I agree with what Tim Duncan had to say but will add my thoughts below.
Molds are fungi, but they are not decay fungi. Molds can be an early warning sign of moisture problems in the wood. Mold fungi attack the readily utilizable material such as starches and sugars and mostly affect the appearance and permeability of the wood. Most molds occur at or near the surface of the wood and are usually shallow enough to come off with planing.
Most sources indicate that a wood moisture content of at least 20% is required for mold fungus to grow on wood. Some have reported, however, that molds can occur even as low as 18% MC.
In my opinion, lumber manufacturers use their inline moisture meters to insure that their kiln dried dimension lumber meets the grade specifications for moisture content. (That is, the meter, as Tim points out, can set an upper limit to operate a tipple or spray wet lumber.) For lumber represented as KD 19 that means the moisture content should not exceed 19%. Pine lumber dried to meet the KD 19 specification and is at or below 19% MC should not readily mold.
If the pine lumber was high temperature dried to meet the KD 19 requirement it’s surface should be well below the moisture content at which mold will develop. Of course lumber can pick up moisture, even after it has been kiln dried, if placed in a humid environment, and it is possible for the wood moisture content to gain enough moisture to reach 19% if exposed to air which has a relative humidity of about 85% or above (or if it is placed in the rain). Hence mold can occur in kiln dried lumber if it is stored in excessively humid conditions long enough.
I invite southern yellow pine producers to contact me to discuss their mold issues.