Crown gall is a bacterial disease that infects hundreds of plant species, but it is most common on creeping euonymus, grape, raspberry, and rose. The causal bacterium, Agrobacterium tumefaciens, enters the plant through a wound, and the plant forms a gall in response to this infection. Galls appear on the trunk, crown, roots, and sometimes on the stems of the host plant. Young galls are white or tan, usually round, and are quite soft and spongy. As the gall ages, it develops an irregular, convoluted, rough, corky surface and a dark brown, hard, woody interior. These galls might be mistaken for insect galls, but if you cut into the gall, you will see the difference. Galls from crown gall disease appear as a mass of undifferentiated tissues; insect galls have galleries or pockets with or without insects present.

This disease is quite persistent because Agrobacterium can survive in the soil more than five years. It is easily spread in soil water or rain splash but can penetrate plants only through fresh wounds. Such wounds might be made during pruning, cultivating, transplanting, budding, or grafting, or during feeding by insects or other pests. If you let your dog run through the planting, enough wounding will occur to let the pathogen enter.

Controlling this disease is very difficult. If you decide to remove plants and start over, use plants that will not host this disease. For instance, if you had a bed of creeping euonymus with crown gall, do not put healthy creeping euonymus back in that bed. They will become infected in time. If you are moving to a new site, inspect new plants for galls. Do not buy plants with galls. Because plants may have crown gall disease and remain symptomless, do not try moving seemingly healthy plants from your infected bed to the new site.

Some plants that are not reported to host crown gall include barberry, hornbeam, true cedars, ginkgo, goldenrain tree, tulip tree, mahonia, spruce, linden, boxwood, catalpa, beech, holly, larch, magnolia, black gum, pine, Douglas-fir, bald cypress, hemlock, birch, firethorn, redbud, smoke tree, sweet gum, deutzia, serviceberry, yellowwood, yew, and zelkova. For more information on crown gall, consult Report on Plant Disease No. 1006.