Stability and pre-emergence herbicidal potential of citronella (Cymbopogon nardus) essential oil-based nanoemulsion during storage

Abstract

Natural herbicides from essential oils (EOs) are widely used in sustainable weed control. A citronella (Cymbopogon nardus) EO-based nanoemulsion was fabricated for using as a natural herbicide. It was created using a high-energy emulsification method in a microfluidizer. A gas chromatograph-mass spectrometer (GC-MS) was employed to determine the chemical composition of the citronella EO. The major components of the EO were 33.59% citronellal, 21.42% geraniol, 11.23% citronellol and 4.38% limonene. The citronella EO was formulated to nanoemulsion with a nonionic surfactant mixture (Smix). The Smix at hydrophilic-lipophilic balance (HLB) 14 consisted of Tween 60 (91.2% w/w) and Span 60 (8.8% w/w). The droplet size of the nanoemulsion decreased from 78.6 to 35.2 nm with an increasing number of microfluidization cycles, from 1 to 3 cycles at 15000 psi. The optimal number of microfluidization cycles was 3, which produced the smallest droplet size. The effect of stability storage on droplet size and herbicidal activity of the nanoemulsion was investigated for 10, 20, 30 and 60 days. Droplet size increased with storage time through to 60 days (from 35.2 to 55.2 nm). The herbicidal activity of the nanoemulsion at concentrations of 62.5, 125 and 250 µL L^-1 was determined on  Amaranthus tricolor L. During 60 days of storage, the inhibitory effect percentage on seed germination and seedling growth decreased slightly. Also, the inhibition of seed imbibition and a-amylase activity showed non significantly changed with storage time. Our findings provide essential information for using and storing citronella EO nanoemulsion. The results revealed that the nanoemulsion could be stored at 4 °C for at least 60 days without phase separation occurring. The results show that the citronella EO-based nanoemulsion can be used as a natural herbicide and long shelf life.