By mold I assume you mean powdery mildew, an extremely common mid- to late-season problem with any type of cucurbits (squashes, pumpkins, melons, cukes, etc.). It is often prompted by warm, moist, low light conditions and crowding or poor air circulation is often a contributing factor as well. Although there are many different types of PM, most specific to certain types of plants, few are considered to be much more than a cosmetic issue. One exception is the strain which infects the squashes and their relatives -- this can be fatal to the plants.

A proactive approach - treating before the symptoms appear - is generally considered the most effective. This should include good cultural controls as well as fungicidal treatments, organic or otherwise.

Here is a link that might be useful: powdery mildew on squashes

Here is a link to organic control of Powdery Mildew.

Here is a link that might be useful: Organic control of PM