Pale Bramble Rust - Kuehneola uredinis

Pale Bramble Rust (Kuehneola uredinis) affects Rubus species (brambles).  There is no host alternation, and it is considered to be a gall-causer.  Small yellow aecia are on the upper side of the leaves.   Later, yellow uredinia are present on leaf undersides and often stems and petioles.  The yellow or white telia are under the leaves, but are rarely found.

This can be very similar to Phragmidium species on brambles, but these species usually bear the aecia on the leaf undersides.  On Raspberry, Phragmidium rubi-idei has aecia on leaf uppersides.  The aecia of Phragmidium violaceum, the Violet Bramble Rust, may also appear on stems; microscopic examination may be needed to distinguish from the uredinia of Kuehneola uredinis.  

host/aecia on uppersides of leaves

Photograph the rust on the host.  Ensure you have noted the host-plant species in your comments.  Microscopic examination or confirmation by an expert may be needed.

Brambles