The glassy-winged sharpshooter can wreck a vineyard

While the Season Is Young, Sharpshooters Have Already Been Found Twice in Imported Plants "We are concerned," said John Hibble, Executive Director of the Santa Cruz Mountains Winegrowers Association. "To import a pest that has  that potential for tremendous damage to the industry is very scary." 

There are an estimated 500 acres of commercial wine vineyards in Santa Cruz County. The 2,000 tons of grapes harvested from local vines every year can produce up to 120,000 cases of wine. Sale prices vary widely, but the annual value of local wines is estimated at $12 million to $20 million. Monterey County's wine industry is much larger. There are 40,000 acres of wine grapes in Monterey County, worth an estimated $200 million. 

Smaller Sharpshooter is Native to Santa Cruz 

bdvineyardnews The makings of a Pierce's disease outbreak are always present in the Santa Cruz Mountains. Much of the vines in Santa Cruz County grow within a stone's throw of wild plants such as French broom and raspberry that harbor Pierce's disease without showing symptoms. And an endemic species of sharpshooter, the blue-green sharpshooter, is always present in Santa Cruz County.  

But the invasive glassy-winged sharpshooter is the one that really gives vineyard owners the nervous jitters. It is much larger, travels farther, and is active for more of the growing season.  "The blue-green [sharpshooter] can only feed on the very young plant, so the timeframe in which it can infect plants is much shorter," explained Barry Jackson of Equinox, a respected champagne producer in Santa Cruz. Jackson serves as a liaison between winegrowers and the Ag Commissioner's prevention  program.  He said the inspection program, along with mitigation measures in Southern California, has helped to prevent a major incursion of the big sharpshooters. Jackson also credits nursery operators since "they bear the brunt of the inspections." 

Local Vineyards Devastated in Early 1990s 

In the early 1990s, a slew of vineyards in Santa Cruz County were hit hard by Pierce's disease. At David Bruce Winery in Los Gatos, an entire estate of 30-year-old vines was destroyed. "If you have a vineyard that has been affected by Pierce's disease, you are in an ongoing mitigation," Jackson said. "You have to take that plant out and the surrounding plants out and burn them." For some, replanting is successful. Former UCSC Chancellor Dean McHenry's four-acre vineyard in Bonny Doon was devastated by Pierce's disease in 1994. But the vines have been replanted and the winery has since recovered. 

Others choose to move on. Next door to McHenry, Randall Grahm's Bonny Doon Winery was ravaged the same year. Grahm chose to sell the 32-acre property and shift grape production to Soledad, where the terrain includes fewer riparian corridors that serve as sharpshooter breeding grounds. Grahm recalls the battle with Pierce's disease as a sort of "biblical plague." And it didn't take the glassy-winged sharpshooter to kill his vines.  "We got wiped out by the wimpy sharpshooter," he said. But Grahm is relatively unfazed by reports that sharpshooters have appeared in Santa Cruz County.  "The problem with worrying about Pierce's disease is it's sort of like worrying about avian flu. You don't know enough to be really knowledgeably worried," he said.  

As a result, Grahm is not convinced that the inspection regimen and restrictions on imported plants are effective. Around the time that his Bonny Doon vineyard was struck with Pierce's disease, researchers at UC Berkeley discovered that local sharpshooters reproduce on the vines, rather than in adjacent habitat. Grahm thinks there may be other hidden mechanisms at work that put the disease on a 10 or 12-year cycle. If that's the case, Santa Cruz County could be due for a serious outbreak.  

But prevention is difficult. Since pesticides also kill spiders and wasps that feed on sharpshooters, Grahm tries to prevent outbreaks by fostering healthy vines, and using biodynamic compost to boost their immune systems. Jackson said that clearing brush adjacent to vineyards and planting barrier plants that sharpshooters don't feed on can help as well.  "Viticulturists who are aware of the problem are keeping an eye on it," Jackson said. "They are in an ongoing battle with [the pest]."