Stem canker is rarely a problem in Kansas, but it is easily confused with Phytophthora root rot. The fungus survives in stubble or can be seed-borne. Spores are windblown or water-splashed onto plants. Sunken, brownish cankers with dark brown margins form on lower nodes with green stems above and below the canker. The canker is usually on one side of the stem but can girdle the stem causing the upper portion of the plant to wilt and die. Crop rotation, removal of debris, and use of tolerant cultivars aid in management.
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.
Pest photo source
Dean Malvick, Department of Plant Pathology, St. Paul