Control of Glyphosate-Resistant Palmer amaranth in DHT Cotton.

1. Control of Glyphosate-Resistant Palmer amaranth in DHT Cotton. Culpepper and Chaffin; University of Georgia Braxton and Richburg; Dow AgroSciences

2. Georgia counties confirmed to be infested with glyphosate-resistant Palmer amaranth. 2004 – 1 county 2005 – 2 counties 2006 – 7 counties 2007 – 10 counties 2008 – 18 counties

4. Hand weeding cotton during 2009 Acres Hand Weeded • 52 counties surveyed • Acres in survey: 799,000 • Acres hand weeded: 437,660 • 54% cotton hand weeded Grower Costs • $3 to $100/A • Average $26 • $11.4 million

5. Some of the hand weeding expense was from the removal of plants from the field.

6. GR Palmer amaranth control in dryland conservation tillage systems Prowl + Reflex PRE Roundup+ Dual POST Diuron + MSMA PD Prowl + Reflex PRE Ignite + Dual POST Diuron + MSMA PD

7. Palmer Amaranth regrowth after being treated with Ignite.

8. 2,4-D- Resistant Cotton Being Developed 2,4-D resistant cotton 2,4-D sensitive cotton

9. Objective • Begin to determine the most effective 2,4-D weed management systems for glyphosate-resistant Palmer amaranth.

10. Experiments 1. Single application study (non-crop) 2. 2,4-D weed management systems (DHT cotton)

11. Experiment 1: Single Application Macon County (2 locations) Tift County (1 location)

12. Factorial Treatment Arrangement (Experiment 1: Single Application) 2,4-D (Weedar) Option: 0, 1.0, 1.5, or 2.0 pt/A Ignite Option: 0 or 29 oz/A Palmer was 8 inch at time of application (15 GPA)

13. Percent GR Palmer amaranth control at 20 d. Average 3 loc., GA, 2009. 96 a 91 a 92 a 79 b 77 bc 73 bcd 69 cd Ignite (29 oz) 0.5 lb 0.75 lb 1.0 lb 0.25 lb 0.5 lb 1.0 lb 2,4-D 2,4-D + Ignite

14. 12 DAT Non-treated Ignite

15. 12 DAT Non-treated 1.5 pt 2,4-D

16. 12 DAT 24 DAT 1.5 pt of 2,4-D

17. 12 DAT Non-treated Ignite + 2,4-D

18. Residual programs PRE Prowl Prowl Prowl Prowl POST (4-6” Palmer) Weedar Ignite + Weedar Ignite None TRT 1 2 3 4 Prowl + Reflex Prowl + Reflex Prowl + Reflex Prowl + Reflex Weedar Ignite + Weedar Ignite None 5 6 7 8 Direx + MSMA directed to all systems. Prowl 2.1 pt/A; Reflex 1 pt/A; Ignite 23 oz/A; Weedar 1.5 pt/A; Direx 2 pt/A; MSMA 2 lb ai/A. Experiment 2: Systems

19. Total POST programs POST 1 (4-6“ Palmer) Weedar Weedar + Ignite Ignite None POST 2 (3-6” Palmer) Weedar Weedar + Ignite Ignite None TRT 1 2 3 4 Direx + MSMA directed to all systems. Weedar 1.5 pt/A; Ignite 23 oz/A; Direx 2 pt/A; MSMA 2 lb ai/A. Experiment 2: Systems

20. One inch of rainfall occurred within 5 days of planting and PRE treatments. Rainfall continued throughout the season.

21. Percent GR Palmer amaranth control 28 d after layby. Macon Co. GA, 2009. 99 a 99 a 99 a 93 ab 86 bc 82 c 82 c 20 d + Reflex + Reflex + Reflex + Reflex Prowl Prowl Prowl Prowl Ignite Ignite + 2,4-D Ignite + 2,4-D 2,4-D POST None 2,4-D Ignite None Direx + MSMA directed to all systems.

22. Percent GR Palmer amaranth control at harvest. Macon Co. GA, 2009. 93 a 90 a 90 a 81 b 50 c 48 c 43 c + Reflex + Reflex + Reflex + Reflex Prowl Prowl Prowl Prowl Ignite Ignite + 2,4-D Ignite + 2,4-D 2,4-D POST None 2,4-D Ignite None Direx + MSMA directed to all systems.

23. Seed Cotton Yield (lb/A). Macon Co. GA, 2009. 1120 a 1100 a 1080 a 955 a 530 c 490 c 140 d + Reflex + Reflex + Reflex + Reflex Prowl Prowl Prowl Prowl Ignite Ignite + 2,4-D Ignite + 2,4-D 2,4-D POST None 2,4-D Ignite None Direx + MSMA directed to all systems.

24. Percent GR Palmer amaranth control comparing POST and residual programs 28 d after layby . Macon Co. GA, 2009. 99 a 93 ab 94 a 88 b 81 c + Reflex Prowl POST Ignite + 2,4-D Ignite + 2,4-D 2,4-D 2,4-D Ignite Ignite Ignite + 2,4-D Ignite + 2,4-D POST 2 Direx + MSMA directed to all systems.

25. Non-treated Control (July 5)

26. Glyphosate-resistant Palmer amaranth response to sequential POST applications. Macon Co., 2009. Ignite + 2,4-D Ignite + 2,4-D 2,4-D 2,4-D

27. Percent GR Palmer amaranth control with POST programs at harvest . Macon Co. GA, 2009. 93 a 85 b 81 b 50 c 50 c + Reflex Prowl POST Ignite + 2,4-D Ignite + 2,4-D 2,4-D 2,4-D Ignite Ignite Ignite + 2,4-D Ignite + 2,4-D POST 2 Direx + MSMA directed to all systems.

28. Seed cotton yields (lb/A) with total POST programs. Macon Co. GA, 2009. 1100 a 1026 a 955 a 550 b 440 b + Reflex Prowl POST Ignite + 2,4-D Ignite + 2,4-D 2,4-D 2,4-D Ignite Ignite Ignite + 2,4-D Ignite + 2,4-D POST 2 Direx + MSMA directed to all systems.

29. Summary (Experiment 1, Single Application) • Ignite (29 oz) controlled GR Palmer amaranth 73% • 2,4-D (1 to 2 pt) controlled GR Palmer amaranth 69-79% • Ignite + 2,4-D controlled GR Palmer amaranth 91-96%

30. Summary (Experiment 2, Systems) At harvest • Prowl fb 2,4-D or Ignite fb Direx + MSMA controlled Palmer 50%. Mixing Ignite with 2,4-D improved control at least 31%. • Prowl plus Reflex fb Ignite, 2,4-D, or Ignite + 2,4-D controlled Palmer 90 to 93%. • Total POST programs with sequential Ignite or 2,4-D applications provided only 50% control. Mixtures of Ignite plus 2,4-D improved control 35%.

31. Summary (Experiment 2, Systems) Highest seed cotton yields • Prowl fb Ignite + 2,4-D fb Direx + MSMA • Prowl + Reflex fb Ignite, 2,4-D or Ignite + 2,4-D fb Direx + MSMA • Sequential Ignite + 2,4-D applications fb Direx + MSMA

32. Conclusions • The addition of 2,4-D in a systems approach offers growers a significant advantage of managing emerged glyphosate-resistant Palmer amaranth • Physical movement of 2,4-D is of great concern; however, research to address this is in progress