Interim results from AHDB Cereals & Oilseeds’ autumn wheat bulb fly (WBF) survey show significant variability in WBF risk, with pest pressure generally higher in northern England.
Wheat bulb fly can attack all cereals (except oats) and lays its eggs in late summer in bare soil following fallows, early harvested crops or between rows of crops such as potatoes, sugar beet and onions.
The pest is most prevalent in eastern England, the east Midlands and north-eastern England.
The survey involves taking soil samples in September from 30 fields prone to wheat bulb fly attack (split equally across eastern and northern England).
To date, eight fields have been tested in eastern England and six fields have been tested in northern England.
In 2014, only one high-risk sample was identified from all 30 fields sampled.
In 2015, based on the 14 fields sampled to date, two high and one very high-risk sample have already been identified.
Caroline Nicholls, AHDB Cereals & Oilseeds Research Manager, said: “In higher-risk situations, growers will need to keep an eye out for the pest early next year to determine the need to spray, especially for later-drilled crops or those with only one or two tillers at the time of wheat bulb fly hatch.”
Typically, seed treatments are only effective on crops drilled from November onwards and, for such crops, a lower ‘moderate-risk’ threshold of 100-249 eggs/m2 is considered appropriate.
In northern England, all sites assessed to date have been classed at or above the ‘moderate risk’ threshold.
In the east of England, only two out of the eight sites assessed to date have been classed as at or above the ‘moderate risk’ threshold.
Seed treatments are most effective in shallow-drilled crops (drilled to a depth of 2.5–4cm) and are particularly valuable for late-sown wheat.