Grapevine Pierce's disease (Xylella fastidiosa) is a bacterial pathogen. It was first detected in Anaheim in 1892.
This disease became a real threat for California's wine industry and overall economy when the Glassy-winged sharpshooter,a vector of the bacterium and native from South East United States, was discovered in the Temecula Valley in California in 1996. When a vine becomes infected, the bacterium causes a gel to form in the xylem tissue of the vine, preventing water from being drawn through the vine. Leaves on vines with Pierce's disease will turn yellow and brown and eventually drop off the vine.