Herbicide-resistant waterhemp continues to spread and is problematic for many North Dakota soybean farmers. Waterhemp will germinate throughout the growing season, which means obtaining a crop canopy is an important part of waterhemp management. Iron deficiency chlorosis (IDC) is an agronomic problem that can delay canopy closure in many soybean fields in North Dakota, which can also prolong the window for waterhemp germination in fields that have IDC issues. Oats can be inter-seeded into soybeans to help alleviate IDC symptoms. Fall seeded cereal rye can suppress early-season flushes of waterhemp, but spring-seeded oats have not been evaluated for waterhemp suppression. This project will look at the early-season companion crop suppression capabilities of a spring-seeded oat cover crop, as well as the role the oat companion crop can play in late season waterhemp management due to quicker canopy closure of soybeans not stressed by IDC.