6 November 2001
Growers warned of beet pest

By Tom Allen-Stevens

SUGAR-BEET growers have been warned to look out for a potentially serious pest that caused severe damage in some parts of the 2001 crop in Norfolk.

Dr Alan Dewar of IACR-Brooms Barn says the chances are that numbers of beet leaf miners, commonly known as mangold flies, will build up as a result.

“Populations next spring will depend on the level of predation or parasitism. But unprotected crops could well be at risk again next year,” he says.

The previous significant outbreak was back in 1991, when damage was widespread across all beet-growing areas except Yorkshire.

The small, bristly, grey-green fly lays its chalky-white 1mm-long eggs on the underside of young beet leaves.

When the maggots hatch four to five days later, they tunnel into the leaves to produce characteristic blistering.

If the attack coincides with poor growing conditions, plants may not survive, while the blisters also increase the risk of herbicide absorption, leading to damage.

“Growers should look out for the sluggish-moving flies and check the undersides of leaves for signs of eggs up to the four-leaf stage,” suggests Dr Dewar.

He says that Brooms Barn trials have shown those crops from seed treated with Gaucho (imidacloprid) should be spared any serious damage.

Soil-applied insecticide Temik (aldicarb) is equally as effective, according to the trials.

Norfolk-based agronomist Pat Turnbull backs this up: “Gaucho-treated seed has proved worthwhile on many crops.

“The exception is sugar beet grown on light soils that are liable to docking disorder, which will need an aldicarb treatment instead to control the nematodes.”

Leaf miners over-winter as pupae about 50mm beneath the soil surface and produce about two or three generations each year.

Only severe attacks on young seedlings affect yield, which comes from the first generation hatched in May.

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