Phytophthora may occur any time during the season if soils remain wet. The fungus survives in soil and produces swimming spores that infect roots. Phytophthora symptoms include preand postemergence damping off. Older plants may turn yellow and leaves may wilt. Roots usually appear rotted and a brown discoloration extends from the soil line up into branches and petioles. Conditions encouraging disease include poorly drained soil, flooding from heavy rains, or overirrigation. Resistant or tolerant varieties are the best means of management. There are many races of Phytophthora and varieties should be selected accordingly. Any improvements in drainage also will help.
Taken from Kansas State University Agricultural Experiment Station and Cooperative Extension Service Publication #C-449. Soybean Diseases, Dr. Douglas J. Jardine, Extension State Leader, Plant Pathology Program.