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Causal organism - Gaeumannomyces graminis
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Gaeumannomyces graminis var. tritici attacks wheat, barley,
rye and may attack some grass species, particularly couch grass (Elymus
repens). Oats are immune.
Gaeumannomyces graminis var. avenae attacks oats, wheat, barley,
rye and many grass species.
Near to maturity, patches of stunted plants and bleached heads (whiteheads)
appear, 
particularly after a dry period. Whiteheads generally contain small grains
or, occasionally, no grain. If diseased plants are pulled up, the roots can
be seen to be blackened and rotten.
In severe outbreaks the base of infected plants may also show blackening.
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