What is "powdery mildew"

Mildew \Mil"dew\, n. [AS. melede['a]w; akin to OHG. militou, G. mehlthau, mehltau; prob. orig. meaning, honeydew; cf. Goth. milip honey. See Mellifluous, and Dew.] (Bot.) A growth of minute powdery or webby fungi, whitish or of different colors, found on various diseased or decaying substances.

powdery mildew a fungal disease of plants caused by an ascomycete of the order Erysiphales, characterized by a powdery white film on the surface of the affected plants. It is damaging to, e.g., roses and lilacs. Also, a fungus that causes such a disease.

n. any of various fungi of the genus Erysiphe producing powdery conidia on the host surface

Powdery mildew is a fungal disease that affects a wide range of plants. Powdery mildew diseases are caused by many different species of fungi in the order Erysiphales, with Podosphaera xanthii (a.k.a. Sphaerotheca fuliginea) being the most commonly reported cause. Erysiphe cichoracearum was formerly reported to be the primary causal organism throughout most of the world. Powdery mildew is one of the easier plant diseases to identify, as its symptoms are quite distinctive. Infected plants display white powdery spots on the leaves and stems. The lower leaves are the most affected, but the mildew can appear on any above-ground part of the plant. As the disease progresses, the spots get larger and denser as large numbers of asexual spores are formed, and the mildew may spread up and down the length of the plant.

Powdery mildew grows well in environments with high humidity and moderate temperatures. In an agricultural setting, the pathogen can be controlled using chemical methods, genetic resistance, and careful farming methods. It is important to be aware of powdery mildew and its management as the resulting disease can significantly reduce crop yields. Greenhouses provide an ideal moist, temperate environment for the spread of the disease.