Phytophthora infestans, one of the potato’s most lethal pathogens, causes the late blight of potato disease. This pathogen was responsible for the Irish potato famine of 1845–1849. P. infestans causes the leaves and stem of the potato plant to decay, eventually causing the tuber to stop growing. In addition, the tubers are attacked by the pathogen and rot. It has been estimated that during the potato famine 1.5 million Irish people emigrated from their country and moved to various parts of the world, but most immigrated to the United States. An estimated 400,000 people perished during the famine due to malnutrition.