Forest Pests: Insects, Diseases & Other Damage Agents

Fusicoccum Canker - Fusicoccum spp.

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. - Cankers and dieback caused by Fusicoccum spp. are most severe on sites where trees are growing poorly. Small branches are most affected, although the bole can be attacked. Canker development is usually arrested on trees with vigorous growth; however, cankers may girdle small limbs resulting in dieback and wind breakage.

Identifying the Disease. - Annual cankers appear pale brown when young, but eventually turn dark brown with a distinct boundary between the living and dead tissues. Old, inactive cankers appear sunken and may be surrounded by callus. Dead bark may separate from the wood and disappear from old cankers not covered by advancing callus. Symptoms alone are sometimes insufficient to identify this disease.

Identifying the Fungus. - The fungus forms white masses of conidia within minute, asexual fruiting bodies (pycnidia) embedded in cankers of diseased branches. Conidia must be examined microscopically for identification.

Biology. - The biology of this disease is incompletely known. Numerous conidia, produced and exuded from pycnidia in cankers during wet periods, are spread by splashing rain and mechanical means. They germinate and produce hyphae that enter wounds on branches resulting from insects, frost, or mechanical damage. Stressed trees are more easily infected and colonized.

Control. - Cankers can be minimized through wound prevention, pruning out and removing limbs with cankers from landscape trees during winter, and establishing vigorous planting stock on good sites.

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