Produtos naturais derivados de plantas: controle de plantas daninhas em pré e pós-emergência e atividade de enzimas antioxidantes

Abstract

Weeds limit both the quantity and quality of agricultural production, and their management represents one of the main challenges in agriculture, whether in organic and agroecological systems or in conventional ones. The intensive use of synthetic herbicides in conventional systems has been widely questioned due to environmental and human health impacts, as well as the selection of resistant biotypes. In this context, natural products with bioherbicidal potential have emerged as promising alternatives for more sustainable management strategies. The objective of this study was to evaluate the bioherbicidal potential of different dose proportions (0.00x; 0.15x; 0.30x; 0.56x; 1.00x; 1.64x; 2.43x) of Pinus sylvestris L. oil, Pinus spp. terpene, D-limonene, and Eucalyptus globulus Labill. essential oil applied in pre- and post-emergence on morning glory, hairy beggarticks, wild poinsettia, and Alexandergrass, as well as to investigate physiological responses associated with oxidative stress. The products were chemically characterized by GC-MS and evaluated for compatibility with the adjuvants TW80 and SP80. Greenhouse experiments were conducted to develop dose–response curves, assessing emergence percentage and control levels in pre- and post-emergence, respectively. Plant height (cm), number of leaves per plant, and shoot and root dry biomass (g) were also evaluated. Pre-emergence assessments were carried out between 14 and 35 days after application (DAA), and post-emergence assessments between 3 and 21 DAA. Additionally, the response of the enzymes superoxide dismutase (SOD) and ascorbate peroxidase (APX) was investigated after the application of contrasting doses of the natural products. Overall, treatments resulted in variable responses. In pre-emergence, pine oil and pine terpene stood out, promoting significant reductions in emergence and growth of the dicotyledonous species, whereas Alexandergrass showed lower sensitivity, with marked effects only for pine terpene. In post-emergence, the 1.64x and 2.43x proportions of pine oil achieved satisfactory control (≥ 80%) of hairy beggarticks until the last evaluation and of wild poinsettia up to 14 DAA, followed by recovery through regrowth. Pine terpene was particularly effective in controlling Alexandergrass, with the 2.43x dose resulting in plant death from 7 DAA onward. The highest doses of D-limonene provided satisfactory control only at specific evaluation times for wild poinsettia and Alexandergrass. None of the natural products provided efficient control of morning glory, despite reductions in growth variables. Eucalyptus essential oil was the least phytotoxic product, failing to achieve effective control in any evaluation. The analysis of SOD and APX activity suggests an association between oxidative stress induced by the natural products and the observed phytotoxic effects. Increased enzymatic activity was related to greater plant tolerance to the natural products, whereas reduced activity was associated with cellular damage. It is concluded that the evaluated natural products show potential for use as bioherbicides in weed management, provided that appropriate formulation, dose, and target species are considered. Future studies are recommended to assess sequential applications in pre- and post-emergence, as well as repeated post-emergence applications using reduced doses.