Destructive fungal disease confirmed in Iowa corn crops

DES MOINES, Iowa — A destructive fungal disease has been found in corn crops in four different Iowa counties.

Iowa State University Extension and Outreach said that on July 21, reports of southern rust were confirmed in Benton, Mahaska, Muscatine, and Louisa counties. In all the counties, the disease was found on just a few plants at low severity.

Last year, southern rust resulted in estimated yield losses of 7.5% in Iowa. Many experts said it was one of the worst outbreaks of the disease seen in the state in several decades.

According to Crop Protection Network, southern rust is caused by the fungus Puccinia polysora and thrives in high heat and humidity. If left untreated, the disease can kill plants prematurely, significantly impacting yields.

ISU Extension and Outreach said the pathogen blows up to Iowa from southern states, but for it to become established, there needs to be enough leaf moisture. So far this year, experts said dew points have been lower than in 2025, and leaves aren’t staying wet for long periods, meaning there could be fewer cases in 2026 if those conditions continue.

If farmers are concerned their “race-horse” type hybrids or hybrid crops that were impacted last year could develop the disease this year, experts advise applying a fungicide.

Other diseases affecting Iowa corn crops this summer include gray leaf spot, tar spot, northern corn leaf blight, Cuvularia leaf spot, bacterial leaf streak, and Goss’s wilt. Unlike other diseases, experts say southern rust can’t survive Iowa winters.

Iowa news

For the latest news, weather, sports, and streaming video, head to WHBF - OurQuadCities.com.