Definition of powdery mildew
1
: an ascomycetous fungus (family Erysiphaceae) producing abundant powdery conidia on the host
2
: a plant disease caused by a powdery mildew
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Merriam-Webster unabridged
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Time Traveler for powdery mildew
The first known use of powdery mildew was in 1889
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