Bluegreen aphids & oat aphids

Philip Stoddart (Landmark) reports finding aphid species around the central tablelands and central slopes of NSW. Aphids have been found in both irrigated and dry lucerne paddocks. In several cases, bluegreen aphids (Acyrthosiphon kondoi) were found in high numbers and required spraying. Phil says bluegreen aphids have been a problem over the last few years in Mudgee and surrounding districts.

The bluegreen aphid (BGA) is a large species, measuring up to 3 mm 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.

Agronomist, Peter Spencer (IK Caldwell), says oat aphids (Rhopalosiphum padi) have been found invading a variety of cereals in many parts of the Northern Country in Victoria and southern Riverina, NSW. Philip Hawker (Western Ag Supplies) has also reported oat aphids in the Western district around Derrinallum, Victoria. Thus far, numbers are low, but will need to be monitored closely.

Oat aphids (sometimes called ‘cereal aphids’) can be found on all cereals including wheat, barley and oats. They vary in colour from olive-green to black and are characterised by a dark reddish patch on the tip of the abdomen. Adults are pear-shaped and have antennae which extend half the body length. 

Both BGA and oat 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. Importantly, BGA and oat aphids can spread barley yellow dwarf virus (BYDV). Transmission can occur with very few aphids and must occur early in the life of the plant to cause subsequent yield losses.

Entomologists are concerned that the overuse of inexpensive synthetic pyrethroid insecticides as ‘insurance sprays’ could be leading to the development of resistance in target and non-target species. Rather than spraying aphids to prevent the transmission of BYDV, it is best to implement sound agronomic practices. Click here to obtain more information on BYDV and management options.

Beneficial insects which attack aphids include parasitoids (tiny wasps) and predators (ladybirds, hover flies and lacewings). These are a very reliable form of control during the warmer days of spring and when low to moderate numbers of aphids are present. However, they have less impact on heavy infestations of aphids.