Symptoms and Signs
Crown gall is caused by a bacterium that produces galls at the base of the stem, root crown or on other plant parts. The bacterium infects only through fresh wounds. If infected at a young age, plants may be stunted and not grow properly.
Comments on the Disease
A wide variety of both woody and herbaceous plants are susceptible. The disease is most damaging to trees because the galls are perennial and increase in size with growth of the tree. Galls may occur on roots, stems, and even leaves. Aerial galls are common on grapes and caneberries. Under moist conditions aerial galls are often seen on chrysanthemum. The disease may have further impact on growers, because regulations prohibit the sale of some plant materials infected with crown gall.
Gall tissue is disorganized growth with an enlarged cambium layer and irregular vascular tissue. Movement of water and nutrients is severely impaired by galls. The early stages of gall formation can be difficult to distinguish from normal callus tissue. Isolation of the pathogenic bacterium is the most common method of confirming that the bacterium is present. Callus tissue, which is soft and easily wounded, can be a common site of infection.
The bacterium Agrobacterium tumefaciens is common in many agricultural soils. When the plant is wounded, the bacterium attaches to an exposed plant cell and transfers a portion of its genetic material, DNA (deoxyribonucleic acid), into the cell where it is incorporated into the genetic material of the host cell. The host cell is induced to become a tumor cell and also to produce a unique substance (opine) that only the crown gall bacterium can readily utilize. Agrobacterium tumefaciens is then able to multiply between cells and in cracks of the gall with somewhat less competition from other microorganisms.
The only useful method of treating soil for crown gall pathogen is with heat. The common soil fumigants reduce the amount of bacteria but do not result in satisfactory control of the disease. Steam (at 140°F for 30 minutes) or solarize (double-tent at 160°F for 30 minutes or 140°F for 1 hour) the soil. For flower production in open fields, solarization in warmer climates has been successful for control of crown gall. Steaming and solarization are acceptable for organic production.
Sanitation is very important in a control program, especially where cuttings are produced. Rose propagative material and work areas are often soaked or cleaned with hypochlorite solution to kill any bacteria that may be present on the surface. Grape propagative material, and perhaps some others, have also been treated in this manner. In some plants, such as grape, the bacterium may occasionally enter the xylem. Cuttings taken from such plants may develop crown galls.
Tools and surfaces that contact the propagative material should be cleaned and periodically treated with a disinfectant.
Monitoring and Treatment Decisions
The K-84 strain of Agrobacterium tumefaciens (formerly A. radiobacter), which is available for use in preventing infection by the crown gall pathogen, is an excellent biological control agent.
Galls on many woody plants can be treated with a mixture of chemicals that are toxic to and kill crown gall tissue but are safe on uninfected woody tissue. The mixture, which is currently marketed under the name Gallex, was previously sold as Bacticin. It has been used with success on rose crown galls.
|Common name||Amount to use||REI‡|
|(Example trade name)||(hours)|
|Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least likely to cause resistance are at the top of the table. When choosing a pesticide, consider information relating to the pesticide's properties and application timing, honey bees, and environmental impact. Always read the label of the product being used.|
|A.||AGROBACTERIUM TUMEFACIENS K-84|
|. . . or . . .|
|AGROBACTERIUM TUMEFACIENS K-1026|
|COMMENTS: Products may list bioagent under former name A. radiobacter. Prevents infection by the crown gall pathogen if it is applied to fresh wounds. It must be applied as soon as possible after wounding; i.e., within 24 hours. It has been used with success on Prunus spp. and Rosa spp.|
|COMMENTS: For killing of existing galls; apply directly to galls winter through spring.|
|#||Acceptable for use on organically grown ornamentals.|
|‡||Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing.|