Samantha Ward As the green peach aphid settles into some establishing canola crops, our reliance on chemical control methods is being put to the test.
Don’t let these tiny adversaries compromise your crop’s potential – stay informed about the latest developments in insecticide resistance and arm yourself with the most effective management strategies.
Know thy enemy: tips for identifying green peach aphid
Correct aphid identification is crucial for effective management. Among the three aphids that target brassica plants (turnip aphid, cabbage aphid, and green peach aphid), green peach aphid is arguably the most damaging early in the season and presents specific control challenges.
Despite their name, green peach aphid can also be pale yellow, orange, or pink. To identify them accurately, look beyond colour and focus on physical traits. Notice their slender, elongated antennae that are longer than their body and their “exhaust pipes” or siphuncli that reach beyond their cauda (the tail-like structure at the end of their abdomen).
If you can’t get a close-up view of the aphid, behaviour can be a giveaway too. Dense aphid colonies on the upper leaves of the plant during spring? You’re likely dealing with turnip or cabbage aphid. But if it’s winter and you find scattered aphids on the underside of lower leaves, enjoying their personal space, chances are that it’s the green peach aphid.
Seasonal abundance and crop impacts
Green peach aphid populations peak twice in the season: in early spring and in autumn. From March through to June they will migrate into newly sown winter crops from any green bridges present, meaning we’re in the risk season now. During this pre-establishment crop phase, characterised by vulnerable seedlings and slow initial growth, green peach aphid feeding is at its most damaging. Heavier infestations can result in stunted growth, leaf curling, and even seedling death.
But the challenges posed by green peach aphids go beyond direct feeding damage. They also act as a vector for more than 100 plant viruses, including the turnip yellows virus, which can reduce crop yields anywhere from 10% to 80%.
The changing landscape of insecticide resistance
Understanding the green peach aphid’s resistance and sensitivity to different chemicals is vital for supporting management strategies.
Currently, there is high-level resistance to synthetic pyrethroids and carbamates widespread across Australia, rendering field rates totally ineffective against resistant populations.
Additionally, there is widespread low-level resistance to organophosphates and neonicotinoids. This mechanism allows resistant individuals to detoxify these chemicals at a faster rate than their susceptible counterparts, meaning there is still an inherent risk of control failure.
More recently, shifts in susceptibility to sulfoxaflor and spirotetramet in green peach aphid, initially observed in Western Australia, have been detected spreading beyond its original boundaries. These chemicals remain effective for now, however cautious and strategic use is essential to prevent further sensitivity shifts and preserve their efficacy.
Given the ability of green peach aphid to evolve resistance to new chemistries, a recent study conducted by Aston Arthur and our team at Cesar Australia, supported by a GRDC investment, has provided essential sensitivity data for flonicamid and afidopyropen. The research team found no evidence indicating sensitivity shifts, as these insecticides possess unique modes of action that remain unaffected by the resistance mechanisms utilized by the green peach aphid. Further testing which has since been undertaken, also found no evidence for sensitivity shifts.
Another important point about flonicamid and afidopyropen is that unlike their broad-spectrum counterparts, they target aphids while minimising harm to beneficial insects, making them valuable additions to integrated pest management programs or pesticide rotations.
Management strategies: protecting crops, preserving chemistries
Insecticides are an important tool in a grower’s toolbox, but their judicious and strategic application is paramount. Before reaching for the sprayer or opting for seed treatments, it is always recommended to assess the seasonal and regional aphid infestation and TuYV risk.
In seasons with lower risk, cultural control methods, such as green bridge management and sowing into stubble, can help to manage both TuYV and green peach aphid. These strategies reduce aphid host plants and TuYV reservoirs between growing seasons and reduce aphid migration into fields.
Insecticides should be viewed as a last line of defence, reserved for high-risk situations where alternative measures have proven insufficient. When warranted, rotate insecticides with different modes of action to mitigate resistance risks.
When using insecticides, exercise caution to avoid jeopardising the beneficial insects that contribute to biological control. Routine spraying of insecticides, particularly those with broad-spectrum activity, harms the very allies that support long term pest management. Establishing a thriving population of beneficial insects at this time of year may be difficult, but supporting beneficials is an investment in the future, securing their presence (and services!) for the seasons to come.
Resilient Pests, Resilient Solutions
Navigating the challenges posed by green peach aphid requires a multi-faceted approach that combines accurate identification, awareness of insecticide resistance, and the implementation of integrated pest management strategies. By balancing the use of chemical control practices and considering the broader context of our management strategies, we can both protect our crops and safeguard the longevity of these vital chemistries.
Resources
When in doubt, always consult the Best Management Practice Guide and the Green Peach Aphid Resistance Management Strategy.
Support your beneficial insects by utilising the Beneficials Chemical Toxicity Table.
Acknowledgements
This research was conducted by Cesar Australian scientists Aston L. Arthur, Samantha Ward, Lisa Kirkland, Evatt Chirgwin, Anthony van Rooyen, Paul A. Umina. Additional thanks to Alex Slavenko for producing the resistance maps. This research was undertaken as part of a Grains Research and Development Corporation investment, ‘Insecticide resistance in the green peach aphid: national surveillance, preparedness and implications for virus management (CES2001-001RTX)’. This investment is led by Cesar Australia in collaboration with CSIRO and the WA Department of Primary Industries and Regional Development.
