When considering early planting of soybeans, there are two diseases that should be considered: 1) Sudden death syndrome (SDS) and 2) Pythium root rot (PRR)
Both SDS and PRR are favored by cool, wet weather. In the case of SDS, early season infections can reduce stands, and also result in colonization of root systems. The SDS pathogen remains in the lower portion of the stem and roots until the the plant reaches the reproductive stages. Heavy, alternating rains during reproduction can cause the fungus to more aggressively colonize the plants, as well as produce toxins, which can cause defoliation, wilting, and reduced yields.
If considering early planting into fields with a history of SDS, ensure that you select a cultivar with excellent SDS resistance and consider an SDS-seed treatment if it fits your production practices.
PRR is actually a complex of Pythium species that each have their own unique characteristics. It is now understood that individual Pythium species and even isolates within species can differ significantly in their optimal temperature for infecting seedlings. Regardless of temperature, if the growth of your soybeans is reduced due to soil water saturation or cool conditions, you may see increased stand issues. There are specific seed treatments that can be effective for suppressing Pythium.
However, it is important to realize that these treatments provide a window of protection that is intended to protect the emerging seedling and allow it to establish. This window typically is 2-3 weeks. Seed treatments will not protect a submerged seed from dying due to flooding, and will not provide protection after that window of protection is reached. Remember, seed treatments are not fumigants — they are short-term, protective barriers. Tile can be a great investment in fields prone to flooding and subsequent PRR issues.