What is in this article?:
- Water management tops wine grape challenges
- Disease watch
- “No one in the valley has any surplus water this year,” says Mendocino County grape grower Zac Robinson. “We’ll have to get by with whatever we have in our ponds.”
“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.