Flowering Plum Black Knot: Identification and Control

Upstate NY flowering plum has dark growths on branches, split bark. Owner had canker on Rose of Sharon. Expert confirms black knot (fungus Apiosporina morbosa). Affects plums and cherries. Greenish soft knots turn coal black and hard. Spores spread in spring at bloom. Control: prune 2–3" below knots on twigs; on large branches, cut out knot + 1" clean wood in August. Remove knots before spring. Dormant lime-sulfur spray. Destroy badly infected trees. Plant resistant varieties away from wild plums/cherries.

Integrated Management

1. Prune out knots in winter/dormant season.
2. Apply lime-sulfur at dormant stage.
3. Remove wild hosts within 500 ft.
4. Choose resistant cultivars for new plantings.

Persistence is required; black knot is chronic but manageable.