Health Protection, Southern Region
caused by Nectria galligena and N. magnoliae
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.
Target-shaped nectria canker
on walnut. (Click for detail. JPG 38K).
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.