31 May 2002

Midge menacing

BLOSSOM midge looks set to hit wheat crops hard this summer, following favourable warm weather in early May and recent wet weather.

Strong winds hampering spraying during ear emergence could mean damage is more widespread than normal, warns ADAS entomologist Jon Oakley.

Wheat blossom midge is now so widespread in soils, especially in East Anglia and Lincs, that it only needs the right conditions to merit treatment, he explains.

"We saw some awfully poor grain samples in Norfolk and Bedfordshire last year, and we are anticipating a big hatch at the end of May and in early June – just when crops are most susceptible."

Until recently the spray control trigger was the number of adults on ears, linked to whether crops were for feed or seed/milling. But there is a better approach, suggests Mr Oakley.

"I have a lot more confidence using yellow sticky traps that can be bought at garden centres and elsewhere. UK manufacturers include Oecos and Agrisense."

Two left just above crop height in each field give a much better idea of the need to spray than trying to count adults on a fine evening, he says.

"The threshold for treatment is 10 midges on either trap before the start of flowering. The most vulnerable time is when the ear is half out. Once the crop has started to flower you can safely ignore them."

For crops just meeting the threshold a pyrethroid product should prove adequate provided it is applied soon enough, he says.

"None of the pyrethroids carry a label recommendation for midge, but a lot of people use them around now against aphids and claim some midge control. But if you are well over the threshold you are back to chlorpyrifos, as in Dursban."

Threshold spraying is increasingly important, both for economic and environmental reasons, stresses Mr Oakley. "We certainly dont advise spraying everything on spec, and whatever you use you should leave a 12m untreated field margin."

A prescription form to help decide whether to spray Dursban has been issued by supplier Dow Agrosciences (see box). Only if all five points receive a yes should spraying go ahead.

BLOSSOM MIDGE PLANNER

FWAG environmental review carried out to identify sensitive areas.

Crop ears emerging (GS55-60).

Adult midges found in crop.

Number of midges:

one adult/six ears for seed/milling crops,

one adult/three ears for feed crops.

Leave unsprayed headland of at least 12m.

BLOSSOM MIDGE PLANNER

&#8226 FWAG environmental review carried out to identify sensitive areas.

&#8226 Crop ears emerging (GS55-60).

&#8226 Adult midges found in crop.

&#8226 Number of midges:>one adult/six ears for seed/milling crops,>one adult/three ears for feed crops.

&#8226 Leave unsprayed headland of at least 12m.