Root rots, seed rots and damping off (death of seedlings before or after emergence) are major diseases of snap beans, lima beans and Southern peas. Seed rots and damping off are collectively referred to as seedling disease. These diseases cause poor stands and reduced plant growth and yield. The fungi that cause seedling disease and root rots can be found in most soils, but the occurrence of these diseases is unpredictable. When conditions are favorable for vigorous plant growth, root rot fungi do little damage. These fungi can survive in the soil for long periods and can be moved with the soil from place to place. They are rarely carried on the seed.
The fungi that can cause root rots and seedling disease are Rhizoctonia solani, Fusarium solani f. sp phaseoli and several Pythium species. These fungi often occur together and are difficult to distinguish visually. Since the control methods differ, you should obtain assistance in identifying the disease from your local UT Extension office.
"SP277-O-Root Rots and Seedling Disease of Beans and Peas," The University of Tennessee Agricultural Extension Service, 07-0052, http://trace.tennessee.edu/utk_agexdise/48