Beech Leaf Disease Mystery: A Nematode is the Main Suspect

By Wendy Diaz EMGV

One of the trees in the north corner of my triangle-shaped yard that has a very large presence and provides beneficial shade is a native American beech tree (Fagus grandiflora)1. I love my beech tree and it came with the house as the developer left a forested buffer along the back property boundary. Its low branches of bright green leaves and its smooth grey bark on its wide trunk contrast nicely with the rough-textured bark of the mainly tall bare narrow trunks of the pine, white oak and sweet gum trees that dominate our backyard. So, when I heard2 about a new disease called Beech Leaf Disease (BLD) affecting these beautiful trees in Northeastern Ohio, I became concerned and wanted to learn more. 

American Beech in my backyard. Photo by Wendy Diaz May 28, 2020

American Beech Primer

The American beech is an important anchor species or ‘foundational species’ which means other living organisms and the functioning of the forest ecosystem depend on these beech trees3. This important deciduous tree of our Eastern forest is slow growing and can reach about 80 feet in height and a lifespan of between 300 and 400 years1. The American beech is a common shade tree and is most recognizable by its distinctive smooth gray bark which it maintains throughout its lifespan unlike other hardwood species. The smooth light bark tempts many a knife carver and it often has letters carved in its bark along trails in the state. Its nuts are an important food source for wildlife and a favorite of blue jays. Beech trees have shallow root systems and prefer well-drained acidic soil4. The serrated oblong leaves turn golden yellow in the fall.

BLD Discovery and Spread

In 2012, Beech Leaf Disease was first discovered by John Pogacnik, a biologist, in a beech tree grove atop a ravine in Concord Township north of Columbus in central Ohio5. As of January 2019, the disease had spread as far north as southern Ontario in Canada and decimated large tracts of beech trees in many counties in Northeast Ohio, Western Pennsylvania and New York. In October 2019, the disease was confirmed in Connecticut and Long Island. It spreads about 150 miles eastward each year and movement towards the east has been rapid but movement to the west has been much slower. The map below illustrates the distribution of the BLD disease.

Image courtesy of Ohio Department of Natural Resources website

Suspected Source

To date the cause of the disease is unknown. Suspects include a new species of nematode discovered in 2017 by Dave McCann, a plant pathologist of Ohio Department of Agriculture. He observed 2mm long nematodes when he examined diseased leaves under the microscope5.  Lynn Carta, a plant disease specialist with the U.S. Department of Agriculture (USDA) in Beltsville, Maryland first described the new nematode as a subspecies of nematode described by Japanese scientists and named it Litylenchus crenatae ssb mccannii (Anguinata) 6. This is the first example of a leaf-eating nematode infecting and potentially killing a large live forest tree in North America according to L. Carta and it may have originated in a Pacific Rim country. Nevertheless, Enrico Bonello, a plant pathologist at Ohio State University, found nematodes in both healthy and diseased leaves so he attributes the true cause of the disease to a microbial pathogen and postulated that the microscopic worms may be simply transmitting the pathogen.7


BLD Symptoms

Diseased beech leaves exhibit interveinal greening or dark green bands between veins of the leaf, thickening and often chlorosis in leaves6 and sometimes leaves blister, thicken and become shriveled. Later, the diseased leaves become uniformly darker, shrink and get crinkly8,9. Eventually the canopy starts thinningand limbs stop forming new buds and eventually the tree dies. The disease has been found in European and Asian beech tree species in nurseries and at the Holden Arboretum in northeastern Ohio.

Classic dark green banding between veins of beech leaves and symptom of Beech Leaf Disease (BLD). Photo courtesy of Ohio State University Buckeye Yard & Garden online article entitled More Beech Diagnostics, author Jim Chatfield. Published on August 28, 2017
No dark banding between leaf veins in healthy Beech leaves. Photo taken by Wendy Diaz May 28, 2020

What can we do now? Not much because they don’t know how it spreads as yet10. We have to try and prevent the introduction of BLD to our southeast forests and monitor them for signs and symptoms of the disease11. USDA’s Animal and Plant Health Inspection Service, the agency responsible for dealing with invasive tree killers, is also studying the disease but is not taking action to limit the disease until more is known about how the disease spreads and its cause.7 In the meantime people can help with BLD surveys by downloading the Tree Health App3 and it is always a good practice not to move firewood between locations. If you purchase European and Asian varieties of beech trees be careful because long-range spread is probably assisted by anthropogenic transport, especially of nursery stock8. Let us hope they determine the cause and discover a remedy soon before this disease spreads south to our beech forests here in North Carolina. For now, I will pay more attention to my beech tree and spread more leaf litter over its shallow roots to prevent stress during our summer dry spells and I definitely won’t be carving my initials its smooth bark.

Closeup of smooth gray bark of the American Beech. Photo taken by Wendy Diaz May 28, 2020


  4. NCSU Plant Toolbox:
  6. Carta LK, Handoo ZA, Li S, et al. Beech leaf disease symptoms caused by newly recognized nematode subspecies Litylenchus crenatae mccannii (Anguinata) described from Fagus grandifolia in North America. For Path. 2020;00:e12580. Link (
  9. Ohio State University More beech diagnostics Jim Chatfield August 28 2017
  10. on May 17, 2020

Note: At the time of this post not all resources were accessible as the Ohio Department of Natural Resources and Division of Forestry website was under redevelopment.