WASHINGTON -- Rockies manager Jim Tracy says right-hander Aaron Cook "realizes the fact that he has to pitch better."
Cook is 0-4 with a 5.82 ERA in six appearances. He broke a finger in spring training and missed the season's first two months.
Tracy says Sunday that Cook will start Colorado's fourth game after the All-Star break. The second-half rotation will begin with Ubaldo Jimenez on Thursday, followed by Juan Nicasio, Jhoulys Chacin, Cook and Jason Hammel.
Tracy wants to split up the rookie Nicasio and the struggling Cook, so the bullpen won't get heavy workloads in consecutive games.
Tracy says Cook "needs to get the ball down" and his "sinker can't go side-to-side across the plate, it has to go down toward the plate."