Black Knot Fungus-photo submitted by Arboretum visitor, Melissa Sallade

Black knot fungus attacks cherry and plum trees causing galls to form.  The galls are particularly noticeable in winter and spring when trees are leafless.  Since the fungus can kill smaller trees and weaken larger trees, people who grow cherry and plum trees at home should monitor their trees carefully pruning out any knots that form in winter.