Evidence of green peach aphid (Myzus persicae, GPA) evolving resistance to sulfoxaflor (Transform™) has been confirmed for the first time in Australia, after a small number of aphid populations from Western Australia were shown to have reduced sensitivity to the insecticide.
Details of the detection
Five GPA populations collected from Esperance, WA were tested in the laboratory for sensitivity shifts to sulfoxaflor. A reduction in sensitivity to the insecticide was detected in four populations, and this was shown to persist after the colonies were maintained in the laboratory for several generations. This suggests that there is a genetic basis to these sensitivity shifts.
The discovery was made through collaborative research between cesar, CSIRO and the Western Australian Department of Primary Industries and Regional Development. The research was the result of a co-investment by GRDC and Corteva Agriscience™.
Why this detection is important
Sulfoxaflor is registered for use to control GPA in in broadacre canola crops. While GPA can inflict direct feeding damage when in high numbers, controlling the aphids is usually undertaken to prevent turnip yellows virus (TuYV) spread.
GPA has evolved varying degrees of resistance to other alternative registered chemistries in canola — sulfoxaflor is the only remaining active registered in canola available for use as a foliar spray that is still reliably effective.
In Australia, GPA is already known to have widespread resistance to four different chemical mode of action sub-groups – synthetic pyrethroids, organophosphates, carbamates, and neonicotinoids.
GPA has evolved high level resistance to synthetic pyrethroids (e.g. alpha-cypermethrin) and carbamates (e.g. pirimicarb) and results in complete insecticide ineffectiveness and control failures.
The evolution of resistance to organophosphates in GPA is more complicated. The mechanism behind the resistance is unusual because it can be ‘switched on’ in response to insecticide exposure. Using organophosphates against GPA is therefore risky; it could be effective in some instances but not others.
The resistance mechanism behind neonicotinoid resistance is also not straightforward. Only one form of neonicotinoid resistance, known as metabolic resistance, has been found in Australian GPA. This confers low-level resistance, which means growers will not experience complete control failures or a dramatic loss of efficacy of neonicotinoid seed treatments at this stage.
However, while neonicotinoids are still a reliable tool for GPA management, in canola they are restricted to use as a seed dressing, providing protection at the early stages of crop growth. As TuYV can impact canola yield if the infection occurs up until the rosette stage, effective foliar insecticides are needed in the toolbox for high-risk virus years.
In short, if resistance to sulfoxaflor spreads or evolves to a higher level, it would be problematic in seasons that favour spread of TuYV.
Management advice for growers and advisors
To limit the spread and curb the further evolution of resistance, it is critical that sulfoxaflor is used judiciously and as part of a sound insecticide resistance management strategy.
Given that there are limited alternative mode of action groups to rotate for GPA control, non-chemical approaches to management are a must, especially in TuYV low-risk years.
Green bridge control and deterring aphid landings during autumn by sowing into standing stubble are two preventive tactics that growers can use to reduce reliance on insecticides.
Conserving beneficial natural enemies of aphids such as spiders, predatory mites, ladybird beetles, lacewings, hoverflies and parasitoid wasps, through use of ‘soft’ chemistries will also help to reduce reliance on insecticides.
If considering spraying, ensure correct ID of the aphids, as cabbage aphid and turnip aphid which can colonise young canola but have not evolved insecticide resistance, can be mistaken for GPA.
If spraying with sulfoxaflor is warranted, adhere to the following guidelines:
- Ensure optimum coverage as the insecticide will not move downwards in the plant, only upwards. Use high water volumes and ensure correct nozzle type and ground speed.
- If GPA are colonising older leaves, spray canola before the canopy closure
- Do not cut label rates – lower rates may not provide control and will increase the selection pressure for resistance to sulfoxaflor.
Growers are asked to keep a close eye on establishing canola crops this year and to contact cesar (03 9349 4723) if aphids survive a Transform™ application.
More information: Paul Umina, 0405 464 259, firstname.lastname@example.org
Dr Rob Annetts (Corteva Agriscience™), Jenny Reidy-Crofts (CSIRO), Dr James Maino (cesar), Lisa Kirkland (cesar), Anthony van Rooyen (cesar), Emma Clarke (DPIRD), Alice Butler (DPIRD) and several agronomists for aphid collections.