EFEITO DA ASSOCIAÇÃO E DA CONCENTRAÇÃO DE ÁCIDO PIROLENHOSO NA EFICÁCIA DO GLIFOSATO E DO 2,4-D NO CONTROLE DE PLANTAS DANINHAS

Abstract

Weed management is one of the main challenges in tropical agricultural production, causing significant yield losses when not carried out within the critical interference period. The use of adjuvants in herbicide spray solutions is a strategy to enhance active ingredient efficacy, and wood vinegar (pyroligneous acid), a by-product of charcoal production, presents acidic physicochemical properties as pH, organic acids and phenolic compounds that qualify it as a natural adjuvant for post-emergence herbicides. This study aimed to evaluate the effect of the association and concentration of wood vinegar on the efficacy of glyphosate (1,440 g a.e. ha⁻¹) and 2,4-D (670 g a.e. ha⁻¹) for weed control under field conditions in Araguatins, Tocantins, Brazil, between June and July 2026. A randomized complete block design was used, with eight treatments and four replicates. Herbicide efficacy was monitored through the VARI and TGI vegetation indices, extracted from RGB drone orthomosaics across seven assessment dates from 0 to 22 days after application (DAA), complemented by phytotoxicity ratings using the EWRC scale and a baseline phytosociological survey of the weed community. Wood vinegar combined with glyphosate did not enhance the efficacy of that herbicide, with similar performance observed among treatments with adjuvant at 2% and 4% v/v and glyphosate alone, which produced the greatest reduction in vegetation indices among all treatments evaluated. In contrast, combining wood vinegar with 2,4-D reduced herbicide efficacy in a dose-dependent manner, with the highest adjuvant level rendering the treatment equivalent to the untreated control, indicating an antagonistic effect possibly related to physicochemical incompatibility between the strongly acidic adjuvant and the amine-salt herbicide formulation. Wood vinegar applied alone showed no detectable herbicidal activity. The results indicate that the benefit of wood vinegar as an adjuvant depends of the associated herbicide, being neutral for glyphosate and antagonistic for 2,4-D under the evaluated conditions, which calls for caution against its generalized recommendation.