If you find that it has spread to other plants, try a foliage spray of 10% baking soda and water. If things don't improve, then the next step would be to spray the soil with a 5% bleach and water solution, but you have to rinse with plain water the next day. This will kill the fungus or mold that is attacking your crop.

You may want to add another vent fan if you keep having this happen in the future. Temps above 80 and RH above 60% promotes fungus, mold, and mildew.
Hope this helps.