It is called white mold. White mold comes when you have poor ventilation, and moisture. Do you have good thick plastic on the ground throughout your crawl space. Do you have enough vents, and are they all open and working properly. You can google white mold, for more information.

Thanks for the response. Most of the crawl space is dirt covered by plastic. There is a small area - maybe 20'x20' that has a concrete floor and is not covered by plastic. That is where most of the white mold is growing.

I am assuming that maybe moisture is coming up through the concrete.