Citrus trees are sensitive to sun and have natural defenses against it. They grow medium- and low-laying branches to shade their trunks during the hottest parts of the day. Sometimes homeowners cut lower branches off a tree--to open a pathway or prevent damage to a home, for example. In Arizona, it is essential to whitewash the cut area and any exposed spaces to prevent the trees' trunks from burning in the hot desert sun.
Mix together 1 part white latex paint and one part water in a bucket.
Paint the whitewash over the effected area of the tree's trunk, and the stubs where branches were cut away.
Inspect the tree to ensure the exposed area is covered. Inspect again during the time of day when that part of the tree is exposed to direct sunlight. Cover any areas that you missed.