BYDV Risk – South East Farmer – Neil Watson

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neil watsonAccording to Neil Watson, technical support manager for Hutchinsons, this autumn many farmers have been forced into drilling wheat and barley later because of the wet soil conditions.

“Ironically this is a good cultural method of reducing BYDV in your crop. However with recent milder autumns, we are seeing aphid flights extending later in the year. BYDV is a damaging virus affecting wheat and barley mainly in the warmer south and transmitted by two main aphid species (grain aphid, bird cherry aphid) in October and early November. Early infections kill patches of plants resulting in yield losses of up to 30% in wheat and up to 70% in barley. Symptoms of leaf yellowing and stunting are seen in the spring by which time there is nothing you can do about it."

“It has become a challenge to control BYDV as we no longer have seed dressings that used to give up to six weeks protection. We have to rely upon cultural control or pyrethroid insecticides. The risk of BYDV is dictated by the season and the level of aphids carrying viruses. This year infectivity in aphids is very high at 20-30% on average for aphids tested in the last few weeks. Some agronomists use the TSum of 170°C (accumulated daily air temperature) to determine spray timing from crop emergence. This is when the second generation aphids spread viruses within the crop from initial infections. I would not necessarily rely on this solely if there is a major flight on late emerging wheat. The smaller the plant, the greater the impact of the virus."

"Another way of minimising risk is to destroy any green bridges where aphids pass from one crop to another. Prophylactic spraying of pyrethroids will increase resistance and also, because of their broad spectrum nature, they will kill beneficial insects. We need to move away from spraying pyrethroids every year and use more cultural methods of reducing BYDV. In future a greater reliance is likely to be placed on tolerant varieties. We already have a tolerant barley variety and in 2020 there is a tolerant wheat variety being developed. If the other growing characteristics of these varieties are acceptable, they may be a useful tool, but they still need managing," says Neil.