Insecticide resistance in redlegged earth mites in Western Australia

Western Australian farmers are urged to report cases of insecticide spray failures against redlegged earth mites to the Department of Agriculture and Food.

Twelve properties have tested positive for resistant mite populations in the past four years. Eleven properties are located in southern WA from north of Esperance to the Cranbrook-Green Range area and one property is in the Boyup Brook area.

Department entomologist Svetlana Micic said insecticide resistance was a concern, and potentially there were more properties with resistant mite populations.

"The main concern is that cross resistance to both synthetic pyrethroids and organophosphate chemical groups could occur,” she said.

"We encourage farmers and their agronomists to either send in mite samples for testing or alternatively we can come to farmers and collect mite samples for analysis.”

Ms Micic said WA grain growers were in an enviable position of having access to affordable insecticides which currently provided excellent control against most pests.

The practice of adding an insecticide into a spray tank while a paddock is being sprayed with herbicides or other pesticides is convenient and cost effective, but could be over-used and inadvertently accelerate insecticide resistance,” she said.

To combat the further spread of resistant mites, Ms Micic said it was important for farmers to limit ‘insurance’ or prophylactic spraying unless there was a genuine risk of pest problems.

"While insurance sprays, especially on canola, are attractive from a timing and cost point of view, each additional spray increases the chance of insects developing resistance to insecticides increases,” Ms Micic said.

Ms Micic said it was also important to rotate chemicals rather than use the same chemicals on every paddock each year.

"Where practical, it is best to monitor for pests and spray only when levels are likely to lead to economic losses, she said.

"It is also worth considering the long term implications of unnecessary insurance sprays. Crop inspections to monitor pest levels may be time consuming but this approach will be more sustainable in the long term and provide environmental and health benefits to operators and consumers.”

Growers wishing to take advantage of the current free testing service for redlegged earth mite resistance should contact Svetlana Micic at the department’s Albany office on 9892 8444 or John Botha at South Perth on 9368 3755.