Progress 07/01/08 to 06/30/14
Outputs
Target Audience: The primary audience reached by my efforts included growers, consultants, agribusiness, and county agents with emphasis in agriculture. These audience members are all groups that experience problems with herbicide resistant weeds in row crop production. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?
Nothing Reported
How have the results been disseminated to communities of interest? A total of 105 grower and agribusiness centered meetings were held at the county, regional, and state levels across South Carolina from 2008 through 2013. Methods and results for managing herbicide resistant AMAPA in cotton, soybean, corn, and peanut were presented and discussed with the audience. Information was well received by the clientele audiences at the meetings . The incidence of adoption of overlapping soil residual programs and mixing herbicide modes-of-actions have increased significantly over the past 5 years in response to herbicide resistant weeds. What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
Project Impact: Glyphosate herbicide in conjunction with glyphosate-resistant crop cultivars, has dominated weed management practicesin corn, soybean, and cotton throughout the United States since the late 1990's. In the U. S., one, or in many cases two, three, or more, application(s) have been applied to approximately 140 million acresduring the past decade. As a result of this intense selection pressure,Palmer amaranth populations werediscovered to be resistant to glyphosate in Georgia in 2005. Resistance was confirmed in South Carolina in 2006 and in many other areas throughout the Southern United States. Due to the loss of effective herbicide(s), growers responded by adopting costlier and less environmental friendly approaches to manage these weeds including tillage, hand-pulling, and higher-priced seed. This project sought to quantify herbicide resistant weed distribution in South Caroline and develop alternative chemcial management practices for row crop producers. These results showed thateffective herbicides areavailable forherbicide resistant Palmer amaranth control. Although not as simple and low-cost as glyphosate, the use of soil residual herbicides provided excellent control of Palmer amaranthduring all years of our studies. Weed size played a critical role in application timingfor our remainingover-the-top herbicides, especially with our older products that predate glyphosate tolerant crops. The use of soil residual herbicides increased grower input costs by about $35/acre; however, competition from Palmer amaranth can reduce crop yields up to 100%. For example, a loss of $96 millon for cotton if Palmer amaranth is not controlled in one year.By aggressively adopting our recommedations, growers in South Carolina, have implemented weed scouting, rotation of herbicide modes-of-actions, and overlapping use of soil residuals during the early part of the growing season that effectively reducedweed incidencewhile still practicing conservation systems. Goal1. To survey corn, soybean, and cotton producing areas of South Carolina to determine the extent of herbicide-resistant weed problems: Palmer amaranth seed samples were collected at the request of growers during the fall/winter of 2008 through 2013. Seeds were grown in the greenhouse and out of all samples collected, resistance to glyphosate and ALS-inhibiting herbicide families in Palmer amaranth was detected. As of 2013, 32 out of 46 counties have confirmed multipleresistance.These results were shared with growers throughout the state and provided growers with detailed information about their fields for proper management of Palmer amaranth. Proactive measures to manage Palmer amaranth were readily adopted after sharing these results. Goal2. To evaluate and refine weed management programs that provides consistent control of herbicide resistant weeds, including glyphosate-resistant Palmer amaranth. Field studies were initiated in2008 and continued through 2013to determine impact of preemergence (soil applied) and postemergence (over-the-top) programs efficacy on herbicide resistant weeds in corn, cotton and soybean.In cotton at the first postemergence application, all treatments containing a residual burndown and/or residualpreemergence treatment provided 94% or betterPalmer amaranth control. Palmer amaranth control at planting was better with preplant flumioxazin (77%) compared to both rates of preplant fluridone (52-59%). Prometryn and diuron alone residual activity on Palmer amaranth declined rapidlycompared to the fluridone and fomesafen + diuron treatments. At plant fluridone, fomesafen, and fomesafen + diuron provided good to excellent control of Palmer amaranth during the early part of crop growth and development. In soybean, flumioxazin plus thifensulfuron plus chlorimuronandmetribuzin plus chlorimuronfollowed byglufosinate postemergence provided excellent control (100%) of Palmer amaranth and annual morningglory in the glufosinate-tolerant soybean.In the glyphosate-tolerant system, Envive and Canopy provided longer residual control of Palmer amaranth. The addition ofpyroxsulfone tometribuzin plus chlorimurongreatly improved annual grass control (100 vs 93%). Glufosinate based systems were more consistent in controlling Palmer amaranth compared to the glyphosate based systems. The addition of premeregence program would add consistency to soybean producers in their management of herbicide-resistant Palmer amaranth. In corn, combinations of Isoxaflutole followed by glyphosate or glufosinate also provided excellent Palmer amaranth and pitted morningglory control. Two pass programs of isoxaflutole and tembotrione provided the greatest consistency amoung studies when compared across years. In conclusion, isoxaflutole and tembrotrione based programs provided an excellent broad spectrum control package for corn with greater residual efficacy compared to atrazine alone. In addition, these herbicide programs provide an additional mode of action for rotation with atrazine in corn, especially where corn is planted on a continuous basis. Goal 3. To test current and upcoming herbicide tolerant technologies for corn, soybean, and cotton for fit in the management of herbicide resistance Field studies were initiated in2011 and continued through 2013to determine the effectiveness of dicamba- and 2,4-D based programs for control of herbicide resistant Palmer amaranth in cotton and soybeans. In cotton, herbicide treatments included dicamba, 2,4-D, glyphosate, glufosinate, diuron, fomesafen, flumioxazin, s-metolachlor, and acetochlor. In the dicamba systems trials, all treatments provided greater than 90% Palmer amaranth control. The dicamba, glyphosate, and glufosinate containing treatments provided excellent control. Programs that included an at-plant soil residual herbicide followed by a timely POST application had the highest seed cotton yields because of reduced weed competition. In summary, dicamba-based herbicide programs provided good to excellent control of Palmer amaranth and pitted morningglory. In soybean, dicamba PRE followed by glyphosate plus dicambafirst postemergence applicationprovided excellent control in all 3 weed species (>97%). In general, dicamba alone preemergence was not as effective as flumioxazin alonepreemergence when rated 2 weeks after second post emergence.In general,all treatments with at least one postemergence treatment wereeffective on controlling all 3 weed species. Results from the studies showed flumioxazin PRE followed by glyphosate, dicamba mixfirst postemergenceand second postemergence as the most effective treatment in Palmer amaranth and large crabgrass with 100% and 99% control respectively. Overall, Palmer amaranth was the easiest to control weed across all treatments and dicamba plus glyphosate premixture POST application provided excellent control for all 3 weeds species. Similarly, glyphosate and glufosinateplus 2,4-Dprovided excellent control of Palmer amaranth. For both technologies, weed size will still a limiting factor with regard to the success ofpostemergence dicamba, 2,4-D,and glufosinate applications on glyphosate-resistant Palmer amaranth. In addition, the long-term sustainability of 2,4-D and dicamba cropping systems will rely on use of additional herbicide modes-of-action and other cultural practices to minimize the development of resistance. Growers awareness of these potential pitfalls will increase adoption of these practices. Major accomplishments generated by this research project included a greater awareness across the state of herbicide-resistant weeds, notably Palmer amaranth. In addition, growers were made aware of alternative herbicides that can control Palmer amaranth in the absence of glyphosate. In addition, this research dissemeninated knowledge that allowed growers are better weed managers on their farm and made them aware of potential pitfalls on relying on a single management tactic for weed control.
Publications
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2014
Citation:
Price, A. J., S. A. Culpepper, J. A. Kelton, M. W. Marshall, R. L. Nichols, J. K. Norsworthy, L. E. Steckel. 2014. Managing Weeds in Conservation Systems: Overcoming Herbicide-Resistant Super-Weeds in the Mid-South and Southeastern U.S. Soil and Water Conservation Society International Conference.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2014
Citation:
M.W. Marshall. 2014. Combinations of At-Plant Brake and Reflex for Weed Control in Cotton, p. 1047. In Proceedings Beltwide Cotton Production Conferences, National Cotton Council of America, Nashville, TN.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2014
Citation:
M.W. Marshall. 2014. Envive and Canopy Based Programs in Liberty-Link and Roundup Ready Soybean. Proc. Southern Weed Science Society 67-184.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2014
Citation:
D.D. Joseph and M.W. Marshall. 2014. Effect of Weed Size on Selected Herbicides. Proc. Southern Weed Science Society 67:66.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2014
Citation:
C.H. Sanders and M.W. Marshall. 2014. Weed Management Systems in Dicamba and 2,4-D Tolerant Cotton. Proc. Southern Weed Science Society 67:63.
- Type:
Books
Status:
Published
Year Published:
2014
Citation:
M.W. Marshall (Editor), F.P.F. Reay-Jones, R.G. Bellinger, J.K. Greene, J.D. Mueller, T. Davis, D.T. Gooden, B. Fortnum, M. Hood, G. Yarrow. 2014. 2014 South Carolina Pest Management Handbook.
- Type:
Books
Status:
Published
Year Published:
2013
Citation:
3. M.W. Marshall (Editor), F.P.F. Reay-Jones, R.G. Bellinger, J.K. Greene, J.D. Mueller, T. Davis, D.T. Gooden, B. Fortnum, M. Hood, G. Yarrow. 2013. 2013 South Carolina Pest Management Handbook.
- Type:
Books
Status:
Published
Year Published:
2012
Citation:
M.W. Marshall (Editor), F.P.F. Reay-Jones, R.G. Bellinger, J.K. Greene, J.D. Mueller, T. Davis, D.T. Gooden, B. Fortnum, M. Hood, G. Yarrow. 2012. 2012 South Carolina Pest Management Handbook.
- Type:
Books
Status:
Published
Year Published:
2011
Citation:
M.W. Marshall, F.P.F. Reay-Jones, R.G. Bellinger, J.K. Greene, J.D. Mueller, T. Davis, D.T. Gooden, B. Fortnum, M. Hood, G. Yarrow. 2011. Pest Management Handbook for Field Crops
- Type:
Books
Status:
Published
Year Published:
2010
Citation:
M.W. Marshall, F.P.F. Reay-Jones, R.G. Bellinger, J.K. Greene, J.D. Mueller, T. Davis, D.T. Gooden, B. Fortnum, M. Hood, G. Yarrow. 2010. Pest Management Handbook for Field Crops.
- Type:
Books
Status:
Published
Year Published:
2009
Citation:
M.W. Marshall, F.P.F. Reay-Jones, R.G. Bellinger, J.K. Greene, J.D. Mueller, T. Davis, D.T. Gooden, B. Fortnum, M. Hood, G. Yarrow. 2009. Pest Management Handbook for Field Crops.
- Type:
Books
Status:
Published
Year Published:
2008
Citation:
M.W. Marshall, F.P.F. Reay-Jones, R.G. Bellinger, J.K. Greene, J.D. Mueller, T. Davis, D.T. Gooden, B. Fortnum, M. Hood, G. Yarrow. 2008. Pest Management Handbook for Field Crops
|
Progress 01/01/13 to 09/30/13
Outputs
Target Audience: The primary audience reached by my efforts included growers, consultants, agribusiness, and county agents with emphasis in agriculture. These audience members are all groups that experience problems with herbicide resistant weeds in row crop production. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?
Nothing Reported
How have the results been disseminated to communities of interest? 14 grower and agribusiness centered meetings were held at the county, regional, and state levels across South Carolina. Methods and results for managing herbicide resistant AMAPA in cotton, soybean, corn, and peanut were presented and discussed with the audience. Information was well received by the clientele audiences at the meetings and planned on implementing for upcoming growing season. The incidence of adoption of overlapping soil residualprograms and mixing herbicide modes-of-actions have increased significantly over the past 5 years due to the increase of herbicide resistant weeds. What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
Glyphosate in conjunction with glyphosate-resistant crop cultivars, has dominated weed management in corn, soybean, and cotton throughout the U. S. and many other areas. In the U. S., one, or in many cases two, three, or more, application(s) have been applied to approximately 140 million acres for a decade. This unprecedented selection pressure has generated resistance in several difficult-to-control, cross-pollinating weed species including Palmer amaranth. The resistance has forced growers to adopt costlier and less environmental friendly approaches to manage these weeds including tillage, hand-pulling, and higher-priced seed. Dissemination of chemical practices that reduce infestations of Palmer amaranth through less reliance on topical herbicide programs. 1. To survey corn, soybean, and cotton producing areas of South Carolina to determine the extent of herbicide-resistant weed problems. Palmer amaranth seed samples were collected at the request of growers during the fall/winter of 2012-2013. Seeds were grown in the greenhouse and out of all samples collected, we detected resistance to glyphosate and ALS-inhibiting herbicide families. As of 2013, 32 out of46 counties have confirmed resistance. 2. To evaluate and refine weed management programs that provides consistent control of herbicide resistant weeds, including glyphosate-resistant Palmer amaranth. Field studies were initiated to determine the efficacy and long-term residual potential of fluridone for Palmer amaranth control and cotton yield. Field experiments were conducted at the Clemson University Edisto Research and Education Center (EREC) located near Blackville, SC. Study 1. Phytogen Widestrike 499 cotton was planted on May 21, 2013 at EREC. Preemergence (PRE) herbicides were applied in water on May 22, 2013, at EREC, at a carrier volume 15 gallons per acre. Palmer amaranth percent visual control ratings were collected 2, 4, and 8 weeks after PRE application treatment (WAT) on a 0 to 100 percent scales with 0 indicated no control and 100 equal to complete control. Palmer amaranth control data and seed cotton yields were analyzed using ANOVA and means separated at the P = 0.05 level. Preemergence treatments included fluridone at 0.125, 0.25, 0.375, and 0.5 lb ai/A, prometryn at 1.0 lb ai/A, diuron at 1.0 lb ai/A, fomesafen at 0.25 lb ai/A, fomesafen plus diuron at 0.25 plus 0.5 lb ai/A, and untreated control. Fluridone provided 91% or greater control of Palmer amaranth at 8 WAT at the EREC location, which was similar to fomesafen and fomesafen + diuron treatments.Prometryn and diuron alone residual activity on Palmer amaranth declined rapidly at 8 WAT compared to the fluridone and fomesafen + diuron treatments.Cotton yields were lower in prometryn and diuron treatments compared to the fluridone treatments, fomesafen, and fomesafen + diuron. Fluridone (all rates), fomesafen, and fomesafen + diuron provided good to excellent control of Palmer amaranth. Study 2. Preplant burndown herbicides were applied on April 18, 2013 at EREC. Preemergence (PRE) herbicides were applied on May 22, 2013 at EREC. Post-emergence (POST1) on June 13, 2013. Post-emergence (POST2) on June 25, 2012. Preplant burndown herbicide treatments included glyphosate at 0.75 lb ae/A plus 2,4-D at 0.5 lb ai/A, glyphosate plus 2,4-D plus flumioxazin at 0.064 lb ai/A, glyphosate plus 2,4-D plus fluridone at 0.25 lb ai/A, and glyphosate plus 2,4-D plus fluridone 0.38 lb ai/A. Preemergence (PRE) treatments included paraquat at 0.75 lb ai/A, reflex at 0.25 lb ai/A, and diuron at 0.5 lb ai/A. All treatments were followed by two post-emergence application of glufosinate at 0.53 lb ai/A, with the exception of the check. Preplant AMAPA percent control ratings were collected at the preemergence herbicide application timing, PRE AMAPA percent control ratings were collected at the POST1 timing, and POST1 AMAPA control ratings were collected at the POST2 timing. Palmer amaranth control data were analyzed using ANOVA and means separated at the P = 0.05 level. At the EREC site, approximately 0.5 in precipitation occurred within 7 days after preplant application. Flumioxazin and fluridone at 0.38 lb ai/A preplant treatments provided highest AMAPA control (96-99%). At POST1, all treatments containing a residual burndown and/or residual PRE treatment provided 94% or better AMAPA control. Palmer amaranth control at planting was better with preplant flumioxazin (77%) compared to both rates of preplant fluridone (52-59%). AT POST2, POST 1 glufosinate following either preplant flumioxazin or preplant fluridone following diuron plus fomesafen at plant provided greater than 99% AMAPA control. In conclusion, fluridone needed about 0.5 in rainfall within 7 days of application to activate. Under dry conditions, AMAPA control from preplant flumioxazin was greater than fluridone regardless of rate. In contrast, AMAPA control was similar between prelant flumioxazin and fluridone during normal precipitation. At POST1, benefit from residuals was evident compared to the glufosinate only programs. 3. To test current and upcoming herbicide tolerant technologies for corn, soybean, and cotton for fit in the management of herbicide resistance Research studies were initiated to determine the effectiveness of dicamba-based herbicide programs and 2,4-D based programs for control of Palmer amaranth and other important broadleaf weeds and yield response of cotton. Field experiments were conducted at the Clemson University Edisto Research and Education Center located near Blackville, SC in 2013. Dicamba-tolerant cotton was planted on May 29, 2013. Fomesafen at 0.25 lb ai/A, dicamba at 0.5 lb ai/A, acetochlor at 1.125 lb ai/A, and diuron at 1 lb ai/A were applied preemergence (PRE) shortly after planting. Approximately 30 early-postemergence (EP), 37 mid-postemergence (MP), and 49 late-postemergence (LP) days after planting, various combinations of dicamba at 0.5 lb ai/A, glyphosate at 1 lb ai/A, glufosinate at 0.53 lb ai/A, and acetochlor at 1.125 lb ai/A were applied postemergence (POST) with the same application parameters discussed above. 2,4-D tolerant cotton was planted on June 21,2013. Fomesafen at 0.25 lb ai/A was applied preemergence (PRE) shortly after planting in water at a carrier volume of 15 GPA with a pressure of 34 PSI. Approximately 20 (EP) and 45 (LP) days after planting, various combinations of 2,4-D choline at 1.0 lb ai/A, glyphosate at 0.75lb ae/A, glufosinate at 0.53 lb ai/A, metolachlor at 0.95 lb ai/A, and acetochlor at 1.125 lb ai/A were applied post-emergence. Palmer amaranth, pitted morningglory, and large crabgrass percent visual control were measured for dicamba tolerant cotton 23 days after PRE, 7 days after (EP), 7 days after (MP), and 9 days after (LP) applications. Palmer amaranth, pitted morningglory, and large crabgrass percent visual control were measured for 2,4-D tolerant cotton 20 days after PRE, 15 days after (EP), and 25 days after (LP) applications. Seed cotton yield and weed control data were analyzed using ANOVA and means separated at the P=0.05 level. Fomesafen PREin 2,4-D tolerant cotton provided excellent control of Palmer amaranth, but did not provide control of pitted morningglory and large crabgrass. The EP treatments in 2,4-D tolerant cotton except for glufosinate EP provided greater than 95% control of Palmer amaranth, pitted morningglory, and large crabgrass. In the dicamba tolerant cotton variations were observed in the PRE treatments for Palmer amaranth, pitted morningglory and large crabgrass. The EP, MP, and LP treatments showed good to excellent control of the weeds (>90% control). These results show evidence that using dicamba or 2,4-D combined with either glyphosate or glufosinate based herbicide provided an effective control for small glyphosate and ALS resistant Palmer amaranth biotypes and other important weeds in cotton.
Publications
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2013
Citation:
M.W. Marshall, A.C. York, and A.S. Culpepper. 2013. Does At-Plant Fluridone Application Reduce Postemergence Herbicide Needs in Glyphosate- and Glufosinate-Tolerant Cotton? Proc. Southern Weed Science Society 66:188.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2013
Citation:
D.D. Joseph, C.H. Sanders, and M.W. Marshall. 2013. Palmer Amaranth and Pitted Morningglory Control Using Various Combinations of 2,4-D, Glyphosate, and Glufosinate. Proc. Southern Weed Science Society 66:53.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2013
Citation:
M.W. Marshall, A.C. York, and A.S. Culpepper. 2013. Comparison of Fluridone and Flumioxazin-Based Preplant Burndown Programs in Glufosinate-Tolerant Cotton. Proc. Southern Weed Science Society 66:38.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2013
Citation:
C.H. Sanders, D.D. Joseph, and M.W. Marshall. 2013. Selected Herbicide Programs for Broadleaf Weed Control in Dicamba-Tolerant Cotton. Proc. Southern Weed Science Society 66:35.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2013
Citation:
M.W. Marshall, A.C. York, and A.S. Culpepper. 2013. Long-Term Residual Efficacy of Fluridone in Southeast Cotton, p. 309. In Proceedings Beltwide Cotton Production Conferences, National Cotton Council of America, Nashville, TN.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2013
Citation:
M.W. Marshall, A.C. York, and A.S. Culpepper. 2013. Comparison of Fluridone-Based Preplant Burndown Programs in Southeast Cotton, p. 863. In Proceedings Beltwide Cotton Production Conferences, National Cotton Council of America, Nashville, TN.
- Type:
Journal Articles
Status:
Awaiting Publication
Year Published:
2013
Citation:
5. E.P. Prostko, T.M. Webster, M.W. Marshall, R. Leon, T.L. Grey, J.A. Ferrell, P.A. Dotray, D.L. Jordan, W. J. Grichar, and B.J. Brecke. 2013. Glufosinate Application Timing and Rate Affect Peanut Yield Response. Peanut Science. In Press.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2013
Citation:
M.W. Marshall. 2013. Isoxaflutole and Tembotrione Based Herbicide Programs for Palmer Amaranth, Pitted Morningglory, and Goosegrass Control in Field Corn. Proc. Southern Weed Science Society 66:192.
|
Progress 01/01/12 to 12/31/12
Outputs
OUTPUTS: ACTIVITIES: Herbicide-resistant Palmer amaranth's (AMAPA) rapid growth rate, drought tolerance, and high reproductive potential make it the one of the most troublesome weeds in agronomic production fields in South Carolina. Biotypes resistant to both glyphosate- and ALS-inhibitors are present in South Carolina. Glufosinate-based programs for control of herbicide-resistant Palmer Amaranth continue to increase in South Carolina. Weed size plays an important role in performance and activity of several foliar applied herbicides, including glufosinate, dicamba, and 2,4-D. Several field projects were initiated in 2012 at Edisto REC (EREC) and sites throughout the Southeast. Each project was replicated times. Weed control data were analyzed using ANOVA and means separated at the P = 0.05 level. First project examined efficacy of Liberty (glufosinate), glyphosate, Clarity (dicamba), and 2,4-D selected weed sizes in the field; Second study examined the efficacy of various combinations of preplant burndown and preemergence Valor (flumioxazin) and Brake (fluridone) programs for AMAPA control in cotton. Field experiments were conducted at three locations across the southeast (including EREC). Preplant burndown (PPB) and preemergence (PRE) herbicides were applied at selected timings at three locations across the southeast. Preplant burndown herbicide treatments included glyphosate plus 2,4-D, glyphosate plus 2,4-D plus flumioxazin, glyphosate plus 2,4-D plus fluridone, and glyphosate plus 2,4-D plus fluridone. Preemergence treatments included paraquat, fomsafen, and diuron. All treatments were followed by two postemergence application of glufosinate, with the exception of the check. EVENTS: Field results/recommendations were presented at the Pee Dee REC Summer Field Day (2012), Edisto REC Corn and Peanut Field Day (2012), Edisto REC Cotton and Soybean Field Day (2012), NRCS/ Agent Training at EREC (2012), NRCS Grower Training Field Day (2012), Weed Science Society of America Annual Meeting (2012); Beltwide Cotton Conference Annual Meeting (2013), and the Southern Weed Science Society annual meeting (2013). PRODUCTS: Based on results observed in these field studies conducted in 2012, weed management recommendations were revised, updated, and incorporated in the printed and web-based versions of 2012 wheat production guide, the 2012 peanut moneymaker production guide, and 2013 pest management handbook for field crops. DISSEMINATION: Approximately 12 grower and agribusiness centered meetings were held at the county, regional, and state levels across South Carolina. Methods for managing herbicide resistant AMAPA in cotton, soybean, corn, and peanut were presented and discussed with the audience. Information was well received by the clientele audiences at the meetings and planned on implementing for upcoming growing season. Growers that faced herbicide resistant AMAPA were more receptive to recommendations than ones where herbicide resistant AMAPA was not present. PARTICIPANTS: Colton Sanders and Dwayne Joseph, graduate students working on their M.S. degrees were key participants in this project. TARGET AUDIENCES: Target audiences for this project was growers, retailers, consultants, and government employees in South Carolina and throughout the Southern region of the United States. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
OUTPUTS: [Project 1] Field studies using a weed population in a non-crop showed that control of Palmer amaranth and pitted morningglory at the 6-8" growth stage were very similar for the 2-4" growth stage. Results indicated that regardless of the rate of glufosinate or size of pitted morningglory control was greater than 95% regardless of 2,4-D or dicamba tank mix partner or rate. Glufosinate alone, glufosinate plus 2,4-D, and glufosinate plus dicamba provided greater than 99% of small (2-4") and medium (6-8") sicklepod. In field cotton trials, fomesafen, dicamba, and dicamba + fomesafen PRE provided excellent control of AMAPA. Similarly, glyphosate + dicamba, glufosinate + acetochlor, glyphosate + dicamba + acetochlor, and glufosinate + dicamba EP provided 93 to 100% control of AMAPA and pitted morningglory, regardless of the PRE program. Glyphosate + dicamba + acetochlor POST1 provided 94% AMAPA control compared to greater than 98% with glyphosate + dicamba, glufosinate + acetochlor, and glufosinate + dicamba POST1. All treatments provided 100% control of Palmer amaranth and pitted morningglory at the 35 days after last post application. In the second study [Project 2], Flumioxazin and fluridone at 0.38 lb ai/A preplant treatments provided highest AMAPA control (96-99%). At first postemergence application (POST1), all treatments containing a PPB and/or PRE treatment provided 94% or better AMAPA control. At the POST1 application, PRE AMAPA control was greater than 95% with flumioxazin and fluridone at 0.38 lb ai/A preplant alone or followed by fomesafen plus diuron plus paraquat PRE. After the second postemergence application (POST2), POST1 AMAPA control was 98% or better following two applications of glufosinate regardless of residual program. At the Macon County site, very little precipitation occurred within 7 days after preplant application. Palmer amaranth control at planting was better with preplant flumioxazin (77%) compared to both rates of preplant fluridone (52-59%). AT POST2, POST 1 glufosinate following either preplant flumioxazin or preplant fluridone following diuron plus fomesafen at plant provided greater than 99% AMAPA control. IMPACTS: Fluridone needed about 0.5 in rainfall within 7 days of application to properly activate. Differences between normal and dry precipitation environments influenced fluridone activity on AMAPA. At POST1, benefit from residuals was evident compared to the glufosinate only programs. Overlapping soil residual programs are the key to herbicide resistant AMAPA management; however, these programs cost the grower up to $125/ha. Hand-weeding, cultivation, and crop abandonment, would increase production costs up to $800/ha. Currently, fomesafen and flumioxazin are key foundation products for glyphosate- and ALS-resistant AMAPA. Fluridone did slow emerged AMAPA allowing POST treatments better control of escapes and suppress future weed flushes. In our studies, glufosinate + 2,4-D or dicamba has provided excellent control of AMAPA and other broadleaf weeds. Weed size and application timing is critical for their success.
Publications
- M.W. Marshall. 2012. Herbicide Programs for Control of Italian Ryegrass in Winter Wheat. Weed Science Society of America Proceedings 265.
|
Progress 01/01/11 to 12/31/11
Outputs
OUTPUTS: ACTIVITIES: Palmer amaranth's (AMAPA) rapid growth rate, drought tolerance, and high reproductive potential make it the most common and troublesome weed in agronomic production fields throughout South Carolina and the southeastern United States. Glyphosate- and ALS-resistant AMAPA are present in South Carolina. This has dramatically narrowed herbicide control options for AMAPA. With glyphosate-tolerant varieties (such as Phytogen widestrike that are tolerant of over-the-top applications of glufosinate), these combinations of glufosinate and glyphosate-based need to be examined for glyphosate-and ALS-resistant AMAPA management. Field studies were conducted in cotton and soybeans during the summer of 2011 at Edisto Research and Education Center (EREC) and Pee Dee Research and Education Center (PDREC) to evaluate different combinations of preemergence (PRE) and postemergence (POST) herbicides for glyphosate-resistant Palmer amaranth control in South Carolina in cotton and soybeans. Cotton PRE treatments included pendimethalin at 1.1 kg/ha, diuron at 0.28 kg/ha, and fomesafen at 0.28 kg/ha. Cotton POST treatments included glyphosate at 0.84 kg/ha, s-metolachlor at 1.46 kg/ha, glufosinate at 0.59 kg/ha or 0.79 kg/ha, and pyrithiobac at 42.5 or 62.5 g/ha. Soybean PRE treatments included flumioxazin at 71 g/ha, pendimethalin at 1.1 kg/ha, sulfentrazone at 0.15 kg/ha, chlorimuron at 60 g/ha, and metribuzin at 0.23 kg/ha. Soybean POST treatments included glyphosate at 0.84 kg/ha, lactofen at 0.22 kg/ha, and fomesafen at 0.28 kg/ha. EVENTS: Field results were presented at the Pee Dee REC Summer Field Day (2011), Edisto REC Corn and Peanut Field Day (2011), Edisto REC Cotton and Soybean Field Day (2011), Agronomic Agent Training (2011), Beltwide Cotton Conference Annual Meeting (2011), and the Southern Weed Science Society annual meeting (2011). PRODUCTS: Based on results observed in these field studies conducted in 2011, weed management recommendations were revised, updated, and incorporated in the printed and web-based versions of 2011 cotton and 2011-2012 wheat production guides, the 2012 peanut moneymaker production guide, and 2012 pest management handbook for field crops. DISSEMINATION: During 2011-2012 winter meeting season, 14 grower and agribusiness centered meetings were held at the county, regional, and state levels across South Carolina. Methods for managing herbicide resistant AMAPA in cotton and soybeans were presented and discussed with the audience. As with previous years, information was well received by the clientele audiences at the meetings and planned on implementing for upcoming growing season. Growers that faced herbicide resistant AMAPA were more receptive to recommendations than ones where herbicide resistant AMAPA was not an issue. PARTICIPANTS: Jacob Stokes is currently finishing his M.S. project working under this project. TARGET AUDIENCES: South Carolina and other southeast U.S. row crop producers with herbicide resistant weed management issues. Clemson University Extension personnel, USDA-NRCS, consultants, S.C. and southeast corn, cotton, soybean commodity associations. Agribusiness firms in agriculture including seed and herbicide companies. University research and extension personnel. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
RESULTS: At the end of 2011, 20 South Carolina counties have confirmed AMAPA populations with ALS- and glyphosate-resistance in the same biotype (multiple resistant biotypes). In cotton 14 days after treatment (DAT) at EREC, AMAPA control was excellent with the use of pyrithiobac + diuron, fluometuron, pendimethalin and fomesafen; fluometuron + diuron, and diuron + fomesafen. At 28 DAT, AMAPA control (80-83%) declined rapidly in the pyrithiobac, pyrithiobac + diuron, fluometuron, and fluometuron + pendimethalin, whereas, fluometuron + diuron and fomesafen alone remained above 90%. At PDREC, PRE AMAPA control was similar at 14 DAT and 28 DAT. At the EREC site, AMAPA control was 95% across all treatments at 14 DAT after treatment. At 60 DAT, AMAPA control was similar in both glyphosate-based programs and glufosinate-based programs (at least 88% control of AMAPA). At the PDREC site, AMAPA control was at least 95% across all treatments at 14 DAT. At 60 DAT, AMAPA control declined to 88% in the pendimethalin + diuron. Fomesafen-based programs performed similarly in control of AMAPA as diuron programs. Similar to previous soybean studies, a PRE herbicides provided excellent control of glyphosate-resistant AMAPA (>97%); however, control diminished due to late season AMAPA. A companion herbicide to glyphosate at the early POST timing increased the control of AMAPA. If significant rainfall occurs shortly after application, then growers can expect approximately 14-21 days of weed control activity. The key to managing AMAPA in a glufosinate- and glyphosate-based system is the use of overlapping residual herbicides. OUTCOMES: With glyphosate- and ALS-resistance spreading throughout South Carolina, our herbicide options will become more limited in cotton and soybeans. Soil residual herbicides and some form of tillage become the preferred method to manage herbicide-resistant AMAPA. An aggressive soil herbicide program costs the grower up to $100/ha. In addition, hand-weeding, cultivation, and crop abandonment, will increase that cost up to $750/ha including lost revenue from yield decreases and increased variable costs. Management of AMAPA with soil residual herbicides is unpredictable in dryland crop production given the rainfall patterns in South Carolina. Currently, fomesafen and flumioxazin are foundation soil residual products to control glyphosate- and ALS-resistant AMAPA which could lead to similar resistance development. Alternatives in soybean, including metribuzin, s-metolachlor, acetochlor, and alachlor, will provide a rotation for the PPO-inhibitor herbicides. New herbicide tolerance crops are being tested and developed by industry to combat glyphosate resistance. In soybeans and cotton, glufosinate-tolerant varieties are the only viable option in heavily infested fields. In our studies, glufosinate has provided excellent control of glyphosate-resistant AMAPA. The development of these new technologies will provide control of AMAPA; however, application timing is critical for success.
Publications
- Marshall, M.W. 2012. Palmer Amaranth and Pitted Morningglory Control in Dicamba-Tolerant Cotton. 2012 Beltwide Cotton Conferences.
- Monks, C.D., A.J. Price, A.S. Culpepper, J.A. Kelton, M.W. Marshall, R.L. Nichols, M.G. Patterson, and L.E. Steckel. 2012. Integrated Resistant Pigweed Control in the Southeast. 2012 Beltwide Cotton Conferencs.
- Stokes, J.G. and M.W. Marshall. 2012. Herbicide Programs for Glyphosate-Resistant Palmer Amaranth Control in South Carolina Cotton. 2012 Beltwide Cotton Conferences.
- Marshall, M.W. 2012. Evaluation of Dicamba-Based Herbicide Programs in Dicamba-Tolerant Cotton. 2012 Southern Weed Science Society Annual Meeting.
- Stokes, J.G. and M.W. Marshall. 2012. Palmer Amaranth Control in Glyphosate- and Glufosinate-Tolerant Soybean. 2012 Southern Weed Science Society Annual Meeting.
- Stokes, J.G. and M.W. Marshall. 2012. Herbicide Programs for Management of Palmer Amaranth in Cotton. 2012 Southern Weed Science Society Annual Meeting.
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Progress 01/01/10 to 12/31/10
Outputs
OUTPUTS: ACTIVITIES: Glyphosate-resistant Palmer amaranth (Amaranthus palmeri S. Wats.) has emerged as one of the most severe threats to crop production in South Carolina. Surveys of the distribution of ALS- and glyphosate-resistant Palmer amaranth in South Carolina were continued in the fall of 2010. Suspected grower fields were sampled for escaped Palmer amaranth populations and their locations recorded using a GPS unit. Palmer amaranth seed heads were collected and screened for glyphosate- and ALS-resistance. Palmer amaranth seed was planted in the greenhouse and grown to the 4-leaf stage. At the 4-leaf stage, plants were sprayed with glyphosate at 0, 0.84, and 1.68 kg/ha, and thifensulfuron (ALS-inhibiting herbicide) at 0, 23, and 46 g/ha. At 21 days after treatment, plants were visually rated (yes = alive or resistant or no = dead or susceptible) to determine level of resistance to glyphosate and thifensulfuron. Field studies were conducted in the summer of 2010 at Edisto Research and Education Center (EREC) and Pee Dee Research and Education Center (PDREC) to evaluate different combinations of preemergence (PRE) and postemergence (POST) herbicides for glyphosate-resistant Palmer amaranth control. Cotton PRE treatments included pendimethalin at 1.1 kg/ha, diuron at 0.28 kg/ha, and fomesafen at 0.28 kg/ha. Cotton POST treatments included glyphosate at 0.84 kg/ha, s-metolachlor at 1.46 kg/ha, glufosinate at 0.59 kg/ha or 0.79 kg/ha, and pyrithiobac at 42.5 or 62.5 g/ha. Soybean PRE treatments included flumioxazin at 71 g/ha, pendimethalin at 1.1 kg/ha, sulfentrazone at 0.15 kg/ha, and metribuzin at 0.23 kg/ha. Soybean POST treatments included glyphosate at 0.84 kg/ha, lactofen at 0.22 kg/ha, and fomesafen at 0.28 kg/ha. EVENTS: Field results were presented at the Pee Dee REC Summer Field Day (2010), Edisto REC Fall Field Day (2010), Agronomic Agent Training (2010), Beltwide Cotton Conference Annual Meeting (2011), and the Southern Weed Science Society annual meeting (2011). PRODUCTS: Based on field studies conducted in 2010, weed management recommendations were revised and incorporated in the 2011 Pest Management Handbook for Field Crops, 2010 wheat production guide, 2011 Peanut Moneymaker Production guide, and 2011 corn, cotton, and soybean production guides. DISSEMINATION: During 2010-2011 winter meeting season, 15 grower-orientated meetings were held at the county, regional, and state levels. At each meeting, methods for managing herbicide resistant Palmer amaranth in cotton and soybeans were presented and discussed with the audience. As with previous years, clientele audiences were pleased with the information in the meetings and planned on implementing for upcoming growing season. Growers that faced herbicide resistant Palmer amaranth were more receptive to recommendations than ones where herbicide resistant Palmer amaranth was not an issue. PARTICIPANTS: Jacob Stokes worked extensively on this project as a Master's graduate student. He will be completing his degree program in December 2011. TARGET AUDIENCES: South Carolina and U.S. row crop producers with weed management problems; South Carolina and U.S. County Extension personnel; South Carolina and U.S. row crop consultants and scouts; South Carolina and U.S. cotton, soybean and corn commodity and grower associations; agribusinesses such as seed companies and chemical companies; University and USDA researchers and extension personnel. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
A majority of the survey sites sampled were confirmed in the greenhouse to have both ALS- and glyphosate-resistant Palmer amaranth. As of 2011, 20 South Carolina counties now have confirmed Palmer amaranth populations with both ALS- and glyphosate-resistance in the same plant (multiple resistant biotypes). Preemergence (PRE) control of Palmer amaranth declined at PDREC where soil seedbank populations were higher. The highest level of control of Palmer amaranth at both locations was obtained by fomesafen PRE plus pyrithiobac, diuron, or pendimethalin. Diuron PRE provided similar levels of control as fomesafen PRE when tank mixed with pendimethalin and pyrithiobac PRE. Pyrithiobac applied at the early postemergence timing provided excellent control of Palmer amaranth. Most treatments provided 90-95% control throughout the study. In soybean, plots treated with a PRE herbicide, control was good to excellent (85-100%) at 8 weeks after treatment; however, control diminished due to prolonged germination of Palmer amaranth and decline of soil residual herbicide activity. The addition of a companion herbicide (fomesfen, thifensufluron, or acifluorfen) to glyphosate postemergence treatment provided control of escapes in the soil herbicide PRE treatments. Palmer amaranth size was critical at the time of application due to size restrictions. After Palmer amaranth exceeds this size, control will fall dramatically. These studies underscore the importance of controlling Palmer amaranth through prevention of seed germination. OUTCOMES: With glyphosate- and ALS-resistance spreading throughout South Carolina, our herbicide options will become more limited in cotton and soybeans. Soil residual herbicides become the most adopted method to manage herbicide-resistant Palmer amaranth. An aggressive soil herbicide program costs the grower up to $85/ha; however, hand-weeding, cultivation, and crop abandonment, will cost South Carolina growers up to $5,000/ha in lost revenue/increased costs. Hand-weeding and other practices to manage herbicide resistant Palmer amaranth will cost South Carolina soybean growers up to $2,250/ha. With unpredictable rainfall patterns in South Carolina, success in managing Palmer amaranth with soil residual herbicides in dryland crop production becomes an issue. Over-reliance on PPO-inhibitor type herbicides, particularly fomesafen and flumioxazin, to control glyphosate- and ALS-resistant Palmer amaranth will put similar resistance development pressures on those chemistries. Alternatives, including metribuzin in soybean, will provide a mode-of-action rotation for the PPO-inhibitor herbicides. New herbicide tolerance crops are being developed to combat glyphosate resistance, but they are based on old chemistries, such as 2,4-D and dicamba, which have drift concerns. Glufosinate has provided excellent control of glyphosate-resistant Palmer amaranth in glufosinate-tolerant soybeans and cotton. The development of these new technologies will almost certainly add more input costs to growers in the form of new seed traits.
Publications
- Marshall, M.W. and J.G Stokes. 2011. Confirmation of Multiple Herbicide Resistant Palmer Amaranth (Amaranthus palmeri) Biotypes in South Carolina. Southern Weed Science Society Annual Meeting.
- Marshall, M.W. and J.G. Stokes. 2011. Palmer amaranth biotypes confirmed resistant to glyphosate- and als-inhibiting herbicides in South Carolina. Beltwide Cotton Conferences.
- Stokes, J.G. and M.W. Marshall. 2011. Management Programs for Glyphosate-Resistant Palmer Amaranth (Amaranthus palmeri) in Cotton. Southern Weed Science Society Annual Meeting.
- Stokes, J.G. and M.W. Marshall. 2011. Ignite-based herbicide programs for glyphosate-resistant Palmer amaranth in south carolina cotton. Beltwide Cotton Conferences.
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Progress 01/01/09 to 12/31/09
Outputs
OUTPUTS: ACTIVITIES: Glyphosate-resistant Palmer amaranth (Amaranthus palmeri S. Wats.) has emerged as one of the most severe threats to reduced tillage row crop production in South Carolina. Abandonment of conservation practices will lead to degradation of the soil resources and the environment. A survey of the distribution of ALS- and glyphosate-resistant Palmer amaranth in South Carolina was continued in the fall of 2009. In cooperation with county agents, a minimum of 3 grower fields per county were sampled and their locations recorded using a GPS unit. Palmer amaranth seed heads with mature seed were collected and screened for glyphosate- and ALS-resistance. Seedheads from each field was composited, dried, and cleaned. Palmer amaranth seed was planted in the greenhouse and grown to the 4-leaf stage. At the 4-leaf stage, plants were sprayed with glyphosate at 0, 0.84, and 1.68 kg/ha, and thifensulfuron (ALS-inhibiting herbicide) at 0, 23, and 46 g/ha. At 21 days after treatment, plants were scored to determine activity of glyphosate and thifensulfuron. Field studies were conducted in the summer of 2009 at Edisto Research and Education Center (EREC) and Pee Dee Research and Education Center (PDREC) in 2009 to evaluate different combinations preemergence (PRE) and postemergence (POST) herbicides for glyphosate-resistant Palmer amaranth control in South Carolina. Cotton PRE treatments included pendimethalin at 1.06 kg/ha, diuron at 0.28 kg/ha, and fomesafen at 0.28 kg/ha. Cotton POST treatments included glyphosate at 0.84 kg/ha, s-metolachlor at 1.46 kg/ha, glufosinate at 0.59 kg/ha or 0.79 kg/ha, and pyrithiobac 42.5 or 62.5 g/ha. Soybean PRE treatments included flumioxazin at 71 g/ha, pendimethalin at 1.06 kg/ha, sulfentrazone at 0.15 kg/ha, chlorimuron at 60 g/ha, and metribuzin at 0.23 kg/ha. Soybean POST treatments included glyphosate at 0.84 kg/ha, lactofen at 0.22 kg/ha , and fomesafen at 0.28 kg/ha. EVENTS: Field results were presented at the Pee Dee REC Summer Field Day (2009), Edisto REC Fall Field Day (2009), Beltwide Cotton Conference (2010); Southern Weed Science Society annual meeting (2010). PRODUCTS: Weed management recommendations were generated, based on the field research, for inclusion in the 2009 cotton and wheat production guides, and the 2010 peanut production guide and 2010 pest management handbook. DISSEMINATION: During 2009-2010, a total of 45 grower-orientated meetings were held. At each meeting, Palmer amaranth management recommendations for corn, cotton, and soybeans were discussed. Based on the interaction from the audience and discussion with the agents afterwards, recommendations were well received and implemented for upcoming growing season. PARTICIPANTS: Michael W. Marshall (PI), H. David Gunter, Jacob Stokes, and William Bonnette TARGET AUDIENCES: County Agents, Growers, Crop Consultants, and Agribusiness Industry PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
RESULTS: A significant number of survey sites were confirmed (18 out of 22 fields sampled) in the greenhouse to have both ALS- and glyphosate-resistant Palmer amaranth. At PDREC, all PRE treatments at 2 weeks after treatment (WAT) showed excellent Palmer amaranth control (>95%). All treatments received an activating rainfall 3 days after application (1.0" rainfall event). No differences were noted between the irrigated and rain-fed plots; therefore, data were combined across environments. At 2 WAT following the early POST treatments, pendimethalin + diuron combinations in the glyphosate plots showed significant decrease in Palmer amaranth control (70%). This indicated that fomesafen is active longer in the soil compared to a similar rate of diuron. Glyphosate plus s-metolachlor treatment provided good to excellent control (where fomesafen was the foundation soil herbicide treatment). Although glufosinate alone controls Palmer amaranth, a tank mix of s-metolachlor or pyrithiobac plus glufosinate provided excellent control of Palmer amaranth (>95%) while providing soil residual activity of Palmer amaranth. At EREC, Palmer amaranth control was similar to treatments at PDREC; however, temporary cotton injury was observed with over-the-top applications of glufosinate on Phytogen 485 cotton variety (15-20% injury). In soybeans, fomesafen, thiefensulfuron, lactofen, and glufosinate applied POST provided good to excellent control of glyphosate-resistant Palmer amaranth (>95%). At 6 WAT, metribuzin, flumioxazin, and sulfentrazone applied PRE also provided excellent control of glyphosate- and ALS-resistant Palmer amaranth (>95%). OUTCOMES: Since our POST herbicide options are limited in cotton, soil residual herbicides are the preferred method to control glyphosate- and ALS-resistant Palmer amaranth. An aggressive soil herbicide program costs the grower approximately $80/ha; however, hand-weeding, cultivation, and crop abandonment, will cost South Carolina approximately $3,500/ha in lost revenue. With reliance on PPO-inhibitor herbicides (fomesafen, flumioxazin, and sulfentrazone) to control glyphosate- and ALS-resistant Palmer amaranth, the use of metribuzin in soybean will provide a much needed break in that cycle. Overall, a foundation program of fomesafen or diuron plus pendimethalin improved Palmer amaranth control in cotton. Glufosinate-based systems will control glyphosate-resistant Palmer amaranth, but growers cannot rely exclusively on glufosinate, especially considering the fast growth habit of Palmer amaranth (up to 5 cm per day). In soybeans and cotton, glufosinate-tolerant varieties are an option to use in heavily infested Palmer amaranth fields. In our field experiments, glufosinate provided excellent control of glyphosate-resistant Palmer amaranth in glufosinate-tolerant soybeans In the near future, glyphosate and glufosinate-tolerant technology will be combined in cotton and soybean varieties; therefore, research is needed to determine the best time to position glufosinate application during the growing season while taking advantage of glyphosate's ability to control larger susceptible weeds.
Publications
- Marshall, M.W. and H.D. Gunter. 2010. Update on Herbicide Resistant Palmer Amaranth (Amaranthus palmeri S. Wats.) in South Carolina. 2010 Annual Beltwide Cotton Conference. Marshall, M.W. 2010. Update on Glyphosate-Resistant Palmer amaranth (Amaranthus palmeri S. Wats.) in South Carolina. Southern Weed Society Society Annual Meeting.
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Progress 01/01/08 to 12/31/08
Outputs
OUTPUTS: ACTIVITIES: A survey was conducted in the fall of 2008 throughout the major soybean and cotton growing areas of South Carolina. In cooperation with county agents, approximately 3 fields per county were surveyed and their locations recorded using a GPS unit. Palmer amaranth seed heads with mature seed were collected and screened for glyphosate- and ALS-resistance. Field research was conducted in 2008 to demonstrate alternative management practices for herbicide resistant Palmer amaranth. Herbicide resistant Palmer amaranth has emerged as one of the most severe threats to reduced tillage crop production in South Carolina. Abandonment of conservation practices will lead to degradation of the soil resources and the environment. Field studies were conducted to evaluate different combinations preemergence (PRE) and postemergence (POST) herbicides for glyphosate- and ALS-resistant Palmer amaranth control. Cotton PRE treatments included pendimethalin, alachlor, fluometuron, and fomesafen. Cotton POST treatments included glyphosate, s-metolachlor, and pyrithiobac. Soybean PRE treatments included flumioxazin, pendimethalin, chlorimuron, chloransulam, sulfentrazone, and metribuzin. Soybean POST treatments included glyphosate, lactofen, fomesafen, and aciflourfen. EVENTS: Results were presented at the Pee Dee REC Summer Field Day (2008), Edisto REC Fall Field Day (2008), Beltwide Cotton Conference (2009); Weed Science Society of America annual meeting (2009). PRODUCTS: Management recommendations were generated, based on the field research, for use in the 2009 corn, soybean, cotton, peanut, and wheat production guides, and the 2009 pest management handbook. DISSEMINATION: During 2008-2009, a total of 12 grower meetings were conducted. At each meeting, Palmer amaranth management recommendations were presented. Based on the interaction from the audience, recommendations were well received and implemented for upcoming growing season. PARTICIPANTS: Michael W. Marshall (PI) and David Gunter TARGET AUDIENCES: The main target audience for this project is county agents, growers, crop consultants, and agribusiness. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
RESULTS: Based on the survey work, 12 counties were confirmed to have glyphosate-resistant Palmer amaranth populations. In cotton, all PRE treatments, except alachlor + fluometuron fb glyphosate + pyrithiobac, controlled Palmer amaranth greater than 95%. Treatments containing fomesafen PRE provided good to excellent control of Palmer amaranth, regardless of the herbicide tank mix partner. In the pendimethalin + fomesafen PRE treatments, glyphosate + pyrithiobac early POST cotton yields were significantly higher than the glyphosate + s-metolachlor early POST yields. In contrast, alachlor plus fomesafen or alachlor plus fluometuron in the glyphosate treated plots provided nearly 100% Palmer amaranth control. However, alachlor plus fomesafen or fluometuron in the glufosinate only blocks did not provide the same level of control (60%). Fluometuron was inconsistent in controlling Palmer amaranth. Alachlor + fluometuron followed by glyphosate + s-metolachlor early POST had the highest cotton yield compared to all other treatments. Flumioxazin, alachlor, chloransulam, chlorimuron, and metribuzin provided good to excellent PRE control of Palmer amaranth in soybeans. Overall, the addition of fomesafen or flumioxazin to the herbicide program in soybeans dramatically improved Palmer amaranth control. OUTCOME: Pyrithiobac controlled Palmer amaranth in cotton at both locations indicating that these were not ALS-resistant populations. Overall, the addition of fomesafen to the preemergence herbicide program dramatically improved Palmer amaranth control in cotton. Fluometuron provided good to excellent control of Palmer amaranth; however, inconsistencies were noted in control due to soil textural differences commonly found in South Carolina. Glufosinate is a fair to good herbicide alternative for control of small Palmer amaranth (less than 7.5 cm tall). If irrigation or rainfall is timely, preemergence programs combined with glufosinate tolerant crop programs will continue to play an important role in managing glyphosate-resistant Palmer amaranth. In soybeans, flumioxazin, alachlor, chloransulam, chlorimuron, and metribuzin provided good to excellent preemergence control of Palmer amaranth in soybeans. In addition, acifluorfen and lactofen controlled any Palmer amaranth escapes. Overall, the addition of fomesafen or flumioxazin to the preemergence herbicide program in cotton or soybeans dramatically improved Palmer amaranth control. If irrigation or rainfall is timely, preemergence programs combined with glufosinate-tolerant programs in cotton or glyphosate plus aciflourfen or lactofen in soybean will continue to play an important role in managing glyphosate-resistant Palmer amaranth. Glufosinate-tolerance technology in soybeans is scheduled to be released in 2009 which will provide another alternative in soybean production. Although, these preventative PRE programs ultimately cost the grower extra (approximately $62.00 per hectare), the crop would not be harvestable if Palmer amaranth if left in the crop resulting in a loss of $2,300/ha.
Publications
- R. L. Nichols, M.G. Burton, A. S. Culpepper, C. L. Main, M. W. Marshall, T. C. Mueller, J. K. Norsworthy, R. C. Scott, K. L. Smith, L. E. Steckel, and A. C. York. 2008. Distribution and Impact of Glyphosate-Resistant Palmer Amaranth in the Southern United States. Resistant Pest Management Newsletter. Vol 17. No. 2.
- Marshall, M.W. 2009. Herbicide Program Alternatives for Glyphosate-Resistant Palmer Amaranth in Cotton. Annual Beltwide Cotton Conference.
- Marshall, M.W. 2009. Complementary Herbicide Programs for Palmer Amaranth Control in Glyphosate-Tolerant Cotton and Soybeans. Weed Science Society of America Annual Meeting.
- R. L. Nichols, J. Bond, A. S. Culpepper, D. Dodds, V. Nandula, C. L. Main, M. W. Marshall, T. C. Mueller, J. K. Norsworthy, A. Price, M. Patterson, R. C. Scott, K. L. Smith, L. E. Steckel, D. Stephenson, D. Wright, and A. C. York. 2009. Glyphosate-Resistant Palmer Amaranth Spreads in the Southern United States. Resistant Pest Management Newsletter. Vol 18. No. 2.
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