Monday, January 14, 2013

Cold weather and pecans

    We woke up this morning to a world covered with frost and ice. The temperature had plunged down to 10 degrees F (-12 C) and the trees still had a sheen of ice covering their branches from a storm that passed through the area Saturday (photo above). If you look carefully at the photo of native pecan trees above,  you can see where these trees were broken off in the December 2007 ice storm and have now developed a profusion new nut bearing branches.

    The cold temperatures we experienced this morning made me stop and remember the times when we have seen cold injury even on "northern" pecan trees. Cold injury on the cultivars we have under test does not appear until temperatures drop below -15 degrees F (-26 C). A couple of years ago, temperatures fell to -17 F (-27 C) in mid-winter. Shortly after that freeze, I cut twigs from both the Pawnee and Lakota cultivars (photo at right). I used my knife to cut into the stem and reveal the health of the inner bark and the cambium. Lakota was not injured (light green inner bark) while Pawnee suffered cold injury (brown inner bark).  Fortunately, the amount of injury that occurred in Pawnee did not prevent our Pawnee trees from bearing a crop the following summer.
    Back in 1989, temperatures in late December dropped to -27 F (-33 C). At those low temperatures, most trees suffered cold damage. During the fall of 1990, we harvested only 120 Lbs/acre (10% of normal) from our native pecan plots. Of all the cultivars we had under test at that time, Major, Peruque, and Colby were the only trees to produce a decent crop. Most cultivars and many native trees showed some terminal dieback while the more southern cultivars, such as Maramec and Mohawk, had major limb loss or were frozen all the way back to the ground.