Pembrokeshire's potato growers are being warned to be vigilant to the threat of a new strain of blight capable of rapidly wiping out crops.

The so-called genotype 13 poses a much more serious threat to potatoes than more established strains because it is resistant to some fungicides.

Julian Lees, agronomist at Haverfordwest-based Puffin Produce Ltd, said growers have always relied on these fungicides to keep blight at bay. In cooler conditions, genotype 13 can form large lesions that sporulate sooner than other genotypes, he explained.

"This means spray intervals will have to be tight when the threat of blight is high," said Mr Lees, who was among agronomists, industry experts and researchers at the latest British Potato Council blight forum.

"It is one of the first strains to appear in the crop so vigilance in the early part of the season will be vital this year."

Good husbandry is essential, he said, and warned farmers against dumping graded out potatoes in fields. These, together with infected seed and potato volunteers, are the main source of blight.

In Pembrokeshire, 1,200 acres of potatoes are grown for Puffin.

Last year, which was a record year for potato blight, the fight against the disease cost Puffin growers an average of £100 an acre, but this year's threat could see costs rise further.

The British Potato Council (BPC) is urging growers to support the Fight Against Blight campaign and to sign up to the BlightWatch service to assess risk.

"It is a system that has been proven to nip potential blight outbreaks in the bud, but it only works if growers stay alert and react," said the BPC's research and development director, Mike Storey.

"We are dealing with a different type of blight than we were in the past but current best practice is still the best control strategy. Our current fungicide armoury, used well, will bring good control."