[Illustration: 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.