Prices for seasonal food products fall at demand peaks. Price declines are not driven by falling agricultural input prices; indeed, farm to retail margins narrow sharply. I use electronic scanner data from a sample of US supermarkets to show that seasonal price declines are closely linked to market concentration, and are much larger in markets with several rivals than where a single brand dominates. Seasonal demand increases reduce the effective costs of informative advertising, and increased informative advertising by retailers and manufacturers in turn may allow for increased market information and greater price sensitivity on the part of buyers.