Efeito arrastante de herbicidas pré-emergentes sobre diferentes níveis de palhada

Abstract

Straw mulch offers several benefits, including the release of allelopathic substances and the physical suppression of weeds. However, when combined with chemical control, it may interfere with the effectiveness of herbicidal products. Pre-emergent herbicides are applied directly onto the mulch or soil, remaining exposed to adverse conditions and thus subject to retention and degradation, which can hinder their reach to the soil seed bank (SSB). Therefore, this experiment aimed to evaluate the interference of different levels of radish straw (0, 2, 4, 6, and 8 t ha⁻¹) on the efficacy of pre-emergent herbicides (S-metolachlor and pyroxasulfone + flumioxazin), under different irrigation timings after application: 1 hour, 12 hours, and 24 hours post-application, simulating rainfall. Two bifactorial experiments were conducted (herbicides, mulch levels, and irrigation timings), using a completely randomized design with three replicates. To assess the interference of mulch, the following variables were evaluated: germination speed index, weed control percentage, number of leaves in both weed and crop species, leaf area index of the crop, and fresh and dry biomass of both species. Data were subjected to analysis of variance (ANOVA), and when significant, means were compared using Duncan's test (p < 0.05). It was concluded that the efficiency of S-metolachlor was negatively affected by increasing mulch levels, especially above 4 t ha⁻¹, whereas pyroxasulfone + flumioxazin maintained its efficacy regardless of mulch quantity, making it more suitable for no-tillage systems with high crop residue cover.