Field Insights

Modern Fungicides are Doing More for Your Crops

Protecting yield potential and the disease triangle should factor into your foliar corn fungicide decisions.

Each year, when budgeting for a foliar fungicide application, corn producers weigh fighting disease development with expected returns on investment. But the decision isn’t as simple as it seems, and industry leaders say growers should consider several factors including plant health, hybrid disease susceptibility, weather forecasts, and cropping and disease history.

In addition, AgriEdge® growers may benefit from whole-farm management products available through the Cropwise™ platform for their decision-making around fungicides.

The Cropwise platform tracks input costs, provides in-season satellite crop imagery and helps calculate potential ROI, says Ryan Ploeger, Syngenta AgriEdge specialist and certified crop advisor (CCA) in north-central Iowa. “We’re really striving to put a dollar value on the decisions growers make,” he says.

Beyond Disease Control

Ploeger says most of his growers apply a foliar fungicide at the VT-R1 growth stage regardless of disease pressure because they’ve seen returns that go beyond disease control.

“What’s driving it is the newer fungicides are more robust and more consistent,” he says. “In a drought year with no disease present, we still see very consistent results because the fungicide is going to help mitigate stress and help the plant use water more efficiently. It’s going to keep the plant cleaner and utilize water more efficiently.”

Mark Baer is a CCA and sales manager for Sun Ag Inc., which has six locations in central Illinois. He says growers in his area typically budget for a foliar fungicide every year. “It’s something they do to protect their investment,” Baer says.

In grower trials, Baer says he’s seen a 5-to 45-bushel-per-acre yield improvement with Miravis® Neo fungicide applied at VT-R1. The wide variation is due to hybrid disease susceptibility, disease pressure “and everything to do with the environment,” he says.

A Bird’s-Eye View

Justin Bellcock, who farms corn and soybeans with his father and brother in northwestern Iowa, says they also typically apply a foliar corn fungicide. He tracks his inputs using Cropwise Financials, an AgriEdge farm management software enabling data-driven decisions.

“We use it in planning so we can figure out how much of everything we need as far as chemicals and seed and other things,” Bellcock says.


In a drought year with no disease present, we still see very consistent results because the fungicide is going to help mitigate stress and help the plant use water more efficiently.

Ryan Ploeger Syngenta AgriEdge specialist and certified crop advisor (CCA)

A variety of digital tools will be available to growers enrolled in the AgriEdge program with the launch of the Cropwise ecosystem. This season, Bellcock monitored crop progress and plant health three or four times by viewing the platform’s satellite crop imagery. He plans to view it even more frequently in 2023 with the Cropwise Imagery platform. “I’ll look at it more in the future,” Bellcock says of the imagery. “I know the new platform will be a lot better.”

Ploeger agrees, adding it’s another tool AgriEdge growers can use to track fungicide efficacy. “With Cropwise Imagery, it’s showing that the plants are healthier,” he says.

Protect the Plant’s Powerhouse

In Iowa, the foliar corn diseases of concern include gray leaf spot, tar spot and northern corn leaf blight. Alison Robertson, Ph.D., Iowa State University professor and Extension field crop pathologist, says growers need to keep the disease triangle in mind before deciding to apply a fungicide. “To have disease, you need to have the pathogen, a host and the right environment,” she says. “If one is missing, no disease will occur.”

To calculate the risk of disease development, growers should consider the environment, Roberston explains. Fungal diseases need moisture as well as mild temperatures to reproduce.

Leaf moisture, particularly with tar spot, is also a driver for disease development that may come from overhead irrigation, a high dew point or precipitation. “When it’s very dry, we’re not going to see as many of these diseases,” Robertson says. “If the leaves are wet at 8, 9, 10 o’clock in the morning, that’s when you’re going to be at risk for the disease.”

Just before tasseling, Robertson recommends growers and consultants scout the lower canopy for disease. “When you think about diseases, they increase exponentially,” she says. “One spot will grow into 10 spots, then 100 spots, then 1,000 spots. Just the presence of a few spots in the field and knowing you have the right conditions for disease puts you at the start of that exponential curve.”

The goal is to protect the ear leaf and those above it since those produce 75% to 90% of the carbohydrates for grain fill. A few spots on the ear leaf likely won’t affect yield, but she says they’re a good indication of conditions conducive for disease development.

“In addition to disease control from fungal pathogens,” says Tyler Harp, Ph.D., technical development lead for Syngenta, “plant health fungicides such as Miravis Neo and Trivapro can help protect corn plants from abiotic stresses like heat and drought.”

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Staying Vigilant on Corn Diseases

Fungicides are a critical tool in fighting tar spot and southern rust, each of which can devastate yields. Tar spot, a relatively new disease in Midwestern corn caused by the fungus Phyllachora maydis, typically shows up later in the season.

Because of the potentially devastating effects of this disease, Baer says, “we’re really vigilant watching for that until the corn gets to the maturity level where tar spot won’t be a problem.”

Tar spot’s actual impacts depend on when the crop was planted, hybrid susceptibility, hybrid relative maturity, when tar spot arrives in an area, and the environment. “Last year it came in early and was a real problem,” Baer says. “In 2020, it came in really late, so it had no impact on yield, and this year we hadn’t really seen it.”

And in Arkansas, southern rust — caused by the fungus Puccinia polysora — is the main foliar corn disease, says Travis Faske, Ph.D., University of Arkansas System Division of Agriculture Extension plant pathologist. Fortunately, he says, tar spot has not been confirmed in the state.

Unlike some corn diseases, southern rust doesn’t overwinter in plant residue. Wind currents carry rust spores from tropical areas each year and initially infect corn in the southern United States, Faske says. The spores move north during the cropping season, with environmental conditions playing a large role in potential disease development.

To help growers and consultants stay abreast of spore movement and plan for fungicide applications, the Corn IPM PIPE website,, maps southern rust positive reports.

“If I see Trey Price and Tom Allen in south Louisiana and Mississippi have found it, it will be two weeks before I’ll find it in south Arkansas, then another two weeks before it crosses I-40,” Faske says. “Then it will be another two weeks before it gets to the north parts of the state. This provides a general guide for scouting and so you don’t spray too early.”

Faske emphasizes that the IPM PIPE model is just a tool and doesn’t replace boots on the ground. When southern rust is an immediate threat, he says the best time to make a fungicide application for grain yield protection is VT-R3.

  • For disease development, you must have a pathogen, a host and a conducive environment.
  • Corn fungicides work best against most foliar diseases applied at late vegetative through VT-R1.
  • Scouting and preventive fungicide applications help to ensure maximum value and return on investment (ROI) potential.