Carbamate resistance detected in green peach aphids

Populations of green peach aphids (Myzus persicae) have been found to have resistance to pirimicarb, which belongs to the carbamate group of insecticides. Resistant populations were detected from two locations, near Kojonup and Moora, in Western Australia. These properties are over 350 km apart. These are the first recorded cases of green peach aphid resistance to pirimicarb in Australia, and were discovered after control difficulties were experienced using high rates of pirimicarb to control aphids attacking canola crops. Peter Mangano (Western Australian Department of Agriculture) says there are several farmers that have reported control failures using pirimicarb this season, indicating resistance in green peach aphids could already be more widespread than first thought.

Green peach aphids have previously developed resistance to the organophosphate and synthetic pyrethroid classes of insecticides. The confirmation of resistance to pirimicarb in Australian populations is a blow to pulse and oilseed growers in particular, because this chemical has until now been seen as a fall-back for aphid populations resistant to other chemical groups. Pirimicarb is also an IPM-compatible product as it is aphid specific and less harmful to other invertebrates when applied to crops.

It is not clear at this stage whether eastern Australian populations of green peach aphids are resistant to pirimicarb. The risk of spread outside Western Australia is potentially higher than for many other aphid species because of the association of green peach aphids with plants in the gardening and horticultural industries.

Entomologist, Dr Owain Edwards (CSIRO), who confirmed the presence of pirimicarb resistance, is hopeful it may still be possible to control green peach aphid populations with currently available chemicals. Growers should keep an eye out for any control difficulties that arise when applying chemicals as per label instructions. It is important to rotate insecticide classes to help prevent resistance from developing further.

In recent years, the increased usage and reliance on low cost insecticides has accelerated the selection pressure placed on pest populations. To reduce the risk of problems developing in the future, the use of ‘insurance sprays’ should be avoided. Only apply insecticides after careful monitoring and correct identification of pest species. Although green peach aphids can spread many important plant viruses, direct feeding damage requires large populations before economic losses are encountered.