The soil aspect and worrying about contractors washing off tools is going down the wrong road. That's how construction is everywhere. Over or under-watering or lack of transplanting care is the first place to look for issues with new plants.

I agree with yard - it’s the handling/planting methods used, perhaps watering too soon or the plant was somehow otherwise compromised.

@Yardvaark, I guess I should have mentioned those (watering and transplanting) were the first two issues we addressed. We spoke to two master gardeners in our area about the issue, and they suggested a soil analysis.

FWIW, these agaves came from the home of my perfectionist sister. The agaves were in perfect condition when we planted them, then boom, within 2 days they started looking droopy, developing white patches and also yellowing on the outer leaves. Foxtail agaves are everywhere in our neighborhood (both in yards and in patches of no man's land). No one I know waters them or gives them a second thought and yet they thrive somehow.

When people are stumped, or think they are, they start looking elsewhere, often speculating and pointlessly grasping at straws. Master gardeners are only making guesses, trying to compare, usually, a partial history with various possibilities. They're not looking at anything under a microscope. analyzing samples in a spectrometer or actually doing any scientific tests.

I don't believe either MG claimed to be soil analysts or own microscopes. They listened carefully to our transplant story, asked about watering, and then concluded (separately, as they don't know each other) that we might consider a soil analysis as there was (is) quite a lot of stucco chunks, etc. in the dirt.

There is a nonprofit in our area that does low-cost soil analysis, so I guess we'll try that.

Cheers.

"I don't believe either MG claimed to be soil analysts or own microscopes"

A reasonable assumption :-) Their MG training would be only superficial in that regard and it would be rare to have extensive horticultural training in addition to the MG program.

But there really isn't anything in the discarded construction materials you list that would necessarily contaminate the soil unless it was all concentrated in a single, small area. And even that would be a temporary thing at best.

I too would focus on the watering and the soil.......and not what might have been washed into the soil but how heavy it is and how well it drains. In fact, sharp, fast drainage would be my primary focus.

And that's all I'm pointing out ... that MG are not doing scientific study. They're speculating on causes. And I'm not faulting them for this. I'm just saying don't expect a scientific revelation to come out of it.

Low cost soil analysis is going to be looking for the common nutrients, not analyzing for toxins for a court case. Having stucco chunks in the yard is like having rocks. It's not going to mean anything. As Gardengal said, looking at the native soil structure (ability to drain) would be more valuable.