Store sweet potatoes at 55 to 60 degrees F and 90 percent relative humidity. Bacterial Soft Rot Bacterial soft rot, also known as bacterial stem and root rot, is caused by the pathogen Erwiniachrysanthemi. Rotting can occur in the field as well as during shipment and storage. The disease is known to occur only in the United States. Lesions on storage roots often have a dark brown margin.
Some storage roots appear healthy from the outside but are decayed internally.
Infected roots show black streaks in the vascular tissue and eventually undergo a soft, moist decay. Mother roots often decay in plant beds. Sweet potato with symptoms of bacterial soft rot. In the field, brown to black, water-soaked lesions appear on stems and petioles. Eventually, the stem may become watery and collapse, causing the ends of vines to wilt.