Squash & cucumbers are tender leaf plants, they need the morning dew to evaporate quickly not sit on the leaf all day. Good morning sun is very important to help stop white spotty mold. If the plants are over crowded, not only is it hard to walk down the row for plant care or harvesting but the air & sun cannot dry the leaves which helps cause spotty mold. The same is true for container gardening you need good plant spacing. Baking soda & water is good to help get rid of white spotty mold or there are products available to treat mold.