Applying a foliar fungicide in corn is a go-to practice every year for Chad Eitmann, who grows corn and soybeans in southwest Iowa, near Treynor.
“It wasn’t that way 15 years or so ago, but it is now,” says Eitmann, who says he takes a proactive approach to foliar fungicide use, applying product before he can see any disease show up in the crop.
“The scout and spray method just doesn’t seem to work as well,” he says. “By the time you see any disease, there’s so much that already happened in the plant that you’re over the curve.”
Eitmann says he is particularly concerned about tar spot this year, as the disease is moving into his area. Here’s a look at where tar spot and southern rust were confirmed in the U.S. during the 2024 season. The northern reach of the latter was particularly surprising to the plant science community last year.
Eitmann says he saw corn crops in his area last year that weren’t treated soon enough for tar spot, and the yield outcomes were affected significantly.
“Some guys [held off] using a fungicide because of the commodity prices and emotion. They were like, ‘No, we’re not going to spend any more money.’ It looked to me like that decision cost them 40 to 50 bushels an acre – maybe more,” Eitmann recalls.
Address Environmental Stressors
Kim Tutor, a technical marketing manager with BASF, says using a preventive application of a premium quality fungicide helps with environmental stress mitigation and optimizes growth efficiency.
A proactive application keeps stomatal conductance working efficiently in corn plants. Essentially, stomates function like small vents on the leaf surface of corn plants, helping with respiration and photosynthesis.
Along with stress reduction, a foliar fungicide application can address diseases in the latent stage of development in the plant — that period between initial infection and reproduction.
Essentially, you can’t see the disease yet with the naked eye, but it is present, invading crop tissue and producing toxins that wreak havoc inside the plant, decreasing productivity and, ultimately, yield outcomes.
Every Disease Is Different
Tutor says a latent period exists for all diseases in corn and soybean crops. Some of the latent periods for economically concerning diseases include:
• Frogeye leaf spot – 7 to 10 days
• Target spot – 8 days
• Southern rust – 7 to 10 days
• Tar spot – 14 to 20 days
The increased risk from tar spot has Eitmann trying to decide how to time his foliar applications this season to get the most residual control possible.
University of Nebraska Extension says most FRAC Group 11 QoI (formerly called strobilurins) and FRAC Group 7 SDHI fungicides are expected to provide between 21 and 28 days of protection of leaves from infection by some fungi.
“Group 3 triazoles can provide some systemic or locally systemic curative activity, but only for infections that have just occurred in recent hours or couple of days,” Extension reports. “Thus, fungicides applied a day or more after infection will not stop all lesion development and some disease development may still be observed.”
Tutor encourages growers to think through their fungicide application timing in order to maximize results for as long as possible. Here is the strategy she recommends, which includes three options, specific to BASF products:
Option 1
BASF commonly recommends farmers use a planned, preventive application of a fungicide with multiple active ingredients and a long residual – at least once per season – to protect corn and soybeans from disease before its presence can be seen on the plants.
“Generally speaking, if I take all the data I have access to and summarize it, the sweet spot for fungicide applications in corn is going to be right around VT R1,” Tutor says. “That’s going to give you the best bang for your buck in terms of a return on your investment with one application.” Tutor recommends a 7 oz. per acre application rate of Veltyma.
Option 2
For growers who have the tar spot inoculum in fields or know it’s in nearby fields, Tutor advises going with a higher product rate rather than assuming two fungicide applications are needed.
“We’re going to recommend you optimize that rate and you take Veltyma up to 10 oz. per acre, again at the VT R1 timing. “Those additional 3 oz. are going to provide a good bit more residual control, and that has the potential to carry you through the rest of the season,” she adds.
Option 3
In those areas where farmers expect heavy disease pressure this season, Tutor does advise going with a two-pass program.
“With that first application, we’re going to recommend you put your best foot forward and go out with the 7 oz. rate of Veltyma at that tassel timing. Then, follow it up a couple of weeks later at the R3 timing, again with a 7 oz. rate of Veltyma or another good product like Headline Amp at 10 or 14.4 oz. per acre.”
Evaluate Results To Determine ROI
Mike Pellett, a farmer near Atlantic, Iowa, says he routinely makes at least one foliar fungicide application in corn, as the payoff has been consistent across acres for multiple years.
“We’re big data people, and the proof is in the results that come off the field,” Pellet says. “We’ve got years and years of data that show a benefit, some years more than others, but as a whole, we definitely know it’s a better decision to spray than to not spray, and sometimes by a big amount.”
Pellett, Eitmann and Tutor discussed fungicide use as part of the BASF media program at the 2025 Commodity Classic.
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