November 2014 Plant Disease Update

Marginal leaf scorch on English oak
Marginal leaf scorch symptoms on English oak (Quercus robur). Notice the yellow band between green and brown tissue that is a very characteristic symptom of bacterial leaf scorch; however, this symptom is not always present. Courtesy of John Hartman, University of Kentucky, Bugwood.org

Symptoms of bacterial leaf scorch usually appear in late summer and progress through the fall. The most characteristic symptom of this disease is marginal leaf scorch. Often a yellow band is evident between brown and green tissue. 

Symptoms of bacterial leaf scorch often appear on only one or two branches before gradually spreading to more branches in subsequent years. Diseased trees may also leaf out later than normal in the spring and leaves may be stunted. The severity of bacterial leaf scorch on an individual tree can vary considerably from year to year. However, trees often gradually decline and lose vigor as defoliation and dieback continue. Eventually the disease may kill the tree. 

Northern Red Oak Bacterial Leaf Scorch Dieback
A northern red oak (Quercus rubra) with significant dieback caused by Xylella fastidiosa, the bacterium that causes bacterial leaf scorch. Courtesy of John Hartman, University of Kentucky, Bugwood.org

Marginal leaf scorch symptoms caused by other factors, such as drought-stress or root disease, are often mistaken for symptoms of bacterial leaf scorch, so laboratory identification of the causal bacterium (Xylella fastidiosa) from affected petiole and leaf tissue is necessary for confirmation of the disease. Bacterial leaf scorch is most often observed on oak, elm, and sycamore; however, many other tree species are susceptible to this disease. The bacterium that causes bacterial leaf scorch colonizes the tree’s water-conducting tissue (xylem) where it disrupts water movement and reduces water availability to the leaves. There are currently no curative controls for bacterial leaf scorch. For more information on this disease refer to the Virginia Cooperative Extension factsheet Bacterial Leaf Scorch of Landscape Trees.