Glyphosate-resistant Horseweed found in Wisconsin

horseweedContact: Vince Davis, (608) 262-1392,

A glyphosate-resistant horseweed population in Wisconsin has been identified by University of Wisconsin-Madison/Extension researchers from a 2012 sample taken in Jefferson County.

“Although the weed usually follows a winter annual life cycle, it has the ability to germinate later in the year, choking out spring and summer crops,” said Vince Davis, UW-Extension cropping systems weed specialist at UW-Madison. “Horseweed has tiny seeds that can easily be carried great distances by wind, therefore, the threat of this weed spreading herbicide-resistant biotypes to new locations through naturally occurring seed movement is high.”

He noted that the adoption of no-till cropping systems in past decades has allowed horseweed to become a major problem in agricultural fields.

“Farmers use a zero tillage agricultural technique to decrease costs, decrease soil erosion, and improve soil health. However, the weed seeds left from the season before also remains near the surface and creates a higher chance of growing again in the next crop,” said Davis. “Increasing the number of weeds in the crop often means increasing the chances for selecting herbicide-resistant weeds.”

Horseweed is a broadleaf species of weed problematic to agricultural fields in Northern America. The Weed Science Society of America says the best way to stop the spread is to manage it first. For more information on how to best manage weeds and reduce the risk of herbicide resistance go to

The Wisconsin glyphosate-resistant horseweed population was identified through the Late-Season Weed Escape Survey in Wisconsin Corn and Soybean Fields, which is primarily funded by the Wisconsin Corn Promotion Board. The survey will be conducted again in 2013.  If you are interested in participating in this survey, please see the survey announcement here:

Moreover, if you have horseweed, or other weeds that survive post emergence applications and you have concern about glyphosate resistance, contact your local county Ag Extension Agent who can help you further evaluate the situation.


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