161 



some areas. An anthracnose disease is plaguing both the flowering dogwood in east- 

 ern forests and the Pacific dogwood in the Pacific Northwest. It has killed over 80 

 percent of the trees in some areas (US Forest Service 1991a). First discovered in 

 Washington State in 1976 (Byiher and Davidson 1979) and subsequently in New York 

 in 1978 {cf. Pirone 1980), the disease has spread rapidly throughout eastern and west- 

 ern forests (Britton 1993). In southeastern North America, an estimated 5.7 million 

 acres of forest were affected by 1990 (Chellemi et aL, in press). The fungus is most viru- 

 lent in cool, continuously moist conditions, eg., high elevation dogwood populations 

 proximal to water. 



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Dogwood anthracnose is a leaf and twig disease that is initially detected by leaf necro- 

 sis. The fungus Discula destructiva is now recognized as the causal agent (Redlin 

 1991). Wliilc the exact origin of the fungus in North America is uncertain, many sci- 

 entists believe that ilie disease was Introduced as it was first discovered near large 

 port cities. Once infested, a tree will eventually become defoliated and mav take sev- 

 eral years to die. Occasionally u-ees are killed by annual cankers that can girdle the 

 stem. Studies by Anderson et aL (1993) suggest that acid rain may predispose dog- 

 woods to infestation and increase the severity of the disease. Contrary to forest- 

 dwelling dogwoods, well-maintained trees in landscape plantings with full sun expo- 

 sure often can 5ur\-ive (Swank and Smith, personal communication). 



Public concern for the species' existence was increased when research failed to show 

 resistance in population samples from 20 different sutes (Santamour et aL 1990). As 

 a result, certain southern universities and the Forest Service have become extensively 

 involved in assessing the spread, impact, and conu-ol of this pesL Surveys in Catoctin 

 National Park have located puuiive resistant u-ecs in areas where dogwood popula- 



