Mid-Season Soybean Diseases to Scout for and Best Management Practices

Soybeans are a vital crop for global agriculture, providing essential oils and proteins. However, soybean production can be impacted by various diseases during the mid-season growth period. Timely identification and appropriate management of these diseases is crucial for maximizing yield and quality potential. Outlined below are common mid-season soybean diseases and best management practices.

Common Mid-Season Soybean Diseases

• Frogeye Leaf Spot (Cercospora sojina)
  • Identification: Frogeye leaf spot is characterized by small, circular lesions with dark borders and gray to brown centers on the upper leaf surfaces (Figure 1). The lesions can coalesce and cause considerable leaf damage.
  • Management: Utilize tolerant soybean products and rotate crops with non-host plants. Delaro^® Complete Fungicide is labeled for control of frogeye leaf spot.

• Brown Spot (Septoria glycines)
  • Identification: Brown spot manifests as small, irregular brown spots on the lower leaves, which can cause premature defoliation (Figure 2). In severe cases, the entire plant may be affected. Bacterial leaf spot, which cannot be managed with fungicides, is similar to brown spot but begins in the upper canopy and is often associated with leaf tattering.
  • Management: Implement crop rotation and residue management to help reduce pathogen carryover. Delaro^® Complete Fungicide is labeled for control of brown spot.

• Sudden Death Syndrome (SDS) (Fusarium virguliforme)
  • Identification: SDS causes interveinal chlorosis and necrosis on leaves, often accompanied by root rot (Figure 3). Severe SDS can cause cupping of the leaves and defoliation with petioles still attached. Symptoms typically appear after flowering and can lead to substantial yield losses.
  • Management: Plant tolerant soybean products in well-drained soils to help reduce the risk of infection. While foliar fungicides are generally ineffective against SDS, seed treatments with ILeVO^® (fluopyram) help protect seedlings from initial SDS infection and soybean cyst nematodes (SCN).

• White Mold (Sclerotinia sclerotiorum)
  • Identification: White mold is identified by white, cottony growth on stems and pods, leading to wilt and plant death (Figure 4). Hard, black sclerotia (fungal structures) may be present on infected tissues.
  • Management: Use tolerant soybean products and rotation with non-host crops. Delaro^® Complete Fungicide is labeled for suppression of white mold.

• Anthracnose (Colletotrichum truncatum)
  • Identification: Anthracnose is characterized by dark lesions on stems, petioles, and pods. Infected plants may exhibit premature defoliation and dieback; however, this disease is most prevalent when plants mature (Figure 5).
  • Management: Employ crop rotation and use certified disease-free seeds. Delaro^® Complete Fungicide is labeled for control of anthracnose.

Best Management Practices for Soybean Diseases

• Regular Scouting
  • Consistent monitoring of soybean fields is essential for early disease detection. Scouting should involve checking multiple areas of the field, focusing on different growth stages and environmental conditions.
• Crop Rotation
  • Rotating soybean with non-host crops (such as corn or small grains) can help reduce the buildup of pathogens in the soil. This practice disrupts the life cycle of many soybean-specific diseases.
• Tolerant Products
  • Planting disease-tolerant/resistant soybean products is one of the most effective strategies to manage diseases. Channel^® brand soybean product profiles provide information on the resistance levels of different pathogens.
• Fungicide Use
  • The judicious use of fungicides is critical for managing soybean diseases. It is essential to use a premix of fungicides with multiple modes of action to help prevent the development of resistant pathogen strains. Delaro^® Complete Fungicide, with its combination of prothioconazole, trifloxystrobin, and fluopyram, is a versatile and effective option for controlling or suppressing a range of mid-season soybean diseases. Follow label recommendations for application timing and rates to ensure effectiveness and environmental safety.
• Soil Health Management
  • Maintaining healthy soil through balanced fertilization and increasing organic matter can help improve plant vigor and tolerance to diseases. Practices such as cover cropping and reduced tillage can help enhance soil structure and microbial diversity, contributing to disease suppression.

Conclusion

Effective management of mid-season soybean diseases requires a comprehensive approach combining regular scouting, resistant soybean products, and appropriate fungicide use. By implementing these best management practices, including the use of Delaro^® Complete Fungicide, soybean producers can help mitigate the impact of diseases, ensuring healthy crops and optimal yield potential. Staying informed about emerging disease threats and adapting management strategies accordingly is key to successful soybean production.

Channel Agronomist
Brandon Beck

Sources

Strunk, C. 2022. Mid-to-late soybean disease management. South Dakota State University Extension. https://extension.sdstate.edu/mid-late-soybean-disease-management

Yang, XB. 2010. Mid-season soybean diseases: scouting and management. ICM News. Integrated Crop Management. Iowa State University Extension and Outreach. https://crops.extension.iastate.edu/cropnews/2010/07/mid-season-soybean-diseases-scouting-and-management

Esker, P., Gaska, J., Conley, S., and Grau, C. Diagnosing late season soybean diseases. Cool Bean Advisor. University of Wisconsin. https://www.coolbean.info/pdf/soybean_research/mid_late_season/Diagnosing_Late_Season_Soybean_Diseases.pdf

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