In early growth stages, corn or soybeans can survive for only two to four days under water in anaerobic conditions. Moderate water movement can reduce flood damage by allowing some oxygen to get to the plants, keeping them respiring and alive. Drainage within one to two days increases the chance of survival. Cool temperatures may prolong survival. However, cold, wet weather favors disease development.
Seed treatments are effective, but limited in protection.
Seedling development slowed or delayed two to three weeks allow soil-borne pathogens a greater opportunity to cause damage. Seed rots, seedling blight, corn smut and crazy top affect corn plant development later even though ponding occurred earlier. Delayed soybean growth allows diseases such as Fusarium root rot, Phytophthora rot and Pythium rot to establish and weaken or destroy seedlings. Limited hybrid and variety resistance to these diseases and difficulty in predicting damage makes evaluation difficult. Carefully assess damage before deciding to replant or before tearing up the existing stand.