ear of corn
NEARING THE END: Kernels on this ear are “almost home” but not quite. The black layer, which seals the kernel, hasn’t formed yet.

Follow kernel development all the way to harvest

Corn Illustrated: Understanding kernel development is key in a late planting year.

This year, many cornfields in the Midwest will be in the grain-fill stage all the way into October. Hence, it’s important to understand what goes on during corn reproduction so you can tell what stage of maturity your crop is in.

There are several stages in kernel development. The process from pollination to kernel maturity is amazing to watch. If you know the stages of kernel formation, it might help you understand the importance of foliar fungicide or insecticide application at the right time. It will also help you make harvest decisions for each field, as well as hybrid selections for next year.

Here’s how a kernel develops:

Pollination and silking. This is the first stage in kernel development. The systematic process of pollen shedding from the tassel’s middle spike first to silk developing on the ear, with the first silks emerging from the butt of the ear, is fascinating. How pollen enters the pollen tube and travels the length of the silk and deposits its nuclear contents in the ovule within 24 hours with double fertilization to produce the embryo and endosperm is almost magical. It takes 50 to 55 days from fertilization to physiologic maturity, depending on the hybrid.

Kernel blister. This stage begins 10 to 12 days after silks are pollinated. Kernels appear like small blisters on the cob. The radicle root, coleoptile and first embryonic leaf have formed in the embryo. We still need 980 to 1,000 growing degree days to reach black layer from this point.

Kernel milk. This stage starts 18 to 20 days after pollination. Kernels are mostly whitish-yellow and contain a milky, white liquid. Starch accumulation continues in the endosperm, which is like the egg white. Sufficient moisture availability is needed during grain fill so kernels won’t abort. Kernel moisture during the milk stage is about 80%.

Kernel dough. This stage starts about three weeks after silks are fertilized. The milky fluid starts to solidify and feels like the consistency of dough as more starch is accumulated by the plant. By this stage, about four embryonic leaves are formed, and kernels have 50% to 55% of their final weight. Kernel moisture is 65% to 70%. We still need about 600 more GDDs to reach black layer.

Kernel dent. Next, dent stage is reached 30 to 35 days after silks are pollinated. Most of the kernels on the ear should be dented by now. The fifth and final embryonic leaf and lateral seminal roots are developed in the kernel. Watching kernels develop into little plants is almost like watching a little baby develop in a mother’s womb by ultrasound! The dry matter in the kernel is only 45% to 50%, and we’re still about 30 days from black layer. We’re not out of the woods yet!

Black layer. Finally! This last stage is reached when a film develops at the tip of the kernel as placental cells die, darken and create a barrier that blocks movement of starches into or out of the kernel. During this final reproductive stage, plants try to draw nutrients from leaves, and sacrifice even the stalks to fulfill the needs of the growing embryo before the black layer forms — not very different from a human mother!

Nanda is director of genetics for Seed Genetics-Direct, Jeffersonville, Ohio. Email him at dave.nanda@gmail.com or call 317-910-9876.

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