Widespread infestations of green peach aphids (GPA) (Myzus persicae) during autumn and winter have contributed to an outbreak of beet western yellow virus (BWYV) in southern Australia. Canola crops across the lower and mid north regions of South Australia, western Victoria and some parts of NSW have been severely affected by the virus.
In many cases, growers have been unable to achieve adequate control of GPA populations due to the prevalence of resistance of GPA to insecticides. High levels of resistance to carbamates (e.g. pirimicarb) and pyrethroids are now widespread across Australia. Moderate levels of resistance to organophosphates have been observed in many populations, and there is evidence that resistance to neonicotinoids (e.g. imidacloprid) is evolving. cesar is currently screening GPA populations for resistance using DNA diagnostic tools; these results are being used to assist growers with recommendations for spraying both pulse and canola crops.
It is important to only use insecticides registered for the crop and situation, to comply with the label directions for the application method, to not exceed application or frequency rates, and to follow all withholding periods. Take advantage of the GPA resistance maps to determine the most effective control method for your region.
The decision to spray GPA should consider the proximity and impact on local beehives. We recommend providing beekeepers with sufficient advanced notice so that bees can be withdrawn if necessary. Do not spray when bees are foraging.
Follow the link below to see a resistance map for your region:
For oganophosphate insecticides, please note:
The amplified carboxyl-esterase mechanism leads to organophosphate resistance in the green peach aphid. This mechanism is unusual because it is regulated by DNA methylation, and can be ‘switched on’ in response to pesticide exposure. As a result, aphid populations can quickly adapt to survive organophosphates, even though they may have recently been effective.
For aphid populations found to have resistance through our DNA testing, the likely field efficacy of organophosphates is uncertain. Some control may still be achieved, particularly if using high rates. However, the use of organophosphates is risky and may not be effective (particularly if the population has been exposed to insecticides already this season). It is advisable to spray a test strip within the paddock to determine field efficacy.
If you have any queries, please feel free to contact us:
Dr Siobhan de Little
Phone: (03) 9349 4723