X. fastidiosa causes Pierce's disease of grapes (Vinis vinifera). Some strains of the pathogen cause bacterial leaf scorch of several woody ornamentals, such as maple (Acer sp.), oak (Quercus sp.), mulberry (Morus sp.), elm (Ulmus sp.) and sycamore (Plantanus sp.). The bacterium also infects citrus, causing the disease called citrus variegated chlorosis. Other diseases caused by this pathogen include phony peach diease, almond scorch and alfalfa dwarf.
Diseases caused by Xylella fastidiosa result in decline and death of infected hosts. The pathogen is spread by several species of sharpshooter leafhoppers. Pierce's disease is a major limiting factor in vineyard production in the southern U.S., and is a serious threat to grape cultivation in California. Bacterial leaf scorch causes significant dieback in shade trees in urban areas.
Xylella diseases occur in Northern America, Central America, northern South America and Taiwan. In the United States, X. fastidiosa is found primarily in southern and mid-Atlantic states, and in California. Bacterial leaf scorch has recently been confirmed in Indiana on sycamore in Tippecanoe County, and on red oak in Hamilton County.