At the 2025 Great Ontario Yield Tour, Dr. Peter Sikkema of the University of Guelph highlighted the persistent challenge of Canada fleabane, one of Ontario’s most problematic weeds.
Once easily controlled with glyphosate, the weed has now developed resistance not only to glyphosate but also to multiple herbicide groups, creating widespread management difficulties across the province.
Canada fleabane’s spread has been rapid, with confirmed cases in at least 29 Ontario counties in August when the presentation was made.
Surveys indicate that up to 75 percent of populations tested show resistance to both glyphosate and Group 2 herbicides. This has forced approximately 60 percent of corn and soybean farmers in Ontario to adjust their herbicide programs in response to the weed.