Debbie Carlson, for CME Group
At a Glance:
- As of mid-August, almost a third of the U.S. corn crop is in dent stage.
- Weather will play an important role in final crop development.
In the August Crop Production report, the U.S. Department of Agriculture (USDA) surprised many market participants by estimating a national average corn yield above trade expectations.
In the USDA’s first survey-based report using both what farmers reported and its own drone-based surveys, the agency projected this year’s corn crop could yield on average 188.8 bushels per acre (bpa), which would be at the high end of trade expectations. Prior to the report, the USDA had penciled in the trendline estimate of 181 bpa. If realized, 2025’s yield would be a record and could result in a national corn crop of 16.7 billion bushels, up 1.8 billion from 2024.
The USDA will fine-tune the national yield estimates each month until the final report comes out in January, but this first report gives market participants a sense of where the crop’s size is trending. It’s where the trading adage “big crops get bigger and small crops get smaller” originates.
Considering that by early fall much of the corn crop is in its final development stage and nearing harvest, looking for a trend makes sense. For 2025, by mid-August, 28% of the U.S. corn crop was in dent stage – the last stage before final maturity – which is slightly ahead of the five-year average.
Since the USDA won’t survey actual fields until the September crop report, the days between the August and September crop reports may see more active trading activity as weather changes could significantly affect actual harvest size.
Ahead of these potentially market-moving reports, more market participants are turning to Ag Weekly options to manage short-term risk. A record 24k Monday-Thursday Weekly options were traded on June 30 when the Acreage Report was released, and the entire CME Group Weekly Ag options suite is up 36% from last year.
Weather Is Key
With nearly a third of corn crop just reaching dent stage in late August, now is a critical time for development. Dent stage is where the kernels begin to dent at the top and take on their characteristic look as the crop starts to accumulate starch and dry matter. Research from Purdue says at dent stage, dry matter content is only about 45% of the final weight and has about 30 more days before it is mature.
Jim Roemer, publisher of WeatherWealth Newsletter, forecasts “decent” harvest weather for the Corn Belt, with few scattered delays or wet weather. Harvest generally starts in September and continues through October. The potential for a very weak La Nina, a negative Indian Ocean Dipole (the warmth or coolness of certain sea surface temperatures in the Indian Ocean) and weather patterns over Eurasia suggest drier-than-normal weather over 75% of the corn belt.
This year was the second-wettest July on record, which helped crop growth during key development times. Roemer says historically, neutral El Nino or weak La Nina events, coupled with wet July corn belt weather, are often good for harvest.
Crop Tours Showing Healthy Plants
Ahead of the USDA’s field surveys, private crop scouts fan out in parts of the corn belt and two recent crop tours underscored what USDA’s reports suggested: big healthy corn crops. The Pro Farmer Crop Tour 2025, a four-day tour across key Corn Belt states during the third week of August, showed increases in 2025’s estimated corn yields – estimates were higher than last year’s figures for all seven states they visited, except Illinois, which was down 2.2% from 2024. Pro Farmer’s average corn yield estimate is at 182.7 bpa, lower than USDA’s 188.8 bpa figure.
AgResource conducts another closely watched tour of Illinois and Iowa, the country’s two biggest producers. The firm’s findings suggest that this year’s crop could produce record yields. Dan Basse, founder of AgResource, says in a video that the firm’s scouts found several surprises, with the biggest one being a record number of ears in their survey plots. “It was really hard to find a blank stalk,” he says, noting that kernels per ear were a record as well.
AgResource has ear counts dating back to 2015 and its research correlates well to USDA’s data. Although the kernel depth is not as big as Basse would like, “there are so doggone many ears out there that it’s still going to give us a very big yield, regardless of what some of the ears may weigh,” he says.
There is some Southern Rust, a fungal disease impacting corn crops, in Iowa that could trim the state’s yields slightly. When corn is in the dent stage, the disease may cut yields by 5% to 7%, but he doesn’t think it will be a big deal. AgResource is estimating a corn yield in Illinois and Iowa of 244 bpa. “This is just a monster crop,” he says.
Do Big Crops Get Bigger?
The idea that big crops get bigger may be an old trading chestnut, but research from University of Illinois professors suggests that the facts are complicated, but overall, there is more lore than truth to the saying.
In a farmdoc daily research report from October 2024, “Revisiting Big Corn and Soybean Crops Get Bigger,” University of Illinois Department of Agricultural and Consumer Economics professors Scott Irwin and Darrel Good looked at average yield forecasts in September and actual U.S. average yields as reported in USDA’s final January crop data for the 54-year period from 1970 through 2023. They defined a big crop as one with an average yield (or yield forecast) above trend value.
Their research shows that the variability of USDA yield estimates between September and January for market participants is too big to bank on the idea that big crops get bigger so early in the crop forecasting cycle.
“The evidence usually cited as justification for this marketing adage is actually backward-looking and biased because it is based on information – final January yield estimates – that is not available in real-time,” Irwin and Good wrote.
That happened last year, when late summer and early fall Corn Belt weather turned detrimental and what was expected to be a record national corn yield of 183.1 bpa turned out to be only 179.3.
However, they say the trend between August and September is a more accurate barometer of crop size.
“If the September yield forecast for corn is above the August forecast, there is about a 70 percent chance that the final January yield estimate will also be above the September forecast,” the professors wrote.
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