Witch's broom

Witch's broom is a disease or deformity in a woody plant, typically a tree, where the natural structure of the plant is changed. A dense mass of shoots grows from a single point, with the resulting structure resembling a broom or a bird's nest.

Diseases that may cause a witch's broom include:
 * Aster yellows, a disease of several herbaceous plants in the Aster family of plants.
 * Potato spindle tuber viroid, a virus of potatoes and other Solanaceous plants.