The bacterium is Xylella fastidiosa, which invades the sap-conducting xylem cells, is associated with a leaf scorch of at least five tree species.
Bacterial leaf scorch affects elms and several species in the red and black oak group including northern red oak, Quercus rubra; pin oak, Q. palustirs; scarlet oak,
- coccinea; southern red oak, Q. falcata; laurel oak, Q. laurifolia; shingle oak,
- imbricaria; and the black/water oak, Q. nigra, sycamore, maple, mulberry, plum and citrus are also susceptible.
Bacterial leaf scorch has been observed most often in the mid-Atlantic and southeastern states. However, oak leaf scorch has been seen as far north as New York; affected sycamores are common in Texas; and diseased mulberries have been seen as far west as Nebraska. These diseases have been detected in other regions.
Xylem-feeding leafhoppers transmit X. fastidiosa. In a typical life cycle, marginal leaf scorch symptoms begin to develop in mid-to-late June and increase in severity throughout summer and early fall. Scorch appears as an irregular, scalloped browning along the leaf margin and may be bordered by a yellow halo. As browning spreads toward the mid-vein, leaves may curl and drop early. Symptom severity progresses from older to younger leaves on a branch; newest leaves at the tip sometimes remain unaffected. Symptoms recur each year and spread over the tree’s crown. Chronic infection results in branch dieback, crown decline and death.