This is definitely Powdery Mildew. In my experience, powdery mildew tends to be more of a cosmetic problem than anything. It is certainly far less aggressive than other diseases/fungal problems. Plants typically survive a long time with the disease and continue to grow and send out new leaves. Fruits are typically unaffected and grow mostly normally. My zucchini suffer from this disease in mid to late summer every year, later spreading it to my cucumbers, but I rarely bother even attempting to treat it as they all survive to a killing frost and produce scads of fruit even with the disease.
In my opinion, 'organic' controls do not work that well for many diseases. Prevention is more key, and can be done by using resistant varieties of plants, keeping them well spaced and with good air circulation, avoiding over-fertilizing, and using pre-emptive applications of fungicide, organic or otherwise. Hand picking of infected leaves may help with minor infestations. Baking soda + some dish soap in water is also supposed to help with prevention if applied periodically throughout the season.
It's obviously too late for you to prevent it now. You are unlikely to be able to get it to go away once it has appeared, although you may be able to control it or help to limit its spread. If you do wish to try to fight it, you may try copper fungicides, neem oil spray, or a milk solution.
please provide pictures. From a distance and close up. That helps. Also, are they in a patch with others? What do the others look like over 9 years ago.