Barley Yellow Dwarf Virus: forward planning – July 2020

Barley yellow dwarf virus (BYDV) has been seen in several winter and spring cereals this season.

Aphids are slowly building up numbers on crops and volunteers. There is a risk of cereal aphids picking up BYDV from infected plants and spreading the virus to cereals being sown this autumn.

The loss of neonicotinoid seed treatments has impacted the management of BYDV in cereals. As a result, there is a reliance on the use of pyrethroid insecticides for the management of aphids and the transmission of BYDV into cereals. Grain aphids in Scotland have resistance to the pyrethroid aphicides. Consequently, reliance on a pyrethroid aphicide spray is a risk as grain aphids may not be adequately controlled, elevating the risk of BYDV.

The most effective way of managing the ‘green-bridge’ of aphids on volunteers and stubble is to kill off any aphid host plants before sowing. Ideally, stubble from the previous crop should be desiccated with a herbicide, ploughed in 7-10 days later and left for another 2 weeks before sowing the next crop. This will ensure that any aphid host plants will be dead and any aphids on them will have starved to death. Alternatively, stubble can be ploughed in and sowing delayed for 4 weeks to allow enough time for plants to die along with the aphids.

Both of these approaches will reduce the threat from walking aphids by killing off their host plants that could keep the aphids (and BYDV) ticking over. Aphids are quite resilient and can work their way up to the soil surface after ploughing, so killing off the plants is essential so that they won’t have anything to feed on underground. However, for aphids flying into the crop at crop emergence aphicide sprays are the only option.

A combined approach of tackling the ‘green-bridge’ for the walking aphids and using an aphicide to target the flying aphids is the only option available this autumn to reduce the risk of BYDV. Reducing the availability of BYDV reservoirs in cereals and volunteers/stubble, and in aphids overwintering on winter cereals will reduce the risk to spring cereals, where a pyrethroid aphicide spray at early crop emergence is again the only option currently available, and this may not take care of the grain aphid due to widespread resistance.

Because of the resistance issue in the grain aphid, try to avoid the use of pyrethroid aphicides on cereals for BYDV unless absolutely necessary – aphid colonies on the leaves in the autumn rather than individual aphids is the trigger for an aphicide treatment.