Wild carrots are becoming resistant to glyphosate: The first case of glyphosate resistance in Daucus carota L. is from Marlborough vineyards

Glyphosate is the most frequently used herbicide in vineyards. Ryegrass (Lolium spp.) evolved resistance to it in 39% of surveyed vineyards across New Zealand. Seeds of wild carrot (Daucus carota L.) suspected of resistance were collected from two sites (near Renwick and Waihopai Valley) in Marlborough. Seed was also collected from two other vineyards (near Riverlands and Grovetown). Seeds were sown in trays and treated with 720 g. ai. ha^-1 glyphosate (the recommended rate for annual seedlings). The Riverlands population was susceptible to glyphosate and populations Renwick and Waihopai were resistant. Seed from Riverlands and Renwick populations (other populations had insufficient seed) were sown into pots for two dose-response assays, repeated in time, with seven replicates and eight rates. Biomass and survival were measured three weeks after treatment. To estimate the GR₅₀ and the LD₅₀ dose response curves were fitted using the ‘drc’ package in R, using a log-logistic model LL.4 for biomass and W1.2 for survival. GR50 values (g. ai. ha^-1 glyphosate) were: Riverlands = 80.0, Renwick = 531.4. LD50 values were: Riverlands = 373.9, Renwick = 1139.1. Renwick had resistance factors of 6.6× (ED₅₀) and 2.9× (LD₅₀) compared to the susceptible Riverlands population. Wild carrot is the next weed to have evolved glyphosate resistance in New Zealand; this species has not yet been reported as glyphosate resistant elsewhere worldwide.