"A Request for Help"

[phil geis]

Kevin had a good idea.  Maybe you could use Dutch Elm disease and
sporotrichosis (human disease) - cite story in the time period through
which the existing tree pathogen expands its range to include humans. 
How about an experimental fungicide that intends to plant a lethal
plasmid in the tree fungus, a plasmid that undergoes an unantcipated
modification by an innocuous fungus.
Good luck.