WITCHES'-BROOM

symptom of plant disease that occurs as an abnormal brushlike cluster of dwarfed, weak shoots arising at or near the same point; twigs and branches of woody plants may die back. There are numerous causes, including rust (Gymnosporangium and Pucciniastrum); Apiosporina, Exobasidium, and Taphrina fungi; mites; insects; viruses; mycoplasmas; bacteria; and mistletoes. Susceptible plants include alder, alfalfa, Amelanchier, birch, California buckeye, Chamaecyparis, cherry, cherry laurel, elm, fir, hackberry, Holodiscus (ocean spray), honey locust, juniper and red-cedar, manzanita, mountain heath, mulberry, oak, potato, rhododendron, rose, sophora, spruce, and strawberry.