Hmm, after reading different posts, I decided to do a little research for myself.
Kathy is right based off some websites I've checked out - corn festivals happen in August mostly and one I found in mid-September. However, I also doubt the series jumped from August to November between episodes.
My guess? They meant to call it a Harvest festival - that would fall in late October/early November and would also explain how most of the people in Smallville, according to Clark, grow wheat and not corn. Silly Los Angeles-based writers who have no perception whatsoever about farming.
