After worrying about whether southern rust would repeat this season, many Corn Belt farmers are getting a break.
Near Walker, Iowa, Benton County farmer Trent Kuhn says his bigger concern than disease pressure this season has been the impact of weather.
“Considering all the rain we’ve had, our corn crop is looking pretty decent,” Kuhn says. “There for a while, the ground was just so saturated the soils just needed oxygen so the roots could breathe.”
The same stretch of hot, dry weather helping Kuhn’s Iowa cornfields recover is also slowing disease development.
Illinois Returns to Traditional Fungicide Strategy
That’s true in central Illinois, too. According to Farm Journal Field Agronomist Ken Ferrie, the conversations he has with farmers there have focused recently more on protecting yield potential.
With disease pressure not at emergency levels like it was in some areas in 2025, Ferrie says central Illinois growers can return to a more traditional fungicide strategy in corn. He says to focus on applications that protect the top leaves, which drive grain fill and final yield.
“We can go back to thinking about normal fungicide applications, meaning keeping the fungicide in the upper canopy, protecting what we call our high-dollar leaves above the ear,” he explains.
Keep Scouting Despite Slow Disease Development
Even though tar spot development has been slow, Ferrie warns growers not to become complacent about potential disease pressure and to keep scouting. Hot weather, he notes, does favor southern rust.
“But if it does flare, it’ll be in the upper canopy this year, not below the ear like it was last year,” Ferrie says. “So even if southern rust comes in, we’ll want to keep the fungicide high...that’s very different from how we typically manage tar spot. Usually, we want that fungicide lower in the plant canopy to address it.”
To date, the Crop Protection Network has verified southern rust in only five southwest Missouri counties. The disease has not been identified in states north or east of there.
Aphids Emerge as New Concern
Another issue farmers in central Illinois need to consider now is aphids. Ferrie says some growers are considering pre-tassel insecticide applications, particularly in susceptible hybrids.
With roughly 60 days remaining until black layer in many May-planted fields, Ferrie encourages growers to continue scouting, verify sprayers are reaching the upper canopy of the crop with fungicide and continue to monitor for southern rust development.
Timing Is Everything for Fungicide Applications
University of Missouri Extension Plant Pathologist Mandy Bish agrees that protecting the ear leaf should remain farmers’ priority, but she cautions against spraying too early.
While tar spot appeared early in Missouri this summer, Bish says disease pressure remains relatively low in the state. However, she adds that crop development has been uneven because of weather and that means a one-size-fits-all fungicide timing doesn’t work well.
“We really want to protect the ear leaf of the corn. That’s our goal with our fungicide applications,” Bish says.
Rather than reacting to the tar spot first lesions they see, she recommends farmers monitor fields until the disease reaches roughly one leaf below the ear before making an application.
“With tar spot, it really is monitoring until we get to seeing it maybe one leaf below the ear leaf. You really want to hold off to spray between tasseling and through that R3 growth stage,” she says.
Single Application Outperforms Two-Pass Programs
That recommendation comes after many growers sprayed too early last season, she says, only to have fungicide protection fade before southern rust arrived in the state.
Bish adds that research continues to support a single, well-timed fungicide application instead of a two-pass program.
“That single pass, usually a little bit later than VT — maybe nearer to the R2 stage — has given us our best performance,” she says.
Economics Drive Decision-Making on the Farm
While agronomists are focused on best timing to address disease pressure, farmers continue needing to balance biology with economics this season.
In southern Illinois farmer and broker Sherman Newland says he has already finished fungicide applications on his corn, and the crop is through pollination. He isn’t planning to spend the money on a soybean application.
“I am not planning to spray fungicide on my beans this year to help keep my costs down,” he says.
His decision is based on recent experience with not getting any ROI from treating soybeans.
“The last four years we haven’t got rain in August. I don’t care what you do, spray fungicide or not, if it doesn’t rain in August you won’t get your money back in soybeans.”
Newland’s approach underscores the reality many growers face this summer: successful disease management isn’t just about protecting the crop. It’s also about knowing when an input is likely to pay — and when it isn’t.
