Ag Weather Forum

Early Iowa Corn Dent Rate Bears Watching

Bryce Anderson
By  Bryce Anderson , Ag Meteorologist Emeritus
Connect with Bryce:
The percentage of Iowa corn that has reached the dent stage is the highest at this point in the season since 2012. (Cook Seed photo)

The Aug. 7, 2023, weekly USDA Crop Progress report has a detail that bears some study: The report shows that 16% of Iowa's corn crop is assessed as moving into the dent stage. That is a week ahead of average. From the state of Iowa crop progress report: "Sixteen percent of the corn crop has reached the dent stage, nine days ahead of last year and one week ahead of normal."

The corn denting rate tripled from 5% the previous week to 16% in the Aug. 7 report. A year ago, the corn denting rate had only reached 4%, and the five-year average is just 6%. To find a comparable year for this pace of corn reaching the dent stage, you have to go back to 2012 when 27% of the Iowa corn crop had moved into the dent stage in early August. That occurrence was a full two weeks ahead of normal.

Interpreting this pace of denting is not straightforward. There is certainly the possibility that drought stress is involved. Iowa State Extension Cropping Systems Specialist Mark Licht touched on that aspect in an email to DTN.

"Denting earlier than normal can mean excessive stress," Licht said. "It can also mean too many heat units that (are) driving faster development. It could also mean smaller kernels due to lack of moisture in the early reproductive time period ... This year it is likely to be stress related."

The ahead-of-average onset of denting may also have some connection to the pace of corn planting this year. By the end of May, the Iowa crop progress report noted that 98% of the state's corn had been planted, eight days ahead of last year and 11 days ahead of the five-year average. USDA Midwest Climate Hub Director Dennis Todey told DTN in an email that the faster rate of planting could be reflected in the rate at which corn was noted reaching the dent stage.

"I have been noting the quicker progress in Iowa. There is some stress around in the state," Todey said. "But I think the progress overall was just early planting and early season warmth."

An important reminder of where the dent stage fits into the entire corn production cycle is offered in a discussion from Purdue University, authored by Dan Quinn and titled "Why the R5 Growth Stage in Corn Still Matters." The article noted that the dent stage is the final growth stage of corn, with about a month left before the kernel reaches physiological maturity.

"At the beginning of the R5 growth stage, even though corn is getting close to maturity, percent total kernel dry weight is only 45% ... This means that there is still approximately 50 to 55% kernel dry weight left to be accumulated. Therefore, if significant environmental stress (drought, nutrient deficiency, etc.) were to occur during beginning R5, significant yield losses can still occur," the article stated.

That detail underlines why the pace of corn denting is a cautionary note, but not the final word -- even with a corn crop that is earlier than average in the onset of this final growth phase. It also shows how the corn market will continue to pay close attention to see if the weather pattern in August continues on a milder temperature track with more periods of rainfall in the Corn Belt than we saw at the start of the season in May and June.

See more about the August weather pattern coming up from DTN Ag Meteorologist John Baranick's blog at….

Bryce Anderson can be reached at

Follow him on X, formerly known as Twitter, @BAndersonDTN


To comment, please Log In or Join our Community .