text: what fungus changed the course of irish history?   the potato blight was caused by phytophthora infestans.  p. infestans is naturally occurring and typically occurs close to the soil.  when potatoes are grown too close to the surface of the ground, and p. infestans is present, the very outside of the potatoes turn green.  it is common to find potato chips that are green around the outside.  it's caused by the same thing that caused the potato blight!  although i don't eat green potato chips, they are allegedly not harmful to eat.