The cold weather we’ve been fearing for a couple of weeks since it became apparent that some pecan trees would break bud really early will arrive this week. Forecasted temperatures for Wednesday night (March 15)/Thursday morning (March 16) are from 27-30 degrees as you move south from the Ft. Valley area toward Valdosta. Areas north of Macon such as Madison are expected to dip into the mid to low 20s.
So, what effects should we expect for pecan from the return of below freezing temperatures? Those areas with forecasts for 30 degrees or more should be ok. Other areas that reach temperatures of 28 degrees or less could see damage to any foliage that may already be out. Fortunately, there is very little of this. I have seen and heard of a little sporadic budbreak here and there—mostly on newly planted or very young trees. Those on which the outer scale has split and you just see a little green peeking through or the buds are just swollen should be ok. But, any new growth that has started to lengthen and expand will be most susceptible if temperatures stay at 28 degrees or less for a few hours.
Most mature trees still have buds closed or are barely showing some green (most of this is deep into south Georgia). Those trees on which the buds are still closed should be fine. The level of damage a tree receives in this type of situation is completely dependent upon its level of dormancy.
Developing foliage exposed to 28 degrees or less for several hours (usually 3 hours or more) will be burnt off by the freeze. The trees will bud out again but that will probably wipe out any crop on a mature tree for the year. Since there are not many trees out this far yet, we should be ok. Even those on which we see budbreak only have a small percentage of the shoots breaking bud, so this will help.
The biggest danger will come in the form of cold injury, mostly to younger trees. This damage is usually expressed as longitudinal bark splitting, separation of bark from wood, and sunken areas on trunks, browning of the cambium (the normally bright green tissue normally observed just under the surface of the bark when scraping with a pocket knife), and sparse canopy development. Much of this may not be readily obvious until temperatures heat up in May/June and the water demand increases. The freezing temperatures destroy the cambium cells and the tree then can’t get the water and nutrients it needs. Sometimes the trees may have enough healthy tissue to keep it going for a year or more before it collapses. The more dormant the tree is, the less susceptible it will be. If the sap is rising, there is a risk for cold injury. Trees in low elevation areas will be most susceptible. Any damaged trees will then become more attractive and susceptible to ambrosia beetles, so be vigilant for these as well.