Tidemann, B. D., Hall, L. M., Johnson, E. N., Beckie, H. J., Sapsford, K. L., Willenborg, C. J. and Raatz, L. L. 2014. Additive efficacy of soil-applied pyroxasulfone and sulfentrazone combinations. Can. J. Plant Sci. 94: 1245-1253. Efficacy of soil-applied herbicides can be influenced by edaphic factors including soil organic matter (OM) content, as well as by interactions with herbicide tank-mix partners. Field trials were conducted over 6 site-years in 2011 and 2012 across western Canada to examine the interaction of pyroxasulfone and sulfentrazone when co-applied for control of false cleavers (Galium spurium L.) and wild oat (Avena fatua L.) in field pea. In the greenhouse, the nature of this interaction was further investigated for these two weed species, plus barley and canola; in a separate experiment, the effect of OM content on pyroxasulfone and sulfentrazone efficacy was examined using three soils with 2.8, 5.5, and 12.3% OM content, respectively. Efficacy of pyroxasulfone and sulfentrazone combinations was additive under both field and greenhouse conditions. Higher OM content generally required higher rates of herbicide to achieve similar efficacy for all tested species. Pyroxasulfone and sulfentrazone can be combined to aid in herbicide resistance management and broaden the weed spectrum compared with each product used alone, although rate selection may be OM dependent.