Trunk problems on orange trees are more rare than pest problems and tree diseases, but that doesn't mean a trunk problem won't cause harm to your backyard orange tree. Both fungi and weather cause trunk diseases. To keep your orange tree healthy, choose a variety that's zoned for your area and plant it in well-draining soil, then provide protection from winter frost.
Sun scald occurs when winter days are sunny and warm, then drop to freezing at night. The warm weather activates cells in the tree's trunk; freezing temperatures at night kill these cells. The bark may change color and fall off the tree, exposing dead tissue underneath.
To guard against sun scald, paint the citrus tree trunk with white latex paint or cover the entire trunk using breathable tree wrap. The University of Tennessee cautions against painting trees under two years old and against using exterior-grade latex paint, as this may damage the tree. Gardeners can also create a soil bank to bury the tree trunk, providing insulation as well as protection from sun scald.
Freeze damage occurs when gardeners fail to protect their citrus tree during the winter. Bark on the trunk and on limbs appears to loosen from the tree and can fall off. Some orange trees display cold cankers that ooze sap; this can be mistaken for gummosis.
To prevent freeze damage, bury the tree trunk in a soil bank or cover the orange tree with burlap. You can also wrap Christmas lights around the branches and trunk of the tree and turn them on during cold nights or provide a small space heater during frost periods.
Gummosis often occurs in weak and injured trees and is purportedly infectious. Salt damage, a high water table and freeze damage can invite the Phytophthora fungus, which causes gummosis. Affected trees get blisters which ooze gum; the wood below turns pinkish-orange in color. Over time the bark dries out, cracks and falls off. Orange trees that develop gummosis eventually die as the sores encircle the trunk and choke the tree. According to Jacksonville University, there is no reliable cure for affected trees so gardeners should focus on preventing other trees from contracting this disease.