Blister bark, a scaly bark-type disorder of ‘Delicious’ apples (Malus domestica Borkh.) is shown to consist of 3 similar disorders. Two of these, blister bark 1 (the one most commonly encountered in the Northwestern United States) and blister bark 2, are graft transmissible. The 3rd disorder, blister bark 3, was not transmitted. The symptoms are described and the differences discussed. Another bark disorder, a form of internal bark necrosis, is shown to be graft-transmissible. A key to differentiate the blister bark complex is presented.
Received for publication May 27, 1980.
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Plant Pathologist. I wish to acknowledge the photographic assistance of Peggy Burts (now deceased).