Big yellow spot on squash plant as well. Is this from overhead watering at night?
White Spots on My Cucumber Plants
Certified GKH Gardening Expert
Are the spots powdery in nature or bleached out looking? It could be attributed to either powdery mildew or from water spots associated with overhead watering or splashing of the leaves. Limiting overhead watering will help with these water spots. The powdery mildew can be treated with neem oil, which is an effective and safe fungicide. It will also guard against many insect pests. Here is more information: https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm