Grain bane (5)
I believe the answer is:
ergot
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">grain bane</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 "problem with cereal" , "One across disease of rye" , "Parasitical fungus" , "problem with grass" , "Plant problem" .)