Cowpea aphids

Surprisingly large infestations of cowpea aphids have been recorded in the Victorian Mallee, perhaps a sign of issues arising from summer rains and the ‘green bridge’.

 

Where have they been reported?

Surprisingly large infestations of cowpea aphid have been recorded on a young vetch crop near Robinvale in the Victorian Mallee. They consisted of a mixed population of adults and nymphs and were in colonies of 20-30 aphids on approximately one in ten plants. Although the crop was not showing any immediate signs of feeding damage, the population continued to increase due to the warm conditions. The heavy rain (50-100 mm) on April 10th appeared to have little impact on the aphids, which were subsequently sprayed (Thanks for the reports!*).

Cowpea aphid habits and behaviour

Cowpea aphids (Aphis craccivora) favour legume hosts and are commonly found on vetch, faba bean, lentils, medic, lucerne, clover and lupins. It is unusual to experience cowpea aphid problems in autumn. It is likely that the aphids arose from the significant ‘green bridge’, which was present across the Mallee as a result of heavy February and March rainfall. Mild weather conditions in winter allow further aphid development and spread, which can result in the establishment of many small colonies throughout a crop in late winter.

Cowpea aphids can transmit important plant viruses including cucumber mosaic virus, bean yellow mosaic virus, alfalfa mosaic virus and pea seed-borne mosaic virus.

Our advice

Although cowpea aphids are most prominent in spring, they are often active during autumn and will persist through winter. We suggest regular monitoring of vulnerable crops in regions where there may have been an early build up. This is particularly important later in the season during bud formation to late flowering. Aphid numbers fluctuate greatly with weather conditions and are difficult to predict.

Control options

Organophosphates are registered against cowpea aphids. A border spray in autumn/early winter, when aphids begin to move into crops, may provide sufficient control without the need to spray the entire paddock.

Description

The cowpea aphid is easily distinguished from other crop aphids. Adults are shiny black and nymphs are dull grey in colour. All stages have white and black coloured legs. Winged adults move into crops where they reproduce and colonise on the growing tips of host plants.

 

* Source of field reports of cowpea aphids

Andrew McMahen - Agronomist, Landmark (Victorian Mallee)