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Horseweed an emerging problem in Southern Illinois

An extension ag educator says Marestail or Horseweed is an emerging issue in southern Illinois because of the resistance it has developed.

Talon Becker says it has been confirmed that Horseweed is glyphosate and ALS inhibitor resistant in some populations and farmers are either spraying too late or not using multiple sites of action to kill the plant.

“With these resistance problems we see more and more escapes, where a plant will get a little bit burnt, but then eventually come out of it.”

Becker recommends doing more than one burn down and using residual herbicides to remove Horseweed.

“In your Spring applications, or at least your last one, you’ll want to be using residual herbicides. These are herbicides that contain sulfentrazone, flumioxazin, and metribuzin are common ones. 2,4D or Dicamba are usually pretty good as well.”

He says Horseweed will fully flower and produce seeds before harvest, so it is critical to take early action. Brownfield interviewed Becker at the University of Illinois crop management conference.