Leaching of the S-metolachlor herbicide associated with paraquat or glyphosate in a no-tillage system

Abstract

The combined use of desiccant and residual herbicides is a common management practice under no-tillage systems. However, the effect of desiccant herbicides and mulch on the leaching of residual herbicide is unknown. This study aimed at assessing the leaching of the S-metolachlor herbicide applied to ryegrass sequentially or in association with paraquat or glyphosate. A randomized blocks design was used, with four repetitions and treatments distributed over split-plots. The desiccant herbicides paraquat (600 g ha-1) or glyphosate (720 g ha-1) were used in the main plot, while S-metolachlor (2,800 g ha-1) was applied sequentially or in association with the desiccant herbicides in the subplots. There was also a control containing only desiccant herbicide, with no application of residual herbicide. The type of desiccant did not affect the leaching of the residual herbicide. In addition, the chosen method to apply the residual herbicide, sequentially or in association with the desiccant, did not impact the S-metolachlor behavior in the soil. The bioavailable concentration in the soil, 25 days after the application, was 90 g a.i. ha-1, at a depth of 18 cm.

Leaching potential of S-metolachlor in a medium-textured Oxisol soil with bioindicator plants

“…Generally, the greater precipitation caused greater leaching of S-metolachlor molecules, increasing groundwater contamination potential. In this case, the potential estimation of leaching calculated by the GUS index classified the S-metolachlor as having high leaching potential once the sorption is intermediate (K oc = 200 mL g -1 of soil) and it presents high water solubility (480 mg L -1 at 25 ºC) (Inoue et al, 2010;Nunes & Vidal, 2016), which corroborates the results found in this study for cucumber.…”

Growth and Tolerance of Sesame (Sesamum indicum L.) Varieties to Pre and Postemergence Graminicides

“…Selectivity of metolachlor and alachlor is positional; hence, given the research was a pot experiment on sandy loam soil with low organic matter content and poor water holding capacity, this might have led to the confinement of sesame roots to the leached herbicide zone following heavy irrigation. Nunes and Vidal [19] reported that 90% of applied metolachlor was concentrated in the first 10 cm of crop root zone. Sesame seeds that were planted at 5 cm depth also received the metolachlor leachates, thereby, predisposing them to herbicide injury and suppressing the emergence process due to herbicide absorption.…”

Mineralization of S-metolachlor in soil as affected by moisture content, application history, and association with glyphosate

“…For example, glyphosate's addition increased the cumulative degradation rate of fluometuron relative to fluometuron alone (Lancaster et al, 2008). For S-metolachlor, a study has demonstrated that association with burndown herbicides such as glyphosate decreased soil persistence under Brazilian conditions (Nunes, Vidal, 2016). It is important to study the combination of S-metolachlor and glyphosate and to study the effect of moisture content as this herbicide is being used in areas prone to excess of water.…”