Black swellings of cherry black knot.
Black knot, caused by Dibotryon morbosum, is prevalent throughout the Southeast (with the exception of southern Florida) wherever black cherry grows, and in orchards on plums and domestic cherries.
The most prominent symptoms are the elongated black swellings which appear in summer on small twigs and branches. Heavily infected trees appear quite grotesque, with large swellings which may be several times the diameter of the twigs. Cankers occurring on black cherry trunks usually ruin the commercial tree value. Initial infection occurs on lateral branches and twigs in the spring, but the swellings do not become noticeable until the following spring.
The most practical control for black knot is removal of infected black cherry from the stand. Twigs and branches with knots should be burned.
NECTRIA CANKER
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.
Target-shaped canker of Nectria on sassafras and yellow-poplar.
