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Group J Herbicides under Resistance Pressure

At the recent GRDC updates Chris Preston from the University of Adelaide gave a talk on the latest information in herbicide and weed management.  The talk included the current concern for annual ryegrass resistance to Group J herbicides which include triallate and prosulfocarb. Over a decade ago trifluralin resistance was significantly increasing which led to the adoption of Boxer Gold®. Once ryegrass became resistant to trifluralin (group D) there was lots of pressure on Group J herbicides for pre-emergent use and resistance developed.

Annual ryegrass resistance to Group J herbicides has now occurred in SA, VIC and NSW and in all cases the plants are also resistant to trifluralin. Sometimes resistance levels can vary among sub-groups and products within herbicide groups, but in this case when resistance is found to a Group J herbicide it is the same across all products in the group.

In-crop herbicides for annual ryegrass control in cereal crops already have high levels of resistance so pre-emergent herbicides are a critical management option. If pre-emergent herbicide options from Group D and J become compromised it only leaves Group K e.g. pyroxasulfone (Sakura®) and propyzamide.

In an almost worst case scenario a population of annual ryegrass on the Eyre Peninsula has resistance to Group A, B, D and J and more concerning it also has reduced susceptibility to Group K.  Populations like this could threaten our ability to manage annual ryegrass with pre-emergent herbicides. The level of resistance is highlighted in table 1.

The best way to manage this situation is to mix and rotate pre-emergent herbicides.  By adding a mixing partner to Group J pre-emergent herbicides you will help extend the amount of time before herbicide resistance becomes an issue. Population size also has an effect on the speed in which herbicide resistance develops. By maintaining a very low annual ryegrass population and incorporating non-chemical options such as harvest weed seed control you will extend the life of valuable herbicides.


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