Powdery mildew (caused by the fungus Sphaerotheca fuliginea) of squash and cucumber can be a serious economic problem wherever these plants are grown in California. Heavily infected plants may decline in vigor prematurely with subsequent loss of yield. The studies reported here are of experiments with fungicides used for control of powdery mildew in both squash and cucumber. Some of the materials mentioned are not registered for use in these crops and the information is not to be considered a recommendation of the University of California or USDA.