Vigilance was the word on every agronomist’s lips earlier this week after a warmer weather forecast for the coming weekend strengthened the likelihood of an orange wheat blossom midge attack in susceptible wheat crops.

“I’m expecting a lot of activity this weekend as long as it is as warm as they are forecasting at the moment,” ADAS entomologist Jon Oakley said on Tuesday (30 May).

“That’s going to be the first big showing.”

Pupation started last week at eight out of 13 sites being monitored for Dow AgroSciences by ADAS, with, in general, the more northerly sites the odd ones out.

Hatching has been delayed further by cooler than expected temperatures over the bank holiday weekend.

“They’ve been getting ready to hatch but it has been a bit cold,” Mr Oakley said.

“They just need it to warm up a bit; the soils are plenty wet enough so that’s not a limiting factor.”

Rising temperatures – air temps of above 15C are particularly favourable – following rainfall stimulate adult hatch.

“The odd adult has been spotted flying about already but there haven’t been any major flights.”

Whether wheat crops would be at risk from egg-laying females depended on crop stage when adults are flying, he said.

“Some early crops might be through the susceptible stage by then, but others will be right in the frame.”

Crops are at risk from ear emergence until flowering.

Vigilance was likely to be needed for the next week to 10 days, ProCam technical director David Ellerton warned.

“If the weather settles down the risk is likely to be high.

We’re going to need to be extremely vigilant until flowering starts.”

Treatment should only be done on a need basis, Hampshire Arable System’s Steve Cook said.

“The pest can be over-hyped by the trade – so many conditions need to be right for it to be a problem – so there shouldn’t be any thought of spraying unless conditions are right.”

That was best judged by careful monitoring via traps or through vigilance at dusk when most flights tended to happen, Dr Ellerton said.

Product choice was between chlorpyrifos and Hallmark Zeon (lambda-cyhalothrin), according to Mr Oakley.

The latter has a new recommendation for orange wheat blossom midge this season, but has a much narrower application window.

“You’ve got to get on quickly if you’ve got a problem.”

Timing has to coincide with the peak period of adult flight.

If a major outbreak did occur this weekend it would need to be sprayed by the early part of the weekend, Mr Oakley suggested.

“Spray because you’ve found a lot in pheromone traps.”

Using the traditional threshold of seeing one midge laying eggs per three feed wheat ears or six milling or seed wheat ears would be too late for Hallmark, he added.

“That threshold is fine for chlorpyrifos.”

mike.abram@rbi.co.uk