Check out this article from Building Science Corporation regarding humidity control in high performance dwellings in the south.

As a rule, keeping interior relative humidity below 60% is recommended. When relative humidity levels reach 70% or higher mold and other biological growth can occur.

Including a dehumidifier in your HVAC system can ensure higher air quality and comfort while reducing the risk of mold and other biological contaminants.

Link to article below:

https://www.buildingscience.com/documents/confpapers/cp-9302-humidity-control-in-the-humid-south/view