My Orange Tree Trunk Is Rotting

Foot Rot

• Foot rot, so named because of its proximity to the "foot" of the orange tree at ground level, is a product of the Phytophthora fungus. A soil-borne disease, Phytophthora foot rot may extend upward to the trunk or downward into the root system where it produces root rot. On the trunk of the orange tree, symptoms of foot rot first display as water-logged lesions on the bark in a series of irregular spots, which may be accompanied by an oozing of sap.

Damage

• As the disease progresses, orange tree bark begins to dry, crack and drop away, displaying a diseased, stained wood underneath. Scar tissue may form around the diseased area in an attempt to limit the spread of the fungus. Because of the damage to the trunk, the flow of water and nutrition to the canopy is limited, producing a lack of vigor in leaf and fruit growth, dieback of twigs and premature defoliation. In especially severe cases of foot rot, fruit may also prematurely drop.

Foot Rot Prevention

• The Phytophthora fungus normally enters the tree via wounds in the bark, so gardeners should go to great lengths to ensure that they are careful when moving around the tree. Foot rot infections initiate during periods of humid, rainy weather and when standing water surrounds the tree or inundates the soil. Orange trees that are planted on beds that are slightly raised to encourage water runoff enjoy a reduced likelihood of being attacked by foot rot.

Management

• Encouraging the circulation of air at ground level helps to dry the lower section of an orange tree trunk and prevent the disease. Mulch should never be piled against the trunk as the mulch retains moisture and offers an easy pathway from the soil to the tree for the fungus. Specimens already infected with foot rot can be treated by the scraping away of diseased bark to expose healthy wood, which should be followed by an application of copper paint. Fungicides are also available to help prevent and manage foot rot of an orange tree.