Description
Galls are growths on plants. They may be simple lumps, or they may have a complicated structure. Some galls are brightly colored. Galls form on leaves, twigs, and branches. In most cases they are unsightly but not damaging to the plant, although small plants may be stunted. The water and nutrient circulatory system of a small plant may be disrupted by the galls. Some galls form when insects (certain wasps, midges, and aphids) or mites feed on or lay eggs in leaves, stems, and twigs. While feeding or laying eggs, these insects inject a toxin that stimulates rapid and abnormal cell growth. Galls may also develop as a response to infection by any of several kinds of fungi, bacteria, and viruses. Galls caused by fungi and bacteria are usually most numerous in wet years. A soil-inhabiting bacterium (Agrobacterium tumefaciens) causes a common plant disease called crown gall. For more information about crown gall, see Crown Gall.
Control
Pruning off gall-infested growth usually takes care of the problem. If galls are especially unsightly and numerous, you can control the insects or diseases that are causing them. Look up your plant in the index to determine which pests may be causing the galls.
