Diplocarpon mespili (entomosporium leaf spot on photonia)

Taxonomy

Domain	Eukarya
Kingdom	Fungi
Phylum	Ascomycota
Subphylum	Pezizomycotina
Class	Leotiomycetes
Subclass	Leotiomycetidae
Order	Helotiales
Family	Dermateaceae
Genus	Diplocarpon

Scientific Name

Diplocarpon mespili

Scientific Name Synonyms

Entomosporium maculatum

Fabraea maculata

Entomosporium mespili

Common Name

Entomosporium leaf spot

Author: Mary Ann Hansen, Virginia Tech

Reviewed by: Anton Baudoin, Virginia Tech and Karen Rane, University of Maryland

Pathogen

Diplocarpon mespili is an Ascomycete whose asexual stage is a member of the Coelomycetes. Diplocarpon mespili (syn. Diplocarpon maculatum, Diplocarpon soraueri, Entomopeziza mespili, Entomopeziza soraueri, Entomosporium maculatum, Entomosporium mespili, Fabraea maculata) produces conidia in fruiting bodies called acervuli. Conidia are 4- or 5-celled. Conidial cells have appendages that make them look like microscopic insects, hence one of the synonyms for the genus, Entomosporium. Acervuli are circular or irregular and can be up to 200 µm in diameter. Conidia consist of a larger basal cell, an upper cell, and 2 or more smaller, lateral, hyaline cells that form a cross pattern. The apical cell is globose with an obtuse apex; the basal cell is short cylindrical with a truncate base; and the lateral cells are globose. Apical and lateral cells each have a single, cellular, unbranched, flexuous appendage. Conidia are 15-22.5 µm X 5.5-9.5 µm overall; lateral cells are 4-7 µm long; appendages are 7-15.5 µm long. The sexual stage of the fungus, which has been reported in northern climates, produces fruiting bodies called apothecia, which produce hyaline, 2-celled ascospores.

Symptoms and Signs

Leaf spots on photinia first appear as minute, slightly raised dots on either surface of the leaf. Older spots have a slightly depressed center with raised margins. On the juvenile, reddish colored foliage of P. x fraseri, the tiny, new, circular leaf spots are a darker red than the surrounding healthy tissue. Older necrotic spots (up to 3-4 mm in diameter) have ashen gray centers and dark purple margins surrounded by an indefinite lighter purplish halo. The centers of the necrotic spots are dotted with minute black specks, which are the acervuli of the fungus. Leaf spots are discrete in light infections, but in heavy infections they often coalesce to form large, blighted areas. Infection is mostly limited to the leaf blade, but occasionally spots may occur on petioles and tender, young shoots. Heavy infections cause premature defoliation.

Ecology and Spread

The fungus overwinters as mycelium in fallen, infected leaves from the previous year and on leaves that remain on the plant. In late winter or spring, the fungus produces conidia that are dispersed by wind and splashing water to healthy tissue. Infection occurs most commonly on the lower leaf surface, but lesions appear on the upper leaf surface. Symptoms first appear about 10-14 days after infection on the new growth of the lowest branches and spread gradually upward. Secondary cycles of conidia production begin in early summer and can continue throughout the year in areas with mild climates. The fungus preferentially infects tender, new growth; mature leaves are resistant to infection. Mild, wet summers, air temperatures of 15-25^oC and 9-12 hour periods of leaf wetness favor disease. Both leaf spotting and defoliation can be severe in wet seasons. Production of the sexual stage (apothecia) of the fungus on fallen leaves has been reported in northern areas, but its role in the disease cycle is unknown.

Geographic Distribution

The disease has been reported in the United States in most states where photinia is grown. It has also been reported in Canada, the United Kingdom, France, Germany, Rumania, Austria, Italy, Russia, Japan, Malawi, Kenya, Cyprus, Zimbabwe, India, New Zealand and Australia.

Management

Cultural Control

Collect and remove fallen leaves in the winter to reduce sources of fungal inoculum before new growth appears in the spring. Plants pruned in late summer may suffer infections on new, succulent growth into the fall. Avoid frequent pruning and summer fertilization to avoid stimulating succulent growth, which is highly susceptible to infection. Avoid overhead irrigation, which spreads spores. In nursery production, take cuttings only from disease-free plants and discard diseased stock plants.

Resistance

Of the photinias, red-tip photinia (Photinia X fraseri) is the most susceptible to the disease and no cultivars are known to be resistant. Japanese photinia (P. glabra) is less susceptible, but occasional outbreaks have been reported. Diplocarpon mespili also infects other hosts in the subfamily Pomoideae of the Rosaceae family, including: Amelanchier, Aronia, Chaenomeles, Cotoneaster, Crataegus, Cydonia, Eriobotrya, Heteromeles, Malus, Mespilus, Pyracantha, Pyrus, Rhaphiolepis, and Sorbus.

Chemical Control

Preventative fungicides can be used for control, but they must be applied on a regular basis, generally every 10 to 14 days, beginning at budbreak and throughout the season for effective control.

Diagnostic procedures

Fruiting bodies (acervuli) readily produce conidia when infected plant tissue is placed in a moist chamber overnight. Conidia can be viewed in wet mounts with a compound microscope.

Resources and References

• Jones, R.K. and D. M. Benson. 2001. Diseases of Woody Ornamentals and Trees in Nurseries. APS Press, St. Paul, MN.
• Sinclair, W.A. and H.H. Lyon. 2005. Diseases of Trees and Shrubs. Cornell University Press, Ithaca, NY, and London.

• Sutton, B.C. 1980. The Coelomycetes: Fungi Imperfecti with Pycnidia, Acervuli and Stromata. Commonwealth Mycological Institute, Kew, Surrey, UK.

Reviewed by:Name, Organization

Acknowledgements

• National Institute of Food and Agriculture, U.S. Department of Agriculture, under Agreement No. 2011-41530-30708 as part of "Diagnostic Image Series Development for Supporting IPM in the Southern Region" (USDA-NIFA-RIPM-003351)