Most corn around the Pee Dee is in the R5 stage now. This is the last stage before physiological maturity, or R6. The R5 stage is distinguished by the milk line progressing toward the base of the kernel. It takes roughly 33 days for the milk line to move all the way down the kernel, though this depends on the hybrid and weather conditions. Here is an ear where the milk line is nearly half way down. We could call this R5.5.
The milk line progresses down the top half faster than the bottom half, so this ear probably still has 20 days or so before physiological maturity. Below are some ears from the same field. R5 is also frequently called the dent stage and its easy to see why when looking at the kernels.
During R5, we are still susceptible to yield loss from environmental stress. Stess can reduce the amount of carbohydrates provided from the plant reducing the final weight of the kernels. We won’t be totally in the clear until we reach R6.
R6 will be distinguished by the black layer that has formed at the base of the kernel. At this point the kernels are usually below 35% moisture. Growers without the ability to dry their grain will need to wait until the moisture is closer to 15.5% to harvest.
Here is a great corn physiology resource where you can read all about the stages of corn growth and development.