(Bloomberg) - Italy’s wine production may slide about 14 percent this year after a rainy summer brought overcast conditions and fungal rot, according to a forecast from the country’s association of wine-industry technicians.

Italian winemakers may produce 41.6 million hectoliters (1.1 billion gallons) this year from 48.16 million hectoliters last year, the Associazione Enologi Enotecnici Italiani wrote in an online report dated Sept. 5.

The drop would mean France overtakes Spain and Italy as the world’s biggest wine maker, based on government production statistics. Volumes are predicted to slide in 12 out of Italy’s 15 production regions, including Piedmont, home to the Barolo and Barbaresco wines, the association estimates.

“The weather didn’t grant any respite to the wine industry,” the Milan-based group, known as Assoenologi, wrote. “The 2014 vintage was an obstacle course, full of hope, reversals and disappointments.”

Italy’s average rainfall in July was 73 percent above the long-term average, with 22 rainy days in the north of the country, according to Assoenologi. Parts of mainland Italy and Sardinia got twice to four times normal rain in July, it said.

The wet conditions were “optimal” for development of fungal disease such as mildew and botrytis, forcing growers to make a grape selection in the vineyard, Assoenologi said. The grape crop was about 10 percent harvested as of Sept. 5, the association wrote.

Production in Veneto, Italy’s biggest wine-growing region and known for its Valpolicella reds, is forecast to decline 15 percent to 7.78 million hectoliters. Output in Emilia-Romagna, which produces Lambrusco, is forecast to fall 10 percent to 6.66 million hectoliters.