what is the prevention of black knot?

Answer 1

Black Knot spores are active during warm, wet weather in late spring to early summer. To prevent black knot infections you need to select ornamental cherry & plum trees resistant to back knot disease. Also, always check your nursery plant material before you purchase for signs of black knot. When pruning cherry & plum trees, prune when dormant in winter or early spring before bud break. The spores are not active at these times and your trees will heal the fastest when they come out of dormancy in spring. Be careful around your cherry & plum trees. Damage to the bark from lawnmowers, string trimmers, etc. can become an entry for this disease. Finally, remove any prunus volunteers that could become a nurse tree for black knot. Inspect your prunus trees yearly & prune out any new infections you find the following dormant period. Prune at least 6-8" below the black knot galls. Clean your pruners between every cut with a 10% bleach solution. Fungicides available to homeowners are not very effective on black knot and are best used in commercial orchards.

Answer 2

If you are referring to the disease stone-fruits get, I have included a link for treatment.

http://www.ag.ndsu.edu/pubs/plantsci/hortcrop/pp689w.htm