Discula destructiva (anthracnose of dogwood)

Identity

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Preferred Scientific Name

Discula destructiva Redlin 1991

Preferred Common Name

anthracnose of dogwood

EPPO code

DISCDE (Discula destructiva)

Summary of Invasiveness

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Since there is a very strong presumption that D. destructiva is alien to North America (Trigiano et al. 1995), this pathogen is clearly very invasive in US deciduous forests, seriously modifying their understorey composition and biodiversity by destroying species of Cornus which form a characteristic element of this ecosystem.

Taxonomic Tree

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Domain: Eukaryota
Kingdom: Fungi
Phylum: Ascomycota
Subphylum: Pezizomycotina
Class: Sordariomycetes
Subclass: Sordariomycetidae
Order: Diaporthales
Family: Valsaceae
Genus: Discula
Species: Discula destructiva

Notes on Taxonomy and Nomenclature

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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.

Description

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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.

Distribution

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D. destructiva was detected in 1995 in the UK on imported Cornus florida from the USA.

Distribution Table

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The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Last updated: 12 May 2022

Continent/Country/Region	Distribution	Origin	First Reported	Reference
Europe
Germany	Present, Few occurrences	Introduced		Stinzing and Lang (2003) CABI and EPPO (2004) EPPO (2022)
Italy	Present, Localized			CABI and EPPO (2004) EPPO (2022)
Netherlands	Absent, Confirmed absent by survey			EPPO (2022)
United Kingdom	Present, Widespread			EPPO (2022) CABI and EPPO (2004)
North America
Canada	Present, Localized			Redlin (1991) CABI and EPPO (2004) EPPO (2022)
-British Columbia	Present, Localized	Introduced		Redlin (1991) Daughtrey et al. (1996) CABI and EPPO (2004) EPPO (2022)
-Ontario	Present, Localized	Introduced		Daughtrey et al. (1996) CABI and EPPO (2004) EPPO (2022)
United States	Present, Widespread			Redlin (1991) Zhang and Blackwell (2002) CABI and EPPO (2004) Cheng et al. (2011) Seebens et al. (2017) EPPO (2022)
-Alabama	Present, Localized	Introduced		Daughtrey et al. (1996) CABI and EPPO (2004) EPPO (2022)
-California	Present, Localized	Introduced		Daughtrey et al. (1996) CABI and EPPO (2004) EPPO (2022)
-Connecticut	Present, Localized	Introduced	1983	Daughtrey et al. (1996) CABI and EPPO (2004) EPPO (2022)
-Delaware	Present, Localized	Introduced		Daughtrey et al. (1996) CABI and EPPO (2004) EPPO (2022)
-District of Columbia	Present, Localized			CABI and EPPO (2004) EPPO (2022)
-Georgia	Present, Localized	Introduced		Daughtrey et al. (1996) Zhang and Blackwell (2002) CABI and EPPO (2004) EPPO (2022)
-Idaho	Present, Localized	Introduced		Daughtrey et al. (1996) CABI and EPPO (2004) EPPO (2022)
-Illinois	Present, Localized	Introduced	1995	Schwegman et al. (1998) CABI and EPPO (2004) EPPO (2022)
-Indiana	Present, Localized	Introduced		Daughtrey et al. (1996) CABI and EPPO (2004) EPPO (2022)
-Kansas	Present, Localized	Introduced	1994	Daughtrey et al. (1996) CABI and EPPO (2004) EPPO (2022)
-Kentucky	Present, Localized	Introduced		Daughtrey et al. (1996) CABI and EPPO (2004) EPPO (2022)
-Maryland	Present, Localized	Introduced		Redlin (1991) Daughtrey et al. (1996) Zhang and Blackwell (2002) CABI and EPPO (2004) EPPO (2022)
-Massachusetts	Present, Localized	Introduced		Redlin (1991) Daughtrey et al. (1996) CABI and EPPO (2004) EPPO (2022)
-Michigan	Present, Localized	Introduced	1993	Daughtrey et al. (1996) CABI and EPPO (2004) EPPO (2022)
-Mississippi	Present, Localized	Introduced	1994	Daughtrey et al. (1996) CABI and EPPO (2004) EPPO (2022)
-Missouri	Present, Localized			CABI and EPPO (2004) EPPO (2022)
-New Hampshire	Present, Localized	Introduced	1991	Daughtrey et al. (1996) CABI and EPPO (2004) EPPO (2022)
-New Jersey	Present, Localized	Introduced		Daughtrey et al. (1996) Zhang and Blackwell (2002) CABI and EPPO (2004) EPPO (2022)
-New York	Present, Localized	Introduced		Daughtrey et al. (1996) Zhang and Blackwell (2002) CABI and EPPO (2004) EPPO (2022)
-North Carolina	Present, Localized	Introduced		Daughtrey et al. (1996) Zhang and Blackwell (2002) CABI and EPPO (2004) EPPO (2022)
-Ohio	Present, Localized	Introduced		Daughtrey et al. (1996) Zhang and Blackwell (2002) CABI and EPPO (2004) EPPO (2022)
-Oregon	Present, Localized	Introduced		Daughtrey et al. (1996) Zhang and Blackwell (2002) CABI and EPPO (2004) EPPO (2022)
-Pennsylvania	Present, Localized	Introduced		Redlin (1991) Daughtrey et al. (1996) Zhang and Blackwell (2002) CABI and EPPO (2004) EPPO (2022)
-Rhode Island	Present, Localized	Introduced	1992	Daughtrey et al. (1996) CABI and EPPO (2004) EPPO (2022)
-South Carolina	Present, Localized	Introduced		Daughtrey et al. (1996) CABI and EPPO (2004) EPPO (2022)
-Tennessee	Present, Localized	Introduced		Redlin (1991) Daughtrey et al. (1996) CABI and EPPO (2004) Cheng et al. (2011) EPPO (2022)
-Vermont	Present, Localized			CABI and EPPO (2004) EPPO (2022)
-Virginia	Present, Localized	Introduced	1987	Redlin (1991) Daughtrey et al. (1996) CABI and EPPO (2004) EPPO (2022)
-Washington	Present, Localized	Introduced		Redlin (1991) Daughtrey et al. (1996) Zhang and Blackwell (2002) CABI and EPPO (2004) EPPO (2022)
-West Virginia	Present, Localized	Introduced		Daughtrey et al. (1996) CABI and EPPO (2004) EPPO (2022)

History of Introduction and Spread

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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 D. destructiva in 1991. The disease then spread rapidly and caused serious losses. Genetic studies have revealed a lack of diversity among isolates from the two 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 an introduced pathogen.

Risk of Introduction

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In the USA, the further spread of D. destructiva poses a strong phytosanitary risk for native Cornus spp. grown both as ornamentals and occurring naturally in forests. Particularly in the eastern states, dogwoods have a strong emblematic value. A 10-point control programme has been developed with the support of a Dogwood Anthracnose Work Group, involving researchers, foresters, nurserymen and regulatory personnel (Daughtrey et al., 1996). Limiting interstate movement of infected host material is recommended. Though there is a general tendency for disease severity to decrease, it remains high at the southern edge where the disease is still spreading. In principle, there is also a risk for other continents where Cornus spp. occur or are grown as ornamentals, particularly Europe. The main hosts Cornus florida and C. nuttallii are not native, but are valuable amenity plants for parks and gardens. Of the two native species, Cornus mas has been found to be resistant, while the susceptibility of the much more abundant C. sanguinea is not known. However, neither wild nor cultivated species in Europe have the particular importance of the dogwoods in North America. Other species of Cornus occur through the remainder of the Palaearctic region. If only by default (as the disease was not previously known in either North America or Europe), it seems possible that D. destructiva originates in Asia, on native species whose resistance has made it inconspicuous.

Habitat List

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Category	Sub-Category	Habitat	Presence	Status
Terrestrial

Hosts/Species Affected

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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 Plants and Other Plants Affected

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Plant name	Family	Context	References
Cornus alba (red-barked dogwood)	Cornaceae	Other
Cornus controversa (giant dogwood)	Cornaceae	Other
Cornus florida (Flowering dogwood)	Cornaceae	Main	Cheng et al. (2011); Redlin (1991); Zhang and Blackwell (2002)
Cornus kousa (Kousa dogwood)	Cornaceae	Unknown	Redlin (1991); Zhang and Blackwell (2002)
Cornus nuttallii (Pacific dogwood)	Cornaceae	Main	Redlin (1991); Zhang and Blackwell (2002)
Cornus sericea (redosier dogwood)	Cornaceae	Other
Cornus stolonifera	Cornaceae	Other

Growth Stages

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Flowering stage, Seedling stage, Vegetative growing stage

Symptoms

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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.

List of Symptoms/Signs

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Sign	Life Stages	Type
Leaves / abnormal colours
Leaves / necrotic areas
Leaves / yellowed or dead
Stems / canker on woody stem
Stems / dieback
Stems / witches broom
Whole plant / plant dead; dieback

Biology and Ecology

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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).

Notes on Natural Enemies

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dsRNA has been detected in isolates of D. destructiva (i.e. a fungal virus; Yao and Tainter, 1996). There is a possibility that this could be associated with a decrease in virulence. By analogy with the control of chestnut blight (Endothia parasitica [Cryphonectria parasitica]), it is conceivable that hypovirulent strains could be used in disease control.

Means of Movement and Dispersal

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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.

Plant Trade

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Plant parts liable to carry the pest in trade/transport	Pest stages	Borne internally	Borne externally	Visibility of pest or symptoms
Leaves	fungi/hyphae; fungi/spores	Yes		Pest or symptoms not visible to the naked eye but usually visible under light microscope
Stems (above ground)/Shoots/Trunks/Branches	fungi/hyphae; fungi/spores	Yes		Pest or symptoms not visible to the naked eye but usually visible under light microscope

Plant parts not known to carry the pest in trade/transport
Bark
Bulbs/Tubers/Corms/Rhizomes
Flowers/Inflorescences/Cones/Calyx
Fruits (inc. pods)
Growing medium accompanying plants
Roots
Seedlings/Micropropagated plants
True seeds (inc. grain)
Wood

Wood Packaging

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Wood Packaging not known to carry the pest in trade/transport
Loose wood packing material
Non-wood
Processed or treated wood
Solid wood packing material with bark
Solid wood packing material without bark

Impact Summary

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Category	Impact
Animal/plant collections	None
Animal/plant products	None
Biodiversity (generally)	Negative
Crop production	None
Environment (generally)	Negative
Fisheries / aquaculture	None
Forestry production	None
Human health	None
Livestock production	None
Native fauna	Negative
Native flora	Negative
Rare/protected species	None
Tourism	None
Trade/international relations	None
Transport/travel	None

Impact

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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.

Environmental Impact

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In the USA, a significant proportion of woodland dogwood populations has been killed. In 1984, a survey in a national park in Maryland showed, in a severe case, that only 3% of dogwoods were free from anthracnose and 33% were dead. In 1988, 89% trees were dead and all remaining trees were infected. In the short term, at least, the disease is causing a clear change in forest understorey composition in eastern forests (Jenkins and White, 2002), with a substantial effect on their amenity value for the public. Nevertheless, the impact of the disease varies with site and past history (Chellemi et al., 1992; McEwan et al., 2000), so dogwoods are not seriously endangered. Indeed, the importance of the disease appears to be declining in areas where it was first introduced.

Impact: Biodiversity

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D. destructiva is clearly very invasive in deciduous forests in the USA, seriously modifying their understorey composition and biodiversity by destroying species of Cornus, which form a characteristic element of this ecosystem. It may secondarily affect other forest plants and animals by modifying the canopy structure and the availability of dogwood leaves and fruits as food (Rossell et al., 2001).

Social Impact

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Dogwoods are emblematic plants in the eastern USA, in nature and in gardens (for example, dogwood is the state flower of North Carolina). Their decline has a clear aesthetic impact.

Similarities to Other Species/Conditions

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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.

Prevention and Control

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Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

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.