Diseases – Corn
- Fungal disease caused by Puccinia polysora pathogen.
- Favored by high humidity and temperatures in the 80s and 90s.
- More frequent in the South, but may also spread into the Midwest by wind-blown spores, usually in late summer.
- Spreads very rapidly when conditions favor development. New infections may occur every seven days, epidemics may occur over large areas so fields may be damaged very quickly.
Figure 5. Corn leaf infected with southern rust. Note round to oval pustules, light brown to orange in color.
Northern Corn Leaf Blight
- Also known as the fungus Exserohilum turcicum, that overwinters in corn debris.
- Infection occurs when free water is present for 6-18 hours and temperatures are 65-80ºF (18-20ºC).
- Spores spread by rain splash or are carried on air currents.
- Infection can occur during any growth stage, but plants are most susceptible after pollination.
- Fungicides are available to manage this pathogen, if necessary.
Figure 6. NCLB lesions on corn leaf.
Figure 7. Close up of NCLB lesion.
- Depletion of nitrogen due to leaching makes stalks more prone to rotting.
- Specific rots are weather dependent.
Figure 8. Stalk depicting both anthracnose and Gibberella stalk rot.
Gray Leaf Spot
- Fungal disease caused by Cercospora zeae-maydis pathogen.
- GLS builds up in corn residue over time.
- Favored by warm temperatures and high humidity.
- Disease often spreads rapidly with favorable weather during late summer and early fall (during the grain fill period of corn development).
Southern Corn Leaf Blight
- Fungal disease caused by Cochliobolus heterostrophus (also known as Bipolaris maydis).
- Development is favored by warm (70 to 85ºF), moist weather and free water on the leaf.
- Thrives in warm-temperate or subtropical corn-growing environments, including the southeastern U.S.
- Spores are windblown or splashed by water to new crop leaves where they germinate and infect the plant.
Figure 9. GLS lesions (rectangular shape).
Figure 10. SCLB lesions (irregular shape).
- Caused by the fungus Phyllachora maydis in the United States, can complex with Monographella maydis in Mexico.
- Dark fungal fruiting spots, associated with the name, can inhibit photosynthesis.
- Pathogen is favored by cool temperatures; 60-70ºF, or 16-20ºC; a high relative humidity, 75% or more, cloudy days, or 7+ hours of dew at night.
- Research is ongoing to determine the best management practices for this disease.
Figure 11. Tar spot of corn leaf. (Photo courtesy of Martin Chilvers.)