2 August 2002

Keep up pressure on potato blight

POTATO growers busy with the cereal harvest are being urged to maintain their defences against blight.

So far this year, control of the foliar disease has been good, says Dennis Walsh, agronomist with East Anglia-based QV Foods. But it is in just such seasons that tuber blight tends to be more troublesome, because growers ease up on programmes towards the end of the season.

"Dont lose control at the last minute." Infection from private gardens and even organic crops remains a threat, he advises.

"Tuber blight is dynamite, because it is difficult to detect. For early lifted potatoes the first we might know about it is when the bag collapses on the supermarket shelf. For the over-wintered crop it is when the potato store collapses."

So even when blight pressure appears low and workloads are heavy it is risky to stretch spray intervals, he warns. "Dont be tempted to extend the spray interval from seven to 10 days unless you base programmes on protectant and systemic products with kick-back, or you can guarantee a low blight risk period."

Translaminar products offer the best kick-back, says Mr Walsh, and with Curzate (cymoxanil + mancozeb) down about 33% in price since last year it offers particularly competitive control.

"But we still recommend that growers spray every seven days when the weather is blighty."

The final two treatments should be tin-based, he advises. "Ranman and Shirlan are potential tin replacers, but they are more expensive."

As an extra safeguard before lifting check that the foliage has died naturally and not because of blight, and make sure the skins are set, he adds. &#42

&#8226 Threat still present.

&#8226 Cereal harvest hassle.

&#8226 Maintain programmes.

&#8226 Kick-back needed if delayed.