Todd wrote:

Ok, I plan to cover the dirt in my crawlspace with plastic, as a
temporary measure to reduce humidity down there. Yes, I realize that
this is not a permanent fix, and yes, I realize that I need to address
the source of the moisture problem.

Here is my question: Do I need to treat the dirt with a chemical spray
first, before laying plastic? If so, what chemical? I am thinking
that if mold/mildew is a potential problem, that something nasty could
happen to the dirt if it is cozy in plastic for the winter. Opinions
please...

Todd

Most crawl spaces are dirt. But, the standard is to cover
the dirt with 4-6 mil plastic. And no, it is not a
temporary fix, it is essentially permanent. The plastic
does not deteriorate in the dark. The dirt isn't normally
treated and there is no reason to do so. Mold and/or mildew
under the plastic is of no importance. When you put down
the plastic you overlap the edges about 15 inches, Do Not
Seal. If water should enter the crawl space, it will drain
out through the overlaps.

Opinions aren't worth much, or rather, you are likely to
receive some rather strange ideas. I suggest that you take
a look at current building codes in your city or county.
Not that you have to follow the code, but the codes will
tell you what the standards are.