There’s an old entomology proverb that provides some guidance on the seed rate required for the drilling of arable crops which says:
One for the blackbird, one for the crow,
One to die and one to grow.
This provides a perfect summary of a new approach we are taking to the control of wheat bulb fly (WBF). This collaborative AHDB Cereals and Oilseeds project aimed to minimise the risk of yield loss from WBF by accounting for and manipulating the ability of a crop to tolerate damage from the pest.
Current treatment methods for Wheat Bulb Fly
Currently in the UK, only one seed treatment is available for chemical control of WBF but this is only effective for crops sown after the end of October. Most wheat crops are sown before this date. The risk of WBF attack varies annually. This can be estimated by soil sampling and extracting and counting the eggs of the pest but this is both laborious and time-consuming. The AHDB project aimed to tackle both of these problems by developing an integrated pest management (IPM) strategy for the pest.
Physiology research tells us that wheat crops need about 500 shoots/m2 at growth stage 31 to achieve their potential yield. Crops regularly produce more than 1000 shoots/m2 by this growth stage so in theory some of these excess shoots could be sacrificed to pests without affecting yield. Ultimately, we are advocating allowing ‘one (or more) for the wheat bulb fly’ although this does not scan quite as well as the original. WBF egg numbers are determined by a range of meteorological parameters and previous work has attempted to use this to predict pest risk. Our project looked to refine this even further and ultimately provide an alternative to soil sampling.
The result was two predictive models that can be used for the integrated management of WBF. The first predicts pest levels and the second the number of shoots a winter wheat crop will achieve when sown at a specific seed rate on a specific sowing date. The proposed IPM strategy for WBF is described below.
Both models had a predictive accuracy of 70% and so provide a foundation for a future IPM strategy minimising crop damage by WBF.
A research paper entitled ‘Development of a pest threshold decision support system for minimising damage to winter wheat from wheat bulb fly, Delia coarctata’ authored by Daniel J Leybourne, Kate E Storer, Pete Berry, and Steve Ellis is currently undergoing revisions for publication in the Annals of Applied Biology. A preprint of the research can be viewed here.