What Causes the Bark Around the Bottom of an Orange Tree to Split?

Foot Rot

• The bark around the bottom of an orange tree splits when it is infected by Phytophthora foot rot (Phytophthora gummosis). This fungal disease is caused by two microorganisms that live within the soil surrounding an orange tree: Phytophthora parasitica and P. citrophthora. Symptoms of the problem are discovered at or below the soil line, first displayed by a cracking of the bark and the presence of a gummy, oozing substance.

Symptoms

• Upon brushing away soil, the bottom bark of the orange tree will be slimy and waterlogged with a reddish-brown color that eventually progresses to black as the disease worsens. The injured bark is easy to pull away, and later stages of the infection will result in yellowing and defoliation of the leaves. As the foot rot girdles, or strangles, the roots of the specimen, the orange tree will eventually lose all vigor and die.

Brown Rot

• The disease also transfers to the fruit of the tree, usually during warm and wet seasons in spring and fall. This period of the disease is referred to as brown rot because of the brown spots that develop on the fruit. Orange trees planted in dry, desert conditions are likely to see the disease display only on the lower bark and root system, while upper sections of the tree and fruit are most likely to be affected in humid, wet locales like Florida.

Management

• Excessive irrigation lends itself to the development of Phytophthora foot rot, and orange trees should be planted deeply enough in a hole to allow for proper drainage. Trees that stand in water are most susceptible to this disease. Several fungicides are available to help manage Phytophthora and should be applied to the soil, trunk and crown of orange trees with splitting bark around the bottom. The fungicide can be applied to young trees as a preventative measure.