Contributor: Tyler McKee
With smooth grey bark and bronze leaves lasting deep into winter, the American beech (Fagus grandifolia), is a popular and easily recognizable tree in the eastern forest. It is an ecologically important tree, as it is one of the lone hard mast producers and a climax species of the northern hardwood forest. For over a century, this species has been under threat from beech bark disease. Partially caused by the invasive beech scale insect, the disease was discovered in Nova Scotia in 1890 and has since spread to most of New England and beyond. Beech bark disease has had a devastating impact on beech trees, but there is a newer threat to this species that has researchers on the lookout – beech leaf disease (BLD). As beech trees are so visible this time of year, beech leaf disease has been selected at MISC’s February IOTM.
In 2012, a number of trees in Lake County, Ohio were found with distinct symptoms on their leaves, marking the discovery of beech leaf disease. The symptoms of beech leaf disease were not seen on any other beech trees in the U.S. or the rest of the world. This led biologist John Pogacnik, the discoverer of BLD, to believe that it may be caused by local weather stresses or other abiotic factors. However, after observing the exponential rate of spread, it was determined to have a biotic cause.
By 2014, the disease had spread to three new counties in Ohio. In 2018, signs of beech leaf disease could be found in 24 counties in Ohio, Pennsylvania, New York and Ontario. While the spread has been rapid, the effects have not been entirely consistent; areas like Lake County have seen nearly all trees infected but to varying rates of decline. Hopefully, this bodes well for disease resistance and, if necessary, breeding a resilient population.
The disease can initially be identified by the darkening bands between the leaf veins, which appear in spring and can still be seen on bronze winter leaves. Later symptoms include the total darkening (while still not crossing the veins), shrinking and ruckling of the leaves. The leaves in the second stage of symptoms are thicker and leathery in the darkened areas. Symptoms generally start at the lower portion of the tree, working up to the crown. After the leaves are affected, buds can be terminated, leading to dieback, decline and possibly death. Mortality is more likely to be seen on saplings and young trees, though limited mortality has been observed on larger trees.
The cause of the disease, whether a complex or single agent, is not yet determined. At Ohio State, research is underway, comparing DNA found in infected trees to uninfected ones. Any differing results could point to the cause. The Ohio Department of Agriculture has also found Litylenchus nematodes on infected leaves, though more research must be conducted to determine if they are the sole cause of beech leaf disease. Litylenchus crenatae nematodes are found on beech trees (Fagus crenatae) in Japan. The species was described in 2018, and the American population has since been described as a subspecies.
In Maryland we are a good distance from infected areas, and there is still hope that we won’t see the disease spread to us. However, it’s good to keep a watchful eye and stick with best management practices, like not moving firewood. If you think you see signs of beech leaf disease in your area, contact: Forest Pest Management at 410-841-5922.
Photo Sources:
Jim Chatfield, OSU Extension, https://bygl.osu.edu/node/1176
Sources
Ewing CJ, Hausman CE, Pogacnik J, Slot J, Bonello P. Beech leaf disease: An emerging forest epidemic. For Path. 2019;49:e12488. https://doi.org/10.1111/efp.12488
Popkin, G. (2018). An arboreal murder mystery: What is killing beech trees? The Washington Post. Retrieved from, https://www.washingtonpost.com/national/health-science/an-arboreal-murder-mystery-what-is-killing-beech-trees/2018/07/27/95d18ebc-8c59-11e8-a345-a1bf7847b375_story.html
Wike, C. (2019) A Mysterious Disease is Killing Beech Trees The Scientist Retrieved from, https://www.the-scientist.com/news-opinion/a-mysterious-disease-is-killing-beech-trees-65358
More information:Beech Leaf Disease – Ontario’s Perspective: Dr. Sharon Reed https://www.youtube.com/watch?v=tDBbik7cUrI