The disease occurs worldwide and is especially troublesome in nurseries. Losses in orchards are sporadic. The disease is caused by the bacterium, Agrobacterium tumefaciens . The formation of galls on roots and crowns of plants are characteristic of crown gall. Galls are often located at pruning wounds, especially on apple.
Small galls are initially smooth on the surface.
As they enlarge they become dark, hard, woody tumors with gnarled, irregular surfaces. Gall shapes and sizes vary . The same root or crown may contain numerous galls. The bacterium causing crown gall is spread from infected nursery stock which can contaminate orchard soils. These bacteria enter the roots and crowns of plants through wounds.