Crown gall was recently diagnosed on a euonymus samplesubmitted to the Plant Disease Clinic. Crown gall is a bacterialdisease caused by Agrobacterium tumefaciens. Crown gall can affectmany species including ornamental shrubs and vines, particularilyeuonymus, honeysuckle, and rose. Certain perennial flowers, suchas chrysanthemums, asters, and daisies, are also susceptible.Blackberry, raspberry, and tomato are hosts. The disease can alsooccur on young nursery stock including shade trees, nut-bearingtrees, pome fruits (apple and pear), and stone fruits (peach,cherry, etc.).
Galls usually are restricted to the roots, lower stems, andlower branches of infected plants. In some cases crown gall mayoccur in the upper branches. Galls are somewhat round, rough, andvary in size from 1/2 to several inches in diameter. The tissueinside these galls is usually very firm, but later may show decay.Keep in mind, though, that galls can be caused by factors otherthan the crown gall organism. Certain insects can cause gallformation. Environmental insults that cause wounds can also leadto callus tissue that appears gall-like.
The crown gall bacterium enters plants through wounds made bytransplanting, cultivation, grafting, and pruning. Other woundscaused by insects, animals, or people can serve as avenues forinfection to occur. Affected plants may be stunted, produce smallchlorotic leaves and may become more sensitive to environmentalstresses such as winter injury. Severely infected plants declineand eventually die.
To control crown gall, avoid wounding susceptible plants at ornear the soil line. Prune infected branches and roots well backinto healthy tissue. To prevent possible spread of the disase,sterilize pruning tools between cuts with a 10% household bleachsolution. Plant removal may necessary when galls are extensive.Chemical treatment may be practical for commercial growers orhomeowners with valuable landscape plants. Galltrol-A and Gallexare two products available. Galltrol is a biological controlmaterial used for the prevention of crown gall. Galltrol is aculture of the bacterium Agrobacterium radiobacter Strain K84.Galltrol prevents disease by disrupting the crown gall infectionprocess. Seedlings, cuttings, roots, or crowns are immersed orsprayed with a suspension of the bacteria. The Galltrol bacteriaproduce antibiotics that are toxic to the pathogen, and thebacteria also physically exclude the crown gall pathogen bycolonizing all the available attachment sites on the plant. Gallexis a product for eradicating crown gall. The product is painted ongalls and cut surfaces in the spring and early summer. It consistsof a flowable emulsion of water in kerosene derivatives.
This article originally appeared in the August 11, 1993 issue, p. 137.