Phytotoxic effects of leaf extract of 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 (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 (, , , and ), 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 least affected and most sensitive. Phytotoxic effects increased with concentration, except for , 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 leaf extract varies among the weed species evaluated, primarily affecting germination with minimal impact when applied to leaves. Thus, demonstrates potential as a bioherbicide for pre-emergent applications against the species studied.