Paraquat resistant ryegrass story more problematic than first thought!
Just received the official Quick-test® results on the paraquat resistant ryegrass from the southern WA vineyard and low and behold, we also have moderate glyphosate resistance.
The virtual loss of the two main knockdown herbicide modes of action begs the question about longer term weed management in all vineyards. The owners have recently used a robust rate of Fusilade® to kill the ryegrass. I have suggested however that while this solves a short term problem Group A herbicides should not be used by themselves in the longer term.
This situation is an excellent example of how rotating herbicide modes of action only delays the development of resistance while creating multiple resistance in the longer term.
What must be used is a series of tactics (herbicide and mechanical) within a season that ensures that potentially resistance survivors of the previous tactic are prevented from setting seed. This is the ONLY way you manage herbicide resistance. Ensure you always use the higher end of the herbicide label rate with the best possible application methods and under the best possible conditions.