Field studies were conducted to examine the dissipation of three soil-applied residual herbicides for bare soil compared with soil under low-density polyethylene (LDPE) mulch in 2003 and 2004. Studies indicated that halosulfuron and S-metolachlor dissipation was more rapid for bare soil than soil under LDPE mulch. Sulfentrazone dissipation from bare soil was equal to soil under LDPE mulch in 2003. However, sulfentrazone dissipation in 2004 was more rapid for soil under LDPE mulch than for bare soil. The order for half-life, defined as time for 50% dissipation (DT50), varied by herbicide and soil exposure. Averaged across 2003 and 2004, metolachlor DT50 was 2 d, halosulfuron 7 d, and sulfentrazone 16 d for bare soil. S-metolachlor DT50 was 4 d, halosulfuron 10 d, and sulfentrazone 13 d for soil under LDPE mulch. Correlation between quantified herbicide dissipation and bioassay for bare soil compared with soil under LDPE mulch in 2004 indicated that assay species root dry weights were negatively correlated with herbicide concentration. Data indicated that S-metolachlor and sulfentrazone bioassays, with oat and cotton, respectively, could be used to assess the level of dissipation for each herbicide.
Nomenclature: Halosulfuron; S-metolachlor; sulfentrazone; low-density polyethylene mulch; cotton, Gossypium hirsutum L; oat, Avena sativa L