Birch anthracnose fungal infections attack birch trees. The fungus infects the foliage of birch and other trees, causing anthracnose, resulting in young leaves being distorted or curled, leaf yellowing and early leaf drop of infected mature leaves; the infection causes the distinctive brown spots outlined in dark brown to black.

River birch leaf; last photo shows underside, traversed by a Pill Woodlouse.

For River Birch (Betula nigra), cf. inaturalist.org/observations/88513457
For Common Pill Woodlouse (Armadillidium vulgare), cf. inaturalist.org/observations/89013194