Bacterial Leaf Scorch
Bacterial Leaf Scorch
By: Karen Rane,
Symptoms of bacterial leaf scorch (BLS), caused by the xylem-inhabiting bacterium Xylella fastidiosa, are developing now on infected trees, especially red oaks. Infected trees develop large sections of foliage with brown margins ("leaf scorch"), often with a yellow or reddish "halo" between the brown and green leaf tissue. Other tree species commonly affected include red maple, sycamore, American elm, mulberry and sweet gum. Initially, symptoms develop on just one or a few branches, but after a few years many branches can be affected. Trees with restricted root zones, such as those planted along streets, often show severe dieback symptoms more quickly than trees without added root stress issues. However, most infected trees develop significant dieback within 7-10 years after symptoms are first observed. The bacterium overwinters in infected trees and weed species (Xylella has a very large host range), and is spread by xylem-feeding leafhoppers. There is no cure for an infected tree. Cultural practices that maintain tree vigor and reduce root stress issues can help slow the pace of symptom development.
Symptoms of BLS can mimic leaf scorch from drought, root damage or other abiotic stress factors; in the UMD Plant Diagnostic Lab we use a serological test to confirm the presence of Xylella in a symptomatic tree. The best sample for diagnosis consists of small branches that have several symptomatic leaves still attached. Check out the UMD Plant Diagnostic Lab website at http://extension.umd.edu/plantdiagnosticlab for sample submission forms and contact information.
Symptoms of bacterial leaf scorch