Agrovista advises that those who have opted for the no insecticide SFI option, the use of one might be a wise decision this autumn.
Many farmers who have taken the payment will be loath to spray insecticides but with widespread reports of aphids, gout flies and increasingly leafhoppers being spotted in cereal crops from emergence, economically it could be the right decision, suggests Agrovista’s Lewis Butlin.
“SFI guidance states that where growers have C/IPM4 in place, should they need to spray insecticides to prevent a financial loss, growers should do so at the earliest opportunity. Given the high risk of barley yellow dwarf (BYDV) 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.
Assess risk
The new AHDB BYDV model is helpful in assessing risk, suggests colleague Mark Hemmant. “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 notes.
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. “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.
“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.”
Rapid species upturn
According to Prof Tom Pope, professor of applied entomology at Harper Adams University, 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 adds. “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 cautions.
