Phytotoxic effects of essential oils from Nepeta glocephalata Rech.f. and N. ispahanica Boiss. on se-lected weed species

In the present study the bioherbicidal activity of essential oils hydrodistilled from Nepeta glocephalata Rech.f and N. ispahanica Boiss were investigated on four weed species (barnyard grass (Echinochloa crus-galli (L.) Beauv), redroot pigweed (Amaranthus retroflexus L.), lambsquarters (Chenopodium album L.) and canary grass (Phalaris canariensis L.)). A total of 37 components were identified from the essential oils of N. glocephalata and N. ispahanica constituting approximately 98.61 % and 96.1 % of the oils, respectively. In laboratory bioassay different concentrations (0, 1, 2, 4 and 8 μl ml-1) of two Nepeta essential oils on germination, root and shoot length were studied. Results showed by increasing the concentration of oils, all studied traits of the weeds were decreased compared with control. In a glass house 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 (7-days after spray) ranging from chlorosis to necrosis of plant weeds. In foliar application under glasshouse conditions, both Nepeta essential oils reduced the seedling dry mass and concentrations of chlorophyll a chlorophyll b. The study concludes that Nepeta essential oils have phytotoxic effects and could be used as bioherbicides but the selectivity of these compounds should be considered also.