The How does herbicide resistance evolve?
Herbicide resistance is the inherited ability of a plant to survive and reproduce following exposure to a dose of herbicide that would normally be lethal to the wild plant. Resistance happens with the repeated use of the same herbicide, or herbicides with similar site of action on a weed population.
Signs of Herbicide Resistance
- Failure to control weeds normally controlled with same herbicide and rate.
- Adjacent weeds are controlled.
- A spreading patch of a particular species (all other species controlled)
- Surviving plants mixed with controlled plants of the same or different species.
Example of herbicide resistant weeds
- Broadleaves Grasses
- Annual ryegrass
- Barnyard grass
- Prickly lettuce
- Russian thistle
Herbicide resistance is sometimes hard to identify and in fact 90% of weed control failures are due to factors other than resistance* including:
- Application issues – (calibration, skip, etc.)
- Weather conditions – (temperature, rainfall, etc.)
- Weed factors – (size, new germination, stress)
- Shadowing of smaller weeds (poor coverage)
- Soil factors (moisture, organic matter, debris)
If herbicide resistance is suspected, confirmation using an approved scientific method should obtained. Download our solution sheet. Contact your local Ministry of Agriculture department for testing options.