There are several milestones during every corn-growing season: emergence, V6 stage with growing point aboveground, knee-high, waist-high, tasseling, silking and the list goes on. Perhaps none is more anticipated than black layer at the end of the season.

“It signifies that corn has reached physiological maturity and is safe from frost,” says Dan Quinn, Purdue Extension corn specialist. “It also gives you a handle on approximate moisture content, and where that field is as far as maturity and moving toward harvest.”

Here is all you need to know about the black layer stage in corn. Some information was gleaned from the 2024 Purdue Corn and Soybean Field Guide.

What black layer is. Technically, the black layer at the tip of a corn kernel is a layer of placental cells that die and collapse, effectively “closing the door” on transport of materials in or out of the kernel.

Relation to physiological maturity. Quinn notes that physiological maturity occurs just after the milk line in the kernel disappears and just before the black layer forms. Dry weight has reached its maximum per kernel, and kernels are safe from frost.

Color progression. The layer of dying cells is first olive green in color, then brown, and then finally, a thin, black layer lying horizontally across the tip of the kernel.  

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YES AND NO: Here are kernels from two ears. The one on the left shows a black layer, while the one on the right is not quite to that stage yet.

Why it matters. Severe stress after black layer does not affect harvested yield, unless the integrity of the stalk or ear is compromised, Quinn explains. Insects like European corn borer that cause ear drop or a severe windstorm that causes lodging could result in harvesting losses not related to the kernels themselves.

Premature development. Severe stress, including a killing freeze, drought or disease, can cause the black layer to form prematurely. Fortunately, this is a rare occurrence.

Moisture content. Agronomists suggest corn at black layer should be around 30% to 32% moisture, but it can range from 40% down to 25%. A variety of conditions can result in a higher or lower moisture content at black layer.

Timing since R1 phase began. R1, or the first reproductive phase, occurs at silking, Quinn notes. Black layer typically occurs about 55 to 65 days after R1. Corn specialist Bob Nielsen, now retired, discovered that when corn is planted late, say in late May, the same hybrid may progress through these stages to black layer in a shorter amount of time than if planted on May 1. However, that phenomenon did not hold up in 2019, a very late planting year. Some fields planted in very late May in 2019 didn’t reach black layer until early October.

How to find it. Flick out a kernel and look at the very tip. The black layer will be evident if it has formed. Or, split a kernel in half. The thin black layer of cells will be visible at the base of the split kernel.

Across the rows:
Dry weather, disease show up in crop reports

The prospect for above-average corn yields still appears to hold across most of the Corn Belt. However, there are a few chinks in the “high-yield armor” in places. Here is a closer look:

In Ohio. Ohio is very much a mixed bag for potential yields, as some are looking at record yields, while others, particularly in southeast Ohio, are in extreme drought conditions with little crop to harvest.

Of the Buckeye State’s 88 counties, 87 were highlighted as parched when the U.S. Drought Monitor released its updated map Sept. 3. Nearly a third of the state is in extreme or exceptional drought conditions.

In Fairfield County, one of the 23 primary counties designated a USDA disaster area, Jay Brandt is farming 750 acres corn, soybean and wheat with a cover crop and no-till system.

“With no-till, we have subsurface moisture that’s helped us out, but it’s really starting to dry down now,” he says. “But we did get planted in late April to early May, so the timing of crop maturity is about right for us.

“We’ve had some timely one-tenth or two-tenth rains to keep things going, but corn has been rolled up through most of the summer,” he says.

Pickaway County south of Columbus has been the epicenter of exceptional drought (D4) — the worst rating by USDA. Brandt, just to the east of Pickaway, expects his yields to be fairly average, but neighbors with conventional tillage are experiencing more stress. “Their corn is drying down much faster than ours,” he says.

The no-till and cover crop system has helped conserve moisture, he contends. “We can dig into the soil and see that it does have some moisture about an inch or 2 down from the surface,” Brandt says, while noting that his newly planted cover crop following wheat has found those moisture reserves in the soil profile and is sprouting.

According to the U.S. Drought Monitor report on Aug. 27, D4 exceptional drought was introduced to Ohio for the first time since the U.S. Drought Monitor’s inception in 2000. On Sept. 5, D4 increased to 7.35% of the state, while other categories of drought, D1 to D3, significantly expanded. Traditionally, D4 conditions only occur once every 50 to 100 years. — reported by Jennifer Kiel, editor of Ohio Farmer

More from Ohio. “The 2024 crop season has brought extended periods of dry weather for many parts of Ohio, mostly affecting corn during the grain fill stages. Among the many negative effects of dry weather, cornstalk quality can be compromised. Crop stress conditions increase the potential for stalk lodging. For instance, cornstalk rot, and consequently, lodging, are the results of several different but interrelated factors.” — Osler Ortez, lead author for “Dry conditions in corn and stalk quality concerns” in the OARDC C.O.R.N. newsletter for week of Sept. 9

In Illinois. “Another dry week. In travels across northeast Illinois, we see both green corn and soybean fields, and in others, plants that have browned, dropped leaves and are likely only weeks from harvest. We have had reports of hand-shelled corn samples near 30% moisture. For areas that have heavier soils, received timely rains and have higher water-holding capacity, yields will be impressive. A visit to the Sandwich Fair this week judging corn entries demonstrated sizable ears. If they are representative, it will be interesting to see final yields from these locations. Tar spot continues to spread in corn, even in earlier fungicide-treated fields.” — Russ Higgins, Illinois Extension commercial agriculture specialist, Grundy County

In Nebraska. Wet weather that persisted during the early 2024 growing season was very favorable for development of some corn diseases in Nebraska. Diseases caused by fungi were favored by repeated rainfall events and high relative humidity, fog, and so forth. On some susceptible varieties and hybrids, diseases developed early and quickly. In some areas, disease severity is increasing, but in most areas, diseases are still at low severity and not a threat to yield.

Foliar fungicides were applied to some fields to mitigate losses due to disease or in pursuit of plant health benefits. However, low commodity prices and narrow profit margins make foliar fungicide application decisions more difficult as producers weigh the application costs and the uncertainty about what to expect from diseases and growing conditions through the remainder of the season. — Tamra Jackson Ziems, University of Nebraska Extension disease specialist, and Jenny Rees, UNL Extension, authors of “Corn disease update: Fungicide expectations for disease control,” UNL Cropwatch, Aug. 30 edition