Must be a lightning strike that caused the spot. Who'd a thought? Had my doubts about the phytophthora(SP) because it was just in that small area and nowhere else to be found.  

I have once seen a tree that was hit by lightning. The thing was split in half and blew out a 4 foot hole before hitting underground cables. That was a sight.  

 Now what do you think actually killed the beans? The electricity or the heat emitted from the strike?