I went out of town for a week. When I left the elm forest was happy as could be. We got back last night and amost of the old leaves ha turned yellow, some with pretty big black spots, and a lot had fallen off. The problem is not under watering. It may have rained a lot before the kid who waters came by so maybe too much water (The yew has mushrooms growing in its bark). The other elms grown from the same batch of seeds are doing fine. One has one leaf that may look like this.

Fungus? Bugs? Neem oil? Something else?

It could be water, but that would be fast. You sure someone has not sprayed it with something?

I can't remember exactly what the substrate is, but it should be half akadama, quarter lava, quarter pumice, and some coffee grounds, about half as much as lava rock. Yes, I know that adds up to more than one. Water seems to drain through adequately. Usually. I water sort of early, but I think he came over late afternoon so maybe there was some stress there. Every other tree is doing fine, so I know he watered.
In Atlanta there was a lot of rain, some would guess there was a lot here, too. There is a lot of new growth so I could just water it adequately and move it out of the sun, but if there is a fungus or bug issue I would like to get it now.

Dunno

I looked at a couple of online sites and every place hinted strongly at root rot. So, I waited until it stopped raining, pulled the whole mass out of the pot gently and water poured out of the root ball, which had grown to fit the pot. The pot is a large oval shape and only had holes at four places close to the edge. There was water standing in the center. Since I don't have anything to put the pot in, and since the root ball had grown out to the edge, I got the drill, drilled two large holes in the center bottom, put a layer of pumice in the bottom, and put the root ball back in the pot, after draining a lot of water out. The weather man predicts I won't have much direct sun for several days, so I think I have done enough for now. Next week I will put some biogold on it.