Rough Bark of Aspen and Aspen Gall

Compiled by Ned Tisserat, Colorado State University:

Taxonomy

Domain	Eukarya
Kingdom	Fungi
Phylum	Ascomycota
Subphylum	Pezizomycotina
Class	Dothideomycetes
Order	Botryosphaeriales
Family	Botryosphaeriaceae
Genus	Diplodia

Scientific Name

Diplodia tumefaciens

Common Name

corky bark disease

Curcurbitaria staphula or various fungi and Diplodia tumefaciens

Hosts

Susceptible hosts are aspen, cottonwood and poplar, most often in high altitude, forest sites.

Diagnosis and Damage

Symptoms of rough bark of aspen are rough oval spots and fissured bands of grayish-black, corky bark that often extend all or part way around the trunk or branches. The damage caused to the trees by rough bark is unknown but presumed to be unimportant, although some of the fungi affect the bark periderm, cortex, and phloem. Lichens and one or more fungi often are found fruiting on the corky ridges; consequently, a microscopic examination is necessary to identify them. Aspen gall (D. tumefaciens) produces galls when infecting aspen branches and rough bark when infecting large stems. Other cork-bark diseases of aspen have been identified in Canada, some are wide spread in the West. Rhytidiella baranyayi causes angular, rough bark without forming a band around the trunk and is frequently initiated around branch stubs. Seimatosporium etheridgei forms cushion-like swellings, more circular in outline and smaller that the other rough barks, the central portion later assumes a cork-bark appearance. These diseases do not kill trees, but heavy infection does make ornamental trees unsightly and thus reduces their value.

Biology and Disease Cycle

Spores that gain entrance to the tree by wounds or natural openings such as lenticels cause most infections. In the case of Diplodia tumefaciens, penetration is no deeper than the outer layer of the cortex, because it apparently stimulates the formation of a protective periderm. The sequence of fungal invasion and formation of a protective barrier against the pathogen continues for years, resulting in the formation of rough bark and branch galls.

Management

No control guidelines have been established for these diseases, although management could include wound avoidance of host trees, maintaining high tree vigor with appropriate cultural practices, and removal of heavily infected trees.

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