Crown Gall
Causal Agent
Agrobacterium tumefaciens
Hosts
More than 600 plant species in over 90 families are susceptible, although relatively few species sustain significant damage. Some of the common hosts include apple, blackberry, cherry, euonymus, forsythia, grapes, peach, pear, plum, poplar, raspberry, rhododendron, rose, and willow.
Symptoms
Galls form on roots and stems, especially at the root collar, or root crown. Aerial
galls are common on such highly susceptible plants as poplar, rose, willow, and euonymus.
Young plants with numerous galls tend to be stunted and predisposed to drought damage
or winter injury. Floral display or fruit production may be suppressed. Damage is
most severe when galls encircle the root crown, but few plants are killed by crown
gall alone. Severely diseased plants are subject to attack by secondary pathogens
that enter through decaying galls. Crown gall bacteria are dispersed in soil or irrigation
water, on horticultural implements, and on or within plants. Plants with latent infection
are a big problem, because dormant nursery stock that became infected at the time
of harvest may not develop galls until after planting in a new location. Tumor development
is most favored by temperature near 72°F. Temperature above 86°F prevents transformation
of normal cells to tumor cells, but does not prevent gall growth after transformation.
Control
If only a few galls are present, cut off and destroy the stems on which they occur. Dip pruning shears in a 10 percent bleach solution between prunes to prevent the spread of the bacteria. Heavily infected plants should be removed and destroyed. Good control can be achieved by treating barerooted nursery stock with an antagonistic strain of Agrobacterium prior to transplanting. Please contact your local county extension office for the most current information.