Sharpshooter discoveries ?in Sonoma, ?Marin counties

Agricultural inspectors in Sonoma County recently found an egg mass and a nymph of the glassy-winged sharpshooter, a grasshopper-like insect associated with a devastating vineyard disease.

But area vineyard managers are not concerned about either the pest or the disease, thanks in part to the aggressive efforts local agricultural authorities have been taking to manage the threat.

The evidence of infestation was found by inspector Travis Howard of the Sonoma County Department of Agriculture in a local shipment of citrus plants from Ventura County. A similar find was reported in Marin County the day before, in a shipment from Santa Barbara County.

The glassy-winged sharpshooter is a well-known vector for Pierce’s disease, a devastating bacterial infection that can quickly destroy a vineyard. Pierce’s disease costs the state’s wine industry $104 million a year, according to a 2014 estimate.

Though the blue-green sharpshooter is endemic to the North Coast, its larger and more hazardous glassy-winged cousin is widely found in Southern California. Sharpshooters are types of leafhoppers, plant feeders that suck sap from grass, shrubs or trees. An adult glassy-winged sharpshooter is only half an inch long, yet still larger than its blue-green counterpart.

The glassy-winged sharpshooter’s appearance in Temecula, Riverside County, led to widespread vineyard devastation there in the mid-1990s, and alerted state agriculture authorities to the menace of the insect, native to the southeastern United States.

Pierce’s disease is spread by both sharpshooter species when they feed on vegetation and injecting a bacterium into the grapevine’s tissue, resulting in the eventual fatal dehydration of the plant. The bacterium, Xylella Fastidiosa, is also found in citrus trees and oleander, both sometimes used in vineyards landscaping.

Tony Linegar, the county’s Agricultural Commissioner, said that when nursery stock is shipped from southern California into other parts of the state, like Sonoma and Marin, they have to ship it with a notice that the shipment must be inspected by the county agriculture department before it is put out for sale.

“When we find an infested shipment basically we make them put it on the truck and take it back to southern California,” said Linegar. “We don’t take any risk at all; we write a notice of rejection for the shipment and we send it back, the whole shipment.”

Pierce’s disease is present in Sonoma county, usually spread by the native blue-green sharpshooter, but it usually erupts in a more manageable scale. The blue-green sharpshooter prefers riparian habitat, so vineyards placed next to streams or creeks are more prone to an outbreak. “If you have a vineyard in close proximity to a riparian area, you potentially could be exposed to Pierce’s disease through the blue-green sharpshooter,” said Linegar.

Steve Sangiacomo agrees. “We’ve never really had any problem with Pierce’s,” he said. “Maybe a few cases along creekbeds that we could take care of, but nothing serious.” Sangiacomo Family Vineyards has 1600 acres of grape vines in the Sonoma Valley.

In June, a consortium of grape growers including the Family Winemakers of California, the California Association of Winegrape Growers and the Wine Institute voted overwhelmingly to continue their assessment on wine grapes to fund research on Pierce’s disease and other pests and diseases that threaten California’s wine grapes. The assessment is currently 75 cents per $1,000 value of wine grapes; it has raised over $32 million since it was implemented in 2001.

That research is focused at least in part on developing disease-resistant vines. Chardonnay and pinot noir vines are especially susceptible to Pierce’s disease, though muscadine vines are resistant to the disease. Rootstock resistance to phylloxera helped dampen several infestations in both Europe and the U.S. over the past century.

The other part of the assessment helps support inspection programs like Sonoma County’s. “It’s actually been a very effective program,” said Linegar of the inspection program, “because we have kept the glassy-winged sharpshooter in check, and kept it from infesting the wine grape regions of northern California.”

Though Linegar is skeptical that there is any way to completely eradicate Pierce’s disease – “the insect is here to stay” – he said containment through inspection programs and research into a “PD-resistant vine” are keys to controlling the infection.

“The growers know there’s a lot of value in this program, and we’ve prevented the (glassy-winged sharp shooter) from becoming established in this part of the state. It’s been going on for years, so we’ve shown what we’re doing works.”

Email Christian at christian.kallen@sonomanews.com.