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      Damage from Discula destructiva (Photo: Clemson University - USDA Cooperative Extension Slide Series, www.forestryimages.org) - Click for full size   Shoot dieback from Discula destructiva (Photo: Robert L. Anderson, USDA Forest Service, www.forestryimages.org) - Click for full size   Leaf dieback caused by Discula destructiva (Photo: Robert L. Anderson, USDA Forest Service, www.forestryimages.org) - Click for full size   Leaf spots caused by Discula destructiva (Photo: Robert L. Anderson, USDA Forest Service, www.forestryimages.org) - Click for full size   Leaf spots caused by Discula destructiva (Photo: Robert L. Anderson, USDA Forest Service, www.forestryimages.org) - Click for full size   Twig dieback from Discula destructiva (Photo: Robert L. Anderson, USDA Forest Service, www.forestryimages.org) - Click for full size
    Taxonomic name: Discula destructiva Redlin (1991)
    Synonyms:
    Common names: dogwood anthracnose
    Organism type: fungus
    Discula destructiva is a fungus that has caused serious losses to North American native flowering dogwood (Cornus florida) and other native and introduced species (C. nuttallii and C. kousa, respectively) of dogwood found in the natural environment and in ornamental plantings. Infection is more likely to occur at higher elevations and on moist to wet sites, and shade increases the risk of infection and mortality. Spores are washed onto new leaf tissue during periods of wet weather or sprinkler irrigation. Spores of Discula destructiva land on shoots and leaves penetrating them directly and causing the quick death of the plant tissue due to the production of several toxins by the fungus. Larger trees often die 2 to 3 years after the first symptoms are found in the leaves. Management of Discula destructiva is not readily available, but there are strategies available to enhance high value and ornamental populations of dogwoods through extensive care of individual trees.
    Description
    The USDA Forest Service: Northeastern Area (UNDATED) states that, "Conidiomata of D. destructiva may form on necrotic leaf or bark areas. Masses of white to salmon coloured conidia ooze as cirrhi from the reddish to dark brown conidiomata during wet weather." The USDA Forest Service: Southern Region (UNDATED) adds that, "Initial symptoms of D. destructiva are small tan leaf spots that develop into large tan blotches. Often a purple border occurs between dead and healthy tissues and occasionally the entire leaf is killed."
    Occurs in:
    natural forests, planted forests, ruderal/disturbed, urban areas
    Habitat description
    The USDA Forest Service: Southern Region (UNDATED) states that, "Infection begins in leaves and spreads to twigs and branches, which dieback. Main-stem infections cause cankers, which kill the trees. In the South, infection is most likely at higher elevations and on moist to wet sites. Shade increases risk of infection and mortality."
    General impacts
    The USDA Forest Service: Northeastern Area (UNDATED) states that, "Discula destructiva Infections often progress down the petioles of blighted leaves into shoots, resulting in cankers. Direct infection of shoots, resulting in tiny cankers, may occur on C. florida during spring and fall. Girdling cankers typically develop at leaf nodes, causing twig dieback. On C. nuttallii , fall blighting of terminal leaves is common, resulting in death of terminal buds. Twig dieback is most common in the lower crown following years of extensive spring or fall leaf blighting. As a result of twig dieback, succulent shoots proliferate on the lower trunk and main branches of affected trees. These branches are very prone to infections, which may progress into the main stem Multiple cankers can girdle individual branches or kill the entire tree." The USDA Forest Service: Southern Region (UNDATED) adds that, "Cankers may not be present on all the dead trees. Larger trees often die 2 to 3 years after the first symptoms are found in the leaves." The fungal growth and virulence at 28 C and higher is significantly decreased (Ning and Blackwell, 2002).
    Notes
    The USDA Forest Service: Northeastern Area (UNDATED) states that, "The origin of this disease is unknown. The fungus may have been introduced or a change in environment may have altered host/parasite relationships, enabling a previously innocuous fungus to become a significant pathogen." The USDA Forest Service: Southern Region (UNDATED) states that, "The dieback of twigs and branches in the lower crown led to the original name of "lower-branch dieback" (Pirone 1980, in USDA Forest Service: Southern Region, UNDATED). Further knowledge of the pathogen allowed the disease to be renamed 'dogwood anthracnose.'" Zhang and Blackwell (2002) suggested that the fungus was introduced based on genetic data.
    Geographical range
    Native range: If the native range is outside of North America as suggested the native range is unknown. According to Zhang and Blackwell (2001, 2002) the fungus is believed to have been introduced into North America in the 1970s, when it appeared suddenly in the northwestern and northeastern USA, apparently in separate introductions.
    Dogwood anthracnose has been reported in British Columbia and Ontario in Canada (Canadian Forestry Service).
    There have been reports of its presence in Europe: It was intercepted in 1995 by United Kingdom on imported C. florida from the USA; it was first found in Germany in 2002, (EPPO); The dogwood anthracnose disease has just been confirmed in Italy (Tantardini, A. et al., 2004).
    Introduction pathways to new locations
    Nursery trade:
    Other: The origin of this disease is unknown. The fungus may have been introduced or a change in environment may have altered host/parasite relationships, enabling a previously innocuous fungus to become a significant pathogen
    Management information
    Preventative measures: The USDA Forest Service: Northeastern Area (UNDATED) states that, "Dogwoods receiving good cultural care will be better able to withstand D. destructiva during years in which the disease is favoured by weather conditions. Remove succulent branches as they form to prevent trunk canker formation. Avoid high nitrogen fertilizers, which stimulate succulent branching."

    The USDA Forest Service: Southern Region (UNDATED) also offers suggestions for managing D. destructiva: "Inspect trees frequently to detect the presence of the disease in its early stages. Select healthy planting stock. If symptoms are seen on the planting stock, dispose of the infected trees. Avoid sites along streams, lakes, or ponds where moisture will remain on the foliage for many hours after sunrise. Prune and completely remove or destroy dead wood in the tree and leaves on the ground yearly. Avoid mechanical and chemical injuries to the trees. Lawnmower and string-trimmer wounds are particularly troublesome."

    Chemical: Fungicides should be used only to supplement a cultural control program. Applications of chlorothalonil, mancozeb will protect against leaf infections. Apply fungicides registered for prevention or control of dogwood anthracnose when it is necessary to do so. Fungicides should be applied as buds are breaking in the spring and at least twice thereafter as the leaves are expanding (USDA Forest Service).

    Nutrition
    Necrotrophic parasitism
    Reproduction
    Asexual reproduction by conidia produced in structures called acervuli; sexual reproduction unknown (Redlin, 1991).
    Lifecycle stages
    Pecknold et al. (2001) states that, "On the underside of the leaf spots the fruiting structures of the causal fungus Discula destructiva, may be visible as small raised tan or brown specks scattered randomly over the lesion surface. Spores from these structures are washed onto new leaf tissue during periods of wet weather or sprinkler irrigation. If cool wet weather persists leaves may become severely blighted. "The Plant Disease Diagnostic Clinic (2001) states that, "Reproductive structures of D. destructiva form underneath leaf spots and on the surface of twig cankers. Huge amounts of asexual spores are formed inside and, in the spring, ooze out in slimy beige clusters. Local dispersal of the spores occurs by splashing rain while long distance dispersal may also occur via insects and birds. Transportation of diseased stock into new areas spreads the disease as well, especially into areas where dogwoods are not native. Spores of the fungus land on shoots or leaves penetrating them directly causing the quick death of the plant tissue due to the production of several toxins by the fungus." Redlin (1991) states that D. discula produces acervular and subcuticular conidiomata on leaves and twigs of the host. Conidia are ellipsoidal and nonseptate. A sexual state is unknown.
    Reviewed by: Ning Zhang and Meredith Blackwell, Department of Plant Pathology, Pennsylvania State University, and Department of Biological Sciences, Louisiana State University.
    Compiled by: National Biological Information Infrastructure (NBII) & IUCN/SSC Invasive Species Specialist Group (ISSG)
    Last Modified: Friday, 31 March 2006


ISSG Landcare Research NBII IUCN University of Auckland