Scout Soybean Diseases: Quick Identification Guide
BROWN SPOT
Caused by: Septoria glycines
Thrives in: Warm, humid conditions
Infects: As early as first true leaves
Looks like: Light to dark brown lesions on lower leaves with possible yellowing; more irregular as they expand
Results in: Damage to leaf tissue, defoliation, reduced yield
Pro tip: An in-season application of Miravis® Neo fungicide helps protect the lower canopy from early defoliation and keeps plants greener longer.
CERCOSPORA LEAF BLIGHT
Caused by: Cercospora kukuchii
Thrives in: Warm, moist conditions, mostly in Southern geographies
Infects at: Seed set
Looks like: Light purple pinpoint spots on upper leaf surface that expand to irregular patches; leaves become leathery and purple
Results in: Damage to leaf tissue, reduced seed quality (purple stain), reduced yield
Pro tip: Combine crop rotation, tillage, and Miravis Neo fungicide to help protect plant health and support a stronger finish at harvest.
FROGEYE LEAF SPOT
Caused by: Cercospora sojina
Thrives in: Warm, humid environments
Infects: Severity increases as plants mature at R3-R5
Looks like: Small, dark, water-soaked circular lesions with gray-brown border on young leaves
Results in: Damage to leaf tissue, reduced yield
Pro tip: By the time you see frogeye leaf spot, it's already spreading. Apply Miravis Top or Miravis Neo fungicide at R3 to protect green tissue during pod fill.
POWDERY MILDEW
Caused by: Microsphaera diffusa
Thrives in: 60–70°F, damp conditions
Infects in: May to July
Looks like: Raised, fluffy or powdery white spots on lower leaves
Results in: Damage to leaf tissue, reduced yield
Pro tip: A timely application of Miravis Neo fungicide helps stop powdery mildew from creeping up the canopy and cutting into pod fill.
RED CROWN ROT
Caused by: Calonectria ilicicola
Thrives in: 77–86°F, wet conditions
Infects: At planting/early-season (soilborne)
Looks like: Brick red mushroom-like structures at base of plant; yellow speckled spots on leaves (similar to SDS)
Results in: Poor stands; root damage; reduced water and nutrient uptake, leaf tissue damage, reduced yield
Pro tip: Red crown rot is an emerging threat that’s still on the move! Start strong with Saltro® seed treatment* to protect your soybean roots early and suppress infection before it threatens yield potential.
SUDDEN DEATH SYNDROME (SDS)
Caused by: Fusarium virguliforme, often in fields with active soybean cyst nematode
Thrives in: Cool, wet conditions
Infects: At planting/early-season (soilborne); visible symptoms appear in August
Looks like: Yellow-brown flecks on leaves (similar to brown stem rot); blue mold present on taproot
Results in: Damage to leaf tissue, reduced water and nutrient uptake, reduced yield
Pro tip: Protect roots early with Saltro seed treatment, which delivered an average yield boost of 3.1 bu/A1 over ILEVO® in trials under SDS pressure.
TARGET SPOT
Caused by: Corynespora cassiicola
Thrives in: Warm, wet conditions
Infects at: Canopy to R6, beginning with the lower leaves
Looks like: Round to irregular dark brown spots on lower leaves with yellow halos that resemble targets
Results in: Damage to leaf tissue, heavy defoliation, reduced yield
Pro tip: Target spot thrives when humidity runs high and the canopy becomes dense. Apply Miravis Top fungicide at R3 to stay ahead of leaf damage and hold onto yield.
WHITE MOLD
Caused by: Sclerotinia sclerotiorum
Thrives in: Cool temps, wet soil, high humidity
Infects: At flowering; can survive in soil for 6–10 years
Looks like: Fluffy white substance; trumpet-shaped, mushroom-like structures in soil at plant base
Results in: Damage to plant tissue, reduced yield potential
Pro tip: When flowering starts under cool, wet conditions, white mold risk goes up fast. Apply Miravis Neo fungicide at R1-R2 to protect your canopy and help suppress white mold before it sets in.
PHYTOPHTHORA ROOT ROT
Caused by: Phytophthora sojae
Thrives in: Warm, wet conditions and poorly drained soils
Infects: At planting and early-season
Looks like: Brown stem lesions near the soil line; plants wilt and collapse
Results in: Root damage, stand loss, reduced water uptake, yield decline
Pro tip: Protect roots and boost emergence with CruiserMaxx® APX seed treatment, containing two strong modes of action against Phytophthora, delivering a 2 to 5 bu/A advantage over untreated seed in Ohio State trials2.
1 Syngenta US trials with SDS pressure (n = 48), conducted from 2015–2023 in AR, IL, IA, KS, KY, MI, MN, MO, TN, and WI.
2 2018 Ohio State University Phytophthora trial; α = 0.05
*Syngenta supports a FIFRA Section 2(ee) recommendation for Saltro for suppression of Red Crown Rot in Arkansas, Illinois, Indiana, Iowa, Kentucky, Missouri, Ohio and Tennessee. Please see the Section 2(ee) recommendation to confirm that the recommendation is applicable in your state. The Section 2(ee) recommendation for Saltro should be in the possession of the user at the time of application.
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