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Powdery mildew (Blumeria graminis)

Powdery mildew

Powdery mildew: biology

Parts of the disease cycle are poorly understood for western North America. Seed transmission has not been proven and it is uncertain whether the overwintered bodies can release viable spores. Rapid spread is due to prolific production of wind-blown spores that can infect without rain or dew.

Powdery mildew: Damage description

Powdery white spots appear on leaves when the plants are flowering and, under rain-free conditions spread rapidly to cover all leaves, stem, tendrils and pods. As foliage ages, pinhead-sized overwintering bodies of the pathogen speckle the mildewed surface. Powdery mildew is often most conspicuous on late maturing crops or groups of plants.

Powdery mildew reduces seed yield. In heavily mildewed crops, the uptake of desiccants is restricted and seed may have a musty odor.

Powdery mildew: Management

Plant resistant varieties. Crop rotation is of limited value because production of airborne spores isprolific and dissemination very rapid. Monitor crops intensively from early flowering and, if mildew spots are observed when foliage is still green, spray a fungicide immediately. Spraying when the foliage is completely white is useless.

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