USDA Forest Service, St. Paul, MN, 55108
Michigan Department of Natural Resources, Roscommon 48653
Michigan Department of Natural Resources, Marquette 49855
Michigan State University, Dept. of Entomology, East Lansing, MI 48824
Beech bark disease of American beech (Fagus grandifolia) is caused by the interaction of an introduced scale insect (Cryptococcus fagisuga) and the native fungus Nectria galligena, or N. coccinea var. faginata, which is thought to be introduced. Infestations of the insect precede development of the disease, and N. galligena is often found before N. coccinea var. faginata. Previously published records indicate that the beech scale extends as far west as eastern Ohio (2) and southern Ontario (Sajan, personal communication). The scale is now well established in several locations in both the Upper Peninsula (UP) and Lower Peninsula (LP) of Michigan. The scale insect has been found in beech stands throughout three counties (Oceana, Mason, and Muskegon) along the Lake Michigan shore in the LP, extending for at least 100 km from north to south, and occurring up to about 80 km inland. In the eastern UP, beech scale has been found in four counties (Alger, Chippewa, Luce, and Schoolcraft). The heaviest beech scale infestations are distributed around Ludington State Park in the west central LP and the Bass Lake Forest Campground in the eastern UP. The extent of the insect infestation suggests that it has been present in Michigan for many years, with anecdotal accounts placing the first observations of beech scale at Ludington State Park around 1990. These infection centers are distant from previously known beech scale infestations and are located in heavily used recreation areas, suggesting that the insect may have been transported by human activity. Perithecia of N. coccinea var. faginata were found in Ludington State Park in the LP at N 44° 1.951', W 86° 29.956' and perithecia of N. galligena were found at the Bass Lake site in the UP, at N 46° 27.748', W 85° 42.478'. The identity of the fungi collected from each location was confirmed by measurements of perithecium and ascospore morphology (1). Perithecia at both sites were scarce and difficult to find. Surveys planned for the summer and fall of 2001 will further delimit the occurrence and distribution of the pathogens involved in the disease in Michigan. To our knowledge, this is the first report of the beech scale and beech bark disease in Michigan, with N. galligena and N. coccinea var. faginata identified as the pathogens.
References: (1) H. V. T. Cotter and R. O. Blanchard. Plant Dis. 65:332--334, 1981. (2) M. E. Mielke et al. Plant Dis. 69:905, 1985.