Allelopathy Journal

The herbicidal effect of volatile oils from leaves of Eucalyptus citriodora against the noxious weed Parthenium hysterophorus was tested. In a laboratory bioassay, seed germination and seedling length, chlorophyll content and respiratory activity of Parthenium decreased with increased concentration of eucalypt oils from 0.2 to 5.0 nL mL⁻¹. Germination was completely inhibited at 5.0 nL mL⁻¹ eucalyptus oils. Further, for 4-week-old plants of Parthenium sprayed with different concentrations of volatile oils, visible damage increased and chlorophyll content and respiratory activity decreased with increased concentration from 0 to 100 muL mL⁻¹, the week after spraying. At concentrations up to 50 muL mL⁻¹, plants showed some recovery over time but plants sprayed with 75 and 100 muL mL⁻¹ died 2 weeks after treatment. Plants sprayed with 50 muL mL⁻¹ and higher concentrations of eucalypt oils were desiccated and wilted in appearance. At concentrations of 5–75 muL mL⁻¹, eucalypt oils caused a rapid electrolyte leakage from the Parthenium plants thereby indicating an effect on membrane integrity. It is concluded that volatile oils from E. citriodora possess weed-suppressing ability and could be used as a potential bioherbicide for future weed management programmes.