Cereal crops are at the lowest overall risk from wheat bulb fly (WBF) since monitoring began, according to findings from the annual AHDB autumn survey of this pest.

Soil samples were taken 30 fields prone to WBF attack in September and the number of WBF eggs counted.

Historically, the threshold of 250 eggs/m2 has been used to provide a measure of overall risk. For the first time since monitoring began in 1984, none of the 30 soil samples was found to exceed this threshold.

Despite the low risk, some sites sampled had egg levels above the seed treatment threshold relevant to later-drilled crops, with the risk higher at sites located in the north of England.

Good progress was made with the winter wheat harvest in 2017, despite unsettled weather, and 90 per cent of the crop had been harvested by the first week of September, which is ahead of the five-year average.

Report author, Dr Steve Ellis of ADAS, said: “It’s possible the good progress with harvest limited the opportunity for the fungi that adult wheat bulb fly like to consume to develop in cereal ears.

“When food sources are restricted, we know the females produce fewer eggs and this could have contributed to the low-risk year for this pest.”

Due to recent withdrawals, chemical options for control of WBF are limited to seed treatments. Early-sown winter wheat crops (before November) are unlikely to benefit from seed treatment as they have more time to tiller and are better able to withstand WBF attack. For late-sown winter wheat crops (November to December), seed treatments should be considered where WBF populations exceed 100 eggs/m2 (moderate risk) and for late-winter/spring-sown crops (January to March), seed treatments should be considered irrespective of the WBF population size.