Informational table showing disease name, symptoms, pathogen/cause, and management of Hackberry diseases. Disease Symptoms Pathogen/Cause Management Witches’ broom Many short twigs develop close together from a swelling on a branch. The tree may be covered with witches’ brooms. Sphaerotheca phytophila (a powdery mildew) and an eryophyid mite (Eriophyes celtis) Remove unsightly trees.