Crown gall is a tumorous growth of tissue up to several inches or more in diameter. It is generally found at the soil line or on roots and usually has a rough surface.
Crown galls differ from natural burls.
The crown gall bacterium lives in the soil and enters the plant at the site of a wound, perhaps from a shovel or a lawn mower. Once inside the plant, the bacteria stimulates gall formation. Infected plants often grow very slowly and continue to decline in vigor year after year. Avoid wounding plants when transplanting, cultivating or mowing. Dig up and destroy infected plants, removing the surrounding soil carefully and disposing of it away from cultivated plants.