Colour - Yellowish to olive green with black legs.
Body - 1.4 to 2.4 mm long, soft bodied, sometimes with waxy dusting and dark bars on abdomen.
Legs - 6, black.
Wings - winged (4) and wingless.
Development rate is determined by temperature. Aphids multiply rapidly under warm, moist conditions from late winter to spring. This favourable weather for rapid aphid development generally coincides with flowering times of canola when it is most susceptible to yield loss. Over summer they persist in low numbers on alternative cruciferous species and weeds.
Outbreaks are favoured by mild winters and cool, mild springs. Late flowering canola crops are usually affected more than early flowering crops.
Habitats:Origin and History:
The Turnip Aphid characteristically forms dense clusters or colonies on the tips of their hosts. They infest cruciferous species especially canola. By their direct feeding on the growing tips they can greatly reduce seed set and subsequently yield. Cases whereby severe infestations of the turnip aphid on canola have resulted in losses of up to 80% have been recorded.
Management and Control:Demeton-s-methyl, Pirimicarb, Thiometon and Endosulfan are used for control.
Thresholds:On Canola, if aphids cover a 25 mm length of flowering stem on most plants and biocontrol agents (such as ladybirds, lacewings, hover fly larvae, wasps and fungi) are not active then it is usually worth spraying. (Hart et al 1995). In the medium to high rainfall zones of WA, Canola usually compensates for aphid damage with little loss of yield or oil content. Monitor from late winter to the end of flowering.
Others have used 20% of flowering stems with 20 aphids as a threshold at mid flowering or earlier.
Related Species:Similar Species:
See Significance: under the Description for Aphids for a key to distinguish different species that are common on canola.
References:WADA Farmnote "Aphids in canola".
Hart et al 1995.
Berlandier 1998 pers comm.
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