New study confirms beech leaf disease threatens european beech trees, too

KIRTLAND, OHIO — A new study from Holden Forests & Gardens and a team at USDA Agricultural Research Service confirms that beech leaf disease—a fast-spreading disease already devastating American beech across eastern North America—also affects European beech (Fagus sylvatica). The research raises concerns that the disease could spread globally, threatening the health of forests across Europe.

European beech is a cornerstone of native forests in Europe as well as a common ornamental species planted across North America. To date, beech leaf disease has not been reported in Europe. 

Published in the journal Plant Pathology, the study used advanced microscopy to trace how the BLD-causing nematode, Litylenchus crenatae subsp. mccannii, alters leaf structure and function in European beech, with American beech used as a comparison. Under the microscope, the same signature symptoms—misshapen leaf biology and dense nematode populations in buds—were observed in European beech leaves and buds exposed to the invasive pest.

These findings mark the first time the full disease process has been documented in European beech, from nematode infestation in the buds to visible leaf symptoms and internal tissue damage.

“This is the first in-depth cellular-level evidence that European beech is susceptible to beech leaf disease,” says Mary Pitts, a research specialist in the David Burke Lab at HF&G and lead author of the study. “We found clear signs of infection and structural damage in both the buds and leaves, similar to what we see in American beech.”

For the study, the team collected buds and leaves from symptomatic European beech and American beech at the Holden Arboretum, as well as asymptomatic European beech from the Dawes Arboretum (Newark, Ohio), where the disease had not yet spread. 

After processing the leaves and buds in the lab, the team could peer inside and view the actual nematodes as well as what the damage looks like on a microscopic level. They soaked samples in alcohol to clear out green pigments, then used a magenta stain that highlights the nematode, making them stand out clearly against the leaf tissue. The resulting imagery is striking.

They also examined cross-sections of the leaves to better understand the nematode’s effects at the cellular level. The researchers observed abnormal cell growth, disorganized stomata, and severe changes to internal leaf layers—changes that reduce the tree’s ability to breathe and photosynthesize effectively.

The team’s findings raise new concerns about the disease’s potential spread beyond North America. Researchers hope that these cellular-level insights can help tree health experts better understand how the disease weakens trees from the inside out.

“This study helps us understand how the disease works in different beech species, which is key for understanding the basic biology of this disease and potentially help managing its spread,” says Paulo Vieira, researcher with the USDA-ARS (Beltsville, MD) and senior author on the study. “We're still amazed by the cellular processes involved in this disease. While it's highly detrimental to the tree, it is undeniably interesting from a scientific perspective. It’s a reminder that plant diseases don’t respect borders. We need to be vigilant and safeguard our natural forest ecosystems.”

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Citation: Mary Colbert-Pitts, Mihail R. Kantor, Andrew Jansen, David J. Burke, & Paulo Vieira. 2025. “Cellular dynamics of beech leaf disease on Fagus sylvatica.” Plant Pathology, 0:1–18.

About Holden Forests & Gardens: Holden Forests & Gardens is made up of two of Northeast Ohio’s most important environmental and cultural institutions—the Holden Arboretum and Cleveland Botanical Garden—whose mission is to connect people with the wonder, beauty, and value of trees and plants, to inspire action for healthy communities. One of the largest public gardens in the country, HF&G has 21,000 member households and an annual attendance of nearly 350,000 for whom we strive to provide inspirational and educational visitor experiences.