2025 October Stewardship Advocate

2025 October Stewardship Advocate

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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).

Figure 1. Southern rust on a corn leaf.

Management of Southern Rust

Fungicide applications may be beneficial when applied before or during the R3 (milk) growth stage, especially with severe disease pressure. Table 1 shows the benefits of applying fungicides based on the growth stage of the crop. Figure 2 shows that fungicide applications at R3 were effective in significantly decreasing the severity of southern rust in a research trial in central Iowa in 2024.

Crop stage when southern rust is first detected	Benefits from spraying	Treatment
Vegetative	Not likely to find southern rust at this stage unless corn is planted very late for the region	Scout fields for disease
VT (tasseling)	Yes	May need a second spray
R1 (silking)	Yes	May need a second spray
R2 (blister)	Yes	Less likely to need a second spray
R3 (milk)	Yes	No second spray needed
R4 (dough)	Maybe, with severe disease pressure	No second spray needed
R5 (dent)	Unlikely	No second spray needed
R6 (black layer)	No

Table 1. Benefits (by growth stage) from applying fungicides to protect against southern rust.

Source: An Overview of Southern Rust; Crop Protection Network (8/1/2019).

Will Southern Rust be a Problem in the 2026 Corn Crop?

Farmers have been asking if southern rust is something they need to plan for every year, and fortunately the answer is no because the fungus does not overwinter in Iowa, meaning that each year starts over without rust spores lying dormant in Iowa fields. This is unlike other corn diseases like tar spot, gray leaf spot, northern corn leaf blight and anthracnose leaf blight that overwinter in corn residue. There are differences in susceptibility of southern rust, so talk to your seed representative about which hybrids exhibit tolerance to diseases, not only southern rust, but also diseases that overwinter in Iowa.

Source: Alison Robertson and Rebecca Vittetoe: Integrated Crop Management News, and Iowa State University Extension and Outreach. August 12, 2025.

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Will Cannon has been producing corn, soybeans, forages and cereal rye for over 20 years in Jasper County. His passion for conservation is demonstrated throughout his operation as he practices no-till, strip till and cover crops. He also has worked at Ag Leader Technology in tech support and product development for ten years.

Will currently serves as an Iowa Corn Growers Association Director representing District 5 and as Chair for the Research & Business Development Committee. He is a graduate from the Iowa Corn I-LEAD Class 4 and has hosted the World Pork Expo International Dinner for multiple years. He is also active with the Iowa Soybean Association and previously sat on the Jasper County Farm Bureau Board. Outside of agriculture he is a member of City Church of Ames in the Des Moines area.

Soil health and sustainability both environmentally and economically are important to Will. That is why he hosts many conservation field days on his farm as well as stays informed on both private and public programs trying to incentivize farmers in his area to use conservation programs. While farmer education is a huge passion of his, Will also finds value in educating consumers where their food comes from. He is proud of his "open farm gate policy" allowing him to host thousands of interested guests on his farm. Because his farm is located only 20 minutes from Des Moines, he takes this responsibility seriously to be an ambassador to farming in his own way. Will is truly ready to bring the knowledge he has gained combined with his passion for farming to make a difference in this industry.

Will and his wife Cassie raise two children, Oliver and Case, whom he hopes to have the opportunity to live the great farm lifestyle.

Upcoming Events:

November 4: Cover Crop and Water Quality Field Day; Drost Farm, 2215 212th St. Oskaloosa, IA. RSVP: 515-294-5429 or [email protected].

November 10: 2025 Farming for the Future Conference

November 12, November 24, and December 10: Iowa Nutrient Research Center webinar series; Fall 2025 Water Quality Seminar: Regional Collaborative Research | Iowa Nutrient Research Center

Throughout November: ISU Extension Calendar of Events.

Throughout November: Iowa Learning Farm webinars; Events - Iowa Learning Farms.

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