WINNIPEG – Poor herbicide rotations are sowing the seeds for a plague of wild oats that is resistant to chemical control, said a Manitoba Agriculture weed specialist.
Dave Kelner said he hopes alarming results from a survey conducted by University of Manitoba researchers will prod farmers into paying closer attention to what is becoming a serious economic problem.
The growing list of herbicide-resistant weeds affects farmers across the prairies, but the problem is accelerated in Manitoba where there is more continuous cropping, he said.
Yet farmers have been slow to respond to repeated warnings from extension workers and herbicide manufacturers about the risks associated with using the same group of herbicides every year.
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“There’s a mentality out there that ‘this problem is not going to happen to me’,” Kelner said. “This is the kind of thinking that is out there, it’s like people think with cancer – it’s never going to happen to you.”
But research shows almost half the cropped land in Manitoba stands a “very serious chance” of developing wild oats resistant to the over-used used Group 1 herbicides, Kelner said.
The finding is based on a review of crop insurance data which shows how often farmers used a specific herbicide on each field. Farmers who used the same group of herbicides more frequently than one year in two, over the past five years, are deemed high risk.
About one-third of the province is at moderate risk, based on the number of producers who had used the products more than one year in three.
In a field survey of one township in south-central Manitoba, resistant wild oats were found in one out of every six fields.
Researchers have now identified wild oats that are resistant to both Group 1 and Group 8 herbicides. “But it is by no means just wild oats,” Kelner said.
Foxtail has become resistant to Group 1 and Group 3 herbicides, wild mustard is resistant to Group 2 and Group 4 products, and there are now areas in which kochia resists Group 2.
Farmers are being urged to check their fields for patches of weeds which did not succumb to spray this year. “Suspicious patches must not be allowed to set seed,” warns a Manitoba Agriculture bulletin.
An average wild oat plant produces about 250 seeds and there can be up to 2,000 plants per square metre in severely infested patches.
Patches should be mowed, or treated with a non-selective herbicide. If the infested area is large enough, the bulletin recommends farmers consider cutting it for hay before the wild oats set seed.
Kelner said over the longer term, farmers must re-think their weed management strategy.
“We’re encouraging a ‘back to basics’ approach to weed control – the types of things farmers used to do before they had all these chemicals,” he said.
Such strategies include more crop rotations and the re-introduction of forage crops.
