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corn kernel that has reached black layer Tom J. Bechman
MATURE KERNEL: This kernel has reached black layer. Note the brown to black tip. The kernel is safe from frost.

Corn should reach black layer soon in many fields

Corn Watch: Progress toward maturity is much farther along than in 2019.

One year ago, it was a race to the wire to see if many cornfields would mature ahead of a killing frost or freeze. Since the first killing frost in most areas was normal or late, most fields made it. But the race was tight because 2019 featured a wet spring, and planting progress was extremely slow.

That wasn’t the case this year, although there were some areas where corn planting was still delayed somewhat by spring rains. In 2020, however, they were the exception rather than the rule. As a result, Dave Nanda says many fields are either reaching black layer now or will be very soon.

“It’s a big deal because once corn reaches black layer, it is physiologically mature and safe from a killing frost or freeze,” explains Nanda, director of genetics for Seed Genetics Direct, sponsor of Corn Watch ’20. “Once the black layer forms, starch can no longer move in or out of the kernel. This typically occurs when corn is around 30% moisture, but it can be at higher moisture levels when black layer occurs, too.”

Checking to see if corn has reached black layer is simple, Nanda says. Remove a kernel from a cob and use a pocketknife to carefully investigate the end that attached to the cob.

“What you’re looking for is a very thin layer of cells, usually dark to black in color, which forms and shuts off materials from going in or out of the kernel,” he says. “Once it forms, the kernel still must dry down, but it has all the starch it is ever going to have.”

Why date matters

When corn reaches black layer is important for more reasons than just the fact that it is safe from frost at that point, Nanda says. “If it reaches black layer on time, say in mid-September, then there is still a good chance it will dry more in the field before you decide to harvest it,” he explains.

“When it doesn’t reach black layer until early to mid-October, which was the case with the Corn Watch field last year, it is already well up into fall,” he says. “Normally, drydown rates for corn still in the field fall off in October, particularly by late October. That’s why even though many fields still yielded well in 2019, lots of corn was wet and had to be dried.”

When corn reaches black layer in mid-September, odds favor better drydown conditions. If it’s still warm and there is ample sunshine, corn can lose several points of moisture in a relatively short period of time.

Typically, a hybrid planted in late May or early June, about a month later than normal, requires about 200 fewer growing degree days than if the hybrid were planted May 1 or earlier. Bob Nielsen, Purdue University Extension corn specialist, and Peter Thomison, his counterpart at Ohio State University, proved that phenomenon in research trials a couple of decades ago. However, in 2019, their theory didn’t hold true. Hybrids that needed 2,500 GDDs to reach maturity still needed 2,500 GDDs, even when planted June 1.

“We’re hoping things are more normal this year, and fields reach black layer on time,” Nanda says. “Then you can decide the best moisture to harvest which fits your operation.”

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