This study measured impact of cool-season crops on seedling emergence, survival, and seed production of weeds common in corn and soybean. Weed dynamics were monitored in permanently marked quadrats in winter wheat, spring wheat, and canola. Three species, green foxtail, yellow foxtail, and common lambsquarters, comprised more than 80% of the weeds observed in the study. Seedling emergence was reduced by winter wheat, but not by spring wheat or canola, when compared with adjacent quadrats without a crop canopy. Approximately 10% of seedlings in spring wheat and canola developed into seed-bearing plants, but no seed-bearing plants were present in winter wheat at harvest. Common lambsquarters produced more than 1,100 seeds/plant, whereas a foxtail plant produced 85 seeds, averaged across spring wheat and canola. At harvest, new seedlings were present in all crops; thus, control after harvest will be required to prevent seed production in the fall. Winter wheat may provide an opportunity to disrupt population dynamics of weeds common in corn and soybean without requiring herbicides.