Friday, August 15, 2014

Spring frost impacts Pawnee nut development

     Back on April 15, we had a freeze that killed emerging pecan buds on the lower portions of tree canopies. As the spring flowering season arrived, I noticed that primary buds at the base of frost damaged shoots emerged to produce pistillate flower clusters. Today, I used our hydraulic lift to check nut development of Pawnee trees that had suffered cold injury on the lower portions of their canopies.

   Overall our Pawnee trees look to be bearing a light to medium crop (following last year's big crop). In the photo at right, you can see that the shoot cut from the upper portion of the canopy (above the frost line) broke bud from the terminal of last year's wood and produced three new shoots each bearing a cluster of nuts. On the shoot cut from the lower portion of the canopy, you can see a frost damaged terminal (in red oval) and two nut bearing shoots that emerged from the lower portion of that frost damaged shoot.
    In collecting nut samples from the upper and lower portions of Pawnee trees, it looks like last Spring's frost impacted nut size (photo at left). However, what you are actually seeing is a difference in nut development stage created by differences in time of bud break. The shoots above the frost line started to grow and develop sometime during the first week of April. Below the frost line, initial bud break was frozen and basal buds didn't begin to emerge until late April.

    When I cut open nuts from upper and lower portions of the canopy, I found that the delay in time of bud break for shoots in the lower canopy is now displayed as a delay in nut development. In the photo at right, the nut collected from the upper portion has  expanded to roughly 3/4 water stage while the nut from lower in the canopy is at 1/2 water.
    Come this fall, I wonder if I will time of shuck split will differ with tree height. I bet it will.