Crown gall—Agrobacterium tumefaciens
Agrobacterium tumefaciens causes crown gall on fruit trees, euonymus, rose, willow, and other broadleaf trees and shrubs. Another bacteria, possibly Agrobacterium pseudotsugae, causes a similar bacterial gall on stems of douglas-fir, especially under wet stressed conditions. The crown gall bacteria cause rough, wartlike growths or galls principally on the root crown at the soil line or just below the soil surface. Galls first appear as smooth swellings and develop rapidly into large tumors with a rough, warty, or cracked appearance. Galls sometimes also form on roots, limbs, and trunks of many woody plants. On blackberries, raspberries, and grapes, galls may also form on stems or canes. Crown gall usually does not seriously harm woody plants unless galls occur in the root crown area when plants are young; then plants become stunted and subject to wind damage and drought stress. If galls are large, young plants can be girdled and killed.
Identification | Life
You can greatly reduce problems with crown gall by obtaining planting material from a reputable nursery. Examine bare-root trees and vines before purchase, and plant only high-quality nursery stock. Avoid susceptible varieties. Where crown gall has been a problem, plant only resistant species, including birch, cedar, magnolia, pine, redwood, and tulip tree. Avoid injuring trees during transplanting, and avoid injury or pruning wounds that will come into contact with soil. Plants can be infected through wounds, growth cracks, injured roots, or freezing injuries. Existing galls may be excised by cutting into healthy wood around galls, then exposing the tissue to drying. Cut out galls only during the dry season and minimize the amount of healthy tissue into which cuts are made. Disinfect pruning tools before using on healthy plants. Remove and destroy severely infected plants. Solarization during the hot dry season before planting may reduce crown gall bacteria in the soil. Larger trees and vines can usually tolerate the development of crown galls.
Galls on blackberry roots
Swollen outgrowths found on stem
Galls on roots
Warty tumors of large roots near the crown area of tree