Soil residual activity and plant-back periods for the herbicides saflufenacil and topramezone.

To quantify soil residual activity and plant-back periods for two maize herbicides, saflufenacil and topramezone, different rates were applied to a cultivated soil and samples (0-5 cm) collected at regular intervals for glasshouse bioassays. Phytotoxic residues of saflufenacil applied at 17 g ai/ha, the rate used for conservation tillage and pasture renovation, persisted in the soil for < 2 weeks for the susceptible species, viz. white clover, onion, carrot and radish. Residual activity from 102 g ai/ha, the rate recommended for maize, dissipated within 4 weeks for all species. Wheat, ryegrass, carrot, squash, onions and tomato were not affected by topramezone residues from rates up to 202 g ai/ha in soil collected 2 weeks after treatment (WAT). However, peas, white clover and radish all suffered damage in samples collected 2 WAT. By 4 WAT, only white clover and peas exhibited minor phytotoxicity.