Autumn survey of wheat bulb fly incidence

The problem

With the exception of oats, all cereals can be attacked by wheat bulb fly (WBF). Damage is most frequently reported in winter wheat. The pest is most prevalent in eastern England but numbers fluctuate considerably from year to year. Due to recent withdrawals, chemical control options are limited to seed treatments. The thresholds for treatment are as follows:

• Early-sown wheat crops (before November) are unlikely to benefit from seed treatment
• For late-sown wheat crops (November to December), seed treatments should be considered where WBF populations exceed 100 eggs/m2
• For very late-sown crops (January), seed treatments should be considered irrespective of the WBF population size (unless no eggs are present)

*An autumn survey of the pest levels, based on egg extraction from soil samples, has been conducted since 1984. The survey results help the industry make crop management decisions, especially those relating to seed treatments. However, the survey approach is relatively costly and time consuming. As a result, there is a need to identify alternative approaches to assess WBF risk.

Note: Drill treated seed at the recommended depth of 2.4–4.0 cm in a firm, even seedbed. Signal 300 ES (cypermethrin) seed treatment must only be applied to cereal seed sown in the autumn/winter. Treated seed must not be sown after 31 January, as this is defined as the end of the winter period by CRD.

The project

This project will support the long-term monitoring of WBF through the traditional autumn survey. The survey involves taking soil samples in September from 30 fields prone to WBF attack (split equally across sites located in the East and North of England) and calculating the number of WBF eggs per square metre. An early indication of risk, based on a subset of sites, is published in September. The final indication of risk, based on all sites, is published in October.

The work will also investigate the potential to predict WBF risk using a meteorological model. A molecular method to detect WBF DNA in soil samples will also be validated as part of the project.

The benefits

The project will indicate the need for seed treatment against WBF. It will also investigate more rapid, lower-cost monitoring methods. If an indication of WBF risk can be provided earlier in the autumn, better decisions on seed treatment, sowing date and seed rate could be made.

Autumn 2023: wheat bulb fly risk is relatively low

Final results from the 2023 survey suggest the UK is on track for another low-risk season for this cereal pest.

The survey results are similar to 2022. Once again, about one-third (9/30) of sites were above the seed treatment threshold for late-sown wheat crops.

Eastern England survey results (15 sites)

• Ten were in the low-risk category (<100 eggs/m²)
• Three were in the moderate-risk category (101–249 eggs/m²)
• Two were in the high-risk category (250–500 eggs/m²)
• No sites were in the very-high-risk category (<500 eggs/m²)
• The average egg count was 81 eggs/m²
• The highest egg count was 370 eggs/m² (following sugar beet at a site in Cambridgeshire)

North of England survey results (15 sites)

• Eleven were in the low-risk category (<100 eggs/m²)
• Four were in the moderate-risk category (101–249 eggs/m²)
• No sites were in the high-risk or very-high-risk categories
• The average egg count was 72 eggs/m²
• The highest egg count was 123 eggs/m² (following potatoes at a site in North Yorkshire)

Full details are in the annual project report for 2023 (available from the 'Downloads' section above).

How to manage wheat bulb fly risk in cereals

What the long-term monitoring data shows (Agronomists' Conference 2022 video)

New tools for a post-insecticide era (February 2023 CPM article)