Certified GKH Gardening Expert
It is heavily infected with, either, a fungus or bacteria.
The heavy watering has made the soil the perfect breeding ground for the infection. A fungicide would have been in order, as well as much less watering.
At this point, the disease has taken over, and the death of the tree should be expected.
At this time, you will need to remove the tree, treat the area with fungicides, or solarize the area before planting again.
Here are some articles that will help:
Make sure that the soil has plenty of time to dry out between waterings, thoroughly, at least down to 3 or 4 inches.
This article will help you to measure soil moisture: