This plant disease doesn't look like other bacterial diseases. There is no spotting with halos, no bacterial streaming, and certainly no secondary soft rot or tissue dropping out of the foliage. The crown gall bacterium causes the plant to produce woody galls on stems, crowns, or roots.
Crown gall is a bacterial disease infecting hundreds of plant species, both woody and herbaceous. The most common hosts in Illinois include creeping euonymus, grape, raspberry, crabapple, and rose. The causal bacterium, Agrobacterium tumefaciens, enters the plant through a wound. The plant forms a gall in response to this infection. Galls appear on the trunk, crown, and 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. Cut into the gall to investigate the cause. The galls from crown gall disease will appear as a mass of undifferentiated tissues whereas insect galls will have galleries or pockets with or without insects present. There are a few fungi that may cause galls on plant tissue too, so check a good disease reference book to see what else might be affecting your plants.
Plants may survive for years with galls of crown gall. Still, you will not be able to cure the plants of the malady even if you remove the galls. My own creeping euonymus survived many years with crown gall. They were finally killed during one severe winter, weakened by the crown gall infection.
The bad news is that this disease is quite persistent. The Agrobacterium bacterium can survive in the soil more than 5 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 feeding by insects or other pests. If you let your dog run through the planting, enough wounding may occur to let the pathogen enter.
Control of this disease is very difficult. If you decide to remove plants and start over, you will need to 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 like their predecessors. If you are moving to a new site, inspect new plants for galls before planting. Do not buy plants with galls. Because plants may have the crown gall disease and remain symptomless, do not try moving seemingly healthy plants from your infected bed to the new site.
Here are some options for you to try in an area infested with crown gall: barberry, hornbeam, true cedars, ginkgo, golden-raintree, tuliptree, mahonia, spruce, linden, boxwood, catalpa, beech, holly, larch, magnolia, black gum, pine, Douglas-fir, baldcypress, hemlock, birch, firethorn, redbud, smoke tree, sweetgum, deutzia, serviceberry, yellowwood, yew, and Zelkova. For more information on crown gall, consult Report on Plant Disease (RPD), no. 1006, available in Extension offices or on the Extension Vista Web site.