New study confirms beech leaf disease threatens European beech trees, too
Researchers at the Holden Arboretum and the USDA-ARS used advanced microscopy to trace how the BLD-causing nematode affects American and European beech
image:
A scanning electron microscope reveals nematodes (highlighted in green) inside the spongy mesophyll of a European beech (Fagus sylvatica) leaf infected with beech leaf disease (BLD). Eggs are marked in red for enhanced visualization. Natural fractures in the leaf surface suggest pathways for nematode migration from within the leaf to its outer surface. New research confirms that European beech is susceptible to BLD, raising concerns about global forest health.
view moreCredit: Colbert-Pitts et al. 2025 Plant Pathology © British Society for Plant Pathology
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.
Chlorophyll-depleted European beech (Fagus sylvatica) leaves stained with acid fuchsin reveal the presence of beech leaf disease (BLD)-causing nematodes (pink) in symptomatic samples (right), while asymptomatic samples (left) show no nematodes. These findings confirm that European beech is susceptible to BLD.
Credit
Colbert-Pitts et al. 2025 Plant Pathology © British Society for Plant Pathology
Journal
Plant Pathology
Method of Research
Observational study
Subject of Research
Not applicable
Article Title
Cellular Dynamics of Beech Leaf Disease on Fagus sylvatica
Article Publication Date
28-Apr-2025
New pests and diseases will cut UK tree growth
University of Exeter
The arrival of new plant pests and diseases is likely to severely damage UK trees and woodlands in the coming decades, new research shows.
The ash dieback epidemic prompted the government to assess all pests and diseases that could potentially enter the UK and affect our trees and agricultural crops.
In the new study, University of Exeter scientists assessed the 636 tree pests and diseases to work out the invasion probability and likely effects on tree growth.
Based on recent rates of pest and disease arrival, they estimate that – by 2050 – more than half of tree growth could be lost (compared to growth if no new pests and diseases arrived from now onwards).
Tackling pest and disease invasions is very difficult in a world of global trade and travel, but tight biocontrol would slow the process – and tree-planting policies can also boost resilience.
“The defence against uncertain risk is always diversity,” said Professor Dan Bebber.
“In the UK, we have relatively low tree diversity – both in terms of the number of tree species and the genetic diversity within each species.
“The ash dieback epidemic showed us how devastating a single tree disease can be, and how urgently we need to learn about these threats and protect our biodiversity.”
Professor Bebber added: “As well as issues about biosecurity, our research raises social and cultural questions about what we think our woodlands should look like – for example which species should we plant?
“We need to consider this – in light of pests, diseases and climate change – when we think about the future of UK woodlands.”
The at-risk trees highlighted in the study include pine, cherry, spruce, larch and oak.
In recent times, about one new tree pest or disease has established itself in the UK per year – and the sheer number of possible invaders makes further arrivals almost certain.
Tree cover fell below 5% of UK land area at the beginning of the 20th Century, but grew again to about 13% in 2018. This contrasts with a European average of 39% forest area.
UK reforestation has primarily involved fast-growing exotic conifer species, which now comprise about half of total forest area. Ancient woodlands (continuously tree-covered since 1600) cover just 2.5% of the UK.
Current government policy is to increase tree cover to 16.5% in England by 2050, 21% of Scotland by 2032, and by 2,000 hectares per year in Wales.
Professor Bebber said: “Our study highlights the need for care in carrying out these projects, to ensure they are resilient to future pests, diseases and climate change.
“This work is a stark reminder that emerging plant pests and diseases pose a severe threat to UK trees, and the biodiversity benefits and ecosystem services they provide.”
The study was funded by the Engineering and Physical Sciences Research Council (EPSRC) project ADD-TREES – a pioneering Artificial Intelligence research project providing innovative technologies that will aid crucial decisions about land-use changes, with a focus on initiatives to create new woodlands and forests.
The paper, published in the journal Plants People Planet, is entitled: “Potential impacts of plant pests and diseases on trees and forests in the UK.”
Journal
Plants People Planet
Article Title
Potential impacts of plant pests and diseases on trees and forests in the UK
Article Publication Date
28-Apr-2025
