Tuesday, July 16, 2019

Squirrel kills established graft

   While working in my pecan orchard today, I noticed a young tree with brown, dried-up leaves (photo at right). This is a tree I top-worked a couple of years ago (graft union marked with white paint) and it looks like only the graft was effected. Below the graft union the trunk is sprouting all kinds of new shoots. But what caused this graft to die in mid summer? Let's take a closer look.
    Just above the graft union the bark of the scion has been stripped off (photo at left). This kind of bark stripping is caused by fox squirrels looking for nutrition from the cambium of tree stems. damage occurs in late winter or early spring especially during seasons following a short nut crop (the 2018 pecan crop was tiny).  Squirrels prefer to strip smooth barked pecan limbs and my vigorously growing graft must have looked especially delicious.
    The tree still had a thin strip of live bark on the side of the tree protected by my tree training stake (photo at right). This bark strip provided enough water to the upper portion of the tree to allow the graft to bud out and begin new growth this past spring. However, as the heat of summer arrived, the tree was unable to keep enough water and  nutrients flowing to the top of the tree and it finally wilted and died.
   Below the graft union I had sprouts growing everywhere (photo at left). Since I lost the entire top of this tree I searched though all these trunk sprouts to find a good candidate to be my new central leader.
   Once I identified my new main stem, I pruned off all competing stems and cut the trunk at a 30 degree angle just like I was training a bark graft (photo at right).

  Until a trunk sprout grows some new wood for a couple of years, the joint between old trunk and new sprout is fairly weak. To prevent possible wind breakage, I attached a 8-foot-long pole to the side of the tree and tied the new shoot to it.
    Next spring, I'll re-graft this tree on my new central leader.