Bacterial Leaf Scorch is caused by a vascular clogging bacterium Xylella fastidiosa that multiplies rapidly in the active plant xylem. Bacterial Leaf Scorch is a chronic and eventually fatal disease that displays its most noticeable symptoms in the late summer/early fall. These symptoms include premature leaf browning, marginal necrosis, and defoliation. Distinct scorch-like leaf symptoms are followed by twig and branch death. The following year the trees leaf out normally but leaves on a few more branches turn prematurely brown in late summer. This is repeated over a period of years until the entire tree is affected and death occurs. BLS is known to occur on several species of Oak & Maple, dogwood, elms, planetrees and sweetgum.
Elm leaves showing BLS symptoms
Sweetgum leaf showing BLS symptom
The Bacterial Leaf Scorch bacterium can be spread from a diseased plant to a healthy plant by the feeding of common xylem-feeding insects such as leafhoppers and treehoppers. The bacterium is also believed to be present in some symptomless shrubs, grasses and weeds in the landscape. The leafhoppers and treehoppers may be obtaining the bacterium from other hosts rather than from tree to tree.
Leafhopper
Treehopper
There is no known cure for bacterial leaf scorch. There have been some studies done through the University of Kentucky by John Hartman, but various treatments didn’t seem too promising. Some of the various management practices to extend the longevity of mature specimen trees already infected include reduction of water stress by proper mulching and watering and managing secondary insects and diseases.
Bacterial Leaf Scorch can be confused with other disorders, it is best to have the suspect tree tested by collecting samples for analysis. For Ohio, the tree may exhibit the highest degree of symptoms in late summer through September. This will vary depending on weather, location and possible overall health of the tree.
BLS symptoms on Ginkgo
photo by J. Hartman
BLS symptoms on sycamore
photo by J. Hartman
Pin Oak leaves showing BLS symptoms
In 2010, the Ohio Division of Forestry performed a preliminary survey involving city foresters looking for symptomatic trees. The survey resulted in the submission of 61 samples throughout the state. All these samples were examined using standardized laboratory testing. Of the 61 submissions, there were 8 positive samples for Bacterial leaf scorch.
Click here to see a map showing the distribution of samples and the positive sample sites.