13 January 1999
Yield reduction from BYDV


HERE in New Zealand we had a mild winter and aphid flights are early (before the usual weed spray and insecticide) and much spring sown barley has been struck with yellow dwarf virus. Typically, can you tell me what sort of yield reduction results from average BYDV attacks, and whether this would be offset by increased nitrogen use?


Jon Oakley, ADAS Bridgets


ITS difficult to give a definitive answer to this question as we cant control BYDV on spring barley with insecticides.

Hence we dont have yield responses to work from as with winter cereals, where a response range of 1-2.5 t/ha is normal with significant attacks.

With spring barley in the UK, nearly all the damage is done by alate (winged) aphid-vected BYDV giving a very dispersed and even distribution of virus compared to the typical patches in winter cereals.

From transmission studies we know that, depending on when the plant is infected, the yield loss drops from 100% at the one-leaf stage to zero at the start of stem-extension (GS 31). The worst cases are in late-sown cereals infected early after emergence, and I have known some total write-offs in such cases.

Earlier infections resulting in yield loss are likely to show as yellowing of more than one leaf. Later infection resulting in little yield loss can show as a yellow tipping of the flag leaf.

Some varieties of spring barley are more tolerant to certain strains of the virus, and we know of a gene (YD2) which is resistant to the PAV strain of BYDV and has been tried in the UK, but is not present in any currently grown varieties.

We dont have any evidence of nitrogen affecting loss, if levels were sub-optimal extra, it could help uninfected plants to compensate for damage if the infected plants were badly damaged and stunted.