If you see a grape grower, give him a hug. He probably needs it.

Growers are enduring one of the most stressful seasons in recent memory due to tough economic conditions and the European grapevine moth invasion.

And now a new threat, known as green rot, has emerged in Sonoma County vineyards because of persistently damp, cool weather.

The outbreak of green rot in the Russian River Valley is the worst since farmers first started noticing it in the 1970s, said Duff Bevill, founder of Bevill Vineyard Management in Healdsburg.

"It's been a long time since it's been this cold. The green rot is a telling indicator," Bevill said. "This is a year for disease."

Green rot is technically Botrytis, a mold that infests grape clusters and destroys the fruit. Botrytis usually doesn't appear in great quantity until much closer to harvest, often triggered by early rains. Late in the season, growers call it bunch rot.

But "this mold is already taking off. It didn't wait for the rain," said Rhonda Smith, a viticulture adviser with the UC Cooperative Extension in Sonoma County. "The thick marine layer has provided the moisture."

When Botrytis makes an early appearance like this, farmers give it a unique name because it forms in young, unripened grape clusters that are often still green -- hence green rot.

Once the mold takes hold, it spreads, so farmers have little option other than to prune infected bunches.

"We've probably had to cut off 3 tons," said Kyle Cameron, 14, who helps manage the family's 10-acre Sunny Valley Vineyards in Fulton. "Every year you find a little bit. But this year is much more."

Vineyards in warmer parts of the county, such as Dry Creek Valley, Alexander Valley and Sonoma Valley, have seen far fewer outbreaks, although those areas are still spraying sulfur to combat powdery mildew, Bevill and others said.

"We're not immune to those problems here," said Steve Hill, general manager of Durell Vineyard in Sonoma. "But they are less severe than places that are socked in with fog for longer periods."

Persistent fog in some areas is drenching vineyards in cooler regions closer to the coast, and low temperatures are preventing grape clusters from completely drying out during the day. The green rot appears to be affecting all the varietals common to these cooler regions, including sauvignon blanc and pinot noir, but chardonnay appears hardest hit.

"It's been foggy for weeks," Bevill said. "We need a break. We need a week of 90- to 100-degree days. That will stop the rot cold in its tracks."

For now, growers have trimmed leaves around grape clusters in hopes the meager sunlight of recent days will help dry out the fruit.

The prospect of early rain looms as a major threat in the minds of growers, who will likely be harvesting two to three weeks later this year because of the cool weather.

"If it rains, we've got some real serious problems," Bevill said. "If it stays foggy like it is now, it will be a chronic problem we'll have to fight all season."

The outbreak of green rot added a third threat to an already difficult growing season.

The stricken economy has left many farmers still searching for wineries to buy their crop. These growers could see their work go unpaid unless buyers begin to step forward. Many local wineries have held off buying grapes because budget-minded consumers have flocked to cheaper wines often made from lower-priced grapes from the Central Valley.

Making matters worse locally, the European grape moth is threatening a D-Day-style invasion of vineyards in Sonoma County, having already occupied Napa County.

Nick Frey, president of the Sonoma County Winegrape Commission, said the conditions have heightened anxieties.

"Farming is never easy, but these series of factors, one building on another, are not making this a pleasant year for growers," said Frey, an understated man. "The stress level is unusually high."

You can reach Staff Writer Nathan Halverson at 703-1577 or nathan.halverson@pressdemocrat.com.