Red alert sounded on mite resistance

RED-legged earth mite resistance to all known chemical control methods is just a matter of time in the eastern states, an expert has warned.

Red-legged earth mite. crop pest

RED-legged earth mite resistance to all known chemical control methods is just a matter of time in the eastern states, an expert has warned.

University of Melbourne entomologist Garry McDonald says only two groups of chemical foliants are effective against the mite, and resistance has been found to both in Western Australia.

Dr McDonald, who has been working with a team from Cesar to test for resistance in WA cropping areas, said they had identified two separate selection events, which meant the problems that were occurring in separate parts of the state were unrelated.

Garry McDonald

“These are not airborne insects,” he said. “Reports of resistance were spread over thousands of kilometres ... genetic studies indicate two — possibly more — unique situations that gave rise to resistance.

“What was alarming was the rate of which it (resistance) spread.”

Dr McDonald said resistance had not been found anywhere other than in Western Australia, but the likelihood of it occurring was high.

“For us (in the eastern states) it’s risky,” he said.

“My gut feeling is that it will appear. We’ll either select for it ourselves or it will appear in the form of eggs or gene flow coming from WA. I suspect it’s only a matter of time.”

Dr McDonald said farmers needed to be aware of the risk and manage accordingly by alternating between synthetic pyrethroids and organophosphates when spraying.

He suggested an alternative might be no chemicals.

Red-legged earth mites are generally active from autumn to late spring and feed on all crops and pastures, causing leaf damage in the early stages of development.

A resistance management strategy is expected to be released by the GRDC’s Grains Pest Advisory Committee before the winter cropping season begins this year.