Kristen Obeid, OMAFRA Weed Management Specialist

Herbicide resistant weeds are not a novelty anymore, they are the norm.  New cases of confirmed and suspected weed resistance to herbicides are steadily reported in all crops and cases of multiple resistances (weed biotypes resistant to more than one group of herbicides) are becoming more common.

 We hear about glyphosate resistant weeds in field crops regularly. Fruit and vegetable crops are not spared from this epidemic.  From my perspective, resistant weeds are an even more pressing issue in fruit and vegetable crops because there are far fewer herbicides available and resistance management can very quickly translate into costly hand weeding.

In 2017, a limited survey was conducted in vegetable crops to aid in the development of quick tests to confirm suspected cases of herbicide resistant weeds. To detect resistance as quickly as possible genetic tests are ideal. These quick tests will provide producers with results in 2 weeks.  This will allow for in season management and prevent the resistant weeds from spreading.  In comparison, conventional tests can take up to one year to complete.

A total of 10 quick tests have been developed.  These include:


  • Group 2 (e.g. Pursuit, Prism, etc.) resistant giant foxtail (Setaria faberii)
  • Group 2 (e.g. Pursuit, Prism, etc.) resistant redroot pigweed (Amaranthus retroflexus)
  • Group 2 (e.g. Pursuit, Prism, etc.) resistant common ragweed (Ambrosia artemisiifolia)
  • Group 2 (e.g. Pursuit, Prism, etc.) resistant waterhemp (Amaranhus rudis)
  • Group 2 (e.g. Pursuit, Prism, etc.) resistant common chickweed
  • Group 2 (e.g. Pursuit, Prism, etc.) resistant Eastern black nightshade (Solanum ptychanthum)
  • Group 5 (e.g. Sencor, Sinbar, Princep, Gesagard, etc.) resistant lamb’s-quarters (Chenopodium album)
  • Group 7 (e.g. Lorox) resistant common ragweed (Ambrosia artemisiifolia)
  • Group 9 (e.g. glyphosate) resistant waterhemp (Amaranhus rudis)



If you suspect you have resistance to any of the weeds listed above, please send in samples to get confirmation.  Knowing what you have will help you make the best management decisions.

 This summer we will be:

  1. Collecting samples of suspected glyphosate resistant Canada fleabane to develop a quick test for this resistant weed.
  2. Collecting samples of suspected Group 1 resistant large crabgrass to determine its spread across the province.

If you have issues with either of these weed species on your farm we will collect samples and test them for you.

The development of quick tests for resistance will help catch resistant weed populations when they are small, prevent their spread by pollen and seed and will help to maintain the use of the few herbicides fruit and vegetable producers have.  So, please help us help you.  If you suspect that you have herbicide resistant weeds on your farm please contact me at: or 519-738-1232.  The more samples we obtain the more quick tests we can develop.

AAFC, OMAFRA and MAPAQ have been working together to develop these tests in the hopes that lab services in Ontario and Quebec will eventually provide these quick tests as a service to growers.

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