Forest Pests: Insects, Diseases & Other Damage Agents

Nectria Canker - Nectria galligena Bres. in Strass.

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. - Perennial Nectria canker is among the most common and easily recognized diseases of ashes and other hardwood trees in the East and South. The disease is prevalent in cool, humid climates or where isolated pockets of cool air collect, especially on poorly drained soils.

Identifying the Disease. - Cankers begin as small, inconspicuous, dark depressions on young stems. The fungus penetrates the cambium and establishes a perennial infection. It repeatedly kills callus tissue that forms annually at the edge of the lesion, giving rise to a targetlike, perennial canker with concentric rings of dead callus. Cankers seldom girdle the bole.

Identifying the Fungus. - The small (1 to 2 mm diameter), bright-red to orange perithecia form from autumn through spring, near young cankers with bark, in bark crevices, or at the margins of old cankers lacking bark. Occasionally, microscopic cream-colored sporodochia form during moist weather.

Biology. - Ascospores expelled from perithecia during rainy periods in the spring and autumn are dispersed by wind and water to wounds such as frost cracks, sunscald lesions, leaf scars, hail wounds, and senescing lower branches. The ascospores germinate to produce hyphae that infect stems and initiate canker development throughout the growing season. The fungus overwinters as mycelia in cankers and as ascospores in perithecia.

Control. - Nectria canker can cause significant damage to individual trees, but the low incidence and minimal losses attributed to this disease rarely warrant control. This disease is easily prevented by avoiding bark wounds during cool, humid conditions.

[ Contents ]     [ Previous ]     [ Next ]     [ Home ]