Phylum: Basidiomycota Family: Phragmidiaceae
Phragmidium violaceum (Schultz) Brockm.
Violet Bramble Rust
A common rust fungus that primarily attacks Bramble Rubus fruticosus. The early stage (uredinial) appears as a yellow power followed in late summer by the dark telial stage that overwinter
References:
Termorshuizen & Swertz (2011) Dutch Rust Fungi
Wilson & Henderson (2011 reprint) British Rust Fungi