Wednesday, March 26, 2014

Early spring pruning on last year's bark graft

    I made a quick trip into my pecan orchard this morning to look at last summer's grafts. I stopped by the tree pictured at right to check the health of the scion and to trim the graft union. I grafted a Kanza scion onto this 1.5 inch diameter tree last May. After pruning the scion to one shoot in early July, this graft put on five feet of new growth during the summer of 2013. I removed the deer cage and quickly checked the scion's bark for signs of winter injury.  Even though this new graft had grown vigorously well into the Fall and this type of late growth can be prone to winter injury, my Kanza stem had green and healthy looking tissues inside the bark.
    I next turned my attention to the graft union. Last summer, I had cut off the green plastic tape that held the plastic bag around the scion allowing it to grow in diameter without being restricted. I left the remaining grafting wraps in place (photo at left). As is often the case, it looks like a bird had ripped open the plastic at the top of the stock, split the aluminum foil apart, and feasted on the ants that take up residence under the foil wrapper. I guess I should have taken my own advice and painted the graft union with white paint last summer.
    Once I removed all the graft wrappings, I could see how the tree was attempting to grow over the large wound I made by cutting the stock and inserting the scion (photo at right). The scion had grown to roughly 1/3 the diameter of the stock. Callus tissue had formed around the scion and had begun to cover the cut surface of the stock. Between the bark and the wood of the stock, I could see that a roll of callus tissue had developed part way around the circumference of the tree. This roll of callus is thickest near the scion then seems to dive down under the bark farther away from the scion.

    On the opposite side of the tree from the scion, the bark of the stock dies downward. To encourage rapid wound healing, I like to trim out the dead corner of the stock. I make the cut at about a 30 degree angle which seems to follow the natural way the tree is already forming callus tissue (photo at left).

      After trimming the stock,  I'm ready to replace the deer cage and move to the next tree (photo at right). Note that I still have the graft tied to a bamboo stake to prevent wind damage. The bamboo is attached to the stock with electrical tape and I used flagging tape to attach the scion to the stake. I'll keep the stake in place until the graft union is completely healed over. Once growth starts in the spring, I'll come back to this tree to make some "directive" pruning cuts to ensure I maintain a strong central leader.