Black Knot on Flowering Plum/Cherry: Prune and Spray

The black, knotty growths every foot on your flowering tree's branches are black knot (Apiosporina morbosa), a fungal disease of Prunus (plum, cherry, chokecherry).

Symptoms

• Black, rough, elongated galls on twigs/branches.
• Galls expand yearly, eventually girdling and killing branches.
• Tree declines, flowers poorly, dies back.

Control

1. Prune NOW (winter best): Cut 6–8 inches BELOW visible knot. Sterilize tools between cuts.
2. Destroy pruned material (burn, bury, trash)—spores release from galls.
3. Fungicide (spring): Chlorothalonil (Daconil) or thiophanate-methyl at bud break, repeat 2–3 times at 7–10 day intervals.
4. Annual inspection: Catch new galls early.

Prevention

• Plant resistant species: Japanese tree lilac, Amur chokecherry (less susceptible).
• Avoid planting Prunus near wild chokecherries (reservoir hosts).

Consistent pruning + spring fungicide can control black knot. Neglected trees eventually succumb.