University Park, Pa. -- While Dutch elm disease has posed the major ongoing threat to elms in the Centre Region over the last half-century, another disease, elm yellows, is moving into Centre County, bringing with it the potential for a major impact on American elms at University Park and the surrounding area.
Long known for its majestic elms, the University Park campus is home to one of the most mature remaining elm stands in the country. The elms are considered a landmark on the campus and the University has long maintained a commitment to preserving the elm trees through a nationally recognized elm management and preservation program.
Penn State arborists from the Office of Physical Plant and the State College Borough are working with experts from the Departments of Plant Pathology and Entomology to prepare for this new infestation. Unfortunately, there is no known way to protect elms from elm yellows disease or to cure an elm tree once it is infected. No varieties of North American elms are resistant to elm yellows.
Recently the disease, also known as elm phloem necrosis, was positively identified as the cause of several elm tree deaths in Walnut Springs Park in the borough, along the lane to the Penn State president's home adjacent to campus, and along state routes 26, 45 and 64, as well as U.S. Route 322 close to State College. It appears that the disease has already infected elms within State College.
Elm yellows is caused by a bacteria like organism that is spread from tree to tree by the whitebanded elm leafhopper. The only reported host plants for the whitebanded elm leafhopper are elm trees. The leafhopper adults are 4 to 5 millimeters long with roof-like brownish wings. Both adult and nymphal stages can acquire and transmit the elm yellows disease.
A major dilemma for arborists on campus and in the Centre Region is that all North American elms are susceptible to elm yellows. European and Asiatic elms and some hybrids of these with North American elms have resistance, although some elm hybrids are susceptible.
"There are no good varieties of elms that can be planted to replace the towering, graceful elms on campus and around State College," said Gary W. Moorman, a professor of plant pathology at Penn State. "Despite the time and effort that has gone into managing elms for Dutch elm disease on campus and in the borough, there is a distinct possibility that elm yellows may devastate the elm population."
The University is developing an action plan as the situation unfolds.
Here are the key components of that plan:
-- Penn State arborists have deployed monitoring traps to detect the leaf hoppers responsible for spreading the disease.
-- The tree crew from the Office of Physical Plant will move quickly to remove diseased trees on the Penn State campus.
-- The Departments of Plant Pathology and Entomology will provide assistance with additional research and with the development of reliable
diagnostic techniques.
-- The Office of Physical Plant will assess the current IPM (Integrated Pest Management) strategy for Dutch elm disease and make the appropriate modifications to accommodate this new concern.
Campus and borough arborists will continue to monitor and map the spread of the disease, but officials say based on experience in other areas of the country, the prognosis for the elms in our region is not good.
For information, contact, Gary W. Moorman, Penn State Department of Plant Pathology, gmoorman@psu.edu or (814) 863-7401; and Gregory A. Hoover, Penn State Department of Entomology, gah10@psu.edu or (814) 865-3256.