Moyes will bid to claim his first piece of silverware as United boss at Wembley after being appointed successor to the hugely-successful Sir Alex Ferguson at the end of last season.
The Latics will head for the national stadium as huge underdogs and Perch is not expecting the Premier League champions to treat the contest as a friendly.
"It's going to be a difficult game because it's David Moyes' first competitive game in charge of Man United and for a club like that it's always important that they win trophies," the summer signing told Wigan's official website.
"I'm sure he and his team aren't going to want to pass the Community Shield by, they're going to want to win it as much as we do.
"They're a very good side and they're not going to just take this as a friendly game and certainly neither are we."
Moyes has had a difficult pre-season with unconvincing results in friendlies, the continued speculation about Wayne Rooney's future and the failure to persuade Barcelona to part with Cesc Fabregas.
In contrast, Latics have strengthened their squad with nine new recruits this summer and started their Sky Bet Championship campaign by thrashing Barnsley 4-0 on Saturday.
Perch added: "We've got off to a good start in the league and it's a chance to use that as a positive ahead of Sunday.
"We want to take the way we played on Saturday into the game against Man United but we know it's going to be a tough one, which means we really do have to be at our best."