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Powdery Mildew

© Purdue University, Plant and Pest Diagnostic Laboratory

Pathogen(s) causing disease:

Erysiphe graminis f. sp. tritici


White or gray-brown powdery or cottony patches of mycelium (fungal threads) on the upper surface of lower leaves. Tiny, brown-black specks (cleistothecia) are visible in older gray-brown areas. Yellowing is usually visible on the undersides of leaves opposite the powdery patches.


 Disease development is favored by early canopy closure, high plant populations, high humidity and cool temperatures. Powdery mildew thrives where high rates of nitrogen have been used. Nitrogen not only promotes tiller formation, causing dense stands, but also increases the susceptibility of the crop. Use a correct and balanced fertilization program with proper levels of N, P and K. Watch for mildew in fields receiving greater than 70 lb N per acre.


Crop rotations, resistant variety, destruction of residues, proper fertilization, foliar fungicides. Do not plant susceptible seed prior to fly-free date.


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