What is it? Black Knot Fungus is a very common disease in Prunus family (common cherry trees, mayday tree, schubert choke cherry tree, plum trees in calgary). It is a fugus called Apiosporina morbosa. It will affect the look and the health of your tree. Symptoms Damages What to do? Other resources: https://www.calgary.ca/parks/pests/black-knot-fungus.html https://tidcf.nrcan.gc.ca/en/diseases-caused-by-pathogens/factsheet/4 https://www.alberta.ca/black-knot