Mark Houser saw something in late May and the first part of June he hadn’t seen in 30 years of grape growing grapes — his seven acres of Pinot Noir looked like they were covered with yellow flowers.
“The vines should have been green,” says Houser, who manages grape production at Hoot Owl Creek Vineyards and Alexander Valley Vineyards, Healdsburg, Calif. “But, at bloom Suddenly the tops were a bronzy, yellow color.”
It was caused by new growth of leaves on tops of the shoots, replacing those that had died from an unexplained malady that appeared not only in his area of Sonoma County, Alexander Valley, but also in the Carneros Region and Russian River Valley.
“The top five or six leaves were fried off in about five to seven days,” Houser says. “Ten to 12 days later, the shoots pushed out new leaves. It was a pretty uniform symptom on just about every vine down the row. By the end of June, the vines looked normal.”
No other varietals in his or other affected vineyards in the county exhibited this dieback.
“It was quite specific to Pinot Noir,” he says. “In fact, the two Zinfandel vines in the middle of that block showed no symptoms.” It also affected other Pinot relatives to some extent, including Pinot Munier and Pinot Blanc. But, the symptoms varied among the Pinot Noir clones. In his case, the 115, 777 and Pommard clones seemed to lose more leaves than 2A.
It’s doubtful that this dieback is a new disease or the signs of a new invasive pest, observers say. Houser, for one, suspects it was related to unusually heavy rainfall in May. “We had five to six inches of rain — every two or three days, it was raining.”
Nick Frey, president of the Sonoma Wine Grape Commission, says this isn’t the first year the condition has affected the county’s Pinot Noir.
“We’ve had it every year for the last two or three years. It’s not nearly as likely to occur if spring weather is dry and warm. This dieback is a physiological symptom; we don’t know if it’s due to cool temperatures, high rainfall or a combination. Samples have been sent for laboratory analysis to determine if a metabolite is accumulating in Pinot Noir.”
Whatever the cause, Houser doubts the condition will hurt production this year.
“It will make for some odd looking vines but I don’t expect it to adversely affect yield or quality,” he says. “New leaves came out; the fruit didn’t fall off; the vines didn’t die; and the bunch count looks normal. But, because it may result in more leaves or laterals, we may have to spend an extra $50 per acre to open up the canopies and get good circulation in the vines.”