Friday, August 8, 2014

Rain, weevils, and nut development

   It rained a little over one inch on Thursday and that's usually enough moisture to loosen up the soil and allow pecan weevils to start emerging. But female weevils can't lay eggs inside a pecan until all the embryonic fluid inside the expanding nut is replaced by kernel tissue (i.e. water stage changes to dough stage).

   Over the past several weeks, I have been cutting open nuts of several pecan cultivars to determine stage of kernel development. However,  I thought it would be a good idea to check on the status of our native crop. So I climbed up into our hydraulic lift and grabbed nut samples from 9 native trees (photo above).
   The first thing you should notice is that native pecans are generally smaller than the improved cultivars I photographed earlier this week. The second thing to notice is the wide variation we find among natives in size and shape. After cutting into each of these nuts I found that many of these nuts are still expanding.

    The photo at left shows the cross-section of each native nut. By cutting into each nut I found that kernel development ranged from 1/4 kernel expansion (nut B) to the very first stage of kernel deposition (nut H). None of these nuts would be suitable for pecan weevil egg laying.
    The early pecan weevils that will emerge this weekend will migrate to nut clusters seeking a mate and feeding on developing pecans. Nuts in the water stage and punctured by weevil feeding will stop expanding and drop from the tree.
    If your grove has a history of heavy pecan weevil damage you might consider applying an insecticide to reduce the weevil population as early as next week. At the Pecan Experiment Field, we will be applying an insecticide starting on Monday that will be aimed primarily at stinkbug control but should also control early emerging weevils.