More aphid reports

There have been further reports of aphids causing damage to various crops around Victoria. Agronomist, Doug Perryman (Bridgewater Farmware), reported cabbage aphids (Brevicoryne brassicae) in several canola crops around Bridgewater, in the Northern Country district of Victoria. Doug says numbers have built up very rapidly over the past fortnight, and some plants are now fully covered from top to bottom. Numbers are higher in dry-land crops compared with those that have been irrigated, adding further damage to the already moisture stressed plants. Because dry-land crops are close to windrowing chemical control is unlikely, however Doug says some of the irrigated crops may require chemical applications in order to protect crop yields.

Agronomist, Greg Toomey (Landmark), reports finding high numbers of cabbage aphids in many canola crops near Elmore, in the Northern Country district of Victoria. Greg says about two-thirds of crops in the area have required chemical control, and estimates yield losses could have been as high as 10-20% without spraying.

Cabbage aphids grow up to 3 mm in length and have a dull grey-green coloured body. Under favourable conditions, dense colonies form, which appear bluish-grey and are covered with a fine, whitish powder. Click here for images of cabbage aphids and refer to PestFacts Issue No. 7 for more information.

Green peach aphids (Myzus persicae) have been identified for research agronomist, James Sewell (PGG Wrightson Seeds), from newly sown forage brassica crops near Smeaton, in the North Central district of Victoria. Seedlings are only about 2 cm high and groups of 7-8 aphids can found on each leaf across the majority of affected paddocks. James says the aphids appear to be causing some damage although it is difficult to determine because the plants are also moisture stressed.

The green peach aphid is a pest of many crops, but particularly fond of crucifer vegetables, oilseeds and some pulses, such as lupins. Unlike cabbage aphids, which form dense clusters, green peach aphids are usually sparsely distributed within a crop, mainly on the underside of leaves. Some populations are resistant to insecticides and growers are urged to rotate their use of chemical groups to prevent resistance from developing further.

Adult green peach aphids have an oval shape body and may be pale yellow-green, orange or pink in colour. Winged adults have a dark patch on the abdomen. They are approximately 3 mm long. Click here for images of green peach aphids and here for further information on aphid management in canola crops.