With potentially damaging populations of over-wintering orange blossom midge already recorded in soils in continuous wheat at ADAS Boxworth, Cambs and locally elsewhere in the midlands and southern England, wheat growers are being urged to plan for control.

The pest is thought to have cost them £6m two years ago, and if May is warm a big attack can be expected, especially on fields then in wheat.

ADAS midge specialist Jon Oakley advises using pheromone traps to monitor adult emergence on such fields during the susceptible ear emergence stages, typically in the last half of May and early June.

Because pupation of the soil larvae tends to be triggered by heavy rains attacks can be localised, he says.

“There is a huge potential difference in levels of attack, where attacks will occur and the timings involved.

Any attempts to forecast over a large area are speculative.”

The critical factor is whether the vulnerable growth stages coincide with the egg-laying of the females.

There are now two insecticides available – Dursban WG (chlorpyriphos) and recently approved pyrethroid Hallmark (lambda-cyhalothrin).

compromise
Controlling the pest is all about compromise and flexibility, says Dow Agroscience’s Andy Leader.

Farmers need to make a single well-targeted application of an insecticide that delivers maximum yield benefit with minimal long-term effect on beneficial insects, he says.

“Pyrethroids may give ‘acceptable’ control of adult midges present at application.”

But the aim should be “maximum” control of as many adults as possible, he says.

Dursban WG controls both adults and eggs laid on the exposed parts of wheat florets.

Depending on temperature, it offers protection for up to 10 days, whereas a pyrethroid is likely to give only two days control even under favourable conditions, says Mr Leader.

The risks to beneficials can be minimised by following the guidelines in HGCA leaflet Orange wheat blossom midge – assessment and control, which can be downloaded from the Crop Research page at www.hgca.com

andrew.blake@rbi.co.uk