The spring rains that brought welcome relief from the drought last year also set the stage for an outbreak of a bacterial disease that is killing grapevines in Northern California's famed wine country. Pierce's disease is plugging up water-carrying vessels in vine trunks, causing sudden scalding or drying of leaves, shrivelling of fruit and almost certain vine death, according to Andrew Walker, assistant professor of viticulture at UC Davis. A winged, leaf hopper-like insect known as a sharpshooter spreads the disease as the insect migrates from streamside vegetation or home landscaping into the vineyard. Walker estimates that several hundred acres, or approximately 5 percent of the North Coast vineyard acreage, has been affected so far. "It's an isolated problem, because the disease doesn't spread rapidly," he says. "But in areas where the disease is present, you simply can't grow grapevines." He advises vineyard managers to avoid planting in areas vulnerable to the sharpshooter.