On a warm, late-spring day, Vermont Forest Health Program Manager Josh Halman traveled down to Windham County to take a walk in Jamaica State Park.
The leaves were out on the trees, giving Halman an opportunity to check up on the status of beech leaf disease, which is caused by an invasive pest that only recently arrived in the state.
First detected in 2023, beech leaf disease was found in only two towns that year. By last year it had spread to 43, mostly in southeastern Vermont.
Halman was told that he might have to search around for signs of the disease, but just a few minutes after leaving the parking lot, he stopped at a beech sapling and held a leaf up to the sun, revealing rows of dark bands running parallel to the leaf’s veins.
“Oh wow. Look right here,” Halman said. “That’s beech leaf disease right there.”
The dark area is hundreds of microscopic worms called nematodes that are munching on the cells of the leaf.
This is probably the pest that we are probably thinking about and trying to track more so than any other this season.Josh Halman, Vermont Department of Forests, Parks and Recreation
Halman said he expects to find signs of beech leaf disease in more towns this summer.
“This is probably the pest that we are probably thinking about and trying to track more so than any other this season,” he said.
Beech leaf disease was first discovered in Ohio in 2012, and Halman said it has spread at an alarmingly quick rate.
As the nematodes consume the leaf matter, leaves shrivel up and die, leaving the tree unable to photosynthesize.
Scientists don’t know how the worms move around — whether it’s through water or wind, or possibly by attaching themselves to animals.
Over the next few decades, Halman said, it’s likely the pest could kill every beech tree in the state.
“Yeah, it’s sad, and it’s alarming,” he said. “But it’s not like all hope is lost.”
As Halman and his staff search for signs of beech leaf disease, scientists around the country, including University of Vermont associate professor Nick Aflitto, are trying to learn more about the worm responsible for its spread.
“We’re very much in a discovery phase with this disease,” Aflitto said. “So it is kind of an all-hands-on-deck in that sense where we just have to try different things and figure out what’s working.”
Aflitto is leading a project in the UVM research forest in Jericho to try to figure out what’s attracting the nematodes to the beech leaves, using chemicals that give off smells of the beech tree buds.
If Aflitto can determine which scents attract, or repel, the nematode, then it might be possible to better control how they move through the forest.
We’re very much in a discovery phase with this disease.Nick Aflitto, UVM associate professor
Invasive insects most likely arrive in this country on wood products.
Back in the countries where they originate, trees have developed natural ways to combat their spread. But when they arrive here, the trees don't have those defenses.
The disease will most likely continue to spread across the state, but Aflitto said he and other researchers will continue working to try to help Vermont’s forests adapt to the changes that humans are bringing on.
“We’re not going to stop invasive species from coming, and that’s sort of the reality we live in,” he said. “So I think we need to just figure out how we can bridge the gap to the new paradigm we’re in.”
The state has a website, vtinvasives.org, where the public can report outbreaks of beech leaf disease.
