1. Spring Applied Burndown Options for Control of Glyphosate-resistant Horseweed
T.W. Eubank
D.H. Poston, V.K. Nandula, D.B. Reynolds, D.R. Shaw, H.R. Robinson, J.B. Blessitt, R.T. Coleman, and T. Evans

2. Horseweed (Conyza canadensis)

3. Horseweed Emergence vs Temp1
Eubank, 2006
1Averaged 3 locations

4. Introduction
Horseweed has been documented to be resistant to many herbicide modes of action across the U.S. including,
Glyphosate
Paraquat
ALS Inhibitors
Triazines
Ureas
Heap, 2005

5. Introduction
The widespread adoption of glyphosate-resistant crops and the advent of glyphosate-resistant horseweed (Conyza canadensis (L.) Cronq.) has created a need for research investigating alternative measures of control for this troublesome weed.

6. Introduction
Determining the most efficacious chemical means for controlling horseweed is imperative in reducing possible crop yield losses due to competition.

7. Objectives
Determine the most effective chemical burndown options for emerged horseweed populations.
Evaluate the impact of various burndown herbicides on horseweed populations.

8. Chemical Control

9. Chemical Control Materials and Methods
RCB, 4 replications
Plots: 10 x 40 ft
Tractor mounted 15 gal/acre
Applied April 5, 2005 and March 15, 2006
Horseweed: 4 – 6 in tall

10. Chemical Control Materials and Methods
Burndown treatments alone/+ tank-mix
Roundup 0.77 lb ae/a
Gramoxone 0.75 ai/a
Ignite 0.42 lb ai/a
Burndown treatments alone
Roundup 1.12 lb ae/a
Gramoxone 0.88 ai/a
Ignite 0.53 lb ai/a

11. Chemical Control Materials and Methods
Tank-mixed herbicide treatments
lb ae/a
lb ai/a
lb ai/a
0.5 lb ai/a
1 lb ai/a
Harmony lb ai/a
Clarity lb ai/a
Untreated

12. Chemical Control Materials and Methods
All data analyzed in SAS with the PROC GLM procedure
Means separated using Fisher’s protected LSD test (p = 0.05)

13. Horseweed Control with WeatherMax Based Burndown1
1 Treatments shown based on 4 WAT. Horseweed 4-6 in tall lbs ae/a with all tank mixes. Averaged from 2005 – 2006.
LSD (0.05) = 8

14. Horseweed Populations with WeatherMax Based Burndown1
1 Horseweed plants/m2 at 6 WAT lb ae/a with all tank mixes. Averaged from 2005 – 2006.
LSD (0.05) = 41

15. Untreated 4 WAT

16. WeatherMax 0.77 lb ae/a 2 WAT

17. WeatherMax 0.77 lb ae/a 4 WAT

18. Horseweed Control with Inteon Based Burndown1
1 Treatments shown based on 4 WAT. Horseweed 4-6 in tall lb ai/a with all tank mixes. Averaged from 2005 – 2006.
LSD (0.05) = 8

19. Horseweed Populations with Inteon Based Burndown1
1 Horseweed plants/m2 at 6 WAT lb ai/a with all tank mixes. Averaged from 2005 – 2006.
LSD (0.05) = 39

20. Inteon 0.75 lb ai/a 2 WAT

21. Inteon 0.75 lb ai/a 4 WAT

22. Horseweed Control with Ignite Based Burndown1
1 Treatments shown based on 4 WAT. Horseweed 4-6 in tall lb ai/a with all tank mixes. Averaged from 2005 – 2006.
LSD (0.05) = 5

23. Horseweed Populations with Ignite Based Burndown1
1 Horseweed plants/m2 at 6 WAT lb ai/a with all tank mixes. Averaged from 2005 – 2006.
LSD (0.05) = 14

24. Ignite 0.42 lb ai/a 2 WAT

25. Ignite 0.42 lb ai/a 4 WAT

26. Conclusions
WeatherMax alone provided only 63 – 73% control of horseweed 4 WAT.
The addition of 2,4-D or Clarity improved WeatherMax control to greater than 90% and reduced horseweed populations by 99% compared to the untreated check.

27. Conclusions
Inteon alone treated plants quickly recovered and by 4 WAT provided only 55 – 60% control.
The addition of 2,4-D or Clarity to Inteon significantly improved control to 83%, however, horseweed populations were reduced by only 44% and 52%, respectively, when compared to the untreated.

28. Conclusions
Ignite applied alone provided better than 92% control of horseweed and all tank-mix treatments were generally better than 86%.
Horseweed populations were reduced by greater than 88% when Ignite was tank-mixed, while Ignite alone reduced populations only 65%.

29. Conclusions
New horseweed emergence, after burndown alone treatments, could be responsible for slight increase in horseweed populations as compared to burndown + tank-mix treatments.

30. Special Thanks V.K. Nandula R.T. Coleman J.B. Blessitt T.H. Gibson
T.A. Evans
H.R. Robinson
E. Graves

31. Questions?