What to know about the mysterious disease plaguing Massachusetts’ beech trees


There is no proven treatment for beech leaf disease, which threatens trees in forests and yards alike.

A century old Beech tree in Swampscott that will be cut down this month. It suffers from a relatively new illness plaguing trees across the Northeast. Erin Clark/Globe Staff

In the coastal town of Swampscott, Mass., the expansive canopy of a 100-year-old beech tree has presided over picnics and given refuge to shade-seekers for longer than most of the town’s residents have been alive. But it’s dying, and soon it will have to be cut down. 

There are multiple suspected culprits. Several summers of intense drought may have played a role. But another factor was beech leaf disease, a relatively new and mysterious affliction that destroys beeches’ leaves, and with them the trees’ ability to photosynthesize.

“It’s not true beyond a shadow of a doubt that this 100-year-old tree succumbed to beech leaf disease,” emphasized Jim Olivetti, the chairperson of Swampscott’s Tree Committee. “It might have had an impact,” but there were multiple factors at play, and we don’t know enough about the disease to be certain.

Whether or not beech leaf disease sounded the death knell for this particular tree, the news it would be chopped down provoked a surge of concern and media coverage surrounding the future of the state’s beeches. That concern is warranted, according Nicole Keleher, the Massachusetts Department of Conservation and Recreation’s forest health director.

“We are seeing a lot of decline, and we do expect to lose a significant number of beech trees,” Keleher said. 

“Beech have a really ecologically important value in our forests,” Keleher explained. They produce nuts and offer habitats for wildlife. “And then in our state, beeches are really culturally important as well: We have a lot of planted European Beech, some that are well over 200 years old. And they’re these big, beautiful trees that come all these different cultivars and leaf colors.”

This new disease threatens beeches growing in forests and yards alike, Keleher said. Public and private research teams are on the case, but much is still unknown about the disease, including how to treat it. 

What is beech leaf disease?

Beech leaf disease can be identified by dark bands that appear on the leaves of infected trees. Researchers believe the disease is spread by nematodes — microscopic roundworms — that damage the leaves’ tissue and can eventually kill the entire tree. Their working theory is that the nematodes are transported among trees by birds, wind, and water droplets.

The nematodes aren’t harmful in and of themselves, Keleher explained. “They’re present everywhere, on every surface on plants, but for [them] to be pathogenic and causing damage to a tree is pretty much unheard of. There’s no other disease that functions like this.”

By killing the leaves, the pathogenic nematodes inhibit the trees’ ability to photosynthesize and produce nutrients. When the disease has infected enough leaves, limbs and eventually entire trees wither and die.

Tyler Ledin is a Needham-based arborist. He said his company, Hartney Greymount, has seen the number of beech leaf disease cases rise “dramatically” since the disease was first detected in Massachusetts in 2020.

Once a tree has been 25% infected with beech leaf disease, Ledin said, it’s usually only a matter of time — about three to eight years — before the tree is completely dead.

How widespread is the disease?

Beech leaf disease was first detected in Ohio in 2012, and has since been found in  Connecticut, Maine, Massachusetts, Michigan, New Hampshire, New Jersey, New York, Ohio, Pennsylvania, Rhode Island, Virginia, and Ontario, Canada. 

The Mass. Department of Conservation and Recreation documented its first cases of the disease in 2020, and by 2022 had found it in every county in the state, according to Keleher. She isn’t sure how many individual towns have reported cases of the disease, but she estimates it’s close to 100.

“My team just keeps confirming new towns while they’re out during surveys,” Keleher said. “We’ve had over 500 public reports of it this year alone. So it’s very abundant and causing a lot of really noticeable damage.”

According to one estimate by a plant pathologist from UMass Amherst, beeches make up about 10% of Massachusetts forests. That’s a huge proportion, the pathologist told GBH, whose loss could cause “catastrophic ecological consequences.” 

How do you treat beech leaf disease?

Scientists, arborists, and private companies are all trying to answer that question. But none of them have developed and tested a sure-fire treatment yet, Keleher said.

Ledin sometimes recommends a course of PolyPhosphite 30, a quasi-fertilizer that’s injected into the infected tree’s root system. It doesn’t target the nematodes directly, but it helps “build the tree’s immune system,” Ledin said.

Pesticides take time to develop, Keleher said, because rigorous testing and trials are involved. Then you have to contend with individual states’ regulations on the chemicals. Testing non-chemical treatments, like thinning out tree stands or removing infected trees from the forest entirely, is a similarly lengthy process. Researchers may eventually be able to breed infection-resistant beeches, but that could take decades, the peer-reviewed journal Science reported in 2021.

“We don’t currently recommend any of the treatment options that are out there,” Keleher said. The options that do exist are costly, and untested.

Keleher and Ledin both encouraged homeowners to contact an arborist if they think their beech leaf disease-infected tree poses a safety risk. If a limb hangs over your home or vehicle, it may need to be removed as a precaution.

Is climate change a factor?

Jim Olivetti, the Swampscott Tree Committee chairperson, wonders whether milder winters brought on by climate change have anything to do with the higher incidence of beech leaf disease in recent years. Perhaps more pathogenic nematodes were surviving the milder New England winters, he posited — as is the case for other infection-carrying pests, including ticks.

Olivetti was the first to admit he’s not a scientist, just a tree enthusiast with a theory. But Keleher and Ledin both said he could be on to something.

During milder winters, Ledin said, there’s a risk that pests like nematodes could survive the cold season, resulting in “multiple generations” being present on a tree at a time.

“Climate change is definitely impacting our trees,” Keleher said, though she couldn’t say definitively how significant it was in the spread of beech leaf disease. “For some species, being a little bit warmer helps them do a little bit better. Warmer conditions also can allow us to have invasive species established here that weren’t able to establish before — maybe our colder winters killed them off, or our slightly shorter growing season, or certain timings and things didn’t work out.” 

Research is ongoing to determine the root causes of the disease. What’s certain, Keleher and Ledin agreed, is the risk.

“Everywhere you go there’s there’s a lot of beech, and maybe you don’t always notice them,” Keleher said. “But when you start losing these trees, it does become really noticeable.”