Crown Gall

Crown gall is a bacterial disease that creates wooden baseballs (galls) on many woody and herbaceous plants (including my roses).

Crown galls growing on rose bush

Crown gall is caused by Agrobacterium tumefaciens. These bacteria are in most soils around the world. Blueberries, cane berries, sunflowers, and grapes are just a few plants susceptible to crown gall. Apple, pear, cherry, apricot, and almond, citrus, and walnut trees are also prone to crown gall.

Crown gall bacteria enter healthy plant tissue through fresh wounds. As tiny as bacteria are, these wounds can be a thorn poke, a squirrel claw mark, or those hand trimmers you keep forgetting to sanitize. Bacteria may enter at any location on the plant. When they do, they reprogram nearby host plant cells to start reproducing the bacteria, like a virus or cancer. Galls may form on roots, stems, or even leaves.

​Symptoms of crown gall

Aboveground woody, ball-shaped growths are easy to diagnose. Since galls may form underground, it is not always easy to determine why a particular plant isn’t flourishing. Galls are clusters of disorganized growth. They tend to have irregular vascular tissue and an enlarged cambium layer. All these distortions interfere with the flow of water and nutrients. Wilting and stunting are common early signs.​

Crown gall control

The crown gall bacteria can survive in the soil for 15 to 20 years. Heat is the only management tool available to combat the crown gall bacteria. Infected plants should be removed and disposed of immediately. Susceptible plant varieties should be avoided for at least five years once crown gall has occurred in your landscape. To (temporarily) eliminate the bacteria from the soil, the application of 140°F steam for 30 minutes or solarization at 160°F for 30 minutes or 140°F for 1 hour has been shown effective. Most of us don't have the time or tools for that treatment. You can purchase genetically altered anti-crown gall bacteria if you want to go that route. And sanitize your garden tools regularly with a household cleaner. 

I hold fast to my policy of only growing (watering, pruning, feeding, etc.) plants well-suited to my microclimate, soil, and personal preferences.