Black knot shows up as conspicuous long black swellings on smaller twigs and as galls--hard, round knots--on larger branches of apricot, cherry, and plum trees. They may girdle and kill branches beyond, or even the whole tree. Prune out diseased wood in early spring, cutting at least four inches below the swelling. Apply lime sulfur while the tree is dormant, or use captan during the growing season. Remove or treat any nearby wild cherry or plum trees.
