Managing green peach aphid in spring-sown canola

As the weather warms up, green peach aphid populations can flourish.

For newly sown or emerging spring-sown canola crops this means an increased risk of direct feeding damage and turnip yellows virus infection.

If you’re dealing with green peach aphid this spring, ensure you’re up to date with the latest resistance information and the best management practices.

Balmy conditions for aphid growth

Like all aphids, the development of green peach aphid, Myzus persicae, is regulated by climatic conditions, especially temperature.

Aphids develop and reproduce best within a certain temperature range depending on species. Higher temperatures within this range speed up generation times, supporting population growth.

For green peach aphid, daily temperatures of 20-25°C are optimal for survival and reproduction. This is why we often see an uptick in green peach aphid numbers during spring.

Usually, this isn’t a problem for autumn-sown canola that’s already maturing, which is unlikely to be impacted by direct feeding damage from green peach aphid or the effects of turnip yellows virus (TuYV) at later growth stages.

But as spring sowing of winter canola varieties becomes more common, green peach aphid can be a key pest of these crops at this time of year.

Green peach aphid in spring-sown canola

In autumn-sown canola, green peach aphid is typically more concerning as a carrier of TuYV rather than for direct feeding damage during establishment. Cooler winter temperatures slow aphid development and tends to keep their populations in check, minimising the impact from direct feeding damage on young plants.

However, with canola seedlings establishing in spring when conditions are ripe for optimal aphid growth, the risk of direct feeding damage is greater.

There is also the risk of TuYV transmission into spring-sown canola. This could impact these crops during vegetative growth and the following year when livestock are taken off the paddocks for grain production. Spring-sown canola paddocks can also become reservoirs of virus in the landscape around next year’s autumn-sown crops. This is particularly relevant for southern NSW where there was an outbreak of TuYV this year.

A large population of green peach aphid in an establishing forage brassica. Photo courtesy of Thomas Parker

Managing green peach aphid

Current insecticide resistance status

If you are considering chemical controls, it’s important to be aware that green peach aphid has evolved resistance to various insecticide groups.

High level resistance to synthetic pyrethroids* and carbamates (e.g. pirimicarb) is widespread among Australian populations of green peach aphid, meaning these insecticides can be completely ineffective for control. If considering using pirimicarb for green peach aphid control, we strongly encourage growers to do a test patch first. The efficacy of pirimicarb is greatest when applied between 20-30^oC.

Green peach aphid has also evolved low-level resistance to organophosphates* and neonicotinoids, in which resistant individuals detoxify these chemicals at a faster rate than their susceptible counterparts. This metabolic resistance to neonicotinoids shortens the effectiveness of insecticide seed treatments applied to canola, allowing green peach aphid to colonise crops sooner after emergence.

Some green peach aphid populations in Western Australia, Queensland, New South Wales, Victoria and South Australia also have low-level resistance to sulfoxaflor (Transform™). In situations where spray coverage may be compromised, it is advisable to use the high label rate of Transform™ (100 g/ha) when targeting green peach aphid in canola.

Spray considerations

There are no thresholds for managing aphid-vectored virus, though it takes relatively few green peach aphid individuals to transmit TuYV. In areas of elevated virus risk monitor aphid activity closely, particularly along field edges to detect movement in.

In areas where virus transmission is risk is low, unless there are very large numbers of aphids present, spraying is likely not justified. Beneficial insects are abundant during spring and can help keep aphids at bay.

Where insecticides are required to control green peach aphid, we recommend applying a single application of flonicamid (Mainman®), afidopyropen (Versys®) or sulfoxaflor (Transform®). If multiple sprays are needed, rotate between these products as part of a resistance management plan.

These insecticides are selective and do less harm to beneficial insects than broad-spectrum products, especially flonicamid and afidopyropen.

And remember, green peach aphid is only one of several insects that can flourish in spring-sown canola. Other pests include cabbage aphid, diamondback moth, cabbage centre grub, and cabbage white butterfly, all of which can be supressed by beneficial insects if left uninterrupted.

If spraying insecticides, ensure grazing withholding periods are observed.

Want more information?

The ‘Green Peach Aphid Best Management Practice Guide’ has just been updated to give you the latest strategies and insights for managing this pest effectively.

Whether you’re looking for identification tips, resistance management information, or management techniques, this guide has everything you need.

Download the updated guide today and equip yourself with the information needed to manage green peach aphid with confidence!