Minimizing yield loss starts with identifying which pathogen is the culprit. Here are the top yield-limiting soybean diseases and their symptoms.
Frogeye leaf spot
Frogeye leaf spot was responsible for 5.4 million bushels of yield loss in 2025.¹ When temperatures rise above 77 F, humidity is high and leaves are wet, the pathogen that produces frogeye leaf spot, Cercospora sojina K. hara, starts producing spores, splashing onto plants and increasing the risk of infection.
Identifying frogeye leaf spot
Frogeye leaf spot primarily affects the leaves of soybean plants during the reproductive stages. Start scouting for frogeye leaf spot during R1.
Symptoms include:
- Eye-like circular or angular lesion on leaves
- Spots measure 1 to 5 mm in diameter
- As spots grow, their centers turn pale gray. Borders turn red, brown or purple.
- A small black dot like a pupil may appear in the “eye” of the spot
Managing frogeye leaf spot
Frogeye leaf spot management starts with careful seed selection. You can also manage and prevent infection through cultural practices and fungicide application of Revylok® or Revytek®.
Septoria brown spot
Responsible for 1.4 million bushels in yield loss in 2025², Septoria brown spot is a threat particularly in warm, wet weather. Hot, dry weather curbs disease development but it may become evident near soybean maturity.³
Identifying septoria brown spot
Look for these symptoms:
- Small, irregular brown lesions or blotches
- Leaf necrosis
- Premature leaf drop
- Plant death in severe cases⁴
Septoria brown spot management
Foliar fungicides such as Priaxor® and Revylok® applied during R3 through R5 can protect yield potential by slowing disease progression into the middle and upper canopy.
Rhizoctonia aerial blight
Rhizoctonia aerial blight caused 158 thousand bushels of soybean yield loss in 2025.⁵
The fungus that causes Rhizoctonia aerial blight overwinters in soil or crop residue and spreads to plants when temperatures reach 77 to 90 F and conditions are wet. It’s primarily a problem for Southern growers using a soybean and rice rotation.
Identifying Rhizoctonia aerial blight
Symptoms typically appear on the lower portion of the plant after canopy closure in late vegetative growth stages, including:
- Grayish green, water-soaked lesions that turn tan to brown at maturity
- Reddish-brown lesions on infected petioles, stems, pods and petiole scars.
- Small 1/16 to 3/16” diameter, dark brown sclerotia on infected plant tissue⁶
Rhizoctonia aerial blight management
Rotating soybeans with non-host crops for multiple years can reduce this disease, as can wider row spacing and lower plant populations. Consider fungicides including Priaxor® and Revylok®.
Cercospora leaf blight and purple seed stain in soybean
Cercospora leaf blight (CLB) was responsible for 5.4 million soybean bushels of yield loss in 2025.⁷
CLB and its counterpart manifestation, purple seed stain, are both caused by the same soybean fungal disease, Cercospora kikuchii and Cercospora spp.
Identifying Cercospora leaf blight
CLB is most noticeable during R5–R6, when foliar symptoms are prominent. Look for:
- Reddish-purple bronzing on upper leaves.
- Black ovate lesions on petioles and pods, and lost leaves.
- Significant defoliation (in severe cases).
Managing Cercospora leaf blight
Choosing high-quality, uninfected seed, widening row spacing in fields with a history of CLB and applying a preventive fungicide application such as Revylok® can help.
Soybean mosaic virus
Soybean mosaic virus (SMV) can cause average yield losses up to 30% annually, with outbreaks exceeding 50% in some years.⁸
Identifying soybean mosaic virus
SMV symptoms are most noticeable in cool weather and can nearly disappear as temperatures rise, making it difficult to accurately assess the infection. Symptoms will appear more severe in younger plants and when temperatures are cooler.
The effects of SMV on soybean can vary based on seed variety, growth stage, and environmental conditions. Common SMV symptoms include:
- Stunted growth
- Fewer pods
- Light- and dark-green mosaic patterning on trifoliate leaves, which may also blister
- Leaf curling, wrinkling or distortion
Managing soybean mosaic virus
SMV cannot be controlled chemically. Manage by using tested virus-free seed and soybean varieties with the best SMV-resistant genetics, and by controlling aphids (many of which are vectors for SMV).
Experts are available to help you manage soybean foliar diseases (as well as root and stem diseases). Reach out to your seed retailer, a nearby extension office agent or a seed company professional like your regional BASF representative.
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Endnotes
- “Soybean Disease Loss Estimates from the United States and Ontario, Canada — 2025.” Crop Protection Network, 6 Mar. 2026, cropprotectionnetwork.org/publications/soybean-disease-loss-estimates-from-the-united-states-and-ontario-canada-2025. Accessed 22 June 2026.
- “Soybean Disease Loss Estimates…” Crop Protection Network.
- “Septoria Brown Spot of Soybean.” Crop Protection Network, 19 Mar. 2019, cropprotectionnetwork.org/encyclopedia/septoria-brown-spot-of-soybean. Accessed 22 June 2026.
- “Efficacy of Foliar Fungicides on Septoria Brown Spot Severity and Yield in Soybeans in Southeast Pennsylvania, 2024.” APS Online Publications, 15 Oct. 2025, apsjournals.apsnet.org/doi/abs/10.1094/PHP-04-25-0113-PDMR. Accessed 22 June 2026.
- “Soybean Disease Loss Estimates…” Crop Protection Network.
- “Aerial Blight of Soybean.” Crop Protection Network, 15 Jan. 2021, cropprotectionnetwork.org/encyclopedia/aerial-blight-of-soybean. Accessed 22 June 2026.
- “Soybean Disease Loss Estimates…” Crop Protection Network.
- Wang, Tao. “Enhanced Soybean Immunity to the Soybean Mosaic Virus Through RNA Interference Targeting the CP Gene - PMC.” PMC, 30 Jan. 2026, pmc.ncbi.nlm.nih.gov/articles/PMC12899861/. Accessed 22 June 2026.
