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A New Threat to Beech Trees in Pennsylvania?

Posted: October 13, 2016

As if American beech weren’t afflicted enough, a new disease - simply called Beech Leaf Disease - may soon affect trees in Pennsylvania’s forests!

For decades now, American beech have been impacted by Beech Bark Disease, caused by a combination of an insect and pathogen. It begins with the infestation of the beech scale insect, Cryptococcus fagisuga, which bores into the outer bark, leaving a small open wound. If you have ever seen small white powdery “cottonballs” on the bark of the tree, that is evidence of the scale. This wound then serves as an entry point for a fungus of the genus Nectria, leading to mortality in the bark tissues.   

Beech bark disease was first detected in Nova Scotia and has slowly spread south and westward through northeastern North America. By the 1940s the disease had spread south from northern Maine and into New Hampshire, Vermont, and New York by the 1950s and 1960s. It first reached Pennsylvania soon thereafter and has severely affected forests in much of the northern half of the state. As beech bark disease has advanced through the area, forests have undergone several phases of the disease. The first phase of the disease infects and kills the larger beech trees and causes severe defects in others. This initial mortality leads to the second phase where beech root suckers form around parent trees. These forests then become rich in understory beech, which is sometimes referred to as ‘beech brush.’ These root suckers are often a major interference to more desirable regeneration in many of our forests.

The latest disease to impact beech, Beech Leaf Disease, is hitting forests from the west and moving north and eastward. It was originally discovered in Ohio, and has now been spotted in at least one western Pennsylvania County and in southwestern New York. Beech Leaf Disease affects the leaves and buds of the trees. The first visible sign is a discoloration of the leaves in which the areas around the veins appear markedly darker than the rest of the leaf. The interior parts of the leaf between the veins then become paler and chlorotic (i.e., yellowish), resulting in a distinctive striped appearance. Eventually the leaves shrivel or curl before falling prematurely. It is still not positively known what pathogen is causing this disease, but is thought to be a phytoplasm.

The disease appears to be spreading fast, and documenting its movement in the next few years is important. If you think you’ve seen evidence of Beech Leaf Disease in your forest, consult with your local DCNR Bureau of Forestry service forester to confirm the diagnosis.

Written by , Forest Resources Educator, Penn State Extension.