The Time to Test for Bacterial Leaf Scorch is Now!

Some of the scorch showing up on trees may be weather induced. Also, root damage or presence of wilt or canker fungi can cause a leaf scorch. However, one disease to consider is bacterial leaf scorch, the symptoms of which are best evident during late summer (August and September). While this disease affects many trees, we have detected it most commonly in oaks.

Although symptoms of bacterial leaf scorch vary slightly with each species, they typically include late-season marginal leaf scorch that begins on the older leaves and moves toward leaves at the branch tip. In most, but not all tree species, browned, dead areas of the leaf are separated from green tissue by a narrow yellow border. On oaks, this scorch may be mistaken for the scorch created by oak wilt. With oak wilt, however, the apical part of the leaf scorches uniformly; whereas, with bacterial leaf scorch, the scorch develops from the leaf edges and works toward the mid-vein. In some tree species, scorched leaves will abscise early. Leaves on severely affected branches will appear normal in the spring but later show symptoms. For some species such as oak, branch dieback and decline over several seasons is common. To an untrained eye, these symptoms may be mistaken for those produced by vascular wilt diseases, oak wilt and Dutch elm disease. The difference in most instances is that the scorch and decline occurs over several seasons rather than occurring over a period of two or three months.

The best time to test for the presence of this bacterium is in late summer or early fall, when the bacterium titer is the highest. If you feel that you have a tree with these symptoms, the MU Extension Plant Diagnostic Clinic can perform the test for a fee of $25.00. For more information regarding this disease, see the following Website at http://agebb.missouri.edu/pdc/trees/oak.htm or contact the clinic.

Laura Kabrick, Extension Assistant, Plant Diagnostic Clinic, UMC (573)882-3019