According to U.C. Davis entomologist Bruce Kirkpatrick, “(the) bacteria Xylella fastidiosa has such a wide plant host range — in agricultural crops, ornamental plants, riparian plants, and many common weeds — I’m certain that there are plants infected with the bacteria in nearly every part of the state.” He further clarified, “The exceptions may be in counties that experience significantly cold winters, i.e., snow is on the ground for a month or so. We know that Xylella fastidiosa, the bacteria that causes Pierce’s disease, is killed in some plants that undergo a severe cold weather dormancy. That’s probably why Pierce’s disease has never been reported in Oregon, Washington, and New York states. In addition, we have never found Pierce’s disease in Sierra foothill vineyards above 2,000 or 3,000 feet. However, for all the rest of the state (California) where grapes are grown, I’m sure that the bacteria and GWSS can overwinter quite nicely.”
A vector, like the GWSS, which taps into an infected plant, spreads the bacterium from plant to plant. Xylella fastidiosa is able to hold fast to the inside surfaces of the insects’ throat. While the GWSS dines on the watery sap in the plants’ xylem, the Xylella fastidiosa is transmitted directly into the new plant where they “move around in the xylem of the grapevine,” says Alexander Purcell, a U.C. Berkeley entomologist.
The groundbreaking Genome Project, in August, 1997, stated that “Xylella fastidiosa is the casual agent of many economically important plant diseases including Pierce’s disease in grapevine (PD), alfalfa dwarf, phony peach disease (PPD), periwinkle wilt (PW), leaf scorch of plum, mulberry, pear, almond, elm, sycamore, oak, maple, coffee, and citrus variegated chlorosis (CVC).”