Managing Black Knot on Cherry Trees

Black knot (Apiosporina morbosa) is a serious fungal disease on cherry and plum trees, forming rough black galls that girdle and kill branches. On a 7-acre Minnesota property with many infected trees, aggressive management is needed.

Pruning Protocol (Winter/Dormant Season)

1. Cut 2–3 inches below visible gall.
2. On large limbs/trunks: chisel out knot + 1 inch healthy bark around it; taper cuts to points.
3. Burn all prunings before spring bud break—spores mature on dead wood.

Fungicide Schedule (Supplement Only)

Begin at green cluster (early bloom), repeat every 7–10 days until mid-June:

• Benlate 1.5 Tbsp + Captan 1.5 Tbsp per gallon water.
• Or lime sulfur / tribasic copper sulfate per label.

Fungicides alone won't control black knot—sanitation is key.

Landscape Management

• Remove nearby wild cherry/plum hosts.
• Monitor annually; prune new galls promptly.
• Consider resistant varieties for new plantings.