Addressing corn disease pressure in-season is rarely a matter of “if” and more likely “when.” Coming off heavy disease pressure from 2025, now is the time to put your plan together for how you’ll address challenges like northern corn leaf blight, tar spot and others this season. Plan your moves with these five recommendations, so you are ready to take action when disease pressure hits:
1. Use A Proactive Scouting Plan.
Success begins with staying ahead of disease, according to high-yield corn grower David Hula. “You have to stay proactive with your scouting and willing to go with earlier fungicide or even multiple applications, depending on what shows up,” he says.
While planning, consider the following:
1. Know your potential threats. Depending on the disease, some pathogens survive the winter on previously infected crop residue (e.g., northern corn leaf blight, tar spot). Other diseases move into northern growing areas on winds from southern locations (e.g., southern corn rust). For a suitable environment, many foliar diseases need warm, humid, and wet conditions to propagate.
2. Have your budget in place. Be ready for at least one in-season fungicide application. Use tools like the Newly Designed Fungicide ROI Calculators to guide your investment in products and applications. By inputting costs, market prices, and disease severity, these calculators provide research-based estimates of net benefits and breakeven probabilities, helping you make a more informed decision.
3. Delegate the scouting job, if necessary. If you cannot scout personally, assign the task to a family member, employee, or employ a professional service.
“Lots of great pest managers work in retail,” says Ken Ferrie, Farm Journal Field Agronomist. “Their success depends on you being successful also.”
2. Leverage Friends, Neighbors And Industry Expertise.
Don’t monitor disease pressure in a vacuum. Stay informed about what’s moving into your neighbors’ fields; track regional pressure by tapping into local agronomists and organizations like the Crop Protection Network.
Randy Dowdy, Hula’s partner in Total Acre, notes that in the Southeast, farmers are constantly receiving feedback from Extension and industry experts regarding southern rust.
Similarly, Elliott Henderson, who farms in Buchanan County, Iowa, has a group of farmers there that he connects with on a regular basis during the growing season.
“It’s a network of dozens of us farmers that call each other, bounce ideas off each other,” he says. “The things we’re talking about are often time-sensitive. It can be a daily thing.”
3. Select The Right Chemistry.
Applying the wrong product in the heat of battle with disease pressure is a common mistake. For aggressive diseases like tar spot or southern rust, Farm Journal Field Agronomist Missy Bauer recommends using “Cadillac” type chemistries — newer technologies that feature multiple modes of action.
To ensure you are using the right tool:
- Consult Your Experts. Use the Crop Protection Network’s Fungicide Efficacy tables to see which products perform best against specific diseases.
- Match Product to Problem. Ensure the product is labeled for your specific issue and is capable of handling high-pressure scenarios.
4. Optimize Applications for Maximum ROI.
If you need to apply a fungicide, make sure it delivers the results you need.
“It’s all about coverage,” Dowdy says. “Drone applications can be fine, but no matter what you do, if a guy is spraying two to three gallons, and you compare it to a ground rig spraying 15 to 25 gallons, I mean, there’s just no comparison in that coverage.”
Another aspect of coverage, Hula adds, is making sure the fungicide gets into the plant canopy far enough to have the desired effect. That becomes even more critical as the season advances.
“Fungicides have a tendency to work from the leaf they’ve come in contact with and move up,” Hula says. “So, if you’re trying to protect at least that ear leaf – and I like to protect the leaf opposite and below the ear – you’ve got to get penetration with that product.”
Hula says growers might have to spend a couple extra dollars to get sufficient volume for the product to get down below the canopy, if using a drone for application.
“If that’s what needs to be done, let’s do it,” he encourages. “If I’m spending $30 or more an acre, then I want to at least have the success that I’m paying for.”
5. Commit To Protecting Corn Through The Entire Season.
Modern corn genetics have significant “back-end” potential, enabling them to add yield through kernel fill late into the season. Hula and Dowdy advise against walking away from the crop early. They say evaluating fungicide applications during later reproductive stages can often yield a high return on investment.
D hybrids are of particular concern late-season, Ferrie says. These are hybrids that have kernel depth changes, positive or negative, based on populations and environmental conditions during the last 30 days of grain fill.
Missy Bauer, Farm Journal Field Agronomist in Michigan, zeros in on corn growth stage to guide uber-late-season fungicide applications.
“If I had a field that has no fungicide at all on it, and I had fairly heavy disease pressure from something like southern rust or tar spot, and I’m at early R4, I would still apply the fungicide,” she recommends.
