Neem is a pretty effective fungicide but it does depend on the fungal organism as to how successful it might be and when it is applied. Like most fungicides, neem is only preventative, not curative.

Remove all the weeds from around the base of the tree...that will help. Is the wood there soft or still firm?

Has someone been weedeating around the trunk of that tree?

That looks like bacterial canker, not a fungus.
If it is, that low on the trunk, it's a goner, and even higher, it's very difficult to eradicate. Here is UC Davis' view:

http://ipm.ucanr.edu/PMG/r602101011.html

Carla in Sac