Deadly Infection Threatens Penn State U. Elm Trees

More than 15 percent of the 287 landmark elm trees on Pennsylvania State University’s University Park campus have contracted elm yellows, a deadly bacterial infection for which no cure is known. Some of the 47 infected trees are being removed this winter, according to The Daily Collegian, the university’s student newspaper.

Elm yellows, or elm phloem necrosis, infects the trees’ roots and phloem, the layer of living cells beneath the bark that carries nutrients to the leaves. A frequently-asked-questions Web page that the university created says that “research on elm yellows is relatively sparse, and little is known with absolute certainty,” but that the disease is believed to kill all the trees it infects, usually within a year or two.

Mike Bezilla, a spokesman for the university, told The Daily Collegian that the university had lost a “sizable” number of elm trees to Dutch elm disease since the late 1960s. But he said that “with Dutch elm, you can stop the spread—we can’t even control elm yellows at this point.” The disease is believed to be spread from tree to tree by tiny insects called elm leafhoppers, which live only on elm trees.

The first big planting of elm trees on the university campus came in the 1890s, Mr. Bezilla said, with another round of planting in the 1920s. Some of the trees are as tall as 115 feet, and some spread over an area as wide as 100 feet. The university plans to save the wood from trees it cuts down.