Photos by Debbie Roos, Agricultural Extension Agent.
Notes from Dr. Turner Sutton, NCSU Apple Specialist: The problem on the apples is “burr knot”. It’s where adventitious roots are trying to develop. A few apple varieties (especially early “June” apples) appear particularly prone to the development of the burr knots, as does some rootstocks such as MM111. No one knows exactly what causes it although it has been associated with wooly aphid feeding injury. There is no control. A product known as Gallex can be painted on burr knots and will result in at least some of them forming callus and “healing”. Often various organisms (i.e. dogwood borers) get in the burr knots predisposing the tree to secondary wood rot fungi that can girdle branches, or even the trunk, weakening the tree. This tree is not likely to be productive in the future and should be removed.
This page last updated January 8, 2011.