Beech bark disease has been causing mortality of American and European beech (Fagus grandifolia and Fagus sylvatica, respectively) trees since its discovery prior to 1849 in Europe, although until 1914 beech scale was solely being blamed. We now know that the cause is a combination of scale damage and fungal infection. Beech bark disease is caused when the bark is altered by the insect pest, beech scale (Cryptococcus fagisuga) leaving it weakened, open and susceptible to infection by the fungus Nectria coccinea var. faginata. Introduced into Nova Scotia in 1890, by 1932 mature trees in the maritime provinces and south central and eastern Maine were succumbing to the damage caused by the Nectria fungus and beech scale. Additional isolated infestations were found in southwestern Maine and eastern Massachusetts, spreading north into Quebec and west and south into New York, New Jersey and Pennsylvania. In 1981, an outbreak of beech bark disease was found in West Virginia covering 70,000 acres.
An infestation of beech bark disease follows a general pattern; forests with large mature trees are targeted and a small population of scale begins to feed and reproduce, as those populations increase damaged bark becomes susceptible and the Nectria fungus moves in resulting in heavy mortality. The stand of trees that is left has some remaining large trees and many small clumps of younger trees often the product of root sprouting and some young stems rendered radically defective by the established populations of Nectria fungus, beech scale and vulnerable to damage from other pests.
Research by the USDA Forest Service has shown that trees over 8 inches in diameter are more prone to infection than smaller ones. Data collected from plots in New Hampshire, Vermont and Maine showed that 28% of the large beeches affected had died, 22% were dying while many of the remaining trees were very severely injured.
The white, woolly wax secretions may be the first sign visible sign of a beech scale infestation; “wool” spots appear on rough areas of bark, beneath branches, mosses and lichens. Eventually the entire bole may be covered in feeding scale, which in itself can weaken and stress a tree. But the more severe damage is the invasion of the Nectria fungus through wounds made by scale feeding. Next, a reddish-brown, tar-like substance oozes out of dead spots, this is the first sign of Nectria infection. Perithecia will begin to colonize around these spots and dead areas may extend to sapwood. If outer bark is cut back, an orange color may be seen where Nectria is actively infesting the wood. Nectria cankers can infect large portions of the tree, sometimes girdling them.
Trees dying from beech bark disease may produce leaves in the spring which never mature, making the crown appear thin and sickly. Leaves prematurely turn yellow but persist on the tree throughout the summer. There are control methods and treatments for beech bark disease, discuss any concerns regarding beech trees on or near your property with your arborist. He or she will be able to assess the tree for presence of scale or fungus and gauge the progression of the disease, if present, then prescribe a treatment plan.
Houston, David and O’Brien, James ” Beech Bark Disease” United States Department of Agriculture Forest Service, Forest Insect and Disease Leaflet #75. Web. April 1998