It's a prospect carousel in the Cubs system today.

In addition to the big promotion of shortstop Starlin Castro from Double-A Tennessee to the big leagues, the organization also promoted righthander Andrew Cashner to Triple-A Iowa and third baseman Josh Vitters to Double-A.

Cashner, 23, dominated the Southern League and leaves the circuit with a 2.75 ERA, 42 strikeouts and 13 walks in 36 innings. He'll join righthander Jay Jackson to give Iowa one of the best one-two punches in any starting rotation in the Pacific Coast League.

Vitters, 20, hit .291/.350/.445 for Daytona in the high Class A Florida State League. He's not going to have a Kevin Youkilis approach at the plate, but Vitters has drawn eight walks in 28 games this year; last year it took him 71 games to get eight free passes.

The Cubs also moved 23-year-old second baseman Ryan Flaherty from Double-A down to Daytona. Flaherty struggled with Tennessee, hitting .183/.286/.254 in 23 games. Flaherty had been splitting time at second base with Tony Thomas, and the move should get Thomas more regular playing time at second. Thomas, 23, is off to a .288/.439/.423 start with the Smokies through 19 games.