The discussion of the role of Ceratocystis spec. in oak decline increases in the last years in west and east Europe. These investigations show that Ceratocystis spec. obviously are very wide-spread in oak stands. They are living endophyticaly in undamaged oaks and they develop after predisposition by different stress factors. Therefore they are a part of a characteristic complex disease. The pathogen of oak wilt, Ceratocystis fagacearum (Bretz) Hunt, couldn't be found yet. The pathogenicity of new described Ceratocystis spec. and different strains of known species is obviously negligible. In infection experiments these species induce brown necroses, but no typical wilt.
