Herbicidal potential of essential oils of oregano or marjoram (Origanum spp.) and basil (Ocimum basilicum) on Echinochloa crus-galli (L.) P. Beauv. and Chenopodium album L. weeds

Bioassay studies were conducted to assess the effects of essential oils extracted from four sweet basil (Ocimum basificum L.) cultivars and six oregano or marjoram (Origanum spp.) populations, grown in the Mediterranean region, on barnyardgrass [Echmochloa crus-galli (L.) P. Beauv.] and common lambsquarters (Chenopodium album L.) germination and root growth. The activity of these essential oils was compared with corresponding commercially available essential oils. The essential oils of oregano originated from Agrafa and Rapsani (Greece), the commercially available essential oil of oregano (unknown species), and the essential oil isolated from the Egyptian marjoram were the most phytotoxic to barnyardgrass and common lambsquarters. Essential oils of basil cultivars and sweet marjoram were least phytotoxic. The least inhibition on barnyardgrass or common lambsquarters was caused by the essential oil isolated from the 'red robin improved' or 'minette', respectively, sweet basil cultivar. Barnyardgrass germination and root length inhibition caused by oregano or marjoram essential oils ranged from 64.6 to 96.5%, while the inhibition from the sweet basil essential oils ranged from 2.3 to 49.7%. The corresponding inhibition of common lambsquarters was 40.9 to 86.3% and 29.8 to 69.4%. The essential oils from some oregano or Egyptian marjoram populations with high concentrations of phenols inhibited the emergence and initial growth of annual weeds and could be used as natural herbicides in future.