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Glyphosate-Resistant Palmer Amaranth Response To Dicamba

Glyphosate-Resistant Palmer Amaranth Response To Dicamba. R. D. Wallace, A. S. Culpepper, W. K. Vencill, A. C. York, and T. L. Grey University of Georgia and NC State Department of Crop and Soil Sciences January 2008. Cotton In Georgia (2006). Most widely grown row crop

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Glyphosate-Resistant Palmer Amaranth Response To Dicamba

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  1. Glyphosate-Resistant Palmer Amaranth Response To Dicamba R. D. Wallace, A. S. Culpepper, W. K. Vencill, A. C. York, and T. L. Grey University of Georgia and NC State Department of Crop and Soil Sciences January 2008

  2. Cotton In Georgia (2006) • Most widely grown row crop • 1.4 million acres produced 2.3 million bales of cotton National Agricultural Statistics Service, USDA

  3. GA ranked second among cotton producing states in 2007 (thousands of acres) 60 47 455 380 500 515 175 51 173 860 180 1,030 400 660 335 4,925 85 National Agricultural Statistics Service, USDA

  4. Glyphosate-Resistant Cotton • Glyphosate-resistant cotton was commercialized in 1997 • Rapidly adopted by growers

  5. Percent of cotton acreage planted to RR varieties 2006 97 98 59 100 99 99 98 83 75 97 100 98 98 97 99 66 98 USDA, AMS. 2006. Publ. mp-cn833.

  6. Advantages of Glyphosate-Resistant Cotton • Ease of system • Properties of glyphosate • Agronomic value of the cotton • DP 555 BGR in GA

  7. Control of Susceptible Palmer Amaranth by Glyphosate 22 oz/A WeatherMax on 16” Palmer Amaranth Prior to 2005, glyphosate was an effective and economicaltool

  8. Glyphosate-Resistant Palmer Amaranth • Resistance to glyphosate in Palmer Amaranth was confirmed in 2005 in GA • Factors influencing glyphosate-resistance in GA • Dependence on a single management tactic • Monocultural production system • Low use rates • Application in stressed situations

  9. Glyphosate-Resistant Palmer Amaranth in Cotton 33 oz WeatherMax applied to 2” Palmer Amaranth

  10. Georgia counties infested with glyphosate-resistant Palmer amaranth. 2005 2006 2007 (more sites being tested) Confirmed in 83 of 149 fields sampled

  11. Glyphosate-Resistant Palmer Amaranth • Current management tactics are not very successful • New technology is needed • Dicamba-tolerant cotton (2014)

  12. Objective Determine glyphosate-resistant Palmer amaranth response to dicamba programs.

  13. Two Studies to Evaluate Palmer Amaranth Control by Clarity in 2007 Mount Olive * * Macon Co.

  14. Field Trial Macon Co. GA • 4 Clarity rates: 4, 8, 12, or 16 oz/A • 3 Palmer amaranth heights: 3, 6, or 12” • 12 oz/A sequential application 21-30 days after initial Clarity application • Visually evaluated for % control

  15. Glyphosate-resistant Palmer amaranth control by Clarity. Macon Co., GA 2007. 99 a 97 a 86b % Control 45c Evaluations 26 d after initial application

  16. Glyphosate-resistant Palmer amaranth control by Clarity. Macon Co., GA 2007. 99a 96a 92ab 86b % Control Evaluations 23 d after sequential application

  17. Glyphosate-resistant Palmer amaranth control by Clarity. Macon Co., GA 2007. 91 a % Control 65 b 60b 35c Evaluations 24 d after initial application

  18. Glyphosate-resistant Palmer amaranth control by Clarity. Macon Co., GA 2007. 98a 91 a 70 b % Control 38c Evaluations 23 d after sequential application

  19. Glyphosate-resistant Palmer amaranth control by Clarity. Macon Co., GA 2007. 78a % Control 46 b 46 b 43 b Evaluations 19 d after initial application

  20. Glyphosate-resistant Palmer amaranth control by Clarity. Macon Co., GA 2007. 80a % Control 58 b 55 b 43 c Evaluations 23 d after sequential application

  21. Clarity 8 oz/A 3 inch 6 inch

  22. Clarity 16 oz/A 3 inch 6 inch

  23. Field TrialMt. Olive, NC • 1 Palmer amaranth height: 6-7” • 5 Treatments of Clarity: • 8 oz/A • 8 oz/A fb 8 oz/A • 16 oz/A • 16 oz/A fb 8 oz/A • 16 oz/A fb 16 oz/A • Visually evaluated for % control

  24. Glyphosate-resistant Palmer amaranth control byClarity. Mt. Olive, NC 2007. % Control Evaluations 42 d after sequential application

  25. Conclusions – Macon Co. • Palmer amaranth control was affected by plant size, Clarity rate, and the use of sequential applications • >90% control was achieved when: • 3” Palmer amaranth • 12 oz/A, 16 oz/A, 8 oz/A fb 12 oz/A • 6” Palmer amaranth • 16 oz/A, 12 oz/A fb 12 oz/A, 16 oz/A fb 12 oz/A

  26. Conclusions – Mt. Olive • Palmer amaranth control was affected by Clarity rate and the use of sequential applications • >90% control was achieved when 6-7” Palmer amaranth was treated with 16 oz/A fb 8 oz/A and 16 oz/A fb 16 oz/A

  27. Future Studies • Evaluate control of glyphosate-resistant Palmer amaranth through herbicide mixtures • Evaluate control of other problematic row-crop weeds through herbicide mixtures

  28. Acknowledgements Committee Members Dr. Alan York University of Georgia Weed Science Unit

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