After looking at nut clusters for signs of pecan nut casebearer larvae for the last 3 weeks , I've seen a sudden increase in nut size just this past week (photo at left). Our pecans have how entered the period of rapid nut enlargement. It is during this stage of nut development that pecan nuts become most susceptible to pecan scab.
Nuts are expanding in response to signals set out by healthy, developing embryos. If you carefully slice open a nut at this time of year, you'll see a tear-drop shaped structure imbedded inside (photo above). This is the earliest stage of kernel development. At the apex of the small tear-drop structure is the embryo. The round, water-filled sack below the embryo is the developing nut kernel.