Wild carrot (Daucus carota L.) is resistant to glyphosate in vineyards in Marlborough, New Zealand

Glyphosate is the most frequently used herbicide in vineyards. Ryegrass (Lolium spp.) has developed resistance to glyphosate in vineyards across New Zealand. Recently, two vineyards in Marlborough were suspected to have glyphosate-resistant wild carrot (Daucus carota L.). Seeds from those vineyards, and two others without suspected resistance, were collected and tested with recommended rates of glyphosate (720 g ai ha−1), glufosinate-ammonium (1500 g ai ha−1) and amitrole (4000 g ai ha−1). Glyphosate did not kill wild carrot plants from the suspected resistant vineyards but glufosinate-ammonium and amitrole were effective. Wild carrot seedlings from a putative-resistant population (Renwick) and susceptible population (Riverlands) were treated again with glyphosate in dose–response assays. The other two populations had insufficient seed or poor germination and were excluded. Dose–response assays revealed that wild carrot plants from one of these vineyards (Renwick) were 2.91–6.64 times less sensitive to glyphosate (LD50 versus GR50) than plants from a susceptible population (Riverlands). The Renwick population exhibited 91% survival at the recommended rate of glyphosate (compared to 13% survival for Riverlands). Frequent usage of glyphosate in vineyards has been selected for resistance in wild carrot. This is the first study to document glyphosate resistance in wild carrot globally.