Wednesday, December 16, 2015

First year grafts: What can happen when you're not watching

   With all the recent rainfall, this year's pecan harvest has come to a halt. Although I'd rather be out harvesting nuts, the muddy field conditions gave me the opportunity to check on some of the young trees I grafted last spring. While most trees looked great with strong, well-calloused graft unions and a single central leader, I found two trees that got overlooked.
    The tree pictured at right was grafted during the spring of 2015.  It is clear that I made at least a couple of trips back to this tree after grafting. A month after grafting, I trimmed the scion down to a single new shoot and attached a bamboo training stick. In mid-summer, I used orange flagging tape tie the new shoot to the bamboo stick. Unfortunately, that was the last time I worked on this tree.
   In response to a summer of plentiful rainfall, this graft kept growing well into August. The new graft out-grew the bamboo support stick and produced  numerous stalked buds near scion's apex. These stalked buds began growing in late summer and created a dense cluster of foliage at the very top of the tree. All of a sudden the tree became "top-heavy" and a strong wind snapped the graft in two.
   To prevent this kind of damage, I should have returned to this tree last August and replaced the small bamboo stake with a longer and stronger stake. Also, I should have made sure to pinch off all stalked buds that kept forming the way into mid-September. For now, I'll leave this tree alone until next spring. When buds start to grow on the scion below the broken stem, I'll chose one new shoot to be my central leader and prune off the broken top.
   The tree pictured at left is a great example of what can happen when you simply- "graft and forget". For some unknown reason, I never revisited this tree after placing a graft on a vigorously-growing, seedling rootstock last April. The scion sprouted one strong shoot from the top bud on the scion (red arrow) and two weaker shoots from the lower bud. The stock tree also sprouted several new shoots from below the graft. Two stump sprouts (yellow arrows) grew so fast they achieved twice the diameter of the scion shoot.
    Next spring, I'll need to prune off all the stump sprouts, trim the scion to a single shoot, and place a strong stake next to the tree to help train the tree. Since the two biggest stump sprouts grew from roughly the same spot but on opposite sides of the trunk, pruning them off will leave two narrow strips of bark on either side of the trunk. Ultimately, these pruning wounds will heal over, but until they do, my pruning efforts will create a weak point in the tree's trunk. Tying the tree to a strong stake should prevent the development of fractures in the trunk.