Wheat bulb fly risk highest in late crops
Later drilled and slow developing wheat crops are at greater risk from wheat bulb fly this coming spring, but growers are being urged to examine the reasons for the telltale “deadheart” symptoms before applying any treatments.
Every year crops exhibit some type of “deadheart” symptoms to some degree, says Suffolk’s Frontier agronomist Brian Ross. “Correct identification is the first step to efficiently dealing with pest problems.”
Establishing when the symptoms first showed is important because two of the main pests responsible do not show until the early new year. Previous cropping can help indicate which of the pests is likely to be the culprit.
The three main culprits are: frit fly, wheat bulb fly and yellow cereal fly. Frit fly can be found after grass or maize, and deadhearts can appear in the autumn in early drilled cereals. Yellow cereal fly will only show in the early spring behind grass and other graminaceous species. Meanwhile, wheat bulb fly appear in January/February after any ground that is bare or sparsely populated during July/August.
Therefore, if deadhearts are seen in the autumn then they are likely to be caused by frit fly and though they are capable of moving from tiller to tiller, it is unusual for them to require treatment unless they are in very high numbers, says Mr Ross.
Yellow cereal fly are generally less of a problem than the other two species. As they remain in one tiller, only low plant populations and early-sown crops in sheltered fields close to woodlands will be at risk.
The worst deadheart pest, particularly in the East, is the wheat bulb fly. These can attack all cereals (apart from oats) and it is the unpredictability of numbers that make it such a problem for farmers, he says.
Recent HGCA-funded sampling in conjunction with ADAS looked at 30 fields split between northern and eastern England in September and the threshold of 250/sq m was reached in only one field, the equal lowest recorded since 1984. “Mean egg counts showed a slightly higher risk in the East than the North (96 v 79/sq m, respectively).
This means that wheat bulb fly are unlikely to be a threat to crops drilled before November this season. However, later sown or slower developing crops could potentially be at risk at the egg hatch timings in January/February.
The threshold for these would be down to 100 eggs/sq m and the survey showed 47% of sampled fields in the East were above this and 27% in the north.
Up until this year Austral Plus seed dressing (tefluthrin + fludioxynil) was the only product available to use on late-sown crops and is a recommended late treatment for later sowings of wheat and barley made before the end of egg hatch in those areas that are at risk of wheat bulb fly.
But there is a new seed treatment available: Signal 300ES, based on cypermethrin (300g/t), which performed as well as the standard in a Frontier trial this year. As it is a single purpose dressing it is compatible with a range of other fungicidal seed treatments.
