Bacterial Leaf Scorch of Shade Trees.

Abstract

Bacterial leaf scorch (BLS) affects many different shade tree species such as American elm, red maple, sweet gum, sycamore and London plane, and a number of species of oak (Fig. 1) (Table 1) (11,13,20,34,35). The disease has been identified in the urban forest (landscapes, street plantings, and small woodlots) throughout the eastern United States and as far west as Texas. BLS is one of a group of diseases caused by Xylella fastidiosa. This bacterial pathogen is distributed throughout the Western Hemisphere, has a very wide host range, and causes diseases with two basic types of symptomology (leaf scorch or stunt) in a number of economically important hosts (Table 2). X. fastidiosa also resides in alternative hosts, many of them common landscape ornamentals and weeds, where no discernible symptoms of disease may occur (Table 3) (19). As its name suggests, X. fastidiosa lives in the xylem tissues of host plants, and the bacterium is transmitted (or vectored) by insects that feed on xylem fluid, such as leafhoppers or sharpshooters (17). Fig. 1. Bacterial leaf scorch of oak (Quercus rubra). Look for a pronounced marginal discoloration with a dull red or yellow halo between scorched and green tissues. (Courtesy A. B. Gould)