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Causal organism - Blumeria graminis
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There are several forms of the disease which are specific to individual crops and do not cross infect:
B. graminis f. sp tritici affects wheat.
B. graminis f. sp hordei affects barley.
B. graminis f. sp avenae affects oats.
B. graminis f. sp secalis affects rye.
Symptoms of powdery mildew can be found on leaves, stems and ears, but leaves
are most commonly infected. Typically, white pustules appear which produce
masses of spores and assuming a powdery appearance 
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As the mildew pustules become older, they darken to a grey or brown colour.
Eventually, black spore cases (cleistothecia)
can be found embedded in the mildew pustules
- usually towards the end of the season
