My squash, zucchini, acorn squash are all doing poorly. They are in a very sunny area. I am watering them, and put mulch on the beds about two weeks ago. The leaves are full of a white powder. I have harvested 3 zucchini and one small green round squash. I have harvested 2 cucumbers. The squash grows a tad and then begins to shrivel. I have an organic garden so I do not use pesticides.
You have powdery mildew on your squash and zucchini. Here is a CSU extension sheet that will give you the information on what to do next for your organic garden. As a first step, dispose of all affected leaves and stems with white powder and bag for the trash. Do not compost!
Squash from the plants will not be affected by the powdery mildew, so you can feel safe to eat those as they ripen.