Photographer: USDA Forest Service – North Central Research Station Source: Bugwood.org Copyright: CC BY 3.0 US
The beech bark disease is a disease complex made up of two pathogenic fungi Nectria coccinea var. faginata and N. gallingena that are transmitted by the beech scale insect (Cryptococcus fagisuga). The scale insects are minute (up to .04 inches) and are a beige color. In North America the only beech species is the American beech (Fagus grandifolia). However, European beech trees (Fagus sylvatica) have been imported and established themselves in Canada and the Northeastern United States. This adds another host species that can help the fungus spread to American beech.
Symptoms of this disease start with the appearance of white wax secreted from the scale. Eventually the entire tree trunk can be covered. Once the fungus is transmitted serious damage becomes evident. The first sign of Nectria spp. infection is a red-brown slime will start oozing out from larger dead spots in the trunk. The dead areas can then expand deeper into the sapwood, form cankers, and spread to other places on the trunk. Beech bark is usually very smooth, so large cankers and crater-like scars on the bark surface is a conspicuous sign of infection. Nectria spp. can infect large areas on trees, completely girdle the tree and ultimately kill the whole tree. In the spring following severe infestation, leaves will not emerge. The crown will thin, and by the end of the year most leaves will have turned yellow.
The American beech is a widespread tree in the United States, providing habitat, shelter and oxygen for animals and northern hardwood forest ecosystems throughout their range. It is a major nut-producing tree that provided food for black bears, squirrels, chipmunks, porcupines, deer and birds. When a tree dies of infection it is removing the habitat it provides, while also creating a gap in the forest’s canopy. By changing the canopy structure and presence of beech trees this pathogen has serious ecological impacts.
In order for this fungus to be present the beech bark scale (Cryptococcus fagisuga) must first be established. The scale insects reproduce parthenogenically, and deposit yellow eggs on the bark. In late summer through early winter the eggs hatch. The scale insects feed on tree fluids via stylets. If the scale insects are infected with the fungi species they will inject spores into and on top of the bark. Spores will start to produce fruiting bodies called perithecia that are small, bright red and oblong shaped. The perithecia can produce viable spores the following year, and spores produce asexually or by vegetative means.
This disease was first documented in Canada in the 1890s, and reached the United States in the 1930s. It has spread throughout the Northeastern United States and is as far south as Tennessee and North Carolina.
The insect vector Cryptococcus fagisuga, was introduced from Europe.
U.S. Habitat: Has the potential to spread anywhere American beech trees (Fagus grandifolia) are present. Map of native range click here.
U.S. Present: CT, MA, ME, MI, NC, NH, NJ, NY, OH, PA, RI, TN, VA, VT, WI and WV
Animated map of the Beech Bark Disease invasion provided by the U.S. Forest Service click here.
An important management practice is killing the scale insects. Since these insects transmit the fungi to trees, if the scales are managed via insecticides, dormant oils and insecticidal soaps, it will disrupt the spread of the fungi. A soft brush or strong stream of water can be used to remove the scales on small trees. However, this is more applicable in a residential or recreational areas. In forested areas, the practical method is cutting down dead and diseased trees. No large scale pesticide application or biological control methods currently exist. Luckily, a few beech trees have shown resistance to the beech bark disease complex. They are currently being studied by researchers in hopes of finding disease-resistant trees that can be bred for long-term management.
Gwiazdowski, R.A., R.G. Van Driesche, A. Desnoyers, et al. 2006. Possible geographic origin of beech scale, Cryptococcus fagisuga (Hemiptera: Eriococcidae), an invasive pest in North America. Biological Control 39(1):9-18.
Houston, D. R. 1994. Major new tree disease epidemics: beech bark disease. Annual review of phytopathology, 32(1): 75-87.
McCullough, D.G., R.L. Heyd, and J.G. O'Brien. 2005. Biology and Management of Beech Bark Disease (PDF | 2.77 MB). Michigan State University. Extension Bulletin E-2746.
Morin, R. S., Liebhold, A. M., Tobin, P. C., Gottschalk, K. W., & Luzader, E. 2007. Spread of beech bark disease in the eastern United States and its relationship to regional forest composition. Canadian journal of forest research, 37(4): 726-736.
Shigo, A. L. 1972. The beech bark disease today in the Northeastern United States. J. For. 70: 286-289.