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. 180 4,925 60 515 85 1,030 47 500 335 380 660 175 51 860173 400 455 GA ranked second among cotton producing states in 2007 (thousands of acres) National Agricultural Statistics Service, USDA

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

5. 100 66 97 99 98 99 100 98 83 9775 97 59 Percent of cotton acreage planted to RR varieties 2006 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 Prior to 2005, glyphosate was an effective and economical tool 22 oz/A WeatherMax on 16” Palmer Amaranth

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. Evaluations 26 d after initial application 45 c 86 b 97 a 99 a % Control

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

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

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

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

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

21. Clarity 8 oz/A 3 inch6 inch

22. Clarity 16 oz/A 3 inch 6 inch

23. Field Trial Mt. 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 by Clarity. Mt. Olive, NC 2007. Evaluations 42 d after sequential application % Control

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