Later a slimy, foul smelling rot may destroy the tuber. This species is characterized by coenocytic mycelium and the production of biflagellate, motile zoospores. The fungus is heterothallic and can reproduce sexually in the presence of an opposite mating type. Sexual reproduction follows fertilization of an oogonium by an antheridium resulting in the production of an oospore. After germination both will result in the production of sporangia which can germinate directly by means of a germ tube or indirectly by means of the motile zoospores.
Germination is followed by encystment and appresorium formation.
Penetration of the leaf surface is by means of an infection peg followed by intercellular invasion with penetration of the cells by means of an haustorium. Invasion of he leaf is rapid, eventually resulting in necrosis and death of the leaf tissue. Under favorable conditions, the sporangiophores emerge through the stomata with a fresh crop of sporangia within 4 to 5 days of the initial infection. This multicycle, airborne pathogen can therefore spread rapidly within crops and from one crop to another. Apart from starvation, the lack of food led to other diseases such as scurvy, dysentery, typhus and cholera.