In Illinois, crown gall is probably most common on creeping euonymus, grape, raspberry, and rose, though it may occur on hundreds of plants, as described in Report on Plant Diseases No. 1006. This disease is caused by the bacterium Agrobacterium tumefaciens. It appears as galls or overgrowths on the trunk, crown, roots, and sometimes stems. Galls are initially white or tan, more or less round, soft and spongy, and possibly two inches or more in diameter. As galls age, they turn dark brown and develop an irregular, convoluted, rough, corky surface and a hard, woody interior. To distinguish crown gall from an insect gall, cut it open. Crown gall shows a mass of undifferentiated tissue. Insect galls have compartments or small capsules where insects grow and develop.
The causal bacterium survives for many years in the soil and is easily spread in soil, water, or rain splash. The bacterium penetrates plants only through fresh wounds, such as those incurred by pruning, cultivating, transplanting, budding or grafting, or even by feeding of insects and other pests. A dog walking across a euonymus bed can cause enough wounding to provide infection sites. The disease interferes with the transport of water and nutrients, which makes infected plants stunted, weak, and more susceptible to winter injury.
Control of crown gall is difficult. Pruning galls is not helpful--it only provides more wound sites for possible infection. Begin by digging and destroying all severely infected plants. Do not replace them with a susceptible species; the soilborne bacterium will infect new plants. Also, before purchasing plants, inspect them for galls. Try to help plant vitality by watering in periods of drought and fertilizing in the fall with a balanced fertilizer.