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Pea aphids and bluegreen aphids

We have identified pea aphids (Acyrthosiphon pisum) for senior development specialist, Stewart Druce (Bayer CropScience). The aphids were found in a lucerne paddock near Dubbo, in the Central West Slopes and Plains district of New South Wales. Stewart says the number of aphids within the paddock was only moderate, and has since declined dramatically. The cold weather conditions recently experienced is likely to be the key factor behind this decrease in population size. Cold climatic conditions, particularly frosts, have been shown to significantly impact aphid survival. Stewart reported that other lucerne paddocks near Dunedoo, north-west of Dubbo, have also been found with aphid infestations.

In addition to pea aphids, we have received reports of bluegreen aphids (Acyrthosiphon kondoi) in a paddock of vetch near Rochester, in the Northern Country district of Victoria. Bluegreen aphids have also been found in lucerne near Wagga Wagga, in the South West slopes district of New South Wales. In both cases, only low numbers were observed and spraying is unlikely to be warranted.

The pea aphid is a large aphid (about 4 mm in length) that has distinctive dark knee joints and antennal segments. Pea aphids are a minor pest of some pulse crops, lucerne, vetch, clover and other leguminous grasses. Pea aphids feed on the upper leaves, stems and terminal buds of host plants. Heavy infestations can result in various types of damage to plants including deformed leaves, wilting and yellowing, stunted plant growth, leaf curling and leaf drop, and reduced dry matter production. Secretion of honeydew can cause secondary fungal growth, which inhibits photosynthesis and can decrease plant growth. Pea aphids can transmit several important plant viruses including cucumber mosaic virus, bean yellow mosaic virus, alfalfa mosaic virus and pea seed-borne mosaic virus.

Bluegreen aphids grow to about 3 mm long as adults. Both the winged and wingless forms are a matt bluish-green colour. Annual medics, lucerne, subterranean clover and lupins are susceptible to bluegreen aphids. In lucerne and medics, heavy infestations cause stunted growth, leaf curling and leaf drop. In subterranean clover, leaves wilt before turning brown and dying. Bluegreen aphids favour growing tips of medic and lucerne, while in clover they are widely dispersed under the canopy. 

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