Mildew is the general name for the superficial growth of many types of fungi often found on plants and material derived from plants. Powdery mildews are caused by fungi belonging to the Ascomycetes order Erysiphales, the powdery effect being due to the masses of spores). These fungi commonly infest roses, apples, phlox, melons, etc. Downy mildews are caused by Phycomycetes. They commonly infest many vegetable crops. Both types of disease can be controlled by used of fungicides.