Pseudomonas syringae van Hall, 1904
Rosmarinus officinalis, Belgium, prov. East Flanders, De Pinte © Dirk Duytschaever. The shrub is growing already for several years in the garden of the photographer.
the malignant growth erupts through the bark
This gall seemingly is not mentioned in the European gall literature. The only indication that I could find was a photo on the website of the Missouri Botanical Garden, where P. syringae is mentioned as the possible causer.