Key points:
- Ryegrass which is resistant to Group B (ALS inhibitor, sulfonyl-urea) herbicides has been detected in the Methven area.
- In a FAR trial, ryegrass plants suspected of resistance were treated with five different Group B herbicides.
- Slight damage was apparent in the resistant ryegrass biotype seven days after herbicide treatment, but the plants quickly recovered.
- There was significantly more damage in the susceptible annual and perennial ryegrass lines than in the resistant ryegrass biotype 21 days after treatment.
- The susceptible lines suffered significantly more damage from all five of the sulfonyl-urea herbicides tested than the resistant line.
- Farmers need to check to ensure ryegrass is killed by applications of sulfonylurea herbicides and destroy any potentially resistant surviving plants.