Courtesy of Cornell University

Despite treatment for a few hundred of Cornell's trees, many thousands more are expected to die from the invasive beetle.

November 30, 2018

An Epidemic Among Ash Trees: Up to 100,000 Cornell Trees to Die From Invasive Beetle

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This October, the over-a-century-old tree on Libe Slope located near the Sesquicentennial Memorial died and was cut down. This tree marks one of over 2,100 ash trees on Cornell grounds that will be cut down within the next few years because of emerald ash borer, an invasive insect species that kills ash trees.

The larvae of the emerald ash borer beetle feed on the inner bark of ash trees, preventing the trees from transporting water and nutrients and gradually killing them. Since EAB entered the United States from Asia over 15 years ago, the insect has killed hundreds of millions of ash trees in the United States, spreading across 35 states, according to the USDA. In the spring it was confirmed to have reached Tompkins County.

Once EAB invades, it only takes two to four years for an ash tree to die. Within one year of dying, ash trees begin to fall apart. Most of the estimated 50,000 to 100,000 ash trees covering Cornell grounds will succumb to EAB, according to Todd Bittner, director of natural areas at the Botanical Gardens.

The University is attempting to provide proactive measures and treatments to deal with EAB for a small subsection of the trees, and around 165 trees have already been treated with a pesticide that will protect them from EAB for up to three years. These trees largely consist of rarer types of ash trees and trees with historical or geographical value.

To keep these ash trees alive, they will need to be treated with pesticides indefinitely. Rather than stopping EAB, this treatment only “buys more time,” said University Landscape Architect David Cutter, who manages the ash trees directly on campus. Additionally, the trees treated with pesticides represent a small fraction of the total ash trees on Cornell grounds.

“The sheer cost of trying to keep thousands of trees alive, potentially in perpetuity, just doesn’t make sense from a cost-benefit perspective,” Bittner told The Sun.

Dead and weak ash trees can become significant public hazards as they may fall on people and buildings, and Bittner plans on taking preemptive measures to minimize the safety risk by removing an estimated 2,100 on-campus ash trees from areas close to buildings and walkways. The remaining ash trees — located in woods farther away from buildings — will be left to die and fall on their own.

Emerald ash borer lacks sufficient natural predators to control its population size, and Cutter hopes that, once enough ash trees die, EAB population will decrease to the point that new ash trees can grow again. However, he is not sure that ash trees will ever flourish at Cornell again.

“It is very frustrating, and it’s also concerning to think about when we talk about how our climate is changing and what potential impacts could be,” Cutter said. “There’s probably going to be a lot more pests from migration [including] ones that were kept out [by] our colder weather. This is just the beginning.”

EAB has existed in the United States for less than two decades, and the way EAB population cycles change is still being researched. Future knowledge may yield more solutions on how to deal with the invasive beetle.

For now, Cutter plans on planting new trees in the empty spaces that once held ash trees. These new trees will take 10 years before fully maturing, and Cutter hopes they will not face the same fate as the ash trees today.