Discula destructiva: addition to the EPPO Alert List
Discula destructiva is causing serious problems in North America on Cornus species both in natural environments (including forests) and amenity lands. It has been hypothesized that D. destructiva is an introduced exotic species, although its possible area of origin remains unknown. In Europe, this pathogen has been intercepted on imported nursery plants and has been found in Germany (see EPPO RS 2003/138). Although, the host range of D. destructiva is apparently limited to American species of Cornus (in particular, C. florida and C. nuttallii) which are not widely grown in Europe, the EPPO Secretariat decided to add it to the EPPO Alert List because it may present a risk to the nursery industry.
Discula destructiva (dogwood anthracnose)
Why :Discula destructiva attracted out attention because it was recently found in Germany on Cornus species of American origin and is reported to cause serious problems in North America both in forests and amenity parks.
Where: Dogwood anthracnose was first reported in the USA in 1978 on flowering dogwoods (Cornus florida) in north-eastern States (New York and Connecticut). It was later realized that similar symptoms had also been observed on C. nuttallii on the west coast in 1976. In both cases, the causal agent was identified as Discula destructiva in 1991. The disease then spread rapidly and caused serious losses. Genetic studies have revealed a lack of diversity among isolates from both coasts. Considering the rapid spread around points of entry (New York and Seattle) and the severity of the disease, it is supposed that D. destructiva is a introduced pathogen.
North America: Canada (British Columbia, Ontario), USA (Alabama, California, Delaware, Georgia, Idaho, Indiana, Kentucky, Maryland, Massachusetts, New Jersey, New York, North Carolina, Ohio, Oregon, Pennsylvania, South Carolina, Tennessee, Vermont, Virginia, Washington, West Virginia).
EPPO region: first found in Germany in 2002. Intercepted in 1995 by United Kingdom on imported C. florida from USA.
On which plants: Cornus florida (flowering dogwood) and C. nuttallii (Pacific dogwood). C. kousa is reported as relatively resistant. In Europe, the main species present are C. mas and C. sanguinea. C. mas is considered as resistant and there is no data for C. sanguinea.
Damage: Initial symptoms are small leaf spots with purple margin which then develop into large necrotic blotches. In many cases, infected mature leaves die prematurely. Sometimes, they remain attached to the stems after normal leaf fall. Infection expands from leaves to small twigs and then branches. Twig and branch dieback start in the lower crown (hence the original name of the disease ’lower branch dieback’). Numerous epicormic shoots often form at the basis of the trunk or on branches. D. destructiva causes cankers which can kill the tree. The fungus can kill trees of all sizes, but is more severe on young seedlings and understory forest dogwoods. In USA, consecutive years of infection have killed high proportions of woodland and ornamental dogwood populations. In 1984, a survey in a national park in Maryland showed that only 3% of dogwoods were free of anthracnose and 33% were dead. In 1988, 89 % trees were dead and all remaining trees were infected. Infection is favoured by cool, wet spring and autumn, but can occur throughout the growing season.
Dissemination: Short distance dispersal of conidia probably occurs via rain splashes and field dispersal by coccinellids (Hippodamia convergens) has been observed. Trade of infected plants ensures long distance dispersal.
Pathway: Plants for planting of C. florida and C. nuttallii from North America. The British interceptions and the findings in Germany demonstrate that this pathway exists.
Possible risks: Control of the disease is difficult, particularly in forests. In parks and gardens, cultural control (adequate watering and fertilization, pruning, removal of fallen leaves) and chemical control can be used. Data on the susceptibility of European Cornus species is lacking (in particular on C. sanguinea ; C. mas appears as broadly resistant). In Europe, the main hosts C. florida and C. nuttalii are not naturally present in forests, but they are valuable amenity plants for parks and gardens. Therefore, D. destructiva could present a risk to the nursery industry.
EPPO RS 2003/138, 2003/139
Panel review date - Entry date 2003-09
Daughtrey, M.L. ; Hibben, C.R. ; Britton, K.O. ; Windham, M.T. ; Redlin, S.C. (1996) Dogwood anthracnose. Understanding a disease new to North America. Plant Disease, 80(4), 349-358.
Stinzing, A.; Lang, K.J.(2003) [Dogwood anthracnose. First detection of Discula destructiva on Cornus florida in Germany.] Nachrichtenblatt des Deutschen Pflanzenschutdienstes, 55(1), p 1-5.
NPPO of Germany, 2003-09.
Canadian Forest Service. L’anthracnose du cornouiller (Discula destructiva) se manifeste en Ontario. Nouvelles Express. Service Canadien des forêts. Centre de foresterie des Grands Lacs. Bulletin no .1. http://www.glfc.forestry.ca/frontline/print_html/bulletin1_f.html
Cornell University. Anthracnose of flowerig dogwood Discula destructiva. Cornell Cooperative Extension. http://www.cce.cornell.edu/suffolk/grownet/tree-disease/anthdgwd.html
USDA Forest Service. St. Paul Field Office. How to identify and control dogwood anthracnose. http://www.na.fs.fed.us/spfo/pubs/howtos/ht_dogwd/ht_dog.htm
USDA Forest Service. Southern Region. Dogwood anthracnose and its spread in the south by R. L. Anderson, J.L. Knighten, M. Windham, K. Langdon, F. Hedrix, R. Roncadori. http://fhpr8.srs.fs.fed.us/pubs/dogwood/r8-pr26/dwr8pr26.htm
Wissenschaftszentrum Weihenstephan für Ernährung, Landnutzung und Umwelt, München, Germany. http://www.forst.uni-muenchen.de/EXT/LST/BOTAN/LEHRE/PATHO/CORNUS/discula.htm