Plants Susceptible to Crown Gall
Stone fruit trees such as cherry, peach and plum
are susceptible, along with related ornamentals. Brambles, grapes,
roses, willows and euonymus are also affected.
‘Emerald n’ Gold’ is
a cultivar of wintercreeper euonymus, which is particularly
susceptible. Young galls are smooth and greenish-white to tan. As
they mature, galls become dark, hard and woody; they eventually
crack and decay. Crown galls are a solid mass of tissue all the way
through, unlike insect galls.
Emerald n' Gold Euonymus
Plants suffering from crown gall often exhibit stem dieback and
stunted growth, because the galls disrupt the movement of water and
nutrients between roots and leaves. This certainly detracts from
their ornamental value, and severely infested plants may die.
The severity of the disease depends on the size, number, and
location of the galls. Galls at the crown of young plants cause the
greatest damage, and can eventually kill them. Crown gall may have
little noticeable effect on older, established plants.
Try to Reduce Plant Stress
It sounds like your plants are not severely affected yet, and there
are steps you can take to keep them growing well. There is no
chemical control for this disease. Agrobacterium radiobactor, a
related bacterium that is antagonistic to Agrobacterium tumefaciens,
is used to treat crown gall, but it is really meant for propagation
nurseries rather than home gardeners. Be sure to care for the
infested plants well so that other stresses do not allow the galls
to overwhelm them. For example, provide supplemental water during
times of drought. Avoid wounding the stems, especially near the soil
line, because that is the main way the causal bacteria get into
Crown gall on an older Euonymus
Severely infested plants should be removed. Do not replace
them with susceptible plants. Crown gall can spread to unaffected
plants since it becomes established in the soil. The bacteria can
persist in the soil for two or more years, even when susceptible
plants are not present on the site. If you need to prune infested
plants, disinfect your pruners between cuts by dipping them in 70
percent alcohol and allowing them to air dry. If the galls are very
visible and unsightly, you can try to prune them out carefully.
However, crown gall is systemic; removing the galls after the fact
does not get rid of the disease.
Some gall resistant plants that you may be able to work into your
planting include: Boxwood (Buxus spp.); deutzia (Deutzia spp.);
elderberry (Sambucus spp.); holly (Ilex spp.); and doghobble (Leucothoe
Over 600 species of plants are susceptible to crown gall. Examine
plants carefully before bringing them home from the nursery, and
avoid those with suspicious swellings on the roots or stems. In the
case of crown gall, an ounce of prevention is worth a pound of cure!
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