When we returned from vacation in early August during the stretch of 100+ temperatures, I noticed one of our cedar elms was under stress. The leaves were gray green with brown spots; some were yellow and many were dropping. Figuring the heat was the culprit, I soaked the tree for several days at a time over the next few weeks. In Sept, the tree dropped piles of buds and flowers (2 healthy cedar elms may have contributed also). Since then, the remaining leaves seem to be hanging on, but have brown veins and spots and the green color is dull. I should also say that this tree is next to a driveway and patio so about 1/4 the drip line area is under concrete.

Do I need to be concerned about a disease that may attack my other two trees? Was this due to drought or something else? (The trees have been thriving for almost 10 years.)

Cedar Elms drop their leaves every fall.

Yes, but it lost about half its leaves about 3 months before the other ones. I just wanted to know if this one possibly had a disease. Although it didn't (couldn't) recover its color, it seems to be holding on to the remaining leaves.

Are you able to do anything to improve the areas that are not concrete? I think it's definitely a problem for the roots to be under that much concrete, so my next thought (if it were my tree) is whether there is anything to be done to improve the soil and the health of the tree through the soil that is available to it.