Nectria canker of hardwoods, caused by _Nectria galligena_ and _N.
magnoliae_, is frequently found on yellow birch and black walnut. Common
hosts also include bigtooth aspen, sassafras, northern red oak, red
maple, beech, Carolina poplar, paper birch, and sweet birch. A closely
related canker disease is also found on yellow-poplar and magnolias. The
range of this disease includes the Lake States, the Northeast, and the
southern Appalachians.
[Illustration: Target-shaped canker of Nectria on sassafras and
yellow-poplar.]
[Illustration: (cont.)]
Older Nectria cankers are easily recognized in forest stands because of
their typical “target” shape. “Target” cankers have rings, each of which
represent a year’s growth. Younger cankers tend to be grown over by bark
and callus tissue attempting to heal the wound. Such cankers are
difficult to recognize, but close examination of the affected area may
reveal tiny red bodies, which are the fruiting bodies of the Nectria
fungi. Mortality rarely occurs from this disease, but stems may break at
canker locations during high winds.
Control of Nectria canker is the same as for Strumella canker—the
removal of infected trees during thinning operations.