Managing Dogwood Anthracnose

More options exist for managing ornamental dogwoods in landscaped areas than natural populations in forest sites. Cultural conditions that favor the growth of dogwood, such as optimum fertilization, trickle irrigation (Daughtrey and others 1988, Mielke and Daughtrey 1989), mulching, and at least 30 percentfull sun, have been recommended for ornamental dogwoods (Bailey and Brown 1991, Gould and Peterson 1994). Under severe disease pressure, these cultural treatments should be combined with fungicide applicationto provide adequate control. Theprotectant fungicides chlorothalonil, mancozeb, or mancozeb plus thiophanate-methyl and thesystemic fungicides: propiconazole, tebuconazole, andtriforine are registered for control of dogwood anthracnose(Anderson and others 1993, Windam and Windam 1991). Pruning to reduce inoculum, although originally recommended, has proven ineffective or only slightly effective (Anderson and others 1993, Windam and Windam 1991). These management guidelines for ornamental dogwoods are summarized in a 10-point control program (Bailey and Brown 1991) and further refined into a decision tree (Andersonand others1994, Daughtrey and Hibben 1994, Daughtreyand others1996).

In forest environments, managing individual trees for dogwood anthracnose is prohibitively expensive.Sometimes, however, it is practical to managethe diseasewith stand-level treatment. Clearcutting forest sites where dogwood regeneration is desired may lead to the development of a C. florida population that is less susceptible to anthracnose (Brittonand others1994). Britton and others (1994) found anthracnose was less severe in stands of C. florida where the timber had been clearcut 30 years previously than in stands where timber had been partially harvested. However, the effects of harvesting stands after anthracnose is present are not yet known. Identifying ideal sites for dogwood will be as important as identifying site factors most likely to favor anthracnose (Langdonand others1991, Windhamand others1993). Disease severityoften islowon undisturbed sites that support the largest C. florida populations, possibly because these are the most favorable sites for the species (Chellemiand others1992, Daughtrey and Hibben 1994, Daughtreyand others1996).

Resistant host material may be the greatest hope for long-term management of anthracnose. Research continues to find potentially resistant trees in woodlands where dogwood anthracnose was present. Potentially resistant survivors have been identified from populations of flowering dogwoods devastated by anthracnose in southeastern New York (Hibben and McArdle 1992) and in Catoctin Mountain Park (Graham and Windham 1993). These selections can be included in breeding programs after their disease resistance is confirmed (Daughtrey and Hibben 1994, Daughtreyand others1996).

Resistance genes in other dogwood species make them useful as current planting alternatives for high-hazard areas, as well as candidates for resistance gene donors. Cornus kousa is a known host of D. destructiva but seldom shows severe symptoms. The first-generation hybrids of C. florida x C. kousa, introduced as the Stellar series by Rutgers University, possess increased genetic resistance to anthracnose (Britton 1993b). Other resistant species native to North America include C. racemosa and C. canadensis, C. amomum, C. alternifolia, and C. mas (Brownand others1992, Daughtrey and Hibben 1994, Daughtreyand others1996).