The control of insect-transmitted viruses of cereals

Barley yellow dwarf virus is the most widespread and damaging of insect-transmitted viruses of cereal crops in Britain but the losses it causes differ greatly in different parts of the country and from year to year. Isolates of the virus differ in virulence and not all are transmitted equally well by the several species of aphid vector. Crops in south and south western counties are worst affected because the mild winters enable vectors to overwinter on hosts of the virus infected with virulent isolates. Field studies of the occurrence of infective aphids in eastern counties have helped to show when insecticides should be applied, but the virus spread too little in the experiments for spraying to have large effects on yield. It is hoped that the virus incidence can eventually be predicted from knowledge of overwintering vectors and when and how many carry virus into the crops.