Forest Health Protection, Southern Region

Importance. - Nectria canker is the most common canker disease of hardwood trees. It seriously reduces the quantity and quality of forest products. This disease usually does not kill trees, but causes serious volume losses. It is common on yellow birch, black walnut, and sassafras. It also occurs on aspen, red oak, maple, beech, poplar, and birch.

Identifying the Fungus. - The fungus can be identified by the creamy-white fruiting structures that appear on cankers soon after infection. It can also be identified by the pinhead-sized, red, lemon-shaped perithecia near canker margins after 1 year.

Identifying the Injury. - Well-defined localized areas of bark, cambium, and underlying wood are killed by the fungus. Concentric, annual callus ridges develop around the expanding canker, and bark sloughs off the older parts of the canker. After several years, the canker resembles a target.

Biology. - The fungus survives through the winter in cankers, and produces spores during the spring. Windblown and watersplashed spores infect tree wounds and branch stubs.

Control. - Cankering may be minimized in high value areas by avoiding wounds and pruning out branch cankers. Sterilize pruning tools before moving to an uninfected tree and conduct pruning operations during dry periods when spores are less abundant.