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Black Knot Fungus

Identifying and managing black knot fungus on trees in Springside.

What Is It?

Dibotryon Morbosum

Black knot primarily affects trees in the Prunus family — including Mayday trees and
chokecherries, common in Springside. It appears as rough, black, elongated growths
(galls) on branches, typically 1–10 cm long.

Paint Colours Quick Reference

  • SRA common-area trees: Email info@springsideresidents.com. The SRA will arrange assessment and treatment.
  • Your property: Prune 15–20 cm below the gall. Dispose in garbage — do not compost.
  • City trees: Call 311 to report to the City of Calgary.

Best time to prune is late winter or early spring before spores are released. Sterilize pruning tools between cuts.

Paint Colours Quick Reference

  • Rough, black, elongated swellings on branches
  • 1–10 cm long, irregular in shape
  • Affected branches may die back
  • Most visible in late summer and fall

External Resources

Alberta Government

alberta.ca/black-knot

City of Calgary — Report via 311