An Oak Canker Caused by a Gall Midge

Abstract

In parts of southern England an annual canker is sometimes to be found in association with peck marks made by woodpeckers on the stems of young oak. Cross-sections reveal that this canker is the result of the death of a patch of bark during a single dormant season followed by the recovery growth of callus tissue. Evidence is presented that the cause of canker formation is a gall midge, Resseliella sp. which lays its eggs in recently formed peck marks during the months of July and August. Bark death occurs principally in September and October, during which time the larvae of the gall midge develop to the final instar. In early summer of the following year the larvae emerge from the bark, presumably to pupate in the soil. Various fungi, in particular Ceratocystis piceae (Munch) Bakshi and Fusarium Solani (Mart.) Sacc, can readily be isolated from the necrotic tissue, but they are thought to play only a secondary role.