Tree cutting crews chop down American elms at the Castine golf course on Monday, July 25, 2022, after they had been infected with Dutch elm disease. Credit: Courtesy of Don Tenney

A lethal tree disease that plagues American elms is surging in Maine this year and has taken root in more than two dozen trees in Castine, one of the Northeast’s last remaining hubs for the towering giants.

Though there is no official statewide count, a state forestry expert estimated that the amount of elms with Dutch elm disease in 2022 is at least three times higher than in years past, and sickened trees are deteriorating faster due to dry conditions going back to 2021.

Dutch elm disease cases are “noticeably higher this year, and the symptoms are progressing much more rapidly,” said Aaron Bergdahl, a forest pathologist with the Maine Forest Service.

The disease is caused by a fungal pathogen spread via spore-carrying elm bark beetles. The fungus then works its way through a tree’s vascular system, prompting the tree to create its own plug-like structures in an attempt to contain it. But those blockages also stop nutrients and water moving throughout the tree, and the elms essentially starve themselves.  

Why there are more cases now isn’t clear, according to Bergdahl, but he said that sporadic rainfall means trees are already under duress and more susceptible to the disease.

Reports of cases appear to be coming in throughout the state, Bergdahl said, but the recent development may be most worrisome for Castine, a small coastal town that boasts more than 200 elms and is a throwback to a time when elm trees were a common sight along New England streets.

In the 19th and 20th centuries, many towns throughout the U.S. planted exclusively elms along city streets because of how their branches splayed out like fountains, creating scenic and shaded downtowns. But it also made it easy for the Dutch elm disease to spread like wildfire after it arrived in the U.S. in the mid-1900s, said Jan Ames Santerre, an urban forester with the state forest service.

In addition to being carried by beetles, the disease can also spread through an elm’s root system. Because they were planted in dense rows along streets, multiple trees’ roots often grafted together, so one case could quickly spread to whole swaths of trees.

Possibly because of its isolated location, Castine escaped that carnage and now stands as one of the few communities that still has a large number of elms lining its streets.

Arborists work to cut down elms.
On Monday, July 25, 2022, Castine arborist Bill Burman chops branches off an elm tree along Main Street that had been infected with Dutch elm disease. The town, like the rest of the state, has seen a rise in cases in the disease in 2022. Credit: Ethan Genter / BDN

The town of about 800 people has worked hard to keep this point of pride — the local motto is “Under the elms and by the sea” — and has a tree committee, tree warden and $25,000 budget dedicated to overseeing their preservation.  

But even with such a robust infrastructure, the town hasn’t been left totally unscathed.

This year there have already been about 30 cases in town. Six trees were cut down on Monday to prevent the pathogen from spreading, said Don Tenney, the town’s tree warden. That is a large jump compared with the past, when there were usually no more than five cases annually.

The town regularly inoculates about 75 of its trees with a vaccine-like compound that makes them resistant to the disease. Most of the elms that are currently falling to the pathogen are untreated and on private property.

Tenney hoped they could save some of the infected trees but suspected most of them are a lost cause.

“We have a serious uptick,” he said. “Most of them will have to be removed.”