Herbicidal activity of volatile oils from Eucalyptus citriodora against Parthenium hysterophorus.

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 µL mL^-1, the week after spraying. At concentrations up to 50 µL mL^-1, plants showed some recovery over time but plants sprayed with 75 and 100 µL mL^-1 died 2 weeks after treatment. Plants sprayed with 50 µL mL^-1 and higher concentrations of eucalypt oils were desiccated and wilted in appearance. At concentrations of 5-75 µL 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. [ABSTRACT FROM AUTHOR]