Controlling Black Knot on Flowering Plum

Black Knot Disease: Pruning, Sanitation, and Fungicides

Your ornamental plum had black knot last year. You pruned out the galls—good start. But spores from nearby infected trees reinfect via wind in spring. Garlic cloves in the soil won’t help.

Effective Management Plan

1. Thorough pruning: In fall/winter before growth starts, remove all visible knots. On large branches, cut out the knot plus 1 inch of healthy bark around it. Make cuts 2–4 inches below the knot.
2. Destroy debris: Burn or bury pruned material—spores survive weeks on the ground.
3. Fungicide spray schedule: Use Benomyl (Benlate 50% WP) at ½ tbsp/gallon.
   • First spray: spring at green tip.
   • Second: just before and after bloom.
   • Continue every 2 weeks until terminal growth stops (early–mid June).
4. Buy clean stock: Never purchase nursery trees with visible knots or swellings.

Consistent sanitation and timely sprays are the only reliable control.