Early egg counts reveal wheat bulb fly risk divide in 2020

Tuesday, 15 September 2020

Two East of England monitoring sites are at high risk from damage from the cereal pest wheat bulb fly. However, the other ten sites monitored fell into the ‘low risk’ category.

Conducted by ADAS, the survey uses soil samples from 30 fields, split equally across sites located in the East and North of England that are prone to attack, to calculate the number of pest eggs per square metre.

Each year, results from the East of England are available first and published to provide an early indication of the pest-pressure trend.

Of the 12 sites monitored in the East of England so far, ten are ‘low risk’, as they had egg counts under 100 eggs/m2 (average 24 eggs/m2). Conversely, the other two sites are ‘high risk’ and ‘very high risk’. Located in Cambridgeshire (404 eggs/m2) and Norfolk (850 eggs/m2), respectively, both had sugar beet as the previous crop.

The results indicate the potential risk of economic damage to wheat and show whether the use of treated seed could potentially reduce the risk of unacceptable crop losses.

Seed treatment thresholds

  • Early-sown winter wheat crops (before November) are unlikely to benefit from seed treatments, which lack persistence to offer full protection. Excess shoot production also makes these crops more resilient. However, wheat bulb fly pressure at which impacts on yield might be expected is 250 eggs/m2
  • For late-sown winter wheat crops (November to December), consider seed treatments where populations exceed 100 eggs/m2
  • For late-winter/spring-sown crops (January to March), consider seed treatments irrespective of the population size (unless no eggs are present)

Although the actual damage threshold varies considerably, the simple rule of thumb is the greater the number of tillers at the time of attack, the lower the risk of economic damage.

Charlotte Rowley, who manages pest research at AHDB, said: “Our survey frequently detects large variations in wheat bulb fly egg numbers, both across and between regions.

“The AHDB website provides comprehensive information on the factors that influence risk. At this time of the year, if egg counts are high, the least risky option is to avoid winter wheat.”

Later this autumn, AHDB will publish egg count results for three further sites in the East of England and all fifteen sites in the North of England.

Access survey results and threshold information via the dedicated AHDB web page: ahdb.org.uk/wbf