Southern Rust
- 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.
![Photo - Corn leaf infected with southern rust. Photo - Corn leaf infected with southern rust.](/content/dam/dpagco/pioneer/na/us/en/agronomy/crop_focus/corn/diseases/leaf-infected-with-southern-rust.jpg)
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.
![Photo - Northern corn leaf blight lesions on corn leaf.. Photo - Northern corn leaf blight lesions on corn leaf.](/content/dam/dpagco/pioneer/na/us/en/agronomy/crop_focus/corn/diseases/nclb-lesions-on-corn-leaf.jpg)
Figure 6. NCLB lesions on corn leaf.
![Photo - Close up of Northern corn leaf blight lesion. Photo - Close up of Northern corn leaf blight lesion.](/content/dam/dpagco/pioneer/na/us/en/agronomy/crop_focus/corn/diseases/nclb-lesion-closeup.jpg)
Figure 7. Close up of NCLB lesion.
Stalk Rots
- Depletion of nitrogen due to leaching makes stalks more prone to rotting.
- Specific rots are weather dependent.
![Photo - Corn stalk depicting both anthracnose and Gibberella stalk rot. Photo - Corn stalk depicting both anthracnose and Gibberella stalk rot.](/content/dam/dpagco/pioneer/na/us/en/agronomy/crop_focus/corn/diseases/anthracnose-and-gibberella-stalk-rot.jpg)
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.
![Photo - Gray leaf spot lesions. Photo - Gray leaf spot lesions.](/content/dam/dpagco/pioneer/na/us/en/agronomy/crop_focus/corn/diseases/gls-lesions-leaf.jpg)
Figure 9. GLS lesions (rectangular shape).
![Photo - Southern corn leaf blight lesions. Photo - Southern corn leaf blight lesions.](/content/dam/dpagco/pioneer/na/us/en/agronomy/crop_focus/corn/diseases/sclb-lesions-leaf.jpg)
Figure 10. SCLB lesions (irregular shape).
Tar Spot
- 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.
![Photo - Tar spot of corn leaf. Photo - Tar spot of corn leaf.](/content/dam/dpagco/pioneer/na/us/en/agronomy/crop_focus/corn/diseases/tar-spot-corn-leaf.jpg)
Figure 11. Tar spot of corn leaf. (Photo courtesy of Martin Chilvers.)