Tests show elm yellows disease still threatens campus trees

November 06, 2008

University Park, Pa. — The American elm trees on Penn State's University Park campus face a battle for their lives. Recent tests have detected elm yellows disease, a deadly bacteria-like infection for which there is no known cure, in 47 of the campus' approximately 290 elms, according to Bill Mahon, vice president of University Relations.

University experts first identified elm yellows in a handful of campus elms last fall.

"Test results show that elm yellows is progressing a bit more slowly than we had initially feared, but the situation is still serious." Mahon said. "There is no known way to absolutely halt the spread of the disease from tree to tree, or to cure trees that have become infected.

"Office of Physical Plant tree personnel are working with faculty experts in plant pathology and entomology to combat elm yellows, but we are definitely going to lose some trees in the short term, and the long-term outlook is uncertain."

The campus elms are among Penn State's most treasured landmarks and include one of the nation's largest stands of mature elms. The oldest trees date from the 1890s, reaching 115 feet in height and 100 feet across.

"The elms as an iconic symbol of Penn State are nearly as recognizable as Old Main and the Nittany Lion shrine," said Gordon Turow, director of campus planning and design. "The University is absolutely committed to their protection, and we will work vigorously to combat the elm yellows threat no matter how inevitable the outcome might seem."

Previous research nationwide has identified a tiny insect, the elm leafhopper, as a carrier of elm yellows. The leafhopper transports a bacteria-like organism that infects root cells and the phloem, or inner bark, preventing the tree from getting proper nutrition. Infected trees typically die within a year or so of malnutrition.

After elm yellows was discovered in the State College area, Penn State arborists deployed traps to detect leafhoppers, while plant pathologists developed a technique of sampling trees' DNA to confirm the presence of infection.

Trees having elm yellows have been removed along Schreyer Lane north of Park Avenue, where the infection is most concentrated, and several more will be removed from central campus.

However, not all infected trees will be removed, at least in the near term.  As an experiment, the University will inject a sampling of infected and healthy trees with a fluid analogous to an antibiotic. The goal is to see if the treatment can slow down the spread of elm yellows or protect uninfected trees.

The treatment is strictly an experimental procedure, and is not based on any previous data that has a promise of success.

The University also will continue to monitor the elms for indications of elm yellows and the presence of other leafhoppers, and will remove diseased trees in certain campus areas. No tree will be removed unless multiple tests have confirmed the presence of elm yellows.

Elms that have been removed will be replaced by other species of trees having higher known disease resistance while still offering the majestic canopies associated with elms.

The University has created an interactive Web site at http://elmyellows.psu.edu to keep the Penn State community informed about ongoing efforts to understand issues relating to elm yellows and the campus elms, and facilitate public discussion of these issues.


(Media Contacts)

Last Updated November 23, 2009