December 24-28 was one of those freeze events that we knew would come. To some extent, every citrus variety has suffered from cold-damage due to this recent 5-night freeze event. The site of our citrus research plots in Valdosta reached a low of 16 degrees which is the lowest I have recorded since the trials were installed. From December 24-28 low temperatures were 18, 20, 16, 21, & 22 degrees. I am sure other areas in the southern half of Georgia were event colder. When temperatures are that low for that long
there is not much that can be done to protect citrus and damage is to be expected. Hopefully this will help you answer some of the citrus questions you may be getting.
What is happening with cold damaged citrus trees?
It takes time to know the extent of damage that has occurred to citrus trees. Obvious early symptoms of damage are leaf curl and tanned foliage. After a few days many trees begin to shed leaves. Some green foliage that looks ok may also drop. This is actually a good sign because trees and or limbs that are killed by a freeze do not drop leaves. Foliage that turns tan and sticks to the tree indicates the limb or tree has died. It is common to see younger late season growth die back from freezes while order growth on the same tree appears ok.
What do I do now to my damaged trees?
Do not prune citrus trees now. We do not yet know the extent of damage to limbs, branches, and the trunks of trees. By May or June limb damage will be obvious. Wait until then to prune these dead limbs by pruning into the green wood below the dead wood. Any fruit left on trees was frozen and is no longer good. In general, frozen fruit is only good to use as juice but fruit should be juiced within a couple of days after freezing.
How can I protect my trees for the rest of the winter?
Our winter has just begun so it is possible there will be more damaging freezes. With trees already damaged and with much less foliage they will be more susceptible to freezes so things can get worse. Growers with freeze protection should use this if there are more predicted freezes. At this point it is better to be safe than sorry so if there is any question go ahead and freeze protect. The goal of freeze protection is to save as much of the trunk above the graft union as possible at the expense of the rest of the tree during these extreme events. If the graft union is saved the tree will regenerate but a year or two of production will be lost. For homeowners the best option is a heat lamp under a blanket or frost cloth that completely covers the tree to the ground.
What varieties were the most damaged?
From my observations at this point it appears the satsumas have handled the freeze the best. This is expected as they are known for cold-hardiness and that is why many have been planted in Georgia. Lemons, grapefruit, and limes appeared to have the most damage. Everything else is somewhere in between.
The silver lining!
This freeze event will let us know the cold tolerance of many citrus varieties. I have conducted Brix and Acid tests on 30 varieties just around Lowndes county so there are a lot of varieties planted. We will find out which varieties we need to plant and the ones we need to avoid. Also, with the threat of Huanglongbing (HLB) looming all around, these low temperatures will no doubt harm any Asian Citrus Psyllid (ACP) population that may be trying to establish in Georgia. ACP vectors HLB.
Refer to the below publication for more info and some good photos of citrus damage and let me know if you have any questions.
https://edis.ifas.ufl.edu/publication/HS1275