Nanotechnology-based formulations of thyme essential oil to enhance its herbicidal efficiency for controlling weeds...

Thyme is an aromatic plant known as a rich source of bioactive compounds with eco-friendly herbicidal potential. Despite the herbicidal potential of thyme essential oil, its effectiveness under field conditions is limited due to its high volatility, poor water solubility and susceptibility to environmental degradation. Nanoformulations can overcome these limitations by enhancing stability, dispersibility, bioavailability, and prolonging herbicidal activity. Hence, this study was applied to evaluate and compare the effectiveness of aqueous extracts from thyme leaves and thyme essential oil against weeds. A preliminary pot experiment tested different concentrations of thyme leaf aqueous extracts (0, 10, 20 and 30% w/v) and thyme essential oil (0, 3, 6 and 9% v/v). Based on these results, two subsequent pot experiments were conducted during two consecutive summer seasons using lower concentrations (0, 2, 4 and 6% v/v) of crude thyme essential oil, its nanoemulsion and β-cyclodextrin nanoencapsulated formulations. Healthy weed-free maize plants and unweeded controls were included for comparison.

The preliminary experiment revealed that thyme essential oil was more efficient in controlling weeds than aqueous extracts in weed control, where 9% thyme essential oil achieved complete suppression with stimulatory response in maize plants (11.4 g dry biomass) but this stimulatory response was lower than 6 and 3% concentrations (11.9 and 11.5 dry biomass, respectively). In the main experiment, nanoemulsion and β-cyclodextrin significantly outperformed raw essential oil in weed suppression and crop safety. At 90 DAS, NE-Th oil at 6 and 4% achieved the highest reduction in barnyard grass dry weight (83.48 and 81.72%, respectively) and purslane (89.27 and 82.41%, respectively) compared to the unweeded control. Regarding maize plants at 90 DAS, NE-Th oil at 6 and 4% showed the best performance, significantly exceeding the unweeded control dry weight (50.83 and 45.48 g), respectively. These results indicate that nanoformulations not only enhance weed suppression but also improve crop performance under weed stress competition.

Both nanoemulsion and β-cyclodextrin inclusion complex formulations enhanced the stability and herbicidal efficiency of thyme oil. Therefore, nanoemulsified thyme oil at 4% and 6% achieved the best balance between effective weed suppression and improved maize growth.