Wheat is the only host of E graminis f. sp. tritici.
Although similar powdery mildews occur on other small grains
and many grasses, these mildews are other strains of the group
species, E. graminis. The barley cultivar, 'Advance,'
is very susceptible to powdery mildew.
Symptoms and Signs
Powdery mildews are among the easier plant diseases to diagnose,
since the fungus forms patches of a white to gray, powdery superficial
coating consisting of mycelium and conidia on green above-ground
parts of the plant, that is, leaf blades and sheaths, stems and
heads. As the season progresses, many small, dark cleistothecia
form in the mycelium (Photo 18). Chlorotic patches develop on
infected leaves, but often the tissue directly under the fungus
remains green. This pattern of symptom development is called
the "green island" effect. Lower leaves are usually
the most severely infected because of the high humidity around
The fungus over-winters as cleistothecia, or in mild climates
as mycelium and conidia. Wind- or rain-borne ascospores or conidia
are the primary inoculum. The fungus requires high humidity but
not free water for spore germination and infection. The fungus
penetrates only into the epidermal cells, where it forms specialized
food absorptive structures called haustoria. Sporulation on the
plant surface ensues and resultant conidia are dispersed by wind
to induce secondary disease cycles. Heavy, lush growth favors
the disease by promoting high humidity through the plant canopy.
Powdery mildew is not considered economically important in Washington,
and control is not required. However, appropriate fungicides
can control the disease. Use of resistant cultivars is the best
defense, unless they succumb to new races of the pathogen.
Kingsland, G.C. 1982. Triadimefon for control of powdery mildew
of wheat. Plant Disease 66: 139-141.
Purdy, L.H 1967. Wheat powdery mildew, a 1966 epiphytotic
in eastern Washington. Plant Dis. Rep. 51:94-95.
Other Interesting Powery
of Saskatchewan, Winter Wheat Production Manual -- description
Agriculture, Food and Rural Affairs -- description and pictures.
Diseases * Barley
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Edited and reviewed by Ed Adams, WSU Extension Plant Pathologist
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