Threat of herbicide resistance can't be ignored
By Peter Sikkema
June 01, 2010
Changes are needed. That’s the message we should be taking from news that glyphosate-resistant giant ragweed has been confirmed in Ontario.
Quite simply, growers need to ensure there is diversity in their long-term weed management strategy. This can be accomplished by including multiple crops and herbicide groups or farmers may pay a steep price in terms of increased cost of weed control in the future, lower crop yields and possibly fewer choices in which crops they can grow.
So far, we have only confirmed one instance of glyphosate-resistant giant ragweed from one farm in Essex County, however we are testing suspect cases from across southern Ontario. We think this glyphosate-resistant variety of this extremely aggressive and yield-robbing weed is with us to stay.
Interestingly, in the field where glyphosate-resistant giant ragweed was confirmed, the Essex County farmer had never grown Roundup Ready soybeans until 2002. Over the next years, he grew Roundup Ready soybeans along with one crop of winter wheat. This was not wild risk-taking by any means. This farmer never dreamed resistance would show up so quickly. Until it did.
Weed scientists like myself and herbicide manufacturers learned a lesson here too. We need to do a better job of communicating responsible use of herbicides, especially glyphosate. Crop and herbicide rotation cannot be seen as optional. In fact, even a two-crop rotation is risky.
Farmers have to use different herbicide groups in a strategic and planned manner. Every farmer should have a rolling multi-year plan for every field that allows for intelligent balancing of both economic and agronomic factors.
If you allow the short-term price outlook to determine what you plant and which herbicide you use each spring, you may implement a weed control strategy that increases the potential for the selection of herbicide-resistant weeds.
Growing soybeans at this location is now going to be an extremely challenging proposition because the giant ragweed is resistant to both the group 2 and group 9 herbicides.
This may occur on numerous other grain and oilseed farms in every part of the country if growers do not incorporate diversity in their weed management programs.
