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.