Friday, January 13, 2017

Branch growth pattern: Gauging the potential for native pecan productivity

    Recently, I took a short drive down the gravel roads in the Neosho River bottom to take a look at native pecan trees in mid-winter.  I passed native groves that have had a history of intensive management and then further down the road I came across groves that receive minimal or no inputs during previous growing seasons.  As I studied the canopies of native trees on this cold clear day, I noted striking differences in branch structure between well-managed and un-managed trees (photos below).

    The first tree I stopped at was located in a well manage native grove. What I mean by well managed is that this native stand has received fertilizer applications, both Fall and Spring, for well over 15 years. The grove is also sprayed regularly to control pests and the ground cover is both grazed and mowed. Choosing a tree at random within this grove, I looked upwards and photographed a portion of the tree’s canopy (above right).  Immediately, I noticed the numerous shucks that still hung from the branches. This tree produced a good crop of native nuts in 2016. But, I also noticed a vigorous branching pattern. The twigs within the canopy were long, thick, and light grey in color. This healthy growth pattern can only be appreciated after being compared to the branches of an un-managed native pecan tree.

    Down the road, I came to one of those native pecan groves that suffer from a lack of attention. If the trees in the grove look to be producing a few nuts, the orchard gets mowed and raked just before the harvesters come in to collect a meager crop of nuts. This grove has been starved of soil nutrients but is occasionally sprayed for pecan weevil control.  Again I picked a tree at random and took a photo of the tree’s branch structure (above left).  There was little evidence that this tree produced a nut crop in 2016.  The tree had short, thin branches that appeared dark in color. In comparing the canopies of managed and un-managed trees, it is almost hard to believe they are both the same tree species.

    After taking the photographs of tree branch structure, I used a pole pruner to cut a sample of twig growth from both trees (photo above). In the photo, the two dark twigs to the left of the ruler came from the un-managed grove. To the right of the ruler, I set down a single light-colored twig from the well managed grove. The reason I photographed two twigs from the un-managed grove is to give you some idea how poorly this tree bore nuts. Of the four terminals pictured from the un-managed tree, only one terminal had a pedicel attached indicating the formation of a nut cluster. Based on the size of the nut attachment scars on this one pedicel, I guarantee that all the nuts in this cluster were aborted by mid-season due to scab infection. In comparison, the branch from the well-managed tree displayed prominent pedicels on both terminals.  This twig had borne two nut clusters in 2016.

But the twigs pictured above have an even greater story to tell.  Note the diameter of the shoot growth. Un-managed twigs are thin and spindly. The twig cut from the managed tree has shoots that are longer and thicker. And here’s why this all matters. I can look at the branches of any native tree and predict its future productivity.  Branch growth is a reflection of total tree vigor. Vigorous thick shoots indicate that the tree will have the internal reserves to produce an abundant pistillate flower crop in the Spring.  Short, small-diameter twigs may produce a lot of catkins but female flowers will few in number.

   If you are still grumbling about a poor crop in 2016, take the time to go out and look at your trees this winter. If you don’t see vigorous branch growth, your native grove is not on the path of good annual nut production.  To increase annual nut production your first step should be to apply enough nitrogen fertilizer to stimulate the growth of strong, thick twigs. If the grove has been un-managed for several years, it will take several years of annual fertilizer applications (both Fall and Spring) to see a response from large native trees. Eventually, you’ll see better shoot growth and subsequently much better nut production.