Mold On Sub Floor Block
The mold growing on the sub floor framing was caused by
excessive moisture in the crawl space area. This becomes a bigger
problem when the floor insulation is packed tightly in between the floor
joist and snuggly up against the block.
If you look at the subfloor sheathing, you'll notice there is no discoloration or staining, this would eliminate a possibility of water leaking from above floor. This can help us come to a conclusion that the mold on the wood block was caused from excess of moisture in the crawl space, instead of a water leak.
Now the mold growing on the floor joist in the above picture was cause from a water leak above the floor. The arrows are pointing to water stains in the floor sheathing.
Most mold can be killed by using bleach or chlorine but make sure that you read the instructions located on the storage containers of these products before application.