Looks like a classic case of transplant shock, and sometimes with that it leaves the tree vulnerable to all types of pathogens, and insect pest. That’s why when planting a new tree you don’t want to prune it, or fertilize it until it’s second season. This helps keep all the energy where the tree needs it most, in the roots so that they can get established faster and easier. Now that trees doesn’t look too bad, cut off any dead wood and I’d spray it with Eagle 20 ER, a systemic fungicide, the tree will absorb it and it will help cure the problem, apply two sprayings 10 days apart, after that use a topical fungacide like Deconil every 2-3 weeks, and mix Liquid Seven with both fungicides. Use your finger and push it into the ground next to the tree, as long as the dirt is moist you don’t have to water it, if your finger comes out dry give it a gallon of water, do this a couple times per week, especially if it’s hot, and make sure you mulch the tree well and keep the area around it free of fallen leaves, dead branches weeds and grass.
Good Luck,
Paul