Erysiphe euphorbiae-cotinifoliae is a species of powdery mildew in the family Erysiphaceae. It is found in North America, where it affects Euphorbia cotinifolia.
The fungus forms diffuse white patches on the leaves of its host. Erysiphe euphorbiae-cotinifoliae, like most Erysiphaceae, is highly host-specific and infects only the one species. A variety of other species of Erysiphaceae are found on other species of Euphorbia.
The fungus was formally described in 2024 by S. Fernández-PavÃÂa & S. Takamatsu. The type specimen was collected in Mexico, on Euphorbia cotinifolia. The specific epithet derives from the type host.