Crown gall is a bacterial disease that creates wooden baseballs (galls) on many woody and herbaceous plant crowns (including my roses).
Crown gall is caused by the Agrobacterium tumefaciens bacteria, which is commonly found in many soils. The crown gall bacteria enters healthy plant tissue through fresh wounds. As tiny as bacteria are, these wounds can be as small as 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, very much like a virus or a cancer. Galls may form on roots, stems, or even leaves.
How to identify crown gall
Roses, caneberries, sunflowers, and grapes are just a few of the plants susceptible to crown gall. Apple, pear, cherry, apricot, and almond trees are also prone to crown gall. When woody, ball-shaped growths are seen above ground, it is easy to diagnose. Since galls may form underground, it is not always easy to determine why a particular plant isn’t flourishing. Galls (pictured) 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.
How to control crown gall
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, and susceptible species should not be planted in that location for at least 5 years. 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. Tools that have come into contact with infected plants should be cleaned with 9 parts water and 1 part bleach. There are some genetically altered anti-crown gall bacteria available for purchase, if you want to go that route.
Personally, I hold fast to my policy of only growing (watering, pruning, feeding, etc) plants that are well suited to my microclimate, soil, and personal preferences.
You can grow a surprising amount of food in your own yard. Ask me how!