Cubs president Theo Epstein said Thursday that Josh Vitters and Brett Jackson will open 2013 at Triple-A Iowa. The Cubs are unlikely to be competitive in the National League Central next season, so they'll keep their top prospects marinating down on the farm. Vitters, a 23-year-old third baseman, batted .121/.193/.202 in his first 36 major leagues games this summer. Jackson, a 24-year-old outfielder, hit .175/.303/.342.