Chinese Elm Trees dropping green leaves
Long post with a lot of detail. Any help or insight would be appreciated. Some background. I am a landscape architect, so know a few things about trees, but am by no means an arborist. We have been in our house for about 5 years, and are in the process of renovating the front yard, so in the pictures, you will see that this past weekend, I cropped the grass short, added some sand to the low areas. We also had a ficus tree that had die back from the winter. (third time in five years, so I had it taken out). That will explain some of the pictures for you detectives out there.
I am concerned about the elm trees growing in my front yard. We have a mature elm that is about 40' tall and maybe as wide in the canopy, planted right in the center of our lawn. This past fall, we planted two new 24" box elms, 'truegreen'. They seemed to leaf out later than the older one this spring, but eventually did, and looked good.
About 3 weeks ago, we had been doing some work on the pool in the back yard, and i inadvertently left the filter on "backwash", which drains to our front yard. Overnight, it put half our pool in the front yard (10,000 gallons). Our yard used to get flood irrigation, so it didn't go anywhere. About a 4 days later, one of the small elms started dropping its leaves. This elm was at the backflow discharge, and the low point in the yard, where most of the water pooled.
It would drop its leaves while green. They seem to separate easily from the twigs and branches, still dark green and looking perfectly normal. Maybe about 3-5% of the leaves had a touch of yellow, or a brown spot, but very few. In general, they still looked as green as the other tree, but blew off in the slightest breeze. I assumed I had drowned it. I turned off the irrigation in the lawn area for about 1 week, and watched the tree. At 7-9 days, it eventually lost all of its leaves, but the twigs and branches were still flexible. There were green buds, and some new leaves came on. Relieved, I noted to turn the irrigation back on in that area in a couple days. I also investigated a little further, and noticed that the tree had been planted to deeply (crown was about 6-8" below the soil). (Yes, I should have caught that, but we are also talking about the same guy who left the pool on backwash). Anyway, concerned that this was part of the problem, and that it would reoccur, I decided to raise it while it was still stressed out.
At the end of the week (now 1 1/2 weeks since the pool water fiasco) I turned back on the irrigation. A couple days later, while in the yard, I noticed that the other small elm started dropping its green leaves. Same symptoms. Stayed green, dropped with the slightest touch or breeze. The pool water had only come right up to this tree, it was not completely submerged. I probed the soil, and it was hard, not fully getting a screwdriver in the ground. I extended the run time on the tree drips (my set-up: each small tree has two tree bubblers with drip emitters, and a soaker hose in a filter fabric wrap that is buried at the tree drip line)
Now, it is three weeks later.
The first small tree has been raised up to grade. It has new leaves on about 5% of its branches. They do not fall off in my hand.
The second small elm has almost lost all of its leaves. No new ones seen yet. I checked its crown, which was right at the soil line.
Now, the large elm appears to be droppings leaves. This may be coincidence, the heat, I am not sure. Its leaves do not fall off by touching them. There are just a scattering of leaves on the yard. They are yellow tinted.
About the pool water, as a part of our renovation, I had it 'closed', and its chlorine was near or at 0, but it did have high TDS since it was pretty old pool water.
Thoughts? Did I drown the first, but the second and third were heat and too little water (irrigation off)? Did I dump a bunch of salts in the yard? Were all three heat stressed, but the one planted to deeply showed the stress first?
I posted a picture of the first small tree. Below is a link to see all of the tree photos.
Any help would be appreciated.