Back to June 2020

The Woe of Winter in the Heat of the Summer

Leaf burn from this year's late April freeze found on a pecan tree; notice that the growing tip of the terminal bud is undamaged. (Photo by Charles Rohla)

Once again, growers in the Central region were ready to start another pecan season. The producers were prepared to put the previous season in the past and forget about the low prices they received for this last crop that did not live up to their earlier hopes and expectations. The 2020 season started earlier than usual. Trees began to bud out one to two weeks ahead of schedule with higher than normal temperatures and good weather. However, it seems that not everything can be so perfect.

Mother Nature has a way to spoil a good thing; temperatures in Ardmore, Oklahoma reached 91 degrees Fahrenheit on April 8, and then one week later, on April 15, temperatures plummeted to below freezing. At this stage, several pecan trees had already budded out, with a number of them exhibiting significant growth. Typically, pecans will survive at 28 degrees Fahrenheit with little to no damage, but in those low-lying areas where temperatures dropped below that, growers have reported various degrees of damage. Not all growers in the area saw injury, but those along the Red River, both in Oklahoma and Texas, reported some damage. Areas west of Ardmore seem to be the hardest hit.

Damaged by the 2019 Halloween freeze, this pecan tree forces buds out along the trunk. These new shoots are above the graft. (Photos by Charles Rohla)

For the grower that had damage from the late spring freeze, there is still some hope to salvage the year. With the timing of the freeze, some trees still had dormant buds that had not forced yet, meaning that there is still a chance for some of these buds to produce catkins and flowers. Some of the natives and later cultivars had not yet broke bud, so they should be fine. It also appears that this event was a radiation freeze, meaning that it was colder closer to the ground with warmer air higher in the atmosphere. In the orchards at the Noble Research Institute, LLC, we did not see as much damage in the upper portion of the older mature trees as we observed in the lower portion. Our orchard with smaller, younger trees saw even more damage. In our younger improved orchards, we also notice a cultivar effect from the freeze. The ‘Pawnee’ and ‘Kanza’ had a little leaf burn but not enough to cause significant concern; however, the new shoots and leaves of the ‘Choctaw,’ ‘Oconee,’ and ‘Maramec’ sustained greater damage in the same orchard. This difference in sustained damage may be from the fact that these cultivars have southern parentage, compared to the northern parentage of ‘Pawnee’ and ‘Kanza.’

Some growers also see a different type of freeze damage. They have trees that are not budding out as normal. Other growers are seeing substantial injury in their trees, and some even have trees that have completely died back. This freeze damage was not from this year’s late freeze; it was caused by the freeze that we had last year in late October. What became known as the Halloween freeze dropped temperatures below freezing on two consecutive nights. This freeze event occurred across areas of Oklahoma, Texas, and New Mexico. Temperatures in some areas dropped below freezing; particular locations in the Southwest reported temperatures as low as 17 degrees F. In most places, pecans were already opening from their shucks and were not damaged by the freeze. In some locations, though, trees that had later maturing nuts had pecans frozen in the shucks, causing them to be sticktights and unmarketable. Growers in the West reported significantly more damage that resulted in higher amounts of sticktights. The Halloween freeze did some damage to last year’s crop, but now we can see its full effects.

Trees damaged by the 2019 Halloween freeze have buds forcing out at the soil line. These new shoots are below the graft and will need to be regrafted.(Photo by Charles Rohla)

If you recall, most of us had good growing conditions in late summer and throughout the fall with above-average rainfall and warm temperatures. These conditions allowed the trees to continue growing longer than usual, with some trees putting on late secondary growth flushes. This longer growing period resulted in trees that were actively growing instead of shutting down for winter when the freeze occurred. With these growing conditions, the pecan sap remained active, and when a freeze occurs like this one, it can kill the live wood, bark, and cambium tissue. Certain cultivars like ‘Barton,’ ‘Wichita,’ and ‘Mahan’ are more freeze susceptible than others. Trees that are bearing a large crop may be more stressed and, therefore, more susceptible to freeze. This reason is why we are seeing more damage to some trees this spring.

Some producers have asked how to determine the amount of damage to the tree. You can check the tree to see how far down the tree the damage occurred by cutting through the bark with a knife to expose the cambium. If the cambium is green, it is fine and healthy, but if it is brown or has brown streaks, the cambium is dead or damaged. Trees will produce new shoots below the freeze damage and from the ground line. If the damage is back to the trunk, the tertiary buds will take a while to force, so be patient to see what will grow. Growers that have trees that were damaged back to just above the graft will have to be diligent in controlling the suckers that will emerge from the trunk. They will need to allow the shoots that are growing above the graft to continue to grow in order to regrow the trees. With older trees that have a good root system, the emerging shoots will grow fast, and producers may have to cut them back to control their height or stake them up. This action will prevent the wind from breaking them. Also, if you have trees that have been damaged, do not apply fertilizer to them this spring, thinking that you can get them to grow faster. Forcing growth during recovery can cause the regrowth to blow out or grow back weaker.

Author Photo

Charles Rohla

Rohla is Manager of the Center of Pecan and Specialty Agriculture at the Noble Research Institute, Ardmore, Oklahoma.