AgroPages-Australia: Red legged earth mite insecticide resistance spreads east-Agricultural news

By Gregor Heard

Insecticide resistant red legged earth mite (RLEM) continues to push ever further east, with the first confirmed cases officially confirmed in Victoria.

Resistant RLEM have been found in WA for over a decade and were first detected in South Australia in 2016.

The Victorian discovery was the first time resistant RLEM has been found in that state.

The finding of resistance to two organophosphate (OP) based products in omethoate and malathion comes at the time of the year when RLEM are problematic, feeding off fledgling crops.

There was no resistance found to the synthetic pyrethroid group of products.

RLEM are a major pest of broadacre crops, particularly canola and other broadleaf crops.

The good news for Victorian growers is that the resistance is relatively weak, however experts have warned against complacency.

Entomologist Paul Umina, of scientific research organisation Cesar, said a best practice insect pest management (IPM) strategy was critical.

"While the level of resistance detected in Victoria is considered 'low-level', we can't stress enough the importance of having a resistance management strategy at the forefront of RLEM control in south-eastern Australia," Dr Umina said.

In WA there is widespread RLEM resistance to a range of products across chemical groups, while in SA resistance to both synthetic pyrethroids, including bifenthrin and alpha-cypermethrin, and organophosphates, including omethoate and chlorpyrifos, has been detected.

RLEM has a wide appetite, feeding on a range of plants including but not limited to canola, clover, faba beans and lupins.

Dr Umina said growers needed to judiciously manage the insecticide resources they had to ensure they had something in reserve when RLEM infestations were particularly bad.

"If higher levels of insecticide resistance were to evolve to multiple chemistries and across larger areas, RLEM would be far more difficult to control on vulnerable establishing crops than what it is today in south-eastern Australia," Dr Umina said.