Biology and Management of Beech Bark Disease (E2746)
Michigan’s Newest Exotic Forest Pest
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Beech bark disease is one of the latest exotic pest problems to plague Michigan forests. Beech bark disease refers to a complex that consists of a sap-feeding scale insect and at least two species of Nectria fungi. Beech bark disease begins when American beech (Fagus grandifolia) becomes infested with beech scale (Cryptococcus fagisuga Lind) (Cryptococcus fagi Baer.). The tiny scale insects, found on the tree trunk and branches, feed on sap in the inner bark. White wax covers the bodies of the scales. When trees are heavily infested, they appear to be covered by white wool. Minute wounds and injuries caused by the scale insects eventually enable the Nectria fungus to enter the tree. Nectria kills areas of woody tissue, sometimes creating cankers on the tree stem and large branches. If enough tissue is killed, the tree will be girdled and die. Other trees may linger for several years, eventually succumbing to Nectria or other pathogens. Some infected trees will break off in heavy winds — a condition called “beech snap.” Dense thickets of root sprouts are common after trees die or break.
Managing beech bark disease in Michigan will be challenging. Both the scale insects and the fungal spores can be transported in the wind. Eventually beech scale and beech bark disease will affect beech trees throughout Michigan. The goal of this bulletin is to help you understand the biology and impacts of this new pest and potential management options.