Crown gall, caused by the soil-borne bacterium Agrobacterium tumerofasciens, is characterized by the growth of galls on roots or stems. Although found on more than 600 plant species in over 90 families, the disease is of economic importance on relatively few ornamental plants. Some commonly affected ornamentals include rose, Prunus spp. (flowering cherry, flowering almond and ornamental plum), willow and Euonymus (especially wintercreeper).

Symptoms:

Crown gall is a tumorous growth of plant tissue up to several inches or more in diameter. Galls form on stems or more commonly on roots, especially at the stem-root interface. Young galls are light-colored and smooth. Older galls become discolored, hard and woody, and eventually crack, decay and slough off. The severity of this disease depends on the size, number and location of galls, as well as the susceptiblility and age of the plant. Infected plants tend to exhibit a general decline in vigor, although crown gall may have little noticeable effect on older plants. Galls which develop on the crown of young plants have the greatest adverse effect, causing stunting and reduced flower display. Infected plants tend to be more susceptible to drought, winter injury and Armillaria root rot.

Disease Development:

Bacteria can survive in soil for more than 10 years. Crown gall bacteria may be spread through contact with soil, water or contaminated tools. Bacteria require fresh wounds to enter plant tissue. These may result from feeding by insects and nematodes, pruning, transplanting and frost heaves. Upon entry into plant tissue, the bacterium transfers its genetic information to plant cells, resulting in rapid, localized growth of plant tissue. Bacteria can move in plant tissues, causing secondary galls to form around the affected area.

Control:

• Avoid wounding plants when planting, transplanting, and cultivating.
• Clean tools routinely while pruning or grafting.
• Soils where infected plants have grown may support high populations of crown gall bacteria on root fragments left after removal of these plants. Remove surrounding soil when digging out infected plants.
• Select resistant plants as replacements such as bald cypress, beech, boxwood, deutzia, gingko, goldenrain tree, holly, hornbeam, larch, linden, magnolia, pine, serviceberry, spruce, tuliptree, yellow wood, Japanese yew and zelkova.

Adapted from Ohio State University Extension, 1999;
Diseases of Ornamentals, BP-33, Purdue University Cooperative Extension Service, 1999.