Bio-Herbicidal Potential of Nanoemulsions with Peppermint Oil on Barnyard Grass and Maize

Abstract

Bio-based nanoemulsions are part of green pest management for sustainable agriculture. This study assessed the physicochemical properties and the herbicidal activities of the peppermint essential oil nanoemulsions (PNs) in concentrations 1.0-10% stabilized by Eco-Polysorbate 80 on germinating seeds and young plants of maize and barnyard grass. Based on the design of experiment (DOE) results, the final nanoemulsion formulations were obtained with 1, 1.5, 2, and 5% of essential oil concentration. Biological analyses were conducted to select the most promising sample for selective control of barnyard grass in maize. Seedlings growing in the presence of PNs displayed an overall inhibition of metabolism, as expressed by the calorimetric analyses, which could result from significant differences in both content and composition of carbohydrates. Concentration-response sub estimation showed that leaf-sprayed concentration of PN causing 10% of maize damage is equal to 2.2%, whereas doses causing 50% and 90% of barnyard grass damage are 1.1% and 1.7%, respectively. Plants sprayed with PN at 5% or 10% concentration caused significant drops in relative water content in leaves and Chlorophyll a fluorescence 72 h after spraying. In summary, peppermint nanoemulsion with Eco-Polysorbate 80 at 2% concentration is a perspective preparation for selective control of barnyard grass in maize. It should be analyzed further in controlled and field conditions.

Keywords: Chlorophyll a fluorescence; Eco-Polysorbate 80; FT-Raman spectroscopy; isothermal calorimetry; phytotoxicity; polydispersity index; relative water content.

Figure 1

Pareto charts for the influence of input parameters (oil concentration, emulsifier concentration amplitude, sonification time) on (A) average droplet size of nanoemulsions (d. nm), (B) polydispersity Index (PDI).

Figure 2

Approximation profiles for the influence of input parameters on (A) an average droplet size (nm) of nanoemulsions (nm), (B) polydispersity index (PDI).

Figure 3

Saddle plots for desirability for essential oil and emulsifier concentration.

Figure 4

Transmission electron micrograph of peppermint oil nanoemulsion (5% v/v).

Figure 5

The specific thermal power curves of the maize (A) and barnyard grass (B) seedlings growing on the surfactants (S1 light orange line and S5 dark orange line), nanoemulsions with peppermint oil (PN1 light blue line, PN2 cyan line, PN3 dark blue line, PN4 violet line) and water (C green line). The total heat emitted by maize (C) and barnyard grass (D) seedlings growing on the surfactants S1 (1% v/v) and S5 (10% v/v), nanoemulsions with peppermint oil PN1 (1% v/v), PN2 (1.5% v/v), PN3 (2% v/v), PN4 (5% v/v), and water (C). Mean values ± SD. The letters a–g indicate statistically significant differences. Values indicated by the same letters did not differ significantly at p ≤ 0.05 according to Duncan’s test (within the tested species), n = 10.

Figure 6

FT-Raman spectra show the chemical composition of seedling’s endosperm of maize (A) and barnyard grass (B) that were growing on the surfactants (S1, light orange line, and S5, dark orange line), nanoemulsions with peppermint oil (PN1, light blue line; PN2, cyan line; PN3, dark blue line; PN4, violet line) and water (C, green line). The mean values were based on six repetitions. Hierarchical cluster analysis of the FT-Raman spectra of the maize (C) and barnyard grass (D). Surfactants S1 (1% v/v) and S5 (10% v/v), nanoemulsions with peppermint oil PN1 (1% v/v), PN2 (1.5% v/v), PN3 (2% v/v), PN4 (5% v/v), and water (C—control).

Figure 7

Length of aerial parts (A), length of roots (B), dry weight of aerial parts (C), and dry weight of roots (D) of maize seven days after spraying with water—C, herbicide—H, surfactants—S1 (1% v/v) and S5 (10% v/v), and nanoemulsions with peppermint oil PN1 (1% v/v), PN2 (1.5% v/v), PN3 (2% v/v), PN4 (5% v/v), and PN5 (10% v/v). Bars represent mean value ± SD. The letters a–d indicate statistically significant differences. Values indicated by the same letters did not differ significantly at p ≤ 0.05 according to Duncan’s test (within the tested species), n = 4.

Figure 8

Length of aerial parts (A) and length of roots (B) of barnyard grass seven days after spraying with water—C, herbicide—H, surfactants—S1 (1% v/v) and S5 (10% v/v), and nanoemulsions with peppermint oil PN1 (1%v/v), PN2 (1.5% v/v), PN3 (2% v/v), PN4 (5% v/v), and PN5 (10% v/v). Bars represent mean value ± SD. The letters a–d indicate statistically significant differences. Values indicated by the same letters did not differ significantly at p ≤ 0.05 according to Duncan’s test (within the tested species), n = 4.

Figure 9

Relative water content (RWC) of maize (A) and barnyard grass (B) that were growing on the surfactants S1 (1% v/v) and S5 (10% v/v), nanoemulsions with peppermint oil PN1 (1% v/v), PN2 (1.5% v/v), PN3 (2% v/v), PN4 (5% v/v), and PN5 (10% v/v), herbicide (H) and water (C) calculated as (fresh mass—dry mass)/(turgid mass—dry mass)] × 100. The letters a–f indicate statistically significant differences. Values indicated by the same letters did not differ significantly at p ≤ 0.05 according to Duncan’s test (within the tested species), n = 10.

Figure 10

Values of selected Chl a fluorescence parameters of maize (A) and barnyard grass (B). C—water control, H—herbicide, surfactants S1 (1% v/v) and S5 (10% v/v), nanoemulsions with peppermint oil PN1 (1% v/v), PN2 (1.5% v/v), PN3 (2% v/v), PN4 (5% v/v), and PN5 (10% v/v).