• In the U.S., citrus trees are primarily found in California, Florida and Texas.Jupiterimages/Photos.com/Getty Images
  
  Bark diseases can be bacterial, viral and fungal. If they infect a citrus tree's bark, the tree may not be able to produce fruit and may even die. If you are unsure if your tree has a disease, you may consider having a lab test the tree to diagnose any potential disease.
  
  

Citrus Phytophthora Gummosis

• Orange trees are susceptible to Citrus Phytophthora Gummosis, which is an extremely contagious fungal infection. When an orange tree is afflicted with the disease the tree bark cracks and seeps sap, which makes it look as if the bark is bleeding. Eventually the cracks in the bark will spread around the tree, which will split the bark and weaken the tree until it falls. Other signs an orange tree is affected by this disease include decreased foliage that is yellow and a water-soaked soil line at the foot of the tree featuring black or red bark.
  
  

Psorosis

• Psorosis is also called scaly bark disease, and according to the Texas Agricultural Extension Service it is the most serious viral disease a mature orange tree can face. Psorosis spreads through seeds as well as buds afflicted with the virus. This disease is most likely to be found in tangerine trees and sweet orange trees. When psorosis sets in, tree bark scales and over time the tree produces less and less fruit, until it is completely unproductive.
  
  

Exocortis

• Also called "scaly butt," exocortis creates large cracks in tree bark, which eventually forces the tree to split. This virus is only found in old trees, and symptoms include yellow blotches on tree leaves and the shelling of small pieces of bark. According to the University of California, exocortis damage is only found around the root crown of a citrus tree.