This document summarizes weed control strategies for soybeans in 2011. It discusses several pre-emergence herbicide options including Authority XL, Warrant, Verdict, and Fierce. It emphasizes that the number one goal of weed control is yield, not just killing weeds. Pre-emergence herbicides improve early-season control and reduce in-season weed pressure, potentially increasing yields by as little as 1 bushel per acre. Weeds begin reducing yields very early, as little as 2-3 weeks after emergence. The document recommends using pre-emergence herbicides, burndown before planting, tank-mixing for difficult weeds, and spraying when weeds are small. It also provides an

1. Recipe for Success:Weed Control in 2011OK Soy ExpoJoe ArmstrongExtension Weeds Specialist

2. Authority XLFMCPre-mix of Authority & ClassicUse rates: 3.0 – 9.6 oz/acreFall and PRE applications4.0 oz = 3.33 oz Authority DF1.25 oz Classic *36 month rotation restriction for canola

3. WarrantMonsantoSold as MON 63410 in 2010Use rate: 3 pints/acreApply Early POST, V2 – V3 growth stageTank-mix with POST product(s)

4. VerdictBASFPre-mix of Sharpen & OutlookUse rate: 5 – 10 floz/acreFall, burndown, and PRE applications5.0 floz = 1 floz Sharpen4.17 floz Outlook

5. FierceValentPre-mix of Valor & pyroxysulfoneUse rate: 3 – 4.5 oz/acreFall, burndown, and PRE applications3.0 oz = 2.0 oz Valor1.5 ozpyroxysulfone*Not currently labeled for use in OK

6. What is the #1 goal of weed control?(Hint: it’s not always killing weeds)

7. Yield!

8. PRE herbicidesImprove early-season control

9. Less in-season weed pressure

10. Can pay for themselves with as little as 1 bu/acre increaseWhen do weeds begin reducing yields?Adapted from Knezevic et al. (2003) Weed Tech 17:666-673

12. PRE herbicides inno-till soybean (NW OK)glyphosate + 2,4-D alone7 weeks after treatmentAll treatments included glyphosate + 2,4-D ester (32 fl oz + 1 pt)

13. PRE herbicides inno-till soybean (NW OK)glyphosate + 2,4-D alone7 weeks after treatmentAll treatments included glyphosate + 2,4-D ester (32 fl oz + 1 pt)

15. Early POST with residual

16. Herbicide resistance testing update

17. Glyphosate-resistant marestail in OklahomaResistantSusceptibleUntreated1x glyphosate (0.75 lbae)2x glyphosate (1.5 lbae)4x glyphosate (3.0 lbae)Grant County, 2010

18. PSS-2779 “Diagnostic Service to Test for Herbicide-resistant Weeds in Oklahoma”www.weedscience.okstate.edu

19. 2011 Weed ControlUse a PRE herbicide

20. Burndown before planting—start clean

21. Tank-mix to control difficult weeds

22. Spray when weeds are smallThanks to:Cooperators:Lindy BakerJay FranklinBob RossChad OttoCurtis Vap

23. Contact informationJoe ArmstrongOSU Dept. of Plant and Soil Sciencesjoe.armstrong@okstate.eduTwitter: @OSUWeedSciwww.weedscience.okstate.edu