Herbicidal activity of essential oils from four Nepeta species against wild mustard (Sinapis arvensis L.) and winter wild oat (Avena ludoviciana Dur.)

In the present study, the bioherbicidal activity of essential oils from Nepeta menthoides, N. mahanensis, N. elymaitica and N. binalodensis were investigated on two weed species (wild mustard and winter wild oat). A total of 68 components were identified from the essential oils of Nepeta species. Nepetalactone was the main component of the essential oil of N. mahanensis but no nepetalactones were found in N. menthoides essentialoil. 1,8-cineole was the major component of N. menthoides, N. elymaitica and N. binalodensis essential oils. In the laboratory bioassay, different concentrations (0, 1, 2, 4 and 8 μg ml-1) of four Nepeta essential oils effects on germination, root and shoot length were studied. Results showed that germination percentage, and root and shoot length were significantly reduced in a dose–response bioassay. In a greenhouse bioassay, post-emergence application of Nepeta essential oils (1.25%, 2.5%, 5% and 10% v/v) on 3-week-old weed plants caused visible injury. Under greenhouse conditions, foliar application all Nepeta essential oils reduced chlorophyll content. In addition, Nepeta essential oils induced an electrolyte leakage showing membrane damage and loss of integrity and enhanced the level of proline suggesting induction of oxidative stress. Wild mustard was more susceptible to phytotoxic effects of all Nepeta essential oils rather than winter wild oat. Totally, the study showed that Nepeta essential oils have phytotoxic effects and could be used as bioherbicides to control wild mustard and winter wild oat.