Cankers stop enlarging in late fall and can not be distinguished from black rot cankers, caused by Botryosphareia obtusa . Isolation of the pathogen is necessary for correct identification of the causal organism. Spores of the fungus causing black rot are large, dark pigmented structures, where as spores of the fungus causing white rot are much smaller and almost transparent. By spring, small, black pycnidia, the spore-containing structures of the fungus, appear on the smooth surface of new cankers. On older cankers, these may be present throughout the year.
Cankers exhibit a scaly, papery outer bark that is often orange .
Tissues beneath the canker surfaces are watery or slimy and brown. Most cankers are not deep, extending at most to the wood. Fruit rot is first visible as small, slightly sunken, brown spots that may be surrounded by a red halo. As the decayed area expands, the core becomes rotten and eventually the entire fruit. Red-skinned apple varieties may bleach during the decay process and become a light brown.