Italy's 2014 wine harvest will be the smallest since 1950 and is set to cost the country its crown as the world's biggest producer by volume to France, the country's leading farmers' organization said Tuesday.

Total production is forecast at 41 million hectoliters (1.08 billion gallons), according to the organization, Coldiretti – a near 15 percent fall on last year, which was blamed on adverse weather conditions and the consequent prevalence of a number of plant diseases affecting vine yields.

Some of the worst-hit areas were in the south. Falls in output of as much as 30 percent are expected in Sicily and Puglia, the regions most affected by what has been an unusually wet and relatively cold summer in many parts of the country. Average rainfall across the country in July was 73 percent higher than the average, a trend that both significantly reduced tourist spending and diluted the wine-producing potential of grapes.

France will easily supersede Italy's output, with a forecast production of just over 1.2bn gallons, according to the French agriculture ministry, although definite figures won’t be available until the harvest finishes in October.

Some regions in central Italy will see a modest increase in the quantity of grapes harvested, while across the north of the country production will be down on last year.

There was a faint glimmer of light for glum producers – Coldiretti said that if autumn weather conditions were good, with plenty of sunshine and not too much rain, the harvest could improve a little. This year's harvest is starting later than usual because of the weather and will continue until late October or, in some parts of the country, early November. Only about 20 per cent of grapes have so far been picked, Coldiretti said.

Much of Italy, especially the north, was hit by severe storms, flooding and unusually chilly weather, with newspapers declaring that "this was the summer that never was".

The wine sector is estimated to employ around 1.25m Italians, from the vintners and farm workers who tend the estates to the glass factories that make bottles and the trucking companies that transport the wine.

The wine industry is a crucial component of the economy, particularly at a time of stagnation. Italy's growth rate this year will be close to zero, according to Matteo Renzi, the prime minister who came to power in February on promises of cutting red tape, improving competitiveness and reducing chronic levels of youth unemployment.