Citrus Cicatrix

 Question:

I have a very large, old and beautiful orange tree that has developed a fungus on the trunk. I’m looking for help in how I can treat the tree and prolong its life. As you can see, the bark is peeling and there is orange sap oozing out. What can I do?

Tear in tree, from both rat damage and possible sunburn. 

Rat damage scars. 

Answer:

Looks like rat damage, as well as some sunburn. Try painting the trunk and lower limbs with whitewash made of 50% water and 50% indoor white latex paint. 
In nature Citrus rely on their thick canopy of leaves to shade their relatively sun-sensitive bark.  If you trim a citrus tree too hard and too frequently it can develop a black sunburn on its trunk and larger branches. If you want to keep your citrus looking like a tree (it grows best when kept as a large, shrub like tree with its canopy going down to the ground), then it is a good idea to whitewash the trunk and larger branches. This protects them from sunburn and to some degree from insect infestation and rat damage.  Rats and other animals that might partake of the tree's thin bark (either to eat the sugary layer of vascular tissue underneath the bark or to sharpen their teeth) are discouraged by the layer of paint. The best paint to use is a 50-50 mix of water and white latex interior paint (interior latex paint is less likely than exterior latex paint to be loaded with preservatives).