Soil Properties Influence Saflufenacil Phytotoxicity

Saflufenacil, a pyrimidinedione herbicide, is used for contact and residual broadleaf weed control in various crops. Bioactivity of saflufenacil in soil was tested in greenhouse and laboratory studies on 29 soils representing a wide range of soil properties and geographic areas across the United States. A greenhouse bioassay method was developed using various concentrations of saflufenacil applied PPI to each soil. Whole canola plants were harvested 14 d after treatment, and fresh and dry weights were recorded. Nonlinear regression analysis was used to determine the effective saflufenacil doses for 50% (ED50,), 80% (ED80), and 90% (ED90) inhibition of total plant fresh weight. Bioactivity of saflufenacil in soil was strongly correlated to soil organic (R = 0.85) and humic matter (R = 0.81), and less correlated to cation exchange capacity (R = 0.49) and sand content (R = -0.32). Stepwise regression analysis indicated that organic matter was the major soil constituent controlling bioactivity in soil and could be used to predict the bioactivity of saflufenacil. Saflufenacil phytotoxicity was found to be dependent on soil property; therefore, efficacy and crop tolerance from PRE and PPI applications may vary based on soil organic matter content and texture classification.