Friday, February 17, 2012

Identifying pecan trunk injuries

     Today, I enjoyed a late winter walk through our native pecan grove.  In the bright sunshine and without a canopy of leaves, the immense size of pecan trees really struck me.  Many trees are now over 3 feet in diameter and over 100 years old (photo at left).
     As I walked around, I was able to spot some common problems associated with tree trunks. Many of these problems are man-made, the result of pruning trees or mowing the ground cover. Let's take a look.

   A healthy trunk is straight with flared roots at the very base of the tree (photo above). The tree trunk at right has a swollen base that features rough, pebbled bark. This type of trunk is the result of an infestation of wood boring insects that attack a tree already under stress.   The stress is usually water related--either too little water (shallow soils) or too much flooding (high water table). You can tell this tree is in trouble when you look at the tree's crown (photo below).

      The canopy of the tree with a swollen base has several dead limbs and has very narrow crown (photo at left). This tree is not crowded by adjacent trees, it is just simply a tree in decline.  If you are planning a tree thinning operation in your grove, this type of tree should be among the first to be removed.

   Here's an all-too-common trunk problem that I like to call mower blight (photo at right). If you hit a tree trunk with a mower and pop off the bark, you have opened up the tree to wood rotting fungi. The kind of wood rot pictured here took years to develop yet the tree has remained productive. However, there will come a time when advancing decay will make this tree subject to wind throw.  Pecan trees seem to tolerate a lot of abuse but its best to avoid hitting trees with farm equipment.

      A lopsided trunk (photo at left) is usually associated with an old pruning wound. Forty years ago this was a forked tree. At that time, one of the forks was removed to encourage the development of a single trunk.  This tree must have had two fairly large forks at the time of pruning because the crease in the side of the tree is a remnant of the old pruning wound.   However, it seems the pruning was done correctly (pruned on a slant) and the trees remains healthy.

    If the pruning cut to remove a fork in a tree is not preformed correctly,  massive wood rot can occur. Here's an example of a tree fork that was removed with a horizontal cut (photo at right).
The flat surface of the pruning wound held moisture from rainfall and accelerated the rate of fungal wood rot. At this point, the decomposition  of the wood is so advanced that it is proving a place for weeds to grow. Cutting a forked tree to one trunk is a good idea, but the way you make the cut is critical for preserving tree trunk health.