- 1). Prune all shoots and branches with knots. Remove the knots (the sources of inoculum or virus cells) in winter, before any buds appear and ascospore (fungus spores) discharge. Cut each infected branch or twig at least 6 to 8 inches below the knot. Check for, and also get rid of, knots and sources of inoculum in nearby wild plum and cherry trees.
- 2). Safely dispose of infected knot-branches. Place in trash in a sealed plastic bag. Even after knot removal, black fungus knots can continue producing fungal spores that harm other nearby plants.
- 3). Spray fungal parasite. Apply Trichothecium roseum, a biological control agent, to the section of branch or shoot showing symptoms of black knot. Symptoms include thick, black, oddly shaped swellings on fruit tree twigs.
- 4). Try a fungicide. Using fungicide products is dangerous and prohibited in orchards in many U.S. states. A multipurpose fruit tree spray, Bonide, protects fruit trees from fungus and diseases. Use cautiously by following the package instructions.
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