You don't necessarily have to remove it...just kill it. Get a saw and cut through the trunk of the ivy near the base. Paint it with glycophosphate where you cut it.

Ivy is evergreen...walnut is not. Glycophosphate only is absorbed through leaves and injured bark. In the fall after the walnut sheds it's leaves, spray all the surviving ivy with glycophosphate.

Dealing with the fungus is harder...there are systemic fungicides, but they are expensive and don't work great.

Thanks for the response. In the area where the bark peeled off with the vines the wood behind this area was dry and soft and full of black beetles and other crawling insects. I didn't see any termites but didn't thoroughly inspect. I guessing first step will be to flood the tree with systemic fungicide/insecticide. Should I remove more of the bark to expose more of those areas or leave it alone. How much Bark does the tree need to survive? It's around 4-5ft diameter.

Do NOT remove the bar. If even a thin strip of bark all around the tree is peeled off, the tree is killed. The tree sends nutrients up the tree through the bark. The first step is to kill all the ivy.

First step is to kill the ivy...that's the easy part. Next step is to call a certified arborist. You can expect crawling insects to hide underneath anything that wraps the tree, but the wood shouldn't be at all soft. You need to figure out exactly what is going on.

If you cut the ivy stems at the base of the tree, the cut stems are all that you need to apply a herbicide to - the severed top growth will die naturally. And rather than glyphosate (RoundUp), I'd suggest you treat the cut stems with something a bit stronger, like triclopyr (Bayer's Brush Killer). Once the top growth dies, you can pull it off the tree gently.......the rootlets should begin to release on their own. This is a very common practice in my region, where English ivy is a majorly aggressive invasive species and inhabits all manner of trees in tended and untended areas.

Because ivy is evergreen and quite dense when established, it has an ability to trap and retain moisture against the tree bark - that can cause the bark to rot and fall of in places and can make portions of the tree a bit soft and mushy. Trees can lose large chunks of bark generally without issue. You just want to avoid stripping it off completely around the trunk circumference. Getting the ivy removed and letting things dry out properly is likely all you need to do!

to repeat .. cut ivy near ground ... apply killer to cut ONLY ... leave ivy there for a year or two ... and let it rot away its clinging tendrils ... then it will come of easily ...

once very few weeks.. go look and see if new shoots are there.. if so ... cut those and drip on some more killer ...

once leafless ... you will be able to see the tree better ...

tress die in slow motion ... if in fact yours is dying .. there is no real hurry for you to do much of anything in the next few days.. or weeks ...

perhaps in a month of so.. you can get us some pix and we can better see what is going on ..

but the usual suggestions would be an onsite inspection by a local certified tree surgeon .. not some dude with a chain saw ...

if healthy.. trees heal themselves thru encapsulation .. there is no need for you to do anything in that regard.. and in fact.. most things peeps dream up.. are contrary to ma nature ... e.g. no painting of the wood .. it traps in moisture ...etc

ken