Mildew

Mildew, general name for superficial growth of many types of fungi often found on plants and material derived from plants. Powdery mildews, numbering about 50, are caused by fungi belonging to the Ascomycetes order Erysiphales; the powdery effect is due to the masses of spores. Downy mildews are caused by Phycomycetes. Both types of disease can be controlled by the use of fungicides.