Recently, Thomas Butts, a graduate research assistant, Vince Davis, and Dave Stoltenberg confirmed that a common ragweed population in Wisconsin is resistant to an ALS inhibitor. Here is the conclusion from their research paper (linked below) which stresses resistance management strategies.
“These results confirm the first occurrence of ALS inhibitor-resistant common ragweed in Wisconsin. The population was initially identified in Brown County in 2013.
Several components are key to a comprehensive, effective control strategy to combat herbicide-resistant weeds. The use of alternative herbicide sites-of-action and tank-mixing multiple herbicide sites-of-action will improve herbicide-resistant weed control. An early planting date, coupled with the use of a preemergence residual herbicide program, will allow crops to gain a competitive advantage over weeds. All herbicides should be applied at the correct timing, and in particular postemergence herbicide applications should occur when weeds are small and actively growing.
To ensure the greatest efficacy, consult the herbicide label recommendations to ensure application before maximum weed size limits and to use appropriate rates. Furthermore, special care should be used to clean tillage and harvest equipment thoroughly as they can quickly spread weed seed among fields. The focus of these best management practices is to diversify weed control methods, reduce weed seed additions to the soil seedbank, and utilize the most effective methods possible.
For updates on Wisconsin weeds please visit the Wisconsin Crop Weed Science website at http://wcws.cals.wisc.edu/. Further information on controlling Palmer amaranth or other herbicide-resistant weeds can be found at: http://www.takeactiononweeds.com/. Finally, if you believe you may be facing herbicide-resistant weeds in your fields, please contact your local county extension agent.”