The value of a herbicide resistance testing service for the agricultural sector in New Zealand

ABSTRACT A government research grant and industry co-funding allowed us to briefly provide free tests of suspected cases of herbicide resistance using traditional seedling-based assays. Information about the service was disseminated through the Foundation for Arable Research and other weed management professionals. Between 2019 and 2022 we received 248 seed samples collected by rural professionals from individual plants suspected of resistance. We successfully tested 195 samples from eight species from 57 farms. Rural professionals were good at recognising cases of resistance; 77% of these seed samples from 40 farms (70%) had resistance confirmed. We gained insights into contextually unique cases of resistance previously undescribed in the literature in New Zealand, including ryegrass resistance to glyphosate in a barley crop, Poa annua resistance to iodosulfuron in wheat, and Phalaris minor resistance to iodosulfuron in wheat. Resistance was typically confirmed 6–8 weeks after planting seed samples, though for species with seed after-ripening requirements to ensure consistent germination, results took as long as 6 months. The results facilitated conversations about long-term resistance avoidance strategies. Future costs of an independent resistance testing service would ideally be shared by the stakeholders benefitting from the crop protection product value chain, from herbicide producers to land managers.