If you decide to fertilize you might consider using 1/2 strength or 1/2 the usual amount. Or better yet, fertilize with organic fertilizer or compost. I would definitely water if it has not rained weekly. I would mulch several inches deep and all the way out to the drip line, but not up against the trunk of the tree (leave a few inches circle around). It sounds like it was stressed and should recover if it is planted in an area that usually has favorable conditions for it (sun? shade? drainage?). I have a new dogwood, and I don't think I watered it enough last year when it was newly planted. I thought it was a goner but it bloomed this year.
Also make sure your tree is not being bumped or hit with a mower or string trimmer. That kills lots of trees.
Laurie

Thanks so much. I haven't mulched or fertilized this year but plan to at least fertilize. Mulch seems to be a lot of money and I have a lot of garden. I could just mulch around the tree to help it. This year it has rained so much it was quite unseasonal. So last year, being a really hot summer, I obviously didn't water it enough last year. I will help it along this year and hope for a good comeback next year. I only fear that it is too late for it. ???

You might be able to get free tree trimmings that have gone through a chipper shredder from your town, local energy company (they have to trim trees from powerlines) or a tree service company. They will not be as polished looking as the bagged type, but they will serve the same purpose.

Goodluck!

I also have a willow that is suffering--I think it dries out too much. I moved some of them to a lower spot in my yard and they do better there it seems.

If you are having the same heat wave we are, I'd give it a bit of extra water and hope for the best. I tend to avoid fertilizing when plants are stressed unless I can identify a nutrient deficiency. Are the only new leaves turning yellow (chlorosis)? Only old leaves (nitrogen deficiency) or all the leaves in one location of the tree?