Worse than the spotted lanternfly? A new disease is killing beech trees in Pa. and N.J.

The iconic American beech tree has been prized for centuries by people for its dense, shady canopy — and by animals that gorge on its nuts.

But a newly emerging menace has forestry experts worried: beech leaf disease (BLD), which causes leaves to darken, pucker, crinkle and thicken. The crown of the trees thins and branches die, preventing photosynthesis and leading to death.

“This is one that has me concerned,” said Emelie Swackhamer, a Penn State Extension educator with a background in plant pathology. “It has already spread throughout most of the state.”

Swackhamer, based in the extension’s Montgomery County office, lives in Berks County and has seen the damage up close. She was alerted last June to a site in Berks County and could see canopy thinning on some beech trees. The disease also attacks the European and other beech varieties.

“This is an emerging threat,” Swackhamer said, “and if people have an ornamental beech tree that’s high value, I would be watching for this.”

Researchers know little about the disease, she said, and there is no widely accepted treatment. It might take years of research — and funding — before scientists have a firm understanding.

This could pose a bigger threat than the spotted lanternfly, experts say.

The beech is one of the prevalent trees in forests throughout the Mid-Atlantic and New England, and the disease is spreading rapidly. The species is a feature of local forests, parks, and college campuses, with leaves turning a golden yellow in fall.

The chief suspect in BLD is Litylenchus crenatae ssp. mccannii, a newly recognized subspecies of a nematode thought to have originated in Japan. The nematodes — microscopic worms — have been detected in diseased trees. Bacteria and a fungus have also been found and might also be contributing to the disease.

BLD was first discovered in the United States in Ohio in 2012. It first appeared in Crawford County, Pa., in 2016. It’s now present in 65 of 67 Pennsylvania counties, including Philadelphia in 2022. Experts have stopped short of calling the nematode an invasive species, but they are treating it as one.

The disease was first detected in New Jersey in Bergen and Essex Counties in 2020. By last September, the state’s Department of Environmental Protection began urging residents to check trees on their property for signs of BLD and report any findings to the Forest Service. The disease was then present in 12 of the state’s 21 counties. The DEP called the disease “an emerging forest health threat.”

The disease is particularly hard on small trees three to five years old. It is new enough that experts are still unsure how it will impact large, mature, hardy trees. The first sign of BLD are dark bands that appear between leaf veins. As the disease progresses, leaf edges brown and begin to curl. Their texture becomes leathery.

BLD comes as beech trees already face a number of threats, including beech bark disease, bagworm, root rot, and the spotted lanternfly, which hasn’t proven as deadly to most trees as originally feared.

And that has captured the attention of the Pennsylvania Department of Conservation and Natural Resources.

“It’s causing a fair amount of mortality in the younger age cohort,” said Jill Rose, a forest pathologist for the the department’s Bureau of Forestry. “Mature trees take a little longer.”

Beech accounts for a significant amount of Pennsylvania’s tree canopy and is highly valuable to animals. Beechnuts, high in fat, are prized by squirrels, deer, and bear. Birds feed not only on the nuts, but also on insects that live in the trees. Birds make homes in the natural cavities that form in the trees.

“There’s real concern with the onset of this disease,” Rose said. “It’s relatively new enough that we don’t know the long-term impact.”

This nematode infests leaf tissue and does not attack the wood or roots. The eggs hatch in late spring and into summer. Emerging nematodes penetrate the buds. They move about in films of water from rain, irrigation or snow. But it is still unclear how they are spreading so rapidly. It’s possible they are hitching rides on spider mites.

The U.S. Forest Service says there are no current treatments, though several are being studied. A way to fight the disease right now is to try to stop it from moving. That means destroying infected plants, avoiding transporting the trees, including branches, twigs, soil, leaves, and seedlings. Pruning might also decrease severity of an outbreak.

Because it can take six years for the disease to kill a mature tree, it’s unknown how lethal a threat BLD is to Pennsylvania and New Jersey because it was discovered in the region only within the last few years.

But there’s little doubt it is spreading rapidly, said Matt Borden, a plant pathologist with Bartlett Tree Experts.

“It is absolutely out there,” Borden said. “It’s affecting people’s properties, the landscape, and the forest. It’s a big priority for us.”

Bartlett has 100 offices nationwide and overseas, including many in the Philly region. Borden said the company is experimenting with a nematicide, or chemical that kills parasitic worms, in five states and has seen success. But any treatment won’t be widely used until testing is complete.

Borden said the disease has proved difficult to manage, especially in forests.

“There’s virtually no way to easily combat it,” he said. “And it is affecting a species that is really crucial to not only our landscapes but our eastern forest ecosystems. So based on all of those criteria, it’s a far higher threat than spotted lantern fly.”

For now, the best defense is a healthy tree.

“We try to be as proactive as possible, encouraging people to pay attention to the soil and root care of the trees, assess their nutrient needs,” Borden said. “We advise on irrigation and mulching. A healthy plant can withstand things better than a sick plant.”