Checking for Corn Maturity

Jarrod O. Miller, Extension Agronomist,; Cory Whaley, Sussex Co. Extension Ag Agent,

At this point in the season many fields may have started to show signs of dent, but this is a slow transition that sits between two reproductive stages. At the dough stage (R4), the milky fluid is drying down, giving the kernel a soft, dough like consistency (Figure 1). As some of these kernels continue to dry and starch forms at the crown, a dent will form on the outer edge of the kernel. However, to be at the actual dent stage (R5), almost all of the kernels should have the dent feature.

It is important to differentiate between dough and dent stages, where kernel development is still contributing to yield. Not until full maturity (R6, black layer) will your maximum yield be realized. At the dough stage, kernels will still have a dull yellow color, the shelled cob is pink, and the kernels will have a pasty consistency. Some kernels will begin to show dent (Figure 1), but the dent stage start when nearly all of the kernels are fully dented, a hard starch forms at the crown, and kernels will have the typical shiny, dark yellow color we expect of mature corn. For many hybrids, the cob may also be dark red at the dent stage.

The milk line forms shortly after corn plants reach dent (Figure 4). The kernels mature towards the cob and the dry starch line progresses inward. As you watch the milk line progress, keep soil moisture at adequate levels until the kernel has fully matured and black layer (Figure 3) is present. Many of our ears at the station began R4 (dough) last week, and at least one field has begun the R5 dent stage. These fields were planted from late April through mid-May, so expect your fields to follow a similar pattern.

Figure 1. Corn at the dough (R4) stage. Some denting has started.

Figure 2. Corn at the dent (R5) stage. Almost all kernels are at dent and the milk line is more prevalent. Depending on the weather, this ear is 2 to 3 weeks from black layer.

Figure 3. Corn at the R6 (black layer) stage. The black layer will be found at the kernel tip.