Black knot (Apiosporina morbosa) is a fungal disease that causes greenish brown to black swellings in the stems of cherry trees (Prunus spp.). Its spores are released following periods of warm, wet weather and are spread by splashing water, wind, birds, and insects.

The Problem

Black knot deforms branches and reduces their growth. Heavily infected trees often become stunted and may eventually die from the disease.