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Soybean Foliar Disease: What to Know

Posted on June 16, 2023

Like many crops, soybeans are susceptible to diseases, with fungal diseases being among the most common. These fungal diseases typically infect the leaves of soybean plants and can cause defoliation and ultimately affect overall crop yield and profits for the grower.  

Proper scouting and management techniques can help identify any threats early and mitigate the risk of disease spread. Below are several common fungal diseases in soybeans, their symptoms, and information on how growers can combat infection.  

White Mold

One disease growers often battle on soybean crops is white mold. This disease is caused by the fungus, Sclerotinia sclerotiorum, and is not common, yet it can wreak havoc on fields if spotted.  

White mold develops in cool, cloudy, and wet conditions and can be very problematic in soybean fields with high plant populations, narrow row spacing, and early closing canopies that trap soil moisture during flowering at growth stage R1.  

(Photo Source)

Several management practices to help combat white mold in soybeans include: 

  • Implementing crop rotations and planting non-host crops to mitigate the disease.  
  • Managing crop canopy by planting wider rows in fields with a history of white mold development. Also, consider reducing the population at-plant in the next season host crops are planted in that field. 
  • Applying a fungicide immediately when spotted reduces infection of the entire field and neighboring fields.  

Septoria Brown Spot

Septoria Brown Spot is caused by a fungal infection caused by Septoria glycines. It typically begins in the lower canopy of the plant during periods of high moisture and humidity and can progress upward in the canopy of the crop as the growing season continues.  

Symptoms on soybean crops include dark brown, angular spots that range from small, pinhead-size specks to over a quarter inch in diameter. Below is a photo from The University of Kentucky showing infected leaves.  

Alleviate soybean crop stress from Septoria Brown Spot by: 

  • Regularly scouting fields to ensure any infection is caught early for treatment. 
  • Rotating soybeans with non-host crops to break the disease cycle. 
  • Implementing drain tile and other drainage solutions to help reduce standing water and humidity problems in the field. 
  • Applying fungicide at the R3 growth stage.  


Soybean rust can be one of the most costly and significant soybean diseases, causing yield losses of 50 percent or more of a crop. It oftentimes spreads quickly and causes leaf spots and defoliation of the soybean crop.  

(Photo Source)

Symptoms of the disease begin in the lower canopy of the plant and develop on the underside of leaves as blisters or lesions. The disease can occur at any growth stage of the plant, but it is most often found during the middle of the growing season after the plant flowers and pods begin to develop.  

(Photo Source)

Best management practices for combatting soybean rust include:

  • Scouting lower canopies of soybeans, especially after heavy rains and wet weather. 
  • Treating any infection in soybean crops with fungicide as soon as the disease is spotted. 
  • Carefully selecting and planting soybean varieties that are resistant to disease.  

Plan a Season-Long Approach to Soybean Health

Crop health is a marathon, not a sprint. Plan for a season-long approach to crop health with a high-yield program specifically built to maximize soybean yields.  

Download the soybean high-yield program today to learn more about protecting crop health and nutrition, and to plan a season-long approach to increasing overall yields. For any product questions and for pricing information, contact our sales team today. 

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