How do I save this willow tree?

[Andelin]

I have had this tree in my yard for 20 years and love it. But it's not doing good. I've made a circle of mulch under the my many trees in the yard but that one. Now the base is gnarly (see pics), and I suspect it may be why the tree is suffering. It seems that the bark at the base is in such bad shape, it would be impossible to remove the grass too. The foliage is sparse, falling early, and you can see how different the overall foliage looks on the pic compared to the other willow to its left. What can I do to save it or is it too late and I'll have to cut it down?
Thanks ahead for any advice.

 

[derwoodii]

A few question to help us diagnose.

?has the decline in tree canopy been one or over more seasons.
?have you used any herbicide for lawn eg to control broad leaf weed and feed type turf applications.
?has there been any vehicle traffic excavation eg drainage irrigation laid that may have impacted roots.
?are their other willows near by? how are they doing,, ,edit oh wait you do and its ok
any thing else you can add

 

[Andelin]

Hi, thanks for asking!
The tree canopy has been getting worse over the past 2 years, maybe 3, it used to be full.
No herbicides, only lawn fertilizer on lawn twice in the season.
No vehicle traffic excavation. No irrigation work.
Yes, you did see the other willow, looking good.

That's all my hb and I can think about. Do you think we should try to clean that base (not sure how with the gnarly bark/grass embedded) and make a mulch circle around it?

 

[Raintree]

Was the wire basket removed when tree was planted? It's about the size when the root ball starts to press through the cage.
How is it that no herbicide is used and not a single weed to be seen in the lawn?

 

[Andelin]

"Was the wire basket removed when tree was planted? It's about the size when the root ball starts to press through the cage."
Since he planted the tree himself, my hb said he'd removed any wire so I trust that's the case even though it was over 20 years ago.

How is it that no herbicide is used and not a single weed to be seen in the lawn?
He said he uses lawn fertilizer, which, I guess, includes some weed killer since we don't have them.