The R6 stage, figure 50, is reached when all kernels on the ear have attained their maximum dry weight or maximum dry matter accumulation The hard starch layer has advanced completely to the cob now and a black or brown abscission layer has formed, figure 51. This black layer formation occurs progressively from the tip ear kernels to the basal kernels of the ear. It is also a good indication of maximum dry weight (physiological maturity), and signals the end of kernel growth for this season. The husks and many leaves are no longer green although the stalk may be.

Figure 52 displays an R6 kernel on the opposite embryo side (left) and slices laterally cut from the top, middle and bottom of the kernel. 

Management Guides - R6 Stage - Physiological Maturity

The average kernel moisture content at R6 (black layer formation) is 30-35 percent; however, this can vary considerably between hybrids and environmental conditions. The grain is not yet ready for safe storage, which requires 13-15 percent moisture level for shelled corn. Harvesting at R6 or shortly after would be costly because drying the crop is expensive. It may be advantageous to let the crop partially dry in the field after R6 before harvesting, as long as field losses do not become a problem. The rate of field drying after R6 depends on the hybrid and environment.

Harvest silage at R6 or slightly earlier.

figure 50

figure 51

figure 52