Bacterial Leaf Scorch is caused by the bacterium, Xyella Fastidiosa, which colonizes and clogs the tree’s water conducting tissue (xylem). This disrupts water transport in roots, branches, and leaves due to the large amounts of multiplying bacteria and their by-products. The presence of the bacterium in the vascular tissue can only be identified through microscopic or laboratory tests.
Symptoms and Diagnosis
Xyella fastidosa is transmitted to healthy trees by leafhoppers and spittlebugs and possibly other feeding xylem insects or birds. Bacterial Leaf Scorch affects red oak, elm, sycamore, mulberry, maple and sweetgum. Diagnosis can be based on time of symptom development, leaf color change, and the annual progression of the of the disease throughout the tree. Symptoms appear in mid to late summer and on into early fall. Leaf scorch describes the death of tissue along the edge of the leaf. Sometimes called marginal leaf burn, this symptom develops when water needed by the plant cell at the edge of the leaf does not reach those cells in adequate amounts to replace what is lost during transpiration and growth. This occurs in drought conditions, high summer temperatures, soil compaction, root loss, and the fungi or bacteria which invade and plug or destroy the xylem (water conducting vessels) in the plant. This intermediate transition zone appears dull, pale green in color, and has a "water soaked" appearance. Finally the entire leaf dies and turns brown. Symptom development is also hastened during periods of above normal temperatures.
There is no known cure for Bacterial Leaf Scorch and too little information is available on the disease development and spread to recommend an effective control measure. Injecting, disease trees with antibiotics reduces symptom development but cannot eliminate the pathogen, and injections are expensive and must be repeated. In all honestly be prepared to lose the tree in a few years. Tree life, however, may be extended by improving general tree vigor with irrigation, soil amendments and pruning should also be monitored. Branches can be therapeutically pruned well below the leaves, possibly preventing or minimizing the spread of the pathogen in the tree. Remember always sterilize your pruning equipment.