These citrus leaves are showing symptoms of cold injury. This tree is part of a study at the Sandhill REC in Columbia looking at 9 varieties of citrus that are believed to have improved cold tolerance.
So far this winter, we have seen 16 nights with below-freezing temperatures, the coldest of which reached 15.1°F. That is more than cold enough to severely damage many types of citrus.
The foliar damage seen here is not particularly concerning. However, we will monitor the trees closely over the next 5-6 months to see if there is any lasting damage from the cold.. Read more on hgic.clemson.edu