Mar 11, 2022 | Written by Lenny Wells
After a couple of weeks of 80 degree temperatures we are facing low temperatures in the mid 20s this weekend. Forecasts call for temps anywhere from 25 degrees to 28 degrees from middle Georgia down to Valdosta. Temps further north in the Athens area may get down to 23 degrees. What does this mean for pecan trees?
The good news is that we have not seen much bud break yet. We only see a very small percentage of buds even swelling at this point. I have had a few photos sent my way of some buds just beginning to break. The first sign that pecan buds are beginning to expand is a bud stage that is termed outer scale split. This stage is characterized by the outer covering (or scale) that surrounds a dormant bud splitting open when the bud inside starts to expand. Eventually the outer scale is pushed off the end of the bud to reveal a tight green bud underneath. Dormant pecan buds can easily handle 24 degrees but green pecan tissues freeze at around 26 degrees. On most trees, pecan bud development has not yet advanced to a stage that I would be overly concerned about.
If you have buds that have started to elongate, especially if they have pushed the outer scale off completely, even if the green buds are still somewhat compressed tightly, they could still be at risk of damage if temps get down to 26 degrees. But we haven’t seen many trees at this stage yet.
The only trees I have seen with foliage expansion to date are trees in nurseries. Usually these are the first to break bud. Seedlings usually start first and then some early grafted varieties begin.
Whether its in the orchard or nursery, any foliage that has expanded will likely take a hit if we see temps in the 26-28 degree range for a few hours. Fortunately as I said, we havent seen much expanded foliage yet and much of what we have seen has been on nursery trees or newly planted trees. Even if you have foliage expanding in this situation and it gets killed by the freeze, that foliage will regrow as long as the wood is not damaged.
Damage to the pecan wood is of some concern for nursery trees and moreso for newly planted orchard trees and those in the 1-3 yr old range. The most common injury on such trees occurs when the sun warms tree bark during the day and then the bark rapidly cools after sunset. These abrupt fluctuations are most common on south or southwest sides of trunks and branches, and they may kill the inner bark in those areas. Young and/or thin-barked trees are most susceptible to this type of injury especially as the sap begins to flow. Injury may not be visible initially and often shows up a few days to weeks later and will be detected by a browning of the cambium layer as you cut into the bark of the tree. Healthy cambium tissue will appear green. Sometimes the injured area of the trunk takes on a sunken or water soaked appearance. Trunk protectors will help minimize this type of injury on young orchard trees.
Rapid expansion and contraction of water within the wood and bark, particularly under falling night temperatures, can also sometimes result in cracks that may appear on trunks of young trees and also on the branches of older trees. These may be a few inches long and are often found on the southwest side of the tree. These cracks may heal over a little in the summer and can re-open again in winter.
When we have freeze injury to young trees, it sometimes is not detected for a considerable length of time, sometimes 2-3 years, as there is often enough healthy cambium to keep the trees going to a point and then they outgrow the cambium they have left, which can no longer support them, causing the trees to collapse. When this occurs the foliage usually turns brown and the tree may die suddenly. This usually shows up in May or June as the heat and water demand ramp up.
Overall, I expect damage to be minimal , if any to mature pecan trees. We will likely see some injury to young (newly planted-3 yr) trees in some areas if temperatures drop as low as we see forecast and they remain there for several hours.