Early dessication of potato crops showing signs of foliar blight could be the only option to prevent tuber blight infection where weather conditions make it impossible to maintain blight sprays, the British Potato Council is warning.

Adas blight agronomist Nick Bradshaw explained that recent thunderstorms may have washed soil away from the ridges increasing the exposure of tubers and, with it, the risk of tuber infection. "The rain has also flattened crops in some areas making it difficult to achieve good blight spray cover, so the best option will be to burn-off where crops have met their planned specification," said Bradshaw.

He warned growers they face the most critical period so far this season and even in areas that escaped the rain and thunderstorms of last weekend, humidity levels have been high throughout the day and into the night - weather conditions extremely favourable for blight development.

He predicts new outbreaks during the next week and advises growers to use the British Potato Council's (BPC) website www.potato.org.uk for daily updates.

"It is impossible to say where outbreaks might occur because of localised weather patterns but continued reports of scattered infections throughout the crop strongly suggests that there are substantial sources of external inoculum in some areas," he said.

Where it is possible to travel, tight spray intervals will offer the maximum protection. "Where intervals have been extended use curative fungicides and consider a tank mix of products to protect against tuber infection. What's more, following desiccation, blight sprays should be applied until all the haulm is completely dead."

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