What is wrong with my Cleveland Pear Tree?

I have a baby cleveland pear tree that we planted beginning of spring. Now its leaves have all withered and turned black. The branches of the tree are still green and soft, so i don't think it has died. I have sprayed it with fungus spray but its not helping. I have a year warranty on the tree and want to figure out what is wrong with it before the warranty goes out. We water it 2 to 3 times a week with a tree ring around it to hold in the water. Any ideas?