As it moves through California, the new pest known as glassy-winged sharpshooter (GWSS) may significantly increase the spread of plant diseases caused by the bacterium Xylella fastidiosa. The bacterium causes Pierce's disease of grapevines, almond leaf scorch and the newly recognized oleander leaf scorch disease. Currently, almond leaf scorch is a minor problem for California's almonds, but if GWSS becomes established in significant numbers in or near almond orchards, it might increase the incidence of almond leaf scorch. Our studies show that GWSS and two other sharpshooter species can transmit X. fastidiosa from diseased oleanders to healthy oleanders. GWSS also can transmit Pierce's disease strains of the bacterium from grapevine to grapevine and to almond trees. The oleander strain of the bacterium did not infect grapevines, but the ability of GWSS to transmit Pierce's disease strains may increase the spread of this lethal grapevine disease in vineyards bordering citrus orchards or other habitats where invading GWSS may establish permanent populations. Posted 27 December 2000.