Disease Facts

• Fungal disease caused by Puccinia sorghi pathogen
• Favored by moist, cool conditions (temps in the 60s and 70s)
  • Hot, dry conditions typically slow or stop development
• Spreads by windblown spores from southern corn growing areas
• Typically progresses as corn matures in late summer if conditions are persistently wet and cool
• More often a problem in seed production and sweet corn fields than in hybrid fields
• Less likely than southern rust to cause significant yield loss to hybrid corn, so important to distinguish common and southern rust
• Hybrids differ in resistance

Impact on Crop

• Disease lesions reduce functional leaf area and photosynthesis
• Less sugars are produced, so plant uses stalk carbohydrates to help fill kernels
• Stalks are weakened and stalk rot potential increases
• Yield losses may result from poorly filled kernels and 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 are lower
• Latest-planted corn in an area is at higher risk for yield loss

Disease Cycle

Symptoms

• Lesions begin as flecks on leaves that develop into small tan spots
• Spots turn into elongated brick-red to cinnamon-brown pustules with jagged appearance
• Found on both upper AND lower leaf surfaces (unlike southern rust)
• Pustules turn dark brown to black late in the season
• Occurs on leaf only, NOT on sheaths, stalks, ear shanks and husk leaves

Common / Southern Rust:	Common Rust	Southern Rust
Ideal Environment	Cool to warm and moist - 60-77 F	Warm to hot and moist - 77+ F
Appearance of Pustules	Large, circular to elongated	Small circular, pinhead appearance
Pustule (spore) Color	Brown to cinnamon brown	Reddish orange
Location of Pustules	Upper and lower leaf surfaces. Infects leaves only.	Upper leaf surface. May also infect husks.

Common vs. Southern Rust

Management

• Genetic Resistance
  • Pioneer researchers screen hybrids and parent lines for resistance and provide ratings for customers
  • Most hybrids are rated from “3” to “6” on a scale of 1 to 9 (9=resistant), indicating there are clear differences between hybrids, but complete resistance is not available
  • Growers should choose hybrids with a “5” or “6” rating in areas that frequently experience common rust
• Scout corn to detect common 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 Aproach^®, Headline^®, Headline SC, Headline AMP^®, PropiMax^® EC, Quadris^®, Quilt^®, Quilt Xcel^®, Stratego^®, Stratego^® YLD and Tilt^®
• Disease is wind-borne and does not overwinter in U.S.; therefore, rotation and tillage are not effective.