Barley yellow dwarf virus
Barley yellow dwarf virus (BYDV) is widespread in high rainfall areas of Western Australia. It infects cereals and grasses, but grasses (pasture and wild) are the main reservoirs. The virus survives between growing seasons in grasses which persist through the summer. Infection is spread from the grass reservoirs to oats and other cereals through the migration of cereal and grass aphids. Because of the role of aphids in establishing infection, BYDV is always more severe following wet summers when aphid survival and build-up has occurred.
Symptoms first appear three to five weeks after infection as yellow-brown or orange-brown, diffuse blotches near the leaf tip. The blotches enlarge and fuse until most of the leaf is affected and appears orange-brown. Later it changes to crimson-pink which is recognised easily in the field (Figure 9 and Figure 10).
Figure 9 Reddening of oat leaves from the tip down and striping of young leaves is caused by barley yellow dwarf virus
Figure 10 Barley yellow dwarf virus infection is often seen on plants at the edges of the crop
Oats affected as seedlings may show additional symptoms of severe stunting, increased tillering and floret abortion. Infection after tillering causes a characteristic 'reddening' of later emerging leaves and tip-reddening and death of older leaves. The distribution of infection within the paddock is normally patchy but occasionally the whole crop may show symptoms.
Control
Some varieties of oats are tolerant of the virus, while others are highly susceptible (see Oats: choosing a variety).
Trial results indicate that spraying the crop in its early stages with synthetic pyrethroid to prevent aphid establishment can provide good protection and is feasible in high risk areas.