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Black Knot Disease on Flowering Plum: Pruning and Prevention

Flowering plum shows black warty growths on branches with dieback. Same symptoms appearing on second tree.

Black Knot Diagnosis

Fungus Apiosporina morbosa. Greenish soft knots → hard black galls. Spores spread in spring (bloom to shuck fall). Stunts trees; severe infections render worthless.

Control Program

Prune out knots: Cut 2-3" below on twigs; on large limbs, excise knot + 1" healthy wood (best in August).
Destroy prunings: Burn/bury—spores persist weeks after removal.
Dormant spray: Lime-sulfur before bud break.
Sanitation: Remove wild plums/cherries within 500 ft.
Resistant varieties: Select for new plantings.

Urgency

Act now—spread to second tree confirms active epidemic. Combined cultural/chemical approach required.

Plant Diseases: Black Knot on Plum Tree: Prune, Sanitize, Fungicide for Prevention; Flowering Plum Peachtree Borer: Comprehensive Pest Management Guide; Black Knot Disease on Plum: Pruning and Fungicide Protocol; Black Knot on Ornamental Plum: Organic Atomic Grow Treatment; Flowering Plum Black Knot: Identification and Control; Black Knot on Plum Trees: Pruning, Spraying, and Saving Your Tree; Flowering Plum Died After Sucker Pruning: Regrow from Base; Black Knot on Flowering Almond: Prune Out Galls, Sterilize Tools; Black Knot Disease on Plum Tree: Fruit Impact and Control; Flowering Plum Tree Guide: Varieties, Care, and Pruning

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