Late blight on a potato (Solanum tuberosum) plant. Late blight is caused by the water mould Phytophthora infestans. The spores of the mould lie dormant on tubers under the soil during the winter, but spread rapidly in warmer damp conditions. Early symptoms include the appearance of dark blotches on the leaf tips. Later, white mould appears under the leaves and the tubers develop dark regions, leading to the collapse of the whole plant. Here the blight has led to necrosis (cell death) in the leaves.