So my place recently flooded and over the last 2 weeks I have been running a dehumidifier constantly to dry it out. I decided to pull off some of the drywall and have a looksee and found what you see in the picture growing inside. How should I handle this? Is just spraying it with fungicide/bleach and patching up the holes with new drywall ok or should I absolutely replace all infected drywall?
My experience with drywall is that once it gets flooded, you need to replace it. Framing lumber can be dried, and it seems to be fine after bleach treatment. Smooth hard surfaces such as formica or plastic also treat fine with bleach. In some jurisdictions, you are not required to replace the wiring if it passes inspection. Ditto for the plumbing. But drywall and insulation, that is usually a total loss.
Drywall is one of those materials that when it gets wet, it needs to be removed. It is expendable. The time it takes to dry it out to a point where it won't support mold growth is longer than the time it takes mold to grow. In about 72 hours a mold colony can form from spores in the right temperature conditions. In most cases it takes longer than that to dry out drywall. In your case the mold has already established itself and the clean up will be more labor intensive the the removal and replacement. Go at least 12" past the farthest sign of mold. Make sure the framing behind the drywall is thoroughly dried and doesn't show signs of mold before you close it back up.