Iowa Southern Rust Infestations May Be Fewer This Year

Southern rust has been confirmed in four Iowa counties this year, but there's reason to believe that fewer infestations may occur due to lower prevalence of the disease in the southern US. The Crop Protection Network's crop outlook map shows that southern rust was detected on July 21 in Benton, Mahaska, Muscatine, and Louisa counties, with low severity levels.

Historically, Iowa has seen significant yield losses from southern rust, with an estimated 4% loss in 2024 and 7.5% in 2025. However, the pathogen's spread to Iowa is typically facilitated by wind-borne inoculum from the south, which may be reduced this year.

The development of southern rust requires prolonged leaf moisture, and data suggests that dew points have been lower in 2026 compared to last year. This could lead to fewer opportunities for the disease to take hold.

Fungicides can still be used to manage southern rust, but application decisions depend on hybrid susceptibility and past infestation levels. The Crop Protection Network provides a table on fungicide efficacy for corn diseases, which can help guide management decisions.