Southern Leaf Blight

Symptoms of Southern Leaf Blight

Corn leaf with Southern Leaf Blight
Southern leaf blight lesions on corn
  • 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

Southern leaf blight 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
Loss of corn leaf area from Southern leaf blight results in reduced photosynthesis

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
southern leaf blight susceptible and resistant corn hybrids in field

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