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Beech Leaf Disease

Beech leaf disease (BLD) was first discovered in North America in 2012 in Ohio. While the cause of the disease has yet to be determined, BLD has spread quickly and is now found in several of the United States and Ontario. It behaves much like an invasive, alien forest pest. The disease seems to currently be in a rapid expansion phase similar to what has been seen with other invasives, such as the emerald ash borer. From 2012-16, BLD spread across 1250 acres per year in one Ohio county (Ohio State University, 2019). In many of the areas that have been infected with BLD, there are already visible changes in the canopy.



   

  Photo:  Ohio State University, USDA Forest Service, Bugwood.org

Learn about Beech Leaf Disease

Science

Biology and Spread

Though little is known about the biology of BLD, it is believed that it affects the tree’s ability to photosynthesize. The cause of BLD is currently unknown. Recent research has found that Litylenchus nematodes, related to bush-dwelling nematodes from New Zealand, are present on diseased leaves. Research supports that Litylenchus are associated with the disease but are unlikely to be the sole cause. Further research is needed to determine how BLD is caused and spread. BLD appears to spread very quickly, characteristic of an invasive pathogen, and spread does not appear to be influenced by slope, aspect, or soil conditions. Where established, nearly 100% of American beech trees show symptoms (Pogacnik & Macy, 2016). Infected trees also seem to show symptoms of other pathogens, such as beech blight aphid, European beech scale, erineum patches, and other leaf fungi like anthracnose.

Host Trees

BLD is found mainly on the American beech (Fagus grandifolia), the only beech species native to North America. The disease has also been reported on European (Fagus sylvatica) and ornamental beeches in nurseries in the United States. This indicates that the risk of the disease may extend beyond a single species.

 

 

Image result for american beech bugwood
Photo: David Stephens. Bugwood.org


An American beech (Fagus grandifolia), a species susceptible to beech leaf disease infection. 

 

Signs & Symptoms

Symptoms of BLD are only observed on leaves and buds.

In early stages:

  • Striping appears on the leaves, caused by darkening between the leaf veins.

    • The darkened area is slightly raised and is thicker than the rest of the leaf tissue.

    • This is most apparent when viewing from below.

    • Striping is present upon leaf-out in the spring.

  • Very little premature leaf drop occurs during early stages.


Photo: John Pogacnik, Ohio DNR

Early stage leaf striping on beech infected with beech leaf disease.

Disease progression varies based on tree size, with most mortality occurring in saplings. In saplings, progression from early stage symptoms to severe late stage symptoms is rapid and mortality can occur in as little as one year. In larger trees, the disease progresses more slowly, beginning in lower branches and moving upward. On a single tree, some branches may be unaffected where others are heavily infected. Young trees seem to be more susceptible to mortality than mature trees.

 


Photo: John Pogacnik, Ohio Department of Natural Resources

Late stage leaf deformation associated with beech leaf disease.

As the disease progresses:

  • Leaves near branch tips will become shrivelled, discoloured, and deformed.

  • Reduced bud and leaf production will occur



Look-a-Likes

Erineum patch