On the morning of Wednesday, April 15, 2020, many growers woke up to less than optimum temperatures for actively growing pecan trees. Temperatures ranged from 27 to 31 degrees in south-central Oklahoma. Observed damage across the region varied as well, not only due to temperatures, but also due to pecan variety (see “Noble farms damage report” later in this article for examples).
So what can growers who received damage expect? Have they totally lost this year’s crop? Even if the freeze killed the “initial” shoot growth in the lower canopy, there is a good chance that the upper canopy was not severely damaged and will set a crop. It is just difficult to see how much damage there is 60 feet up in the tree.
Additionally, you must remember that the lower canopy may set a “second chance” crop on many of the limbs. Let me explain. Remember how a pecan flowers, male flowers (catkins) on last year’s growth and female flowers (nut cluster) on current season’s shoot growth. Current season’s growth occurs on only the distal tip of last year’s terminal growth. The buds located on the basal half of the limb stay dormant. So at the time of this freeze, a lot of the primary buds at the tip of the limb had already forced, meaning the catkins and shoots were already showing. So this early shoot growth may have been killed in some orchards.
For a healthy pecan tree, some of the dormant buds can produce a new shoot and produce a second set of female flowers. Because this freeze occurred early in the season, many of the primary buds on last year’s growth have not forced, so there should still be adequate catkins produced for pollination of these later female flowers. Most of the primary buds in the top of the tree should have escaped damage and should produce pollen. Additionally, some of the native trees are just breaking bud and should have a full catkin crop, so pollination of damaged trees shouldn’t be an issue.
So even though the lower canopy received a good nut thinning due to the freeze, a healthy pecan tree should still produce a few nuts in the lower canopy and a good crop in the upper canopy.
Figure 1. Leaf damage on Kanza pecan.
At the orchards on Noble Research Institute’s Conrad-McMillan Pecan Farm, located in Marshall County, damage in Pawnee and Kanza was generally limited to leaf damage (Figure 1). Both of these varieties have a northern pecan parent in their background. However, varieties with all southern pecan lineage, such as Maramec, Oconee, and Nacono, suffered damage to leaves, catkins and the occasional terminal bud (Figure 2).
Figure 2. Oconee suffered damage to the leaves, some catkins and the terminal bud.
In contrast, pecans located at our orchard at the Red River Ranch in Love County had more extensive freeze damage in improved varieties compared to native trees. Foliage on improved varieties such as Western (Figure 3) was more advanced and suffered some leaf damage. Typically, native pecans break bud later in the spring than improved varieties, which in this instance allowed the native trees to escape most of the freeze damage (Figure 4). Observed damage was also influenced by tree size. Trees at the Conrad-McMillan orchard are young and generally less than 30 feet tall, while trees at the Red River orchard are much older and more than twice as tall. During a radiation freeze, the air is coldest near the orchard floor and temperature increases as you move up the canopy of the tree. So the greatest damage occurs in the lower canopy and lessens as you approach the top of the tree.
Figure 3. Improved varieties such as Western had more advanced foliage than some of the native trees.
While the Noble orchards managed to escape any major damage, not all growers were as lucky. We have received reports of more extensive damage as you travel west along the Red River. Additionally, there was more extensive damage reported by a grower in Garvin County.
Figure 4. Native tree that was just breaking bud at the time of the freeze.