Kristen Obeid, OMAFRA Weed Management Program Lead – Horticulture

Radio Report, October 20, 2015

Fruit and vegetable growers have been dealing with insect and disease resistance to pesticides for many years.  The challenge of herbicide resistance is no different.  Most of the talk these days is about glyphosate-resistant (GR) weeds in field crops, but we do not hear much about resistant weeds in hort crops.  Should fruit and vegetable growers be worried?  The short answer is YES!

Actually, the first cases of GR weeds were found in orchards, not in glyphosate tolerant (GT) crops.  Worldwide there are 31 weed species (11 grasses and 20 broadleaves) with reported glyphosate- resistance.

Currently, in Ontario there are four:

  • Giant ragweed
  • Canada fleabane
  • Common ragweed
  • Tall waterhemp

All four species have populations that have multiple-resistance to glyphosate and Group 2 herbicides, such as, Prism, Pinnacle, Upbeet and Classic to name a few.

In fruit and veg crops the most concerning herbicide resistant cases are:

  • Crabgrass species resistant to all grass herbicides.
  • Pigweed species resistant to Group 5 and Group 7 herbicides, which includes, Sencor, Gesagard and Lorox found throughout the province.
  • Gramoxone and glyphosate resistant Canada fleabane.
  • Group 2 resistant Eastern black nightshade found throughout the province.

So .. where do we go from here?

  • Continue to use Integrated Weed Management practices.
    • Use multiple herbicide modes-of-action with overlapping weed spectrums in rotation, sequences, or mixture
    • Use the full recommended herbicide rate and proper application timing for the hardest to control weed species present in the
    • Scout fields after herbicide application to ensure control has been achieve Do not allow weeds to reproduce by seed or to proliferate vegetatively.
  • Get any suspect weeds tested immediately for potential resistance.

This has been Kristen Obeid, OMAFRA Weed Management Program Lead for Horticulture Crops

1 comment on “Should Fruit and Vegetable Growers be Concerned about Resistant Weeds?

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