Info from InBev source: all Budweiser products are made from rice. all Busch products are made from corn. Busch was originally produced with the idea that it would be marketed as a premium product but was priced below the price of Bud when first marketed. It surprisingly sold so well as a cheaper alternative than Bud that AB decided to market it as a cheaper beer. But it was developed as a higher end beer and remains the only beer that is made from corn in the Budweiser family.