A herbicide resistance risk assessment for weeds in maize in New Zealand

Despite an extensive history of research into herbicide resistance in New Zealand maize, some aspects remain understudied. Herbicide was first detected the 1980s maize crops, with atrazine Chenopodium album L. and Persicaria maculosa Gray. Since then, has also developed to dicamba, last five years Digitaria sanguinalis (L.) Scop. populations have been reported be resistant nicosulfuron. Here we estimate risk arising 39 common weeds. A list weeds associated generated, omitting uncommon those that grow outside growing season. Weeds were ranked for their evolving a scoring protocol accounts specific herbicides used maize. Seven weed species classified as having high developing resistance: Echinochloa crus-galli P.Beauv., album, Eleusine indica Gaertn., Xanthium strumarium L., Amaranthus powellii S.Watson, Solanum nigrum sanguinalis. Seventeen classed moderate risk, 15 low risk. classes more risk,these included acetohydroxy acid synthase inhibitors photosystem-II inhibitors. Synthetic auxins had but only two this class (dicamba clopyralid) are registered Zealand. Other mode-of-action groups We recommend outreach farmers regarding weed-control strategies prevent high-risk from resistance. High-risk should monitored losses efficacy. Resistance surveys focus on these herbicides.