Lock your doors. Three nasty weeds resistant to multiple herbicide groups are spreading across Western Canada.

Weed resistance isn’t new to Western Canada. But more recently, weeds resistant to multiple groups are showing up.

In the spring of 2021 in Western Canada, wild oats, kochia and green foxtail were commonly found to be resistant to several herbicide groups.

It gets worse. Certain biotypes of kochia are also resistant to Group 9 (glyphosate), Group 2 and Group 4. This resistance to multiple groups increases the complexity and cost of managing resistant weeds.

Even newer weeds are showing resistance to commonly used herbicides. Both palmer amaranth and water hemp are relatively new to Western Canada and have been identified in Manitoba. These two weeds, both from the pigweed family, have aggressive growth and are prolific seed producers. In fact, one palmer amaranth plant can produce up to one million seeds.

Palmer amaranth is known for its herbicide resistance to Groups 2, 3, 5, 9 and 27. Water hemp has shown resistance to Groups 2, 4, 5, 9, 14, 15 and 27. Both weed species can be resistant to glyphosate (Group 9) and certain biotypes have multiple resistance to specific herbicide modes of action.

While these two weeds are currently confirmed in Manitoba, both Saskatchewan and Alberta producers should be prepared. The threat is on their doorstep and it’s only a matter of time before these two weeds resistant to multiple groups of herbicides invade more of Western Canada.

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