First of all, I think it is an Elm tree. Can someone confirm?
This is my first year in this house and I notice the elm tree in my backyard has leaves+barks+branches falling in the middle of the summer. The leaves become yellowish as shown on the pictures below.
At first, I thought it caught the Dutch Elm Disease, but I didn't see any symptoms of 2mm diameter holes drilled through the bark. See close-up pictures below.
Then, I thought it was a drought issue. So I tried to dig up a tree ring and noticed there were 1 or 2 girdling roots around the bottom of the trunk. I removed them and put some mulch, but still it didn't help much.
