MEDICINE HAT, Alta. – A 2007 weed survey of 300 Alberta fields found 40 percent of the wild oats were resistant to Group 1 chemicals.
That compares to a 2001 survey of 250 fields showing 11 percent resistance and 15 percent in 2003.
“If that trend continues we will have half the fields by 2010,” Hugh Beckie said at the Southern Alberta Conservation Association annual convention Dec. 2 in Medicine Hat.
Wild oats, Russian thistle, kochia and green foxtail are troublesome weeds for prairie farmers because of their prevalence and resistance to commonly used herbicides.
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Wild oats is among the worst. It has widespread resistance in the three prairie provinces to Group 1 herbicides, resulting in annual losses as high as $500 million due to lower yield and grains, dockage losses and cleaning costs.
“We estimate 11 million acres on the Prairies had resistant weeds,” said Beckie, a weed scientist with Agriculture Canada.
Herbicides containing “fops”, aryloxyphenoxy-propionate or “dims,” cyclohexanedione in the Group 1 chemistry, demonstrate the greatest problem.
Since Group 1 and Group 2 are the only options for wild oat control in cereals, the loss of their use is a big problem for farmers.
Worst affected areas
Between 1996 and 2006, weed surveys showed resistance to Group 1 chemistries was most prevalent across the parklands and black soil zones of the three prairie province.
Farmers in this region tend to have higher weed populations and greater herbicide use. Group 2 resistance is lower.
Weed surveys rank green foxtail fifth in the list of 10 troublesome weeds, but resistance levels are low.
“So far it is not a big problem. What is a big problem in terms of resistance is kochia,” Beckie said.
Russian thistle abundance is dropping while kochia population is increasing, even though both are part of the same family of tumbleweeds.
Kochia is found throughout Canada and the United States. Resistance to Group 2 herbicides has been known since 1988 and the problem is often associated with reduced tillage systems.
It is a tough plant that can grow two metres tall and send down roots seven metres. It is also tolerant to drought, insects, heat, cold and salinity.
Climate change may have some impact on its spread but Beckie thinks herbicide resistance is the more likely culprit in the last 10 years.’
Group 2 resistance
Of the 112 population sites assessed in Manitoba, about 80 percent were resistant to Group 2 herbicides and a 2007 southern Alberta survey showed 90 percent resistance.
“We are finding the same everywhere,” he said.
Resistance comes with a genetic mutation affecting the way the herbicide binds to the plant.
Many plants examined had more than one mutation because of the way the plant cross pollinates.
“These mutations confer resistance to all Group 2s,” he said.
Evidence based on surveys since 1996 shows that farmers have to assume their kochia stands are resistant to Group 2 herbicides.
Some weeds can come from elsewhere so it is not always the farmer’s fault for not rotating his herbicides.
Some of the problem can be combated with tank mixes and producers should check the Blue Book, the Canadian guide for pesticide use.
So far, no glyphosate resistance has been found in Canada but it has appeared in the corn and soybean growing areas of the U.S. Midwest.
