University Park, Pa. — As Penn State continues to battle several diseases affecting its landmark American elm trees on the University Park campus, the University will begin the removal of nine more affected trees from campus.
"It is unfortunately necessary to remove infected trees, which pose a significant risk to the healthy ones," said Jeff Dice, supervisor of grounds maintenance. "In some cases, deterioration of the infected trees has been rapid. Once infected, they cannot recover and the disease can spread from tree to tree."
The two devastating diseases now facing one of the nation's oldest elm stands are Dutch elm disease, a fungal disease spread by the elm bark beetle and a more recent syndrome known as elm yellows. Dutch elm disease has devastated native populations of elms for decades and native trees have not had the opportunity to evolve resistance to it. Elm yellows, a bacteria-like organism spread by a tiny insect called the whitebanded elm leafhopper, infects the tree's root cells and the inner bark that carries nutrients to all parts of the tree. An infected tree cannot receive adequate nourishment and, by the end of summer, the tree's leaves turn yellow and the tree dies. Elm yellows has devastated trees in 22 states.
"This is a pivotal time right now and our crews are working very hard to hold off the disease," Dice said. "We need to be aggressive in removing the infected trees now, because this could really go either way."
He added that local residents and municipalities can help the situation by having their own infected trees removed to help prevent further spread of the elm diseases in the community.
Though the University has been aggressive in taking action to stop the spread, the lack of a definitive elm yellows treatment and the susceptibility of elms to the disease make it a difficult task.
For more on elm yellows and efforts to control its spread, the University has created an interactive website for information and discussion at http://elmyellows.psu.edu.
Six of the trees to be removed have been confirmed or are suspected to have elm yellows; two more have Dutch elm and yet another has both. Dutch elm has threatened trees in the region for more than 50 years.
The process began Thursday (Aug. 19) with the removal of an elm with advanced elm yellows symptoms next to Henderson North and west of the Peace Garden on campus.
Other trees to be removed are at: Old Main parking lot (Dutch elm); corner of West College Avenue and North Atherton Street (elm yellows); Patterson Building (elm yellows); Borland Building (elm yellows); Dairy Farm House north of Park Avenue (elm yellows); west of Sigma Nu fraternity on North Burrowes Street (Dutch elm disease); intersection of College Avenue and Pugh Street (Dutch elm and elm yellows); and between Electrical Engineering West and Hintz Family Alumni Center (elm yellows).
The University has been battling Dutch elm disease for years, with an organized effort in place since 1990. Penn State first identified elm yellows in a handful of the campus' approximately 290 elms in 2007. To date, including the upcoming removals, the University has removed 82 elms because of elm yellows or Dutch elm since 2007.
Those removed will eventually be replaced by a diversity of species with higher known disease resistance.