Studies on Photo Stabilization of Pyrethrum Flower Extracts using Clay

Abstract

The use of botanical pesticide in the agricultural sector over synthetic pesticide would ensure less pest resistance and reduced environmental pollution. Pyrethrins are effective, environmental friendly pesticides, but are photo-labile, limiting their use in pest control. Clay is a natural occurring mineral and its photo-stabilization of pyrethrins would result in formulation of environmental friendly pesticide. In the present study, montmorillonite (MMT) clays were obtained from natural clay by sedimentation and centrifugation techniques. Organo-clays were prepared by treating the clay with Hexadecyltrimethylammonium bromide (HDTMA) and Trimethylphenylammonium Bromide (TMPA) organic cations. Pyrethrins molecules were loaded onto these organo-clays by mixing them with the pyrethrins solutions to obtain pyrethrins-organo clay composites and the samples were characterized using Fourier Transform Infrared (FT-IR) spectroscopy and X-ray Diffractometry (XRD) techniques. In vitro photo stability tests were done using artificial UV light at 254 nm and 366 nm and in situ tests by exposing the Pyrethrins-clay composite products in sunlight for four hours. Different sample treatments exposed to UV light were used against maize weevils to test their efficacy. The findings demonstrated that HDTMA cations were intercalated more in the MMT clay materials in comparison to TMPA cation. This consequently resulted to more sorption of PFE’s molecules sorption into the HDTMA-clay composites. A great potential of clay to photo stabilize PFE and consequently improve the efficacy of PFE-based pesticides. Bioassay test on maize weevils revealed 100 % mortality rate on PFE HDTMA-clay treatments at 120 hours while the un-protected PFEs exhibited 18% mortality rate for the same duration of time. Pyrethrins were highly photo-stabilized by HDTMA-clay reducing in its photo-degradation. Bioassay study showed that PFE-HDTMA clay can be a potential maize grain protectant against maize weevils (Sitophilus zeamais) due to considerable mortality rates at low dosage. Successful photo-stabilization of the pyrethrins pesticide based formulation would improve the marketability of the pyrethrum flowers, improve economic utilization of clay deposits and consequently boost food security in Kenya and globally at large