The xylem-limited bacterium Xylella fastidiosa, first associated with Pierce's disease of grapevines and alfalfa dwarf disease in 1973 (4) continues to be an economically important pathogen of several commercial crops. It also causes bacterial leaf scorch in urban shade trees such as sycamore, oaks, maples, mulberry, and elm (5). The usual course of action, in an effort to control the spread of this pathogen by insect vectors (9), is to prune out infected branches and vines or to rogue infected plants. Therefore, timely testing of suspect hosts is important.