On stems, branches and twigs black, roundish or slightly elongated excrescences, at first smooth, later on rough; this symptom can be mistaken for those by the ash bark beetle; mesentery-like excrescences, which develop instead of inflorescences, are galls of the ash gall mite Aceria fraxinivora. They may resemble excrescences of ash bacterial canker, but occur only only twigs.
The actual ash-dieback phenomenon (Chalara fraxinea) has nothing to do with ash bacterial canker.
Affected tree species
Ash bacterial canker is produced by bacteria specific on ash. They enter the host tissues via wounds of various size, but even via lenticels. The disease is very common, but generally not endangering the trees; only heavily cankered ashes can be infected by secondary microfungi causing shoot- or branch-dieback
Curative measures In case of heavy infections hygienic measures: removal of infected trees