Herbicide Resistant Weeds Not Just in Field Crops

With far less herbicide options in horticultural crops as compared to field crops, horticulture producers tend to accept more weed escapes. The reality of this practice is that we could be harbouring and increasing herbicide resistant weeds in our fields and orchards. The University of Guelph has a list of confirmed cases of herbicide resistant weeds and the counties across the province that they are found in. Check out their website by typing "Ontario Resistant Weeds" into your web browser.

Growers should be aware that resistant weeds are in horticulture production regions across the province and in the event of control failures herbicide programs need to be changed.

You likely have a resistant weed population if you have a weed that should have been controlled but is healthy even when the correct herbicide rate, timing and weather conditions were followed.

You can report suspected resistant weeds by contacting the Agriculture Information Contact Centre 1-877-424-1300. By taking advantage of this toll-free number, suspicious weed species will be tested for resistance by the University of Guelph. Any information obtained from this service will allow weed researchers to develop control options for resistant weed populations.

You can also send samples directly to the University of Guelph. The University of Guelph will test, free of charge, suspected resistant weeds. Simply type in "Ontario Resistant Weeds" into your web browser and go to "Weed Testing".

In order to prevent the development of herbicide resistance growers should take into consideration the following practices:

1. Rotate herbicides with different modes of action. Avoid making more than two applications of the same herbicide in the same year.
2. Scout orchards and fields to identify weeds. Respond quickly to changes in weed populations by controlling weeds before they spread throughout the entire orchard or field.
3. Use non-selective post-emergence herbicides (Round-up, Ignite, or Gramoxone) in your weed management program.
4. Use herbicides only as-needed.