Black Knot of Cherry

Black knot is a very common fungal disease that occurs on a variety of cherry trees including chokecherry, black cherry, wild cherry, and plum trees. Black knot will cause branch dieback and eventually tree death if not properly managed.

Infection may occur on branches of all sizes and occasionally on the trunk. Black knot initially causes a slight swelling and cracking of the bark. Infected areas later become more noticeable as they turn into hard, swollen, black knots. The appearance has been described as looking like charred marshmallows on a stick. These knots will be visible on branches after leaf drop in the fall. More than one knot can occur on each branch.

Manage black knot infections by pruning branch swellings and knots before growth starts in the spring. The best time to prune is usually in late February through March. Prune branches 5-6 inches below visible knots and swellings. Burn, bury, or throw away all infected material in accordance with local ordinances. Continue to monitor branches for knots and swellings throughout the growing season, pruning any new infections during dry periods. To reduce the number of spores in severe infections, apply lime sulfur or Bordeaux mixture in early spring before new growth emerges.

For more information visit the Yard and Garden Line web site.

Links:
Insects & Diseases of Woody Plants of the Central Rockies