WEED MANAGEMENT IN AGRONOMIC CROPS OF THE LOUISIANA RED RIVER VALLEY

• Sponsoring Institution: State Agricultural Experiment Station
• Project Status: TERMINATED
• Funding Source: STATE
• Reporting Frequency: Annual
• Accession No.: 0217599
• Project No.: LAB03974
• Project Start Date: Jan 1, 2009
• Project End Date: Dec 31, 2013

Project Director
Stephenson, DA.

Recipient Organization
LOUISIANA STATE UNIVERSITY
202 HIMES HALL
BATON ROUGE,LA 70803-0100

Performing Department
Dean Lee Research Station

Non Technical Summary
Approximately 1.94 million acres of corn, cotton, grain sorghum, and soybean were planted in Louisiana in 2007. In 2008, acreage of these crops increased to 1.98 million acres. Despite the acreage increase in 2008, corn, cotton, and grain sorghum acreage decreased 13 to 52%, but soybean increased 41%. Fluctuation in acreage will continue in future years due to commodity prices, ability of the producer to procure a loan, and fertilizer prices. The uncertainty of corn, cotton, grain sorghum, and soybean acreage in the future highlights the need to determine and disseminate effective weed management systems so producers can make knowledgeable decisions. Although crops are produced throughout Louisiana, the Louisiana Red River Valley has traditionally planted a large portion of the crop acreage. In 2007, Louisiana Red River Valley parishes planted 22, 41, 71, and 49% of the corn, cotton, grain sorghum, and soybean acreage, respectively. The inherent pH of Louisiana Red River Valley soils differentiates it from other regions of Louisiana; thus efficacy, crop safety, and persistence of many herbicides can be affected. The high pH of Red River Valley soils in Louisiana necessitates the need for specific weed management programs to thwart possible herbicide persistence issues. In agricultural lands, weeds increase the time and costs involved in crop production, interfere with crop harvesting, and reduce crop yields and quality. The estimated average annual monetary loss caused by weeds in 46 crops grown in the United States was $4.1 billion in 1991. Of this loss, approximately 82% occurred in field crops. It is clear that control of weeds in agricultural crops is absolutely essential for crop production. Primary methods of weed control are cultural, mechanical, and chemical. These methods primary goal is for the prevention of competition between crops and weeds. Although cultural and mechanical weed control practices are utilized, chemical weed control is the most common method of weed management in the United States. Herbicides were applied to greater than 85% of the corn, cotton, grain sorghum, and soybean acreage in 2005. These data indicate that production systems are often based on weed management rather than any other pest problems that may occur. Genetically-modified crops, especially glyphosate-tolerant cultivars, have been a technical, economic, and agronomic success for companies that developed them and the farmers who use them. However, the development of weeds that are resistant to glyphosate due to the massive selection pressure over millions of acres has occurred. Not only is glyphosate resistance a growing problem, weeds resistant to numerous other herbicides have been identified. In most incidences of herbicide resistance, over dependence on a single herbicide or single mode of action, which may encompass many herbicides, is the primary cause of the problem. Herbicide resistance further supports the need to investigate weed management strategies that will control weeds, but also preserve the herbicide-tolerant crop technologies.

Animal Health Component

(N/A)

Research Effort Categories

Basic

(N/A)

Applied

(N/A)

Developmental

(N/A)

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
213	1510	1140	10%
213	1520	1140	10%
213	1549	1140	10%
213	1710	1140	10%
213	1820	1140	10%
216	1510	1140	10%
216	1520	1140	10%
216	1549	1140	10%
216	1710	1140	10%
216	1820	1140	10%

Knowledge Area
216 - Integrated Pest Management Systems; 213 - Weeds Affecting Plants;

Subject Of Investigation
1549 - Wheat, general/other; 1520 - Grain sorghum; 1510 - Corn; 1710 - Upland cotton; 1820 - Soybean;

Field Of Science
1140 - Weed science;

Keywords

weed control

herbicide resistance

weed resistance

weed management

herbicide

Goals / Objectives
The goal of this project is to provide Louisiana Red River Valley crop producers with effective and economical weed management strategies. Four objectives have been developed to accomplish the goal. The first objective is to evaluate herbicides and herbicide-tolerant crops for weed management and crop tolerance in corn, cotton, grain sorghum, and soybean. Evaluation and development of weed management strategies for crops produced in the Louisiana Red River Valley is the second objective. Thirdly, research for the development of weed management systems in reduced tillage crop production systems will be conducted. Finally, identification and evaluation of herbicide resistant weeds in Louisiana for development of herbicide resistant weed management strategies will be performed. Output activities will include the implementation, performance, and analyzing of experiment data. These activities will provide the ability to present research findings at professional conferences, demonstration locations, research/extension field days, training, etc. using all available products such as weed management programs/methods/strategies and curricula designed to educate Louisiana Red River Valley crop producers. The outputs listed above will be accomplished for the purpose of dissemination of information to Louisiana crop producers.

Project Methods
For all objectives associated with in-field experiments, research will be conducted at LSU AgCenter research and extension centers and on-farm research sites. Research will involve small- and large-plot techniques. Small-plot techniques typically include a plot size of 2 to 8, 38-inch rows wide by 30 to 40-feet long with 3 to 4 replications of treatments. For large-plot techniques, plot size will typically equal the width of planting or pesticide application equipment and be at least 200-feet in length with at least three replications. Research will be designed using appropriate experimental design allowing for proper statistical analysis to reveal treatment strengths and weaknesses. Herbicides will be applied with tractor-mounted compressed air systems, CO2-pressurized backpack systems, or with on-farm equipment. Visual estimates of percent weed control and crop injury will be recorded at several intervals after application on a scale of 0 to 100% (0 = no control or injury and 100 = complete control or crop death). Crop yield data and crop and weed growth parameters will also be collected if needed to access the feasibility of the treatment. The weed resistance objective includes locating, identifying, and screening problematic weeds for potential resistance to herbicides in Louisiana. Weed inflorescence with mature seeds will be collected within the main problem area. Weed inflorescence will be collected and transported back to screening location, air dried, hand-threshing to remove the seed, cleaned to remove poor quality seeds, and placed in properly labeled paper envelopes for storage. Weed resistance experiments will be divided into three phases. The first phase will simply determine the absence or presence of resistance to a herbicidal mode of action. Suspected resistant seed and seed from a known susceptible population will be sown in a greenhouse. Following emergence, multiple seedlings will be transplanted to eight pots containing potting mix for continued growth, with each pot acting as a replication. When seedlings have reached the desired growth stage for herbicide application, plants will be thinned to two per pot and treated with a labeled rate of the herbicide in question. Visual efficacy ratings of the herbicide will be determined 14 to 28 days after application and above-ground plant fresh weights data will be used to determine the absence or presence of resistance when compared to the known susceptible plant. If presence of possible resistance is observed in the first phase, a dose-response experiment will be initiated as the second phase. Six doses of the herbicide will be applied to provide a dose-response curve to determine a lethal dose for 50% of the suspected resistant population (LD50) compared to the known susceptible population. The third phase of resistance experiments involves heritability of resistance by the progeny of a confirmed resistant weed. Surviving plants from phase two experiments will be allowed to pollinate and produce seed. Seed will then be collected and sowed in pots following the technique described earlier to develop a dose response curve for progeny.

Progress 01/01/09 to 12/31/13

Outputs
Target Audience: Target audiences for this project include crop producers and weed management professionals. 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? The results have been disseminated to communities of interest through oral and poster presentations at scientific conferences, field days, demonstrations, personal visits, newsletters, and through extension field agents. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? Herbicides containing pyroxasulfone provided excellent control of some grass and broadleaf weeds in corn. However, the co-application of atrazine with pyroxasulfone was needed to provide broad spectrum control of numerous weed species. Research evaluated multiple herbicide treatments applied postemergence to 12-inch corn to discern which treatment would provide acceptable weed control at corn harvest.Applications of glyphosate plus Lexar EZ, Halex GT plus atrazine, and glyphosate plus atrazine and Warrant provided at least 85% control of barnyardgrass, browntop millet, Palmer amaranth, morningglory, sicklepod, and hophornbeam copperleaf based upon ratings at corn harvest. Glyphosate-resistant johnsongrass continues to be problematic for Louisiana cotton producers. Research indicated that three applications of Liberty in Liberty Link cotton provided season-long control of this pest.Sequential applications of Liberty plus Select Max reduced the number of postemergence applications for johnsongrass control to two rather than three. Programs that contained at least four different herbicidal modes of action provided excellent season long control of glyphosate-resistant johnsongrass. Glyphosate-resistant Palmer amaranth also is problematic for Louisiana cotton producers. Weed management programs containing residual herbicides applied preemergence, early-postemergence, and as a late postemergence-directed application provided excellent control of all weeds (including Palmer amaranth)and maximized yield. Research was conducted with soon to be commercialized herbicide-tolerant grain sorghum to investigate its feasibility in fields infested with johnsongrass.Postemergence applications of nicosulfuron plus rimsulfuron provided good to excellent control of johnsongrass with no injury to herbicide-tolerant grain sorghum. In addition, co-applying atrazine with nicosulfuron and rimsulfuron broadened the spectrum of weed control. Research evaluating the utility of numerous preemergence residual herbicides in soybean indicated that Boundary, Envive, Authority MTZ, Fierce, and Valor XLT provided the greatest control of multiple grass and broadleaf weeds for at least 21 days following application.Postemergence co-application of glyphosate plus Zidua or Dual Magnum provided excellent control of numerous grass and broadleaf weeds and sufficient residual weed control to maintain soybean weed free for the 5 week after emergence window to maximize yield. Herbicide-resistant weeds continue to spread in Louisiana; however, the rate at which they are advancing is slowing due to increased use of residual herbicides and better sanitation practices by growers.Glyphosate-resistant Palmer amaranth has been documented in the majority of crop producing parishes in Louisiana. Glyphosate-resistant johnsongrass has only spread to one addition parish bringing the total number of infested parishes to three.Rice flatsedge resistant to a postemergence application of halosulfuron (64 times greater than the labeled rate) alsowas documented indicating that halosulfuron is no long a viable option for this weed in rice.

Publications

• Type: Journal Articles Status: Awaiting Publication Year Published: 2013 Citation: Griffin, J. L., M. Bauerle, D. Stephenson, D. Miller, and J. Boudreaux. 2013. Soybean response to dicamba applied at vegetative and reproductive growth stages. Weed Technol. (In press).
• Type: Journal Articles Status: Published Year Published: 2013 Citation: Stephenson, IV, D. O., J. A. Bond, R. L. Landry, and H. M. Edwards. 2013. Effect of co-applied glyphosate, pyrithiobac, pendimethalin, or S-metolachlor on cotton injury, growth, and yield. Weed Technol. 27:305-309.
• Type: Conference Papers and Presentations Status: Published Year Published: 2013 Citation: Landry, R. L., D. O. Stephenson, IV, and B. C. Woolam. 2013. Glyphosate-resistant johnsongrass (Sorghum halepense) control in soybean (Glycine max) with chlorimuron, clethodim, fomesafen, and glufosinate. In Proc., South. Weed Sci. Soc. 66:73.
• Type: Conference Papers and Presentations Status: Published Year Published: 2013 Citation: Miller, D. K., D. Stephenson, M. M. Mathews, R. L. Landry, and B. C. Woolam. 2013. Evaluation of Anthem in Louisiana soybean production systems. In Proc., South. Weed Sci. Soc. 66:74.
• Type: Conference Papers and Presentations Status: Published Year Published: 2013 Citation: Landry, R. L., D. O. Stephenson, IV, and B. C. Woolam. 2013. Glufosinate rate and timing for control of johnsongrass (Sorghum halepense) in glufosinate-resistant soybean (Glycine max). In Proc., South. Weed Sci. Soc. 66:124.
• Type: Conference Papers and Presentations Status: Published Year Published: 2013 Citation: Hardwick, J., J. L. Griffin, D. Stephenson, M. J. Bauerle. 2013. Soybean response and weed control with pyroxasulfone. In Proc., South. Weed Sci. Soc. 66:136.
• Type: Conference Papers and Presentations Status: Published Year Published: 2013 Citation: Copes, J. T., D. Stephenson, J. A. Bond, R. L. Landry, B. C. Woolam, and J. L. Griffin. 2013. Influence of 2,4-D application on corn growth and yield. In Proc., South. Weed Sci. Soc. 66:164.
• Type: Conference Papers and Presentations Status: Published Year Published: 2013 Citation: Stephenson, IV, D. O., J. K. Norsworthy, R. L. Landry, B. C. Woolam, and B. Johnson. 2013. Effectiveness of glufosinate with and without clethodim as influenced by johnsongrass (Sorghum halepense) height in glufosinate-resistant cotton (Gossypium hirsutum). In Proc., South. Weed Sci. Soc. 66:166.
• Type: Conference Papers and Presentations Status: Published Year Published: 2013 Citation: Culpepper, A. S., A. C. York, L. E. Steckel, J. A. Bond, and D. Stephenson. 2013. Palmer amaranth control significantly influenced by the time of day in which Liberty is applied. In Proc., South. Weed Sci. Soc. 66:168.
• Type: Conference Papers and Presentations Status: Published Year Published: 2013 Citation: Riar, D. S., J. K. Norsworthy, L. E. Steckel, D. Stephenson, T. W. Eubank, and B. Scott. 2013. A survey of weed management practices in midsouth soybean. In Proc., South. Weed Sci. Soc. 66:186.
• Type: Conference Papers and Presentations Status: Published Year Published: 2013 Citation: Woolam, B. C., D. O. Stephenson, IV, and R. L. Landry. 2013. Evaluation of fall-applied herbicide for henbit (Lamium amplexicaule) management. In Proc., South. Weed Sci. Soc. 66:207.
• Type: Conference Papers and Presentations Status: Published Year Published: 2013 Citation: Eubank, T. W., D. Stephenson, J. A. Bond, B. Edwards, R. L. Landry, and B. C. Woolam. 2013. Efficacy of fall- and spring-applied herbicides for control of henbit (Lamium amplexicaule). In Proc., South. Weed Sci. Soc. 66:208.
• Type: Conference Papers and Presentations Status: Published Year Published: 2013 Citation: Norsworthy, J. K., B. Scott, D. Stephenson, D. B. Reynolds, M Peterson, and G. Kruger. 2013. Volatility and off-target movement of formulations containing Colex-D technology. In Proc., South. Weed Sci. Soc. 66:225.
• Type: Conference Papers and Presentations Status: Published Year Published: 2013 Citation: Stephenson, IV, D. O. 2013. Weed management in the absence of a crop. Beltwide Cotton Conf. Consultants Conference. p. 4. In Proc., Beltwide Cotton Conf., National Cotton Council, Memphis, TN.
• Type: Conference Papers and Presentations Status: Published Year Published: 2013 Citation: Woolam, B. C., D. O. Stephenson, IV, R. L. Landry. 2013. Weed management in conventional cotton in Louisiana. p. 316. In Proc., Beltwide Cotton Conf., National Cotton Council, Memphis, TN.
• Type: Conference Papers and Presentations Status: Published Year Published: 2013 Citation: Landry, R. L., D. O. Stephenson, IV, J. K. Norsworthy, B. C. Woolam, and D. B. Johnson. 2013. Glyphosate-resistant johnsongrass (Sorghum halepense) control with Envoke, Staple LX, and Select Max in cotton. p. 318. In Proc., Beltwide Cotton Conf., National Cotton Council, Memphis, TN.
• Type: Conference Papers and Presentations Status: Published Year Published: 2013 Citation: Johnson, D. B., J. K. Norsworthy, H. D. Bell, D. O. Stephenson, IV, D. K. Miller, and J. A. Bond. 2013. Herbicide programs in Glytol-LibertyLink cotton. p. 662. In Proc., Beltwide Cotton Conf., National Cotton Council, Memphis, TN.
• Type: Conference Papers and Presentations Status: Published Year Published: 2013 Citation: Norsworthy, J. K., D. O. Stephenson, IV, D. K. Miller, L. E. Steckel, J. Bond, D. M. Dodds, D. B. Reynolds, and R. B. Lassiter. 2013. Efficacy of Enlist Duo: A summary of trials in Midsouth cotton. pp. 1041-1042. In Proc., Beltwide Cotton Conf., National Cotton Council, Memphis, TN.

Progress 01/01/12 to 12/31/12

Outputs
OUTPUTS: The project generated outputs in the form of presentations at professional conferences and referred journal articles. Additionally, weed management strategies developed from this project were provided to crop producers and other stakeholders in Louisiana. PARTICIPANTS: Daniel O. Stephenson, IV, (PI), LSU AgCenter. TARGET AUDIENCES: Target audiences for this project include crop producers and weed management professionals. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
Research evaluated pyroxasulfone as a component of a weed management program in corn. Pyroxasulfone applied preemergence or postemergence, with and without atrazine, provided excellent control of numerous grass and broadleaf weeds. However, control was generally greater when pyroxasulfone was co-applied with atrazine. A premix of fluthiacet-methyl and pyroxasulfone applied preemergence and/or postemergence did not provide greater control of numerous grass and broadleaf weeds than pyroxasulfone alone. Lexar co-applied with glyphosate to 12-inch corn provided greater than 90% control of many grass and broadleaf weeds until harvest. In other research, 2,4-D applied postemergence to 2- to 4-collar corn significantly injured corn, but yield was not reduced. These data will provide Louisiana corn producers with effective weed management strategies. Research in Louisiana demonstrated that soybean needs to be maintained weed-free for five weeks after emergence to maximize yield. Numerous preemergence herbicides (Boundary, Envive, Canopy EX, Enlite, Prefix, Authority MTZ, and others) provided excellent control of numerous weeds for 28 days after soybean emergence. Boundary and Prefix injured soybean less than other herbicides and are better options to provide weed control without early-season soybean injury. The competition study in combination with the evaluation of preemergence herbicides highlights that Louisiana soybean producers should utilize preemergence herbicides to help maintain soybean weed-free and maximize yield. Other data indicates that Liberty application rate is not as important as application timing, where three applications were needed for season-long control of johnsongrass. Applications of Staple LX and Envoke as compared to Liberty and Select Max did not effectively control johnsongrass in cotton. Also, herbicide programs that included at least four to five unique herbicide modes of action were needed to manage johnsongrass season-long. Liberty controlled Palmer amaranth greater than 95% when applied at least 1 hour after sunrise. Glytol/Liberty Link cotton is tolerant to postemergence applications of glyphosate and Liberty. Research investigating the application sequence of glyphosate and/or Liberty indicated no differences in weed control regardless of which herbicide is applied as the first postemergence treatment.

Publications

• Samples, C. A., D. M. Dodds, L. T. Barber, C. Burmaster, G. D. Collins, K. L. Edmisten, J. Kruse, D. O. Stephenson, IV, and C. L. Main. 2012. Effects of glufosinate application rate and timing on cotton growth, development, and yield. p. 87. In Proc., Beltwide Cotton Conf., National Cotton Council, Memphis, TN.
• D. K. Miller, D. O. Stephenson, IV, and M. S. Mathews. 2012. Weed management and crop tolerance with Warrant in Louisiana cotton. p. 1514. In Proc., Beltwide Cotton Conf., National Cotton Council, Memphis, TN.
• D. O. Stephenson, IV, J. A. Bond, and D. K. Miller. 2012. Evalution of Glytol/Liberty Link cotton in the Midsouth. p. 1522. In Proc., Beltwide Cotton Conf., National Cotton Council, Memphis, TN.
• Dodds, D. M., L. T. Barber, C. Burmaster, G. D. Collins, K. L. Edmisten, M. A. Jones, J. Kruse, D. O. Stephenson, IV, and C. L. Main. 2012. Effect of glufosinate application on Widestrike and Liberty Link cotton varieties. p. 1537. In Proc., Beltwide Cotton Conf., National Cotton Council, Memphis, TN.
• Stephenson, IV, D. O. and J. A. Bond. 2012. Evaluation of thiencarbazone-methyl and isoxaflutole based herbicide programs in corn. Weed Technol. 26:37-42.
• Steckel, L. E., D. Stephenson, J. Bond, S. D. Stewart, and K. A. Barnett. 2012. Evaluation of WideStrike Flex cotton response to over-the-top glufosinate tank-mixtures. J. Cotton Sci. 16:88-95.
• Stephenson, D. and R. L. Landry. 2012. Henbit (Lamium amplexicaule) management with fall-applied herbicides. In Proc., South. Weed Sci. Soc. 65:51.
• Miller, D. K., D. Stephenson, M. S. Mathews. 2012. Evaluation of Fierce for controlling weeds in Louisiana soybean. In Proc., South. Weed Sci. Soc. 65:78.
• R. L. Landry and D. O. Stephenson, IV. 2012. Glufosinate rate and timing for control of glyphosate-resistant johnsongrass (Sorghum halepense) in glufosinate-resistant soybean (Glycine max). In Proc., South. Weed Sci. Soc. 65:109.
• Norsworthy, J. K., K. L. Smith, R. C. Scott, L. Steckel, J. A. Bond, T. W. Eubank, D. Stephenson. 2012. Midsouth weed management survey with emphasis on Palmer amaranth. p. 1544. In Proc., Beltwide Cotton Conf., National Cotton Council, Memphis, TN.
• Brecke, B. J., D. Partridge-Telenko, and D. O. Stephenson, IV. 2012. Effect of tillage and herbicide input on Benghal dayflower (Commelina benghalensis) in cotton. p. 1545. In Proc., Beltwide Cotton Conf., National Cotton Council, Memphis, TN.
• Stephenson, D., D. K. Miller, J. A. Bond, R. L. Landry, and M. S. Mathews. 2012. Utility of pyroxasulfone in Mid-south corn and soybean. In Proc., South. Weed Sci. Soc. 65:111.
• Rasheed, A., N. R. Burgos, T. Tseng, R. A. Salas, E. A. Alcobar, and D. Stephenson. 2012. Genetic divergence of herbicide-resistant and susceptible-Sorghum halepense populations. In Proc., South. Weed Sci. Soc. 65:170.

Progress 01/01/11 to 12/31/11

Outputs
OUTPUTS: The project generated outputs in the form of presentations at six professional conferences, eight proceedings, and one refereed journal article. Weed management strategies developed from this project were provided to crop producers and other stakeholders in Louisiana. PARTICIPANTS: Daniel O. Stephenson (PI), LSU AgCenter. TARGET AUDIENCES: Target audiences for this project include crop producers and weed management professionals. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
A johnsongrass population in Rapides Parish, Louisiana, was identified as resistant to the herbicide, glyphosate. Plants from rhizomes were 28.7 times less sensitive to glyphosate as compared to a glyphosate-susceptible population, indicating that glyphosate is no longer an effective tool for control of this population in glyphosate-resistant crops (corn, cotton, and soybean). For control of glyphosate-resistant johnsongrass, glufosinate applied in sequential applications provides excellent control in glufosinate-resistant soybean and cotton. Preliminary results indicate with fall applications of glyphosate plus Resolve, Canopy EX, Goal, or Valor 60 to 90 days of residual control of henbit. Additional research investigating methods to control henbit just prior to planting corn determined that applying atrazine, Lexar, Callisto, Capreno, and paraquat, following an earlier application of glyphosate and 2,4-D, provided 90% control. These results will provide Louisiana producers with strategies for controlling henbit. In soybean, the utility of preemergence herbicides such as Boundary, Prefix, Envive, and Enlite was highlighted for effective early-season weed management. Their use did not exclude postemergence glyphosate applications in Roundup Ready soybean or Liberty in Liberty Link soybean, which were needed for season-long weed control. Pyroxasulfone provided excellent weed control of many grass and broadleaf weeds; however, it injured soybean when applied preemergence and postemergence, but injury was not observed by 14 days after treatment. In corn, similar pyroxasulfone efficacy results were observed and no corn injury was documented. Research in cotton determined the utility of residual herbicides in conventional, Roundup Ready Flex, and Liberty Link cotton. Residual herbicides are essential to achieve season-long weed control and maximum cotton yield in conventional cotton. However, residuals were not needed for effective weed management in Roundup Ready Flex and Liberty Link cotton, but this was due to the absence of glyphosate-resistant weeds. Experiments were also initiated to investigate weed control in cotton that is resistant to both glyphosate and glufosinate (GlyTol/Liberty Link cotton). The order in which glyphosate or Liberty was applied was not of major importance and overall weed management was similar for all treatments. This program has potential to provide Louisiana cotton producers with an excellent weed management strategy in cotton.

Publications

• Stephenson, IV, D. O., J. L. Griffin, and D. K. Miller. 2011. Battling herbicide-resistant weeds. Louisiana Agriculture 54(2):24-25.
• Stephenson, IV, D. O., D. K. Miller, R. L. Landry, and M. S. Mathews. 2011. Influence of adjuvants when co-applied with saflufenacil and glyphosate on burndown weed control. In Proc., South. Weed Sci. Soc. 64:247.
• Stephenson, IV, D. O., R. L. Landry, and B. C. Woolam. 2011. Glyphosate-resistant Palmer amaranth in Louisiana. In Proc., South. Weed Sci. Soc. 64:246.
• Stephenson, IV, D. O., J. L. Griffin, and N. R. Burgos. 2011. Glyphosate resistant johnsongrass monitoring and management. In Proc., South. Weed Sci. Soc. 64:226.
• Bauerle, M. J., J. L. Griffin, D. O. Stephenson, D. K. Miller, and J. M. Boudreaux. 2011. Soybean response to dicamba simulated drift at vegetative and reproductive growth stages. In Proc., South. Weed Sci. Soc. 64:49.
• Stephenson, IV, D. O., R. L. Landry, and S. B. Blanche. 2011. Effect of planting pattern on sequential application timings of glufosinate in glufosinate-resistant soybean. In Proc., South. Weed Sci. Soc. 64:31.
• Stephenson, IV, D. O., J. A. Bond, J. Seibert, L. Walton. 2011. Control of various weeds with 2,4-D alone or co-applied with glufosinate or glyphosate. p. 1546. In Proc., Beltwide Cotton Conf., National Cotton Council, Memphis, TN.
• Stephenson, IV, D. O., R. L. Landry, and B. C. Woolam. 2011. Glyphosate-resistant Palmer amaranth in Louisiana. p. 1520. In Proc., Beltwide Cotton Conf., National Cotton Council, Memphis, TN.
• Steckel, L, J. Bond, and D. Stephenson. 2011. Tolerance of WideStrike cotton to Ignite tank-mix applications. pp. 1540-1541. In Proc., Beltwide Cotton Conf., National Cotton Council, Memphis, TN.

Progress 01/01/10 to 12/31/10

Outputs
OUTPUTS: The project generated outputs in the form of 18 presentations at professional conferences and 2 referred journal articles. Additionally, weed management strategies developed or refined from this project were provided to crop producers and other stakeholders in Louisiana. PARTICIPANTS: Dr. Daniel O. Stephenson, IV, Assistant Professor, Weed Scientist, LSU AgCenter TARGET AUDIENCES: Target audiences for this project include crop producers and weed management professionals. PROJECT MODIFICATIONS: Not relevant to this project.

Impacts
A Palmer amaranth population located in Concordia Parish, Louisiana, was identified as resistant to the herbicide glyphosate. Data confirms that the resistant population is 54 times less sensitive to glyphosate compared with a glyphosate-susceptible population, indicating that glyphosate is no longer an effective tool for control of this population in all glyphosate-resistant crops (corn, cotton, and soybean). Research results indicate that thiencarbazone-methyl provides at least 90% control of rhizomatous johnsongrass and 85% control of barnyardgrass, browntop millet, and various broadleaf weeds at corn harvest. Thiencarbazone-methyl-containing herbicides can be an effective tool for control of johnsongrass and other weeds in corn. Data indicates that numerous alternatives, such as atrazine:S-metolachlor applied preemergence and/or postemergence, provide at least 80% control of barnyardgrass and browntop millet, which are extremely troublesome weeds in Louisiana grain sorghum. Research has shown that Louisiana grain sorghum producers do not have a herbicide option to provide season-long control of johnsongrass. Louisiana grain sorghum producers are advised to not seed grain sorghum in fields that are infested with rhizome johnsongrass. Research will continue to determine strategies for johnsongrass management in grain sorghum. In soybean, preliminary results indicate good to excellent early-season control of many Central Louisiana weeds with preemergence applications of Authority MTZ, Boundary, Prefix, and Valor SX; however, a postemergence herbicide applications are still needed for season-long weed control. Eight maturity group IV and V soybean varieties suggested for use by LSU AgCenter scientists were tested for tolerance to the herbicide metribuzin applied preemergence. Data indicates differential variety tolerance to metribuzin and these data were disseminated by the LSU AgCenter soybean extension agronomist. Additionally, research determined the need to apply Ignite in Liberty Link soybean by 10 to 15 days following emergence followed by a sequential application 10 to 15 days later for optimum weed management. Experiments in cotton determined the need of preemergence herbicide applications to provide optimum weed control and proved their necessity for mitigation of weeds resistant to glyphosate. Herbicides that provide residual weed control (i.e. fomesafen, fluometuron, diuron, prometryn, and pendimethalin, and flumioxazin) should be applied at or near cotton planting to provide residual control of many broadleaf and grass weeds that infest Louisiana cotton. Herbicides that provide residual control of weeds, such as Dual Magnum and other formulations of metolachlor, should be applied when cotton is at the one to two leaf stage for optimum weed control. Also, co-application of glyphosate, Dual Magnum, and Staple LX causes excessive injury to cotton, but visual injury subsides within 21 days after application and cotton growth and yield are not reduced.

Publications

• Miller, D. K., R. G. Downer, and D. O. Stephenson, IV. 2010. Impact of mixing aqueous capsule suspension formulation of pendimethalin and glyphosate on growth and yield of second-generation glyphosate-resistant cotton. J. Cotton Sci. 14:181-185.
• Miller, D. K., R. G. Downer, and D. O. Stephenson, IV. 2010. Interactive effects of tank-mixed application of insecticide, glyphosate, and pendimethalin on growth and yield of second-generation glyphosate-resistant cotton. J. Cotton Sci. 14:186-190.
• Stephenson, IV, D. O. and R. L. Landry. 2010. 2009 Weed Science Annual Report. Available at http://www.lsuagcenter.com/MCMS/RelatedFiles/%7B20D7D15B-FFD3-43E9-9D 34-8F67C3485C2D%7D/2009+ANNUAL+REPORT-Weed+Sciencel.pdf (verified 10 Mar 2010), Louisiana State University Agricultural Center, Dean Lee Research and Extension Center, Alexandria, LA.
• Stephenson, IV, D. O., D. K. Miller, J. L. Griffin, R. L. Landry, M. M. Mathews, and J. M. Boudreaux. 2010. Comparison of various herbicides co-applied with glufosinate for weed management in glufosinate-resistant soybean. In Proc., South. Weed Sci. Soc. 63:29.
• Stephenson, IV, D. O.and R. L. Landry. 2010. Soybean weed management with premix combinations of glyphosate, fomesafen, and S-metolachlor. In Proc., South. Weed Sci. Soc. 63:27.
• Stephenson, IV. D. O., D. K. Miller, J. L. Griffin, R. L. Landry, M. M. Mathews, and J. M. Boudreaux. 2010. Glufosinate and glyphosate application timings in glufosinate- and glyphosate-resistant soybean. In Proc., South. Weed Sci. Soc. 63:126.
• Steckel, L., S. Culpepper, K. Smith, J. Bond, M. Marshal, A. York, D. Stephenson, T. Mueller, M. Patterson, and A. Price. 2010. Situation in Southern US row crops. Pan-American Weed Resistant Conf. 19-Jan-2010.
• Stephenson, IV, D. O., J. A. Bond, D. K. Miller, E. P. Millhollon, R. L. Landry, J. K. Manning, and J. B. McDuffie. 2010. Effect of pendimethalin and S-metolachlor co-applied with glyphosate and pyrithiobac on cotton growth and yield. p. 1559-1560. In Proc., Beltwide Cotton Conf., National Cotton Council, Memphis, TN.
• Manning, J. K., J. A. Bond, L. E. Steckel, D. O. Stephenson, J. B. McDuffie, and R. L. Landry. 2010. Corn tolerance to Resolve Q. In Proc., South. Weed Sci. Soc. 63:30.
• Bond, J. A., K. L. Smith, J. K. Norsworthy, D. O. Stephenson, IV, L. E. Steckel, J. B. Manning, and J. B. McDuffie. 2010. Regional research addressing glyphosate-resistant Palmer amaranth control in cotton. In Proc., South. Weed Sci. Soc. 63:91.
• Manning, J. K., J. A. Bond, D. O. Stephenson, J. B. McDuffie, and R. L. Landry. 2010. Laudis and Capreno tank-mixtures in Midsouth corn. In Proc., South. Weed Sci. Soc. 63:117.
• Manning, J. K., D. O. Stephenson, J. A. Bond, J. B. McDuffie, R. L. Landry, and J. B. Guice. 2010. Saflufenacil burndown programs in no-till cotton. In Proc., South. Weed Sci. Soc. 63:28.
• McDuffie, J. B., J. A. Bond, D. O. Stephenson, D. K. Miller, R. L. Landry, and J. K. Manning. 2010. Pyrithiobac plus residual herbicide tank-mixtures. In Proc., South. Weed Sci. Soc. 63:26.
• Bond, J. A., K. L. Smith, D. O. Stephenson, IV, J. K. Norsworthy, L. E. Steckel, J. B. Manning, and J. B. McDuffie. 2010. Managing glyphosate-resistant Palmer amaranth with residual herbicides in Midsouth cotton. p. 1533. In Proc., Beltwide Cotton Conf., National Cotton Council, Memphis, TN
• Chapman, J., T. Barber, F. M. Bourland, and D. O. Stephenson, IV. 2010. Effects of cotton seeding rate and row spacing on yield and fiber quality. p. 81. In Proc., Beltwide Cotton Conf., National Cotton Council, Memphis, TN.
• Manning, J. K., D. O. Stephenson, IV, J. A. Bond, J. B. McDuffie, R. L. Landry, and J. B. Guice. 2010. Winter weed management with Sharpen in a no-till cotton system. p. 1514. In Proc., Beltwide Cotton Conf., National Cotton Council, Memphis, TN. In press.
• McDuffie, J. B., J. A. Bond, D. O. Stephenson, IV, D. K. Miller, J. K. Manning, and R. L. Landry. 2010. Performance of residual herbicides applied in tank-mixtures with Staple LX and glyphosate. p. 1515. In Proc., Beltwide Cotton Conf., National Cotton Council, Memphis, TN.
• Miller, D. K., D. O. Stephenson, IV, M. S. Mathews. 2010. Glufosinate and insecticide combinations in Liberty Link cotton. p. 1524. In Proc., Beltwide Cotton Conf., National Cotton Council, Memphis, TN.
• Miller, D. K., J. L. Griffin, D. O. Stephenson, J. Boudreaux, and M. M. Mathews. 2010. Reduced rate dicamba effects on soybean growth and yield. In Proc., South. Weed Sci. Soc. 63:22.
• Miller, D. K., D. O. Stephenson, and M. M. Mathews. 2010. Evaluation of Sharpen for preplant weed control in soybean. In Proc., South. Weed Sci. Soc. 63:20.

Progress 01/01/09 to 12/31/09

Outputs
OUTPUTS: The project generated outputs in the form of presentations at professional conferences. Additionally, weed management strategies developed or refined from this project were provided to crop producers and other stakeholders in Louisiana. PARTICIPANTS: Dr. Daniel O. Stephenson, IV, Assistant Professor, Weed Scientist, LSU AgCenter TARGET AUDIENCES: Target audiences for this project include crop producers and weed management professionals. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
Preliminary results indicate that preemergence applications of the herbicide Corvus provided greater control of johnsongrass than Bicep II Magnum in corn at harvest; however, control of barnyardgrass, browntop millet, and various broadleaf weeds were controlled equally (>85%). Control of grass and broadleaf weeds with Balance Flexx herbicide preemergence in corn was equal to Bicep II Magnum. Capreno herbicide applied postemergence in corn provided greater control of johnsongrass compared to Laudis and Aatrex herbicides, but control of other grass and broadleaf weeds were similar. Preemergence applications of Sharpen and Integrity herbicides in grain sorghum provided 85% or greater control of various grass and broadleaf weeds. Applications of the herbicide Lexar provided greater than 85% control of numerous grass and broadleaf weeds, except Hophornbeam copperleaf which Lexar provided only 75% control. No grain sorghum injury was observed from Lexar applied preemergence at 1, 1.5, 2, 2.5, and 3 quarts per acre. In soybean, preliminary results indicate good to excellent control of many Central Louisiana winter weeds with fall and/or spring applications of Valor SX, Valor XLT, and Sharpen when applied with glyphosate and/or 2,4-D. Specifically, fall applications of Valor XLT provided excellent control of winter/spring vegetation and good control of early summer weeds such as barnyardgrass, entireleaf morningglory, johnsongrass, and Palmer amaranth; however, complete winter vegetation control with Valor XLT may hamper row integrity through winter. Soybean tolerance to various application timings of Resolve herbicide throughout the fall and spring indicated excellent tolerance. Additionally, research determined the need to apply Ignite in Liberty Link soybean by 10 to 15 days following emergence followed by a sequential application 10 to 15 days later for optimum weed management. Experiments in cotton determined the need of preemergence herbicide applications to provide optimum weed control and proved their necessity for mitigation of weeds resistant to glyphosate. Herbicides that provide residual control of weeds, such as Dual Magnum and other formulations of metolachlor, should be applied when cotton is at the one to two leaf stage for optimum weed control. Also, co-application of glyphosate, Dual Magnum, and Staple LX causes excessive injury to cotton, but visual injury subsides within 21 days after application and cotton growth and yield are not reduced.

Publications

• Nichols, R. L., 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 (Amaranthus palmeri) spreads in the Southern United States (U.S.). Resistant Pest Manage. Newsletter 18(2):8-10.
• Stephenson, D. O. and D. M. Scroggs. 2009. Effect of fomesafen on glyphosate plus S-metolachlor application timing in cotton. Proc., South. Weed. Sci. Soc. 62:119.
• Stephenson, D. O. and D. M. Scroggs. 2009. Evaluation of Balance Flexx, Capreno, Corvus, and Laudis in corn. Proc., South. Weed. Sci. Soc. 62:113.
• Ferguson, R. E., D. O. Stephenson, D. K. Miller, and A. M. Stewart. 2009. Effect of pyrithiobac and S-metolachlor co-application on cotton growth and yield. Proc., South. Weed Sci. Soc. 62:297.
• Miller, D., D. Stephenson, D. Scroggs, and M. Mathews. 2009. Liberty Link cotton tolerance to combinations of glufosinate with insecticides and mepiquat chloride. Proc., South. Weed Sci. Soc. 62:93.
• Miller D., D. Stephenson, D. Scroggs, and M. Mathews. 2009. Liberty Link cotton tolerance to combinations of glufosinate and insecticides. Proc., South. Weed Sci. Soc. 62:94.
• Miller, D, D. Stephenson, M. Mathews. 2009. Cotton tolerance and weed control with Staple LX and Dual Magnum combinations with glyphosate. Proc., South. Weed Sci. Soc. 62:121
• Steckel, L., K. Smith, B. Scott, D. Stephenson, T. Koger, J. Bond, D. Miller, S. Stewart, and D. Dodd. 2009. Glyphosate resistant Palmer amaranth in the Mid-south. Proc., South. Weed Sci. Soc. 62:372.
• Stephenson, IV, D. O. and D. M. Scroggs. 2009. Effect of various glufosinate application rates and timings on weed control in cotton. In Annual meetings abstracts. Beltwide Cotton Conf., National Cotton Council, San Antonio, TX.
• Ferguson, R. E., D. O. Stephenson, IV, D. K. Miller, and A. M. Stewart. 2009. Evaluation of pyrithiobac and S-metolachlor co-applications on cotton growth and yield. In Annual meetings abstracts. Beltwide Cotton Conf., National Cotton Council, San Antonio, TX.
• Miller, D. K., D. O. Stephenson, D. M. Scroggs, B. R. Leonard, E. Burris, and M. S. Mathews. 2009. Glufosinate and insecticide co-application effects on Liberty Link cotton. In Annual meetings abstracts. Beltwide Cotton Conf., National Cotton Council, San Antonio, TX.
• Miller, D. K., D. O. Stephenson, D. M. Scroggs, B. R. Leonard, E. Burris, and M. S. Mathews. 2009. Glufosinate and insecticide/PGR co-application effects on growth and yield of Liberty Link cotton. In Annual meetings abstracts. Beltwide Cotton Conf., National Cotton Council, San Antonio, TX.
• Miller, D. K., D. O. Stephenson, M. S. Mathews. 2009. Staple LX and Dual Magnum combination effects with glyphosate on weed control and cotton tolerance. In Annual meetings abstracts. Beltwide Cotton Conf., National Cotton Council, San Antonio, TX.