Powdery Mildew! A sure sign that summer is transitioning to autumn. (& I'm not ready for this, but I do like the fall season.) Some humid days and cool nights we've had aren't helping.
Innocent enough looking at this stage, but don't be fooled. It will spread rapidly to the favorite host plants in the garden. For me that is the delicata squash, cucumbers, and eventually the zucchini (the zucchini variety I'm growing this is supposed to be PM tolerant, though).
So what to do? In my live and let live garden where the squash and cucumbers ramble out of their beds and across walkways, I did jump in the tangle with the snippers and opened up the walkway. This should improve air flow around the plants. I also snipped & removed some of the leaves with PM or other injuries to improve air flow within the plant (these don't go into the compost either). Then I mixed up a water and baking soda mixture (sometimes a little dish soap to help it stick) and sprayed many of the leaves. The baking soda apparently changes the pH level on the surface of the leaves enough to discourage PM.
But then it rained... so I'll check up on them today.
All I try to do is hold it at bay long enough to keep the plant reasonably happy and comfortable until the last of their days and the end of the harvest. If it gets really bad, I remove the plant. Not willing to start spraying anything stronger than baking soda. By then, we're ready to move on to eating something else anyway!