Tuesday, April 15, 2014

Freezing temperatures injure emerging pecan buds

  During the pre-dawn hours of April 15th, temperatures dropped to 26 degrees F at the Pecan Experiment Field. At 26 degrees and lower rapidly expanding green pecan tissue is frozen and killed. A few trees had already developed visible catkins and were pushing out the first new leaves on new shoots. These trees were frozen back completely (photo at right). Fortunately, most trees had hardly started to push out new growth and escaped the freezing temperatures with little or no damage.
   To really appreciate the extent of freeze damage we suffered Tuesday morning, I spent some time up in our hydraulic lift to survey bud health.  Let's take a look.
   The first thing I noticed was an amazing degree of variation within a single tree's canopy. Just look at the photo at left. These two branches are growing on the same Greenriver tree and are even attached to each other a few inches below the view of the photo. The branch on the left is fully green and shows no indication of cold injury while the branch on the right was burned by the frost.  Why or how this happened has no easy explanation.
   However, lets look at the kinds of variation I found within the canopies of some other trees to see if we can learn how this weather event will effect the 2014 pecan crop.
    I stopped at the original Chetopa tree to see how the emerging buds looked. Once again, I found everything from healthy green buds to obviously dead buds (photo at right). Fortunately, the number of green buds on the Chetopa tree far outnumbered the damaged buds.
    You can check the condition of your buds by slicing through a bud with a knife or razor blade. Healthy buds will be green while frost killed buds will be black (photo at right).
    When I looked at a random native tree, I found similar variation in frost injury (photo at left). Once again I cut open some buds to check on their viability. However this time I found something fascinating.
     Once again, the healthy buds were green inside while the frozen buds were black. However, look carefully at the bud in the middle of the photo. This bud, like all terminal pecan buds, comes in three parts. The center vegetative bud is flanked by two, catkin-containing sexual buds. In the photo, the sexual buds are black inside, indicating they were killed by the cold. However, the central vegetative bud is still green indicating live tissue. It will be interesting to follow all our tree over the next several weeks to see how the April 15th freeze impacts pecan flowing in May.