Bacterial Leaf Scorch

Browning of leaf margins (leaf scorch) occurs in mid- to late summer. In elm, some oaks, and mulberry, a yellow margin sometimes develops between scorched leaf margins and healthy green inner leaf tissue. In sycamore and oak, the interior edge of symptomatic leaf tissue often is red-brown. Severely scorched oak and mulberry leaves drop earlier than healthy leaves. In sycamore, symptomatic leaves curl upward but remain attached. Initially a single branch develops leaf scorch symptoms. Symptoms recur each year, with an increase in the number of branches affected. Growth reduction and dieback of affected branches occurs in severely affected trees. No discoloration is visible in the wood of symptomatic branches, in contrast to fungal vascular wilt diseases such as oak wilt or Dutch elm disease. Symptoms of bacterial leaf scorch may resemble those caused by noninfectious disorders such as drought stress or wind desiccation. Confirmation of bacterial leaf scorch involves a serological test performed on petioles of scorched leaves.