Black knot of Prunus

Black knot fungus (Apiosporina morbosa, formerly known as Dibotryon morbosum and Plowrightia morbosum) affects various Prunus species, including flowering plums, native cherries, and certain cultivated stone fruits. This disease infects young twigs, causing crusty black swellings called “knots” to form along branches. In highly susceptible trees, it can result in twig girdling and dieback, general tree weaking, and substantial disfigurement.