Landscape - Galls and Burls on Woody Plants

Galls and Burls sometimes grow on woody plants. The following is an article on these abnormal growths.

Galls and burls are abnormal growths on woody plants. They can occur on branches, trunks and, in some cases, on roots of woody plants. Galls may be caused by an insect or disease; however, the origin or causal factors for burls and other callus outgrowths are unknown. Abnormal growths form through a proliferation of cells. These cells continue to develop and do not differentiate into normal tissue types. In some cases, the outgrowth results from a cluster of shoots. Each year, new shoots are initiated and increase the layers of the mass.

Burl on elm. Photo by USDA Forest Service - Ogden Archive, USDA Forest Service, Bugwood.org.

Cottonwood tree with a very large crown gall (Agrobacterium tumefaciens) high on the trunk. Photo by William Jacobi, Colorado State University, Bugwood.org

Oak galls, photo by James Solomon, USDA Forest Service, Bugwood.org

Gall caused by a wasp. Pennsylvania Department of Conservation and Natural Resources - Forestry Archive, Bugwood.org.

Information from a section of "Abiotic Plant Disorders - Symptoms, Signs and Solutions A Diagnostic Guide to Problem Solving" by Robert E. Schutzki and Bert Cregg, Departments of Horticulture and Forestry, Michigan State University Michigan State University. Go to http://www.ipm.msu.edu/cat08land/pdf/9-19abiotic.pdf for the full factsheet with photos.