Five years of surveys for herbicide resistant weeds

<p>Prior to the herbicide resistance surveys, 14 weed species were reported to be herbicide resistant. The arable and viticultural industries have high agrochemical usage and are believed to be at a high risk for herbicide resistant weeds.</p><p>Arable farms from Canterbury, Otago, Southland, Hawkes Bay and Wairarapa; maize farms from Bay of Plenty, Waikato, Hawkes Bay and Wairarapa and vineyards from Marlborough, Canterbury, Gisborne and Hawkes Bay were surveyed for weeds from 2019-2023. Seed from weeds were collected and tested with a range of herbicides.</p><p>Widespread resistance was observed for weeds already known to be resistant: ryegrass in arable farms (29% of arable farms) to group 1 and 2 herbicides, ryegrass in vineyards (40%) to glyphosate and fathen in maize (31%) to atrazine. Wild oats were observed to be resistant to group 1 and 2 herbicides in arable farms. Willow weed, poa and chickweed were resistant to group 2 herbicides in Southland arable farms. Summer grass appears to be an emerging resistant weed in Waikato maize.</p><p>Several weeds were observed to be resistant for the first time in arable farms in New Zealand: sow thistles to group 2 herbicides, prairie grass to pyroxsulam and lesser canary grass to group 1 and 2 herbicides. Arable farms in the North Island had fewer resistant weed species and a lower proportion of farms with any resistant weeds (15%), than those in the South Island (49%), and vineyards in the North Island also had a lower proportion of resistant vineyards (10%), than those in the South Island (50%). Herbicide resistance was more prevalent in Waikato maize than those of other North Island regions.</p><p>After five years of surveys, the number of resistant weed species recorded is now 21.</p>