Flying in on tropical storms, southern rust aims to steal yield from corn farmers across the south and Midwest. The disease can cause significant yield losses if it hits the crop too early.
Southern rust is aggressive and can cause standability issues and significant yield loss, according to Nebraska Extension. This makes scouting and readiness to apply treatment more important. Catch it before it becomes severe, which can take as few as two weeks of favorable conditions.
“It seems like southern rust has been more prevalent and occurring in the Midwest earlier than usual,” says Mike Meyer, Corteva Agriscience disease management technical expert for North America. “The past few years it has been in Indiana, Missouri, southern Illinois and Kentucky in early July.”
This past week, Nebraska farmers and Extension agents recently discovered the disease in three counties: Fillmore, Saunders and Thayer. Before that, southern rust was positively identified in Arkansas, Georgia, Illinois, Kansas, Mississippi, Missouri and Oklahoma, and it could be in other states but is not yet confirmed.
Identifying Southern Rust
While most farmers are familiar with common rust, southern rust might be a different story and differentiating between the two diseases is important for management.
“We see common rust annually and early in the growing season,” Meyer says. “There are several resistance genes deployed for common rust, which is characterized by cinnamon colored pustules on the upper and bottom leaf surface. With southern rust we don’t have quite the robust levels of resistance, and it is identified by its bright orange, densely clustered [pustules] on the upper leaf surface.”
Warm temperatures, especially the 70s to lower 80s, in day or nighttime favor southern rust development. It also needs high humidity, rainfall or irrigation to spread. Because it doesn’t overwinter on residue, it spreads with summer storms, moving from the south, north.
The disease is at “low incidence” in Nebraska—for now. Lower temperature forecasts over the next week could help keep the pathogen at bay—which is critical.
“There is still time to apply fungicide,” Meyer advises. “There still can be a positive yield benefit and return on investment at later growth stages, especially if southern rust pressure is high.”