Expansion of the range of Pierce’s disease in Virginia
Pierce’s disease (PD) is a vascular disease of grapes caused by the bacterium Xylella fastidiosa Wells et al. and vectored by xylem-feeding sharpshooters (1). Symptoms of PD occur when bacteria proliferate the xylem; both the bacteria (2) and host responses to infection (3) block the flow of xylem fluid to the shoots. Affected grapevines show interveinal chlorosis, marginal necrosis with marginal yellow or red line (Figs. 1 and 2), green islands on shoot bark after normal tissue turns brown, and leaf abscission from the distal end of petioles, leaving characteristic "matchstick petioles" with necrotic tips (Fig. 3). Infection leads to vine decline, yield loss, and, within two to three years, vine death. Although the northern distribution of X. fastidiosa [* see Erratum] extends at least into New Jersey, observations of PD have been limited to vineyards on the Delmarva Peninsula and extreme southeastern Virginia; interior Virginia was considered at low risk of PD because of its low winter temperatures (lethal to the bacteria), based on the results of past research that showed lower pathogen populations in plants grown at low temperatures in a growth chamber (4). Recent warm winters have, however, increased our concerns about vulnerability of other Virginia vineyards to PD. Our objective was to conduct a state-wide survey of Virginia’s vineyards for presence of X. fastidiosa.