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Aphids and BYDV

High levels of barley yellow dwarf virus (BYDV) have been reported by agronomist, Mick Duncan (Northern Agriculture), in many oat crops throughout the Northern Tablelands district of New South Wales. Affected plants are showing classic damage symptoms including a reddish-pink colour from the leaf tips down the length of the leaves, as well as stunted growth. BYDV is one of the most important diseases of cereals, and Mick says the current situation reflects the favorable weather conditions in the region last spring and summer. Good rainfall promoted the growth of grasses and volunteer cereals, and these plants act as a ‘green bridge’ between cropping seasons. They are alternative hosts for both BYDV and the aphid species that vector this virus. BYDV is most problematic when plants are infected early in the season and Mick says early infection appears to have occurred in several instances this year.

Growers should remain on the lookout for aphids and symptoms of viruses in their crops, and pay particular attention to areas of paddocks that had a significant green-bridge of plant material over summer. The most common aphid vectors of BYDV are the oat aphid (Rhopalosiphum padi) and the corn aphid (Rhopalosiphum maidis). The English grain aphid (Sitobion miscanthi) and the rose-grain aphid (Metopolophium dirhodum) are other known vectors but these are less common species.

Oat aphids are similar in appearance to corn aphids, and both species are significant pests of cereal crops and grasses in southern Australia. These 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.

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