Friday, April 25, 2014

Pecan trees restart growth after frost

    A little rain and some warm temperatures have prompted our pecan trees to resume budbreak (photo at right). This week I've spent a lot of time looking at levels of freeze damage have have come to four conclusions.

   1. Trees that had expanding leaves and exposed catkins on April 15 were hardest hit by the freeze.
   2. Cultivar origin had little impact on severity of cold injury. Worst hit cultivars included Hennings (a far northern cultivar) and Maramec ( a southern pecan).
   3. Frost damage much worse on lower branches.
   4. Frost damage varies widely within a tree; from branch to branch and from bud to bud.

    Let me show you some examples of how our trees are responding to the April 15 freeze.

   The photo above shows three branch terminals all growing from a single larger branch of the USDA clone 64-11-17.  The shoot in the middle appears to be growing normally with no apparent cold injury. The shoot on the right has a green terminal bud but mid-shoot buds look frozen and not greening up. The shoot on the left looks totally damaged by the frost. This is the kind of wide variation in cold injury we are seeing throughout the grove.

The photo at left illustrates the variation we are finding in bud injury on a single shoot. The terminal bud of this Chetopa shoot was fully killed by the freeze. Just below is a vegetative bud that suffered freeze injury to its outer scales but the growing point remained unfrozen. The surviving growing point is now emerging to create new leaves. Other buds on this shoot look to be developing normally while still others appear frozen. Have enough buds survived to produce enough new shoots, pistillate flowers and catkins to produce a decent crop this year? We will be watching closely in the weeks to come.

    Some terminal branches suffered complete freezing of all primary buds like the Jayhawk shoot pictured above. In this case, I am seeing growth emerge from secondary and even tertiary buds. From past experiences with late Spring frosts, we know that only 15% of secondary buds will produce shoots with pistillate flower clusters.  that bad new for this fall's Jayhawk harvest.