Phytotoxic effects of leaf extract of <i>Esenbeckia leiocarpa</i> Engl. on germination and initial development of weeds

Bioherbicides, including plant extracts, allelochemicals, and microbial agents, offer sustainable alternatives for weed control in agriculture. In Brazil, the native tree <i>Esenbeckia leiocarpa</i> (guarantã) shows potential phytotoxic effects in weeds species. This study evaluates aqueous extracts from its aerial parts as a substitute for herbicides, focusing on their impact on weed germination and initial growth. The experiment used a completely randomized 7 × 4 factorial design with seven extract concentrations (0, 5, 10, 20, 40, 80, and 100%) and four weed species (<i>Amaranthus hybridus</i>, <i>Bidens pilosa</i>, <i>Euphorbia heterophylla</i>, and <i>Digitaria insularis</i>), with four replicates per treatment. Germination and germination speed index dropped significantly even at 5%, nearly ceasing at 20% or higher. The results indicate a non-linear dose-response relationship, suggesting that increasing the extract concentration beyond 20% does not result in a proportional reduction in germination. Pre-germinated seeds showed reduced radicle length and fresh mass from 5%, with <i>E. heterophylla</i> least affected and <i>D. insularis</i> most sensitive. Phytotoxic effects increased with concentration, except for <i>D. insularis</i>, where phytotoxicity stabilized (90% phytotoxicity) at concentrations above 20%. When applied to leaves, phytotoxicity was minimal, ranging from 5 to 10%, and had negligible effect on reducing fresh mass. The findings indicate that the response to <i>E. leiocarpa</i> leaf extract varies among the weed species evaluated, primarily affecting germination with minimal impact when applied to leaves. Thus, <i>E. leiocarpa</i> demonstrates potential as a bioherbicide for pre-emergent applications against the species studied.