Field Insights
Spot that Corn Disease: Quick Identification Guide
Use this guide to determine which corn disease threats are in your fields.
June 2025
| BY BY SYNGENTA THRIVE
3 Min Read
Grab your magnifying glass — it’s time to test those ID skills! Use this guide to determine which corn disease threat you’re looking at and how to treat it.
ANTHRACNOSE
Caused by: Colletotrichum truncatum
Thrives in: High temps, wet weather
Infects at: Seedling phase or full maturity
Looks like: Long, tan to reddish-brown oval lesions, with possible raised dark spots; affects lower leaves, travels upward
Results in: Damage to leaf tissue, reduced stalk strength and yield potential
Pro tip: Reach for a long-lasting fungicide when you ID Anthracnose! In Kentucky trials, Trivapro® fungicide provided up to 42 days of residual control and added 60 bu/A over untreated1.
Caused by: Colletotrichum truncatum
Thrives in: High temps, wet weather
Infects at: Seedling phase or full maturity
Looks like: Long, tan to reddish-brown oval lesions, with possible raised dark spots; affects lower leaves, travels upward
Results in: Damage to leaf tissue, reduced stalk strength and yield potential
Pro tip: Reach for a long-lasting fungicide when you ID Anthracnose! In Kentucky trials, Trivapro® fungicide provided up to 42 days of residual control and added 60 bu/A over untreated1.
COMMON RUST
Caused by: Puccinia sorghi
Thrives in: Moderate temps, high humidity, heavy dew, 6+ hours of leaf wetness
Infects in: June, July
Looks like: Southern rust, but smaller, lighter pustules; more densely packed on the leaf surface
Results in: Damage to leaf tissue, reduced yield
Pro tip: Scout often and early! A preventive application of Trivapro fungicide can help protect leaf tissue and reduce yield loss.
Caused by: Puccinia sorghi
Thrives in: Moderate temps, high humidity, heavy dew, 6+ hours of leaf wetness
Infects in: June, July
Looks like: Southern rust, but smaller, lighter pustules; more densely packed on the leaf surface
Results in: Damage to leaf tissue, reduced yield
Pro tip: Scout often and early! A preventive application of Trivapro fungicide can help protect leaf tissue and reduce yield loss.
DIPLODIA EAR ROT
Caused by: Stenocarpella maydis, Stenocarpella macropora
Thrives in: Moderate temps, wet conditions; most severe in no-till or reduce-till in corn fields followed by corn
Infects: At and up to 3 weeks post-R1 or silk
Looks like: White mold, which later turns gray-brown
Results in: Reduced grain quality, reduced yield
Pro tip: Apply Miravis® Neo fungicide at R1 to help suppress Diplodia ear rot and support healthy ear development, especially in high-residue, corn-on-corn fields.
Caused by: Stenocarpella maydis, Stenocarpella macropora
Thrives in: Moderate temps, wet conditions; most severe in no-till or reduce-till in corn fields followed by corn
Infects: At and up to 3 weeks post-R1 or silk
Looks like: White mold, which later turns gray-brown
Results in: Reduced grain quality, reduced yield
Pro tip: Apply Miravis® Neo fungicide at R1 to help suppress Diplodia ear rot and support healthy ear development, especially in high-residue, corn-on-corn fields.
FUSARIUM EAR ROT
Caused by: Fusarium verticilliodes
Thrives in: Warm, wet weather before harvest
Infects: Infects at silking, often after insect or hail damage; symptoms appear at R5–R6
Looks like: Scattered clusters of white to lavender kernels with brown streaks throughout the length of the ear
Results in: Increased mycotoxins, reduced grain quality, reduced yield
Pro tip: When late season-ear damage opens the door to Fusarium ear rot, turn to a R1 application of Miravis Neo fungicide, one of the few fungicides labeled for suppression.
Caused by: Fusarium verticilliodes
Thrives in: Warm, wet weather before harvest
Infects: Infects at silking, often after insect or hail damage; symptoms appear at R5–R6
Looks like: Scattered clusters of white to lavender kernels with brown streaks throughout the length of the ear
Results in: Increased mycotoxins, reduced grain quality, reduced yield
Pro tip: When late season-ear damage opens the door to Fusarium ear rot, turn to a R1 application of Miravis Neo fungicide, one of the few fungicides labeled for suppression.
GIBBERELLA EAR ROT
Caused by: Gibberella zeae, the teleomorph stage of Fusarium graminearum
Thrives in: Cooler conditions during silking; overwinters in soil (> 68° F for spore maturation)
Infects at: Silk
Looks like: White to pink mold at ear tip; moves towards base
Results in: Increased vomitoxin (deoxynivalenol, or DON), and other toxins, reduced grain quality, reduced yield
Pro tip: Wet weather at silking? Apply Miravis Neo fungicide at green silk to R1 to help protect corn ears and support clean, high-quality grain.
Caused by: Gibberella zeae, the teleomorph stage of Fusarium graminearum
Thrives in: Cooler conditions during silking; overwinters in soil (> 68° F for spore maturation)
Infects at: Silk
Looks like: White to pink mold at ear tip; moves towards base
Results in: Increased vomitoxin (deoxynivalenol, or DON), and other toxins, reduced grain quality, reduced yield
Pro tip: Wet weather at silking? Apply Miravis Neo fungicide at green silk to R1 to help protect corn ears and support clean, high-quality grain.
GRAY LEAF SPOT
Caused by: Cercospora zeae-maydis
Thrives in: Warm, humid weather
Infects in: June, typically in corn on corn fields
Looks like: Long, narrow, rectangular light tan lesions delimited at leaf veins
Results in: Damage to leaf tissue, reduced yield
Pro tip: Gray leaf spot reduces the photosynthetic leaf area needed for grain fill and can weaken plants prematurely. Apply Miravis Neo fungicide and remove crop residue to prevent overwintering.
Caused by: Cercospora zeae-maydis
Thrives in: Warm, humid weather
Infects in: June, typically in corn on corn fields
Looks like: Long, narrow, rectangular light tan lesions delimited at leaf veins
Results in: Damage to leaf tissue, reduced yield
Pro tip: Gray leaf spot reduces the photosynthetic leaf area needed for grain fill and can weaken plants prematurely. Apply Miravis Neo fungicide and remove crop residue to prevent overwintering.
NORTHERN CORN LEAF BLIGHT (NCLB)
Caused by: Exserohilum turcicum
Thrives in: Moderate to warm temps, moist conditions, extended leaf wetness
Infects: Pre-VT through senescence; rain and wind help spores spread
Looks like: Long, gray-green to tan cigar-shaped lesions form on lower leaves; travel upward through season
Results in: Damage to leaf tissue, reduced yield
Pro tip: Northern corn leaf blight can hit hard, taking out leaf area needed for grain fill. Keep plants performing with a timely tassel application of Miravis Neo fungicide.
Caused by: Exserohilum turcicum
Thrives in: Moderate to warm temps, moist conditions, extended leaf wetness
Infects: Pre-VT through senescence; rain and wind help spores spread
Looks like: Long, gray-green to tan cigar-shaped lesions form on lower leaves; travel upward through season
Results in: Damage to leaf tissue, reduced yield
Pro tip: Northern corn leaf blight can hit hard, taking out leaf area needed for grain fill. Keep plants performing with a timely tassel application of Miravis Neo fungicide.
SOUTHERN RUST
Caused by: Puccinia polysora
Thrives in: High humidity, high temperatures
Infects in: June or July
Looks like: Light orange to red-colored oval pustules, densely scattered on leaf surface
Results in: Damage to leaf tissue, reduced yield
Pro tip: Southern rust thrives in hot, humid conditions and can quickly take over the upper canopy. Protect leaf tissue during kernel fill with long-lasting residual control from Trivapro fungicide.
Caused by: Puccinia polysora
Thrives in: High humidity, high temperatures
Infects in: June or July
Looks like: Light orange to red-colored oval pustules, densely scattered on leaf surface
Results in: Damage to leaf tissue, reduced yield
Pro tip: Southern rust thrives in hot, humid conditions and can quickly take over the upper canopy. Protect leaf tissue during kernel fill with long-lasting residual control from Trivapro fungicide.
TAR SPOT
Caused by: Phyllachora maydis
Thrives in: Cool, humid conditions, prolonged leaf wetness
Infects in: Late summer; can overwinter in residue
Looks like: Small, raised, circular black spots that don’t rub off; affects lower leaves first. Older leaves and stressed plants tend to be more susceptible than newer leaves and younger plants.
Results in: Damage to leaf tissue, stalks and husks, lodging, reduced yield
Pro tip: Apply Miravis Neo or Trivapro at VT/R1. In trials2, Miravis Neo helped deliver 245.7 bu/A compared to 216.2 bu/A untreated.
Caused by: Phyllachora maydis
Thrives in: Cool, humid conditions, prolonged leaf wetness
Infects in: Late summer; can overwinter in residue
Looks like: Small, raised, circular black spots that don’t rub off; affects lower leaves first. Older leaves and stressed plants tend to be more susceptible than newer leaves and younger plants.
Results in: Damage to leaf tissue, stalks and husks, lodging, reduced yield
Pro tip: Apply Miravis Neo or Trivapro at VT/R1. In trials2, Miravis Neo helped deliver 245.7 bu/A compared to 216.2 bu/A untreated.
1 Application timing: R1. Trivapro produced 60 bu/A more than untreated. Additional revenue: $210 per acre. Kentucky, 2016. Revenue calculations based on commodity prices of $3.50/bu corn.
2 8 Syngenta trials, IN, MI, WI (2019–2022); VT/R1 timing; 13.7 fl. oz./A Miravis Neo. Disease: Tar spot – late September evaluations.
2 8 Syngenta trials, IN, MI, WI (2019–2022); VT/R1 timing; 13.7 fl. oz./A Miravis Neo. Disease: Tar spot – late September evaluations.
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