Tharu ethnic communities are rich in ethno-botanical knowledge on the utilization of plants for various proposes to fulfil their daily needs. They have precise knowledge about distribution, abundance, cultural practices, pest management, harvesting, and proper use of these plant resources. Gurau of Tharu communities and elderly people have sound knowledge on medicinal and pesticidal plants. Information on twenty-four locally available plants having pesticidal value, have been collected from the Tharu communities of Dibya Nagar and Meghauli VDCs, Chitwan. Out of them four of the most promising plants were selected to test their efficacy in farmers’ field conditions. In order to assess the effectiveness of plant materials on insect pests of vegetables, a farmers’ field experiment was conducted in Dibya Nagar during the summer of 2006. The plants selected to test efficacy against insect pests of Zucchini are Azadiracta indica, Justicia adhatoda, Persicaria barbata, and Artemisia indica. Plant extracts made from fresh green leaves of the selected plants at a concentration of 1:5 were applied at seven days intervals. It was found that A. indica had most promising effect on the pests, followed by P. barbata. However, all other treatments had positive effect. Similarly, the research result indicated possibility of using plant materials towards development of organic pest management methods.