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Oat aphids

Agronomist, Michael Taylor (Elders), has recently observed aphids within a barley crop near Goolgowi, in the Riverina district of New South Wales. They have been identified as oat aphids (Rhopalosiphum padi). Michael reports the aphid numbers are relatively low, with no obvious feeding damage to the crop at present. Farm manager, Geoff McCallum, has also reported aphids in a newly sown lucerne crop near Parkes, in the Central West Slopes and Plains district of New South Wales. An agronomist has sent aphids from a wheat crop, near Muttama, in the Southern Tablelands of New South Wales. They have been identified as oat aphids, with a high proportion of aphid ‘mummies’ (see below) also found within the sample.

Agronomist, Rick Rundell-Gordon (Elders), says oat aphids are present in cereal crops throughout the Mallee district of Victoria. Although, the distribution of affected paddocks is patchy, Rick says that relatively high numbers can be found in many wheat and barley crops. The aphids do not appear to be causing any significant feeding damage, although many crops are suffering moisture stress, which can confound insect attack. Agronomist, Craig Drum (Elders), has also reported oat aphids in cereal crops in parts of the Wimmera, Victoria. Craig says spraying is not required at this stage, although the crops will be closely monitored.

Oat aphids (sometimes called ‘cereal aphids’ or ‘wheat 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. Oat aphids suck sap, causing yellowing and stunting of plants. They can also spread barley yellow dwarf virus.

Natural enemies are a reliable form of control during the warmer days of spring and when low to moderate numbers of aphids are present. Beneficial insects which attack aphids include parasitoids (tiny wasps) and predators (ladybirds, hover flies and lacewings). These natural enemies will be building up in crops along with aphids, and they can reduce or contain aphid populations to below threshold levels in many cases.

Rick reports that a number of aphid ‘mummies’ (up to 10% of the population) have been observed in many crops within the Mallee. This indicates the activity of parasitic wasps. Small female wasps will often insert an egg into an aphid and the developing larvae feed inside the aphid, eventually killing it. The new adult wasp emerges from the mummy by cutting a hole in the skin.

Click here for images of oat aphids and refer to PestFacts Issue No. 2 for further information.

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