Quiz: Remember the definition of mal de mer?
disease of potato and tomato plants that is caused by the fungus Phytophthora infestans. The disease occurs in humid regions with temperature ranges of between 40 and 80 F (4 and 29 C); hot, dry weather checks its spread. Potato or tomato vines that are infected may rot within two weeks. The Irish potato famines of the mid-19th century were caused by late blight. The disease destroyed more than half of the tomato crop in the eastern United States in 1946, leading to the establishment of a blight-forecasting service in 1947.