Cereal aphids

We have received additional reports of oat aphids building up to significant densities in cereal crops in the parts of northern Victoria and southern New South Wales. To date, reports have been received from agronomists in the Victorian Wimmera, Mallee and Northern Country Districts, and the Riverina and South West Slopes districts of New South Wales. In one crop southwest of Swan Hill, aphids were found in very high numbers (>100/tiller) throughout most of the crop, and as a result the paddock will now be sprayed. Low numbers of corn aphids were also identified in a sample containing mostly oat aphids, from a crop west of Cootamundra, in the South West Slopes district of New South Wales.

Oat aphids (Rhopalosiphum padi) are similar in appearance to corn aphids (Rhopalosiphum maidis), and both species are significant pests of cereal crops and grasses in southern Australia. The two species are sometimes referred to collectively as ‘cereal aphids’, however they can be distinguished in the field relatively easily. Corn aphids have an oblong shaped, light green to olive coloured body with two dark areas on the abdomen near the base of the cornicles. They have antennae, which extend about one-third the body length. Oat aphids are similar in colour but have a pear shaped body with a rusty red patch at the end of the abdomen, and have antennae about half their body length. Corn aphids tend to occur mostly on barley, whereas oat aphids are generally found on oats and wheat; but both species may attack all cereals. Both corn aphids and oat aphids can attack crops at any stage and heavy infestations can result in yield losses.

Both oat aphids and corn aphids are also vectors of barley yellow dwarf virus (BYDV), one of the most important diseases of cereals worldwide. BYDV can cause significant losses in cereal crops, particularly when transmission occurs to young plants. Effectively controlling summer weeds is a good way to prevent the build up of aphid numbers as it removes the ‘green-bridge’ between cropping seasons. Agronomist, Mick Duncan (Northern Agriculture), has reported finding a number of crops, particularly oats, infected with BYDV this season. Mick says plants are showing characteristic symptoms of BYDV, including yellowing or reddening of plant leaves.

Click here for images of corn aphids and here for images of oat aphids.