Mildew - Plant Pathogens

Plant Pathogens

What horticulturalists and gardeners often refer to as mildew is more precisely called powdery mildew. It is caused by many different species of fungi in the order Erysiphales. Most species are specific to a narrow range of hosts, and all are obligate parasites of flowering plants. The species that affects roses is Sphaerotheca pannosa var. rosae.

Another plant-associated type of mildew is downy mildew. Downy mildews are caused by fungus-like organisms in the family Peronosporaceae (Oomycota). They are obligate plant pathogens, and the many species are each parasitic on a narrow range of hosts. In agriculture, downy mildews are a particular problem for growers of potatoes, grapes, tobacco and cucurbits.