Continuous Soybean Management Practices

• Continuous soybean production has become more attractive to some growers due to favorable market prices and lower input costs when compared to corn production.

• Growing a crop year after year in the same field can result in a build-up of pathogens and insect pests which may result in yield penalties.

• Certain management practices such as product disease or insect resistance can help mitigate these issues.

Though continuous soybean production is generally not recommended, some farmers have reported stable yields with no downward trend after nearly 20 years or more of planting soybeans continuously in the same field.¹ Successes like these tend to occur in areas where soils are not prone to holding excessive moisture and where disease and soybean cyst nematode (SCN) problems are minor. Low lying fields and fields with poor drainage are not ideal for continuous soybean production due to the increased potential for disease development. Greater yield penalties and smaller profit margins, due to increased pest control costs, may be expected when soybeans are planted continuously in fields that have a history of insect and disease problems.

Product selection is critical for continuous soybean production. Products should be selected based on yield potential, maturity, and resistance to key insects and diseases. It is a good idea to plant different genetics each year to minimize the proliferation of diseases.

Disease inoculum can build up on crop debris and in the soil each growing season when in the constant presence of a host crop. A field with disease or nematode issues may see a dramatic reduction in yield after the third or fourth year of continuous soybean production.² Diseases such as white mold, sudden death syndrome (SDS), brown stem rot, certain root rots, and SCN remain in the soil or crop residue for several years after a host plant is removed.

Without crop rotation to break pest and pathogen life cycles, other management approaches will be needed. Often, planting a product with disease or insect resistance is the most effective management approach. Phytophthora root rot can be managed by selection of soybean products with racespecific resistance, designated Rps. Products with the appropriate Rps designations relative to the races in a field, combined with partial resistance, will provide the best control^.3 No soybean products are completely resistant to white mold or SDS. Selecting soybean products with partial resistance to these diseases may help reduce damage.

If white mold occurred in the previous year, crop rotation is the most effective cultural practice for preventing future damage. With continuous soybeans, other cultural practices must be considered. Alternative control strategies for managing diseases include lower seeding rates or wider row widths to increase air flow in the canopy for suppression of foliar diseases. Planting later in the season or planting soybean products with shorter relative maturities can help to avoid disease outbreaks during sensitive growth stages.