Controlling Green peach aphid in canola - Elders Rural Services
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Controlling Green peach aphid in canola

With most cropping areas across Australia experiencing a wetter summer this year, and the forecast of further rains ahead, many canola growers are looking forward to another bumper crop in 2021.

While the weather outlook is positive, Corteva technical specialist Chris Brown says that growers should bear in mind that the wetter conditions are likely to create a ‘green bridge’ of weeds that harbour insect pests such as green peach aphids (GPA). GPA will persist over-summer on a variety of hosts, including wild radish, turnips, mustard, volunteer canola and many other broadleaf weeds.

Green peach aphid is the most important vector of turnip yellows virus (TuYV) (96% transmission efficiency) but cabbage aphid can also transmit it (14% transmission efficiency), as can cowpea aphid. Certain strains of TuYV can infect pulse crops in southern Western Australia, New South Wales and South Australia, while other strains are canola specific.

Chris advises that “Canola is most susceptible to TuYV up to the rosette stage, and infections at this point can lead to significant yield losses. Infections after the rosette stage generally have less  economic impact but yield losses are likely up to approximately the mid-podding stage. Infection after mid-podding usually results in minimal yield loss, although oil quality can be affected.”

Compounding these issues is the increasing presence of insecticide resistance in many GPA populations. Ongoing GPA research by Cesar Australia is finding high levels of resistance to carbamates (e.g. pirimicarb) and pyrethroids across Australia. Resistance to organophosphates and neonicotinoids (e.g. imidacloprid) have also been observed in many populations.

Transform® WG insecticide containing Isoclast® active remains the most effective post emergent treatment for GPA. Growers are encouraged to integrate chemical controls with cultural and biological controls to help manage and prevent further resistance issues. Understanding how Transform works and adhering strictly to the resistance management strategy for Transform will help delay GPA resistance to this insecticide.

Best management practices for controlling GPA and TuYV include eliminating the green bridge in and around the target paddocks a minimum of 14 days before sowing. Where possible, sow into standing stubble as aphids tend to fly into crops when they see plants against the backdrop of exposed earth; they are more attracted to open rows of plants with bare earth visible between crop rows. Selecting hybrid varieties that achieve early crop establishment and canopy closure can also help reduce aphid pressure.

Where the risk of aphid pressure is high, a seed treatment can be considered. Neonicotinoid based seed treatments can provide adequate protection early however, duration of control is dependent on seasonal conditions. In years where germination is delayed due to a late break the activity of these treatments may be reduced. In such cases, seed treatments can fail to provide adequate control up to the critical rosette growth stage. Vigilant crop monitoring will determine if or when a foliar insecticide application is warranted.

Sensitivity shifts to Transform have recently been found in a small number of GPA populations in Western Australia, showing the potential for low-level resistance evolution to this active ingredient. For now, Transform remains an effective foliar-applied insecticide for GPA control in Australia.

A sustainable long-term strategy for the control of GPA needs to be considered to manage the resistance risk by integrating selective chemical controls with practical cultural and biological controls. Where monitoring indicates that chemical intervention is required, A soft, selective product such as Transform WG Insecticide will provide effective control of GPA while having low impact on beneficial insects leaving them free to help control later season pest outbreaks such as Diamondback moth. Like all insecticides, Transform WG should be used only at the recommended label rates and according to the labelled resistance management strategy. Ensure spray applications achieve good coverage by using correct nozzles, high water volumes and appropriate ground speeds. Correct application will help prolong the useful life of this very important GPA / TuYV control option.

Article written by Corteva for the Autumn 2021 edition of Seasons Magazine.

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