Southern Leaf Blight
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Symptoms of Southern Leaf Blight
- Lesions are generally:
- from 1/8 to 1/4 inch wide by 1/8 to 1 inch long
- tan in color
- rectangular to oblong in shape
- usually found on leaves
- variable, making identification more difficult than for other diseases
- Lesion type may depend on hybrid genetics
- Lesions usually develop first on lower leaves and work up the plant
Southern Leaf Blight (SLB) may resemble gray leaf spot, but these characteristics differentiate lesions:
Facts on Southern Leaf Blight
- Fungal disease caused by Cochliobolus heterostrophu (also known as Bipolaris maydis)
- Thrives in warm-temperate or subtropical corn-growing environments, including the Southeastern U.S.
- Overwinters primarily in surface debris from the previous corn crop
- Spores are windblown or splashed by water to new crop leaves where they germinate and infect the plant
- Development is favored by warm (70 to 85 F), moist weather and free water on the leaf
- Under ideal conditions, the fungus is able to complete its life cycle in only 60 to 72 hours
Disease Cycle
Impact on Crop
- Can cause significant loss of corn leaf area when conditions favor the disease
- Loss of leaf area results in reduced photosynthesis, lowering yield potential and increasing risk of stalk rots
- The earlier the disease begins in the growing season, the greater the potential for yield reduction
- Ear and cob rots may also occur due to this fungus
Management of Southern Leaf Blight
- Genetic resistance
- Most effective form of management
- Pioneer breeders have selected for resistant parent lines and hybrids for over 30 years
- Hybrid ratings range from "3" to "7" on Pioneer's 1 to 9 scale (9 = resistant)
- Growers in high-risk areas with a history of SLB occurrence in their fields should choose hybrids with a "6" or "7" rating for SLB resistance
- Crop rotation to reduce corn residue level and help break disease cycle
- Tillage to encourage breakdown of crop residue
- Fungicide application
Fungicide Application
- Scout corn to detect SLB early
- Monitor disease development, crop growth stage, and weather forecast
- Apply a foliar fungicide if:
- Disease is spreading rapidly or likely to spread and yield may be affected
- Disease level exceeds threshold established by your state extension plant pathologist
- Common fungicides include Headline, Quadris, Quilt, PropiMax EC, Stratego and Tilt
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