2010 Panhandle Crop Production Clinic. Joe Armstrong OSU Extension Weeds Specialist

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1 2010 Panhandle Crop Production Clinic Joe Armstrong OSU Extension Weeds Specialist

2 Management of resistant weeds What is herbicide resistance? State of herbicide resistance in OK Strategies for successful weed management Frequently asked questions

3 You must properly define the problem!

4 Herbicide resistance the inherited ability of a plant to survive and reproduce following exposure to a dose of herbicide normally lethal to the wild type (Can no longer kill what we used to) Examples: ALS-resistant ryegrass glyphosate-resistant marestail

5 Herbicide tolerance the inherent ability of a species to survive and reproduce after herbicide treatment it is naturally tolerant Examples: 2,4-D and crabgrass glyphosate and morningglory

6 Weed control methods Cultural Chemical Mechanical Biological Many little hammers

7 Weed control methods Cultural Chemical Mechanical Biological

8 How does herbicide resistance develop? Herbicides do not create super weeds Resistance occurs through selection Needle in a haystack

9 Types of resistance Cross resistance Resistant to multiple herbicides within a single mode of action Example: ALS-R Italian ryegrass in OK Finesse, Osprey, PowerFlex, and Beyond

10 Types of resistance Multiple resistance Resistant to multiple herbicide modes of action Example: Triazine-R + ALS-R pigweed

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19 The good news: Not all weeds are resistant

20 The bad news: Many weeds are resistant

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27 Herbicide-resistant marestail

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29 Resistant ryegrass

30 Finesse Untreated

31 50 90% not Osprey controlled with ALS-inhibiting herbicides PowerFlex

32 ALS-resistant ryegrass in OK 08-09: Confirmed in 17 counties

33 All samples controlled glyphosate with glyphosate

34 ALS-resistant cheat in OK Untreated Olympus, 3.6 oz Susceptible Resistant 1 Resistant 2

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37 Resistant Palmer amaranth

38 Resistant waterhemp

39 Emanuel Co. (GA), 2009 From Eric Prostko, University of Georgia

40 Other weeds to watch johnsongrass kochia ragweeds

41 Strategies for weed management Burndown weeds prior to planting Start clean Eliminate alternate hosts for pests Improve conditions for planting Start the crop with the advantage

42 Burndown applications Timing is crucial!

43 Strategies for weed management Consider using a PRE herbicide Improve early-season weed control Include additional MOAs

44 PRE herbicides delay weed growth Days for weeds to reach specific height Days after planting days 32 days 40 days 45 days 0 PRE applied, 6-in weeds Data from Purdue-Ohio State Extension Weed Science 6-in 9-in 12-in No PRE applied

45 PRE herbicide options Corn Sorghum Soybean Sunflower Dual, Outlook, Cinch Dual, Outlook, Cinch Dual, Outlook, Cinch Spartan atrazine atrazine Sencor, Linex Prowl H2O Callisto, Lumax, Laudis, Balance Lumax, Laudis Valor, Authority premixes Prowl H2O Envive, Canopy, Pursuit, Scepter Prowl H2O

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47 OSU Extension Fact Sheet PSS-2778 Herbicide How-To: Understanding Herbicide Mode of Action

48 Strategies for weed management Scout before and after herbicide applications Evaluate weed control Scout for future weed problems

49 Strategies for weed management Use other weed control methods Tillage, narrow rows, competitive varieties, planting dates, cover crops

50 Resistance FAQs How long does it take for herbicide resistance to show up? It depends on production practices and weeds present

51 If the field has never been sprayed, could the weeds be resistant? Probably not

52 I have a glyphosate-resistant weed in my field. Should I quit using that herbicide? Not necessarily, but you must use other options

53 What is the best solution for managing/preventing herbicide resistance? ROTATE crop & chemical Use other weed control methods

54 How do I know if I have herbicide-resistant weeds in my field?

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56 How to submit a sample Collect mature seedheads from areas that were treated Collect from 5+ plants Send sample to OSU Weed Science Extension

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59 2010 Weed Control Treat when weeds are small Scout before and after application Be aware of potential resistance

60 Contact information Joe Armstrong OSU Dept. of Plant and Soil Sciences office: