Diagnosing Apple Tree Crown Gall

Agrobacterium tumefaciens

Symptoms

• Crown gall is caused by a soil-borne bacterium that enters tree wounds caused by mower damage, pruning, frost cracks, insects or planting damage.
• The bacteria stimulate the tree to produce plant hormones that cause a tumor or gall to form.
• The galls most commonly occur on the roots or on the trunk near the soil line.
• At first, the galls appear light-colored and spongy.
• As the galls mature, they turn dark brown and woody.

Crown gall frequently appears near the soil line. (Bruce Watt, University of Maine, Bugwood.org)

Crown gall can enter through pruning wounds. (Manfred Mielke, U.S. Department of Agriculture Forest Service, Bugwood.org)

Management and other important facts

• No cure exists for the disease, and it may kill a young apple tree by girdling the stem.
• A mature apple tree may be able to tolerate crown gall.
• Carefully inspect apple trees to avoid purchasing a tree infected with crown gall.
• If a recently planted tree develops crown gall, remove the tree and adjacent soil; the bacteria can persist for several years in the soil.
• If your property has a history of crown gall infections, avoid planting fruit trees or other susceptible plants.

Author: Esther McGinnis

This website was supported by the U.S. Department of Agriculture’s (USDA) Agricultural Marketing Service through grant 14-SCBGP-ND-0038.

Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the USDA.