Answer: I hope I'm wrong - but white spots usually indicates a fungal disease called powdery mildew. It can attack plants when daytime temperatures are high and nights are cool. Or, if the plants are getting too much shade, are overcrowded or there's poor air circulation. Once a plant is infected, it is a difficult disease to control. I'd pinch off any leaves with white spots in hopes of at least slowing the spread of the disease. I'm glad the calcium spray helped your plants produce squashes. I only hope pinching off the affected leaves will allow your plant to develop more squash! Best wishes with your zucchini!
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