AS MUCH as a tenth of the national wheat crop could be lost to orange blossom midge, growers have been warned.

Record levels of the pest have been seen, especially in northern areas where it has not been a problem before.

But growers have been advised to take care of natural predators and warned not to use products that could do more harm than good.

Half a million ha of wheat are at risk, according to ADAS entomologist Jon Oakley, and the high population level points to a potential yield loss of 35% in badly affected crops.

“The levels of the pest we‘re seeing make it twice as bad as the last bad outbreak in 1993, when we lost 4% of the national crop” he said.

“Hopefully treatments that are going on should reduce the damage, but we‘re still looking at a crop loss of 4-6%.”

Adult midge are now hatching in large numbers across the south.

“We‘ve seen populations five to ten times over threshold levels in Oxfordshire,” reported Mr Oakley.

“But we found the highest numbers of eggs in soils in Yorkshire, so we‘re expecting pressure to be really quite bad there.”

Technical director for JSR Farms Philip Huxtable said that sticky traps in crops on the Yorkshire Wolds had caught four times the threshold level to spray.

“There has undoubtedly been a major explosion of blossom midge this year.”

The group, which farms 4,000ha (10,000 acres) in the area, has only sprayed three times for the pest in the last 30 years.

“We‘re targeting our highest risk crops and leaving headlands unsprayed, but still expect to cover half our wheat area.”

The targeted approach is heavily recommended by UAP technical director Chris Bean.

“Some crops have high populations of the pest, while elsewhere there is no sign,” he reported.

Mr Bean recommends growers monitor crops carefully and take account of variety, timing, crop growth stage and potential damage to beneficial insects before spraying.

“We‘re seeing OWBM in the Cotswolds, for example, but we‘re also seeing high numbers of parasitic wasps, which may keep damage in check.”

Mr Oakley warns against prophylactic spraying and using a chemical that does not have label clearance for OWBM.

“The timing is so tight, the chances are you‘ll do more damage to the natural predator population if you blanket spray.”

Trials suggest chlorpyrifos, applied at the right timing, will give 80-90% control, he added, while pyrethroids and dimethoate offer around 50% and 20% respectively.

“Dimethoate will hit beneficials hard and you could end up with a worse problem than you started with.”