Residual activity of pre-emergent herbicides applied in contrasting soils

Abstract

This study investigated the residual activity of different rates of the herbicides alachlor, oxyfluorfen, prometryne and S-metolachlor applied in pre-emergence in soils of contrasting textures. For that, eight simultaneous experiments were conducted with samples of PSAMENT (sandy texture) and RED LATOSOL (clay texture), which received alachlor (0; 2.40 and 3.36 kg ha^-1), oxyfluorfen (0; 0.48 and 0.72 kg ha^-1), prometryne (0; 0.75 and 1.50 kg ha^-1) and S-metolachlor (0; 1.20 and 1.44 kg ha^-1) applications. The treatments monitoring was made through sowing of bio-indicator (Brachiaria decumbens or Cucumis sativus). Control was assessed by scores from 0 to 100% at 0, 25, 50, 75, 100 days after application (DAA). Regardeless of rate, alachlor provided control around 80% to 66 DAA, in clay soil and up to 50 DAA in sandy. Oxyfluorfen showed control around 80% to 56 DAA to clay soil and up to 36 DAA to sandy, in both rates. Both rates of prometryne in clay soil provided control over 80% to 28 DAA, with residual activity higher in recommended rate (1.50 kg ha^-1). In samples sandy, S-metolachlor provided the same control for both rates, controlling the bio-indicator at 80% up to 52 DAA, and for clay soil in rate at 1.44 kg ha^-1, presented 96% control the 80 DAA. Thereby, there was no increase in residual activity in sandy soil, even with the application of the recommended rate for clay soil.