Bedard had been on the disabled list since June 29 with a sprained left knee. The lefty has been impressive this season, going 4-6 with a 3.00 ERA.
Cust, a 10-year veteran, struggled this year with Seattle, hitting .213 (48-for-225) with 15 doubles, three home runs and 23 RBIs in 67 games. The designated hitter was second on the team with 87 strikeouts. The Mariners have 10 days to trade, release or reassign him to the Minor Leagues.
Seattle manager Eric Wedge said that while Cust made the effort every day and continued to try to improve, it was simply time.
"He was a class act and a pro. He was good in the clubhouse, was a good teammate and a hard worker, but he just really wasn't able to get it going for us this year," Wedge said.
Wedge said that Cust "didn't say much" and took it "like a pro" when he was told he was being designated.
"It was not a lack of effort or dedication or focus, because he was in it each and every day," Wedge said. "He just wasn't able to get it going."
Bedard, 32, has been even better as of late. In his last eight starts before he was put on the DL, Bedard went 3-2 with a 1.72 ERA. With this Sunday's 1 p.m. PT non-waiver Trade Deadline approaching, and Bedard's one-year contract up after this season, several teams have reportedly been interested in trading for the left-hander, and teams are expected to have scouts watching him Friday night at Safeco Field.
In terms of what he expects from Bedard in his first outing since June 27, Wedge isn't exactly sure, but hopes that his starter doesn't try to do too much.
"The only time you get in trouble is when you try to do more than what you're capable of doing," Wedge said. "I just want him to give us a chance at winning the ballgame, whether that's five, six or seven innings. Obviously, we're not going to extend him pitch-count wise, but get him hopefully deep enough in the ballgame to give us a chance to win."
Taylor Soper is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.