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Cowpea aphids

Agronomist, Brett Aitkin (Landmark), reported cowpea aphids (Aphis craccivora) on seedling faba beans and vetch crops around Warracknabeal, in the Wimmera district of Victoria. Brett says most crops in the area contain some aphids, with a few paddocks under attack from very high numbers. In the worst affected crops, aphids are present on every plant and beginning to form colonies. The higher than usual numbers of aphids seen across many regions in the past few months could result in large, damaging populations that peak in late winter and early spring. Growers are encouraged to keep a close eye on all crops, particularly pulses and medics from late winter onwards.

Agronomist, Andrew Newall (NEWAG Consulting), reports that cowpea aphids are commonly being found in various legume crops in the Wimmera district of Victoria, particularly around Horsham. Crops treated with an insecticide seed dressing prior to sowing have few or no aphids. In contrast, Andrew says many of the untreated crops have aphids present and will be sprayed to reduce the risk of plant virus transmission, which was a significant problem in many legume crops in 2009.

The cowpea aphid is easily distinguished from other crop aphids. Adults are shiny black, up to 2 mm long and may have wings (‘alate’ forms). Nymphs are smaller and dull grey in colour. All stages have white and black coloured legs. Cowpea aphids favour legume hosts and are commonly found on faba beans, lentils, medic, lucerne, clover and lupins. Click here for images of cowpea aphids.

Cowpea aphids form dense colonies on individual plants, or in well-defined patches. Infestations start on the growing tips, and spread down the stem, causing leaf bunching and stem twisting. They also produce honeydew, which can lead to the formation of a black sooty mould and reduce plant growth. Cowpea aphids can cause severe damage in moisture stressed crops. Cowpea aphids are also known to be vectors of many important plant viruses.

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