Black Knot Not Black
boggs.47 Wed, 05/04/2016 – 08:13
Black Knot of Prunus is caused by the fungus, Apiosporina morbosa, and is characterized by thick, corky, elongated gall-growths on twigs and branches. The common name of the disease is based on the coal-black coloration of older galls late in the growing season. Currently, newly sporulating black knot galls are olive-green or reddish brown and may have a velvety texture. Newly forming galls may appear as simple swollen growths causing the bark to crack; they may be mistaken for a cankering disease.
While cankers can be pruned from purple plums, in Canada cherry it is so aggressive and virulent that attemps to prune it out or treat it are futile. Arbor Doctor recommendation: do not plant Canada cherry.