Oaks With Scorched Leaves Likely to Appear in the Next Month

The scorch on oak leaves due to bacterial leaf scorch, in contrast to oak wilt begins at the leaf margins and progresses to the mid vein

The Extension Plant Diagnostic Laboratory receives a large number of landscape tree samples each year in which the primary symptom is leaf scorch. In some cases, weather conditions, root damage, or presence of wilt or canker fungi cannot adequately explain the leaf scorch. In some of the samples, it is suspected that the symptoms are due to the bacterial disease, bacterial leaf scorch. While this bacterial disease occurs in the following species: elm, sycamore, red maple and mulberry, we have only diagnosed the problem thus far in oak. In the past two years, we have diagnosed about nine oaks with this disease. Since a diagnostic test is required for positive confirmation, lack of resources for large scale testing of symptomatic trees has limited our ability to assess how wide spread the problem is in Missouri. Based

The scorch due to oak wilt begins at the leaf tip and works back to the petiole

on the number of oaks coming into the clinic with symptoms of scorch that are not explained by oak wilt, root damage, or weather conditions, we suspect there are a number of trees carrying this disease.

Although symptoms of bacterial leaf scorch vary slightly with species, they typically include late-season (August, September) 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. 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.

If you would like to have your tree tested for this bacterial disease, we will begin collecting samples on August 26 and will submit samples for testing on September 16. The cost for the testing will depend upon the number of samples received. The cost to test one sample is $50.00, but decreases with each additional sample. If a large group of samples is collected, the cost for the test could potentially be under $10.00. Submit several 1/2" to 1" diameter branch sections from symptomatic branches. Where possible, include a picture (digital, Polaroid or 35mm) of the diseased tree and provide a detailed history of the tree. Include a description and history of the symptoms and when they appeared and information on any site disturbances and the species and age of the tree. Since a leaf scorch is a general symptom, be sure to look for and rule out any signs of cankers or insect damage on branches and the trunk before considering a bacterial problem.

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