At R5, all or nearly all kernels are dented or denting and the shelled cob is dark red in color (figure 48). The kernels are drying down now beginning at the top where a small hard white layer of starch is forming. This starch layer appears shortly after denting as a line across the kernel when it is viewed from the opposite embryo side (see figure 49). With maturity, the hard starch layer and line will advance toward the base of the kernel (toward the cob). Because the accumulated starch is hard above the line but still soft below the line, pressing the kernel with the thumbnail can aid its detection.

Figure 49 details starch line development with kernels and kernel slices from the R4 (left) and three progressively advanced R5 stages. The kernel slices were laterally cut from the top, middle and bottom areas of the kernel.

Management Guides - R5 Stage - Dent

Stress encountered at this stage will reduce yields by reducing kernel weight. not kernel number. A hard early frost before the R6 stage may halt dry matter accumulation and cause premature black layer formation (see R6 stage). This could also reduce yields by causing delays in harvest operations because frost-damaged corn is slow to dry. To reduce potential frost problems, choose a hybrid that matures about three weeks before the average first killing frost date.

 At the beginning of R5, kernels have about 55 percent moisture content.

figure 47

figure 48

figure 49