Effective Strategies to Control Canada Fleabane Weed
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 presentatio 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.
The economic consequences are severe. Research on commercial farms shows average corn yield losses of 54 percent, representing nearly $600 per acre in lost revenue.
In soybeans, losses reach 65 percent on average, equating to roughly $500 per acre. Under heavy infestations, yield reductions approach 99 percent, threatening total crop failure.
In corn, pre-plant herbicides such as Acuron (Syngenta), Integrity (BASF), and Callisto (Syngenta), plus Atrazine (Syngenta) have demonstrated excellent control levels, often above 95 percent.
Post-emergence combinations with Group 4 or Group 2 herbicides also provide strong results. However, soybeans remain far more difficult, as broadleaf weeds are harder to manage in broadleaf crops.
Pre-plant tank mixes such as glyphosate plus saflufenacil (Eragon from BASF Canada) with metribuzin have shown the most consistent performance in identity preserved and Roundup Ready systems.
In Xtend and Enlist soybeans, additional partners such as dicamba or 2,4-D combined with saflufenacil improve control significantly.
Timing plays a crucial role. Dr. Sikkema emphasized that smaller weeds are easier to manage, and herbicides are most effective when applied during the brightest hours of the afternoon. Environmental conditions, weed density, and genetic variability also contribute to inconsistent control.
Beyond herbicides, integrated practices such as cover crops and occasional tillage can suppress fleabane, though results vary.
According to Dr. Sikkema, Ontario farmers have proven the weed can be managed effectively, but only through zero-tolerance strategies that prevent seed return. Without vigilant control, Canada fleabane will continue to erode farm profitability for years to come.
This article was created based on a presentation by Dr. Peter Sikkema during the Great Ontario Yield Tour event in Osgoode, Ontario, watch the video of his presentation on Canada Fleabane below.