One of the cultivar traits important to northern pecan growers is ripening date. I judge pecan ripening date by recording when at least 50% of the nuts on a tree have split shucks.
I always start scouting my orchard starting in mid-September and pay particular attention to the trees in my pecan breeding plot. One tree, a cross of Pawnee and Greenriver, is always the first to shuck split. Over the previous 4 years, the tree I've labeled 'KT337' has ripened on 19 Sept 2016, 20 Sept 2017, 17 Sept 2018, and 13 Sept 2019. This year, I first checked this tree yesterday (14 Sept 2020) and found some nuts shuck-split (photo above) but the tree had not yet achieved the 50% shuck-split level.
I pulled several nuts off the KT337 tree to show you the variation in ripening you can find on a single tree (photo above). The nut on the far right was pulled from fully split shucks, while the nut next in line was loose in the shuck but I had to forcibly peel back the shucks. You will note that the shell of nut #2 is still partially white, indicating that the nut was not yet fully mature. Nuts #3 and #4 illustrate how the shuck splitting process proceeds. The first sign that pecan ripening has begun is when the shuck starts to pull away from the shell near the tip of the nut. In time, shuck separation moves downwards towards the base of the nut. As the shuck separates, the shell starts to develop cinnamon-colored markings on its white shell surface. These markings will turn jet black and the shell a rich brown when the nut is fully mature.
Update: 18 Sept 2020
By Friday, September 18th, KT337 had reached over 50% shuck-split (photo above). This selection remains the earliest ripening pecan in my pecan breeding block.