Alberta hosts Prairies’ first glyphosate-resistant weed

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Federal researchers have found the Prairies’ first confirmed case of glyphosate-resistant weeds in populations of kochia in three chemfallow fields in southern Alberta.

Weed scientists at Agriculture and Agri-Food Canada confirmed that kochia plants taken from the fields have developed resistance to the broad-spectrum Group 9 herbicide, the active ingredient in Roundup, Touchdown, Credit, Polaris, Vantage Plus and many other herbicides.

Unlike some previous findings of glyphosate resistance in Ontario, however, the fields in question don’t appear to have been used regularly to grow glyphosate-tolerant crops, according to Canada’s best-known glyphosate manufacturer.

AAFC scientists began this specific investigation last summer in the three fields, where “we saw little to no kochia control after (the fields received) multiple applications of glyphosate,” weed scientist Bob Blackshaw said in a release from Monsanto, maker of Roundup and developer of the Genuity Roundup Ready lines of glyphosate-tolerant crops.

The initial findings “prompted us to do further work through the fall and winter that involved collecting samples of seed and completing the necessary grow-out and spraying of plants to confirm resistance,” said Blackshaw, who works for AAFC at Lethbridge.

Blackshaw and fellow AAFC weed researcher Hugh Beckie completed tests on seed samples collected from the fields to validate their findings, testing the survival of the kochia plants at increasing rates of glyphosate, as per standard practice to confirm herbicide resistance, Monsanto said.

Not from RR fields

“What makes this particular case different from some of the previous situations where glyphosate resistance has been confirmed, is that it does not appear to have developed in a Roundup Ready cropping system,” Monsanto said.

The suspected weed species, the company said, was found in fields where the “typical crop rotation… does not appear to have included regular use of Roundup Ready crops.”

Kochia becomes the third weed species in which populations of plants in Canada have been confirmed as glyphosate resistant. Giant ragweed was confirmed in 2009 and Canada fleabane was confirmed in 2011, both in southwestern Ontario.

Farther south, glyphosate-resistant kochia has previously been confirmed in Colorado, Kansas and Nebraska, with suspected cases in South Dakota and the border states of North Dakota and Montana, Monsanto said.

AAFC’s weed scientists are continuing their work on this particular site, the company said. For its part, Winnipeg-based Monsanto Canada said it’s also supporting the AAFC research effort, which includes providing recommendations to help farmers manage glyphosate-resistant weeds once they are identified and confirmed.

New challenges

“We have been fortunate in Canada in that this is not a large-scale weed management issue,” Sean Dilk, technology development manager in Monsanto Canada’s crop protection division, said in the company’s release. “But we have increased communication around this topic and we speak to farmers about this more often to lessen the likelihood of resistant weeds developing.”

Resistance evolves after a weed population has been subjected to intense selection pressure in the form of a repeated use of a single herbicide, without adequate incorporation of “cultural weed management options,” Monsanto said. The herbicide in question then controls all the susceptible weeds, leaving only resistant weeds to reproduce.

“Our history tells us that farmers can, and are, effectively managing the situation with good agronomic practices such as using tank mixes and/or cultural weed control methods,” Dilk said.

However, he warned, this particular finding “could present new challenges if it spreads because of the prevalence of Roundup Ready canola and Roundup Ready sugar beets in this region.”

Roundup herbicides and Roundup Ready crops have continued to be used in areas where glyphosate resistance has occurred in the past, he noted, “and we have some very knowledgeable people looking into this issue. I am confident in our ability to present good options to the growers in the region.”

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