeri), sicklepod (Senna obtusifolia) and southern crabgrass (Digitaria ciliaris). Laboratory germination and growth chamber experiments were conducted evaluating four rates of vinasse (0, 10, 20, and 40 L m^-2) and of biochar (0, 0.5, 2.5, and 12.5 kg m^-2) applied to a sandy loam soil. Overall, the addition of biochar to the soil did not affect the germination of any of the studied species. However, the highest biochar rate decreased growth (10-20% reduction) of sicklepod and southern crabgrass compared to the non-treated control. Vinasse had a negative effect on germination across all species. However, sicklepod germination was less affected by vinasse than the other two species. Vinasse application at 10 and 20 L m^-2 reduced germination of palmer amaranth and crabgrass by 47% and 17%, respectively, compared to the non-treated control, while sicklepod seeds exhibited no reduction when exposed to the same rates. When vinasse was added at 40 L m^-2, palmer amaranth, southern crabgrass and sicklepod germination was 9, 29 and 11 %, respectively while the germination in the non-treated control was 66, 98 and 55 %, for these species respectively. Germination reduction caused by vinasse was due to increased seed mortality. Although when applied at 40 L m^-2 vinasse negatively affected all growth for the three weed species, vinasse applied at 10 L m^-2 increased southern crabgrass and sicklepod biomass compared to the non-treated control. Our results indicated that the use of vinasse as a soil amendment could change weed community structure by differentially modifying germination and growth of weed species.

Control options for kochia can be developed and applied in a timely manner when time and duration of emergence and seed persistence in the field are known.  Since kochia has developed resistance to glyphosate herbicide in many parts of the central Great Plains, detailed studies of the basic biology are required.  The objectives were to 1) determine emergence patterns of kochia populations in crop and non-crop environments and 2) determine the length of time kochia seed from different emergence cohorts persist and are viable when placed at different depths in the seedbank in field sites across the central Great Plains.  In the spring of 2010 and 2011, quadrats (0.25 to 1-m²) were marked in which weekly observations of emergence were documented and emerged seedlings removed by hand or spayed with glyphosate.  Observations were initiated as early as March 1 and continued through July 30 or until no new emergence occurred.  In the subsequent fall of 2010 and 2011, seed were collected from these kochia populations from multiple emergence cohorts (cohort 1, 2, and 3) or from contrasting environments located next to the field experiment studying the emergence profiles of kochia.  Field sites included Colorado (Fort Collins [irrigated and dryland cropland, 3 cohorts each]), Kansas (Garden City [cropland, 3 cohorts, no-till and tilled fields], Hays [cropland, non-cropland], Manhattan [non-cropland], and Stockton [non-cropland, 3 cohorts]), Nebraska (Mitchell [non-cropland, 3 cohorts] and Scottsbluff [non-cropland, 3 cohorts]), Wyoming (Lingle [non-cropland, 2 cohorts]), and South Dakota [cropland].  Collected seed were sent to Manhattan, KS to be cleaned with sieves and an air column separator.  Wire-mesh packets, each containing 100 kochia seed, were made to be buried in the soil.  Packets were sent back to each original location.  A 15-cm diameter wire cage was placed such that soil could be put inside and packets placed at three different depths within each cage at 10 cm, 2.5 cm and 0 cm and a wire cap placed on top to keep packets in place and deter predation.  A total of 16 cages per kochia cohort or environment were established (four replications with four removal times).  Seed persistence was monitored for two years after burial in fall 2010 and again in fall 2011.  Four extractions occurred in March and October in each year.  Extracted packets were sent back to Manhattan KS.  Seed were removed from each packet and placed in a petri dish with filter paper and water in a growth chamber set at 20/10 C day / night temperatures and a 12-hr photoperiod.  Germinated seed were counted and removed for 30 days and a press test was used to determine any remaining viable seed at that time. 

Total season population densities varied among locations and years, ranging from four to almost 332,000 seedlings m^-2.  Earliest emergence was observed in Kansas soon after March 15, while first observations in Wyoming and Nebraska occurred around April 8.  Calendar dates shifted from March to April as study location moved from south to north, while the growing degree days required for 10% cumulative kochia emergence based on air temperatures since January 1 revealed that fewer GDD were needed for seeding emergence to occur when moving from south to north.  This may indicated lower critical temperatures for kochia to emerge in more northern latitudes.  In general, rate of kochia emergence was slower in cropland compared to non-cropland environments.  Between 70 and 95% of kochia seedlings had emerged between the first two observation dates (mid-March) across all locations.  Number of intact seed that were viable and ready to germinate was very high at the first extraction time (March, 4 mo after burial).  For example, at Nebraska 78% or more seed germinated from the extracted packets across cohorts and burial depths.  In an irrigated environment in Colorado, kochia viability ranged from 40 to 69% across on cohorts and in a dryland environment kochia viability ranged from 9 to 45%.  This first extraction date in March corresponded to time when kochia typically emerged across these locations.  Level of seed viability was influenced by cohort or burial depth at the first extraction and depended on geographic location but subsequent extractions (October yr1, March yr2, October yr2) had less than 5% viable seed left in the packets and in many cases, less than 1% viable seed.  Very early season weed control is needed to reduce the size of the first flush of kochia.  Secondary control strategies might include tillage to bury seed at 2.5 to 10 cm depths.  These seed would experience fatal germination (too far from surface to become established) and very low seed persistence was observed with buried seed.   

Weed seed germination patterns and soil seed bank depletion are important areas of research in weed science. Existing, artificial methods to quantify weed seed bank depletion have been shown to over-estimate seed germination and seed bank depletion. No method currently exists to quantify weed seed longevity in situ, because once seed is shed from the maternal plant to the soil, there is no reliable method to differentiate that seed from others already in the soil. The objective of this project was to develop a method for using stable carbon isotopes as tracers so we may better study the impact of land management practices on weed seed banks. Maternal jointed goatgrass plants were tagged under greenhouse and field conditions with a carbon isotope signature, and that signature was passed on to the seed that was produced. δ¹³C values for jointed goatgrass seed produced under ambient CO₂ conditions averaged -26.4, with a 99% confidence interval of -25.4 to -27.4. When maternal plants were exposed to 99-atom % ¹³CO2 for 2 hours during seed production, δ¹³C values in resulting seed was significantly increased. Due to these differences, plants exposed to a single pulse of ¹³CO2 produced seed that was easily and reliably traceable. This line of research may lead to a new understanding of how weed and crop management practices influence weed seed bank dynamics.

The majority of field crops grown in Canada are located in the three western prairie provinces of Alberta, Saskatchewan, and Manitoba. The most commonly used pesticides in this region are herbicides, indicating an opportunity for integrated weed management (IWM) to significantly increase the sustainability of farming systems. Much research has been performed, investigating the feasibility of various individual IWM practices in the Canadian prairies. Extension efforts to communicate this information are generally conducted by the provincial governments and industry. Two major changes have occurred in crop production systems since the 1990s: the adoption of no-till and herbicide-resistant (HR) canola (Brassica napus L.). While it has been shown that herbicide use can be reduced under no-till, our data indicated that growers using no-till tend to also use a greater amount of herbicides. Glyphosate- and imidazolinone-HR canola had lower environmental impact than non-HR canola; however, glufosinate-HR canola had similar herbicide use as non-HR canola. The adoption of other IWM strategies focusing on competitive crops, crop rotations, and preventative management has not been well documented. Our data shows that the adoption rates vary among provinces, possibly due to differing regional priorities. The adoption rate of most practices could be increased, particularly in the areas of crop competitiveness and sanitation. Given the increasing threat of HR weeds, it is important to convey to growers the benefits of adopting IWM practices on their farms.

In Asia, dry-seeded rice production systems are increasing because of water and labor shortages. Weeds, however, are the main biological constraint to the success of dry-seeded rice. Herbicides are used to manage weeds in dry-seeded rice, but the alone use of herbicides does not provide effective, season-long, and sustainable weed control. Therefore, interest has been increased in the application of cultural approaches in integrated weed management programs. Some of the approaches are the use of a stale seedbed technique, making the crop more competitive with cultivars having early vigor, use of cultivars capable of emerging under anaerobic conditions, use of narrow crop row spacing and high crop seeding rate, use of crop residue as mulches, and integration of herbicides with cultural practices to improve the sustainable use of herbicides. Improved weed management techniques in rice should focus on shifting the crop-weed balance in the favor of rice by integrating possible cultural, physical, and biological weed management tools with judicious use of herbicides. Together, these approaches may comprise the component of future integrated package to slow down the evolution of new weed problems in rice production. The improved weed management approaches should aim to reduce the weed seed bank before crop sowing and reduce weed emergence and weed growth in rice.

Is There a Future for Predicting the Competitive Ability of Cultivars? A Case Study of Wheat in the UK.

I. K. S. Andrew*, J. Storkey 1 ; Rothamsted Research, West Common, Harpenden, Hertfordshire, UK. , D. L. Sparkes 2; University of Nottingham, Sutton Bonington Campus, Sutton Bonington, Leicestershire, UK.

Cultivars of wheat vary in their ability to suppress weeds, but this has seen limited application to agriculture because of the current emphasis on cultivar yield potential and the efficacy of modern herbicides. However, there is renewed interest in the contribution of competitive cultivars in UK arable agriculture in response to increasing herbicide resistance and a lack of new modes of action.

Experiments have been conducted in outdoor containers (2011/12 and 2012/13) and in the field (2012/13) at Rothamsted Research, UK. Ten winter wheat cultivars were sown alongside black-grass (Alopecurus myosuroides), currently the most problematic species in UK arable agriculture because of widespread herbicide resistance. Numerous crop traits were measured throughout the growing season, including tillering, plant height and leaf parameters. Final biomass and seed return of black-grass were collected and correlated with cultivar traits. A particular emphasis was placed on ecophysiological traits at the earliest stages of growth, as the allocation of resources before the onset of competition has the potential to affect weed suppression without compromising yield in weed-free situations.

A number of early traits were identified as contributors to suppressive ability in the 2011/12 experiment, including early green area and early height. Not all of these traits were correlated with seed return or weed biomass in 2012/13 but this may have been partly due to an unusually cold winter that led to less variation between the cultivars.   Black-grass seed return is strongly correlated to its tiller production, and early stem extension may be favoured over tillering when the weed detects early warning signs of high light competition later in the season. The ranking of cultivars in terms of the suppression of black-grass was not the same for all cultivars across the two years of study, likely due to contrasting weather conditions.

This project aims to provide a predictive framework to identify competitive cultivars through simple measurements, and modelling employed to evaluate their contribution in integrative weed management strategies, in the context of variable weather.

Izzadora.andrew@rothamsted.ac.uk

In two decades since the initial recognition of the dramatic consequences of herbicide resistance, the challenge of developing additional non-chemical weed control strategies has proven formidable. Throughout this period in Australia the widespread evolution of multi-resistant annual ryegrass (Lolium rigidum Gaud.) populations was the driving force behind the development of harvest weed seed control (HWSC) systems. These systems, including chaff carts, narrow windrow burning, bale direct and Harrington seed destructor all target the weed seed bearing harvest residues, exploiting the biological weaknesses of annual weed species: seed retention at maturity and short-lived seed banks. Extensive field trials conducted across the Australian wheat-belt determined that HWSC systems were similarly effective in reducing annual ryegrass populations where in the absence of herbicides they reduced annual ryegrass populations by approximately 60%. However, a decade of monitoring in-crop weed densities in large WA cropping fields determined that the greatest impact of HWSC systems is realized when they are included in herbicide based weed management programs. In these fields effective herbicides resulted, on average, in a 90% reduction in annual ryegrass densities. However, the inclusion of HWSC systems led to an overall 99% decrease in plant numbers resulting in average plant densities of just 0.5 plants m^-2. Given the genetic diversity of weed populations infesting cropping systems, it is only under very low weed population scenarios that the preservation of weed control techniques can be achieved. The future of sustainable weed control is dependent on an attitude of zero-weed tolerance where weed populations are driven to the lowest achievable levels. The very low weed populations achieved by the inclusion of HWSC systems in herbicide based weed management programs is evidence of a sustainable weed control future for crop production systems.

Double Knock: Sequential Applications for Seed Set Control of Hard-to-control and Glyphosate Resistant Weeds of Sub-tropical Australia.

Michael J. Widderick^*1, Steven R. Walker²

¹Department of Agriculture, Fisheries and Forestry Queensland, Toowoomba, Australia, ²The University of Queensland, Toowoomba, Australia

In the sub-tropical grain region of Australia, which covers approximately a third of the broadacre cropping in Australia, both summer and winter crops are grown.  Between crops it is common to include a 6-12 month fallow (non-crop period) to conserve soil moisture to optimise yields of the following crop.  The majority of these fallows are zero-tilled and 100% reliant on glyphosate for weed management. 

As a result, there are five weed species in the region that have developed glyphosate-resistant populations, including junglerice (Echinochloa colona) and windmill grass (Chloris truncata). In addition, glyphosate tolerant and difficult to control weeds dominate the weed flora, particularly feather fingergrass (Chloris virgata) and annual sowthistle (Sonchus oleraceus).

A new tactic to control these problem weeds is the double knock, which is the sequential application of two different weed control tactics applied in such a way that the second tactic controls survivors of the first tactic. In this paper, double knock refers to the sequential application of either glyphosate or haloxyfop, followed by an application of paraquat. We investigated the efficacy of different double knock treatments and defined the optimal target weed size and interval between knocks for both glyphosate susceptible and resistant populations of junglerice and windmill grass and for populations of feather fingergrass and annual sowthistle.

Overall, the double knock treatments were highly effective (up to 100%) and were more effective than single applications in controlling the target weed species. The optimal interval between first and second knocks differed for different grass species and the herbicide used for the first knock, ranging from 1-21 days. The haloxyfop double knock was more robust than the traditional glyphosate double knock, especially for feather fingergrass. Glyphosate resistance status had little effect on the efficacy and timing of treatments.

A greater weed size decreased the efficacy of the double knock treatment for junglerice and annual sowthistle with optimal control achieved at early tillering and small (>5cm diameter) rosettes respectively. The addition of a residual herbicide as a mix partner in the first or second knock did not effect the efficacy of the double knock on junglerice, except for some antagonism when atrazine was applied with glyphosate in a first knock.

Our research defined the parameters required for optimal efficacy from the double knock tactic. The tactic is effective in stopping weed seed set on both glyphosate susceptible and resistant weed populations and is a useful tactic to assist in preventing herbicide resistance development and to stop its spread. While the haloxyfop double knock was highly effective, a shift toward using acetyl coA carboxylase herbicides in fallow poses a great risk for resistance developing toward this herbicide group if 100% seed set is not achieved. michael.widderick@daff.qld.gov.au

In western Canada, more dollars are spent on herbicides for wild oat than for any other weed.  Consequently, the most prevalent herbicide-resistant weed in western Canada is wild oat.  From 2010 to 2013, an experiment was conducted at eight Canadian sites (Lacombe, AB; Lethbridge, AB; Edmonton, AB; Scott, SK; Saskatoon, SK; Winnipeg, MB; New Liskeard, ON; Normandin, QC) to determine the impact of combining optimal cultural practices for wild oat management.  Treatments included higher than normal crop seeding rates, early-cut barley silage, summer annual (barley, canola, field pea, wheat), winter annual (winter wheat, winter triticale, fall rye), or perennial crops (alfalfa) in combination with 0, 50%, or full herbicide rates.  Wild oat density and biomass after some treatments that excluded wild oat herbicides for three years (2011 to 2013) were similar to those of the standard canola-wheat rotation at full herbicide rates each year.  At all locations, alfalfa and some double seeding rate winter cereal combinations with double seeding rate early-cut silage provided effective wild oat management without wild oat herbicides.  The latter treatments dramatically reduce selection pressure for wild oat resistance to herbicides and will help growers delay wild oat resistance evolution.  However, canola-wheat rotations are currently more profitable than other crops.  Few growers are willing to forgo short-term profit maximization for longer-term delays in wild oat resistance to herbicides – that could change!

With the rapid rise of glyphosate-resistant dicot weeds worldwide, solutions have been sought from a new generation of transgenic herbicide-resistant crops which are resistant to the auxin mimicking herbicides such as  2,4-D (2,4-dichlorophenoxyacetic acid) and dicamba. In order to maintain the effectiveness of the world’s oldest herbicide class, it is necessary to understand the development of auxin resistance in weeds. In this study we examined the evolutionary response of a small, well-characterised 2,4-D-susceptible population of wild radish (Raphanus raphanistrum) when exposed to recurrent sublethal doses of 2,4-D amine. Following four cycles of selection, the progeny of this initially susceptible population was shifted toward 2,4-D resistance, reaching a resistant to susceptible ratio (R/S) of 9.6 at the LD₅₀ level. As resistance shifts were increasing in scale with each selection and there was no reduction in plant fitness at the nil rate, it is expected that the maximum level of 2,4-D resistance achievable via low dose selection was not reached in four generations.

Along with 2,4-D resistance, there were robust increases in cross-resistance to the readily metabolisable acetolactate synthase (ALS)-inhibiting herbicides metosulam (3.5-fold), and chlorsulfuron (2.3-fold) but not imazamox. Conversely,  all selected generations were still found to be highly susceptible to the non-metabolisable ALS inhibitor sulfometuron-methyl,  indicates that the observed ALS cross resistance was non-target-site in nature. Treatment of the base and final 2,4-D selected populations with malathion, a potent inhibitor of cytochrome P450 mono-oxygenases, was found to effectively restore chlorsulfuron to full effectiveness, suggesting that the evolved cross-resistance in the selected population was endowed non target site, detoxification mechanism due to  increased P450 activity.

Due to multiple resistance to herbicides of several mechanisms of action, Phalaris minor (Littleseed canarygrass) has become the most dreaded weed of wheat in north-west India, which is the grain basket of the country. None of the recommended wheat herbicide is effective against the resistant (R) populations, though efficacy varies with herbicides depending on use its history in the field. No new herbicide is in the pipeline to take care of R populations, except pyroxasulfone. Trials were conducted to evaluate its efficacy at research farm of Agronomy department for two years (2011-12 and 2012-13); in the screen house (pot studies) against R and S (susceptible) populations and at resistance affected farmer’s fields. Bioassay studies were conducted by raising Gossipium hirsutum L. (cotton), Sorghum bicolor L. (sorghum) and Vigna radiata (L.) R. Wilczek (mung bean) after wheat harvest without disturbing soil at the research farm. Pyroxasulfone at 85, 102, 127.5 and 255 g PRE was compared with recommended wheat herbicides in a plot size of 9.5 x 2.5 m replicated thrice in RBD design. Wheat was planted on 2^nd Dec. 2011 and 7^th Dec. 2012 and harvested on 25^th April 2012 and 24^th April 2013. Graded doses of pyroxasulfone were compared with pendimethalin in the posts and 127.5 g/ha at farmer’s field. Both field and screen house studies revealed that pyroxasulfone 127.5 g/ha PRE provided good control of P. minor though efficacy was less on Avena ludoviciana. Pyroxasulfone was not effective against broadleaf weeds infesting the research field and resistance affected farmer’s field and need a mixture partner for effective control of mixed weed flora. Pyroxasulfone was effective against R populations of P. minor in the pot studies, but differences were perceptible among the R and S populations when lower rates were used; a warming that lower than recommended rates may have resistance evolution.  No residual pyhtotoxicity of pyroxasulfone at 127.5 and 255 g/ha was observed on cotton and sorghum when planted after wheat harvest; however, some suppression was observed in mung bean under high moisture conditions.

Oxyfluorfen for Fallow Bed Weed Control in Row Crops in the Mid-South USA – 2010 to 2013.  L.C. Walton, A.T.Ellis, R.A. Haygood, V.B. Langston, R.B. Lassiter, R.K. Mann; Dow AgroSciences, Indianapolis, IN

ABSTRACT

Oxyfluorfen (2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl) benzene), a diphenyl ether herbicide, was developed and first registered by Dow AgroSciences in 1979. Oxyfluorfen is a broad spectrum preemergence and postemergence-applied herbicide for use in a number of selected tree nut, vine, row crop and fallow bed cropping systems to control annual grasses and broadleaf weeds.

Goal® 2XL herbicide, one of Dow AgroSciences’ current U.S. formulations of oxyfluorfen, has been used extensively in fallow beds applied prior to planting corn, cotton or soybeans in select Mid South states for control or suppression of several key broadleaf weeds and grasses.  Based upon research conducted by Dow AgroSciences, Goal 2XL at 280 g ai/ha provides both preemergence and postemergence control and/or suppression of key weeds in fallow beds.

Key weeds controlled include henbit (Lamium amplexicaule), smartweed (Polygonum spp.), mustards (Brassica spp.), Carolina geranium (Geranium carolinianum) and pigweeds (Amaranthus spp.).  Prior research has revealed that horseweed (Conyza canadensis) and Italian ryegrass (Lolium multiflorum) have been suppressed with preemergence applications of Goal 2XL at 280 g ai/ha.

From 2010 through 2013, Dow AgroSciences conducted field research with key cooperators in the Southern U.S. with Goal® 2XL applied to fallow beds approximately 30 days prior to planting cotton and soybean.  These trials were conducted to measure the effect of application timing, compared to key commercial standards, on the control of major weeds, and the resulting impact on soybean and cotton tolerance.  The key broadleaf weeds evaluated included Palmer pigweed (Amaranthus palmeri), horseweed (Conyza canadensis) and morningglory (Ipomoea spp.).

The experimental design in all trials was a randomized complete block with four replications. Plot sizes ranged from approximately 13 ft. wide by 30 to 40 ft. in length. Treatments were applied with either a CO₂ backpack or small plot tractor sprayer calibrated to deliver 10 to 15 GPA.

Data from these trials indicated that Goal® 2XL herbicide at 280 g ai/ha tank-mixed with labeled rates of commercial standard burndown herbicides such as Liberty ^TM (glufosinate – 540 g ae/ha), Clarity ^TM (dicamba – 280 g ae/ha) and Roundup PowerMax ^TM (glyphosate – 870 g ae/ha) provided improved control of Palmer pigweed and morningglory species compared to burndown herbicides used alone at 3 to 5 weeks after application.  At 6 to 10 weeks after application, weed control declined with all treatments. Addition of Goal 2XL did not increase control of horseweed versus the burndown herbicides used alone. Goal® 2XL tank mixes caused minimal cotton and soybean injury when applied 30 days or more prior to planting.  

Goal^® 2XL provides another mode of action that broadens weed control spectrum and can contribute to improved management programs designed to reduce herbicide resistant weeds.

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

Goal 2XL is not registered for sale or use in all states.  Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state.  Always read and follow label directions.

Roundup^TM PowerMAX is a registered trademark of Monsanto Company

Liberty^TM  is a trademark of Bayer Crop Science

Clarity^TM  is a trademark of BASF Company

WEED CONTROL IN TOMATO (LYCOPERSICON ESCULENTUM Mill.) THROUGH

MULCHING AND HERBICIDES

Tamana Bakht and Ijaz Ahmad Khan

Department of Weed Science, The University of Agriculture Peshawar,

25130-Peshawar, Pakistan

Corresponding author’s email: tamannabakht@yahoo.com

Abstract

Experiment was conducted at the Agricultural Research Farm of the University of Agriculture, Peshawar during year 2012 to determine the impact of row spacing and weed management strategies on tomato.). Variety ‘Roma’ was planted on a plot size of 4.8m x 3m using a randomized complete block (RCB) design in split plot arrangement, having four replications. The experiment was laid out in a split plot design comprised of ten treatments in the subplots that included five mulches viz. white polyethylene, black polyethylene, wheat straw, newspaper and saw dust; three herbicide treatments i.e. fenoxaprop-p-ethyl, pendimethalin, s-metolachlor along with a hand weeding treatment and a weedy check. The data were recorded on weed density m^-2 at 20 days after treatments, plant height, fruit yield (kg ha^-1). All the studied parameters were significantly affected by the row spacing  and weed management treatments ; however, the interaction effects were non significant. The result showed that with increase in row spacing, of weed m^-2 of 3.39, 4.19 and 4.53 were recorded  for 40, 60 and 80 row spacing, respectively. The overall weed density m^-2 ranged between 3.24 to 4.30 m^-2. The maximum plant height of 62.44cm was recorded in weedy check and minimum 53.31cm plant height was observed in hand weeding treatments. As regards the fruit yield, a highest yield of 2.51 t ha^-1 was recorded at row spacing of 60 cm and the application of poly ethylene black plastic resulted in significantly highest fruit yield (4.04 t ha^-1).

Key words:  herbicides, mulching, row spacing, tomato, yield. 

Harvest weed seed control (HWSC) is an emerging tool that offers a timely weed control alternative, as chemical control of many weed species can no longer be guaranteed due to the widespread evolution of herbicide resistance. However, the high rates of weed control offered by HWSC technologies can potentially apply strong selection pressures on genetically diverse weed populations. One suggested mechanism of evasion of HWSC by weeds is the evolution of early flowering biotypes that are able to shed seed before harvest. This study demonstrates that a small population of wild radish (Raphanus raphanistrum) has the capacity to rapidly shift both the time and duration of flowering at a population level in response to selection for early or late flowering. However, initiation of flowering at the individual-plant level was only 11 days early following five generations of selection for early flowering, indicating that major shifts that could limit the effectiveness of HWSC are unlikely.  Along with shifts in flowering, concurrent shifts in plant biomass and height were recorded, which could impact the fitness of early flowering date-selected biotypes.

Two separate three year field experiments were conducted to evaluate:  1) the role of soil-inversion, cover crops and herbicide regimes for Amaranthus palmeri between-row (BR) and within-row (WR) management in glufosinate-resistant cotton and 2) the role of soil inversion, cover crops and spring tillage methods for Amaranthus palmeri BR and WR management in glufosinate-resistant cotton. In the first experiment, main plots were two soil inversion treatments: fall inversion tillage (IT) and non-inversion tillage (NIT). The subplots were three cover crop treatments: crimson clover, cereal rye and winter fallow; and sub subplots were four herbicide regimes: preemergence (PRE) alone, postemergence (POST) alone, PRE + POST and a no herbicide check (None). The PRE herbicide regime consisted of a single application of pendimethalin at 0.84 kg ae ha−1 plus fomesafen at 0.28 kg ai ha−1. The POST herbicide regime consisted of a single application of glufosinate at 0.60 kg ai ha−1 plus S-metolachlor at 0.54 kg ai ha−1 and the PRE + POST regime combined the prior two components. In the second experiment, the main plots were two soil-inversion treatments fall inversion tillage (IT) and non-inversion tillage (NIT). Subplots were three cover treatments: crimson clover, cereal rye or none (i.e., winter fallow); and the sub subplots were four secondary spring tillage methods: disking followed by (fb) cultivator (DCU), disking fb chisel plow (DCH), disking fb disking (DD) and no tillage (NT).  In the first experiment, at 2 weeks after planting (WAP) cotton, Amaranthus palmeri densities, both BR and WR, were reduced ≥90% following all cover crop treatments in the IT. In the NIT, crimson clover reduced Amaranthus palmeri densities >65% and 50% compared to winter fallow and cereal rye covers, respectively. At 6 WAP, the PRE and PRE + POST herbicide regimes in both IT and NIT reduced BR and WR Amaranthus palmeri densities >96% over the three years. Additionally, the BR density was reduced ≥59% in no-herbicide (None) following either cereal rye or crimson clover when compared to no-herbicide in the winter fallow. In IT, PRE, POST and PRE + POST herbicide regimes controlled Amaranthus palmeri >95% 6 WAP. In NIT, Amaranthus palmeri was controlled ≥79% in PRE and ≥95% in PRE + POST herbicide regimes over three years. POST herbicide regime following NIT was not very consistent. Averaged across three years, Amaranthus palmeri was controlled ≥94% in PRE and PRE + POST herbicide regimes regardless of cover crop. Herbicide regime effect on cotton yield was highly significant; the maximum cotton yield was produced by the PRE + POST herbicide regime. Averaged over three years, the PRE, POST and PRE + POST cotton yields were about three times higher than no herbicide regime. In a conservation tillage production system, a PRE + glufosinate POST herbicide based regime coupled with a cereal rye cover crop may effectively control Amaranthus palmeri and maximize cotton yields.  In the second experiment, averaged over years and soil inversion, the crimson clover produced maximum cover biomass (4390 kg ha−1) fb cereal rye (3698 kg ha−1) and winter fallow (777 kg ha−1). Two weeks after planting (WAP) and before the postemergence (POST) application, Amaranthus palmeri WR and BR density were two- and four-times less, respectively, in IT than NIT. Further, Amaranthus palmeri WR and BR density were reduced two-fold following crimson clover and cereal rye than following winter fallow at 2 WAP. Without IT, early season Amaranthus palmeri densities were 40% less following DCU, DCH and DD, when compared with IT. Following IT, no spring tillage method improved Amaranthus palmeri control. The timely application of glufosinate + S-metolachlor POST tank mixture greatly improved Amaranthus palmeri control in both IT and NIT systems. The highest cotton yields were obtained with DD following cereal rye (2251 kg ha−1), DD following crimson clover (2213 kg ha−1) and DD following winter fallow (2153 kg ha−1). On average, IT cotton yields (2133 kg ha−1) were 21% higher than NIT (1766 kg ha−1). Therefore, from an integrated weed management standpoint, an occasional fall IT could greatly reduce Amaranthus palmeri emergence on farms highly infested with glyphosate-resistant Palmer amaranth. In addition, a cereal rye or crimson clover cover crop can effectively reduce early season Amaranthus palmeri emergence in both IT and NIT systems. For effective and season-long control of Amaranthus palmeri, one or more POST applications of glufosinate + residual herbicide as tank mixture may be needed in a glufosinate-based cotton production system.

Downy brome (Bromus tectorum) control was evaluated using an integrated strategy that combined fire and herbicides.  We hypothesized that removing years of accumulated downy brome litter using a prescribed burn would improve herbicide efficacy and residual control.  Two field sites were established near Loveland, Colorado.  The prescribed burn treatment was designed as a split block and the herbicide applications were arranged in randomized complete blocks with four replications.  The prescribed burn was conducted in January 2012.  Herbicides were applied in March 2012 when downy brome was at the two to three leaf growth stage.  Imazapic, tebuthiuron and glyphosate were applied at 105 g ai ha^-1, 420 g ai ha^-1 and 280 g ae ha^-1, respectively.  Imazapic and tebuthiuron were also tank mixed with glyphosate at the same rates.  Aboveground plant biomass was collected by functional group in August of 2012 and 2013.  Burning alone did not reduce downy brome biomass the growing season following treatment (P=0.0889).  One possible explanation for this lack of treatment effect could be the severe drought in 2012.  In the second season there was less downy brome biomass within the burn only plots (P=0.0002).  There was no herbicide by burning interaction for downy brome control.  All herbicides decreased downy brome biomass by an average of 96% in 2012, while in 2013 all treatments except glyphosate alone decreased downy brome biomass.  There was more perennial grass biomass within the burned study area in the first and second seasons when averaged across herbicide treatments.  To evaluate the impact of downy brome residue on herbicide performance we evaluated imazapic and tebuthiuron herbicide sorption to field collected litter.  Each herbicide was applied to 15 g of litter at the same field study rates.  After seven days, simulated rain-off events of 5 mm and 15 mm were conducted.  At 5 mm of rainfall, 47% of imazapic and 38% of tebuthiuron was rinsed from the litter.  When rainfall was increased to 15 mm, 55% of imazapic and 49% of tebuthiuron was removed from the litter.  These results suggest that herbicide bioavailability may be negatively impacted by the amount of litter covering the soil surface.  Removing litter from the target area through an appropriately time prescribed burn combined with the use of soil residual herbicides can significantly decrease downy brome biomass for at least two growing seasons.  

A study was initiated in 2001 at four locations in western Canada to investigate an integrated approach to managing wild oat, the region’s worst weed. The study examined the effects of combining semi-dwarf or tall barley cultivars with normal or twice-normal barley seeding rates in either continuous barley or a barley–canola–barley–field pea–barley rotation. Herbicides were applied at 25, 50, and 100% of recommended rates. The first phase of the study was completed in 2005. This study reports on the second phase, which was continued for four more years at two of the locations, Beaverlodge and Fort Vermilion, AB, Canada. The objective was to determine the long-term impact of the treatments on wild oat seed in the soil seed bank. In 2009 (final year), the diverse rotation combined with the higher barley seeding rate (optimal cultural practice) resulted in higher barley yields and reduced wild oat biomass compared to continuous barley and lower barley seeding rate (suboptimal cultural practice). In contrast to the first phase, barley yield was higher with the semi-dwarf cultivar, and cultivar had no effect on wild oat management. Wild oat seed in the soil seed bank decreased with increasing herbicide rate, but amounts were often lower with the optimal cultural practice. For example, at the recommended herbicide rate at Beaverlodge, an approximate 40-fold reduction in wild oat seed occurred with the optimal compared to the suboptimal cultural practice. The results indicate that combining optimal cultural practices with herbicides can reduce the amount of wild oat seed in the soil seed bank to almost zero, and result in higher barley yields. The results have implications for mitigating the evolution of herbicide resistance in wild oat.

Energy beets (Beta vulgaris), which are sugar beets grown for non-food sources, are a potential winter cash crop for growers in the southeastern U.S. that are planted in the autumn and harvested in the spring, complementing current summer crop rotations.  The end-product from energy beets will be industrial sugars that can be processed into ethanol, biodegradable plastics, or some other non-food product.  Unlike other potential energy crops, beets have established varieties, agronomic practices, pesticides, and equipment.  The challenge will be to adopt those practices developed in other regions of the U.S. to a winter-based system in the southeastern U.S.  Two studies were conducted near Chula, GA at the USDA-ARS Jones Research Farm and University of Georgia Lang Research Farm to evaluate the yield potential of energy beets when harvested at different times during the spring and summer.  The first study included four non-Roundup Ready beet varieties (EGC-183, EGC-184, EGC-185, and ENC-115) planted 6 October 2011 and 1 November 2012 and the second study had five Roundup Ready varieties (ERR-303, ESR-304, ENR-305, ECR-306, and ERR-313) planted 1 November 2012.  Beets were planted in three rows spaced 45 cm apart on a standard bed with 183 cm wheel tracks.  The herbicide program included ethofumesate PPI in both studies.  In the non-Roundup Ready beets, two POST applications were made at 20 and 40 days after crop emergence and included the tank mixture of desmedipham, phenmedipham, triflusulfuron, clopyralid, and ethofumesate.  In the other study, glyphosate and clethedoim were applied at 30 and 60 days after planting, respectively.  Maintenance fungicides (azoxystrobin and prothioconazole) were applied as needed.  In the non-Roundup Ready beets, there were seven harvest times, initiated approximately 187 days after planting and continuing every three weeks through 318 days after planting.  In the Roundup Ready beets, harvest was initiated at 215 days after planting and continued every two weeks for a total of four harvests.  Data collection at harvest included: root biomass, foliar biomass, and an estimate of sugar content; roots were liquefied and total solids of the beet juice measured.  In the non-Roundup Ready beets, yields were lowest at the first harvest in 2012 (53 to 65 Mg/ha) and 2013 (46 to 64 Mg/ha) and nearly doubled within 6 to 9 weeks, as yields were maximized in mid-June at 250 days after planting in 2012 (103 to 129 Mg/ha) and 230 days after planting in 2013 (90 to 129 Mg/ha).  Plant pathogens (Sclerotium root rot and Cercospora leaf spot) were low at early harvests, increasing in intensity as air temperatures and humidity increased.  Beet yield declined in July and August (in response to increased disease severity), with final yields ranging from 70 to 110 Mg/ha in 2012 and 28 to 61 Mg/ha in 2013.  In the Roundup Ready beets study, yields were 113 Mg/ha during the first week of June and increased to 141 Mg/ha by the third week of July.  In both of these studies, winter beets harvested in the spring and early summer had yields that were at least equivalent to average yields in the Midwest U.S., and consistent with the average yields in the Imperial Valley of California 89 Mg/ha, where peak yields approach 142 Mg/ha.  Theoretical ethanol yields ranged from 4,760 to 6,730 l/ha (509 to 720 gal/a) at the first harvest and 9,315 to 13,350 l/ha (995 to 1,427 gal/a) in mid-June.  In the Roundup Ready beet varieties, the average theoretical ethanol yields over the four harvests ranged from 11,700 to 14,590 l/ha (1,250 to 1,560 gal/a).  There is high potential for successful beet production in the coastal plain of the southeastern U.S., providing an agronomic cash crop during the typical winter fallow period with minimal disruption to traditional summer cash crops.  Additional studies are underway to evaluate optimum autumn planting date for beets that maximizes yield and minimizes potential delays in planting of traditional summer crops in southern Georgia (i.e. corn, cotton, and peanut).

As university employees in agriculture, we commonly respond to grower requests when a field problem arises. Those responses are most often routine, but when they are not our training and experience do not prepare us for the consequences. Identification of regulated Roundup Ready® wheat in an Oregon wheat field in 2013 was one of those events. This event led the need to deal with: issues of confidentiality, sensitivity of the market, lack of transparency of government agencies, requests from lawyers for records, the public and private questioning of scientific credibility, and an onslaught of reporters.  The Roundup Ready wheat caused concern throughout the US wheat industry and immediate market response from overseas customers. The incident triggered an investigation by USDA-APHIS. Requests were filed under Freedom of Information Act for all records of OSU personnel pertaining to the event.  Inaccurate statements were made by the company about OSU testing procedures, capabilities and willingness to cooperate.  The most time consuming aspect was dealing with the media.  Our objective was to be as open and forthright as possible without comprising the investigation or releasing any information about the specific grower or site.   A case study based on this event could provide an excellent learning opportunity for graduate students as well as others in the agricultural community. 

Roundup Ready^® canola was first introduced in Canada in 1996 and was quickly adopted by Canadian canola growers along with other herbicide tolerant canola technologies (eg. glufosinate tolerant and imidazolinone tolerant).  The herbicide tolerant segment now makes up more than 99 percent of the Canadian canola market.  Since their introduction, no new herbicide tolerance biotechnology traits have been commercialized for canola in Canada.  In 2005, Monsanto Canada Inc. began field trials on a second generation glyphosate tolerance canola trait, TruFlex^™ Roundup Ready^® canola, which will be available to Canadian canola producers within the next few years.  TruFlex^™ Roundup Ready^® canola will offer tolerance to higher glyphosate application rates and later application timing compared to the original Roundup Ready^® canola technology by using an improved promoter sequence with the CP4 gene, resulting in greater gene expression and eliminating the need for the GOX metabolizing gene component.  TruFlex^™ Roundup Ready^® canola offers maximum yield potential from enhanced crop safety, improved control of difficult to control weeds and greater flexibility in application timing.  The technology allows for split applications of Roundup WeatherMAX^® herbicide up to 900 + 900 g ae ha^-1 applied from cotyledon to the first flower timing of the crop or a single application up to 1800 g ae ha^-1 from the cotyledon to the six leaf stage of the crop.  Crop safety observations show that TruFlex^™ Roundup Ready^® canola out yields original Roundup Ready^® canola by 5.9 to 6.1% when the crop is sprayed at 1350 g ae ha^-1 or 900 + 900 g ae ha^-1, respectively.  This translates to approximately a 3 bushel per acre yield advantage on crop safety alone.  Enhanced and more consistent control of dandelion (Taraxacum officinale), foxtail barley (Hordeum jubatum), wild buckwheat (Polygonum convolvulus) and cleavers (Galium aparine) are achieved with higher Roundup WeatherMAX^® herbicide rate applications.   Monsanto recommends integrated weed management including the use of diverse crop rotations and alternate modes of action wherever possible to help ensure the sustainability of glyphosate in Canadian cropping systems.

ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. Commercialization is dependent on multiple factors, including successful conclusion of the regulatory process in key export markets, and the registration of new canola varieties in Canada. The information presented herein is provided for educational purposes only, and is not and shall not be construed as an offer to sell until all necessary regulatory obligations are met.

Roundup Ready®, Roundup WeatherMAX® and TruFlex™ are trademarks of Monsanto Technology LLC, Monsanto Canada, Inc. licensee. ©2014 Monsanto Canada Inc.

Recent studies have shown that herbicide-resistant weeds are more likely to be annual species with high seed output than weeds in general and that resistance is overrepresented in the families Poaceae, Amaranthaceae, and Brassicaceae.  When trying to determine if herbicide-resistant weeds differ in their characteristics from weeds in general these studies have compared them to lists of weeds from books (in particular “World Weeds”- 1997 and “World’s Worst Weeds” -1977 by Holms et al.), or to large databases of weeds.  It is apparent that these two sources of comparison may not be optimal, as both contain significant numbers of weeds that are not represented in annual cropping systems, where the majority of herbicide use occurs and herbicide-resistant weeds have been selected.  Ideally we should draw comparison species from the same pool of weeds that the resistant weeds have been selected from.  One way of doing this is to compare resistant weeds that have evolved resistance in particular cropping systems (eg corn/soybean, rice, wheat, cotton) to the weeds listed on the herbicide labels for those cropping system.  The presentation will focus on such comparisons and how they differ from previous comparisons made using data from the books of Holms.  The results of the analysis will be posted on http://www.weedscience.org shortly after the presentation.

Harvest weed seed control strategies are routinely used in Australian grain production as a means of reducing the soil seedbank and selection for herbicide resistance.  With glyphosate-resistant Palmer amaranth currently infesting much of the soybean grown in the Southern U.S. and increasing expansion into the Midwestern and Northern states compounding already existing issues with waterhemp and redroot pigweed, similar strategies to those used in Australia may aid resistance management in U.S. crops.  A key consideration to the effectiveness of this strategy is weed seed retention at crop harvest.  A baseline survey was conducted to estimate the seed retention potential of Palmer amaranth, waterhemp, and redroot pigweed across nine major soybean producing states (Arkansas, Tennessee, Mississippi, Missouri, Indiana, Illinois, Iowa, Nebraska, and Wisconsin).  Soybean fields were visited in each state at crop maturity (crops ready to be harvested) and individual plants that had escaped control were collected along with a thin layer of soil and debris beneath the plant using a soft brush.  The plant samples were dried, threshed, and total seeds retained were counted. The soil samples collected underneath each plant were placed in individual trays in a greenhouse and seedling emergence was documented at weekly intervals for a month period. On average, >99% (97 to 99.9%) of the Palmer amaranth, waterhemp, and redroot pigweed seeds were retained in the plant at the time of soybean maturity, suggesting an excellent potential for employing harvest weed seed control strategies for managing these weeds. Additionally, research was conducted in a soybean production field in Kesier, AR, from 2011 through 2013 to assess the impact of a number of harvest weed seed control strategies on glyphosate-resistant Palmer amaranth in glyphosate-resistant and glufosinate-resistant soybean systems.  Specifically, narrow-windrow burning and chaff collection (collection and removal of chaff and straw behind the harvester) were compared to a standard practice of no additional management at harvest.  Additionally, a chaff cart was constructed and successfully tested in 2013, the first of which to be used for collecting weed seed in U.S. soybean.   Results from this research will be presented along with personal experiences with first-time testing and use of a chaff cart.    

Glyphosate-resistance (GR) in kochia was first confirmed in four populations in Kansas (>100 km apart) in 2007. Reports of poor kochia control with glyphosate increased over the next two years and escalated dramatically in 2010. Glyphosate dose response testing on greenhouse and outdoor grown progeny from seed of eight populations collected in fall 2010 tolerated three- to eleven-times more glyphosate compared to a known glyphosate-susceptible (GS) population. Also, individual plants from those eight populations accumulated less shikimate than plants from the GS population, thus confirming resistance to glyphosate. Additionally, 37 kochia populations from western Kansas and the Oklahoma Panhandle collected in fall 2012 showed varied response to glyphosate, from slightly elevated tolerance to resistance to 0.84 kg ae ha^-1 glyphosate. Further analysis suggested these populations were at different stages of resistance evolution. Levels of shikimate accumulation in leaf discs correlated well with the EPSPS gene copy across all glyphosate concentrations and incubation times (R² = 0.52 to 0.88). Plants with more copies of EPSPS gene generally accumulated less shikimate. Nominal differences in absorption and translocation of ¹⁴C-glyphosate observed between GR and GS populations likely did not contribute to differential response of these populations to glyphosate. An online survey of crop consultants revealed that western Kansas growers increased glyphosate use rate by more than 50% and increased frequency of glyphosate use from two applications per season prior to 2007 to three applications per season in 2011-2012. Most survey respondents reported presence of glyphosate-resistant (GR) kochia in at least in few fields, and half reported GR kochia in a majority of fields. Thus, together with the resistance confirmation studies, it was conservatively estimated that at least one-third of western Kansas kochia populations in 2012 had evolved resistance to glyphosate. Following the widespread distribution of GR kochia, growers decreased exclusive use of glyphosate and diversified weed management practices. Tank mixing dicamba with glyphosate was a common but often ineffective practice for controlling emerged kochia. Greenhouse testing showed low-level resistance to 0.42 kg ae ha^-1 dicamba in 20 of 32 of the same 2012 kochia populations tested for glyphosate resistance and mid-level or greater resistance to dicamba in six of the 32 populations. Additional testing is being conducted.   

In 2012, 18 yr after experiment establishment, wild oat (Avena fatua) from the spring wheat
phase of seven of nine alternative cropping systems (each of three input levels
applied to three levels of cropping diversity) were sampled and screened for
acetyl-CoA carboxylase (ACC)-inhibitor resistance. The frequency or level of resistance in wild oat was
greatest in the diversified annual grains systems (42-60% of individuals), and
lowest in the diversified annual perennial systems (< 3%). The results of
this study demonstrate the importance of perennial crops in slowing the
selection and evolution of resistance in this weed. Moreover, annual cropping
system diversity must be linked with herbicide mode-of-action diversity and
herbicide-use reduction.

Flurprimidol is a plant growth regulator that inhibits gibberellic acid synthesis.  In the turf industry, flurprimidol is used to both reduce the number of mowing events and to remove Poa annua from golf course greens.   Flurprimidol is labeled for use on many turf species grown in the transition zone, however, there is little to no information in the scientific literature regarding the behavior if flurprimidol in these turf grass species.  A laboratory experiment was conducted to study the root uptake and metabolism of flurprimidol in six grass species: creeping bentgrass (Agrostis stolonifera), common bermudagrass (Cynodon dactylon), tall fescue (Festuca arundinacea), perennial ryegrass (Lolium perenne), Kentucky bluegrass (Poa pratensis), and zoysia grass (Zoysia japonica).  Plants for the experiment were grown from individual tillers planted in a 50:50 mix of Maury silt loam and sand.  The tillers were grown in the greenhouse until of sufficient size for the studies.  Before the beginning of the study, plants were removed from the soil by washing and then the roots were placed into 0.25 strength Hoagland’s solution.  The plants were grown at 28C under fluorescent lighting in the laboratory for 7 days before being exposed to flurprimidol.  At the beginning of the experiment, the plants were transferred to covered test tubes containing 0.25 strength Hoagland’s solution and ¹⁴C- flurprimidol (200,000 DPM, 1.56 uM).  This concentration replicates an estimated soil concentration of flurprimidol following application.  The plants remained in the ¹⁴C-flurprimidol for 24 h after which they were transferred to fresh 0.25 strength Hoagland’s solution without flurprimidol.  The plants were harvested 0, 24, 72, and 120 h after the flurprimidol treatment. At harvest, the plants were sectioned into roots and shoots.  Radioactivity was extracted from each part, concentrated, and analyzed for the presence of flurprimidol and potential metabolites using HPLC.  The residue remaining after extraction was oxidized to quantify unextracted radioactivity.  Across all harvest times, the cool season grasses, creeping bentgrass, tall fescue, perennial ryegrass and Kentucky bluegrass, had between 24-27% of the radioactivity recovered within the root system and 73-76% within the shoots.  In contrast, the warm season grasses, common bermudagrass and zoysiagrass, had between 41% and 47% of the recovered radioactivity within the root system and 53% and 59% within the shoots. Regardless of turf species, plant tissue or harvest time, only parent flurprimidol was detected in the plant extracts.  An on-going study is examining the fate of flurprimidol after longer lengths of time.

RESPONSE OF 110 KENTUCKY BLUEGRASS VARIETIES TO METHIOZOLIN. S. S. Rana*¹, S. Askew², K. A. Venner², A. N. Smith²; ¹Virginia Polytechnic Institute and State University, Blacksburg, VA, ²Virginia Tech, Blacksburg, VA (254)

ABSTRACT

INVESTIGATING THE ROLE OF TYROSINE AMINOTRANFERASE INHIBITION ON POA ANNUA RESPONSE TO METHIOZOLIN. K. A. Venner*¹, E. Collakova¹, S. Koo², S. Askew¹; ¹Virginia Tech, Blacksburg, VA, ²Moghu Research Center, Daejeon, South Korea (255)

ABSTRACT

REMEDIATION OF INDAZIFLAM-TREATED TURF AREAS PRIOR TO OVERSEEDING PERENNIAL RYEGRASS. T. Gannon*¹, J. Brosnan², M. Jeffries¹; ¹North Carolina State University, Raleigh, NC, ²University of Tennessee, Knoxville, TN (256)

ABSTRACT

SOD HARVESTING INTERVALS OF FOUR WARM-SEASON GRASSES FOR HALOSULFURON AND SULFENTRAZONE. C. Johnston*, P. McCullough; University of Georgia, Griffin, GA (257)

ABSTRACT

TESTING OF A NOVEL 2,4-D FORMULATION WITH GLYPHOSATE AND ADJUVANTS FOR DRIFT REDUCTION TECHNOLOGY. G. K. Dahl*¹, L. C. Magidow², J. V. Gednalske³, L. J. Hennemann⁴, A. C. Clark⁴, W. Stepanie⁵; ¹Winfield Solutions LLC, St. Paul, MN, ²Winfield Solutions, River Falls, WI, ³Winfield Solutions LLC, River Falls, WI, ⁴Winfield Solutions, LLC, River Falls, WI, ⁵Winfield Solutions, LLC, St. Paul, MN (258)

ABSTRACT

USE OF COMPUTER VISION IN PRECISION FARMING. A. Rana*, J. Derr; Virginia Tech, Virginia Beach, VA (259)

ABSTRACT

VARIABILITY IN CATEGORIZATION OF SPRAY NOZZLES CLASSIFIED ACCORDING TO DROPLET DISTRIBUTION. S. Wedryk*¹, L. C. Magidow², G. K. Dahl³, E. Spandl⁴, J. V. Gednalske⁵; ¹Winfield Solutions LLC, Shoreview, MN, ²Winfield Solutions, River Falls, WI, ³Winfield Solutions LLC, St. Paul, MN, ⁴Winfield Solutions, LLC, Saint Paul, MN, ⁵Winfield Solutions LLC, River Falls, WI (260)

ABSTRACT

DICAMBA FORMULATION ADVANCEMENTS. J. Sandbrink, J. Travers, A. Macinnes*, J. Hemminghaus; Monsanto, St. Louis, MO (261)

ABSTRACT

DICAMBA DRIFT AS AFFECTED BY BEST MANAGEMENT PRACTICES WITH ENGENIA. D. B. Reynolds*¹, J. Cobb¹, J. B. Guice², W. E. Thomas²; ¹Mississippi State University, Mississippi State, MS, ²BASF Corporation, Research Triangle Park, NC (262)

ABSTRACT

VESICLE FORMING SURFACTANTS AS NOVEL SPRAY DRIFT CONTROL AGENTS IN HEBRICIDE APPLICATIONS. S. Sun*, L. Dempsey, Q. He; AkzoNobel Surface Chemistry, Brewster, NY (263)

ABSTRACT

MODIFIED CELLULOSE ETHERS AS DRIFT REDUCTION TECHNOLOGY. L. Dempsey*, S. Sun, Q. He; AkzoNobel Surface Chemistry, Brewster, NY (264)

ABSTRACT

EFFICACY OF DOWNY BROME (BROMUS TECTORUM) BIOCONTROL ON TARGET AND NON-TARGET SPECIES. K. A. Ehlert*, Z. Miller, J. M. Mangold, F. Menalled; Montana State University, Bozeman, MT (265)

ABSTRACT

THE POTENTIAL FOR BIOLOGICAL CONTROL OF SILVERY THREADMOSS WITH TWO FUNGAL PATHOGENS. S. Askew¹, A. R. Post*², D. S. McCall¹; ¹Virginia Tech, Blacksburg, VA, ²Oklahoma State University, Stillwater, OK (266)

ABSTRACT

EFFECT OF BURIAL DEPTH ON SEED FEEDING POTENTIAL OF GRANIVOROUS CARABID BEETLES. S. S. Kulkarni*¹, C. Willenborg², L. M. Dosdall¹; ¹University of Alberta, Edmonton, AB, ²University of Saskatchewan, Saskatoon, SK (267)

ABSTRACT

GRIT APPLICATION CONTROLS WEEDS IN ORGANIC CROP PRODUCTION. M. Erazo-Barradas*¹, S. A. Clay¹, F. Forcella²; ¹South Dakota State University, Brookings, SD, ²USDA, Morris, MN (268)

ABSTRACT

EVALUATION OF COTTON TOLERANCE AND YIELD RESPONSE TO VARIOUS RATES OF PRE APPLIED FOMESAFEN AT THREE LOCATIONS IN GEORGIA. X. Li*¹, T. L. Grey², B. H. Blanchett², W. K. Vencill¹; ¹University of Georgia, Athens, GA, ²University of Georgia, Tifton, GA (269)

ABSTRACT

DENITRIFICATION AND DENITRIFIER COMMUNITY STRUCTURE IN RESPONSE TO PREVIOUS CROP AND WEED MANAGEMENT INTENSITY. R. H. Gulden*¹, M. Tenuta¹, S. Mitchell², T. J. Daniell²; ¹University of Manitoba, Winnipeg, MB, ²James Hutton Institute, Dundee, Scotland (271)

ABSTRACT

COMPLEXITY - ADDRESSING THIS INVASIVE PLANT MANAGEMENT CHALLENGE IN BRITISH COLUMBIA. V. Miller*; BC Ministry of Forests, Lands and Natural Resource Operations, Nelson, BC (272)

ABSTRACT

PLANT INVASIONS IN MOUNTAIN ECOSYSTEMS OF THE ROCKIES. L. J. Rew*¹, B. J. Naylor², F. W. Pollnac¹, T. Seipel¹, K. Anderson³, C. G. Parks²; ¹Montana State University, Bozeman, MT, ²USDA Forest Service, La Grande, OR, ³San Diego Zoo, San Diego, CA (273)

ABSTRACT

ALL THE PRETTY PLANTS: HORTICULTURAL INTRODUCTIONS AND PROPAGULE PRESSURE IN THE PACIFIC NORTHWEST. S. Reichard*; University of Washington, Seattle, WA (274)

ABSTRACT

INVASIVE JAPANESE KNOTWEED IN THE PACIFIC NORTHWEST: ARE THEY ALL CLONES? S. L. Gillies*, A. Janmaat, A. Reid, A. Sum; University of the Fraser Valley, Abbotsford, BC (275)

ABSTRACT

REGIONAL DIFFERENCES IN JAPANESE KNOTWEED MANAGEMENT STRATEGIES ACROSS CANADA. T. G. Larsen*; East Kootenay Invasive Plant Council, Kimberley, BC (276)

ABSTRACT

INTEGRATED CONTROL STRATEGIES OF WILD CHERVIL AND OTHER PERENNIAL WEEDS IN THE PACIFIC NORTHWEST. T. W. Miller*; Washington State University, Mount Vernon, WA (277)

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AQUATIC PLANT INVASIONS AND THEIR MANAGEMENT IN THE PACIFIC NORTHWEST. M. D. Sytsma*; Portland State University, Portland, OR (278)

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REPULSING PLANT INVASIONS BY BIOLOGICAL CONTROL IN THE PACIFIC NORTHWEST &NDASH; SUCCESSES, FAILURES AND EVERYTHING BETWEEN. A. Janmaat*¹, J. H. Myers², L. Scott³; ¹University of the Fraser Valley, Abbotsford, BC, ²University of British Columbia, Vancouver, BC, ³Invasive Plant Program Coordinator for the Okanagan-Similkameen Regional District, Summerland, BC (279)

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OVERVIEW OF BIOPESTICIDES. S. O. Duke*; USDA-ARS, Oxford, MS (280)

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REGULATORY UPDATE OF THE IR-4 PROJECT BIOPESTICIDE AND ORGANIC SUPPORT PROGRAM. M. P. Braverman*, J. Baron, D. Kunkel, M. Arsenovic; IR-4, Rutgers University, Princeton, NJ (281)

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INSIGHTS ON OVERCOMING THE BIOHERBICIDE LAG. L. G. Boddy*, P. G. Marrone; Marrone Bio Innovations, Davis, CA (282)

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PLANT ESSENTIAL OILS AS BOTANICAL HERBICIDES. M. B. Isman*; University of British Columbia, Vancouver, BC (283)

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BIODIRECT(TM) AND MANAGING HERBICIDE RESISTANT AMARANTHS. D. Sammons*¹, D. Wang¹, S. Reiser¹, S. Navarro¹, N. Rana², G. Griffith¹; ¹Monsanto, St. Louis, MO, ²Monsanto, Chesterfield, MO (284)

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WHY THE LIMITED SUCCESS WITH MYCOHERBICIDES? A. Watson*; McGill University, Ste-Anne-de-Bellevue, QC (285)

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MANUKA OIL: NATURAL HPPD INHIBITORS. F. E. Dayan*, D. K. Owens; USDA-ARS, University, MS (286)

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THE DEVELOPMENT OF THE FUNGUS-DERIVED HERBICIDE, MEVALOCIDIN. C. Pearce*; Mycosynthetix, Inc., Hillsborough, NC (287)

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HPPD INHIBITOR RESISTANCE STEWARDSHIP.  THE PERSPECTIVE OF THE HRAC WORKING GROUP. G. D. Vail*¹, W. E. Thomas², P. Porpiglia³, W. J. Patzoldt⁴, R. Beffa⁵; ¹Syngenta Crop Protection, Greensboro, NC, ²BASF Corporation, Research Triangle Park, NC, ³AMVAC Chemical Corporation, Newport Beach, CA, ⁴DuPont Corp, Wilmington, DE, ⁵Bayer CropScience, Frankfurt am Main, Germany (288)

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ABSORPTION, TRANSLOCATION, AND METABOLISM OF GLYPHOSATE IN NICOSULFURON AND GLYPHOSATE-RESISTANT SORGHUM HALEPENSE. A. N. Smith*, S. Askew, S. Hagood; Virginia Tech, Blacksburg, VA (289)

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DISTRIBUTION OF MULTIPLE HERBICIDE RESISTANCE IN MISSOURI WATERHEMP POPULATIONS. J. Schultz*, E. B. Riley, J. D. Wait, K. W. Bradley; University of Missouri, Columbia, MO (290)

ABSTRACT

SOIL-RESIDUAL PROTOPORPHYRINOGEN OXIDASE (PPO)-INHIBITING HERBICIDES AND THE SELECTION FOR PPO-RESISTANT WATERHEMP (AMARANTHUS TUBERCULATUS). R. Wuerffel*, B. Young, J. Young, J. Matthews; Southern Illinois University, Carbondale, IL (291)

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MANAGEMENT OF GLYPHOSATE RESISTANT COMMON WATERHEMP IN TEXAS COTTON CULTURES. J. A. McGinty*¹, P. A. Baumann², G. D. Morgan¹, M. E. Matocha¹, L. M. Etheredge³; ¹Texas A&M AgriLife Extension, College Station, TX, ²Texas A&M University, College Station, TX, ³Monsanto, Llano, TX (292)

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TRIAZINE AND HPPD INHIBITORS-RESISTANT PALMER AMARANTH IN NEBRASKA. A. J. Jhala*¹, L. Sandell¹, N. Rana², G. Kruger³, S. Z. Knezevic⁴; ¹University of Nebraska, Lincoln, NE, ²Monsanto, Chesterfield, MO, ³University of Nebraska, North Platte, NE, ⁴University of Nebraska, Concord, NE (293)

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ASSESSMENT OF HPPD-INHIBITORS APPLIED ALONE OR IN COMBINATION WITH ATRAZINE FOR CONTROL OF GLYPHOSATE-RESISTANT PALMER AMARANTH (AMARANTHUS PALMERI) IN CORN. K. M. Vollmer*, H. P. Wilson, T. E. Hines; Virginia Tech, Painter, VA (294)

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EVALUATING TARGET-SITE MUTATIONS IN NICOSULFURON AND GLYPHOSATE-RESISTANT SORGHUM HALEPENSE. A. N. Smith*, G. Kim, J. H. Westwood, S. Hagood; Virginia Tech, Blacksburg, VA (295)

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RELATIVE COMPETITIVE ABILITIES OF WILD VS CULTIVATED SWITCHGRASS: ASSESSING INVASIVE POTENTIAL FOR MITIGATING BIOFUEL RISKS. D. J. Palik*¹, A. A. Snow¹, A. L. Stottlemyer¹, M. N. Miriti¹, E. A. Heaton²; ¹Ohio State University, Columbus, OH, ²Iowa State University, Ames, IA (296)

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WHY THE ANTHESIS-SILKING INTERVAL IS IMPORTANT IN UNDERSTANDING YIELD LOSSS IN MAIZE. C. J. Swanton*, V. H. Gonzalez, E. Lee, L. Lukens; University of Guelph, Guelph, ON (297)

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USING PERPENDICULAR CULTIVATION WITH A TINE-WEEDER TO IMPROVE IN-ROW WEED CONTROL IN ORGANIC PEANUT PRODUCTION. W. C. Johnson III*; USDA-ARS, Tifton, GA (298)

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IMPACT OF ROW SPACING, PLANT POPULATION AND HERBICIDE PROGRAM ON WEED CONTROL AND YIELD IN SORGHUM. T. E. Besancon*, W. J. Everman, R. Riar, R. Weisz; North Carolina State University, Raleigh, NC (299)

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MOVEMENT OF NITROGEN IN CORN AND WEEDS AS IMPACTED BY DIFFERENT NITROGEN SOURCES, RATES, AND WEED REMOVAL HEIGHT. A. M. Knight*, W. J. Everman, D. Jordan, R. Heiniger, T. J. Smyth; North Carolina State University, Raleigh, NC (300)

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VARIETY, PLANTING DATE AND HERBICIDES AFFECT FIBER AND OILSEED FLAX BIOMASS AND SEED YIELDS IN THE WILLAMETTE VALLEY OF OREGON. A. G. Hulting*, K. C. Roerig, D. W. Curtis, C. A. Mallory-Smith; Oregon State University, Corvallis, OR (301)

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COMPETITIVENESS OF VOLUNTEER CORN IN SUGARBEET. A. C. Harden*, C. L. Sprague; Michigan State University, East Lansing, MI (302)

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EVALUATION OF PENDIMETHALIN IN TRANSPLANTED LETTUCE. S. A. Fennimore*, J. S. Rachuy; University of California Davis, Salinas, CA (303)

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SWEET CORN CYP GENOTYPE RESPONSES TO HPPD- AND PSII-INHIBITOR TANKMIXES. E. Choe¹, M. M. Williams II*¹, R. A. Boydston², J. K. Pataky³; ¹USDA-ARS, Urbana, IL, ²USDA-ARS, Prosser, WA, ³University of Illinois, Urbana, IL (304)

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DO CULTIVAR AND SAFLUFENACIL APPLICATION TIMING INFLUENCE WEED CONTROL AND GROWTH RESPONSE OF SUCCULENT PEA? D. Robinson*, K. E. McNaughton; University of Guelph, Ridgetown, ON (305)

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EVALUATION OF POST EMERGENCE HERBICIDES FOR PURPLE NUTSEDGE CONTROL IN TOMATO AND BELL PEPPER. N. S. Boyd*; University of Florida, Wimauma, FL (306)

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EFFECT OF MOISTURE-LIMITING CONDITIONS ON UPTAKE AND TRANSLOCATION OF GLYPHOSATE DRIFT RATES ON PROCESSING TOMATO. K. E. McNaughton*, P. H. Sikkema, D. Robinson; University of Guelph, Ridgetown, ON (307)

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RESPONSE OF BROCCOLI AND PEPPER TO SIMULATED DRIFT OF 2,4-D AND DICAMBA. D. Doohan*, M. Mohseni-Moghadam; The Ohio State University, Wooster, OH (308)

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EFFECT OF MIXING SAND AND PINEBARK ON PREEMERGENCE HERBICIDE EFFICACY IN BLUEBERRY. P. J. Dittmar*; University of Florida, Gainesville, FL (309)

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EVALUATION OF HERBICIDES FOR FESCUE (FESTUCA SPP.) CONTROL IN WILD BLUEBERRY . G. L. Graham*; NBDAAF, Fredericton, NB (310)

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WEED CONTROL IN CONCORD GRAPE. C. J. Phillippo*, B. Zandstra; Michigan State University, East Lansing, MI (311)

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MAINTAINING RASPBERRY WEED FREE WITH CLOPYRALID AND OTHER HERBICIDES. B. Zandstra*, C. J. Phillippo; Michigan State University, East Lansing, MI (312)

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GENOMICS AND DOMESTICATION OF FIELD PENNYCRESS (THLASPI ARVENSE). K. M. Dorn*, D. Marks, D. Wyse; University of Minnesota, St Paul, MN (314)

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COMPARATIVE GROWTH OF KOCHIA (KOCHIA SCOPARIA) ACCESSIONS FROM NORTHERN AND CENTRAL GREAT PLAINS. A. V. Varanasi*, P. Jha, V. Kumar, S. Leland; Montana State University, Huntley, MT (315)

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FLOWERING BIOLOGY OF RED SORREL (RUMEX ACETOSELLA) IN LOWBUSH BLUEBERRY (VACCINIUM ANGUSTIFOLIUM) FIELDS. S. N. White*¹, N. S. Boyd², R. C. Van Acker³, C. J. Swanton³, S. Newmaster³; ¹University of Guelph, Truro, NS, ²Gulf Coast Research and Education Center, Wimauma, FL, ³University of Guelph, Guelph, ON (316)

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IMPACT OF TEMPERATURE INCREASE ON PHENOLOGY OF AMBROSIA ARTEMISIIFOLIA BIOTYPES. D. L. Benoit*; Agriculture and Agri-Food Canada, Saint-Jean-sur-Richelieu, QC (317)

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FALL PANICUM INTERFERENCE IN SUGARCANE. D. Odero*¹, N. Havranek¹, M. Duchrow²; ¹University of Florida, Belle Glade, FL, ²Sugar Cane Growers Cooperative of Florida, Belle Glade, FL (318)

ABSTRACT

PAST AND FUTURE ROLE OF WILDFIRE, HUMANS AND CLIMATE IN NONINDIGENOUS PLANT INVASIONS. B. D. Maxwell*¹, K. Taylor¹, T. Brummer², L. J. Rew¹, M. Lavin¹, A. Pauchard³, D. Peltzer⁴; ¹Montana State University, Bozeman, MT, ²Lincoln University, Lincoln, New Zealand, ³University of Concepcion, Concepcion, Chile, ⁴Landcare, Lincoln, New Zealand (319)

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THE ABUNDANCE OF BROMUS TECTORUM IN RESPONSE TO WILDFIRE AND FIRE SUPPRESSION. T. Seipel*, E. A. Lehnhoff, L. J. Rew; Montana State University, Bozeman, MT (320)

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ECOLOGY, BIOLOGY AND CONTROL OF SOME EXOTIC - INVASIVE WEEDS IN COASTAL FORESTS OF BRITISH COLUMBIA. R. R. Prasad*; Pacific Forestry Centre, Victoria, BC (321)

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PLANT COMMUNITY RESILIENCE TO DISTURBANCE AND LINARIA VULGARIS INVASION ACROSS AN ENVIRONMENTAL GRADIENT. E. A. Lehnhoff*, B. D. Maxwell, L. J. Rew; Montana State University, Bozeman, MT (322)

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NOVEL BIOENERGY CROPS: SUSTAINABLE ENERGY OR INVADERS IN WAITING. L. L. Smith*, J. N. Barney; Virginia Tech, Blacksburg, VA (323)

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ROLE OF CARBON AMENDMENTS IN REVERSING NICHE CONSTRUCTION IN INVADED ECOSYSTEMS: A CASE STUDY WITH POLYGONUM CUSPIDATUM  (JAPANESE KNOTWEED). V. Suseela*¹, P. Alpert², N. Tharayil¹; ¹Clemson University, Clemson, SC, ²University of Massachusetts, Amherst, MA (324)

ABSTRACT

AN INTRODUCTION TO THE REDUCED-TILLAGE ORGANIC SYSTEMS EXPERIMENT (ROSE). W. Curran*¹, M. Dempsey¹, C. L. Keene², S. Mirsky³, M. Ryan⁴, B. Scott⁵, M. VanGessel⁵, L. Young³; ¹Penn State University, University Park, PA, ²Penn State University, State College, PA, ³USDA-ARS, Beltsville, MD, ⁴Cornell University, Ithaca, NY, ⁵University of Delaware, Georgetown, DE (325)

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WEED MANAGEMENT IN ROSE: THE POWER OF AVOIDANCE, SUPPRESSION, AND SUPPLEMENTAL CONTROL TACTICS. M. A. Dempsey*¹, M. Ryan², C. L. Keene³, W. Curran¹, S. Mirsky⁴, M. VanGessel⁵; ¹Penn State University, University Park, PA, ²Cornell University, Ithaca, NY, ³Penn State University, State College, PA, ⁴USDA-ARS, Beltsville, MD, ⁵University of Delaware, Georgetown, DE (326)

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CORN, SOYBEAN, AND WHEAT PERFORMANCE IN THE ROSE. C. L. Keene*¹, M. A. Dempsey², W. Curran², S. Mirsky³, M. Ryan⁴, M. VanGessel⁵; ¹Penn State University, State College, PA, ²Penn State University, University Park, PA, ³USDA-ARS, Beltsville, MD, ⁴Cornell University, Ithaca, NY, ⁵University of Delaware, Georgetown, DE (327)

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COVER CROP MANAGEMENT IN THE ROSE: THE GOOD, THE BAD, AND THE WEEDY. M. VanGessel*¹, C. L. Keene², W. Curran³, M. A. Dempsey³, S. Mirsky⁴, M. Ryan⁵, B. Scott¹; ¹University of Delaware, Georgetown, DE, ²Penn State University, State College, PA, ³Penn State University, University Park, PA, ⁴USDA-ARS, Beltsville, MD, ⁵Cornell University, Ithaca, NY (328)

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ENGINEERING SOLUTIONS TO IMPROVE THE BIOLOGY: MAKING COVER CROP-BASED NO-TILL CROP PRODUCTION WORK. S. Mirsky*¹, W. Curran², M. A. Dempsey², C. L. Keene³, M. Ryan⁴, M. VanGessel⁵, L. Young⁶; ¹USDA-ARS, Beltsville, MD, ²Penn State University, University Park, PA, ³Penn State University, State College, PA, ⁴Cornell University, Ithaca, NY, ⁵University of Delaware, Georgetown, DE, ⁶USDA, ARS, SASL, Beltsville, MD (329)

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PUTTING THE PIECES TOGETHER: REGIONAL RECOMMENDATIONS FROM THE ROSE. M. Ryan*¹, W. Curran², M. A. Dempsey², C. L. Keene³, S. Mirsky⁴, M. J. VanGessel⁵; ¹Cornell University, Ithaca, NY, ²Penn State University, University Park, PA, ³Penn State University, State College, PA, ⁴USDA-ARS, Beltsville, MD, ⁵University of Delaware, Georgetown, DE (330)

ABSTRACT

LONG TERM MANAGEMENT OF CANADA THISTLE (CIRSIUM ARVENSE) IN A NO-TILL CROPPING SYSTEM. W. E. May*¹, L. T. Juras², K. L. Sasford³, F. A. Holm³; ¹Agriculture and Agri-Food Canada, Indian Head, SK, ²Dow AgroSciences Canada Inc., Saskatoon, SK, ³University of Saskatchewan, Saskatoon, SK (331)

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PERFORMANCE OF PRE-EMERGENCE HERBICIDES FOR THE CONTROL OF RIGID RYEGRASS (LOLIUM RIGIDUM) IN ZERO-TILL WHEAT. S. Kleemann, C. Preston, G. S. Gill*; University of Adelaide, Adelaide, Australia (332)

ABSTRACT

BENEFITS AND ECONOMICS OF  “THE CRITICAL PERIOD OF COMPETITIONâ€� AND “THE ZEROSEED THRESHOLDâ€� WEED MANAGEMENT STRATEGIES FOR TRANSITIONING TO ORGANIC FARMING. M. Mohseni-Moghadam*¹, D. Doohan¹, K. Amisi²; ¹OSU-OARDC, Wooster, OH, ²Grand Valley State University, Allendale, MI (333)

ABSTRACT

ZONE TILLAGE AND COVER CROP SPATIAL ARRANGEMENT EFFECTS ON WEED EMERGENCE AND COMPETITION IN ORGANIC SWEET CORN PRODUCTION. C. J. Lowry*, D. C. Brainard; Michigan State University, East Lansing, MI (334)

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NO-HERBICIDE NO-TILL SOYBEAN IN THE NORTHEASTERN UNITED STATES. J. Liebert*, M. Ryan; Cornell University, Ithaca, NY (335)

ABSTRACT

MERITS OF COVER CROP MIXTURES AND ALTERNATIVE TERMINATION METHODS IN ORGANIC CROPPING SYSTEMS. R. E. Blackshaw*¹, K. Podolsky², M. Entz², S. Shirtliffe³; ¹Agriculture and Agri-Food Canada, Lethbridge, AB, ²University of Manitoba, Winnipeg, MB, ³University of Saskatchewan, Saskatoon, SK (336)

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LIVING MULCHES WITH AND WITHOUT HERBICIDES TO CONTROL ANNUAL GRASSES IN SWEET CORN (ZEA MAYS). R. E. Nurse*¹, R. Mensah², D. Robinson³, G. Leroux⁴; ¹Agriculture and Agri-Food Canada, Harrow, ON, ²Laval University, Quebec, QC, ³University of Guelph, Ridgetown, ON, ⁴Universite Laval, Quebec, QC (337)

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CHANGES IN WEED FLORA AND ITS MANAGEMENT IN DIRECT SEEDED RICE IN NORTH WESTERN INDIA. A. Kumar¹, D. Yadav*², G. S. Gill³; ¹CCS Haryana Agricultural University, Hisar, India, ²CCS Haryana Agricultural University, Karnal, India, ³University of Adelaide, Adelaide, Australia (338)

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MANAGEMENT OF COMPLEX WEED FLORA IN DIRECT SEEDED RICE. M. S. Bhullar*¹, S. Kaur¹, T. Kaur¹, S. Kumar¹, G. S. Gill²; ¹Punjab Agricultural University, Ludhiana, India, ²University of Adelaide, Adelaide, Australia (339)

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A BRIEF HISTORY OF THE PARALLEL EVOLUTION OF HERBICIDE RESISTANCE AND RELATED INDUSTRY EFFORTS. C. Gerwick*; Dow AgroSciences, Indianapolis, IN (340)

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ECONOMIC DRIVERS FOR NEW TECHNOLOGIES AND SUSTAINABLE WEED MANAGEMENT. D. Palmer*; Dow AgroSciences, Indianapolis, IN (341)

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COLLABORATIONS BETWEEN INDUSTRY AND REGULATORY AGENCIES TO ADDRESS RESISTANCE. B. Chism*; US EPA, Washington, DC (342)

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COLLABORATIONS BETWEEN INDUSTRY AND UNIVERSITY EXTENSION TO ADDRESS RESISTANCE. C. L. Sprague*; Michigan State University, East Lansing, MI (343)

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STEWARDSHIP AND HOW IT AFFECTS RESISTANCE MANAGEMENT. B. Glenn*¹, S. McLallen²; ¹CropLife America, Washington, DC, ²CropLife Foundation, Washington, DC (344)

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GLOBAL HERBICIDE RESISTANCE ACTION COMMITTEE - INDUSTRY COLLABORATION TO ADDRESS HERBICIDE RESISTANCE. J. K. Soteres*; Monsanto, St. Louis, MO (345)

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PANEL DISCUSSION - TECHNOLOGICAL ADVANCEMENTS IN WEED CONTROL AND THE PART THEY PLAY IN ADDRESSING HERBICIDE RESISTANCE. M. A. Peterson*¹, B. R. Miller², R. Cole³, A. Cotie⁴; ¹Dow AgroSciences, West Lafayette, IN, ²Syngenta, Minnetonka, MN, ³Monsanto, St. Louis, MO, ⁴Bayer CropScience, Research Triangle Park, NC (346)

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CORN AND ITALIAN RYEGRASS COMPETITION. V. K. Nandula*; USDA-ARS, Stoneville, MS (347)

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WEED DYNAMICS AND PRODUCTIVITY OF WINTER MAIZE + POTATO INTERCROPPING SYSTEM AS INFLUENCED BY DIFFERENT WEED MANAGEMENT STRATEGIES IN SHIWALIK FOOT-HILLS OF NORTH-WEST HIMALAYAS. A. K. Kumar*, J. K. Kumar, B. C. Sharma, P. K. Kour; University of Agricultural Sciences and Technology, Jammu, India (348)

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MANAGING POKEWEED IN PENNSYLVANIA NO-TILL CORN AND SOYBEAN FIELDS. K. M. Patches*, W. Curran; Penn State University, University Park, PA (349)

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CROP RESPONSE TO DICAMBA APPLICATIONS ON  SOYBEAN EVENT MON 87708. P. C. Feng*; Monsanto, Saint Louis, MO (350)

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PERFORMANCE OF ENGENIA^TM HERBICIDE PROGRAMS IN DICAMBA TOLERANT CROPS. J. Frihauf*, S. Bowe, L. Bozeman; BASF Corporation, Research Triangle Park, NC (351)

ABSTRACT

USE OF PROPER APPLICATION TECHNIQUES TO MITIGATE OFF-TARGET MOVEMENT OF GLYPHOSATE + DICAMBA DURING SOYBEAN REPRODUCTIVE DEVELOPMENT. J. K. Norsworthy*¹, L. Steckel², D. B. Reynolds³, T. Irby⁴, T. Barber⁵, A. Mills⁶, R. Montgomery⁷, J. Sandbrink⁸, J. Travers⁸, K. Remund⁸; ¹University of Arkansas, Fayetteville, AR, ²University of Tennessee, Jackson, TN, ³Mississippi State University, Mississippi State, MS, ⁴Mississippi State University, Starkeville, MS, ⁵University of Arkansas, Lonoke, AR, ⁶Monsanto, Scott, MS, ⁷Monsanto, Jackson, AR, ⁸Monsanto, St. Louis, MO (352)

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STEWARDSHIP OF ENGENIA^TM HERBICIDE. W. E. Thomas*¹, L. L. Bozeman², S. Bowe¹; ¹BASF Corporation, Research Triangle Park, NC, ²BASF, Raleigh, NC (353)

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ENLIST WEED CONTROL SYSTEM FOR CANADA. A. W. MacRae*¹, A. McFadden²; ¹Dow AgroSciences Canada, Winnipeg, MB, ²Dow AgroSciences Canada Inc, Guelph, ON (354)

ABSTRACT

DRIFT AND TANK CONTAMINATION OF 2,4-D IN NON-TOLERANT COTTON. M. R. Manuchehri*¹, P. A. Dotray², T. S. Morris³, J. Keeling³, P. A. Baumann⁴, G. D. Morgan⁵; ¹Texas Tech Univ, Lubbock, TX, ²Texas Tech Univ., Texas A&M AgriLife Research and Extension, Lubbock, TX, ³Texas A&M AgriLife Research, Lubbock, TX, ⁴Texas A&M University, College Station, TX, ⁵Texas A&M AgriLife Extension, College Station, TX (355)

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METABOLIC FATE OF 2,4-D IN ENLIST SOYBEANS. J. J. Skelton*¹, D. Simpson², A. V. Lygin³, D. E. Riechers³; ¹University of Illinois, Champaign, IL, ²Dow AgroSciences, Indianapolis, IN, ³University of Illinois, Urbana, IL (356)

ABSTRACT

PEANUT INJURY AND YIELD REDUCTION IN RESPONSE TO SIMUALTED 2,4-D AND DICAMBA DRIFT AT TWO GROWTH STAGES. R. G. Leon¹, B. J. Brecke*¹, J. A. Ferrell²; ¹University of Florida, Jay, FL, ²University of Florida, Gainesville, FL (357)

ABSTRACT

AQUATIC AND RIPARIAN WEED PROBLEMS IN BRAZIL: RESEARCH AND MANAGEMENT OPPORTUNITIES. L. Anderson*¹, D. Matos²; ¹Waterweed Solutions, Inverness, CA, ²Ecologia e Conservacao Depto de Hidrobiologia, UFSCar, Brazil (358)

ABSTRACT

HERBICIDE TRIALS FOR MANAGEMENT OF FLOWERING RUSH IN MINNESOTA. J. D. Madsen*, B. Sartain, G. Turnage; Mississippi State University, Mississippi State, MS (359)

ABSTRACT

METABOLIC PROFILES OF THE SUBMERSED AQUATIC WEED HYDRILLA VERTICILLATA TREATED ALONE AND IN COMBINATION WITH ALS-INHIBITING HERBICIDES AND ENDOTHALL. M. A. Heilman*¹, S. T. Meadows², R. J. Richardson², J. D. Burton²; ¹SePRO Corporation, Carmel, IN, ²North Carolina State University, Raleigh, NC (360)

ABSTRACT

FIELD AND MESOCOSM EVALUATIONS OF GRANULAR HERBICIDE AND PRE-EMERGENT USE PATTERNS FOR CONTROL OF FLOWERING RUSH (BUTOMUS UMBELLATUS). A. Z. Skibo*¹, M. A. Heilman²; ¹SePRO Corporation, Fort Collins, CO, ²SePRO Corporation, Carmel, IN (362)

ABSTRACT

NATIVE PRAIRIE FUNCTIONAL GROUPS TO RESIST INVASION BY CIRSIUM ARVENSE. R. L. Becker*¹, M. J. Haar², L. D. Klossner³; ¹University of Minnesota, St. Paul, MN, ²National Park Service, Interior, SD, ³University of Minnesota, Lamberton, MN (363)

ABSTRACT

CURRENT TRENDS OF INVASIVE WEED SPECIES IN GREATER-HIMALAYAN REGION. A. K. Kumar*, J. K. Kumar, B. C. Sharma, N. S. Sharma; University of Agricultural Sciences and Technology, Jammu, India (364)

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SEED PRODUCTION AND PREDATION OF AMUR HONEYSUCKLE (LONICERA MAACKII). R. J. Smeda*, S. A. Riley; University of Missouri, Columbia, MO (365)

ABSTRACT

AN EMPIRICAL TEST OF A NOVEL MODEL TO DETERMINE THE TOTAL IMPACT OF AN INVASIVE GRASS. D. R. Tekiela*, J. N. Barney; Virginia Tech, Blacksburg, VA (366)

ABSTRACT

AMINOPYRALID RESEARCH SUMMARY FOR AQUATIC LABELING. D. E. Barnekow*¹, V. F. Peterson², J. J. Jachetta¹, P. L. Havens¹, L. A. Brinkworth¹, W. T. Haller³, W. N. Kline⁴, J. L. Troth¹; ¹Dow AgroSciences, Indianapolis, IN, ²Dow AgroSciences, Mulino, OR, ³University of Florida, Gainesville, FL, ⁴Dow AgroSciences, Duluth, GA (367)

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UGA WEED WEBINAR:  HOW WE CONDUCTED 18 COUNTY PRODUCTION MEETINGS IN ONE DAY. E. P. Prostko*¹, S. Culpepper², K. Lewis², P. M. Eure²; ¹University of Georgia, Tifton, GA, ²The University of Georgia, Tifton, GA (368)

ABSTRACT

USING POLYCOM^TM TO REACH MASSIVE EXTENSION AUDIENCES FOR PESTICIDE EDUCATION. F. M. Fishel*¹, L. A. Gettys²; ¹University of Florida, Gainesville, FL, ²University of Florida, Fort Lauderdale, FL (369)

ABSTRACT

WEED SCIENCE IN SOCIAL MEDIA:  LESSON LEARNED AND GAPS IDENTIFIED. J. Person*, J. K. Soteres; Monsanto, St. Louis, MO (370)

ABSTRACT

DEVELOPING A MULTI-STATE WEED SCIENCE TRAINING. T. A. Baughman*¹, P. A. Baumann², P. A. Dotray³; ¹Oklahoma State University, Ardmore, OK, ²Texas A&M University, College Station, TX, ³Texas Tech University, Lubbock, TX (371)

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MANAGEMENT OF GLYPHOSATE AND ALS RESISTANT HORSEWEED. B. Reeb*, M. M. Loux; The Ohio State University, Columbus, OH (372)

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ON-FARM USE OF CHELATED IRON TO SAFEN GRAIN SORGHUM FOLLOWING PYROSULFLTOLE PLUS BROMOXYNIL APPLIED POST. R. M. Merchant*; University of Georgia, Tifton, GA (373)

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CLOPYRALID AND DICAMBA RESIDUE IMPACTS ON POTATOES AND WEEDS. S. Seefeldt*¹, R. A. Boydston², P. N. Kaspari³; ¹University of Alaska, Fairbanks, AK, ²USDA-ARS, Prosser, WA, ³University of Alaska Fairbanks, Delta Junction, WA (374)

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CURRENT AND FUTURE STEWARDSHIP TRAINING FOR ENGENIA^TM HERBICIDE. L. Bozeman*¹, D. Pepitone², S. Wilson², R. E. Wolf³; ¹BASF Corporation, Research Triangle Park, NC, ²BASF, RTP, NC, ³Wolf Consulting and Research, Mahomet, IL (375)

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WEED DISTRIBUTION AND ASSOCIATED FIELD MANAGEMENT PRACTICES IN ALBERTA. C. Neeser*¹, J. Y. Leeson², N. Kimmel³, M. Vadnais³; ¹Government of Alberta, Brooks, AB, ²Agriculture and Agri-Food Canada, Saskatoon, SK, ³Government of Alberta, Edmonton, AB (376)

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HERBICIDE RESISTANT WEEDS IN IOWA; UPDATE AND ASSESSMENT. M. D. Owen*; Iowa State University, Ames, IA (377)

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WEED INVASION- A CASE STUDY FROM PAKISTAN. K. B. Marwat*; SBB University, Sheringal, Dir Upper, Pakistan, Sheringal, Dir Upper, Pakistan (378)

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SIGNATURES OF SELECTION AND EPSPS GENE COPY NUMBER ACROSS GENUS AMARANTHUS AND THE POTENTIAL ORIGINS OF GLYPHOSATE RESISTANCE. A. L. Lawton-Rauh*¹, K. E. Beard¹, N. R. Burgos², S. J. Barfield¹, J. D. Burton³; ¹Clemson University, Clemson, SC, ²University of Arkansas, Fayetteville, AR, ³North Carolina State University, Raleigh, NC (379)

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CURRENT STATUS OF GLYPHOSATE RESISTANT KOCHIA AND MECHANISM OF RESISTANCE IN NORTH AMERICA. P. Westra*¹, E. Westra¹, A. Wiersma², D. Giacomini¹; ¹Colorado State University, Fort Collins, CO, ²Michigan State University, East Lansing, MI (380)

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EPSPS GENE AMPLIFICATION CONFERS GLYPHOSATE RESISTANCE IN KOCHIA (KOCHIA SCOPARIA) POPULATIONS FROM MONTANA. V. Kumar*¹, P. Jha¹, P. Westra², E. Westra², D. Giacomini², C. Vanhorn²; ¹Montana State University, Huntley, MT, ²Colorado State University, Fort Collins, CO (381)

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MECHANISM OF GLYPHOSATE RESISTANCE IN KOCHIA (KOCHIA SCOPARIA). M. Jugulam*, K. Niehues, B. Gill; Kansas State University, Manhattan, KS (382)

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EXTENSIVE GENE AMPLIFICATION OF EPSPS ENDOWS GLYPHOSATE RESISTANCE IN TWO BROMUS DIANDRUS (GREAT BROME) POPULATIONS IN AUSTRALIA. J. M. Malone, S. Morran, P. Boutsalis, N. Shirley, C. Preston*; University of Adelaide, Glen Osmond, Australia (383)

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NEW EVIDENCE FOR MULTIPLE GLYPHOSATE-RESISTANCE MECHANISMS WITHIN A POPULATION OF COMMON RAGWEED (AMBROSIA ARTEMISIIFOLIA). J. T. Parrish*¹, M. M. Loux¹, D. M. Mackey¹, L. K. McHale¹, D. Sammons², D. Wang², E. L. Ostrander³, D. A. D'Avignon³, X. Ge³, P. Westra⁴, C. R. Van Horn⁴, A. Wiersma⁵; ¹The Ohio State University, Columbus, OH, ²Monsanto, St. Louis, MO, ³Washington University, St. Louis, MO, ⁴Colorado State University, Fort Collins, CO, ⁵Michigan State University, East Lansing, MI (384)

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DETERMINING THE MECHANISM OF RESISTANCE TO GLYPHOSATE IN TWO BIOTYPES OF GIANT RAGWEED. T. Jeffery*¹, C. Hall¹, M. McLean¹, F. J. Tardif¹, P. H. Sikkema², D. Robinson², M. B. Lawton³; ¹University of Guelph, Guelph, ON, ²University of Guelph, Ridgetown, ON, ³Monsanto Canada, Guelph, ON (385)

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UPDATES ON MOLECULAR RESPONSE OF GLYPHOSATE RESISTANT GIANT RAGWEED (AMBROSIA TRIFIDA). C. R. Van Horn*, P. Westra; Colorado State University, Fort Collins, CO (386)

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INHERITANCE OF RESISTANCE TO GLYPHOSATE, PARAQUAT AND CLETHODIM IN A MULTIPLE RESISTANT POPULATION OF RIGID RYEGRASS (LOLIUM RIGIDUM) FROM SOUTH AUSTRALIA. S. Morran*, P. Boutsalis, C. Preston; University of Adelaide, Glen Osmond, Australia (387)

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GLYPHOSATE IMPACTS PHYTOHORMONE SIGNALING AND VEGETATIVE GROWTH PATTERNS FROM UNDERGROUND ADVENTITIOUS BUDS OF LEAFY SPURGE. M. Dogramaci*, J. V. Anderson, M. E. Foley; USDA-ARS, Fargo, ND (388)

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ARYLEX MODE AND SITE OF ACTION CHARACTERIZATION. J. L. Bell*, P. R. Schmitzer, A. E. Robinson; Dow AgroSciences LLC, Indianapolis, IN (389)

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UNDERSTANDING THE DIFFERENTIAL RESPONSES OF SETARIA VIRIDIS (GREEN FOXTAIL) AND SETARIA PUMILA (YELLOW FOXTAIL) TO PYROXSULAM. N. M. Satchivi*, G. J. deBoer; Dow AgroSciences, Indianapolis, IN (390)

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PHYSIOLOGICAL BASIS OF REDUCED MESOTRIONE EFFICACY UNDER ELEVATED GROWTH TEMPERATURES IN PALMER AMARANTH. A. S. Godar, P. Prasad, S. Betha, V. Varanasi, C. Thompson, M. Jugulam*; Kansas State University, Manhattan, KS (391)

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EFFECT OF GROWTH STAGE, LIGHT, AND TEMPERATURE ON HAIRY FLEABANE (CONYZA BONARIENSIS) CONTROL WITH POSTEMERGENCE HERBICIDES. M. R. Dennis¹, S. I. Rios¹, K. Hembree², J. Bushoven¹, A. Shrestha*¹; ¹California State University, Fresno, CA, ²University of California Cooperative Extension, Fresno, CA (392)

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A VARIETY OF PSBA MUTATIONS IN AMARANTHUS SP. INFESTING CARROT PRODUCTION. G. Davis*, F. J. Tardif; University of Guelph, Guelph, ON (393)

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