I misspelled the tree, it is a butternut hickory. 

Tree decline usually can't be reversed, unfortunately, and it is often may years in the making by the time symptoms become evident. If you had a certified arborist assess the tree in person, their diagnosis is more thorough than ours from a photo, so we defer to their evaluation. Missing or shedding bark tends to indicate a serious problem or prior trunk damage on tree species that don't have peeling bark as a normal feature (a couple hickory species do, but not this one). Wood decay likely already set in to the wood underneath the bark damage, and this cannot be treated or reversed.

While pruning to remove dead or dying branches is usually recommended and a good practice, in the case of an entire tree canopy declining, it might not be worth the expense or effort. If the tree's eventual death doesn't risk damaging any property or harming people, then leaving it standing can provide great wildlife value (so can retaining the downed branches and trunk, or at least the wood chippings, if you have the space). Otherwise, at some point, it will need to be removed for safety. An arborist with training in hazard tree assessment should be able to make an educated guess of how at-risk if is for falling on its own or in a storm, and therefore how urgent removal may (or may not) be.

Yellow Nutsedge can be challenging to eradicate. If you wish to avoid herbicides (prudent, given their location), you'll need to manually remove any nutsedge clumps that are present. If you can't get the roots out and they resprout, keep removing all regrowth as promptly as possible to exhaust the weed's energy supply, and eventually it will starve and die out. Using mulch or a dense groundcover planting over any exposed soil will help to deter future weed seeds from germinating, but perennial weeds already established won't be suppressed much by either method.

Miri