Powdery mildew can reduce yield and quality of cantaloupes in the arid inland valleys of California. The plants are defoliated, particularly around the crown of the plant. Thus the fruits become sunburned, ripen prematurely, and are lacking in soluble solids, and in general have poor edibility. The ratio of culls to marketable fruit increases tremendously. Powdery mildew is caused by the fungus, Erysiphe cichoracearum.