Insulating your floor causes summer condensation on the bottom of your floor because the insulated floor is cooler than the dew point of the air in the crawlspace. Mold grows when high humidity is there for more than a couple days. Wet below the plastic is normal and indicates the vapor retarder is working. To save heat and stop high moisture crawlspaces, close the vents and insulate the walls with 2" of foil faced foam. If the relative humidity is +60%, dehumidify during the summer. This saves heat and gets rid of odors.