Characterization of saflufenacil release and availability from encapsulation

Abstract Encapsulated saflufenacil uses a solid phase encapsulation, which is different than traditional herbicide encapsulations. Saflufenacil is released following dry conditions that allow the microcapsule to fracture. Thus, encapsulated saflufenacil is not available for foliar uptake using standard application methods. A trace amount of non-encapsulated saflufenacil remains in the formulation from an incomplete purification process and may cause foliar phytotoxicity from postemergence applications. Experiments were conducted using relative photosystem II (PS II) efficiency of corn leaf tissue to determine encapsulated saflufenacil bioavailability and to characterize saflufenacil microcapsule release under extended solution storage time. To evaluate injury potential, non-encapsulated, free saflufenacil was separated from the encapsulated formulation using microfiltration. An open-capsule treatment was created by allowing the encapsulated formulation to dry and then resolubilizing the herbicide. Relative PS II efficiency of the free, open-capsule, and encapsulated saflufenacil formulations were compared over 48 hours after treatment (HAT). By 48 HAT, dry and non-encapsulated saflufenacil reduced relative PS II efficiency greater than the encapsulated saflufenacil, indicating that saflufenacil was not released from the encapsulation unless it underwent a period of drying. Furthermore, the reduced relative PS II efficiency was similar for the encapsulated and free saflufenacil, corroborating that the level of phytotoxicity from foliar encapsulated saflufenacil applications originates from the trace levels of free saflufenacil in the product. Saflufenacil microcapsule stability was evaluated following mixing with water and storage for 0, 1, 3, 5, or 7 days. Phytotoxicity did not increase with extended storage times, as the reduction in relative PS II efficiency from 0 to 48 HAT remained mostly constant across solution storage times. Overall, this research substantiates that saflufenacil encapsulation works to reduce foliar injury and documents the encapsulation durability under extended storage in water solution.