Wednesday, April 21, 2021

Late Spring Frost Damages Pecan Trees

     A strong cold front pushed its way across Kansas on Tuesday April 20. We even saw light snow showers during the daylight hours. But as nightfall approached the sky cleared off and temperatures started to drop. During the early morning hours of Wednesday temperatures hovered around 28 degree F (-2 C) for at least 4 hours. Emerging pecan shoots can withstand light sub-freezing temperatures but 28 degrees seems to be the critical temperature for damage to begin. I took the photo you see above on the afternoon of April 21st.  Two adjacent Kanza shoots can be seen, one damaged by the cold (shoot on left) and one perfectly healthy (shoot on right). This one photo typifies the kind of damage I have seen following this cold weather event. The amount of damage is quite variable and I have no easy explanation for why some shoots were injured while other not. 

    Several new shoots appeared burned by the frost as pictured at left. I've seen this type of frost damage following spring freezes in years past. The outer leaves of the emerging shoot are damaged and will never fully expand to form a normal functional leaf. However, the health of the shoot's growing point is what actually determines if this frost damaged terminal will be able to set a pistillate flower cluster.

   I pulled back the outer leaves of the new shoot and found healthy green tissue at the growing point (photo at right).  What looks like terrible damage today will most likely not impact the yield potential of the shoot.

    For young and recently transplanted pecan trees the amount of freeze damage seems consistently worst. Temperatures are typically colder closer to the ground during cold, clear nights. If you were planning of grafting any young stock this spring, I recommend waiting until you see new green shoots develop on rootstock trees before sharpening your grafting knife.