There are fungal and bacterial cankers on ash, widely distributed but poorly known. First the scientific names of the pathogens: Neonectria ditissima (previously Nectria galligena) and Pseudomonas savastanoi pv. fraxini. The pv stands for ‘pathovar’. The fungal pathogen is found on several hosts other than ash, and is perhaps best known on apple. Psf is a variant of a bacterial pathogen that infects olive and oleander (neither recorded in the UK to the best of my knowledge). You can find P. savastanoi on Forsythia and Ligustrum.
The essential difference between the fungal and bacterial cankers is that the former kills cells while the latter stimulates growth. Put more crudely, hollowing is fungal and swelling is bacterial. Indeed, the bacterial galls are perhaps more accurately described as galls. Things get more complicated, however, with the edges of some fungal cankers becoming swollen and bacterial cankers showing fissures and cavities. I’ll put two selections of each type up for viewing.
What I’m hoping for is that more people will share observations of cankers and note where they occur. We still know little about both diseases. In the several decades since I studied Psf for my PhD, no serious research has been done in the UK or Europe. Bacterial canker is not a major disease but it is surely of interest in the ever-expanding concern about tree health in the UK (and beyond).
Please let me know of any examples you’ve seen.