diseases of plants characterized by excessive branching and the formation of thin, stunted branches with underdeveloped leaves. The branches are usually barren. These diseases are caused by some Exoascales fungi (witches’-brooms of cherry, plum, and birch), rust fungi (witches’-brooms of conifers), and by viruses (witches’-brooms of potato); the disease may also be caused by insect damage to the plants. Control measures consist in pruning diseased branches, spraying plants in the spring with Bordeaux mixture, and destroying potato plants affected with the diseases.