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Insecticide//Bioherbicide

Efficacy of Lemon-scented Phytotoxic action vegetable oils Eucalyptus oil as a of Ageratum with Pirimiphos- potential conyzoides Linn. on methyl against bioherbicide weeds maize weevil The effect of volatile oil from leaves Billy goat weed, Ageratum The major insect pest of of Eucalyptus citriodora Hook. against conyzoides Linn. is a common weed found in waste places and crop fields. stored maize and grain products in some plant species, viz. Triticum Scientists have done assessment of the tropics is Sitophilus zeamais aestivum Linn., Zea mays Linn., Raphanus sativus Linn., Cassia phytotoxic action of this weed on other Motschulsky. The toxicity of occidentalis Linn., Amaranthus viridis weeds and crops. It showed strong inhibition coconut, groundnut and soybean Linn. and Echinochloa crus-galli on Raphanus sativus Linn. (Radish) oils applied at 1, 2, 5 and 10 ml/kg Beauv. was investigated. In a laboratory germination and growth in a bioassay. The and Pirimiphos-methyl at 2.5, 5 and bioassay at Department of Botany, Panjab leaves exhibited a greater suppression than 10µl active ingredient in 2ml of University, Chandigarh, seed germination of the stem and root. The leaves of this herb water/kg of grain alone or in test plants was significantly reduced in when applied at 2tonnes/ha reduced about combination, to adults and response to the different concentrations of 70% of the growth of Echinochloa crus- immature stages of S. zeamais, the the Eucalyptus oil. Maximum germination galli var. formosensis Ohwi and persistence of the treatments in inhibition was observed with A. viridis, completely inhibited emergence of maize grains and their effects on whereas least effect was seen on R. sativus. Monochoria vaginalis (Burm.f.) seed viability were evaluated by Based on the germination response, dose- Persil var. plantaginea Solms. and Aeschynomene indica Linn. in scientists in the laboratory at response curve was generated and LC50 Department of Crop Science, values were calculated. It was maximum for calcareous soil condition. Application of University of Ghana, Accra, Ghana. R. sativus whereas minimum for A. A. conyzoides leaves at 2tonnes/ha in a All the treatments caused significant viridis. Further, seedling growth of the test paddy field 2days after transplanting caused mortality compared to untreated plants and the chlorophyll content in the about 75% paddy weed reduction and controls. Low dosages of the oils and treated seedlings was significantly reduced increased yield by 14% compared with an Pirimiphos-methyl when combined at concentrations 0.12 and 0.3mg/l. Not only treatment. Three phenolic were highly toxic to adult the initial growth, but also the spray compounds were identified in the leaves, S. zeamais. The mixtures treatment on the 4-week-old mature plants stem and root including gallic acid, coumalic completely inhibited the of two weedy species, viz. C. occidentalis acid, and protocatechuic acid, and catechin was found only in the stem. development of immature stages of and E. crus-galli adversely affected the chlorophyll content and cellular p-Hydroxybenzoic acid was detected in both the weevil. Only Pirimiphos-methyl respiration, thereby indicating the adverse leaves and stem. Three additional putative and the mixtures retained some effect of Eucalyptus oil on the allelochemicals were found in the leaves activity 60 days after application. photosynthetic machinery and the energy consisting of p-coumaric acid, sinapic acid Thus, the results revealed metabolism of the target plants. Based on the and benzoic acid. The greater number of that Pirimiphos-methyl could be study, it is concluded that volatile oil growth inhibitors found in the leaves might used at reduced rates if combined Eucalyptus is phytotoxic and could be result in the stronger inhibitory activity than with vegetable oils to control utilized as bioherbicide for future the stem and root. Thus, this weed might be infestations of S. zeamais in stored weed management programmes [Batish a natural herbicide for in maize [Obeng-Ofori & Amiteye, et al, Crop Prot, 2004, 23(12), paddy fields to reduce the dependence on J Stored Prod Res, 2005, 41(1), 1209-1214]. synthetic [Xuan et al, Crop 57-66]. Prot, 2004, 23(10), 915-922].

Natural Product Radiance Vol 4(1) January-February 2005 59

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