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Picture of the Week
for 6 October 2000

Bacterial Leaf Scorch

Bacterial Scorch Bacterial Scorch Bacterial Scorch
Bacterial Scorch on Pin Oak

(Click on small photo to see larger image. Photos by Jim Peter.)

Bacterial leaf scorch was recently confirmed from a pin oak sample from Dubois County. Most of you are probably not familiar with this disease.

Below is some info about the disease from the University of Kentucky by John Hartman: Kentucky Pest News (September 22, 1997).

Symptoms of bacterial leaf scorch are now becoming noticeable from a distance, especially on street-side pin oaks statewide. Affected pin oaks show premature browning of the foliage and premature leaf fall. Healthy trees nearby are still green and have begun to drop their leaves. These contrasting conditions will be quite visible for the next several weeks, until the leaves of healthy trees also begin to turn their normal brown color and drop.

Leaves of diseased trees show symptoms of scorch, in which the leaf tissue between the veins and at the edges of the leaves turns brown while the leaf tissue nearest the veins remains green. Some of the fallen leaves still show the near-veinal green color pattern. The premature browning of affected trees is repeated each year and after several years affected trees begin to show symptoms of twig and branch dieback.

The causal agent, Xylella fastidiosa, a xylem inhabiting bacterium, is thought to be transmitted from tree to tree by xylem-feeding leafhoppers. Since the disease seems to spread slowly from one tree to another, the insects may not be very efficient carriers of the disease. In any case, once inside, the bacteria grow systemically and are probably impossible to control with the technology we have now.

Finally, after many years, affected trees decline and die. Bacterial leaf scorch appears to affect mainly older trees, but young trees can also die from this disease. If a tree is showing bacterial leaf scorch symptoms, be prepared to lose it a few years hence. Plant another tree nearby as a future replacement.

Plant Pathology Fact Sheet: Bacterial Leaf Scorch - University of Kentucky, John Hartman (pdf file)

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The Plant & Pest Diagnostic Laboratory at Purdue University.