Crop Advice Shared for 2026 Season
Published: Friday, February 6, 2026
Area farmers heard the latest in crop research during a Purdue Crop Management Meeting last Wednesday in Middlebury.
Experts from the Purdue University campus in West Lafayette covered corn diseases, Bt corn efficacy, soybean pests and other topics.
For corn, Darcy Talenko, Extension plant pathologist, discussed foliar diseases. One of those, tar spot, occurs when weather conditions favor mild temperatures (64 to 73 degrees F) for 30 days and relative humidity under 90% over a two- to three-week span.
Also, tar spot usually revisits a field that has had a problem in the past.
Long periods of high heat and humidity can hinder disease progression.
Tar spot is treated with a fungicide application. Some products have a shorter window of activity than others, so it is important to compare.
Talenko said fungicides offer two benefits: disease control and yield protection.
Without any chemical treatment, tar spot and other foliar diseases can prevent corn plants from converting sunlight into photosynthesis. However, with corn prices hovering around $4, farmers should consider the return on investment (ROI) before deciding if the treatment will pay off.
Figuring out the ROI is easier with the help of the Crop Protection Network and its Fungicide ROI Calculator (https://crop protectionnetwork.org/fun gicide-roi-calculator). The tool lists the leading fungicide products, their respective cost and the Expected Net Benefit per Acre. Growers can customize the tool to reflect a field with high or low disease severity as well as the current corn price.
Talenko said fungicides provide 3% yield protection on fields with high tar spot infections. At a cost of $30 per acre and corn selling for $4 per bushel, farmers need to get at least 7.5 bushels per acre in extra yield.
Most of the high-end products are too expensive from an ROI perspective, Talenko said, but farmers using generic products could see some benefit.
According to the Purdue plant pathologist, growers see average net returns between $29 and $48 per acre from foliar fungicides under high tar spot pressure compared to no fungicide treatment. Under low disease pressure, the benefits are much less—minus $26 to $1.60 per acre.
With fungicides, coverage matters. It's impossible for the applicator—drone, plane or ground rig—to hit every leaf on a corn plant. Many times, the upper leaves are covered, but the chemistry doesn't reach the lower leaves. The spores will find susceptible leaves.
"It's all a matter of how well that coverage is penetrating the canopy," she said. "Tar spot and Southern Rust are the two diseases that aren't going to be as flexible as the other diseases on their management, because they (spores) are going to find those areas that aren't protected."
Talenko said many producers, after applying fungicide, are disappointed to learn that they still have tar spot in their fields. She said that's normal.
"We're always going to have some tar spot in our fields, because there is no way we apply fungicide that's going to cover all those leaves," she said. "The goal is protecting that ear leaf and above that are feeding that ear's yield potential."
Timing of fungicide application is crucial, Talenko said. If growers spray too early, they risk losing efficacy late in the growing season. However, if they spray too late, they may lose yield.
In a three-year study involving several key corn states, Talenko shared that the best time to apply fungicide is at the R2 stage, when the corn kernels resemble blisters on the ear.
"My window for disease control is VT (tassel) to R3 (milk)," Talenko said. "If we're just targeting tar spot, R2 continues to be the best timing that we're seeing across the board."
In cases of severe tar spot, growers can spray as late as the dough stage. She said this offers yield protection but no disease control. Once the crop has reached the dent stage, there is no benefit to spraying.
Some growers spray twice. Talenko said the best times are at the R2 and R4 stages. She said this works well for disease control, but with low corn prices, two passes may not pay.
"I would rather stick with finding a well-timed single application," she said.
There are resistant hybrids and susceptible hybrids. As expected, the resistant hybrids will perform better in a year with a severe outbreak. But in a dry year with no disease, the susceptible hybrids usually outperform the resistant hybrids.
Talenko's recommendation is to find a really good fungicide product and use the generic form, which is less expensive. For the three-year trial, Headline AMP was used.
"That's what I would pick for my generic if I'm targeting tar spot," she said.
Talenko emphasized the importance of stewardship. Fungicides shouldn't be overused.
"I really want us to make sure we're applying fungicides when we're controlling disease to protect yield," she said. "If we can show we're doing that, then maybe we won't lose some of these products down the line."
In another discussion, Christian Krupke, a Purdue University entomologist, shared the latest research regarding insect pests in early planted soybeans, and the efficacy of Bt corn hybrids.
A generation ago, farmers planted corn first and soybeans second. However, that rule of thumb has switched, and farmers are now planting soybeans as soon as they can get into the fields.
"People are taking advantage of milder winters, earlier springs, and planting soybeans earlier," Krupke said. "That puts soybeans in line for certain pests: wire worms, bean leaf beetles and so on."
There are certain risks associated with planting early soybeans. The biggest risk is the weather: late frosts, cold soils and even snow. While soybeans are resilient, germination can suffer.
In a study funded by the U.S. Soybean Board, researchers, including both Krupke and Talenko, looked at the efficacy of neonicotinoid seed treatments (NST) on early planted soybeans. The trials were conducted at three Indiana locations, including the Pinney Purdue Agricultural Center in Wanatah.
Soybeans were planted on four different dates in April.
Researchers dissected the plants to learn how much of the insecticide remained in them at various points throughout the growing season.
"The reason you can treat a soybean or corn seed with a neonicotinoid is because they are water soluble," he said. "They dissolve well in water. If you try to coat a seed with diazinon or cypermethrin, you are basically waterproofing that seed. It would not germinate. Why? Because those are not water soluble. You need something else as well, adjuvants or compounds, to get that to mix into water."
What researchers found is that the neonicotinoid coating doesn't last longer because the soybeans were planted early, often in cold soils.
"When we plant early, it seems that those soybeans, just sitting there and not growing, they don't pick up that neonicotinoid," he said. "It goes away from the plant and into the soil and groundwater."
Once the plant starts growing, the highest concentration of coating material is on the cotyledons, which are the first leaves that emerge from the seed. Some of that material moves further up as the plant grows, "but not a lot," Krupke said.
The results surprised researchers. They expected the neonicotinoid coating would stay with the plant longer, protecting it from those early season insects.
During the study, there were "significantly higher" pest counts early in the season, but Krupke said the defoliation rate on day one was just 6%.
"We're well below thresholds, which, depending on what you look at, might be 15% or even 25% defoliation," he said. "We're well below even the most conservative threshold."
The defoliation rate declined as the planting dates moved toward mid-April.
Interestingly, most of the defoliation was due to slugs, which are not an insect and cannot be controlled by the neonicotinoid coating.
As for yields, early planted soybeans performed the best. He noted that soybeans are durable and can outgrow the early damage.
"We tended to have consistently greater yields early in the season," Krupke said. "Despite that damage—despite those insects—planting early did yield the best at all the locations we looked at."
"Planting early seems like it is the way to go," he added.
Regarding Bt corn, Krupke indicated that it's an East verses West story. Bt corn, which provides protection against Western corn rootworm, has lost some of its efficacy in the western Corn Belt, where continuous corn is more common. But Bt corn isn't really necessary in the eastern Corn Belt, thanks in large part to the use of crop rotation.
"Indiana is definitely a different story than Iowa and Nebraska," he said.
Bt hybrids were first introduced in 2005. Since then, pest numbers have declined across the entire Corn Belt. The Bt technology is now stacked with other traits, but it's still being used on thousands of acres.
A multi-state research group, of which Krupke is a member, pooled the data from various states and found that the level of root injury to non-Bt corn is going down.
"What does that tell you?" Krupke asked. "The pest pressure is declining."
Meanwhile, Bt corn is still being bundled along with other traits in most seed products.
The researchers found that overall rootworm injury has declined by 20%, but, ironically, damage to Bt corn has increased. He said this suggests the pest is becoming resistant.
"And that's because of the regional differences," he said, adding that the cost of the trait exceeds the benefits—for Indiana growers.
Over an 11-year period, the efficacy rate for Bt corn has gradually declined, from 92% to 80%.
"What drives that is consecutive years of rootworm exposure to the Bt," Krupke said. "Soybeans break that cycle."
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