Crown Gall
Agrobacterium tumefaciens (Rhizobium radiobacter)
Overview
Crown gall is caused by Agrobacterium tumefaciens (and related species) that genetically transform plant cells, producing tumor-like galls on roots, crowns, and sometimes stems. Many woody ornamentals, fruit trees, grapes, and roses are hosts. The bacterium lives in soil and enters through wounds from planting, grafting, cultivation, or insects. Galls disrupt water and nutrient flow and can girdle young plants. Older trees may tolerate small galls, but young nursery stock and vines can be stunted or killed.
Symptoms
Rough, woody, or soft tumors form at the soil line, on roots, or on graft unions. Young galls are light-colored and spongy; older galls become dark and corky. Plants may show reduced vigor, yellowing, or wilting on hot days when vascular flow is restricted. Above-ground galls can appear on canes after wounding. Secondary decay organisms sometimes invade large galls. Symptoms are most obvious when plants are dug or when crown soil is carefully pulled away.
Environmental Conditions
Variable
Prevention
Inspect bare-root and container plants for galls before purchase and refuse suspicious stock. Plant carefully without jamming roots against rocks or hardpan that cause wounds. Use clean pruning and grafting tools. Rotate planting holes for roses and fruit trees after crown gall problems. Choose resistant rootstocks for grapes and fruit trees when available. Keep cultivation shallow near crowns and protect trunks from mower injury.
Management
Remove and destroy severely galled young plants; do not replant the same species in that exact spot without soil improvement and a waiting period. Prune out above-ground galls several inches below the tumor during dry weather and sterilize tools. Biological control dips containing antagonistic Agrobacterium strains are used in nurseries on susceptible stock. Avoid wounding crowns during cultivation. Improve drainage and avoid waterlogging that stresses roots near existing galls.