Experts and BHG readers answer.
white spots on squash leaves
The white spots are probably powdery mildew, which is typical in humid climates. The plants need good air circulation and a full day of direct sun to be healthy. Yellow leaves indicate stress due to drought or too much water. Allow the top inch of the soil to become dry before you water again. The powdery mildew won't kill your plant, but it does stress it a bit. If you have several plants, make sure there is a foot or two of open space around them for the air to circulate--that may mean that you'll have to remove a plant or two to help the others.