While historically more common in southern states, recent warn, humid conditions have allowed southern rust (Puccinia polysora) to move northward. So far, southern rust has been confirmed in Auglaize and Clark Counties this growing season. When scouting corn fields, be on the lookout for the following key identifying features:
- Small, orange to tan pustules (uredinia) that are densely packed and primarily found on the upper leaf surface.
- Pustules are often circular to oval and can appear in clusters.
- Unlike common rust, southern rust pustules are less likely to be found on the lower leaf surface.
Distinguishing southern rust from common rust (Puccinia sorghi) can be difficult. The table below highlights key differences between the two diseases. Samples may also be submitted to the C. Wayne Ellett Plant and Pest Diagnostic Clinic at 234 Selby Hall, 1680 Madison Ave., Wooster, OHÂ 44691.
|
Feature |
Southern Rust |
Common Rust |
|
Pustule Color |
Bright orange to tan |
Dark red to brown |
|
Leaf Surface |
Mostly upper surface |
Both upper and lower surfaces |
|
Pustule Distribution |
Dense clusters |
Scattered, less dense |
|
Disease Progression |
Rapidly under warm, humid conditions |
Slower, less aggressive |
Fungicide application should be considered if southern rust is confirmed and the field is between VT and R3 (milk stage) growth stages, when the crop is most vulnerable and a return on investment is more likely. When considering a fungicide application, be sure to also factor in the weather forecast and the hybrid level of resistance. If you suspect southern rust, please contact your local OSU Extension office.