American beech, Fagus grandifolia, is a common component of eastern North American forests. The species is utilized for lumber and pulp, and it periodically produces beech nuts for wildlife. By the 1950s, an exotic insect-disease complex had become established in northeastern beech populations that was causing extensive mortality. Beech bark disease is due to the activities of the exotic beech scale insect, Cryptococcus fagisuga, and an associated exotic fungus, Nectria coccinea var. faginata (Mahony et al., 1999). The scale insect penetrates the bark during feeding, enabling the associated fungus to enter the tree. The tree is girdled from the resulting multiple cankers (Houston & Valentine, 1988).
Beech scale was introduced in the late 1800s into Halifax, Nova Scotia, probably on nursery stock of European beech (Hawbolt, 1944). However, it was not until around 1920 that an outbreak of beech bark disease was recorded (Houston & Valentine, 1988). The disease spread rapidly and was commonplace in Nova Scotia by 1930. In the United States, the first report of beech bark disease was in Massachusetts in 1929 (Houston & Valentine, 1988). By the early 1970s, the disease had spread throughout New England and into eastern Pennsylvania. The scale and associated fungus are easily transported over long distances by animals and humans, which has resulted in isolated outbreaks and establishments in West Virginia (1981), Virginia (1983), and more recently, in the Great Smoky Mountains National Park (Tennessee) far ahead of the advancing front in Pennsylvania (Houston & Valentine, 1988; S. Schlarbaum, pers. comm., 2002).
There is no practical chemical control of the beech scale in natural forests. The scale has several natural predators, but none has been sufficiently effective to stop the spread of beech bark disease. Resistance to beech scale insect attacks has been discovered in some beech trees (Shigo, 1964; Cammermeyer, 1993; Houston & Houston, 2000) and can be integrated into breeding programs to produce beech bark disease-resistant trees for restoration of the species.
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Hawbolt, L. S. 1944. History of spread of beech scale, Cryptococcus fagi (Baerensprung), an insect introduced to the Maritime provinces. Acadian Nat. 1: 137-146.
Houston, D. R., and D. B. Houston. 2000. Allozyme genetic diversity among Fagus grandifolia trees resistant or susceptible to beech bark disease in natural populations. Can. J. For. Res. 30: 779-789.
Houston, D. R. and H. T. Valentine. 1988. Beech bark disease: the temporal patterns of cankering in aftermath forests of Maine. Can. J. For. Res. 18: 38-42.
Mahony, E. M., M. G. Milgroom, and W. A. Sinclair. 1999. Origin, genetic diversity and population structure of Nectria coccinea var. faginata in North America. Mycologia 91: 583-592.
Schlarbaum, S. E. September 2002. Department of Forestry, Wildlife, and Fisheries, University of Tennessee, Knoxville, TN., personal communication.
Shigo, A. L. 1964. Organism interactions in the beech bark disease. Phytopathology 54: 263-269.