do I need a reservation in September after labor day, or does it change to first come first serve

Most of the time you need reservations in s 9 months in advance

Reservations at Ponderosa State Park are always recommended. If you are committed to staying after Labor Day, you still may not get a space since it fills up quickly.

They have sites that are available without reservations but are first come first serve

That I couldn't tell you, I would contact the Park now before it's too late, that Will answer your question to