A Fast-Spreading Disease Threatens a Foundational Tree of Eastern Forests

Heather Faubert has spent decades working with Rhode Island farmers and landowners to diagnose and manage pests damaging their plants. But when she responded to a call from a concerned resident in 2020, she was shocked by what she found: Sixty percent of the American beech trees on the property had abnormal leaf patterns—a hallmark of beech leaf disease, which was first detected in the state earlier that year.

Since then Faubert, director of the University of Rhode Island’s Plant Protection Clinic, has fielded hundreds of calls from others concerned about their beeches, and has reached a worrying conclusion: “I started thinking we could lose this tree species.”

First discovered in 2012 by a biologist in Ohio, beech leaf disease kills native and ornamental beech trees, and is caused by a microscopic worm called a nematode, though other microorganisms may be involved. Tree diseases are nothing new, but the speed with which this one infects new trees has forestry professionals and scientists concerned for the future of a foundational species that makes up a significant portion of many eastern forests and feeds and shelters an array of birds and wildlife. “When you remove American beech from the equation, it’s like a house of cards,” says Robert Marra, a forest pathologist at the Connecticut Agricultural Experiment Station.

The nematode feeds on and reproduces within beech buds, then attacks emerging leaves. Diseased leaves have distinctive dark bands and a leathery texture. Eventually, infected foliage withers and dies, impeding the tree’s ability to photosynthesize. Mature trees—which can live to 400 when healthy—are typically dead within 10 years.

Scientists believe the nematode is a subspecies of one found in Japan, though the disease isn’t widespread there. Its origins remain unknown, but since its arrival, the sickness has been found in at least 12 states, from the Mid-Atlantic and New England to the Great Lakes, as well as Ontario. Given the small size and limited mobility of the beech leaf nematode, scientists suspect that it travels with the help of insects or even the wind, but birds might also play a role.

An electron microscope image of a mature female nematode found in beech leaves. Photo: Electron and Confocal Microscopy Unit; colorization by Joe Mowery, ECMU

The nematode invades beech buds from mid-summer into fall, stays there through the winter, and enters leaves as they develop in the spring. Tufted Titmouse, Black-capped Chickadee, Downy Woodpecker, and other birds feed on beech buds throughout the winter. That led Danielle Martin, a forest pathologist with the U.S. Forest Service, and other scientists to hypothesize that birds consume infected beech buds and spread the nematode across the landscape in their droppings or in their feathers.

According to Martin, the bird theory could help to explain why beech leaf disease jumped from Ohio to the East Coast so quickly. “We began seeing new occurrences of the disease far from roads or human activity,” she says. “Given a lot of the migration patterns of birds, this theory started to make sense.”

Martin and team have not yet published results from their studies, which involve trapping birds at feeders with beech-leaf infected buds and later collecting their droppings to test for signs of the nematodes. Their research is ongoing, but the team has not yet confirmed that the nematode is present in bird droppings and capable of infecting healthy trees.

So far, there are no proven treatments to stop the disease, but understanding how it spreads is the first step to finding one. Future solutions might include programs to breed trees that can withstand the disease, using genes from beeches that have shown natural resistance. In the meantime, Ohio researchers found that using a chemical fertilizer called PolyPhosphite 30 can help infected trees retain their canopies. And Marra, working with a team investigating the genetics of the nematode, developed a DNA fingerprinting system to help identify pathways of contagion, which could inform future management strategies.

Marra says he remains hopeful but acknowledges that it’s too soon to know how the disease will play out. “What happens next year may not be predictive of the next 20, 30, or 40 years,” he says. “Trees live on a different timescale than humans do.”