Farming News - Potential threat from wheat bulb fly low
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Potential threat from wheat bulb fly low
Results from the HGCA autumn wheat bulb fly (WBF) survey suggest that the current WBF risk ranks among some of the lowest risk levels recorded since the survey started in 1984.
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).
This year, the only high-risk sample (400 eggs/m2) was taken from a site in East Yorkshire where vining peas were grown.
Caroline Nicholls, HGCA Research Manager, said: “The results suggest wheat bulb fly will pose a limited threat to crops drilled before November.
“In fact, the proportion of fields sampled exceeding the high-risk threshold of 250 eggs/m2 has been much lower than average for three years in a row.
“Since the survey began, however, there has always been at least one field found to be above the high-risk threshold.
“This means that growers will still 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 100-250 eggs/m2 is considered appropriate.
In the north of England, 53% of monitored sites were above this level but in the east of England only 13% of sites were above this level.
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.
The low potential threat from wheat bulb fly is good news, especially as deadheart (dimethoate) sprays are no longer authorised for control of wheat bulb fly larvae.
To better understand the various risk factors, growers should look at the revised HGCA publication on wheat bulb fly and the information in the full survey report.