Bio efficacy evaluation of a formulated botanical pesticide for rice leaf folder (Cnaphalocrocis medinalis) under laboratory and field conditions in Sri Lanka

Abstract

Rice (Oryza sativa L.) is the staple food in Sri Lanka, but various pests cause significant losses. Rice leaf folder (RLF; Cnaphalocrocis medinalis) is one of the major rice pests. While synthetic pesticides are commonly used, they pose environmental concerns. This study aimed to evaluate the bio-efficacy of a formulated botanical pesticide (nano-emulsion) for RLF management under laboratory and field conditions during the 2024 Yala season. Laboratory experiments were conducted at the Rice Research and Development Institute, Batalagoda with nine treatments; T1 nano-emulsion I at 80 ml/16 l, T2 nano-emulsion I at 100 ml/16 l, T3 nano-emulsion I at 120 ml/16 l, T4 nano-emulsion II at 80 ml/16 l, T5 nano-emulsion II at 100 ml/16 l, T6 nano-emulsion II at 120 ml/16 l, T7 Azadiractin at 7.5 g/l EC, T8 Chlorantraniliprole at 200 g/l SC and T9 untreated control. Experiments were laid out as a Completely Randomized Design with three replicates. Results showed that T6 and T7 treatments had 80% mortality, followed by T8 with 100%. Based on laboratory results, five treatments were selected for field evaluation: T3 (T1), T6 (T2), T7 (T3), T8 (T4) and T9 (T5) were selected for field evaluation. Field trials were conducted in farmers’ fields in the Kurunegala district using a Randomized Complete Block Design (RCBD) with three replicates per treatment. Each plot measured 500m2. Live larval counts were recorded from 25 damaged leaves at 3, 5 and 7 days after treatment. Data were analyzed using CATMOD in SAS, with mean comparisons performed using Tukey’s test at p<0.05. The highest larval count was recorded in T5 (45) and the lowest larval count was count in T4 (0). T1 recorded a higher larval count (11) than T2 (5) and T3 (5). This study suggests that the tested botanical pesticide; nano-emulsions, represent a sustainable alternative to synthetic chemicals.