put a pic in a reply to this post .. also include location ... ken

Thought I posted pic...central OKLA

Yes, that´'s a little too much to just be harmless lichen. That tree is probably rotting from the inside and dying

Looks like dried slime flux (aka bacterial wetwood) and that is an indication of a bacterial heart rot.

It is definitely not lichen!!

Looks like Irpex lacteus, a parasitic fungus of hardwoods. It's a disease of sapwood, rotting trees from the outside (sapwood) in. An educated arborist can determine the extent of the disease and how dangerous the tree. But there are no cures, just preventative measures.

Besides leaves falling, have any branches been breaking?

Irpex lacteus

But there are white cructose lichens, too. Another reason to have an expert's eyeballs look at it.