Glyphosate-resistant Lolium multiflorum and Lolium perenne populations from New Zealand are also resistant to glufosinate and amitrole

• Control of glyphosate-resistant ryegrass from New Zealand vineyards was studied.
• They were found to also be resistant to glufosinate and amitrole.
• No other multiple-resistance cases are known for these three herbicides.
• These are the three main herbicides used currently in New Zealand vineyards.

This study examined if glyphosate-resistant populations of Lolium multiflorum and Lolium perenne from some New Zealand vineyards were still susceptible to glufosinate and amitrole. The response of plants of one glyphosate-resistant population of L. multiflorum, population A, and two glyphosate-resistant L. perenne populations, populations J and O, to glufosinate and amitrole were evaluated and compared to susceptible populations in two dose–response experiments. Based on the herbicide rates giving 50% reduction in growth (GR50 values), populations A, J and O were 3.9, 4.5 and 3.8 times more resistant to glufosinate respectively, compared to the susceptible populations in a glufosinate dose–response experiment. Populations A, J and O were also found to be 2.9, 5.0 and 13.1 times more resistant to amitrole respectively, in an amitrole dose–response experiment. Very similar results were obtained when both dose–response experiments were repeated. This is the first confirmed report of weed species that have developed multiple-resistance to glyphosate, glufosinate and amitrole. These are the three main herbicides currently used for weed control in New Zealand vineyards.