Optimization of herbicidal activity of essential oil mixtures from Satureja alpina, Thymus satureioides and Myrtus communis on seed germination and post-emergence growth of Amaranthus retroflexus L

Essential oil-based herbicides are promising candidates for the development of safe and eco-friendly botanical pesticides. This study aimed to develop an efficacious preparation by combining the essential oils (EOs) of Satureja alpina (L.), Thymus satureioides Coss and Myrtus communis (L.) and assessing its effects on the germination and early seedling growth of the weed species Amaranthus retroflexus (L.). The result showed that all EOs tested individually and in different combinations, significantly inhibited the germination of A. retroflexus in dosedependent manner, with median effective dose (ED50) values ranging from 1.4 to 2.18 mu L/mL. The mixture design analysis indicated synergistic interactions between the studied EOs, with the optimal combination predicted to be 22% M. communis, 23% S. alpina and 55% T. satureioides. Remarkably, the predicted and validated data showed a significant lower ED50 values (1.28 mu L/mL), compared with those of EOs tested individually and the conventional herbicide 2,4-dichlorophenoxyacetic acid. Application of a nano-emulsified optimal EO mixture in greenhouse experiments during the post-emergence growth stage of A. retroflexus resulted in significant reductions in shoot and root lengths, vigor index, and chlorophyll content. Simultaneously, the relative electrolyte leakage and malondialdehyde levels increased, which ultimately resulted in seedling death. GC/MS analysis revealed that S. alpina EO was mainly characterized by pulegone (81.15%), carvacrol was the major compound of T. satureioides EO (33.05%), while the main constituent of M. communis EO was myrtenyl acetate (43.5%). Overall, these results showed that the preparation based on a mixture of these plant EOs is efficacious and offers a promise as a potential botanical herbicide for controlling this deleterious weed species.