Pierce's disease is a lethal bacterial disease of grapevine caused by the bacterium Xylella fastidiosa. The bacteria are spread by insects belonging to the family of sharpshooter and spittlebug. The disease has the potential to cause millions of dollars of damage to California's multi-billion dollar grape and wine industry. The bacteria also cause alfalfa dwarf disease, almond leaf scorch, phony peach disease and leaf scorch diseases in oak, elm, maple, mulberry, plum and sycamore. If the South American Citrus Variegated Chlorosis strain gets introduced into California, citrus losses are estimated to reach $5 billion. This project will develop a cost-effective assay that can be used for the early detection of the presence of X. fastidosa in grapevine leaves and other neighboring plant species that may act as a reservoir to spread the disease. The assay will be easy-to-use by grape growers to enable on site monitoring of their fields. When infestations are found, then insecticides can be sprayed to kill the insect vectors, and the contaminated vines and neighboring plant disease reservoirs can be destroyed to stop the spread of the disease. The assay may also be used by plant inspection agencies to prevent the importation of infected plants. ANTICIPATED RESULTS & POTENTIAL COMMERCIAL APPLICATIONS OF RESEARCH The developed assay will be used for the early detection of the presence of X. fastidosa in grapevine leaves and other neighboring plant species that may act as a reservoir to spread the disease. The assay will be easy-to-use by grape growers to enable on site monitoring of their fields. When infestations are found, then insecticides can be sprayed to kill the insect vectors, and the contaminated vines and neighboring plant disease reservoirs can be destroyed to stop the spread of the disease. The assay may also be used by plant inspection agencies to prevent the importation of infected plants.