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
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.
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.
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