BETHLEHEM, Pa. — Lehigh Valley residents are noticing the telltale signs of beech leaf disease — leaf striping, a thinning canopy and premature leaf drop, among others.
Usually, that’s when they call an arborist, Andrew St. Clair said.
“We did reach out to other clients who have American beeches on their property, and try to get meetings with them as well,” said St. Clair, an arborist with Joshua Tree Experts, a Stockertown-based tree service company.
“Because there are some landscape trees, not just forest trees, that people have planted over the years that are American beech.
“I'm even talking to clients anytime I see a beech tree on a property, whether it's copper beech, tri-color, etcetera – we're having the conversation, even if we're not seeing symptoms.”
More than a decade since the deadly threat to the American beech first appeared in Ohio, and less than five years after it was recorded in the Lehigh Valley, beech leaf disease has now been reported in all of Pennsylvania's 67 counties.
With no quick cure for the fast-moving, but slow-to-kill, disease, experts said American beech trees could be functionally extinct throughout the state within 10 to 15 years.
"The speed at which this is moving is extremely rapid."Ben Chase, a conservation forester at The Nature Conservancy
“This was pretty exceptional in how fast it moved,” said Ben Chase, a conservation forester at The Nature Conservancy.
“For context, beech bark disease we've been dealing with for 100 years or so, spongy moth we've been dealing with for 100 years.
“But beech leaf disease arrived and moved all the way through the state. Pretty much every tree that I encounter now in the state has beech leaf disease, and that took about 12 years.
"So the speed at which this is moving is extremely rapid.”
What is beech leaf disease?
Beech leaf disease is caused by a microscopic worm, or nematode.
First discovered in Lake County, Ohio, in 2012, when it infects saplings, they usually die within five years, according to the U.S. Forest Service.
Mature trees tend to take several years before dying.
Symptoms include the sudden appearance of dark green bands between the veins of the tree’s lower leaves that eventually spread throughout the tree.
“The way it seems to be killing the trees is by reducing the photosynthetic capacity of the leaf."Ben Chase, a conservation forester at The Nature Conservancy
“The way it seems to be killing the trees is by reducing the photosynthetic capacity of the leaf,” Chase said.
“In the early season, beech will put out all of its leaves — along with all the other trees in the forest — and that's pretty expensive energetically.
“It's putting a lot of resources into growing the leaves, and it's hoping it'll get that and more back in whatever it captures from photosynthesis.”
Research suggests the disease could reduce photosynthetic capacity by up to 60% in a leaf that's heavily infested.
“If you're putting all of this energy into a leaf and you're only getting back about 40 percent of what you thought you would, you're going to be depleting,” he said.
“These trees are depleting their energy stores from their rootstock that they kind of build up over time to weather bad seasons like this.”
Young trees dying faster
Young trees have less of a store than older trees, so they’re dying faster, he said, depending on the health of the tree prior to infection.
“If there's been good forestry management, or it's an open growing tree that has plenty of room to grow and nutrients and water, maybe it could hang on for longer than 10 years,” Chase said.
"There may be a few hanging on here or there, but they're not going to play the same role in the forest anymore.”Ben Chase, a conservation forester at The Nature Conservancy
“But in most forested settings where we're not seeing a lot of management happening, sort of a closed grown forest, the young trees are dying pretty quick, and the older trees are taking a bit longer.
“But, of course, it's been 12 years, and if they take 10 to die, we really haven't seen the big mortality hits quite yet. So we're going to know a lot more about it in the coming years.”
Beech leaf was first recorded in Lehigh and Northampton counties in 2022 and 2021, respectively.
“We're seeing that, there's a 90-percent-plus fatality rate, and if every tree has it now, it's moved faster than our treatment options,” Chase said.
“And so in Pennsylvania, we're probably going to lose the majority of our beech. There may be still trees here or there. Some people may treat trees, but we don't have a forest-level solution.
“And so we're going to lose a lot of the function that beach serves in the ecosystem. There may be a few hanging on here or there, but they're not going to play the same role in the forest anymore.”
‘The science wasn't great last year’
There are preventative measures residents can take, including applying a fungicide, like Arbotect — but it can be expensive and time-consuming.
“It's a systemic fungicide,” St. Clair said. “It's applied via macro infusion, which involves drilling into the root flare of the tree, inserting plugs and then hooking up a infusion device.
"It uses a lot of water as a carrier, and it moves the fungicide into the vascular tissue of the tree, and it's systemic, so it translocates throughout the tree.”
It’s the first year the company is trying out the method, he said.
“This really just came up for us last year, and the science wasn't great last year, so we kind of reserved on a treatment plan until we got some news information,” he said. “Arbotect is the option that we decided to go with for now.
"There are some other treatment options that are out there that are showing promising signs, but nothing at this point we felt comfortable with, and also had readily available product to use.”
More options emerging
Last year, arborists and environmental advocates were stuck in what they called a “wait-and-see” situation while science caught up with the need for preventative measures and treatments for infected trees.
Now it seems like more options are emerging.
However, the approach to treatment is different for those with a beech tree or two in their yards, and those who are dealing with large swaths of forest.
"Those of us that are managing whole forests, really, our tools are pretty limited, and we're just relying on good forest management to help the recovery of the forest."Ben Chase, a conservation forester at The Nature Conservancy
“Those of us that are managing whole forests, really, our tools are pretty limited, and we're just relying on good forest management to help the recovery of the forest,” Chase said.
“So, it's kind of stuff that we want to be doing anyway, but really the work that we did before this sort of disturbance to prepare the forest for disturbance, and then the work that we do afterwards in response will determine how the forest responds.
“It's not really practical to go tree to tree and treat every tree with the chemical.”
