Corn stage by stage

Oct. 1, 2019

Below are descriptions of corn stages:

Corn stages. Photo: University of Illinois Extension

Silking stage or R1
In the first stage, silking, every potential kernel (ovule) develops its own silk. Silks elongate on a cob from the base to the tip until they emerge from the husk. Once emerged, silks have approximately 10 days to capture pollen grains and germinate, otherwise, they deteriorate.

Kernel blister stage or R2
About 10 days after silking, “blisters” (developing kernels) appear on the cob and contain clear fluid. Kernel moisture is approximately 85 percent.

Milk stage or R3
Normally, corn is dented by the last part of August. Kernels are mostly yellow and contain milky-white, sugary fluid. This is the “roasting ear” stage and moisture content is around 80 percent.

Dough stage or R4
In the dough stage, the milky fluid changes to a doughy or pasty consistency as starch accumulates. Moisture content usually drops to about 70 percent; kernals have reached about 33 percent of their mature dry weight. A milk line is still visible. Kernel abortion is now unlikely.

Dent stage or R5
In this stage, all or nearly all kernels are denting near their crowns. Moisture at the beginning of the dent stage is around 60 percent. A distinct line between yellowish and whitish kernel tissue appears, known as the “milk line”. As a kernel matures, it appears near the dent end and moves toward the tip. It takes an average of 33 days from the beginning of the dent stage to reach black layer.

Physiological stage/Black layer
In the physiological stage, black layer forms at the tip of the kernel, shutting off all further movement in and out of the kernel. That’s when corn is physiologically mature and safe from a killing freeze. It has roughly 30-32 percent moisture, depending upon the hybrid. Most combine manufacturers and grain drying experts consider 24-28 percent moisture manageable, even though they classify it as “high-moisture” corn.