The Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) has posted a notice reminding gardeners that Black Knot is easy to see on Prunus sp. at this time. This large genus includes almond, peach, plum, cherry, and apricot among other popular flowering and fruit bearing trees.
Gardeners should monitor gardens and adjacent wild areas for Prunus shrubs and trees with large black growths on previous years twigs.
Below is an image of Black Knot of Prunus from the University of Minnesota Extension Service.
OMAFRA notes that it is important to prune the cankers out, back quite close to the main stem before leaves emerge. Pruning too shallow retains the undetectable, developing canker on the tree and does nothing to limit the disease. And it is important to do a thorough clean up, destroying all pruned twigs.