Biopesticidal Properties of Aqueous Crude Extracts of Tobacco (Nicotiana Tabacum L.) Against Fall Armyworm (Spodoptera Frugiperda J.E Smith) on Maize Foliage (Zea Mays L.) Diets

Abstract

Pesticidal plants offer valuable and sustainable options for managing Lepidopteran pests with considerable health, environmental and economic benefits in smallholder agro-ecosystem. Research was done to determine the efficacy of aqueous extracts of tobacco (Nicotiana tabacum) against fall armyworm (Spodoptera frugiperda Smith) on maize foliage (Zea mays L.) diets. Bio-efficacy of aqueous crude N. tabacum leaf extracts was evaluated under average room temperature at Great Zimbabwe University, Biology laboratory. The treatments were tobacco leaf extracts at four dosage levels (25 %, 33.33%, 41.67 % and 50% W/V) and a negative control of untreated maize leaf foliage (distilled water) was used. A positive control of Carbaryl 85% WP was also used at label rates. The experiment was arranged in a Complete Randomized Design (CRD) replicated three times. Five larvae were placed into each of the experimental jars with maize foliage diets drenched into 10ml of distilled water in each treatment extract to keep the maize leaf foliage moist. Mortality for each treatment was recorded at 2 hourly intervals for 20 hours. Results showed that tobacco crude aqueous leaf extracts had antifeedent activities against FAW larvae. The highest dose of 50% had significantly higher mean FAW larval mortalities (p< 0.05) than lower dosage (25%) and the negative control after 20 hours. However, 50% concentration was not significantly different (p>0.05) from the positive control and that of 33.33% and 41.67% dosages. The bioassay indicated that the 33.33% extract was superior in toxicity to 25% dose and the negative control but similar to higher extract doses though inferior to positive control. However, the mean mortality of 50% extract was not significantly different from that of the positive control. This study recommends that 50% tobacco aqueous crude leaf extract dose to be used when controlling FAW in maize in the smallholder sector.