Information from the wheat bulb fly survey is published every year in September to aid decision-making on seed treatments. Incidence generally increases following a wet harvest period and is lowest after a hot, dry summer.
Wheat bulb fly
All cereals except oats can be attacked by wheat bulb fly (WBF), although damage is most frequently reported in wheat. The pest is most prevalent in eastern England.
Where cereal crops are harvested late, e.g. due to poor weather, adult flies have more time to feed on fungi on cereal ears and mature their eggs.
WBF prefers to lay eggs in bare soil from late July until early September, particularly if it has been freshly cultivated. Risk, therefore, is higher after fallows, early harvested crops, such as vining peas, or row crops, such as potatoes, sugar beet and onions.
Late-sown (after November) winter wheat crops and spring crops (before the end of March) can be more vulnerable to WBF, because the tillering window is short. In fact, many crops may have only a single tiller when the WBF egg hatch occurs, between January and March. Each larva can attack several tillers. Attacked tillers eventually die back to show the classic 'deadheart' symptoms.
Avoid bare ground prior to drilling cereals. Delay cultivation until after egg laying. Drill as early as practical. Avoid deep drilling. Increase seed rates to compensate for attack, especially in late-drilled crops. Top dress early to promote crop recovery.
Due to recent withdrawals, chemical options for control of WBF are limited to seed treatments. The thresholds for treatment are as follows:
- Early-sown winter wheat crops (before November) are unlikely to benefit from seed treatment, as they have more time to tiller and are better able to withstand WBF attack. Seed treatments also lack persistence to fully protect such crops
- For late-sown winter wheat crops (November to December), seed treatments should be considered where WBF populations exceed 100 eggs/m2 (moderate risk)
- For late-winter/spring-sown crops (January to March), seed treatments should be considered irrespective of the WBF population size (unless no eggs are present).
The threshold of 100 eggs/m2 is, therefore, only relevant to late-sown crops.
Wheat bulb fly survey
The AHDB funded WBF survey can aid decision-making on whether a seed treatment is justified. The survey, conducted by ADAS, involves taking soil samples in September from 30 fields prone to WBF attack (split equally across eastern and northern England) and calculating the number of wheat bulb fly eggs/m².
Read our news item for the early 2018 data.