Caused by a fungus, black knot disease primarily infects plum and cherry trees. It is very common in Ohio, especially in home gardens, small orchards, and groves. The fungus apiosporina morbosa, can harm the appearance of ornamental tree varieties and limit fruit production on orchard trees. Spores are produced in mid to late spring and spread by raindrop splashes which release the spores into the air. The spores are then carried by the winds and germinate when they land on other trees. The disease gets its name from the black swellings (knots) that appear on the infected trees. Left untreated, fruit production will be severely affected.
Symptoms: Black knot-like swellings several inches long may be seen on the twigs and branches. New growth and twigs may show wilt.
More information: OSU Extension, University of Maine Extension