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.
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