Black Knot is a fungal disease that can be found in commercial, municipal, private, and natural plantings throughout Alberta. 

What Trees does it Affect?

Black Knot is common of plants in the genus Prunus. This includes Chokecherry’s, Mayday Trees, and Flowering Plums, to name a few.

What are the Risks?

Black Knot reduces the aesthetics of affected trees, and high levels of infection can lead to death of the plant.

What to Look For

The most common way to characterize Black Knot is by its black, tar-like swellings that grow on infected branches. These swellings begin as small, green galls that develop at a growing point or fruit spur and grow until reaching maturity.

Black Knot    Black Knot


Here are some methods prevention methods you can implement to help control Black Knot:

  • Remove all knot-bearing branches to reduce a build-up of the disease
  • Prune infected branches far below knots, sanitize the blades after pruning, and immediately destroy diseased wood
  • Monitor regularly and keep plants healthy and stress-free
  • Practice proper pruning techniques to allow adequate canopy ventilation

Related Links

Black knot Alberta