Common Rust of Corn
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Key Points
- Common rust is a foliar disease of corn favored by moist and cool conditions.
- The fungal pathogen does not overwinter in the Corn Belt; windblown spores bring it north from the Southern U.S.
- Common rust is less likely to cause significant yield loss than southern rust.
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Disease Facts
- Fungal disease caused by Puccinia sorghi pathogen.
- Favored by moist, cool conditions (60-77 °F, 16-25 °C).
- 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 proper identification is important.
- Hybrids differ in genetic resistance.
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Impact on Crop
- Disease lesions reduce functional leaf area and photosynthesis.
- Less sugar is 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.
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 rust - early lesions
More advanced disease development
Common vs. Southern Rust
Common rust
Southern rust
Management
- Genetic Resistance
- Corteva Agriscience 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.
- Disease is wind-borne and does not overwinter in crop residue; therefore, rotation and tillage are not effective for reducing disease severity.
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