Grapegrowers just can't catch a break this harvest season.
First the damp, cool summer led to destructive mold and mildew in vineyards.
Now the sudden, scorching heat of the last two days has sun blasted their grapes, leaving some vineyards with extensive crop loss.
"We have a few blocks that suffered up to 35 percent sun damage," said Steve Hill, general manager of Durell Vineyard in Sonoma. "That fruit is ruined. It will turn into raisins."
The amount of damage varies from vineyard to vineyard. Grape vines sheltered from direct sun had little or no damage, while areas that were directly exposed to afternoon sun were devastated.
Damage to the county's expected 195,000-ton harvest will become more evident in the coming days as growers survey their vineyards, said Nick Frey, president of the Sonoma County Winegrape Commission.
The sun damage comes just as growers were fighting against the exact opposite problem — not enough sun.
In previous weeks, growers had taken aggressive action to stop bunch rot, a destructive mold that was triggered by this summer's unusually cool, foggy weather.
Growers had pruned back leaves to expose fruit to maximum sunlight in an effort to dry out grape clusters during the day. That strategy prevented bunch rot, but left grapes susceptible to overexposure, said Kyle Cameron, who manages two small vineyards in the Russian River.
"Everyone opened up their grapes to get as much sunlight as they could," Cameron said. "Then the sun came out and fried them."