Project Summary: Using Genetic Tests to Confirm Herbicide Resistant Weeds in Ontario Horticulture Crops

Horticulture cropping systems throughout Ontario have been surveyed to better characterize the occurrence and distribution of herbicide resistant weeds. Herbicide resistant weed populations must be detected and managed rapidly because, depending on the species, they may quickly spread within the same field and to adjacent fields or farms. Additionally, because fewer herbicides are available for use in horticulture crops, resistance management can result in costly weeding practices such as hoeing and/or mowing.

Traditionally, to confirm resistance in a weed sample researchers perform trials in a greenhouse, a process which can take as long as six months to complete. This project developed genetic tests that take only a few days to run. These tests allow us to deliver a diagnostic and a recommendation to the grower within the same growing season.

Since 2016 a total of 37 new cases of herbicide resistance have been reported in horticulture crops in Ontario. Also, twelve quick genetic tests have been successfully developed, two of which are new discoveries. In 2018, these tests were shared with the MAPAQ (Ministère de l'Agriculture, de Pêcheries et de l'Alimentation du Québec) "Pest Diagnostic Lab" and made available to extension personal in Ontario and Quebec to submit samples as a pilot project, providing the diagnostic service to growers. Additional tests are developed as new samples are collected and submitted. Overall, 40% of the submitted weed samples tested positive for herbicide resistance using molecular markers. The results from the molecular marker tests are also validated using the traditional greenhouse methods (dose response).

Early detection and rapid confirmation of resistant weeds will help growers:

  1. Make informed management decisions and mitigate the risk of spreading herbicide resistant weeds by managing them in season.
  2. Provide proof that resistant weeds are present to obtain new minor use priorities and support from crop protection companies for new product registrations.
Crop Weed Herbicide Group Total Fields Positive Tests Results %
Grape Canada fleabane
G9
7
2
29
Pea Large Crabgrass
G1
30
2
7
Potato Lamb's-quarters
G5
3
2
67
Pumpkin Pigweed species
G2
2
2
100
Pumpkin Common ragweed
G2
2
2
100
Pumpkin Canada fleabane
G9
2
2
100
Strawberry Lamb's-quarters
G5
7
5
71
Strawberry Canada fleabane
G9
1
1
100
Soybean Waterhemp
G2
3
3
100
Soybean Waterhemp
G9
3
3
100
Total -
-
60
24
40%

The pea / large crabgrass results are highlighted because these fields were sampled as part of a specific survey that did not sample based on suspected resistance. If these results are excluded the percentage of positive resistant weed results increases to 73%.

Collaborators:

  • Saint-Jean-sur-Richelieu Research and Development Centre: Dr. Marie Josée Simard, Dr. Martin Laforest
  • Harrow Research and Development Centre: Dr. Robert Nurse, Dr. Eric Page
  • Pest Management Centre: Dr. Cezarina Kora
  • External Collaborator: Ms. Kristen Obeid (Ontario Ministry of Food and Rural Affairs)

This project was partly funded through the Pest Management Centre's Pesticide Risk Reduction Program.


For more information:
Toll Free: 1-877-424-1300
E-mail: ag.info.omafra@ontario.ca