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
Alberta Weed Monitoring Network
Manitoba Weed Supervisors Association
Weed Testing Services at the University of Guelph
1-519-824-4120 ext. 58372
1. “Detecting Resistance.” Herbicide Resistance Action Committee. Online. 28 Apr. 2016.