Oak Trees Threatened by Bacterial Leaf Scorch

Tree lovers recall with sadness the loss of the American Elm to Dutch Elm Disease and the American Chestnut to Chestnut Blight. Now another very destructive disease is threatening another popular tree- the Red and Pin Oaks.

The disease, called bacterial leaf scorch, is caused by a bacterium called Xyllela fastidiosa, which is spread from plant to plant by a group of insects known as leaf hoppers.

The bacteria reside in the water conducting vessels of the tree, and as their numbers increase they physically block the flow of water upward from the roots, causing the leaves to turn brown prematurely. Within a five-year period, the disease will kill the tree if left untreated. In summer, the foliage of an entire canopy can look like that pictured right. Presently, this disease cannot be eradicated with current chemicals and management practices in use. Infected trees can be injected with an antibiotic (oxytetracycline) which will suppress the symptoms for one year. Trees must be re-injected yearly or the symptoms will reoccur. Regular fertilization, irrigation, and mulching of Red and Pin Oaks is also recommended. We also believe it is appropriate to try and suppress the leaf hopper insects that transmit the disease.

Since these two varieties of oak constitute approximately 10 percent of all trees in the Philadelphia area, this disease is particularly ominous. Right now, our only hope in saving these trees lies in the research community, which has yet to come up with a cure. Meanwhile, you can rely on us to do our best to keep the trees alive.

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