Mildew is ravaging Bordeaux’s vineyards, with harvests expected to fall by up to 70 per cent in the latest of a series of natural disasters in France’s largest wine-growing region.

Few producers have been spared from the outbreak of the fungal disease which they say has been caused by heavy rainfall in the spring. Most expect to lose between 20 and 70 per cent of their crop to mildew.

Bordeaux winemakers also suffered big losses last year with their worst harvest since 1945, caused by severe frost that cut production by 40 per cent.

Mathieu Verdier of Château Bessan said: “With the rain that came after winter, I knew it was going to be a really difficult year. Now we’re seeing mildew appearing on many of the vines. I estimate that my production will fall by about half.”

Aurélie Carreau of Château Mons La Graveyre said: “We’ve just seen mildew appear in the past week. Until then we weren’t affected.”

Both Ms Carreau and Mr Verdier produce organic wine but even treated vines are developing the disease. “I know conventional wine-growers who’ve got the same problems as we have even though they treat their vines systematically,” Ms Carreau said.

Joel Ortiz, a producer who advises the local Chamber of Agriculture, said: “Few vineyards are completely unaffected. It’s widespread, although it hits some varieties of grapes worse than others.”