What is Crown Gall?
Crown gall is a plant disease that causes tumor-like growths, known as galls, to form on stems, roots, or at the soil line of affected plants. These galls interfere with the plant’s ability to move water and nutrients, which can lead to stunted growth and long-term decline.
The disease is caused by Agrobacterium tumefaciens, a soil-dwelling bacterium that enters plants through fresh wounds created by pruning, insect damage, or handling. Warm temperatures and moist soil conditions help the bacteria thrive and spread.
Crown gall affects a wide range of plants, including roses, fruit trees (like apples, pears, peaches, and cherries), grapes, raspberries, blackberries, and many ornamental shrubs.
Life Cycle
The bacteria responsible for crown gall live naturally in soil and plant debris. They enter a plant only when they have access to a fresh wound. Once inside, the bacteria transfer a small piece of DNA into the plant’s cells, causing those cells to grow uncontrollably and form a gall.
As galls mature, they become reservoirs of bacteria. When the gall cracks or breaks down, the bacteria return to the soil, where they can survive for years, even without a living host. Warm, moist environments help the bacteria move through water, insects, tools, and soil particles.
Symptoms
Early Stage
- Small, rounded swellings near the soil line, on stems, or on roots
- Tissue may feel soft or spongy at first
- Slight reduction in plant vigor or leaf size
Middle Stage
- Galls enlarge and become firmer and woody
- Stunted growth and reduced flowering or fruiting
- Wilting during hot or dry periods due to restricted water flow
Late Stage
- Large, corky, cracked galls that may girdle the stem
- Major reduction in plant vigor and leaf density
- Dieback of branches or widespread decline
How to Control Disease Progression
While crown gall cannot be cured once it is established, early intervention can slow its progression and prevent it from spreading to nearby plants.
- Promptly remove and destroy plants that are severely infected.
- Avoid creating wounds during routine care or landscaping.
- Disinfect pruning tools with 70% alcohol or a 10% bleach solution between cuts.
- Improve soil drainage and avoid overwatering to reduce bacterial activity.
- Place mulch around plants to prevent mechanical injury from lawn equipment.
Treatment Options
There is no chemical cure for crown gall, but several management strategies can help limit damage and reduce future infections.
Organic Treatment Methods
- Remove small galls early by cutting away infected tissue with sterilized tools.
- Use approved biological control agents containing Agrobacterium radiobacter strain K84 to protect uninfected plants during planting.
- Support plant health with proper fertilization, watering, and mulching.
Chemical Treatment Options
No chemical pesticides are effective against crown gall. Management relies on sanitation and prevention.
Step-by-Step Treatment Procedure
- Inspect plants carefully to identify galls early.
- For mild infections, prune off galls, removing an inch of healthy tissue around the affected area.
- Dispose of any infected plant material in the trash—never compost it.
- Sterilize tools before and after each cut to avoid spreading bacteria.
- Apply biological control agents to uninfected plants if planting in contaminated soil.
Expected Timeline for Recovery
Plants with minor infections may stabilize over one to two seasons if their overall health is good. Heavily infected plants typically worsen over time and may eventually need to be removed.
Prevention Strategies
- Buy disease-free plants from reputable garden centers and nurseries.
- Choose species or cultivars known to be less susceptible, especially in areas with a history of crown gall.
- Plant in well-drained soil and avoid sites where infected plants were recently removed.
- Water deeply but infrequently to promote strong, resilient root systems.
- Apply mulch to protect trunks and roots from injury.
- Prune during dry weather to reduce the chance of bacterial spread.
- In areas with known contamination, avoid planting highly susceptible plants for several years.
