Crown gall (bacterium – Agrobacterium tumefaciens) first appears as small round overgrowths on stems and roots.As they enlarge, the galls become woody with a rough and irregular surface. Aerial galls can develop but most are found at or just below the soil line. Galls range from pea-size to larger than 1 foot in diameter.
Crown gall is worldwide in occurrence, attacking 140 plant genera in 60 different families. Plants most commonly damaged in Texas by crown gall are pecan, peach, blackberry, grape, apple, pear, willow, pyracantha, euonymus, rose, fig, and crabapple.
Crown gall bacteria infect plants through wounds, such as those arising from cultivation, transplanting, wind damage, insect injury, etc. Wounds that have healed beyond a certain point are no longer susceptible to invasion. After establishing itself in the wound, the bacterium transforms normal plant cells to tumor cells. Once this has taken place, the tumor cells are able to reproduce without the bacterium being present. Although crown gall of plants is very much like cancers in humans and other animals, there is no relationship between crown gall and animal cancers. Crown gall has been studied extensively by scientists in their search to understand cancerous growths.
Damage to infected plants results from interruption of water and nutrient movement up the stem. Galls also interfere with normal growth and development, therefore, infected plants may be stunted and unthrifty. With many plants, the amount of damage depends on where the gall or galls are located and how many are present. Death can result if galls girdle the primary trunk or stem. Infected plants are more sensitive to winter injury and drought stress. Control is primarily dependent on prevention. Pruning off galls is not effective since the bacterium is systemic and gall tissue can reproduce itself. Chemical control with antibiotic drenches has shown promise; however, they are not practical at this time. The following practices pertain to homeowners and/or nurserymen.
- Inspect plants for crown gall before purchasing. Plant only crown gall-free trees and shrubs.
- Remove and destroy heavily infected and weakened plants. Dig up as many roots as possible.
- Replace with a more resistant type plant if possible.
- Avoid wounding plants while mowing, cultivating, etc.
- Keep plants in an active growing state with proper fertility and watering.
- Heavily infected nursery fields should be planted to a grass crop for three years before planting susceptible nursery stock.
- Control root feeding insects.
- Dip grafting and pruning tools regularly in a disinfecting solution, such as 70 percent alcohol, 10 percent sodium hypochlorite (common bleach) or potassium permanganate solution (1 ounce in 2 gallons of water).