Damping off and seed rot, caused by Phytophthora sojae, is an important early season disease of soybean in Iowa. The disease is favored by warm (>60 °F), wet soil conditions. P. sojae is an oomycete that survives in the soil as thick-walled oospores. When soil conditions are warm and wet, the oospores germinate, producing sporangia, which in turn produce many zoospores. These spores have flagella that enable them to swim in freestanding water. The zoospores are attracted to soybean roots by root exudates, where they infect seedling roots and cause disease. Thus, wet soils are essential for infection by P. sojae.