Three American Tragedies: Chestnut Blight, Butternut Canker, and Dutch Elm Disease

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Scott E. Schlarbaum (1), Frederick Hebard (2), Pauline C. Spaine (3), and Joseph C. Kamalay (4)

Abstract. Three North American tree species, American chestnut (Castanea dentata), butternut (Juglans cinerea), and American elm (Ulmus americana), have been devastated by exotic fungal diseases over the last century. American chestnut was eliminated from eastern forests as a dominant species by chestnut blight (Cryphonectria parasitica). Butternut is presently being extirpated, as butternut canker disease (Sirococcus clavigigenti-juglandacearum) spreads into northern populations. Urban and forest American elm populations have been decimated by Dutch elm disease (Ophiostoma ulmi and O. nova-ulmi). A combination of basic and applied research has been directed toward developing resistant trees of each species. Resistant American elms are now available for planting in urban settings. The prospects for reintroduction of resistant American chestnut, butternut, and American elm into eastern forests appear to be promising.

Forest ecosystems are subjected to many biotic and abiotic stresses. Native insects and diseases, droughts, windstorms and wildfire periodically impact forests or specific tree species, leaving dead or weakened trees. The effects of these stresses may be manifested locally or over a large area, yet they do not cause species extinction. In contrast, exotic pests can threaten the continued existence of a species (cf. United States Congress, 1993). Often host species have not evolved genetic resistance to exotic pests, as coevolutionary processes have not occurred.

Three prominent North American tree species, American chestnut [Castanea dentata (Marsh.) Borkh.], butternut (Juglans cinerea L.), and American elm (Ulmus americana L.) have been severely impacted by three exotic fungal diseases, chestnut blight [Cryphonectria parasitica (Murr.) Barr], butternut canker (Sirococcus clavigigenti-juglandacearum Nair, Kostichka & Kuntz), and Dutch elm disease [Ophiostoma ulmi (Buis.) Narruf. and O. nova-ulmi). Below is a brief account of the impacts of these diseases on their host species, examples of research approaches for disease control, and a prognosis for the future of each species.

. Department of Forestry, Wildlife & Fisheries, The University of Tennessee, Knoxville, TN 37901-1071

2. The American Chestnut Foundation, Wagner Research Farm, Meadowview, VA 24361

3. USDA Forest Service, Southern Research Station, 320 Green Street, Athens, GA 30602

4.USDA Forest Service, Northeastern Forest Experiment Station, 359 Main Rd., Delaware, OH 43015-8650.