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Need to know:
- Crown gall causes round galls to form on stems or roots.
- Galls are white or cream colored and spongy when young, but become dark and woody with age.
- The crown gall bacterium enters the plant through a wound and inserts their DNA to that of the plant.
- Galls are uncurable so if a plant is infected, it should be removed.
- A biocontrol agent can be used as a dip for propagative cutting to prevent infection.
Overview crown gall
Crown gall causes round galls to form on stems or roots, often near the soil line of the plant. Galls may vary from the size of peas to over an inch in diameter. When young, the galls can be white or cream colored and spongy or wart-like; as they age, they become dark and woody. Galls can interfere with the plant’s ability to move water and nutrients through the stem, which may result in stunting or decline of the plant. Crown gall can infect nearly all dicotyledonous plants and is most common in euonymus, Prunus spp., brambles, rose, willow, grapes, and many other plants.
Symptoms of crown gall
The crown gall bacterium, Agrobacterium tumefaciens, enters the plant through a wound. It then inserts a portion of its DNA into the DNA of the plant. Once this bacterial DNA is incorporated into the plant DNA, it induces the plant to overproduce plant hormones that stimulate cell division, resulting in a gall that is a perfect home for the bacterium. The bacterial DNA also causes the plant to produce special food called opines that only Agrobacterium can utilize.
Signs of crown gall
No signs are visible, culturing and specialized nucleic acid testing is required to confirm this bacteria causing the symptoms.
Type of Sample Needed for Diagnosis and Confirmation
The Iowa State University Plant and Insect Diagnostic Clinic can help you to investigate and confirm (through testing) if your plant has this disease. Please see our website for current forms, fees, and instructions on collecting and packing samples. If your sample is from outside of Iowa, please do not submit it to the Plant & Insect Diagnostic Clinic without contacting us. For contact information for other diagnostic laboratories in U.S. states, visit the NPDN site.
Want to submit a sample? select special testing on our submission form, and follow the root problem instructions at Submitting annual plants page.
Management of crown gall
Crown gall is usually introduced into a location on infected planting stock, so it is crucial to buy only disease-free plants. Inspect plant root system before transplanting in the garden.
Avoid unnecessary wounding to prevent infection. If galls are present, they cannot be cured, and the plant should be removed. Once crown gall is introduced to a site, the bacteria can remain in the soil for many years.
Practice good sanitation: cleaning tools, pots, and other tools an surfaces, treat them with a disinfectant (rubbing alcohol or diluted bleach).
No chemical sprays are effective against crown gall, but a biocontrol agent made from the bacterium Agrobacterium radiobacter can be used as a dip for propagative cuttings to prevent infection by the crown gall bacterium. This biocontrol is marketed as Galltrol A, Norbac 84C, Nogall, or Diegall. Keep in mind when using biocontrol agents, you are trying to introduce and establish a biocontrol organism in the field onto a very rich soil ecosystem, where a lot of microbial competition can impact the efficacy of this method.
Fungicide applications may be avoided by following good Integrated Pest Management practices like those listed in this encyclopedia article. Often, only preventative application is effective to manage plant diseases. If the problem requires a fungicide, state law requires the user to read and follow all labels accordingly. For more information, read Proper fungicide use.
Dr. Lina Rodriguez-Salamanca is a diagnostician and extension plant pathologist with the Iowa State University Plant and Insect Diagnostic Clinic (clinic.ipm.iastate.edu), a member of the National Plant Diagnostic Network (NPDN, ...
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