Erysiphe berberidis is a powdery mildew which affects Berberis (native and non-native species) and Mahonia species.  The chasmothecia appendages have branched ends.

Phyllactinia berberidis may affect the native Barberry, Berberis vulgaris

host

Photograph on host plant, and add host species to the comments for your record.  If you are recording on Berberis vulgaris, microscopic examination or verification by an expert before submission to NatureSpot may be needed 

Berberis and Mahonia