UNIVERSITY PARK, Pa. -- Drivers on U.S. Route 22/322 this summer between the Millerstown and Amity Hall exits may have noticed a sweep of yellowing and dying trees. This is not the aftermath of a new disease, but the beginning of an attempt to eliminate a roadside menace, according to a researcher in Penn State's College of Agricultural Sciences.

On June 25, Penn State and PennDOT initiated a pilot project to halt the spread of Ailanthus altissima, commonly known as the tree-of-heaven, or -- to some -- the "tree from hell."

"This fast-growing, highly invasive tree -- which resembles our native staghorn sumac, but grows much taller -- is spreading rapidly along the state's highways," says Art Gover, research support associate in the department of horticulture. "It poses a hazard to motorists by encroaching into recovery areas, reducing line-of-sight and dropping limbs easily during storms. For roadside managers, ailanthus is fast becoming Public Enemy Number One."

Ailanthus came to the United States from Asia in the 18th century for use as a fast-growing ornamental tree. It soon was featured in many gardens.

The tree forms dense thickets up to 60 feet high, shading out existing vegetation. Mowing won't control it, because it regrows 5-15 feet in one season. The fast growth results in weak wood that breaks easily in winds or snowstorms. Seedlings also grow up through and block grates in road drainage systems.

And it doesn't stay put. "Once established, ailanthus invades adjacent properties," Gover says. "It spreads readily by seed and root sprouts, invading forests and farm fields. It can cause serious problems for farmers with their mechanical harvesting equipment.

The tree grows in good soils, bad soils and soils highly contaminated with road salts. It has no problems with disease, insects or air pollution. It thrives on disturbance, and moves out of urban and agricultural settings, Gover says, and into less disturbed landscapes. It is much less common in areas of established forest.

"New colonies are easy to identify," he says. "You see a 'mother' tree surrounded by a concentric ring of many smaller trees -- probably root sprouts. With time, all of the trees blend together to form a tree-of-heaven forest."

The pilot management project will consist of two phases. The control phase, which began in June and will last until leaf drop, consists of a high-volume foliar herbicide application, to be followed with a basal bark application to treat stems not controlled by the first application.

The maintenance phase, which will begin with the 2002 growing season, will consist of a backpack-based, low-volume foliar herbicide application to catch any resprouts. This will be an annual undertaking, Gover explains, but essentially unnoticeable to drivers due to the selective nature of the applications and smaller size of ailanthus resprouts.

"Because of the existing level of infestation, the aesthetic results of the initial control efforts have been dramatic," he says. "But these results are temporary, as other plant species will fill in the space left by the ailanthus. Once the current infestation is under control, the subsequent annual maintenance will cause very little disturbance to the existing vegetation."

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EDITORS: Art Gover can be reached at 814-863-1184.

Contact:

Kim Dionis KDionis@psu.edu 814-863-2703 814-865-1068 fax