Canola growers are encouraged to monitor for the green peach aphid (Myzus persicae) in emerging crops through May and June.
The green peach aphid is a widespread pest in Australia and feeds on several types of broadacre, broadleaf pasture and horticultural crops.
Aphids are small, soft-bodied insects and have needle-like mouthparts used to pierce plants and suck sap, which can cause wilting and distortion, and in severe cases, death of plants.
However, unless numbers are very high, economic loss from direct feeding by green peach aphid alone on canola is uncommon.
Green peach aphid is more problematic as a vector of some plant viruses while feeding, particularly the Turnip yellows virus (formerly known as Beet western yellows virus) in canola.
Early infection of canola plants by Turnip yellows virus can lead to considerable yield loss and a reduction in oil quality.
Infected canola plants are often pale and stunted with leaves that may turn yellow to purple and thicken, although plants do not always display symptoms.
Autumn and early winter months are key monitoring periods for the green peach aphid in canola, as plants are at higher risk of yield loss from Turnip yellows virus if they are infected up until the rosette stage of crop development.
Due to insecticide resistance issues, correct identification of green peach aphid is important.
Adult aphids can be wingless or winged, however identification should be undertaken using wingless aphids as it is much easier.
Adult wingless green peach aphid are oval-shaped and grow to around 3 mm.
They can vary in colour from shiny green and pale yellow to orange or pink.
Green peach aphid can be mistaken for other aphids that feed on canola, the cabbage aphid (Brevicoryne brassicae) and the turnip aphid (Lipaphis pseudobrassicae).
While turnip aphid and cabbage aphid can also transmit Turnip Yellow Virus, they do not transmit it as efficiently as the green peach aphid.
The different aphid species also tend to cause greatest damage at different stages of crop development.
While green peach aphid is of highest threat to canola during establishment, the cabbage aphid and turnip aphid tend to be a problem during flowering.
Furthermore, green peach aphid populations in Australia have shown to carry resistance to key chemical actives including carbamates, synthetic pyrethroids, organophosphates and neonicotinoids.
The application of chemical control based on an incorrect identification can lead to control failures and additional expense for growers.
Differences in general appearance can provide clues to distinguishing between the different aphids.
Turnip aphid tend to be a dull olive-green colour and have the appearance of dark ribbed bars across their bodies.
Cabbage aphid are bluey grey, and often have dark blotches on their back and are covered in a layer of white powder.
Green peach aphid meanwhile often looks comparatively glossy or shiny in appearance.
Variations in appearance within a species mean high-level characteristics can be misleading for identification purposes.
A more definitive identification of the green peach aphid can be achieved through examination of the aphid's tubercules under a microscope or with macro lens on a smart phone.
The tubercules are head protuberance found between the aphid's antennae.
In green peach aphid, the tubercules converge inwards and have the appearance of mini horns, while the tubercules of both turnip aphid and cabbage aphid are flatter and less apparent.
A second identifying characteristic of the green peach aphid visible on a microscopic level is the length of the siphuncles.
Siphuncles look like exhaust pipes sticking out from the abdomen either side of the aphid's 'tail' (or more accurately, cauda).
Comparative to the short and stubbier siphuncles of the cabbage aphid and turnip aphid, the green peach aphid's siphuncles are longer and extend beyond the tail.
About the author: Francesca Noakes is a cesar Australia extension scientist.
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