The fungus Taphrina wiesneri affects Prunus avium (Wild Cherry) and Prunus cerasus, causing Witches' Brooms that may persist for many years.  The leaves are slightly thickened and bear a layer of microscopical asci that, when fully developed, may give the surface a mealy aspect. 

Taphrina deformans causes Peach-leaf curl galls on the leaves of Almonds and Peaches; Witches Brooms are not formed

host

Good photographs required showing upper and lower leaf surfaces or Witches Brooms.  Ensure you have correctly identified the host species, and note this when submitted the record