Powdery mildews are one of the most widespread and easily recognized plant diseases. Their common symptom is a grayish-white, powdery mat visible on the surface of leaves, stems and flower petals. They affect virtually a wide range of angiosperms such as cereals and grasses, vegetables, ornamentals, weeds, shrubs, fruit trees, and broad-leaved shade and forest trees. Seventeen fungal taxa found on 30 host plant species in different localities of Iran are documented. Salsola crassa is a new host plant species  for Leveillula saxaouli. Likewise, Fagonia indica, Prosopis fracta, Tribulus longipetalus and Zygophyllum eurypterum are new hosts for Leveillula taurica. Some taxa of powdery mildew fungi reported on new hosts in Iran are as follows: Blumeria graminis on Phalaris paradoxa, Erysiphe polygoni on Polygonum erioptera, E. trifolii on Trigonella, Golovinomyces cichoracearum on Gaillardia, G. orontii on Hibiscus, L. saxaouli on Haloxylon persicum, and L. taurica on Alhagi pseudalhagi.