Looking online I see references to Septoria betulae but this is not listed on the frdbi, and I see no Septoria as species associated with Betula. Any suggestions as to genus or for further examination?
this may be fungal but it’s too early to say; at the moment the black spots seem to just be depressions in the leaf – expect Septoria spp. Ascochyta spp. etc. a month or two later in the season. In any case it would be a microscope job.
