Black Knot


Cut off infected parts


Infected limbs and twigs lose vigor and may eventually die, Black knot is caused by the fungus Dibotryon morbosum. The fungus overwinters in knots on twigs and branches or in the infected wood. In the spring, infective spores are formed in sacs that are contained within tiny fruiting bodies on the surface of the knots. These spores are then ejected into the air during rainy periods and are blown for distances by wind. Only new green twigs of the current season's growth are susceptible to infection.