Efeito alelopático do extrato etanólico de Esenbeckia leiocarpa Engl. sobre a germinação e o desenvolvimento de plântulas de picão-preto (Bidens pilosa L.), amendoim-bravo (Euphorbia heterophylla L.) e capim-amargoso (Digitaria insularis (L.) Fedde).

Abstract

The improper use of herbicides poses risks to both the environment and human health, in addition to contributing to the selection of tolerant weed species or resistant biotypes. In this context, allelopathy emerges as a promising alternative for weed management. In Brazil, Esenbeckia leiocarpa (commonly known as “guarantã”) is a native species with underexplored allelopathic potential. Aiming to identify alternatives to herbicide use, this study evaluated the allelopathic potential of the ethanolic extract of E. leiocarpa at different concentrations on the germination and development of Bidens pilosa, Euphorbia heterophylla, and Digitaria insularis. The experiment was conducted in a completely randomized design (CRD), in a 5 × 3 factorial arrangement, with five extract concentrations (0%, 2.5%, 5%, 10%, and 20%) and three weed species, with four replications. Evaluations included germination percentage (G%), root length reduction (mm), and signs of phytotoxicity in the tested weed species. A concentration of 2.5% already caused a significant reduction in the germination of all evaluated species. E. heterophylla showed slightly greater tolerance at lower concentrations; however, germination was completely inhibited for all species at concentrations equal to or above 10%. In the growth bioassays, root length of the seedlings was reduced by approximately 50% from the 5% concentration. Regarding phytotoxicity, concentrations of 10% or higher induced more than 80% phytotoxicity in all species, indicating severe toxicity. Among the tested species, D. insularis was particularly more sensitive, suggesting a higher susceptibility to the extract. The results indicate that the weed species responded differently to the E. leiocarpa leaf extract, which contains allelochemicals capable of interfering primarily with germination and early development. Therefore, E. leiocarpa shows promise as a bioherbicide for pre-emergence applications against the studied weed species.