It had been raining a lot, even more than usual for Ireland. In October 1845, almost overnight, a dense blue fog settled over our puddled potato fields. An odor of decay permeated the air. When the wind and rain died away, there was a terrible stillness. The potato crop was ruined, destroyed (we learned later) by the fungus Phytophthora infestans. 

― John Davis Cantwell, A Grandfather's Account of the Irish Potato Famine