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Dicamba-tolerant soybeans part of the solution to glyphosate resistance

Canada fleabane: 200,000 wind-dispersed seeds means this particular weed can spread incredibly quickly

By Lauren Benoit, University of Guelph Agricultural Communications Student, for


It wasn’t uncommon in southern Ontario this past summer to see a field of no-till soybeans with huge patches of tall, woody weeds growing, reducing profitability. The unmistakable weed is Canada fleabane, the newest challenge in glyphosate resistance.

This kind of herbicide resistance is becoming a recurring development, and once again rural Ontario will need to prove its innovativeness to find a solution. Since the discovery of Triazine-resistant weeds in the 1980s, every silver-bullet herbicide solution has been followed by a resistance problem a few short years later. With the invention of glyphosate in 1974 followed by glyphosate-tolerant (Round-Up Ready™) crops in 1986, it looked like farmers had an answer to all their weed control problems. It wasn’t until 2009 that glyphosate resistance was confirmed in Canada.

Canada fleabane grows as a summer or winter annual, developing a rosette in the fall, over-wintering then bolting and seeding in the spring of the following year. The plants’ ability to produce on average 200,000 wind-dispersed seeds means this particular weed can spread incredibly quickly. Farmers are crunched for time to discover a solution before glyphosate resistance blankets the entire province. 

Agri-chemical companies and farmers alike are developing innovate ways to combat the issue. Best management practices such as applying herbicides with multiple modes of action or, if applicable, tillage can effectively control the spread of Canada fleabane.

Currently Eragon, a group 14 herbicide developed by BASF Canada Inc. and released to market in 2013, has been the number one product recommended by Peter Sikkema, a weed scientist at the University of Guelph, for the control of glyphosate-resistant fleabane. However, the price of applying Eragon as well as the other chemicals required for total weed control is not always economical for farmers and there is a high demand for a cheaper solution.  

Monsanto might have found that solution. Over the past few years of field trests, Dicamba, a group 4 herbicide, has proven to provide adequate control of glyphosate-resistant Canada fleabane. However, it causes severe damage to soybeans, so Monsanto developed a dicamba tolerant soybean cultivar so farmers can spray dicamba in-crop to control Canada fleabane.

Matt Underwood, a University of Guelph Masters student studying Dicamba tolerant soybeans, calls the development of Dicamba-tolerant soybeans “an exciting time for Ontario agriculture. We haven’t seen brand new technology introduced to soybean varieties in a while. This opens a whole new opportunity for weed control for Ontario farmers.”

If Ontario farmers have learned anything throughout the seemingly never-ending battle with herbicide resistance it’s that there is no silver-bullet. Every individual farmer will need to adapt the best management practices for their respective operation based on their specific needs.

This article is part of Lauren’s course work for the University of Guelph agricultural communications course, instructed by Prof. Owen Roberts.

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