A downy mildew affecting columbines (Aquilegia).  There is a pale purplish-brown down on the leaf undersides and yellowish patches on the uppersides of the leaves.  The leaf margins curl under, and flowering and growth is inhibited. The infection eventually leads to the death of the plant.  It is a serious horticultural pathogen.

host

Photograph the mildew on the host.  Ensure you have noted the host-plant species in your comments

on Columbines, usually in gardens 

It was first noted in the UK in 2013.  See Royal Horticultural Sociey Advice Guide