J.E. Chafin, A.S. Culpepper, and L.B. Braxton University of Georgia

1. Palmer amaranth, benghal dayflower, and broadleaf signalgrass response to glufosinate applied alone or mixed with 2,4-D, or dicamba J.E. Chafin, A.S. Culpepper, and L.B. Braxton University of Georgia Department of Crop and Soil Sciences January 2010

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

3. Biotypes with multiple resistance to glyphosate and ALS herbicides are becoming more common across Georgia. Glyphosate 3 lb Pyrithiobac 0.25 lb

5. Impact of GR Palmer amaranth in Georgia counties with severe infestations.* 88 % acres 45 26 25 20 0 0 0 Acres (%) treated with at least two residual herbicide Hand weeding Glufos. (Ignite) systems Cultivation *Average of Macon, Taylor, Sumpter, Schley, and Dooly counties

6. Dryland Conservation Tillage Prowl + Reflex PRE Roundup + Dual POST Direx + MSMA PD Prowl + Reflex PRE Ignite + Dual POST Direx + MSMA PD

7. Glufosinate 0.42 lb on 5 in. Palmer amaranth “The challenge is making applications of glufosinate to target plants less than 10 cm in height” (Coetzer et al. 2002).

8. Future Technology: 2,4-D or Dicamba Resistant Cotton 2,4-D resistant cotton 2,4-D sensitive cotton

9. Objective • Determine the response of glyphosate- resistant Palmer amaranth to glufosinate, 2,4-D (Weedar), or dicamba (Clarity) applied alone and glufosinate mixed with 2,4-D or dicamba. • Carpetweed, benghal dayflower, broadleaf signalgrass, and pitted morningglory

10. Hypothesis • Tank mixtures of glufosinate + 2,4-D or dicamba will be more effective in controlling broadleaf weeds than glufosinate alone.

11. Trial Locations Macon County (Glyphosate-resistant Palmer amaranth) Chula (Palmer amaranth, carpetweed) Sunbelt Expo (benghal dayflower, broadleaf signalgrass, pitted morningglory)

12. Treatments A factorial arrangement of two “glufosinate” options and seven “tank mix” options Ignite Option: None or Ignite at 0.42 lbs Tank mix option: 2,4-D, dicamba, or none • 2,4-D (Weedar 64) .5, 0.75, 1.0 lb/ac • Dicamba (Clarity) .25, 0.5, 1.0 lb/ac • None

13. Application Methods • Backpack sprayer • Broadcast • Overtop • 15 gal/Ac • Drift Guard T-Jet 11002 VS • Early morning application • 7-9 inch weed

14. Conditions at Time of Application • Moist/Wet • Sunny conditions • Air Temperature: 76-95 F • % Relative Humidity: 56-74

15. Data Reported & Statistical Analysis • Palmer amaranth control was combined over the three locations. • Carpetweed, benghal dayflower, broadleaf signalgrass, and pitted morningglory • Weed control at 20 d is reported; interaction means are reported.

16. Percent GR Palmer amaranth control at 20 d. Average 3 loc., GA, 2009. Herbicide applied alone 90 a 79 b 77 bc 77 bc 73 bcd 69 cd 65 d Glufos-inate 0.5 lb 0.75 lb 1.0 lb 0.25 lb 0.5 lb 1.0 lb 2,4-D dicamba

17. 12 DAT Non-treated glufosinate

18. 12 DAT 24 DAT 2,4-D at 0.75 lb

19. 12 DAT 24 DAT dicamba 0.5 lb

20. Percent GR Palmer amaranth control at 20 d. Average 3 loc., GA, 2009. = control when mixed with Ignite 96 a 96 a 92 a 91 a 91 a 91 a 90 a 79 b 77 bc 77 bc 73 bcd 69 cd 65 d Glufos-inate 0.5 lb 0.75 lb 1.0 lb 0.25 lb 0.5 lb 1.0 lb 2,4-D dicamba

21. 12 DAT glufosinate glufosinate + 2,4-D 0.75 lb

22. 12 DAT glufosinate glufosinate + dicamba 0.5 lb

23. Percent carpetweed control at 20 d. Chula, GA, 2009. 99 a 66 b 63 b 60 b 58 b 55 b 57 b Glufos-inate 0.5 lb 0.75 lb 1.0 lb 0.25 lb 0.5 lb 1.0 lb 2,4-D dicamba

24. 2,4-D 0.5 lb at 10 DAT

25. Percent carpetweed control at 20 d. Chula, GA, 2009. = control when mixed with Ignite 99 a 99 a 99 a 99 a 99 a 99 a 99 a 66 b 63 b 60 b 58 b 55 b 57 b Glufos-inate 0.5 lb 0.75 lb 1.0 lb 0.25 lb 0.5 lb 1.0 lb 2,4-D dicamba

26. Benghal dayflower infesting Roundup Ready cotton

27. Percent benghal dayflower control at 20 d. Sunbelt Expo, GA, 2009. 98 a 98 a 93 a 91 a 84 b 68 c 68 c Glufos-inate 0.5 lb 0.75 lb 1.0 lb 0.25 lb 0.5 lb 1.0 lb 2,4-D dicamba

28. Percent benghal dayflower control at 20 d. Sunbelt Expo, GA, 2009. = control when mixed with Ignite 97 a 98 a 94 a 98 a 93 a 91 a 84 b 68 c 68 c Glufos-inate 0.5 lb 0.75 lb 1.0 lb 0.25 lb 0.5 lb 1.0 lb 2,4-D dicamba

29. Percent broadleaf signalgrass control at 20 d. Sunbelt Expo, GA, 2009. 96 a 0 b 0 b 0 b 0 b 0 b 0 b Glufos-inate 0.5 lb 0.75 lb 1.0 lb 0.25 lb 0.5 lb 1.0 lb 2,4-D dicamba

30. Percent broadleaf signalgrass control at 20 d. Sunbelt Expo, GA, 2009. = control when mixed with Ignite 96 a 93 ab 91 ab 92 ab 92 ab 91 ab 88 b Glufos-inate 0.5 lb 0.75 lb 1.0 lb 0.25 lb 0.5 lb 1.0 lb 2,4-D dicamba

31. Pitted morningglory controlled 97 to 99% by all treatments Everman et al. noted greater than 90% control with glufosinate applied POST on pitted morningglory.

32. Conclusions-Palmer amaranth • Glufosinate alone only provided 73% control • 2,4-D alone provided 69-79% control • Dicamba alone provided 69-90% • Tank mixtures of glufosinate+2,4-D or dicamba at least 91% control

33. Conclusions-Carpetweed • Glufosinate alone provided 99% control • 2,4-D alone provided 58-66% • Dicamba alone provided 55-60% • All rates of glufosinate+2,4-D or dicamba provided 99% control

34. Conclusions- Benghal dayflower • Glufosinate alone provided 63% control • 2,4-D provided 91-98% control; combinations with glufosinate could not improve control • Dicamba control ranges from 68-93% but when combined with glufosinate control ranges from 93-97%

35. Conclusion-Broadleaf signalgrass • Glufosinate alone provided 96% control and no control with 2,4-D or dicamba alone • 2,4-D mixed with glufosinate, control ranged from 88-91%; at 1 lb/ac of 2,4-D the control was 8% less than glufosinate alone • Dicamba mixed with glufosinate provided 92-93% control

36. Future Research 2,4-D resistant cotton 2,4-D sensitive cotton