Field experiments were performed in 2016 and 2017 in Missouri to determine whether interactions exist between PRE herbicides and seed treatments in soybean. The experiments consisted of a randomized complete block design with factorial arrangements of varieties, seed treatments, and herbicides. We selected two genetically similar varieties of soybean, one with known tolerance to PPO-inhibiting herbicides and one with known sensitivity. Each variety of seed received three separate seed treatment mixtures (STMs): (1) STM1, imidacloprid plus prothioconazol + penflufen +metalaxyl plus metalaxyl plus Bacillus subtilis + B. pumilis, (2) STM2, Pasteuria nishizawae plus thiamethoxam plus prothioconazol + penflufen +metalaxyl plus metalaxyl plus B. subtilis + B. pumilis, and (3) STM3, fluopyram plus imidacloprid plus prothioconazol + penflufen +metalaxyl plus metalaxyl plus B. subtilis + B. pumilis. Chlorimuron-ethyl + flumioxazin + pyroxasulfone, chlorimuron-ethyl + flumioxazin +metribuzin, and chlorimuron-ethyl + sulfentrazone were applied PRE to each variety and seed treatment combination at 1× and 2× the labeled use rate. Chlorimuron-ethyl + sulfentrazone treatment at the 2 × rate resulted in greater injury of 8% and 14% to the sensitive variety than the tolerant in 2016 and 2017, respectively; this was the highest injury observed from any herbicide treatment in either year. In 2017, chlorimuron-ethyl + sulfentrazone resulted in the greatest height reductions in both varieties, but this reduction was more evident in the sensitive (19%) than in the tolerant (6%) variety. Overall, yield differences between the two varieties were not consistent between years, and for both varieties, the sulfentrazonecontaining treatments resulted in the highest yield losses. The results of this research indicate that there is a larger interaction between herbicides and varieties than there is between herbicides and seed treatments, or seed treatments and varieties.

Nomenclature: Chlorimuron-ethyl; flumioxazin; fluopyram; imidacloprid; metalaxyl; metribuzin; Pasteuria nishizawae; penflufen; prothioconazol; pyroxasulfone; sulfentrazone; thiamethoxam; soybean, Glycine max (L.) Merr