Exceptionally high levels of BYDV showed up in cereal crops earlier this year and the wet weather this summer has helped to create a green bridge of cereal volunteers and grass-weeds which is now acting as a reservoir for BYDV vectors. This means that growers can expect significantly higher levels than normal of infection risk this autumn. A programmed approach will be needed with well-timed autumn applications of a persistent pyrethroid, even when an effective seed treatment is used, to prevent this yield-damaging virus getting into crops this autumn.Dr. David Stormonth, Technical Manager for Interfarm UK, explains that there are two distinct approaches to the prevention of BVDV, depending on whether the crop has received a seed treatment or not. “The first approach is for cereals that haven’t had an insecticide seed treatment - this is most winter barley and around half of winter wheat crops sown. Autumn-sown crops with no insecticide seed treatment are at high risk from aphids causing BYDV infections from emergence onwards and will need treatment sooner rather than later with an effective pyrethroid.”He explains that temperature is the key indicator for spray timing. “Last autumn some foliar-applied aphicides were applied too late, hence the high incidence of Virus Yellows symptoms seen in the spring. It is a good idea to use the ADAS system of accumulated temperatures from crop emergence onwards when aphids colonise plants, in order to calculate when a foliar treatment is needed." "This temperature-based system can also be used in cereals that have received a seed treatment to calculate when the follow up foliar-applied pyrethroid spray should be timed. In this instance the temperature calculation starts six weeks after sowing, rather than from crop emergence. This is because an effective seed treatment such as clothianidin gives around 6 weeks protection from drilling, not from crop emergence, as some think. Aphids can fly onto newly emerged crops at temperatures above 11°C.”“To prevent the bird cherry aphid transmitting BYDV, an insecticide with rapid initial activity, good repellancy and long-lasting effects gives the necessary protection. Containing esfenvalerate, Sumi-Alpha offers the best persistence of all pyrethroids as well as having strong repellancy activity on aphids.""High risk situations include early drilled crops, crops grown after grass or grassy stubbles, crops in the South and West, crops in sheltered fields close to hedges and coastal areas and in fields with green bridges of weeds and volunteers. For medium risk situations, a dose rate of 125 mls/ha can give four weeks protection and for low risk BYDV situations 100 mls/ha would give similar persistence to cypermethrin. Growers should ask their distributor for the right dose rate to suit the individual farm and field situations,” explains Dr. Stormonth.