Protect cereal crops from Wheat Bulb fly

Wheat Bulb fly egg numbers are reported to be higher than in recent years, meaning vigilance is required in all crops which may be at risk. Growers with cereal crops potentially under threat should carry out Risk Assessments.

• Wheat Bulb fly can be a devastating problem
• Attacked crops are unlikely to yield their full potential
• Badly attacked crops could need re-drilling
• Carry out a Risk Assessment on all crops believed to be at risk
• Dursban WG eliminates the pest before it damages plants
• Applications of Dursban WG can be made to frosty ground, but do not tank mix other products under these circumstances
• An interval of 14 days must be observed between applications of Dursban WG and Broadway Star, or 28 days between Dursban WG and products containing mesosulfuron-methyl and iodosulfuron-methyl

Results from the HGCA's autumn survey of the incidence of Wheat Bulb fly eggs shows the numbers detected to be higher than for several years. Of 33 fields sampled in eastern and northern England, 21% were found to be in the highest risk category, with egg populations greater than 250/m². In autumn 2007 and 2008, fields in this category represented only 9% and 8% of those sampled respectively. The long term mean is 23% of fields in the highest risk category.

A lower threshold of 100-250 eggs/m² is appropriate for later drilled or poorly developing crops. In eastern England in autumn 2007, 67% of fields sampled contained egg numbers within this category. Of the fields sampled in northern England, 47% contained more than 100 eggs/m², with one field having 567 eggs/m².

Wheat Bulb fly - Delia coarctata - is a small fly which lays its eggs in exposed soil in July and August. These eggs hatch from January to March the following year, depending on soil temperatures. Once hatched the larvae move through the soil and bore into the base of cereal plants feeding on the central shoot. This causes the characteristic dead-heart symptoms to appear. Although the outer leaves remain green during early stages of attack plants become dull in appearance and, unless examined carefully, the attack may go unnoticed until dead-hearts become visible in February or March.

Winter wheat, winter barley, rye and early sown spring wheat can all be attacked. Crops that have not started to tiller before they are attacked can be destroyed completely. Spring wheat and spring barley drilled December to March can be killed before emergence. Traditionally the main risk area is eastern England where Wheat Bulb fly is a major pest of winter wheat. Yield losses depend on pest numbers, plant populations and other factors, but a guide is a potential loss of 0.7 tonnes per hectare if 20% of plants are attacked.

Growers with late-drilled, backward or poorly developing crops should undertake a Risk Assessment to clarify the best course of action on their farms. The result of the Risk Assessment will give guidance as to whether an application of Dursban* WG is justified.

As in previous years, Dow AgroSciences, in conjunction with ADAS, will be carrying out Pestwatch monitoring of Wheat Bulb fly egg hatch and subsequent plant invasion. Six high risk sites have been selected in Cambridgeshire, Suffolk, North Yorkshire and East Yorkshire and the results of monitoring are published in Pestwatch reports from mid-January onwards.

Dursban WG provides good control of Wheat Bulb fly and protects crops from attack. Applications at egg hatch, before larvae have entered the plant, means damage is reduced by not having to wait for dead-hearts before deciding to spray. Dursban WG has a residual life in the soil which means that most larvae will be controlled as they hatch over a period of time.

Learn more about Dursban WG  

Learn more about Wheat Bulb fly 

Refer to the Dursban WG Wheat Bulb Fly Risk Assessment Chart (627KB PDF)

Always check the Cereals Pestwatch pages for the most recent bulletins.