First time here, thanks for your advice!

Planted 6 foot tree in May. Recently had 3 inches of rain over several days and it's taken a few more days for the water to drain off the surface. I've watered the tree well every 7-10 days during the, up to this point, very dry and very hot summer (Nebraska) and it was doing fine. I even planted it a few inches above grade since I have clay--I've done this for my ash, pear, and serviceberry as well.

The tree's leaves are turning a light brown all of a sudden, and all over. Is it dieng? Should I try to aerate? Is it iron deficiency? If it loses leaves early will it not have enough energy for winter root growth? Ideas? Thank you!!