Unpacking the Disappointment: 5 Reasons Some Iowa Growers Had Ho-Hum Corn Yields

A growing season that started with tremendous potential in east-central Iowa finished with yield results that left many growers in the area disappointed by average or below-average results, according to Agronomist Nicole Stecklein.

Stecklein details five key factors she believes contributed to disappointing 2025 yield results. Here are her key takeaways from this season as well as some recommendations for 2026.

1. A ‘planting date effect’ occurred: Stecklein says she is an early-plant advocate and likes to see farmers start planting when the soil is fit and a good weather forecast is in the cards.

“In eight years out of 10 years, that usually turns out pretty good. In a lot of cases, the early planted corn will be your best corn, but that wasn’t the case this year,” she says.

Early-planted corn, particularly those hybrids in early to mid-maturities, generally underperformed.

Stecklein identified two main culprits. First, there was considerable localized soil crusting. Even with rotary hoeing, significant variability in ear development and inconsistent pollination impacted the crop and contributed to yield loss.

A second culprit was that the earlier planted corn seemed to bear the brunt of later-season stresses, particularly from disease issues, heavy moisture and above-average temperatures.

Too much rain and disease were problems for Ward Hunter, Ogden, Iowa, especially southern rust. He told U.S. Farm Report’s Tyne Morgan that his early corn hybrid yields were disappointing, coming in at around 220 bu. per acre, even though he applied a fungicide.

“We were at about our APH,” he says. “If it hadn’t been for disease pressure, I think we could have been in the 270s or so [with early maturing hybrids] here in central Iowa.”

For farmers wondering if they should move to later planting dates across the baord in 2026, Stecklein says probably not. Instead, she says to continue to evaluate soils and weather conditions at planting.

Ken Ferrie offers similar advice to farmers in central Iowa and central Illinois. “My advice for farmers is if we have a green light in April, plant some corn,” says Ferrie, Farm Journal Field Agronomist.

However, Ferrie says farmers shouldn’t be afraid to wait until May to get a green light from Mother Nature to start the planting process.

“We never know how the rest of the year will play out. So, breaking the planting window up is a good way to mitigate risk and take the jam out of the fall of having everything ready at the same time,” he explains.

2. High winds were a blow to corn performance: June brought a series of severe high-wind events to large swaths of east-central Iowa.

The damage manifested in root lodging, green snap, and willowing. Corn that had already tasseled before the winds hit fared better, thanks to better developed root systems and brace roots, Stecklein reports.

Conversely, corn that had not yet tasseled suffered the most severe root lodging and green snap, as its rapidly growing, brittle nodes were highly susceptible.

Willowing, which occurs where corn plants bend at the waist, proved to be a stealthy yield robber this summer. The stress from bending, particularly around the developing ear node, led to poorly pollinated ears with short husks, leaving grain exposed to elements, birds and disease, significantly impacting quality and yield.

While wind is an unavoidable reality across the state, Stecklein would advise farmers in consistently windy areas to consider prioritizing root and green snap scores when selecting hybrids for 2026.

“This is not a foolproof way to get around the wind. It’s just knowing that some hybrids have a lower possibility of getting hit by wind in a window when they’re vulnerable, because all corn is vulnerable. The wind is all about timing. But if you shorten that window, then you’re decreasing the chances that you’ll get hit at a vulnerable time,” she explains.

3. Heat took a bite out of yield potential. Another major factor impacting 2025 yields in east-central Iowa was the pervasive overnight heat during grain fill, specifically in July and August.

Stecklein says the general rule of thumb is for each night during grain fill that temperatures stay at 70 degrees Fahrenheit or above, your corn crop will experience about a 1% yield loss in each 24-hour period.

What happens is the result of a lack of equilibrium between the process of photosynthesis during the day and then respiration at night.

“During the day, the plant is taking sunlight and carbon dioxide and making sugars. It’s creating energy,” Stecklein explains. “Overnight, you have respiration occurring. Respiration is using energy to repair cells, And the rate of these processes is very temperature dependent.”

When nighttime temperatures remain high, the rate of respiration dramatically increases. This means the plant burns through its energy reserves much faster.

Stecklein says that in July and August, parts of east-central Iowa had 15 nights that stayed at 70 degrees or greater.

“If you’re good at math, that means a 15% yield loss. If you had 300 bushels to lose at tassel, that brings you straight down to 255, bushels, just based on overnight temperatures,” she says.

4. Disease pressure reached unprecedented levels for some farmers. The big gorilla this season was southern rust, which took most Iowa farmers by surprise.

”Southern rust is the one that everybody is talking about, because it’s so aggressive and because, honestly, in Iowa, we were not prepared for how aggressive it was going to be,” Stecklein says.

Unlike tar spot, southern rust is not a disease that overwinters in residue. It must “blow in” from the South, and it also needs corn to infect to complete its life cycle. For those reasons, Stecklein would advise Iowa farmers to not make hybrid decisions for next year based on concerns for southern rust.

However, she would advise them to take tar spot into consideration as they evaluate which hybrids to plant in 2026.

“If you are going to spray [a fungicide], you’re going to be OK if you do choose a hybrid that’s susceptible, because there are some very good hybrids out there that aren’t super tolerant to tar spot. Make sure that you’re planning on at least making one fungicide pass at tassel. But if you will not spray two passes of fungicide, do not choose a hybrid that has a very poor tar spot rating, because if we get the weather that’s very conducive to tar spot, you’re going to lose some bushels,” she adds.

5. Phantom yield loss showed up at harvest. Based on phantom yield loss data, Stecklein says there’s about 2 bushels lost per percent of moisture. How that translates into a yield loss: if you like to harvest at 22% moisture but the crop is at 16% moisture when you finally combine it, you’re looking at a loss of 12 bushels per acre.

If you find yourself consistently harvesting corn at a drier level than you want, Stecklein would say it’s time to adjust your hybrid maturities. If phantom yield loss isn’t a consistent issue you face, then you’re probably OK to stick with your current maturities.

Her final advice for 2026: “I keep wanting to say that every year I learn something unique, but at the end of the day, my key takeaways from every year have almost always been the same: if you plan for failure and if you give up, you’re going to be met with failure. However, if you are persistent through hardships and manage according to those hardships, you’re setting yourself up for success.”

Watch Stecklein’s recent video, Corn 2025: What happened, for more insights on the east-central Iowa corn results.