Associations Between Causal Agents of the Beech Bark Disease Complex [Cryptococcus fagisuga(Homoptera: Cryptococcidae) andNectriaspp.] in the Great Smoky Mountains National Park

American beech, Fagus grandifolia Ehrhart, is currently threatened by the insect-mediated disease complex known as beech bark disease. The organisms (beech scale, Cryptococcus fagisuga Lindinger, and two pathogenic fungi, Nectria galligena Bresadola and Nectria coccinea variety faginata Lohman, Watson, and Ayers) associated with beech bark disease were assessed using a qualitative rating system and correlated with other biotic and abiotic factors in 10 permanent plots in the Great Smoky Mountains National Park from spring 1994 through spring 1997. Tree mortality, as well as the presence of another scale species [Xylococculus betulae (Pergande)], also were documented and analyzed. During this study, incidence of C. fagisuga and overall tree mortality increased (55.6-87.9 and 16.0-26.8%, respectively). A forward stepwise logistic regression model selected average overall ratings of C. fagisuga, sum of presence of X. betulae, average presence of X. betulae, average overall ratings of Nectria spp., maximum presence of X. betulae, sum of south ratings of C. fagisuga, average south ratings of C. fagisuga, and diameter at breast height (dbh) of the tree as significant variables that best explained mortality of American beech. Pearson correlation analysis showed significant associations between ratings of Nectria spp. and C.fagisuga from both the previous season and previous year during fall 1996 and spring 1997. Moderate correlations between elevation, as well as aspect, and north, south, and overall ratings of C. fagisuga from fall 1995 to spring 1997 were documented. The significant association between presence of C.fagisuga and infection by Nectria spp. suggests that control of C. fagisuga could decrease occurrence and slow the spread of beech bark disease. Unless appropriate control and/or management of the disease complex is identified and implemented, mortality of American beech is expected to increase throughout most areas in the Great Smoky Mountains.