Desenvolvimento de bio-herbicida à base de ácido pirolenhoso e óleo de pinus: caracterização e avaliação do potencial fitotóxico

Abstract

The use of natural products (NPs) as alternatives to conventional herbicides represents a growing trend, driven by the search for more sustainable strategies and the reduction of impacts associated with synthetic agrochemicals. In this study, the association between two NPs, pyroligneous acid (PA), derived from the charcoal industry, and pine oil (PO), as well as an adjuvant (TW80), was evaluated in order to assess the physicochemical characteristics and herbicidal potential of this mixture. In addition, the chemical profiles of pine essential oil (EOP) and pine oil (PO65), used in formulation tests, were analyzed by gas chromatography–mass spectrometry (GC–MS). Among the major components of PO65, α-terpineol was the most abundant (40,33%), followed by terpinolene (18,06%), sylvestrene (9,44%), and o-cymene (5,9%). For EO, α-pinene (44,25%), β-pinene (20,40%), δ-3-carene (17,83%), and limonene (9.63%) were found in higher amounts. For the solutions, a proportion of 17% adjuvant to 83% NP was established, considering a 1 PA:1 PO65 ratio, using 50 L of NP in 150 L of spray solution to prepare six doses (10, 25, 40, 55, 70, and 85% v/v), which were subjected to physicochemical tests of density, viscosity, electrical conductivity, surface tension, and pH, the latter measured weekly. For evaluation of herbicidal potential, distilled water was used as the control (“0% solution”), in addition to an “adjuvant control” containing the lowest adjuvant dose used in the formulations (5.1 mL in 294,90 mL of distilled water). The highest electrical conductivity was observed at the 40% (v/v) concentration, while the highest viscosity occurred in the 85% (v/v) solutions. pH behavior was constant over time and across concentrations, with mean values between 2,83 and 3,16, indicating an acidic profile, which favors penetration of the bioherbicide through leaf cuticles. Density decreased with increasing concentration, reaching values of 0.980 g mL⁻¹, following the same trend observed for surface tension. Phytotoxicity evaluations were conducted at 3, 7, 14, 21, and 28 days after application (DAA) in Bidens pilosa (spanish needle) and Eragrostis plana Nees (south African lovegrass) under greenhouse conditions. Effects were observed shortly after application, at 3 DAA, with greater damage to both species at 14 DAA. In subsequent weeks, E. plana plants showed high recovery, whereas B. pilosa showed 100% control at the 55 and 70% (v/v) concentrations and approximately 56.25% at the 85% (v/v) dose, indicating regrowth in some plants. This formulation can be considered a potential bioherbicide alternative, particularly for B. pilosa. Based on these promising results, complementary evaluations conducted in less controlled environments, such as directly in the field, may help confirm the efficiency of the bioherbicide.