You will probably get more expert advice than mine but some of the wite patches are lichens. They may be a result of poor health but I don't think they cause poor health.

White stuff is lichen. Not a problem for the tree.

But tree looks like planted too deep.
Tree has dead wood, including stubs which should be removed.
Fruit is damaged by, I think, scale.
General overall health is very poor. Likely been going on for years.

A response on your other thread suggested citrus canker. Follow that advice.

http://forums.gardenweb.com/forums/load/citrus/msg0813325818878.html?1

Here is a link that might be useful: other thread

I also need to know the treatment to that it's a

I also need to know the treatment to that it's a