Cause: Species of soil-inhabiting fungi such Rhizoctonia, Fusarium and Pythium.
In many cases, the disease is a continuation of seedling blight. Spots of various sizes occur on the stem, at or near the soil level and on the roots. These spots may vary in color from gray, brown, black, or even bright red. Frequently, these fungi cause the tips of fibrous roots to decay. Wilting, dieback, and poor vigor are common symptoms. Plants are often predisposed to infection by poorly drained soils, crowding, mechanical injury, over-watering, improper balance of plant nutrients or other factors that affect plant growth. Containerized plants often suffer root rot even though factors other than fungi may be the primary cause. Roots on potted plants can be checked for vigor by carefully removing the pot when the container is inverted and the plant is supported at the base with one hand. Dark decaying roots on the outside of the soil mass indicate a root rot condition may exist.
Control is difficult because once symptoms are observed, damage to the stem or roots is usually severe. For small flower beds and potted plants, use a soil drench of a recommended fungicide. A fungicide could also be mixed with soil prior to planting as suggested by the manufacturer. Allow excessively wet soils to dry. Always avoid throwing soil to stems when cultivating and avoid crowding plants in seedbeds or other areas. When transplanting or repotting, place plants at the same soil depth. Do not mulch heavily with partially decomposed organic matter. In the field, cover crops should be plowed under early to allow complete decomposition before a susceptible crop is planted.
Nematodes may cause symptoms similar to stem and root rots. See sections on Nematodes other than Root Knot, Southern Blight, Seedling Blight, Mushroom Root Rot, and Cotton Root Rot. All of these can cause stem and root rot type symptoms