Australian canola farmers are urged to use integrated pest management practices after more populations of the green peach aphid (GPA) were found to have developed resistance to neonicotinoid pesticides.

Research commissioned by the Grains Research and Development Corp in 2017 discovered that a number of new GPA populations in the major grain growing regions of Western Australia, Queensland, New South Wales and Victoria exhibited neonicotinoid resistance, wrote Country News on 21 June.

GPA was a widespread canola pest that could transmit viruses, such as the turnips yellows virus that could reduce oilseed rape yield by up to 26%, and cause crop damage when feeding on the plants in high numbers.

The aphids were confirmed to be resistant to four different chemical mode of action groups, including synthetic pyrethroids, carbamates, organophosphates and neonicotinoids, according to Country News.

Paul Umina, director of research organisation Cesar, said the findings reaffirmed the importance of farmers using integrated pest management practices.

“Resistance to neonicotinoids in GPA is not new, but it is concerning that resistance has now spread to all of Australia’s major grain growing regions.

“Due to the high risk of further resistance developing, it is recommended that, wherever possible, growers assess the risk of damaging infestations or virus risks prior to making management decisions,” said Umina.

When GPA are colonising crop margins and population development is in early stages, Umina recommended border spraying an insecticide in order to prevent or delay further growth of the population and to retain beneficial insects.

Farmers should also assess aphid and beneficial insect population through successive checks to determine if chemical control was needed and to avoid “insurance spraying” at all costs.

Neonicotinoid seed treatments should also be avoided in the same paddocks over consecutive years unless there was a high risk of feeding damage or virus transmission.

“High risk situations for GPA are considered early-sown crops, paddocks containing brassica weeds and/or volunteer canola, and/or regions with a history of outbreaks of viruses,” Umina explained.

As a bit of good news, the type of neonicotinoid resistance discovered was metabolic and not target-site, which meant that it was less likely to lead to high levels of resistance and loss of field efficiency.

Umina said he did not expect farmers to experience complete control failures with neonicotinoids, but added that there was “no room for complacency”.

“Target-site resistance can develop in GPA as has happened overseas. It is important we do what we can to minimise the risk of target-site resistance to neonicotinoids as it would render them completely ineffective,” he said.

Target-site resistance could also make the aphids resistant to Transform, a sulfoxaflor foliar insecticide produced by Dow AgroScience, which remained an effective form of combating GPA.