Widespread reports of high aphid, gout fly and increasingly leafhoppers being spotted in cereal crops from emergence is putting immediate pressure on growers to consider insecticide use, even if they have selected the no insecticide option in Sustainable Farming Incentive schemes.

Many farms who have taken the payment will be loath to spray insecticides, but economically it could be the right decision, suggests Agrovista Rural Consultancy technical manager Lewis Butlin.

“SFI guidance states that where you have C/IPM4 in place, should you need to spray insecticides to prevent a financial loss, you should do so at the earliest opportunity.

“Given the high risk of barley yellow dwarf virus and other pests in many areas, growers should carefully weigh up the loss of the payment with the economic loss from not spraying,” he says.

The new AHDB BYDV model is helpful in assessing risk, Agrovista technical manager Mark Hemmant says.

“For example, the model predicts a 0.5 t/ha loss costing £90/ha from BYDV in a winter wheat crop drilled on 5 October surrounded by arable crops where no treatment is applied.

“That rises to a possible loss of £210/ha if the field is not exclusively surrounded by arable, which can increase risk. Earlier drilling or winter barley crops will also increase risk,” he says.

Where a decision is made to apply an insecticide, growers must notify the RPA within two months, ideally as soon as possible, so they can consider whether a reduction in payment is required, Lewis adds.

Rothamsted’s Insect Survey was catching increasing numbers of bird cherry oat aphids in the first week of October, with triple figure catches at most sites. Over 50% were winged aphids capable of colonising cereal plants, according to live trapping tests at Rothamsted, a much higher proportion than the 10 year mean of 12.9%, while the proportion carrying virus was nearly 40%, according to AHDB reporting.

“We wondered if the hot summer would make it more difficult for aphids to acquire virus with the lack of green material, but the testing suggests the opposite, so it all points to a much higher risk than normal,” Mark says.

“And with agronomists reporting that aphids are easy to find on cereal crops in many cases from crop emergence, there is an increased risk of primary infections of BYDV, which can cause plant loss,” Mark says.

“Remember both the new AHDB and traditional T-Sum models for timing aphicide sprays are designed to prevent secondary spread of aphids, so even if these models are not saying to spray yet, treating to prevent primary infections will be beneficial, especially on low seed rate crops such as hybrid rye or hybrid barley.”

It’s not just aphids where pressure has increased in the past month, according to Prof Tom Pope, professor of applied entomology at Harper Adams University.

“During the summer, there wasn’t particularly high insect pest pressure,” he notes. “But there has been an uptick in several pest species in September and early October.”

Cabbage stem flea beetle, for example, are present in high numbers, albeit maybe not as high as in some recent years, with a peak migration that appears to have been delayed. “Whether that is environmentally related with the hot summer pushing things back is not clear,” Tom admits. “But we have had a much more favourable period for insects in September with warmth and moisture driving population growth.”

Gout fly eggs are being widely found across the country, rather than just in regional hot spots like last year, Mark says. “This year it seems endemic and again are being from emergence. Treating with a pyrethroid within seven days of egg laying should be a priority for control.”

Cereal leafhoppers are also on the rise, he reports, with increasing numbers being found in the south of England. These spread wheat dwarf virus, which was a significant issue in crops from East Anglia to as far west as Taunton.

“Crops are vulnerable from emergence, with early infections causing the greatest yield loss,” Mark says. “Unlike other viral diseases in cereals which often form in relatively large distinct patches, wheat dwarf virus symptoms are often relatively spread out in small, peppered patches across the field as the leafhoppers readily move between plants and spread the virus by primary infection.”

The hot dry summer is likely to have been highly favourable for cereal leafhopper populations, but control is difficult with pyrethroid efficacy “average at best”, Mark says.

In oilseed rape, cabbage stem flea beetle grazing by adults seems to be subsiding, but two other pests are still causing some problems. “We’ve started seeing turnip sawflies again. After seeing them earlier in the season, numbers had dropped, but they’re being spotted which suggests maybe another generation.”

Rape winter stem weevil has also been found in water traps at Wellesbourne in Warwickshire by Prof Rosemary Collier. “That can be difficult to spot in crops,” Mark admits.

“While there is resistance to pyrethroids in France, last year those who sprayed had less of a problem, so the expectation is that pyrethroid sprays can do a reasonable job.

“There’s also some evidence to suggest that pyrethroids reduce flea beetle larvae, so if you are having to spray for rape winter stem weevil you might get some incidental control.”