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Black Knot on Plum Trees: Fruit Safety and Disease Management

Good News: Fruit Is Safe to Eat

Black knot (Apiosporina morbosa) does not affect fruit quality or safety. Enjoy your harvest—the plums are perfectly edible despite the fungal galls on branches.

Understanding the Disease

Fungus infects woody tissue → rough, black, swollen galls (knots).
Stress (including black knot) can trigger heavy fruiting—your bumper crop may reflect tree stress.
Spores spread in spring rain/wind from mature knots (2+ years old).

Management Program

Prune now (dormant season): Cut 4-6″ below visible knots. Sterilize tools between cuts.
Destroy prunings: Burn, bury, or bag—don't compost.
Fungicide spring: Apply chlorothalonil or thiophanate-methyl at bud break, repeat per label.
Annual inspection: Remove new knots promptly.

Long-Term Outlook

Black knot is manageable but rarely eradicated. Consistent sanitation + timely fungicides keep trees productive for decades. Your 7-year-old tree's first heavy crop is a milestone—protect it with good care.

Trees: Premature Fruit Ripening and Drop in Plum Trees: Environmental Causes; Plum Tree with Jelly-Like Sap: Borer Infestation; Black Knot on Plum: A Serious Fungal Disease; Managing Black Knot on Cherry Trees; Stratifying Plum Seeds for Germination; Oak Twig Galls: Identification and Management; Preventing Fruit on Ornamental Plum Trees with Hormone Sprays; Black Knot Disease on Plum Tree: Fruit Impact and Control; Black Knot Disease on Stone Fruit Trees: Pruning Out Infected Limbs; Plum/Cherry Black Knot: Prune Out Knots in Winter, Few Fungicides Work

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