Powdery mildew is a common disease of cucurbits under field and greenhouse conditions in most areas of the world. All cucurbits are susceptible, but symptoms are less common on cucumber and melon because many commercial cultivars are resistant. The disease can be a major production problem. Yields are reduced because of a decrease in the size or number of fruit, or a shortened harvest period. Premature senescence of infected leaves can result in lower market quality because fruit become sunburned or ripen prematurely or incompletely. Winter squash so affected often exhibit inferior storage characteristics; fruit, particularly melons, may have low soluble solids with consequent poor flavor; and pumpkins often have poor rind color and shriveled, discolored handles. Stress from disease can lead to imperfections on fruit rinds such as speckling, raised indentations, and edema. In addition, powdery mildew infection predisposes plants to other diseases, in particular, gummy stem blight.