3 more campus elms fall victim to Dutch elm disease

Three more of the University's stately American elms had to be cut down because of damage from Dutch elm disease. The most recent victims were located beside Recitation Hall in the Old College historic area, near Alison Hall and beside Robinson Hall, both near the South Mall.

Michael Loftus, assistant director for grounds services, said the University constantly monitors its elms for signs of infectious disease, which has decimated most of the American elms across the country. When indications of possible infection appear, specimen cuttings are taken to verify if the disease is present. If these tests prove positive, prompt corrective action is taken.

Sometimes, Loftus said, only the dead wood must be removed. In an effort to slow the spread of the disease, periodic fungicide injections also are made to protect the campus elms.

The disease is caused by a fungus that was first recognized in the early 1900s and is spread by the elm bark beetle, which carries the spores of the fungus from one elm to another. The fungus attacks the tree by moving into the water conducting tissues and blocking the flow of water and nutrients within the tree. Large elms have extensive root systems that aid in the spread of the problem through underground root grafts. Trees that often look fine may be infected.

Mike Eggert, University arborist in Facilities, along with Roger Bowman, grounds manager, routinely monitor the trees for signs of Dutch elm disease.

During the summer, Bowman said, is when symptoms of the disease can be detected. Observers are alerted to a problem when areas of yellow leaves are noticed on the crown of the trees, which is known as "flagging."

Bowman said samples are taken of the flagged area and, depending upon the results of the tests and extent of the damage, surgical removal of affected limbs and/or chemical injections may be necessary.

"When more than 20 percent of the total crown area of a tree is affected," Bowman said, "removal becomes necessary."

Because Dutch elm disease can spread rapidly to healthy trees, Bowman said, it's important to take the tree down as soon as possible to remove it from the rest of the healthy population.

When Bowman arrived on campus in 1972, the University had approximately 90 American elms. Today, he said, about 45 exist. The three trees that were removed this month, he said, are about the normal number that fall victim to the disease annually.

The ages of the trees recently removed, Bowman said, range from about 50 years old, near Alison Hall, to probably about 60 years old near Robinson Hall and about 75 years old near Recitation Hall.

During the last 20 years, Bowman said, the University has been replacing its lost American elms with Japanese zelkovas. They are distant members of the elm family and are similar in appearance to the American elm, but they are not susceptible to Dutch elm disease.

In the future, Bowman said, the campus Mall may see the return of American elms. Three cultivars, or subsets of the American elm species–labeled Valley Forge, Princeton and Heritage–have seemed to develop a strong resistance to the disease. These trees are being grown in nurseries and, Bowman said, as they mature, more will become available on the market.

–Ed Okonowicz

Photo by Kathy Flickinger