Cereal fungus (5)
I believe the answer is:
ergot
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">cereal fungus</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for ergot that I've seen before include "Fungal infection" , "drug supplier" , "Cereal disease" , "Fungal disease of grain" , "Could Roget have a fungal plant disease?" .)