Canada is third in the world for herbicide-resistant weeds

BANFF, Alta. — Producers across Canada battle at least 77 herbicide-resistant weeds every year.

Next to the United States and Australia, Canada has the third-largest population of weeds resistant to one or more herbicides. Most of the problems have appeared in the last 30 years, at a time when few new herbicides have been registered to help get ahead of troublesome plants.

“We are seeing an increase in resistant weeds and a stagnation of the modes of action we have to manage those weeds,” said Charles Geddes of Agriculture Canada.

The most recent weed surveys show British Columbia has one resistant weed species, Alberta has 24 species, Saskatchewan reported 22, Manitoba has 30 and Ontario has found 38 resistant weeds.

Scientists need to learn more about weed ecology and new management options, he said at the Prairie Cereals Summit held in Banff, Alta., Dec. 13.

Geddes is based at Lethbridge and works with the Prairie Wide Diagnostic Testing Service.

If growers suspect they have a resistant type, they can send seeds to the lab where resistance is confirmed. The future direction is to develop high-throughput testing of different species and identify the genes causing resistance. There is also a plan to map the risk areas and determine where these weeds are likely to appear.

“Currently, we do not have capacity to do all types of herbicide resistance so we are focusing on specific cases,” he said.

Kochia is the main target because it is so prevalent.

In the late 1980s, Group 2 herbicide resistance appeared in Alberta and expanded to all the kochia populations in Canada.

In 2011, glyphosate resistance was found in southern Alberta. Around then it was estimated about five percent was resistant to glyphosate. Five years later, surveys showed about half the kochia population was glyphosate resistant.

Resistance to dicamba or Group 4 chemistry was found in 18 populations around the same time. Multiple resistance was found in about 10 populations.

Saskatchewan surveyed its weeds at the same time and found about five percent were resistant. A repeat survey is planned for 2019.

The Manitoba survey of 2013 found two populations resistant to glyphosate but the problem is expanding to new municipalities. This past growing season, they collected 300 samples from Manitoba and these are being screened at the laboratory for various forms of resistance.

Large green patches of kochia are common across the southern Prairies. It remains green and once the farmer notices it has survived a herbicide-control attempt, it is too late to apply a rescue treatment.

If it is cut while it is still vegetative, it will try to regrow and produce seed earlier in the summer. If producers wait until later in August the plant does not have the energy to regrow and produce more seed.

Kochia is used as a forage in dry years but it is not known how long the seeds stay viable.

“If we are cutting these patches too late we could have a viable seed and a portion of that seed could survive rumen digestion,” Geddes said.

Cattle feed on the bales, pass the seeds and move weeds to new sites.

Ensiling damages many of the weed seeds so they will not grow, but 10 to 15 percent could survive, said Geddes.

Another area of research into seed viability is a long-term seed bank study to learn what causes seeds to decay in the soil.

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