Cereal growers are being warned about the increased risk of a key disease, as they prepare to drill winter crops after one of the earliest harvests on record.

While early drilling can ease workload pressures, it also increases the risk of barley yellow dwarf virus (BYDV), warns Ruth Stanley, commercial manager of Sumitomo Chemical.

BYDV is the most serious virus affecting UK cereals, reducing tillering, stunting growth, and slashing yields by up to 60% in winter wheat and 50% in winter barley.

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It is spread by aphids, mainly the bird cherry-oat aphid and grain aphid. The second generation poses the greatest threat, as they colonise crops and rapidly spread infection.

Seed dressing

“The disease was largely controlled by the neonicotinoid seed dressing clothiadin (Deter) until December 2018, when its use was banned in cereals.

“With the loss of this chemistry and insecticide resistance developing in some pest species, along with warmer autumns and winters, it’s a widespread issue across the country,” explains Ruth.

The risk of BYDV increases when accumulated daily mean temperatures over 3C reach a T-Sum of 170, starting from crop emergence or after a pyrethroid spray.

Mild weather allows aphids to remain active well into autumn, boosting their reproduction and the likelihood of virus spread – especially in early-sown crops.

Monitoring aphids in autumn can be tricky. “The bird cherry-oat aphid often looks like specks of dirt and can remain active underground,” she explains.

Green shoots

Aphids are attracted to emerging green shoots, making newly drilled fields especially vulnerable if mild weather continues into October and November.

“In the past, crops drilled after mid-October rarely needed insecticide treatment,” says Ruth, as the seed treatments gave six weeks of protection. “But now, if it’s sunny and 15C, aphids will be flying – even if it feels cool in the shade.”

The only chemical treatment available to growers is foliar sprays with a pyrethroid like esfenvalerate applied once aphid thresholds are reached.

Tools such as the AHDB’s BYDV Decision support can help farmers better time their foliar sprays by tracking aphid activity.