Key points
- Green peach aphids and blue-green aphids have developed resistance to various insecticides, complicating pest management efforts
- Using non-insecticidal control methods is critical to prolong the effectiveness of available chemical options
- Monitoring beneficial insects, rotating modes of action and following label instructions are important to manage evolving pest challenges
Young canola plants may be more susceptible to virus infections this season as green peach aphids evolve resistance to commonly used seed treatments
Insecticides are powerful tools, but green peach aphids and blue-green aphids are the latest pests to develop resistance to several active ingredients, posing new challenges for effective control.
Cesar Australia senior scientist Dr Evatt Chirgwin told the Crop Protection Forum 2024*, held last November, that green peach aphids (Myzus persicae) had developed resistance to at least six insecticide modes of action.
A canola plant showing the purple symptoms typical of turnip yellows virus. Photo: Lilia Jenkins
He said this was concerning because green peach aphids transmit the turnip yellows virus (formerly known as beet western yellows virus) to emerging canola crops.
Traditionally, insecticides such as carbamates (Group 1A, for example, pirimicarb), organophosphates (Group 1B), synthetic pyrethroids (Group 3A) and neonicotinoids (Group 4A, for instance, Gaucho®) have been relied on to manage green peach aphids.
However, in the past few years, the pest has evolved resistance to more of these insecticides, with resistant variants becoming increasingly prevalent.
Neonicotinoid resistance
Dr Chirgwin said that neonicotinoid resistance was now prevalent in green peach aphids. This presents a specific challenge for canola crops, as seed treatments are relied on to protect crops during their most vulnerable (emerging) stages from turnip yellows virus.
“In 2024, the Riverina, Southern Tablelands, South West Slopes and the Central West Slopes of NSW experienced a ‘huge influx’ of green peach aphids that spread the turnip yellows virus to emerging canola,” Dr Cirgwin said.
“Environmental conditions partly drove the influx. A mild autumn may have favoured aphid activity, and wetter conditions facilitated green bridges – host weeds and volunteer plants – that act as virus reservoirs and aid aphid migration.”
While seed treatments are commonly believed to provide five to 10 weeks of protection for emerging canola seedlings, Dr Chirgwin said research suggested this protective period could be reduced to less than two weeks for some aphid strains. As a result, many growers required foliar sprays to manage outbreaks of these pests.
“Given that neonicotinoid seed treatments may provide shorter protective periods than in previous years, we need to be more vigilant in 2025. It is important to check canola early for green peach aphids and virus symptoms and deploy a foliar spray if necessary.”
Carbamate resistance
Cesar Australia senior research scientist Dr Evatt Chirgwin discussed insecticide resistance in green peach aphids and blue-green aphids at the Crop Protection Forum 2024. Photo: LucyRC Photography
Dr Chirgwin said that green peach aphid resistance to carbamate insecticides was also an issue, with resistance levels varying significantly among aphid strains.
“For some strains, carbamate is essentially ineffective. Other strains exhibit low resistance, and carbamates will still provide good control when applied under optimal conditions.
“As such, if growers intend to use pirimicarb for green peach aphid control, we encourage applying it to a small test patch to assess its effectiveness before spraying the entire paddock.
“When applying pirimicarb, the optimum temperature for application is typically between 20oC and 30oC.”
He said control failures were more likely if crops infested with green peach aphids with low levels of carbamate resistance were treated with pirimicarb in cool conditions.
Other insecticides
Most green peach aphids examined by Cesar Australia researchers displayed low resistance to organophosphate insecticides.
In contrast, they showed high levels of resistance to synthetic pyrethroid insecticides, with these chemicals providing little to no control.
Keep an eye out for green peach aphids as canola crops emerge. Photo: Cesar Australia
Regarding the newer insecticide sulfoxaflor (Transform®), Dr Chirgwin said resistance in green peach aphids was low. “If used at label rates, you should see good efficacy.”
However, he said the judicious use of sulfoxaflor and other insecticides was key to prolonging the effective life of these management tools.
Cutting application rates leads to selection pressure, increasing the likelihood of green peach aphids evolving resistance.
“Avoid cutting rates if you apply sulfoxaflor, as this will increase the chance of green peach aphids developing resistance in the future,” he said.
“Given that we have already observed multiple cases of green peach aphids evolving low-level sulfoxaflor resistance, we might observe more significant resistance emerging if this chemical is not used judiciously.”
Spirotetramat resistance
Dr Chirgwin said that green peach aphids had evolved resistance to spirotetramat, the active ingredient in Movento® 240 SC Insecticide.
“While spirotetramat resistance has so far been detected only in a few Queensland locations, it is concerning that the first instance of green peach aphids evolving resistance to this chemical has occurred in this region.”
On a positive note, he said that no resistance to flonicamid (MainMan®) and afidopyropen (Versys®) had been detected in green peach aphids.
“We have run assays in the laboratory attempting to evolve resistance to these insecticides artificially, but we have been unsuccessful, which is encouraging.
“These are two of the most selective insecticides on the market for preserving beneficial species, according to the beneficials chemical toxicity table we developed for the grains industry. Their use can help support biocontrol efforts by enhancing the activity of predators and parasitoids against pests.”
Blue-green aphids
Heavy infestations of blue-green aphids can cause damage to pulses and pasture legumes by directly removing nutrients and spreading viruses such as cucumber mosaic virus, which can deform leaves and cause plants to wilt and become yellow. Photo: Cesar Australia
Blue-green aphids (Acyrthosiphon kondoi) are a pest of legumes, including chickpeas, lentils, lupins, lucerne and subclover.
Dr Chirgwin said that the first insecticide-resistant populations were found near Keith, South Australia, and Temora, NSW. “Blue-green aphids have evolved resistance to three classes of active ingredients: organophosphates, carbamates and synthetic pyrethroids.
“We have observed resistant populations spreading to the Eyre Peninsula and across Victoria. Although there are no cases reported in Queensland, resistant populations have been detected in Tamworth, indicating they are moving north, with detections in multiple crops.”
Eliminate weeds
Dr Chirgwin said that integrated pest management involved using non-insecticide options to delay resistance development and maintain the effectiveness of chemical tools.
“Eliminating the green bridge 14 days or more before sowing helps remove green peach aphids and the weeds along fencelines, which are often the source of viruses.
“Removing weeds destroys these virus reservoirs, and doing so 14 days before sowing is effective because it disrupts the aphid-virus life cycle at a key point before sowing. This reduces the likelihood of aphids transmitting viruses to the emerging crop.”
Standing stubble
He said another cultural control method involved sowing into standing stubble to reduce aphid flights. Aphids struggle to land on young canola crops sown into standing stubble.
“We encourage growers to check crops for damage and monitor for the natural enemies of aphids such as parasitoid wasps, ladybeetles, lacewings and hoverfly larvae.
“If aphid damage is evident and you plan to spray, we recommend downloading the beneficials chemical toxicity table. This resource outlines the impact of a range of insecticides on beneficial insects, helping you select products that are ‘softer’ on the natural enemies of the pests in your paddock, reducing the risk of harming these beneficials.
Supporting the natural predators in your paddock will decrease the chances of pests re-establishing at subsequent periods in the season and reduce the need for repeated insecticide applications.
*GRDC supported the Crop Protection Forum 2024 hosted by the Centre for Crop and Disease Management, the Australian Herbicide Resistance Initiative and Cesar Australia.
More information: Evatt Chirgwin, echirgwin@cesaraustralia.com
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