Confirmation of glyphosate resistance in two species of ryegrass from New Zealand vineyards

Plants were obtained from two populations of Italian ryegrass (Lolium multiflorum) and three populations of perennial ryegrass (Lolium perenne) from different vineyards in Marlborough and Nelson that were suspected of being resistant to glyphosate following many consecutive applications of this herbicide over recent years Each population was multiplied by splitting out tillers and this was also done for plants taken from a population of each species from Manawatu pastures where they had not been exposed to glyphosate application A doseresponse experiment showed that four populations taken from the vineyards were about 10 times as resistant to glyphosate as those plants that had not been previously exposed to the herbicide The experiment was repeated and showed one perennial ryegrass population to have a 30fold level of resistance These are the first confirmed cases of glyphosate resistance within New Zealand