How Excessive Rain Impacts Soybean Planting

If soil around germinating soybeans is waterlogged for two days, yield losses may be minimal. Any longer, and you will see measurable losses — even plant death. So when is the right time to plant soybeans if heavy rainfall is a concern for your region? Read on for more information about the effects of heavy rainfall, diseases and fungus on your soybean plants.

Heavy Rainfall

Soybeans require oxygen to produce energy. But depending on soil type, waterlogged soil may reduce a plant's access to that oxygen. The longer the soil remains saturated, the greater the potential for yield loss. Soybeans can typically withstand overly wet conditions for 48 hours. Keep in mind that clay and silt soils tend to retain moisture longer than sandy soil.

After a rainfall, wait to evaluate planting times until water recedes and the soil is no longer waterlogged. You're looking for at least a 24- to 48-hour period without heavy rainfall before beginning planting.

Diseases and Fungus

Saturated soils increase the risk of seedling diseases in soybeans. Pythium is adept at targeting new seedlings in waterlogged soils and Phytopthora can start infections in early summer.¹

Moist conditions, cooler weather and cooler soil combined  is ideal for fungus like Fusarium (Fusarium virgulifome) and diseases like sudden death syndrome. 

If you have not finished planting, wait until soil drains before planting additional seed. If all seeds are already in the ground, wait until drier conditions to dig up a few plants from across your fields. Are your soybeans turning yellow? Search stands for signs of infection including blackened, withering roots and yellowing leaves. Based on the volume and severity of the disease, additional seed may be necessary to boost stand count, or a full replant may be required.