The Colorado defense has been a strength of the team during Bud Black’s tenure, but the manager acknowledged ahead of the final home series of the first half of the season that the Rockies’ glovework could use some work. That was evident again Wednesday night, when a misplay on a flyball by Ian Desmond — coupled with a quiet night by the Colorado offense — sent the Rockies to a 4-2 defeat and two-game sweep at the hands of the Houston Astros at Coors Field. “It’s frustrating,” Desmond said after the game.