Meaning of black knot

black' knot'

Pronunciation: [key]
— Plant Pathol. Plant Pathol.
  1. a disease of plants, esp. of plums and cherries, characterized by black knotlike overgrowths on the branches, twigs, etc., caused by a fungus, Dibotryon morbosa.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.