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05-11637
PPM point 8.2
Data Sheets on Pests recommended for regulation as quarantine pests
Discula destructiva (anthracnose of dogwood)
This data sheet is based on a CPC data sheet
IDENTITY
Name: Discula destructiva Redlin 1991
Synonyms:
Taxonomic position: Fungi: Ascomycota: Diaporthales
Notes on taxonomy and nomenclature:
No teleomorph is known, but other species of Discula have teleomorphs in the genera Apiognomonia
and Gnomoniella. Zhang and Blackwell (2001) confirm from DNA sequence analyses that D.
destructive has clear affinity with Diaporthales.
Common Names
English: anthracnose of dogwood
Bayer computer code: DISCDE
EPPO list:
EU Annex designation: No status.
HOSTS
The North American species Cornus florida (flowering dogwood) and C. nuttallii (Pacific dogwood)
are particularly susceptible. Cornus kousa, C. alternifolia and C. amomum are reported as relatively
resistant (Sherald et al., 1994). The European Cornus mas is considered resistant in North America
(Stinzing and Lam, 2003), but there is no information for C. sanguinea. Nothing appears to be
reported concerning Asian species of Cornus.
Host List
Primary hosts
Cornus florida (Flowering cornel), Cornus nuttallii (Pacific dogwood)
Secondary hosts
Cornus alba, Cornus controversa (giant dogwood), Cornus sericea (redosier dogwood), Cornus
stolonifera
GEOGRAPHICAL DISTRIBUTION
EPPO region: Present in Germany (few outbreaks, first found in in 2002), Italy (first found in a
nursery in Lombardia in 2003, on C. florida and C. nuttallii). Intercepted in 1995 by United Kingdom
on imported C. florida from USA..
North America: Present.
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.
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).
EU: Present
BIOLOGY
D. destructiva persists as cankers on the trunks and branches of its hosts, or in twigs or dead leaves
carrying conidiomata. Conidia formed in conidiomata (acervuli) on cankers are rain-splashed to newly
expanded leaves in spring, which they infect under humid conditions. Lesions on the leaves may
remain as small spots, form larger blotches, or blight the whole leaf, spreading into the petiole and
infecting the shoot. At flowering, bracts are also infected. Conidia may infect the current season's
shoots directly, forming small cankers which are usually rapidly delimited by callus tissue. However,
shoots infected from blighted leaves become more severely cankered and die back. This shoot dieback
often results in the development of epicormic shoots on the branches and trunk, which become
infected in turn. Heavily infected young trees may be killed but, if conditions become less favourable
for disease development in subsequent seasons, branch and trunk cankers may be contained and the
tree recovers.
In culture, optimal growth is at 21-24°C, no growth occurs at 27°C. Infection is favoured by cool, wet
spring and autumn, but can occur throughout the growing season. Low light intensity and drought
stress are predisposing factors (Erbaugh et al., 1995). See Daughtrey and Hibben (1994) and
Daughtrey et al. (1996).
DETECTION AND IDENTIFICATION
Symptoms
Initial symptoms are small leaf spots with a 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 base 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 understorey forest dogwoods.
Morphology
Conidia are of the typical anthracnose type, 7-12 x 2.5-5.5 µm, hyaline, non-septate, smooth, with a
truncate base and often polar guttules (Redlin, 1991; Daughtrey et al., 1996). In mass, they form a
slimy, white to beige or pinkish ooze. The conidioma (acervuli) form in leaf or twig tissues, erupting
through the surface often around a trichome, typically 30-135 µm diameter and rounded on the
underside of leaves, or 90-340 µm long and slightly elongated on twigs. They appear dark in the
tissues of overwintered twigs. The teleomorph has not been reported.
D. destructiva was initially confused with the anamorph of Glomerella cingulata, already well known
on this host. Various other fungi cause leaf spots of Cornus (Elsinoë corni, species of Septoria,
Ascochyta cornicola, Botryotinia fuckeliana), but these are easily distinguished microscopically.
MEANS OF MOVEMENT AND DISPERSAL
Short distance dispersal of conidia probably occurs via rainsplash. Field dispersal by coccinellids
(Hippodamia convergens) has been observed. Birds and other animals (Holt et al., 1998) may possibly
carry the pathogen, even in fruits or seeds, which have been shown to contain the pathogen (Britton et
al., 1993). Trade of infected plants ensures long distance dispersal.
PEST SIGNIFICANCE
Economic impact
In the USA, in addition to the environmental impacts, consecutive years of infection have killed many
ornamental Cornus spp. in parks and gardens. The disease now presents a considerable problem for
nursery production of healthy plants.
Control
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. In the USA, emphasis is given to: optimum fertilization, trickle irrigation, adequate sunlight,
mulching, pruning, fungicides, resistant cultivars, limiting movement of nursery material (Daughtrey
et al., 1996). Forest management techniques favourable to the survival of understorey dogwoods
remain to be worked out, but Britton et al. (1994) suggest that anthracnose is less severe on stands
which were clear-cut 30 years ago than on those where timber was only partially harvested.
PHYTOSANITARY MEASURES
No international measures are currently applied for D. destructiva. As the main risk of introduction is
by movement of infected plants for planting, it would be appropriate to require such material to come
from a pest-free area or pest-free place of production.
To be completed after PRM
ACKNOWLEDGEMENT
BIBLIOGRAPHY
Britton KO, Roncadori RW, Hendrix FF, 1993. Isolation of Discula destructiva and other fungi from
seeds of dogwood trees. Plant Disease, 77(10):1026-1028.
Britton KO, Pepper WD, Loftis DL, Chellemi DO, 1994. Effect of timber harvest practices on
populations of Cornus florida and severity of dogwood anthracnose in western North Carolina. Plant
Disease, 78(4):398-402.
Daughtrey ML, Hibben CR, Britton KO, Windham MT, Redlin SC, 1996. Dogwood anthracnose:
understanding a disease new to North America. Plant Disease, 80(4):349-358.
Daughtrey ML, Hibben CR, 1994. Dogwood anthracnose: a new disease threatens two native Cornus
species. Annual Review of Phytopathology, 32:61-73.
Erbaugh DK, Windham MT, Stodola AJW, Augé RM, 1995. Light intensity and drought stress as
predisposition factors for dogwood anthracnose. Journal of Environmental Horticulture, 13(4):186189.
Holt HL, Grant JF, Windham MT, 1998. Incidence of arthropods infested with conidia of the
dogwood anthracnose fungus, Discula destructiva Redlin, on flowering dogwoods in the natural
environment. Journal of Entomological Science, 33(4):329-335.
Redlin SC, 1991. Discula destructiva sp. nov., cause of dogwood anthracnose. Mycologia, 83(5):633642.
Sherald JL, Stidham TM, Roberts LE, 1994. Evaluation of eight species of Cornus for resistance to
dogwood anthracnose. Journal of Environmental Horticulture, 12(2):61-64.
Stinzing A, Lang KJ, 2003. Dogwood anthracnose. First detection of Discula destructiva on Cornus
florida in Germany. Nachrichtenblatt des Deutschen Pflanzenschutzdienstes, 55(1):1-5.
Trigiano RN, Caetano-Anollés G, Bassam BJ, Windham MT, 1995. DNA amplification fingerprinting
provides evidence that Discula destructiva, the cause of dogwood anthracnose in North America, is an
introduced pathogen. Mycologia, 87(4):490-500.
Zhang N, Blackwell, 2001. Molecular phylogeny of dogwood anthracnose fungus (Discula
destructiva) and the Diaporthales. Mycologia, 93: 355-365.