It looks like sun scald or transplant shock to me. It could be due to the high temperatures we had. Make sure the tree has good wood mulch around it (never rock) to keep the moisture in and keep the roots cool. If there is rock around it, the rock can heat up enough to damage the roots. But there is also a fine line between not enough water and too much. Watering with a sprinkler system will not give a newly planted tree enough water at all. You should be watering with a slow hose trickle for several hours a few times a week. Just keep checking to make sure the tree also doesn't get too waterlogged though. Hopefully, it will start to come out of this soon.