Like tar spot but in white/grey and on Maple saplings in mixed woodland. Several saplings had it on them.
Caution: Do NOT use iSpot to identify fungi to eat!
Some fungi are very poisonous so a mistaken ID could have serious consequences.
No interactions present.
AlanS, why is it likely to be the S. tulasnei when S. bicornis is the more common species?
These leaves are Norway Maple, so they (apparently) have the powdery mildew that occurs on Norway Maple.
It does have a different look to it, compared with S. bicornis, which is common on Sycamore but suppposedly does NOT occur on Norway Maple.
Note I am not being dogmatic - identification of powdery mildews simply by host, without checking with specialist literature, is not always as reliable as people think.
Lat/Lng: 53.2638656, -1.1932777
OS grid ref: SK539743