During screening fungi as potential biological control agents for plant parasitic fungi, a fungal strain, EML-FAM3, was isolated from powdery mildew leaf lesions caused by Erysiphe platani on sycamore (Platanus occidentalis L.), and another strain, EML-FAMC1, from Erysiphe australiana on crape myrtle (Lagerstroemia indica L.). Based on the morphological characteristics and phylogenetic analysis of the internal transcribed spacers (ITS1 and ITS2) and 5.8S rDNA, the strains were identified as Ampelomyces quisqualis. To our knowledge, this is the first report of new mycohosts, E. platani and E. australiana, of the mycoparasite A. quisqualis on sycamore and crape myrtle plants. The hyperparasite may represent the potential for controlling E. platani and E. australiana epidemics