Squash Plants turning yellow
If you are willing to sacrifice a plant, check and make sure that the roots are healthy and growing.
If you are not willing to sacrifice a plant, then we can assume the yellowing is mostly weather related. Once the soil get going digesting organic matter, the yellowing on the new leaves should diminish. In other words, the new foliage will be more green than the old foliage.
You can speed the recover and growth of the plants by applying a more readily available sourse of nitrogen, such as fish emulsion.
Danny McGrath, OSU Extension