The plant pathogenic fungus Colletotrichum coccodes (Cc) and the plant growth regulator thidiazuron (TDZ) were evaluated in Maryland and Quebec for velvetleaf control in ‘Williams' and ‘Maple Arrow’ soybean. TDZ was applied at 0, 0.1, 0.2, 0.3, and 0.4 kg ai/ha alone or was combined with Cc at 109 spores/m2 when velvetleaf was at the 1- to 2-leaf (Trial 1) or 4- to 6-leaf (Trial 2) growth stages. Velvetleaf control increased with TDZ rate, and TDZ combined with Cc further increased control. TDZ reduced velvetleaf biomass and height, and Cc increased velvetleaf mortality. In Quebec, Cc also reduced the biomass of velvetleaf treated in Trial 1 and interacted positively with TDZ at this growth stage. Cc nearly halved the rates of TDZ required for 90 and 75% mortality of velvetleaf treated at the 1- to 2-leaf and 4- to 6-leaf stages to 0.09 and 0.12 kg/ha, respectively, in Quebec. Cc similarly lowered the rate of TDZ required for 75% stand reduction of velvetleaf in Trial 1 to 0.17 kg/ha in Maryland. Cool wet weather in Quebec contrasted with warm, dry weather in Maryland. Soybean biomass and yield were increased significantly by treatment with TDZ plus Cc in Trial 1 at both locations.