Crown Gall (Agrobacterium tumefaciens): Identification, Removal & Prevention

Crown gall, caused by Rhizobium radiobacter (formerly Agrobacterium tumefaciens), creates swollen, tan-to-black galls at the crown, roots, and lower stems of 600+ plant species. The bacterium injects its DNA into host cells, forcing gall formation. Galls eventually girdle stems, cutting off sap flow. Bacteria persist in soil 2+ years without hosts. Best action: remove and destroy infected plants.

Symptoms

• Galls: tan, spongy initially → hard, dark brown/black.
• Locations: crown (soil line), roots, lower stems.
• Progression: enlarge, coalesce, encircle stem → girdling → decline/death.

Management

1. Remove & Destroy (Primary)

• Dig entire plant + root system; bag/landfill/burn.
• Do not compost—bacteria survive.
• Don't replant susceptible species in that spot ≥2 years.

2. Prevention

• Inspect before buying: Reject any plant with galls (check graft union carefully).
• Avoid wounds near crown: Careful string trimming; mow debris away from plants.
• Sanitize tools: 10% bleach/alcohol between plants.

3. Biological / Chemical Preventives (Pre-Plant)

• Galltrol: Agrobacterium radiobacter strain K84—competes with pathogen at wound sites. Apply to roots at planting.
• Gallex: Chemical eradicant paint for existing galls (limited efficacy).
• Best used preventively, not curatively.

Common Susceptible Plants

• Fruit trees: apple, cherry, plum, peach (Prunus spp.)
• Roses & Rosaceae
• Raspberry, blackberry
• Willow, wisteria
• Grape, euonymus, poplar, many others

Crown gall is a wound disease. The grower who buys clean, plants carefully, protects the crown, and rogues immediately at first gall keeps the bacterium out. The one who plants galled stock or weeds with the string trimmer invites a decade of galls.