Vetiver oil and nootkatone effects on the growth of pea and citrus

Studies have indicated that vetiver oil and one of its components, nootkatone, possess insecticidal and herbicidal activities. The compounds appear to be good candidates as novel pesticides for substrate (soil, wood, and mulch) treatments. Phytotoxicity is a concern for substrate treatment agents against soil dwelling organisms. Using treated potting media the phytotoxic effect of vetiver oil and nootkatone was evaluated on the pea plants (Pisum sativum L.; cv, “Kelvedon Wonder”) in the laboratory and on citrus trees (Citrus unshiu Marcovitch) under field conditions. All the tested chemicals at various concentrations (20, 500, and 2000 μg/g soil) reduced the pea plant growth (plant height, root length, dry weight). Nootkatone treatments had the lowest inhibitory effect on growth, followed by vetiver oil and disodium octaborate tetrahydrate (Tim-bor^®), a registered pesticide with known phytotoxicity. The most inhibitive and injurious effects occurred with Tim-bor^® at concentrations of 500 and 2000 μg/g soil, causing plant mortality of up to 38.9%. No pea plant mortality was observed in nootkatone and vetiver oil treatments. Vetiver oil and nootkatone treatments at the rates of 30 and 100 μg/g potting media had no adverse effect on the citrus plant growth rates. These results support the possible usage of the two chemicals around buildings and in nurseries for the management of termites, ants, and weeds; or in the nursery industry where quarantines may be in place to prevent the movement of invasive pests.