Southern Rust Invades Iowa Corn Crop
Every growing season is different, and 2025 was no different with the rare occurrence of southern rust affecting Iowa’s corn crop. The impact of southern rust on corn in 2025 varied based on a number of factors, including location in the state, local weather conditions, relative maturity, susceptibility, or tolerance of corn hybrids and most notably, treatment with fungicides. Depending on the time, growth stage and severity of infection, yield reductions of untreated corn due to southern rust can be significant.
What does Southern Rust Look Like?
Southern rust is an obligate parasite, meaning that it inhabits and reproduces on living plant tissue. During Iowa winters, southern rust infects living plant tissues in Central America. Then as the growing season begins in Iowa, southern rust spores are carried to the U.S. on southerly winds. The unusually warm, wet summer conditions in 2025 in Iowa were conducive for southern rust to proliferate in corn fields.
Southern rust on Iowa corn plants appears as circular, light brown to orange pustules, primarily on the upper leaves, which may be surrounded by a light green or yellow halo (Figure 1).
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