Appling scored 16 points, followed by Gary Harris with 12, Adreian Payne 11 and Derrick Nix 10. Nix also had six assists for Michigan State (24-7, 13-5 Big Ten).
The third-seeded Spartans will enjoy a first-round bye at the upcoming Big Ten Conference tournament.
The Wildcats (13-18, 4-14 Big Ten) were paced by Kale Abrahamson with 16 points.
Alex Marcotullio also reached double figures with 11 for 11th-seeded Northwestern.