The complex of pathogens that causes seed, seedling, and root rots and damping off of seedlings is the most important cause of poor soybean plant stands and can significantly reduce soybean yields. The most important of these pathogens are the oomycetes, Phytophthora sojae and various Pythium species, often called “water molds” that are most aggressive when soils are saturated or wet for prolonged periods of time. This presentation discusses the biology of these two groups of pathogens, environmental factors that influence disease development, and unique characteristics of Phytophthora sojae and of the Pythium spp. that influence their persistence and aggressiveness as pathogens and our ability to manage oomycete caused diseases. Management of diseases caused by the oomycetes will be discussed with an emphasis on integration of resistance, chemical controls, and cultural practices.
