Tuesday, February 7, 2017

Pruning top-worked pecan trees

    Back in 2014, I decided to top-work some young trees to new cultivars. In previous posts, I wrote about the grafting process and training those new grafts.  Because these trees were fairly large when I placed a bark graft on the central leader, I left several lower limbs on the tree to provide critical leaf area to keep the tree actively growing. For the past 3 growing seasons, I've pruned back the growth on limbs below the graft to encourage growth of the new scion (graft union painted white--photo at right). At this point, the tree's new top has begun to fill out and I can safely start removing limbs below the graft union.
   The tree pictured above was easy to prune. I simply removed the two largest low limbs (photo at left). This left me with a couple of small diameter limbs under the graft union but I'll leave those on for now. One of the disadvantages of top-working a tree this size is how quickly it grows in height. It becomes increasingly difficult to train a central leader 15 feet up in the air. As the new growth begins to burst forth this spring, I'll  get out my 8 foot orchard ladder and practice some directive pruning on the top of this tree.

    The next top-worked tree I needed to prune presented more of a challenge (photo at right). This tree had four strongly growing limbs growing under the graft union (graft union painted white). In fact, it looks like the lower side limbs are actively competing with the scion and slowing the growth of the new top.

   The problem with this tree is that 3 of the 4 limbs growing below the graft union are attached to the trunk adjacent to each other (photo above left). Pruning all these limbs off at one time would leave almost two thirds of the trunk's diameter without bark--limiting the ability of the tree to transport nutrients to the scion. I decided to remove just two of the limbs this year (cuts marked by yellow dashed lines). I'll let the tree callus over these two wounds before I remove the remaining limbs under the graft.

   To help further promote the growth of the scion, I pruned back some of the growth on the remaining low limbs (photo at left). Then, over the course of the summer, I'll continue pruning back the side limbs that are growing out from below the graft.
    The one large side limb I left on the tree will definately try to outgrowth the scion. It will take monthly summer-pruning sessions to keep this limb in check. By mid-summer, I'll probably have this limb cut back to half its current length. In one or two years, the entire limb will be removed back to the trunk.