More kochia resistant to glyphosate in Man.

CARMAN, Man. — Manitoba has more cases of glyphosate resistant kochia, but the details won’t be made public until later this year.

Agriculture Canada and Manitoba government experts confirmed in 2014 that two locations had kochia with resistance to glyphosate in the province’s Red River Valley.

Jeanette Gaultier, Manitoba Agriculture weed specialist, said a number of kochia samples have tested positive for resistance and the locations have spread outside the valley.

“We had about 25 samples of kochia sent in last year,” she said July 5 at the Crop Diagnostic School in Carman, Man. “Some came back negative, but we did have additional positive detects…. We do have some locations that are a little bit more west of (the Red River Valley).”

Gaultier said the number of positive cases won’t be made public until representatives of the Pest Surveillance Initiative, a project of the Manitoba Canola Growers Association and Manitoba Agriculture to monitor clubroot, speak with farmers who have resistant kochia.

Once that’s done, the province plans to publish a map of kochia resistant weeds, similar to its map for clubroot incidence.

The initial discovery of resistant kochia in the Red River Valley surprised experts because the weed is more common in southwestern Manitoba and drier parts of the Prairies.

Rob Gulden, a University of Manitoba weed scientist, said it shows there’s a relationship between glyphosate resistance and certain crops.

Corn and soybeans are more common in eastern Manitoba, and those crops are less competitive with weeds early in the season. Growers subsequently rely heavily on glyphosate, the active ingredient in Roundup, to control weeds.

Testing on the affected kochia indicates that the resistance to glyphosate isn’t as severe as weeds in the United States.

“The resistance mechanism in kochia is gene amplification, similar to the palmer amaranth…. The more gene copies, the higher the resistance to glyphosate…. You can go on (with) a higher rate and you still won’t get any effect,” Gaultier said.

“We’re up to about 25 genes copies (in kochia)…. In the palmer amaranth, in the States, some of the gene copies are up to 180 or over 200.”

Manitoba Agriculture will likely release its kochia incidence map in a few months.

Contact robert.arnason@producer.com

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