How can I remove residue

[Droidess]

Hello Leps,

I have a dozen milkweed plants that apparently have been sprayed with some type
of pesticide or fertilizer that make the plants poisonous to my Monarch larvae.
I have heard people refer to something called an "alcohol wash" and I am
wondering if this process would remove the toxins from my plants. Does anyone
know about this "wash" and how to do it? Is there any other process that I can
use to remove this residue? I have lost two dozen larvae already trying to find
an answer and I don't want to subject a third batch to the same problem.

Thanks, B.J.Reed