Production Blog

Remember those grade school kids impatiently pushing and shoving in the school milk line? At my school, the lunch lady would reach deep into a cafeteria milk cooler to present a half-pint carton of lukewarm milk in exchange for a ticket. Consumption was mandatory and monitored. We were growing, scrawny children who faced a horrible end if we didn't consume enough calcium.

Milk line has a slightly different meaning for corn farmers and this year, hot temperatures appear to be pushing and shoving the crop toward a fast finish in many areas. Whether the crop gets the growing conditions it needs to fill out kernels completely has big implications on final yield.

Reid Thompson is hoping for the agronomic equivalent of some extra milk tickets to continue adding some weight to his crop. The Colfax, Illinois, farmer walked fields and pulled ears last week and was pleased with the overall health of what he found. There was a little tip back, but he expected some since the crop has had a lot of hot days and nights.

What he was surprised to find was some corn in full dent and already exhibiting one-quarter to one-half milk line. "That's two to three weeks ahead of 2024," said Thompson.

Early dent and concerns about what that means to dry matter accumulation were well represented in farmer comments during DTN's recent Digital Yield Tour. Yes, pollination and kernel tip back concerns were in those thoughts too; but the potential to add or subtract kernel weight was also top of mind.

Purdue University Corn Specialist Dan Quinn said there can be a preconceived notion that once corn reaches dent (R5 growth stage) grain yield has been made.

"A significant amount of grain yield is still being determined during this period," Quinn noted in a blog post. "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."

The milk line is the boundary between the darker, hard starch (hard endosperm) accumulation at the top of the kernel, and the lighter colored "dough" or "soft dough" (liquid endosperm) material at the base of the kernel. As moisture is lost from the kernel as the plant approaches maturity, the milk line progresses.

Corn also advances much quicker through the beginning stages of R5 compared to the later stages. By half milk line, for example, kernel dry matter (% total dry weight) is already 90% and there's less chance of adding on.

A table associated with Quinn's blog provides valuable clues to the milk line progression. Find it here: https://extension.entm.purdue.edu/….

Reports of southern rust, tar spot and other plant diseases have been ramping up in recent days. "Any late-season stress, such as foliar disease, nutrient deficiencies or hot/dry weather, will shorten grain fill duration and lead to early maturity," Quinn told DTN.

Identifying the milk line can help identify the approximate kernel moisture, kernel dry matter accumulation and how much time is left until corn reaches maturity. Milk line progression can also help gauge when to terminate irrigation.

Time to head to the field to check out those milk lines -- no tickets required.

Editor's note: To see 2025 DTN Digital Yield Tour estimates for other states and what other farmers are saying about their crops this year, see https://www.dtnpf.com/….

Pamela Smith can be reached at pamela.smith@dtn.com

Follow her on social media platform X @PamSmithDTN

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