Field observation is the first step in confirming a case of weed resistance. The Herbicide Resistance Action Committee looks at these factors when evaluating a potential case of resistance:

  • The level of weed control of other susceptible species. Have related weed species have been controlled effectively?
  • The presence of living plants adjacent to dead ones. Can you rule out different growth stages, incorrect application and crop shielding?
  • Past experience. Have you noticed a gradual decline in control over a period of years?
  • Herbicide history. Have you repeatedly used herbicides with the same mode of action year after year?
  • Occurrence of resistance in the vicinity. Has resistance been confirmed in nearby fields?¹

If you can answer yes to these questions and suspect a case of resistance in your field, contact your provincial weed experts:

Saskatchewan Crop Protection Lab
1-306-787-8130

Alberta Weed Monitoring Network
1-403-310-APSS (2777)

Manitoba Weed Supervisors Association

Weed Testing Services at the University of Guelph
1-519-824-4120 ext. 58372

Sources:

1. “Detecting Resistance.” Herbicide Resistance Action Committee. Online. 28 Apr. 2016.