Monday, October 3, 2016

A tree can produce too many pecans

     Precocious and Prolific--Two words that pecan breeders like to throw around in describing their new pecan cultivars. A precocious pecan cultivar is one that starts to bear nuts at a young age. A prolific pecan cultivar produces a lot of pecans. The tree pictured at right is currently known as USDA 75-8-5. This clone has been touted as both precocious and prolific and you can see by the drooping limbs that this young tree is loaded down with nuts. However, excessive crops present their own set of problems. 

    In previous years, we have attempted summer tree shaking this cultivar as a method to reduce the excessive crop load. Unfortunately, summer shaking does not work well with this clone. In the photo above-left, note that the nut crop is held on the ends of long slender shoots. During a summer shake, these limbs just dance around and very few nuts are dislodged.

   The problem with over production becomes evident at harvest. For the photo above, I cut open three nuts pulled from the USDA 75-8-5 tree and compared them to three nuts harvested from a nearby Kanza tree. Both these cultivars ripened at about the same time but the cross-sections of the USDA 75-8-5 nuts reveals the impact excessive cropping has had on kernel fill. The USDA clone has thin kernels, lots of internal air pockets and the kernel was unable to fully compress the partition between kernel halves. But the real troubles will come this winter and next year. 75-8-5 has set itself up to be damaged by cold winter temperatures. If not damaged by cold, the tree will be unable to set a full crop of pistillate flowers next spring.
   The moral of this story is that heavy nut yield at a young age usually precedes a future of alternate bearing and cold injury. In testing new cultivars, I look for a tree to start bearing early but to build yield slowly always maintaining excellent kernel quality.