Is glyphosate-resistant ryegrass resistant to paraquat?
Sequestration of herbicide into vacuoles is considered to be the main mechanism of resistance to both glyphosate and paraquat worldwide. In New Zealand, the first case of glyphosate resistance was found in ryegrass (Lolium) species, and the restricted herbicide translocation was found to be the main mechanism of resistance in the studied populations, presumably through sequestration. Overseas researchers hypothesised that the mechanism responsible for glyphosate resistance could also cause resistance to paraquat. We examined this hypothesis by comparing a known glyphosate-resistant population of perennial ryegrass with a known susceptible population after spraying with different rates (25–800 g ai/ha) of paraquat. The glyphosate-resistant population responded similarly to the susceptible population at the different rates of paraquat application. This result suggests that the restricted glyphosate translocation mechanism does not necessarily lead to paraquat resistance. These results also suggest that paraquat could be useful for controlling ryegrass when glyphosate resistance has evolved and the application of paraquat is permitted.