Western Australia: Fall armyworm insecticide resistance is becoming a concern

The damaging pest fall armyworm is pushing its way south in Western Australia and in a concerning trend for that state's agriculture sector samples have revealed some samples of the insect are resistant to popular insecticides.

Fall armyworm has spread as far south in WA as Carnavon after only being found in Australia in February in far north Queensland.

The first WA identification occurred in March near Kununurra.

Samples of fall armyworm have been collected by the WA Department of Primary Industries and Regional Development (DPIRD).

These samples involved fall armyworm larvae collected from parts of northern WA such as a maize field in Kununurra, and sorghum and Rhodes grass crops in Broome.

After screening by the NSW DPI it was found all of the larvae contained at least one of the mutations that passes on resistance to Group 1 insecticides, which includes both carbamate and organophosphate groups of products.

DPIRD applied entomologist and fall armyworm project manager Helen Spafford said there were significant amounts of resistance.

"Half of the larvae from Kununurra and 60 per cent from Broome were homozygous resistant for the same mutation," Dr Spafford said.

"While further testing is necessary, this demonstrates the presence of a gene for resistance in fall armyworm across two locations in the Kimberley region, and the potential for the mutations to be more widespread," she said.

Dr Spafford urged farmers to carefully monitor their insecticide use, especially Group 1 products to limit the spread of resistance.

"Growers are encouraged to judiciously select any pesticides to be used, and ensure insecticides are rotated to reduce selection pressure."

Dr Spafford said further genetic testing was being carried out in collaboration with NSW DPI on additional samples collected from throughout the Ord Valley to determine how widely distributed the resistance trait is, and validate preliminary research results.

DPIRD is also working with WA growers, and entomologists in the Northern Territory and Queensland, to understand fall armyworm and alternative ways to manage this threat to decrease reliance on pesticides as the primary management tool for fall armyworm.

The fall armyworm moth can damage a wide variety of crops and internationally is regarded as one of the major crop pests in many nations.

The larvae predominantly feed on crops and pastures from the Poaceae (grass) family, in particular maize, but also sorghum, forage grasses, turf grasses, cereals and rice.

However it is not limited to grass crops and can also feed on broadleaf crops such as cotton, peanuts, vegetables and some fruit crops.