Monday, July 28, 2014

Pecan development: Rapid nut expansion


    Late July is the time of year when pecans are growing rapidly in size. With larger nut size, I can finally stand back, look at a tree and actually see the crop load held in the canopy. So this morning, I decided to collect some nut samples and check on kernel development.  In the photo above, the nuts I pulled from from five pecan cultivars are arranged by average date of nut maturity.  Pawnee and Gardner usually ripen in late September, Kanza ripens in early October, while Giles and Lakota ripen in mid October. By mid summer, a close look at nuts on the tree can give you a rough idea of when a cultivar will mature in the fall. Note that Pawnee, Gardner, and Kanza nuts are larger and plumper than the Giles and Lakota nuts. This tells me that kernel expansion is farther along in the bigger nuts and not as advanced within the smaller two cultivars.  

     I cut each nut in half to check my theory (photo above). Pawnee, Gardner, and Kanza had kernels that were about 1/4 expanded (Gardner looks less expanded but I missed the exact middle when slicing the nut open). Giles had the smallest amount of kernel and was actually just starting into the rapid growth phase of nut development. Lakota was further advanced than Giles but still behind the other three cultivars.
     All this discussion of nut development may seem like an academic exercise but we are rapidly approaching pecan weevil season.  Knowledge of nut development is critical for timing insecticide applications to control the pecan grower's number one enemy, the weevil. Pecan weevils can not lay eggs inside a pecan until kernel deposition begins. Early ripening cultivars will begin laying down solid kernel first and will be the most attractive to egg-laying female weevils.