Canola pest shows resistance

By Country News

Canola and pulse growers are urged to take care when making management decisions for green peach aphid in the wake of more populations of the pest showing resistance to neonicotinoid insecticides.

Resistance to neonicotinoids has been detected in a number of new populations collected from the major grain growing regions of Western Australia, Queensland, NSW and Victoria in research undertaken on behalf of the Grains Research and Development Corporation in 2017.

Green peach aphid, or GPA, is a widespread pest of canola and a range of pulse crops, transmitting viruses including turnip yellows virus, and causing damage by feeding when in high numbers.

It has confirmed resistance to four different chemical mode of action groups — synthetic pyrethroids, carbamates, organophosphates and neonicotinoids.

Paul Umina, director of Melbourne-based scientific research organisation cesar, said recent testing confirmed the importance of growers 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,’’ Dr Umina said.

‘‘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.

‘‘Where GPA is colonising crop margins in the early stages of population development, consider a border spray with an insecticide to prevent or delay the build-up of GPA and to retain beneficial insects.

‘‘Assess aphid and beneficial populations over successive checks to determine if chemical control is warranted and avoid an ‘insurance’ spray at all costs.

‘‘Unless the risk of feeding damage or virus transmission is deemed high, avoid using neonicotinoid seed treatments in the same paddock over consecutive years.

‘‘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 such as turnip yellows virus.’’

Dr Umina said the news was not all bad, as the type of resistance to neonicotinoids was ‘metabolic’ and not ‘target-site’, as the latter will lead to very high levels of resistance and loss of field efficacy.

‘‘We do not expect growers will experience complete control failures of neonicotinoid applications even when resistant GPA are present,’’ he said.

‘‘However, there is 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 neonicotinoids completely ineffective, and very likely confer cross-resistance to Transform.’’ Transform, a sulfoxaflor foliar insecticide, remains an effective means to control GPA in canola crops.

Dr Umina said dry conditions experienced early in the growing season in many parts of Australia had reduced the risk of GPA populations persisting from last season.

‘‘However, it is important that growers continue monitoring paddocks for GPA and be on the lookout for any incidences of spray failures that might indicate the presence of resistance,’’ he said.