Aphids

Agronomist, Allison Glover (Howard Martin & Co), reports finding aphids in canola around Berrigan in the Southern Riverina of NSW. Entomologist, Joanne Holloway (NSW DPI), has identified the species as the green peach aphid (Myzus persicae). Adult green peach aphids are 3mm in length, oval-shaped and may have wings. They vary in colour including yellow, green, orange and pink. The green peach aphid is polyphagous, attacking more than 110 plants worldwide.

Green peach aphids feed by sucking sap usually on the underside of the oldest leaves. Allison says some plants are stunted by large numbers of aphids and extensive feeding is causing distortion of young leaves. The outbreaks are fairly localized and chemical control has been employed in some paddocks.

The green peach aphid is a vector of several important plant diseases, including the beet western yellow luteovirus (BWYV). Studies of the relationship between virus infection and yield have shown that when aphids arrive early in the season, a combination of BWYV and green peach aphids can cause yield losses of up to 50% in canola.

Agronomist, Craig Sharam (Elders), has reported cowpea aphid (Aphis craccivora) on canola crops northwest of Albury, NSW. The aphids are attacking crops in a wide area, although the damage to date has been fairly minimal. Agronomist, Julian Mineham (Landmark), has also observed cowpea aphid in brassica crops in the Southern Tablelands of NSW.

The cowpea aphid is easily distinguished from other crop aphids; the 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.

Researcher, John Roberts (cesar), has observed large numbers of bluegreen aphid (Acyrthosiphon kondoi) within irrigated and dry lucerne crops in parts of the Northern Country, Victoria. The damage reported at this stage is not too bad, although the high numbers suggest monitoring from now and throughout spring is needed.

The bluegreen aphid is a large species, measuring up to 3mm long as adults. Both the winged and wingless forms are a matt bluish-green in colour. This species prefers to feed on legumes and is a common pest of medic and sub-clover pastures.

Aphids suck sap, causing yellowing and stunting of plants. A large amount of sugary solution (honeydew) is secreted by aphids when numbers are high. This can lead to black sooty mould which can reduce plant growth.

It is believed that the overuse of synthetic pyrethroids is leading to the development of resistance in target and non-target species. Rather than spraying aphids to prevent the transmission of viruses, it is best to implement sound agronomic practices. Beneficial insects which attack aphids include parasitoids (tiny wasps) and predators (ladybirds, hover flies and lacewings). Click here for further information on aphid management in canola.