Herbicide cross resistance in Bromus diandrus and B. rigidus populations across southeastern Australia

Abstract

Herbicide resistance to Group A (AC Case-inhibiting herbicides) and B herbicides (ALSinhibiting herbicides) in Bromus diandrus and B. rigidus is becoming more common in southeastern Australia but there is limited information available on its regional distribution in either species. At present it is unclear if resistant brome populations differ in their response to different herbicides within the same herbicide group. Another unresolved question is related to the herbicide dose response of resistant brome populations. This study identified differences between Group A herbicides in their activity on resistant brome. However, increasing herbicide dose only marginally improved weed control in most cases. Varying degrees of Group B resistance was also detected in four brome populations. These initial findings suggest that increasing herbicide dose is unlikely to improve brome control but some Group A and B herbicides are more effective than others in controlling resistant populations.