Growers are being urged to stay alert for signs of insect activity as mild conditions and a lingering green bridge between crops increase the threat from pests.
Warm, dry weather through September and early October has prolonged aphid flights and encouraged multiple pest species to thrive in newly emerged cereals. Agronomists warn that without careful monitoring, early infection could hit yields hard next summer.
Conditions have been ideal for pests like bird cherry–oat aphid, grain aphid, gout fly and leafhoppers, says Will Foss, technical manager with agronomy group Hutchinsons. The message to growers is simple: don’t drop your guard, he adds.
Suction traps
Rothamsted Research suction traps saw a rise in bird cherry–oat aphids in September, with some grain aphids early in the month. Both are key vectors of barley yellow dwarf virus (BYDV), which can reduce yields by up to 60% in wheat and 50% in barley.
“Not all aphids will be carrying the virus,” says Mr Foss, “but the latest data indicates that on average 30% of aphids tested are viruliferous, although with large differences from site to site. This is higher than for the same period in 2024.”
Mr Foss recommends targeting aphids with a pyrethroid insecticide as soon as migration into crops is evident. “Early post-emergence herbicide applications can be an opportunity to add an insecticide for initial control,” he says. Subsequent spray requirements can be judged using digital tools such as the T-Sum 170 function in Hutchinsons’ Omnia system. This calculates the accumulated temperature units needed for two generations of aphid to develop after a first treatment.
During September, T-Sum 170 was reached in just two weeks for much of Great Britain, says Mr Foss. This shows how quickly populations can build and multiply under mild conditions, he adds.
Heightened threat
The same concern is echoed by RAGT technical manager Andrew Creasy, who says the unseasonably warm autumn created the perfect setup for BYDV outbreaks across the region.
Settled weather and abundant green cover from volunteer cereals have allowed aphids to remain active for much longer than usual, explains Mr Creasy. Although some growers held off drilling, most winter crops are now in the ground.
The Agriculture and Horticulture Development Board’s BYDV management tool, suggests many crops drilled in early October will hit the T-Sum threshold for a potential insecticide application by the third week of the month, says Mr Creasy. The Sustainable Farming Incentive (SFI) actions may limit options for some farmers. With more than 700,000ha in the CIPM4 action – ‘no use of insecticide on arable crops’ – participants must forgo chemical sprays to claim the £45/ha payment.
“For most growers, autumn drilling is now nearly complete,” says Mr Creasy. “Where BYDV is a concern, the key is to use the risk prediction tools and apply insecticides only when thresholds are reached. BYDV remains the most economically damaging virus of UK cereals. Long-term, the hope is that genetic resistance will become an increasingly important part of the solution. A high-yielding RAGT BYDV-resistant feed wheat is currently being considered for the AHDB Recommended List. If all goes to plan, it could be a game-changer.
Until then, monitoring crops remains important – although it isn’t always straightforwar. BYDV-infected plants show yellowing or reddening leaves, stunted growth and poor tillering – but by the time these symptoms appear, yield loss is locked in.
“Crop monitoring in the autumn is useful, but in practice it’s difficult,” says Ruth Stanley of Sumitomo Chemical. “Bird cherry-oat aphid is very hard to spot – often mistaken for specks of dirt at the plant base – and can even remain active below ground.” Until its withdrawal in 2018, the neonicotinoid seed dressing clothianidin (Deter) provided strong protection against early aphid attacks. Its loss, coupled with insecticide resistance and warmer autumns, has made control far more complex.
“Historically, crops drilled after mid-October rarely needed an insecticide because there were so few aphids present in early November. That’s not guaranteed anymore. If it’s 15°C in the sunshine, aphids will be flying – even if it feels cooler in the shade.”
Integrated management
The bright green contrast of emerging seedlings against bare soil makes newly drilled fields attractive to insects. If mild conditions persist through October and November, activity may continue well into winter.
Weed treatments can give around six weeks’ protection, but when sowing takes place early and the autumn stays warm, follow-up foliar sprays are often required. Once aphid thresholds are reached, a well-timed pyrethroid remains the most effective option.
Tools such as the AHDB’s BYDV Acronym Model help growers track aphid activity and determine when intervention is needed. Despite some resistance developing in certain populations, pyrethroids still form the backbone of control strategies.
Active ingredients
Mrs Stanley highlights the importance of choosing the right active ingredient. Not all pyrethroids are equal, she says. Esfenvalerate, from Sumitomo Chemical, is long-lasting, so less product is needed for a strong protective effect.
It also persists longer in the field than most other pyrethroids, explains Mrs Stanley. “While many degrade in alkaline soils, esfenvalerate remains active for up to 65 days, with rainfast protection lasting around three weeks.”
Growers face a difficult balance between protecting crops and meeting environmental commitments. IPM remains the cornerstone of responsible control – using cultural and biological methods first, then targeted insecticides when justified.
Regular field walking, forecasting tools, delayed drilling where feasible, and destruction of the green bridge all help to limit pest pressure. In high-risk situations, chemical protection may still be warranted to safeguard establishment and yield.
With the combination of mild conditions, earlier drilling and fewer chemical tools, this autumn really is a perfect storm for BYDV, says Mrs Stanley. Staying vigilant now will save a lot of heartache later, she adds.
Looking ahead
The long-term outlook depends on innovation – both in crop genetics and pest monitoring technology. BYDV-resistant varieties, combined with precision-ag tools that predict aphid movement and infection risk, will be increasingly important.
For now, growers are urged to walk fields frequently, record sightings and keep in touch with agronomists. The mild autumn may have been a boon for drilling, but also means pests are thriving.