In this area, crawl spaces are pretty popular, and so is mold, regrettably. In the new homes that I have built, it's pretty common to find that the floor joists are thickly coated with mold as soon as the house is weather tight. The issues is that the mold is in the wood, and the moisture content of the area is consistently above 50%. In the past I have used a respirator and safety glasses while saturating the joists with straight bleach, applied with a pump sprayer. For some reason, Clorox brand is a lot more effective than store brands. At that point I run a dehumidifier, full time, until the moisture drops below 50%. Then I run the unit 10-12 hours a day, using a plug in timer, as long as the moisture level remains below the required level.
Couple of things I learned over time. This will only work if you manage the incoming moisture. I build on sealed, vent free crawl spaces. If you have a leaky basement wall, open venting, or other issues, a dehumidifier is only going to make noise and give you a bigger electric bill, not solve the problem. Dehumidifiers can be irritatingly noisy, and consume a lot of power. I use a timer to prevent them from running during sleep hours. A cheap indoor/outdoor weather station is a great tool. Get one that shows temp and humidity, and put the remote in the basement or crawl space. Then you can read the temp. and moisture without having to go downstairs, or crawl into a crawl space. Finally, modern dehumidifiers are shit. I'm learning that they often last a few years, then simply quit. They still run but it appears that the compressor fails, and it isn't worth fixing.