Because of the obligate biotrophic nature, host relationships of powdery mildews have long been considered as conservative. Especially, no tree-parasitic powdery mildew species having wide host ranges have been known so far. However, previous reports revealed that powdery mildews occurring on eight genera of tropical fruits trees and other woody plants covering five families belong to a single species, Erysiphe quercicola. The authors found in Indonesia three additional tropical trees infected by E. quercicola, viz., Bauhinia purpurea, Durio zibethinus, and Nephelium lappaceum, which are cultivated widely in tropical regions as fruit trees, flower trees, or industrial crops. This result suggests that these tree species play important roles as alternative hosts for powdery mildew epidemics caused by E. quercicola in tropical regions. Investigations and surveys of the exact host range of E. quercicola are important for the management of this powdery mildew.