Greenriver vs. Oswego: Kernel quality problems

Greenriver kernels, 2017

    Last summer we thinned the nut crop on several pecan cultivars including; Pawnee, Lakota, Faith, Gardner, and Kanza. Later, when we harvested the nuts from these cultivars, we found good to excellent kernel quality inside. However, after cracking open this year's Greenriver nuts, it looks like we should have thinned the crop on this cultivar also.
    The photo at right illustrates the type of kernels I found inside our Greenriver nuts. About 25% had darkened kernels and another 25% had kernels that where somewhat hollow inside.
 

Oswego kernels, 2017

   Oswego originated as a seedling of Greenriver. The nuts produced by Oswego are very similar in size and appearance to its parent. However, when I cracked a sample of Oswego nuts I found the kernels to have better color and nut fill (photo at right).
   Why the difference? It boils down to crop load.  At the Experiment Station,  Greenriver and Oswego are located in the same block of trees, grafted to the same rootstock, with very similar trunk diameters. In 2017, our Greenrivers  were loaded with nuts. In contrast, Oswego trees had a good crop of nuts but the limbs weren't hanging on the ground like our Greenriver trees.
    Over-production reduces kernel quality. With Greenriver, over-production caused a darkening of the kernel and meats that were not solid. Over-production is a manifestation of Greenriver's strong tendency towards alternate bearing. Next year, our energy-drained Greenriver trees won't have the capacity to produce many pistillate flowers. The 2018 Greenriver crop will be tiny.  Summer shaking is the only tool we have for reducing alternate bearing and I wish we would have shook our Greenriver trees last summer.