Erysiphe trifoliorum is a powdery mildew that affects legume species in the Fabaceae family, including Vetchlings, Bird's-foot Trefoils, Clovers, etc. - refer to Woods et al (2024) for more details.  

On some hosts, Erysiphe pisi is very similar and detailed microscopic examination is necessary.

host/microscopy

Photograph the mildew on the host plant, and add host species to the comments for your record.  Depending on host species, microscopic examination is needed to separate from similar species on this host; refer to Woods et al (2024) for details. 

Fabaceae family - legumes, clovers, vetchlings, etc.