Saturday, April 21, 2018

Freeze injury to pecan buds

Kanza buds, 20 June 2018
    On Monday morning, April 16th, a strong cold front ushered in some very cold temperatures. We recorded 24 degrees F (-4 C) just after sun rise. Dormant pecan buds can easily handle 24 degrees but green pecan tissues freeze at around 26 degrees. Pecan bud development had not advanced much by April 16 but after the freeze many buds seemed to remain in a state of suspended animation (photo at above, right).

Kanza buds, 20 June 2018
     I decided to cut open some buds to see if I could spot cold injury (photo at right). Healthy buds should appear bright green. These buds darkened with dark brown streaks, sure sign of cold injury.

Kanza buds, 20 April 2018
     I cut open some more buds and found some were still green while others were black. It seems that this Spring's cold injury will vary widely both withing the canopy of a tree and between cultivars. One thing is certain, the 2018 pecan crop will be reduced.

    I looked at several cultivars and found shoots with damaged buds (no signs of further buds enlargement)  and shoots with nice green buds. The photo at left shows two shoots cut from the same Faith tree. The shoot on the left has emerging pecan buds that are plump and green. The shoot on the right has buds that look almost shriveled and have failed to "green-up" since the freeze. This kind of variation in damage seems very common among several pecan cultivars.
      I was encouraged to find that the two buds I cut open from Hark shoots looked healthy and not damaged (photo at right).
    We have suffered through late spring frosts in previous years with each episode causing different amounts of crop loss depending on the stage of bud development when the frost hit and the health of the trees. Back in 2014, we saw significant bud injury but the trees were able to produce pistillate flowers from buds lower down on the shoot. Come this May, I'll be evaluating pecan cultivars for their ability to produce female flowers following this freeze.
    Although I don't know the full impact this year's Spring freeze will have on nut production, I do know that the start of the Spring grafting season will be pushed back at least a week. I always like to see active green growth on my stock trees before I start grafting.