Forget drought - now Californian grape growers have got mildew to contend with
Californian wine growers are finally enjoying some rain after years of enduring drought conditions, they are now having to contend with mildew as a result of the wetter weather.
“If you don’t find mildew in your vineyards you haven’t looked hard enough,” said Glenn McGourty, a viticulture advisor for the University of California Cooperative Extension (UCCE) for Mendocino County.
From the cooler coastal regions to the Central Valley vineyards, growers are now on high alert for any signs of mildew.
Cooler coastal areas have been ripe for powdery mildew this year, according to Mark Battany, UCCE viticulture advisor for San Luis Obispo and northern Santa Barbara counties. “We've also seen some limited downy mildew, a European import, in a few locations this season,” he said, adding it is "quite rare” for California.
The warm and wet spring weather, following the wet winter has created the perfect conditions for downy mildew to flourish in both counties. Both types of mildew can cause considerable damage to vines, affecting both the quality and quantity of wine.
For mildew to flourish, all that is required are moisture and lower temperatures of between 70 - 85 degrees faranheit, according to Lawrence Sterling, director of operations at Iron Horse Vineyards in Sonoma County's Green Valley."The Russian River Valley and Green Valley are powdery mildew heaven because of the marine layer, which brings the moisture and the lower temperatures that mildew loves,” he told Wine Spectator.
Prevention and early detection are key to getting to grips with mildew, with aggressive spraying and canopy management key weapons in the grape grower’s arsenal.
"In a year like this, we need applications even before bloom to keep mildew under control," said McGourty. "If you don't get on top of it from the start, you're gonna have trouble.”
But Dana Merrill, owner of San Luis Obispo-based Mesa Vineyard Management pointed out that growers can't just rely on sprays.
"Canopy management is a critical component in the mildew battle as well," he said. "Keeping canopies open to facilitate air movement and spray coverage is critically important and increasingly these days that means mechanical leaf removal—certainly in the cooler regions.” Careful canopy management has the added advantage of appealing to growers and consumers who prefer to avoid spraying the vines and grapes.