University of Georgia Plant Pathology, University of Georgia, Bugwood.org
Crown gall can be recognized readily by the formation of tumors or galls on tree roots and crowns. Occasionally, the galls can be seen above ground on trunks or branches. Young galls are light in color and become dark and hard with age. When galls are numerous, or if they are located on major roots or the crown, they might disrupt the flow of water and nutrients. These trees show reduced growth, an unhealthy appearance, and possibly nutritional deficiency symptoms.
The bacteria causing crown gall are distributed widely in numerous soils and can attack many different kinds of plants. Soil might become contaminated if planted with infected nursery stock.
Bacteria entering the plant must do so through a wound. Wounds commonly are made during digging and tree-planting operations, by tillage equipment, and by injury from root-feeding insects and nematodes. Secondary galls can develop a considerable distance from the initial infection. These can be formed in the absence of the crown gall bacteria, apparently due to a tumor-inducing substance produced at the site of the original infection.
Avoid planting infected nursery stock or wounding trees at the time of planting.