Tuesday, May 27, 2014

Winter kill of pecan trees

    Although the winter of 2013-2014 didn't set any records for low temperatures in our area, we did drop down to cold enough temperatures to cause some obvious winter kill. The photo at right shows two Shoshoni trees. The tree on the left has leaved out normally while the tree on the right has only few new shoots growing  on the lower trunk and a few low branches (see close up photo below). This mostly dead Shoshoni tree is a perfect example of an alternate-bearing cultivar that lost winter cold-hardiness following an "on" crop year. A heavy crop pulls massive amounts of plant nutrients out of tree stems in an effort to fill nut kernel. The following winter, depleted branches are less able to withstand cold winter temperatures. Following a heavy crop, cold damage can occur even at moderately cold temperatures (<-10 F).
   The photo at left shows the few green shoots produced by our heavily damaged Shoshoni tree. With the massive amounts of limb loss sustained by this tree it would take 5-7 years for this tree to recover its canopy. In the past, Shoshoni has proven to be a difficult cultivar to manage and trying to help this tree recover is probably not worth the effort. We'll be making only one more pruning cut on this tree--at ground level!

    I've seen one other type of cold injury this Spring. Again the damage occurred on the cultivar, Shoshoni, but this time the damage is not crop load related. The photo at right shows a Shoshoni tree with several large limbs killed by winter cold. It wasn't until I closely inspected the structure of this tree that I discover why only a portion of the tree's canopy was killed during the winter.

 The photo at left reveals that this Shoshoni tree suffered major limb loss during the ice storm of December 2007. Broken limbs were pruned off leaving large branch stubs. New shoots then sprouted out from these branch stubs and grew at an extremely rapid rate. Rapidly growing shoots remain active and full of sap late into the fall. This delay in the normal hardening-off process before the start of winter only leads to a reduction in cold hardiness. The side of this Shoshoni tree that did not break in the ice storm, suffered no winter injury.
  We will be pruning the dead limbs out of this tree. After pruning, this tree will have enough canopy left to support a partial nut crop this fall.