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Bacterial Scorch Update

October 30, 2002

Bacterial scorch (BLS) is a disease that slowly spreads within a tree, branch by branch, until the tree dies. Scorch symptoms from this disease are similar to environmental scorch, with several exceptions. With BLS, often there is a slight yellow margin between the brown (scorched) tissue and the green tissue of infected leaves. The disease causes branch-by-branch scorching rather than a more uniform pattern seen with environmental scorch. In addition, BLS usually appears in July or August, while environmental scorch usually shows in the spring or early summer. Of course, these times vary with the weather and other stress. Trees infected with BLS produce green leaves the next spring; but by the following July or August, scorching returns. Each year, the symptoms spread a bit, ending in tree death in 3 to 6 years. Environmental scorch does not kill trees.

In issue 13 of this newsletter, we reported BLS on pin and shingle oaks. It has since been confirmed on bur oak in the state. At a recent meeting of diagnosticians, I learned that Kentucky plant-disease specialists have confirmed BLS on many other species in their state. This seemed pertinent to us because of geographical proximity. Kentucky reports BLS on pin, red, scarlet, bur, white, willow, and shingle oaks; silver, sugar, and red maples; sweetgum, sycamore, planetree, hackberry, American elm, and red mulberry. If you have seen progressive scorching on these trees, consider BLS as a possibility. Details on sampling and testing procedures, as well as management options, are provided in issue 13. Fortunately, BLS appears to spread slowly and may not move from oak to oak. Still, this disease is one to know if you work in tree care.

Author: Nancy Pataky


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