Young galls are light in color and with age become dark and hard, ½ inch to 3 or 4 inches in diameter. Photo by B. Butler.
The disease is common in tree fruit nurseries and can occur in orchards.
Crown gall is readily recognized by wartlike swellings, or galls, on tree roots and crown. Occasionally, the galls may be seen aboveground on trunks or branches. Young galls are light in color and with age become dark and hard, ½ inch to 3 or 4 inches in diameter. When galls are numerous, or if located on major roots or the crown, they may disrupt the flow of water and nutrients. 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 may become contaminated if planted with infected nursery stock.
Bacteria entering the plant must do so through a wound.
Wounds are commonly made during digging and tree-planting operations, by tillage equipment, and by injury from root-feeding insects and nematodes. Secondary galls may develop a considerable distance from the initial infection. These may 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 stock by closely inspecting the roots of trees prior to planting as well as prevent wounding trees at planting.