An extension agronomist says southern rust was an unexpected disease pressure for growers in 2025.
Meaghan Anderson with Iowa State University says southern rust impacted a large portion of the Midwestern corn crop.
“I think we were all caught completely off guard by how big of a problem it ended up being,” she said. “We don’t typically get the weather conditions that allow southern rust to spread.”
She tells Brownfield there were some lessons learned that should help growers with their management plans during the 2026 growing season.
“Certainly, if we see southern rust in the weather forecast next summer – and it looks again like it’s going to be hot and excessively wet – we don’t want to sleep on some of the fungicide tools we have available to us. We want to be really timely about those applications.”
According to ISU Extension, southern rust thrives in warm (77-82°F) and wet conditions. At least six hours of leaf wetness is required for infection to occur. Anderson says under these conditions, the time between a spore infecting a leaf to the production of a pustule filled with new spores is 7 to 10 days.
