Prolific use of wild oat herbicide contributing to weed issues
MEDICINE HAT, Alta. — More than half the fields in Alberta have herbicide resistant wild oats, and the problem shows every sign of getting worse.
“Wild oat, in Alberta, it’s our most resistant species in terms of herbicide resistance,” Agriculture Canada weed scientist Neil Harker told the Dec. 3 Farming Smarter conference.
“What is the reason for that? It’s because we apply so many wild oat herbicides. It’s the No. 1 herbicide in terms of dollars per acre spent and in terms of the amount of herbicide that’s applied.”
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Herbicide resistant weeds of all kinds are becoming a major problem in North America and have already created severe problems in Australia, where some grassy weeds are resistant to seven groups of herbicides.
In Canada, the problem evolved as more chemicals became available to kill certain weeds, which led farmers to inadvertently select for summer annual weeds.
Producers grew more winter annuals and alfalfa before widespread chemical solutions, which reduced the wild oat seed bank without the use of herbicides.
Harker said the method can be used again. In the same vein, crops intended for silage could be cut earlier to limit wild oat seed production.
Early season tillage and seeding earlier so that the crop gets ahead of the wild oats are two other non-herbicide options. As well, a higher seeding rate makes crops more competitive against weeds.
He said doubling the seeding rate, moving from a short to tall variety and adding an additional rotation crop would help reduce wild oats.
Planting perennial forages is still one of the best ways to reduce the wily weed, he added.
“It is possible to do pretty well on wild oats even without using herbicides,” Harker said, if farmers are willing to vary their crops.
“Until we’re able to say, ‘I’m willing to make a bit of a sacrifice to change something, to do something a little different,’ we’re not going to change weed resistance. If we say, ‘well, I’m not willing to grow anything other than canola-wheat,’ well, we’re going to have more resistance.”
Agriculture Canada has bought a Harrington weed destructor, an Australian invention that destroys weed seeds off the combine.
Harker said it appears the machine will be effective against some weeds but not all and wild oats may be one of the more difficult foes.
However, he encouraged farmers to consider an integrated management strategy to limit herbicide resistant weeds before the problem escalates.
“Weed resistance is continuing to increase at a very rapid pace. Combining single and non-herbicidal practices will be what we need to do for effective wild oat management and for effective weed management going forward,” he said.
“It doesn’t mean that we have to stop using herbicides. We just have to try to use them a little less often to reduce our selection pressure so we’re not in the same place as they are in Australia.”
barb.glen@producer.com
