Black Knot Disease on Plum: Pruning and Fungicide Protocol

Plum tree loaded with fruit but covered in black knot disease on every branch; pruning all would remove tree.

Management

Prune 2-3 inches below galls during dormancy. Sanitation usually controls it. Lime sulfur or tribasic copper sulfate fungicides aid control—multiple applications from pre-bloom to post-fruit set. Fungicide alone insufficient.

Large Branches/Trunks

Cut out knots with knife/chisel including 1 inch healthy bark around knot. Taper cuts for healing. Destroy nearby wild plum/cherry with disease.

Critical

BURN all prunings before spring bud break—spores spread from debris. Chemical: 1.5 Tbsp Benlate + 1.5 Tbsp Captan/gallon, apply at early bloom, repeat 7-10 days until mid-June.