Sept. 11, 2019

Due to late planting this year, many corn fields in the Midwest will be in the grain-fill stage all the way into October. Therefore, it is important to understand what occurs during corn reproductive stages to identify a crop’s maturity stage.

Pollination and silking is the first stage in kernel development and production. The stage begins with systematic pollen shed from the tassels’ middle spike, silk development and the first silk emergence from the butt of the ear. This is followed by pollen formation and the pollen tube traveling the length of the silk and depositing its nuclear contents in the ovule within 24 hours and double fertilization to produce the embryo and the endosperm. Fifty to 55 days from fertilization of the ovule to physiologic maturity, depending on the hybrid, is needed.

Kernel blister stage begins 10 to 12 days after the silks are pollinated. Kernels appear like small blisters on the cob. At this stage, the radicle root, coleoptile and first embryonic leaf have already formed in the embryo. Approximately 980 to 1,000 growing degree days are needed to reach black layer.

Kernel milk stage starts 18 to 20 days after pollination. At this stage, the kernels are mostly whitish yellow and contain a milky white liquid. This is also called the “roasting ear” stage. Starch accumulation continues in the endosperm which is like the egg white. Sufficient moisture availability is required during the grain-fill period so the kernels won’t abort. Kernel moisture during the milk stage is about 80 percent.

Kernel dough stage starts around three weeks after silks are fertilized. During this stage, the milky fluid starts to solidify and feels like the consistency of dough as more starch is accumulated by the plants. By this stage, approximately four embryonic leaves are formed and the kernels have about 50 to 55 percent of their final weight. Kernel moisture is around 65 to 70 percent. Nearly 600 more GDDs are needed to reach black layer.

Kernel dent stage is reached 30 to 35 days after silks have been pollinated. Most of the kernels on the ear should be dented by now. The fifth and final embryonic leaf and lateral seminal roots are also developed in the kernel. The dry matter in the kernel is only about 45 to 50 percent and the plant is about 30 days from black layer.

Black layer 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 in or out of the kernel. During the final reproductive stage, plants try to draw nutrients from leaves and sacrifice even the stalks to fulfill needs of the growing embryo.

Identifying crop maturity: where corn will be in October