The Efficacy of Ethanolic Root and Leaf Extract of Chromolaena Odorata in Controlling Sitophilus Zeamais in Stored Maize

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Sitophilus zeamais Motschulsky is among the important pests which attack stored maize. It is listed in addition to Prostephanus truncatus as the two most damaging species of maize in West Africa. In Ghana about 15% of maize grains harvested is lost to S. zeamais. A laboratory study was conducted at the Entomology laboratory of the Faculty of Agriculture of Kwame Nkrumah University of Science and Technology, Kumasi, to determine the efficacy of Chromolaena odorata (L) R. M. King and H. Robintson ethanolic root and leaf extract for Sitophilus zeamais control. The bioactivity of these extracts was assessed under average laboratory conditions of 26 °C and relative humidity of 80%. The leaf and root extracts at four dosage levels (0.0, 2.5, 5.0 and 10.0 ml) were mixed with 50 g of disinfested MAMABA maize variety in 750 ml plastic containers and the effect on insect mortality, progeny production and grain damage were assessed. The repellent action of these extracts at 0.0, 5.0, 10.0, 20.0 ml on Sitophilus zeamais was also evaluated. The leaf extract showed significant difference between 10.0 and 5.0 ml on one hand and 2.5 and control on the other hand. The 10.0 ml that recorded the highest mortality could inflict only as low as 8.75% after 7 days. There was no significant difference between the different levels of the root extract on mortality. The maize grain treated with the various dosage levels of the leaf extract showed much promise by significantly reducing the number of progeny produced by S. zeamais as compared with the control. Grain weight loss in leaf extract treated grains was dose dependent ranging from 3.51% in the highest dose to 11.34% in the control with significant differences. There were no significant differences in progeny production and grain weight loss with root extract treatments. Both the leaf and root extracts were not repellent to the weevil. The correlation between grain weight loss and progeny production was very strongly positively correlated in the leaf extract effect.
A thesis submitted to the school of Graduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi, as partial fulfillment of the requirement for the award of Master of Science in Crop Protection (Entomology) degree