University Park, Pa. -- Penn State staff and researchers have battled aggressively for years the two primary diseases threatening the landmark American elm stand on the University Park campus. A recent resurgence in one of those diseases -- Dutch elm disease, an old nemesis -- has forced the University to remove 16 elms this summer.
"Diseased trees pose a significant risk to a healthy one, so it is necessary -- unfortunately -- to remove the diseased ones," said Jeff Dice, supervisor of grounds and maintenance. "Once infected, the trees can't recover, and the disease can spread from tree to tree." (For photos from the removal of an elm near Walker Building, go to http://live.psu.edu/flickrset/72157626850576219.)
Since 2007, the University has been simultaneously battling Dutch elm disease and elm yellows, first discovered in campus trees that year. Elm yellows quickly began to infect and force the removal of several campus elms. 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, depriving the tree of nourishment and causing it to die. In recent years, research by Penn State faculty and aggressive monitoring and treatment by the Office of Physical Plant (OPP) has slowed elm yellows on campus, even as it decimates elm populations elsewhere.
Dutch elm disease, meanwhile, has threatened trees in the region for more than 50 years, and Penn State has had a concerted effort in place for decades to combat it. Dutch elm disease is a fungal disease spread by the elm bark beetle. It has devastated native elm populations for decades and trees have not yet evolved resistance to it.
Though elm yellows has slowed, Dice said it may have played a role in the spike in Dutch elm disease. Dice said trees infected with elm yellows provided ideal conditions for elm bark beetles to spread Dutch elm disease.
Including the upcoming removals, nearly 100 of the almost 300 elm trees at University Park have been lost to Dutch elm disease or elm yellows since 2007.
"We have been trying to manage it so that we don’t see a significant number of losses in any given year," Dice said. “There has been a tremendous amount of collaboration across the University to combat elm diseases, and that collaboration has been vital in preserving the elms as well as we have. Without those many efforts, we would see what has happened in most other places with elm yellows: total loss.”
This spring, however, the University began planting a diverse selection of tree species with higher disease resistance to replace the lost elms, with funding supplied by the 1996 Senior Class Gift endowment, initially created to maintain and replace campus elms.
The downed elms have been given new life through the Penn State Elms Collection of high-quality furniture, a collaboration between OPP and the Penn State Alumni Association, with a significant portion of the proceeds going to the class gift endowment.
For more on the planting of new trees, see http://live.psu.edu/story/53537.
"It is very difficult to lose these trees," Dice said. "These elms have meant so much to the campus and to the memories of so many people who have come through here. We have fought hard to preserve them. We will continue that work, while also planting new trees to make the same kind of visual impact in the future that the elms did for so long."
The trees to be removed include five on Burrowes Road, four on Pugh Street Mall, three on Allen Street Mall and two in the Orange C parking lot at Hastings and McKean Roads. Other trees to be removed are at the Electrical Engineering Building walkway near Hintz Family Alumni Center and the north side of Walker Building.