On April 1, Mendocino County wine grape grower Zac Robinson was feeling more upbeat about the prospects for his 2014 crop than he was two months earlier. Since then, the rain has returned to his Anderson Valley vineyards. That includes a total of about 3 inches that fell just in the last six days of March.
“In terms of water supply, we started the year in a dire place and things have gotten better,” he says. “We’re probably out of the range of unprecedented drought and into a severe drought.”
Robinson and Amanda Robinson Holstine, representing the third generation of their family to grow wine grapes, are co-owners of Husch Vineyards. Planted in the late 1960s on ground formerly used to grow apples and grapes, the vineyard’s 30 acres of Chardonnay, Pinot Noir and Gewurtztraminer include some of the earliest varietal plantings on the valley floor.
Storage ponds provide much the water for his vines. This year, for the first time since the late 1970s, he started the season with the ponds less than full. Normally, any extra water needed through the season is provided by the area’s rivers and creeks. But, they’re expected to run dry this summer,
“No one in the valley has any surplus water this year,” he says. “We’ll have to get by with whatever we have in our ponds.”
Of more immediate concern for Robinson is availability of water for frost protection. Bud break started in his Chardonnay in mid-March, about 10 days earlier than usual. Soon after that, buds were opening on the Pinot Noir and Gewurztraminer. By the start of April, shoots had pushed out about 2 inches.
“Starting the season early like this, without full ponds, makes us extra nervous about frost protection,” Robinson says.
Typically, frost remains a risk in this area until about May 15.
So far, he hasn’t had to run his sprinklers much to defend against freezing temperatures. “At some point, it’s likely that the water we use for frost protection will cut into the amount available for irrigation,” Robinson says. “Then, we’ll have to make some hard choices. But, we’ll cross that bridge, if and when we come to it. Water management will be our biggest challenge this year.”
Fortunately, he recently finished a three-year project to add a second drip line to his vineyards that will reduce his water needs, while improving crop quality. This extra line will be used to irrigate only his stronger vines in a given row. Meanwhile, the original drip line will target just the weaker sections.
“This way I can provide water only to areas where it’s actually needed at the time,” he explains. “I won’t have to turn on water for the stronger vines until they need it, which may another four or five weeks later than the weaker vines. Also, because every vine gets the correct amount of water, this system should improve quality of the fruit.”
Dry weather for much of the winter allowed his crews to finish pruning the vines by mid-February. Now, field work is focusing on timing and application of sulfur sprays to stay on top of any powdery mildew threat.
Following identification of red blotch in his vineyards for the first time last year, he’ll be keeping an especially close eye on the disease this season.
“It definitely caught our attention,” he says. “We saw symptoms of delayed ripening, including reduced Brix readings in several fields and submitted samples for lab testing. Results came back positive for red blotch.”
The disease, which has been found in several wine grape-producing states, was first observed in California in 2008. In fact, scientists suspect that red blotch disease is widespread wherever grapes are grown.
Some symptoms of the disease — discoloration of grape leaves in the fall and reduced sugar levels in the fruit — are similar to those of leaf roll disease. In some cases, researchers report, it’s likely that the virus associated with red blotch, GRBaV, was the actual cause of loss in grape quality originally blamed on leaf roll disease viruses.
Research is underway to determine just how much of a threat the red blotch virus poses to grape growers. Some strains of red blotch-associated virus appear to be more detrimental than others. Like any viral disease, there is no cure for red blotch. The only way to prevent the disease is to use virus-free grapevine nursery stock when planting a new vineyard or when replacing infected vines in an existing vineyard.
Because the affected vines in Robinson’s vineyard have been in the ground since the 1990s, he’s assuming the vines already contained the GRBaV virus when he purchased them from a nursery.
“If that’s the case and we didn’t notice any symptoms until last year, we’re not too worried about the disease at this time,” he says.