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Southern Rust

 
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Southern Rust

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Symptoms of Southern Rust

Southern rust
Southern rust
  • Typical pustules are small, circular to oval
  • Light orange to cinnamon-red urediniospores
  • Pustules develop primarily on UPPER leaf surface (unlike common rust)
  • Pustules may also occur on leaf sheaths, stalks, ear shanks and husk leaves
  • Rust will turn white shoes/clothing orange after walking through an infected field

Southern vs. Common Rust

Southern vs. Common Rust
Southern rust
Common rust

Facts on Southern Rust

  • Fungal disease caused by Puccinia polysora pathogen
  • Does not occur as frequently as common rust, but is more destructive when it occurs
  • Favored by high humidity and temperatures in the 80s and 90s
  • More frequent in the South, but may also spread into the Midwest by windblown spores, usually in late summer
  • Spreads very rapidly when conditions favor development
    • New infections may occur every 7 days
    • Individual fields may be damaged very quickly
    • Epidemics may occur over large areas
  • May warrant a fungicide application to help minimize crop damage

Disease Cycle

Southern Rust of Corn Lifecycle

Impact on Crop

  • Disease lesions reduce functional leaf area
  • Photosynthesis is reduced and less sugars are produced
  • Plant uses stalk carbohydrates to help fill kernels
  • Stalks are weakened and stalk rot potential increases
  • Premature plant death may occur
  • Yield losses may result from poorly filled kernels and stalk lodging-induced harvest losses
    • Significant damage to upper leaves early in the life of the hybrid results in higher yield losses
    • If damage is confined to lower leaves or occurs after corn is well-dented, yield losses would be lower
    • The latest-planted corn in an area is at higher risk for yield loss

Management of Southern Rust

  • Scout corn to detect southern rust early
  • Monitor disease development, crop growth stage, and weather forecast
  • Apply a foliar fungicide if:
    • Rust is spreading rapidly or likely to spread and yield may be affected
    • Disease exceeds threshold established by your state extension plant pathologist
  • Commonly used fungicides include DuPontTM Aproach®, Prima, Fortix®, Headline®, Headline SC, Headline AMP®, Quilt Xcel® and Stratego® YLD.
  • Genetic Resistance
    • DuPont Pioneer researchers screen hybrids and parent lines for resistance and provide ratings for customers
    • Most hybrids are rated from "3" to "5" on a scale of 1 to 9 (9=resistant), indicating that genetic resistance is limited for southern rust
  • Disease is wind-borne and does not overwinter in U.S.; therefore, rotation and tillage are not effective.

Author: Steve Butzen, Agronomy Information Consultant

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