Forest Pests: Insects, Diseases & Other Damage Agents

Anthracnose - Gnomoniella fraxini Redlin & Stack

Solomon, J.D.; Leininger, T.D.; Wilson, A.D.; Anderson, R.L.; Thompson, L.C.; McCracken, F.I. 1993. Ash pests: A guide to major insects, diseases, air pollution injury and chemical injury. Gen. Tech. Rep. SO-96. New Orleans, LA: U.S. Department of Agriculture, Forest Service, Southern Forest Experiment Station. 45 p.

Importance. - Ash anthracnose may be the most common foliar disease of ashes in the United States. It is most important in landscape and street-side plantings and in plantations, and is less important in natural forest stands.

Identifying the Disease. - Round to irregular blotches, greenish brown at first, but turning brown with age, appear along margins and midribs of leaflets. Affected leaflets appear scorched and may curl and drop from the tree. Small cankers and dieback may occur on twigs of trees severely defoliated for several years. Numerous small, round lesions with gray centers and purple-brown margins (frogeye leaf spots) may develop late in the season.

Identifying the Fungus. - Acervuli, colorless initially and darkening with age, can be found on leaflets shortly after infection. Acervuli are also common on previous-year petioles and twig cankers. Masses of dull-white, to pale-pink conidia may be seen exuding from mature acervuli. Black perithecia develop over winter on petioles, leaves, and twigs on the ground.

Biology. - Expanding leaflets and shoots are infected in the spring by rain-splashed conidia from acervuli on dead petioles remaining on trees from the previous year. Additional infections may augment the disease during the growing season. Anthracnose is favored by cool, wet, spring weather and a lack of air circulation around susceptible tissues.

Control. - Direct control is rarely needed.

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