Wheat bulb fly hatch threatens backward wheat crops

The wheat bulb fly egg-hatch is well under way in East Anglia and Lincolnshire and has now started in Yorkshire, according to the latest Pestwatch report.

Egg-hatch in Suffolk was reported to be at 20%, the same as that seen on mineral soils in Cambridgeshire/Hertfordshire, while in Lincolnshire the figure was double that at 44%. Egg-hatch on mineral soils in Yorkshire were at 31%, the same as that seen on organic land in Cambridgeshire.

Many later-sown crops are potentially at risk if they have only one or two tillers at the time of wheat bulb fly egg-hatch. An egg-hatch insecticide spray may be worthwhile, even where egg numbers are only in the moderate infestation category of 100 to 250 eggs/sq m, says the report.

Sarah Hurry of Dow AgroSciences advises growers to conduct risk assessments for specific fields, looking at locality, previous cropping, drilling date, plant population, tillering and soil type.

“There are many late-drilled, struggling, backward and thin crops this year that may benefit from an application of Dursban (chlorpyrifos) in order to promote all-important tiller survival.

“Once conditions allow spraying, chlorpyrifos should be applied at egg-hatch at 1kg/ha in 200-1,000 litres of water. In the event of prolonged egg-hatch, a repeat application may be required, particularly on organic soils. If necessary, it can be applied to frosty ground, but should not be tank mixed,” she says.

However, growers are being urged to take precautions to prevent any spray drift by using low-drift nozzles and an extended buffer zone, as part of the industry’s “Say No to Drift!” campaign. Growers are encouraged to use a LERAP-rated three-star nozzle and adopt a 20m buffer zone near watercourses or a 1m zone near dry ditches.

The reports are issued weekly by Dow AgroSciences and ADAS, giving results of soil sampling at a number of UK sites to help growers accurately access risk and optimise timings of soil insecticide applications.

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