Black Knot is a fungus that primarily affects plum and cherry plants, both ornamental and edible varieties. Some commonly used landscape plum and cherry varieties are affected. Brown, swollen growth on twigs and branches that grow larger over time are indicative of Black Knot. Most infections occur during wet conditions and cooler spring temperatures. Plants are most susceptible during their blooming stage. The fungus enters the plant through new growth, a tree wound or by simply penetrating the bark. Infection normally starts on new growth, with smaller twigs dying. The tell-tale Black Knot gall doesn’t appear until the second year of infection. The olive-green knots enlarge in the spring and continue to swell on the branches throughout the growing season, becoming larger and darker. By the fall season the knots may have completely girdled the twig or branch cutting off water and nutrients to the tree. Some branches may take several years to die from the knot growth. Stunted tree growth and leaf wilting are symptoms of Black Knot infection. If left untreated, the fungus will continue to spread and weaken the tree, possibly killing the tree.

Carefully pruning infected branches is the best control method for Black Knot. There are procedures that should be followed to effectively control the spread of Black Knot. Pruning should be done before new plant growth begins, pruned plant material should be discarded and not left in the landscape and the tools used to prune require sterilization between cuts. In addition, pruning cuts need to be made well below the fungal growth.

Kramer Tree Specialists offers the services of Certified Arborists that can properly identify Black Knot disease and propose the best course of action with your tree’s best interests in mind. Call us today for more information and to have a Certified Arborist visit your property.