Leaf tissue testing helps to identify herbicide resistance

Two- to 10-day turn around for test results is much quicker than in the past

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Resistant weeds continue to create problems across Ontario as horticulture growers have far fewer post-emergent herbicide products compared to cash crop growers.

Why it matters: If growers have access to a quick, reliable test for herbicide resistance, they can develop control strategies sooner, and reduce the potential for the weeds to spread.

Kristen Obeid, weed management specialist in horticulture with the Ontario Ministry of Agriculture, Food and Rural Affairs, has been working on a project for nearly four years with a team of scientists from Agriculture and Agri-Food Canada in Quebec and Ontario. Funding from AAFC’s Pest Management Risk Centre has allowed them to create genetic quick tests to help identify herbicide-resistant weeds. These tests can provide results to growers within two to 10 days.

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“It currently takes anywhere from three months to a year to get results back to growers. With these genetic tests we don’t wait to collect the seed, we use leaf tissue, and look at the weeds DNA to determine if there is a change in the sequencing conferring a mutation, which makes the plant resistant,” says Obeid.

Tests have also been developed to differentiate between brassica and pigweed species. The differentiation of the pigweed species tests has aided in confirming new cases of waterhemp in Ontario, Manitoba and Quebec.

“Once confirmed, the waterhemp is then tested for Groups 2, 5, 9 and 14 resistances. These tests have aided Dr. (Peter) Sikkema (University of Guelph) and his graduate students, whom are conducting a waterhemp survey across Ontario in confirming new cases of waterhemp in new counties very quickly,” she says.

Eighty new cases of herbicide resistance have been reported in horticulture crops in Ontario and Quebec, and 24 quick genetic tests have been developed for 12 weed species during this project. Three of these tests are new discoveries.

Test protocols have been shared with Quebec Ministry of Agriculture, Fisheries and Food (MAPAQ) and the weeds laboratory of AAFC’s Harrow Research and Development Centre as a pilot project, since 2018.

About 1,000 samples from farmers’ fields in Ontario and Quebec have been analyzed through these labs and 52 per cent of samples tested positive for resistance.

Obeid says there is more interest in taking part in the project as growers and agri-businesses become aware of the testing.

“Another really unique thing about this work is if the grower thinks they are only having failure to one herbicide group, and we have more tests for that species, we can test it for all different potential resistances. I am finding in many cases, there is resistance to more than one group, when the grower thought they were only having an issue with one. This is significant as it ensures the grower can develop a management program that will work,” says Obeid.

Obeid hopes as producers become more aware of quick testing it will help stop the spread of the weed.

“We hope to carry on the work, to develop more genetic tests for new cases of herbicide resistance as well as provide testing. The more tests we can develop, the quicker we can prevent resistance from spreading.”

About the author

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Jennifer Glenney

Jennifer lives on a farm in Cayuga, Ontario and has a lot of experience in the many aspects of agriculture.

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