Cause Rhizobium radiobacter (formerly Agrobacterium tumefaciens), a bacterium that lives for several years in soil, often spreading from diseased nursery stock. It also may be moved by irrigation water or cultivation equipment. Although the bacterium has a wide host range, plants more likely to have crown gall include all stone and pome fruit, caneberries (such as blackberry and raspberry), euonymus, Photinia, poplar, rose, walnut, and willow. Colt cherry rootstock is reportedly quite susceptible while Gisela 5 and 6 may have useful resistance in contaminated soil.
The bacterium enters plants through wounds, either natural or caused by pruning, grafting, mechanical injury from cultivation, heaving of frozen soils, chewing insects, or the emergence of lateral roots. After the bacterium enters a wound, a small piece of its DNA is transferred into the plant's DNA. The foreign DNA transforms normal plant cells in the wounded area into tumor cells. Once transformed, tumor cells proliferate automatically. The result is a gall, a disorganized mass of hyperplastic and hypertrophic tissue.
Symptoms On young nursery trees, soft, spongy, or wart-like galls develop on the crown or on roots. Gall size on mature trees ranges from a fraction of an inch to several inches across. Galls on woody plants become hard with a rough, fissured surface as they age. Gall tissues are irregular and have no definite growth pattern. If galls completely encircle the trunk of a young tree, it may be girdled and die. Symptoms may not develop for over a year if infection occurs when temperatures are below 59°F.
- Use only pathogen-free nursery stock. Inspect new trees, and do not plant any with gall symptoms.
- Do not plant nursery trees in soil with a recent history of crown gall.
- Preplant soil solarization has been effective for nursery stock in western Oregon. Place clear plastic (preferably anti-condensation film) directly on smooth, rototilled ground, which has been irrigated to field capacity and then allowed to drain for 1-2 days. Bury the edges of the plastic to trap the heat. Solarize for 4-6 weeks (or longer) during the hottest part of the summer, beginning in early- to mid-July.
- Use care in planting trees, avoiding injury to bark around the crown because bacteria in the soil can enter such injuries.
- Destroy seriously declining trees in the orchard if large galls surround the crowns.
- Select well-drained soils for planting.
- Plant when soil temperature is below 50°F.
- Gallex (ready to use) painted on very young galls to reduce further development. Galls may return the following year or, if treated late, may continue to develop. Tissue surrounding the gall may be injured, especially on younger plants. Prepare the surface by removing soil from around the galled area, and allow the area to dry before application. Not registered in Idaho. 24-hr reentry.
Biological control Agrobacterium radiobacter strain 84 is preventive only. Latent infections (symptomless) and existing galls will not be controlled. A suspension of strain 84 may be used as a soak or spray. Thoroughly cover grafting wood, roots, and crown. Spray to runoff. To be effective it must be applied a few hours after wounding.
- Galltrol-A. (Agrobacterium radiobacter K84) Not registered in Idaho. 12-hr reentry. O
- NOGALL at 8.8 oz/2.5 gal unchlorinated water per 2,500 nonbearing plants. Apply within 2 hours of lifting and/or damaging plants. Do not use with any pesticides or fertilizers. 4-hr reentry. O
References Penyalver, R., Begonya, V., and López., M.M. 2000. Use of the genetically engineered Agrobacterium strain K1026 for biological control of crown gall. European Journal of Plant Pathology 106: 801-810.
Pinkerton, J.N., Ivors, K.L., Miller, M.L., and Moore, L.W. 2000. Effect of soil solarization and cover crops on populations of selected soilborne plant pathogens in western Oregon. Plant Disease. 84:952-960.