Bacterial leaf scorch (BLS) is an infectious plant disease caused by a bacterium, Xylella fastidiosa. The pathogen is systemic, living in the xylem. The most frequent U.S. hosts include elm, oak, sycamore, mulberry, sweetgum, sugar maple, and red maple. In Illinois, we have identified the problem on oak. At the U of I Plant Clinic, it has been confirmed it on pin, red, shingle, bur, and white oaks. Kentucky reports BLS on pin, red, scarlet, bur, white, willow, and shingle oaks; silver, sugar, and red maples; sweetgum, sycamore, planetree, hackberry, American elm, and red mulberry. Look for scorch symptoms that occur in early summer to midsummer, intensifying in late summer. The scorched leaf edges or tissue between veins may be bordered by a yellow or reddish brown color, but not in all cases. Symptoms occur first on one branch or section of branches and slowly spread in the tree from year to year. It is one of those situations that you hope will be better but the situation gets worse. On local pin oaks, it seems the bottom branches die each year.

There is no cure. Some have tried injections with oxytetracycline, but none have shown more than disease suppression with this antibiotic. This suppression has been more common in the southern states rather than the Midwest. Because the pathogen is in the xylem, cleaning pruning tools before moving to another tree is important to reduce spread of the disease. Xylem-feeding leafhoppers and spittlebugs are thought to spread the bacterium in landscape trees. It can also be transmitted between trees through root grafts.