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December 03, 2008, 01:38 PM ET
Bacteria Lead to Browning Leaves and Dying Oaks at Saint Joseph's U.
Bacterial leaf-scorch disease, which turns leaves brown as it kills the trees, has affected 40 percent of the oaks at Saint Joseph’s U. (Photos courtesy Saint Joseph’s U.)
Our recent blog about dying elm trees at Pennsylvania State University was one of the most popular items on Buildings & Grounds recently. Well, if you want depressing news about Pennsylvania trees, we can deliver more.
After the elm-tree blog ran, we heard from Saint Joseph’s University, in Philadelphia. Officials there said that the oaks on the campus have been hit by Xylella fastidiosa, more commonly known as bacterial leaf-scorch disease. The pathogen, which attacks arboretums, forests, and orchards all over the world, is spread through leafhoppers.
According to research by Susan Jackson, an adjunct professor in the biology department at Saint Joseph’s, about 40 percent of the oaks on the campus have been infected by the disease, which blocks the xylem, or the vascular tissue that carries water through the plant. Starved of water, the leaves turn brown, and the trees usually die within 10 years. There are no antibiotic treatments.
Pennsylvania and other Eastern states have also been hit by the emerald ash borer, an invasive Asian species whose larvae feed on the soft tissues of the trees, under the bark. Forestry experts estimate that the ash borer has killed about 20 million trees and may wipe out Pennsylvania’s ash population within 12 years.
At this rate, we’ll be left with forests of tenacious invasive species, like bamboo and Ailanthus altissima — or the “tree of heaven” — which leaches plant-killing poison and has a flower with a rather shocking fragrance. —Scott Carlson
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