Crown gall is a plant disease caused by the bacterium Agrobacterium tumefaciens. It typically affects a wide range of plants, including fruit trees, ornamental plants, and vegetables. The disease is characterized by the formation of tumor-like growths, or galls, at the base of the plant stem or roots, which can hinder nutrient and water uptake. The galls are usually rough and can vary in size, often leading to stunted growth and reduced yield. Control methods include removing infected plants, using resistant varieties, and practicing good garden hygiene to prevent the spread of the bacteria.