Powdery mildew is a fungal

Fungus

A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds , as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, and bacteria...

 disease of barley

Barley

Barley is a major cereal grain, a member of the grass family. It serves as a major animal fodder, as a base malt for beer and certain distilled beverages, and as a component of various health foods...

 caused by Blumeria graminis

Blumeria graminis

Blumeria graminis is a fungus that causes powdery mildew on grasses, including cereals . It is the only species in the genus Blumeria. It has also been called Erysiphe graminis and Oidium monilioides or Oidium tritici.-Systematics:Previously B...

f. sp. hordei. The disease has a worldwide distribution and is most damaging in cool, wet climates. The host range of the form species hordei is restricted to barley and other Hordeum

Hordeum

Hordeum is a genus of about 30 species of annual and perennial grasses, native throughout the temperate Northern Hemisphere, temperate South America, and also South Africa....

species.

Symptoms

At first, powdery mildew can be observed as small greyish patches of fluffy fungal growth (mycelium) on the upper surface of the lower leaves. These spots resemble small cushions of white powder. Leaf tissue on the opposite side of an infected leaf turns pale green to yellow. The fungus only infects the epidermal layer and can be easily scraped off with a fingernail. Infections can also occur on the leaf sheaths and ears. Leaves remain green and active for some time following infection, then gradually become chlorotic and die off. As the disease progresses, the mycelium often becomes dotted with minute black points (cleistothecia), which are the sexual fruiting bodies of the fungus.

Disease cycle

The fungus overwinters as cleistothecia on straw, and in milder climates, also as mycelium and conidia on stubble and straw or volunteer barley and certain grasses. Windborne ascospores or conidia are the primary inoculum and can be dispersed over considerable distances. Infection by conidia requires high humidity, but not free water on the leaf surface. Sporulation and spore dispersal are favored by drier conditions. Thus the disease does well under alternating wet and dry conditions. Production of conidia declines markedly as the colony ages. Cleistothecia develop on older leaves as the plant matures. Low temperatures, together with the wetting of the cleistothecia for at least 72 hours, induces the maturations of the ascospores. Ascospores are released following rains, but are relatively sparse in comparison to the condia.

Extension publications

• EPPO - Europe
• Europe: Scotland
• US: North Dakota
• US: Oregon

Research articles