Turnip aphids

Researcher, Aston Arthur (University of Melbourne), has reported low numbers of turnip aphids (Lipaphis erysimi) in an emerging canola crop, near Shepparton, in the Northern Country district of Victoria. Aston said the aphids were found colonising seedlings that varied from cotyledon to the 2-leaf stage. The crop was sown with untreated seed and has not received any early-season insecticide applications. Agronomist, Patrick Connell (PC Agronomy), has found turnip aphids in a 400ha canola crop near Barellan, in the Riverina district of New South Wales. Patrick said about 12ha of the crop has been extensively damaged, with distorted plants and complete plant death in some cases. In addition to aphids, this damage could be due to other pests that have also been found.

Turnip aphids are one of several aphid species commonly found attacking canola and other Brassicaceous crops in southern Australia. Adults are up to 3 mm long, olive to greyish green in colour and have dark bands on the abdomen. Winged adults have dusky veins. They suck sap and can reduce crop yields when numbers are high. Patrick said the aphids were found living in the crown of canola plants, enclosed inside the youngest leaves. They appeared most prevalent on plants within the worst affected parts of the paddock, which could also be affected by a virus. Turnip aphids are known to transmit several plant viruses that can contribute to yield losses, including beet western yellows virus, cauliflower mosaic virus and turnip mosaic virus.

If more than 20% of canola plants are infested with aphids, WA trials indicate control should be considered. When determining economic thresholds for aphids, it is critical to consider several factors before making a decision. Most importantly, the current growing conditions and moisture availability should be assessed. Crops that are not moisture stressed have a greater ability to compensate for aphid damage and will generally be able to tolerate far higher infestations than moisture stressed plants before a yield loss occurs. Thresholds for managing aphids to prevent the incursion of aphid-vectored virus will be much lower than any threshold to prevent yield loss via direct feeding.