Thursday, July 3, 2014

How pecan branches can tell a story

   I was in the orchard looking at our nut crop when I spotted a group of limbs with a story to tell (photo above).  To the causal observer, this photo may look like a simple collection of leaves, twigs and two nut clusters but let me point out several things and the entire recent history of this pecan tree comes to light.

   I'll start with last year's nut crop. The red arrow points to a dark-grey and dried up twig (photo above). This was the pedicel that held last year's nut crop. You can even see the attachment scars where the nuts were held. In time, this old pedicel will form an abscission layer at the point it connects to the main stem and will fall from the tree. However, simply finding this old pedicel tells me that this tree bore nuts in 2013.

     Once a twig produces a cluster of nuts at the terminal, vegetative growth usually stops for the year. However, weather conditions in 2013 helped to promote a second flush of vegetative growth. If you remember back to last summer, we experienced a dry early summer followed by a wet period beginning in late July. The sudden resupply of soil water encouraged two buds right below the nut cluster to break and grow. In the photo above, yellow arrows point to these second-flush shoots.

   In early April of this year, the second-flush shoots began spring bud-break just like all other one-year-old shoots on the tree. However, on April 15, cold weather froze emerging buds killing all exposed green tissues. In the photo above, the orange arrows point to frozen buds still clinging to the tree. Fortunately, pecan trees are not so easily defeated by a little cold weather. Buds lower on the second-flush shoot were fully dormant at the time of the freeze. These buds survived the cold and grew into this year's new shoots.

   In the photo above, the red arrows point to the shoots that developed after the spring freeze. Since these shoots emerged from primary buds they produced pistillate flowers and have since set nuts (in red circles).      
    In the end, a simple, close inspection of twig growth tells the recent life story of this tree. Weather conditions caused a secondary vegetative flush in 2013 but froze emerging buds in 2014. However, in spite of the weather, this pecan tree produced nuts in 2013 and 2014.