Technical Abstract: Powdery mildew of pea (Pisum sativum) is an important disease in the field and in the greenhouse. The most widely documented powdery mildew pathogen on pea is Erysiphe pisi, but E. baeumleri and E. trifolii have also been reported. We recently showed that E. trifolii is frequently found on pea in the US Pacific Northwest. Since detailed studies on host range of this pea powdery mildew were lacking, we tested common legume plants from the region as potential alternative hosts. Twelve species were used in greenhouse cross inoculation studies: Glycine max, Lathyrus latifolius, Lens culinaris, Melilotus albus, M. officinalis, Medicago lupulina, M. polymorpha, M. scutellata, Trifolium pratense, Vicia cracca, and V. faba. Except Glycine max, all the plant species tested in the greenhouse developed powdery mildew lesions in 10-14 days after inoculation with E. trifolii. Results showed that all the above legumes (except soybean) are potential alternative hosts for the pea powdery mildew pathogen E. trifolii. These findings have implications in devising strategies to manage powdery mildew of pea.