As farmers continue to battle through the valley of the current farm economic cycle, they can glean valuable lessons about managing corn disease from the 2025 season. According to Farm Journal Field Agronomist Ken Ferrie, these three takeaways can apply next year:
- Diseases might be severe in one area but nonexistent a few miles away.
- Designating a pest boss and a pest management team pays big.
- Don’t walk away from your crop.
Here You Find Disease, There You Don’t
“In 2025, in many areas of the Corn Belt, farmers experienced 10-to-50-bu. yield losses from corn disease,” Ferrie says. “The big problems were tar spot and southern rust, often in the same field. When disease was discovered in time, damage was somewhat preventable.
“Here’s what made management tricky: One field would be at threshold levels for treatment, but 5 miles away fields were disease-free. It boiled down to the disease triangle, requiring a susceptible host, a pathogen and the right environment. In some areas, where the three components never came together, growers harvested some of their highest yields ever with no fungicide.”
That hit-and-miss disease situation, in a period of tight profit margins, made scouting fields and having a pest boss making timely treatment decisions even more crucial than usual.
“Where disease was present, many growers netted a 25-bu.-to-40-bu. yield response from a fungicide application,” Ferrie says. “Good managers who continued to scout often discovered diseases coming back about two weeks after treatment. Many of them sprayed a second time and netted another 20-bu. or 30-bu. response in addition to improved standability. That’s why I say never walk away from a growing crop.
“Conversely, many farmers who failed to identify disease in their fields and did not apply a fungicide found their yields shrank by 40 bu. per acre from their July estimates.”
Go Low for Rust and Tar Spot
One lesson from 2025 that applies to fungicide application confirmed Ferrie’s previous studies and observations.
“Last season, tar spot and southern rust started low on the plants and worked their way upward,” Ferrie says. “Fungicides had to penetrate deep into the canopy to control them.”
With aerial application, big droplets often fell beneath the aircraft and penetrated the canopy. But the smaller, lighter droplets floated to the outside of the pattern, remaining on the top leaves. Most years, that’s not a problem; but in 2025 it provided streaky results.
“With ground applicators, we did not see that streaking effect, because we got good penetration across the swath,” Ferrie says. “They put the fungicide down low, where it was needed.”
Lesson for 2026: To control tar spot and rust low in the canopy, when using aerial application, narrow your spray pattern.
“If you have both diseases in a field, make sure you use a fungicide that controls both,” Ferrie adds.
Your Pest Management Team
“Don’t have a pest management team yet? The offseason is the ideal time to assemble one. Here’s some advice to help:
- A team can consist of farm employees, retail employees or scouting services. Hesitant to use someone who sells products? “Lots of great pest managers work in retail,” Ferrie says. “Their success depends on you being successful also.”
- You might want to assemble several teams, for various issues such as weeds, disease and insects.
- On a smaller operation, the whole team can be just one person, but make sure someone is authorized to make timely decisions.
- The team must know how to collect accurate data, including good pictures for the pest boss. There’s no room for emotion in their reports.
- Scouting must not stop after a treatment is applied. “If a disease resurges, as many did last year, it can shorten the grain-fill period and turn a great crop into a mediocre one,” Ferrie says.
- Just like the scouts, the pest boss must base decisions on data, not emotion, coffee shop conversation or someone else’s team.
- While market prices influence the economic threshold of when to treat, don’t let them create an emotional situation where the option is to treat or not to treat.
- The pest boss must consider crop insurance coverage when making treatment decisions. Is the operator insured? The landowner? For how much? Do any other insurance factors apply?
