Calibrating the wheat bulb fly threshold scheme using field data

Project Report No. 607

Calibrating the wheat bulb fly threshold scheme using field data

Desk Study

Kate E Storer, Pete M Berry, and Steve Ellis

ADAS High Mowthorpe, Duggleby, Malton, North Yorkshire YO17 8BP


AHDB Final Project Report 598 – Crop management guidelines for minimising wheat yield losses from wheat bulb fly (WBF) – described a potential threshold scheme for this serious pest of winter wheat.

The scheme considers the minimum plant population, latest sowing date and need for an insecticide treatment. It uses information from the autumn survey of wheat bulb fly incidence (September egg counts), expected egg viability, the maximum shoot number the crop could achieve by late winter, the number of shoots that a single larvae could destroy, and the minimum final ear number required to achieve the potential yield for the site.

In order for the scheme to be adopted, a more reliable and up-to-date estimate of the minimum final ear number required for high yielding wheat crops was considered necessary. This desk study looked at this aspect, including whether the number changes in different regions and environmental conditions.

A positive association between yield and final ear number was identified for UK wheat crops. For crops expected to yield up to 11 t/ha, a target final ear number of 500 ears/m2 was deemed a conservative default value. For crops expected to exceed 11 t/ha, a higher target final ear number of 600 ears/m2 was deemed appropriate.

Although there was evidence that the ear number associated with specific yields may vary between varieties and geographic regions, it was not strong enough to recommend its inclusion in the threshold scheme.

Before the scheme can be adopted, further research is necessary. In particular, it is important to quantify varietal differences in relation to shoot number at growth stage 31 and final ear number.

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