California Department of Food and Agricu

Pierce's Disease (PD)

Pierce’s disease (PD) has affected grape production for as long as commercial vineyards have been present in California. Caused by a strain of the bacterium Xylella fastidiosa (Xf), PD causes progressive leaf scorch, desiccation of fruit, defoliation and vine death. All conventional cultivars of Vitis vinifera are considered susceptible to Xf, but there are some differences in symptom expression among cultivars.

The disease has caused sizable losses in California viticulture in the past, but the damage occurred primarily in traditional “hot spot” areas. For example, in coastal areas of California the native blue-green sharpshooter can infect grapevines with Xf. The situation changed dramatically with the arrival of the glassy-winged sharpshooter (GWSS) in the 1990s
in Southern California, which can spread PD to traditionally safe-growing regions.

There is currently no known cure for PD, but extensive research efforts led by the PD/GWSS Board have delivered many potential solutions that are already undergoing field trials. Promising results from these field trials may lead to commercial applications that could ease the statewide threat of PD.

Research Highlights for PD/GWSS

  • Addressing knowledge gaps in PD and GWSS

  • Evaluating various approaches for making winegrapes PD-resistant

  • Testing wine made from PD-resistant winegrapes

  • Protecting grapevines through various biological control techniques

  • Investigating and managing GWSS insecticide resistance

Grapevine showing symptoms of Pierce's disease

Map of PD and GWSS in California