Distribution and frequency of herbicide-resistant wild oat (Avena spp.) across the Western Australian grain belt

In 2005, a random survey was conducted across 14 million hectares of the Western Australian grain belt to establish the frequency and distribution of herbicide-resistant wild oat (Avena spp.) in cropping. fields. In total, 677 cropping. fields were visited, with wild oat populations collected from 150 fields. These wild oat populations were screened with several herbicides commonly used to control this weed. Most of the wild oat populations (71%) were found to contain individuals resistant to the ACCase-inhibiting herbicide diclofop-methyl. Resistance to other ACCase-inhibiting herbicides was markedly lower. Herbicides of alternative modes of action were effective on all wild oat populations. Overall, wild oat resistance to diclofop-methyl was found to be widespread across the Western Australian grain belt, but resistance to other herbicides was relatively low. Therefore, through diversity in herbicide use and with cultural management, it is possible to maintain wild oat populations at a low level and/or minimise herbicide resistance evolution.