Bio-efficacy of Crude Aqueous Leaf Extracts against the Fall Armyworm ( Spodoptera frugiperda ) and Maize Ear Rots in Zambia

Abstract

The use of crude aqueous leaf extracts (=plant extracts) provides an excellent opportunity to explore their potential as an alternative control method to chemical insecticides. Following the invasion of Zambia by Fall armyworm, Spodoptera frugiperda (FAW), huge amounts of chemical pesticides have been procured and applied to control the pest, potentially creating an environmental health hazard. This study was therefore conducted to assess the bio-efficacy of crude aqueous leaf extracts of selected plants against FAW and maize ear rots. A no-choice bioassay set up prior to a field trial revealed that extracts of Azadirachta indica, Gliricidia sepium, Nicotiana tabacum, Ri-cinus communis, and Tephrosia vogelii applied rate of 10% weight by volume exerted more than 40% FAW larvae mortality. These extracts when tested in a field experiment over two seasons, 2020 and 2021 with two checks, chemical insecticide, Lamb-da-cyhalothrin 5EC and untreated control significantly reduced FAW infestation by 21.7 to 33.3%, had low number of larvae per plant, and less leaf damage compared to the untreated control, though significantly higher than that insecticide control. It was further observed that more than two sprays were required to effectively control the pest. At harvest, there were significantly less incidence and severity of maize ear rot, low levels of cob damage and higher grain yield in leaf extract treatments than the unprotected maize. Overall, R. communis followed by A. indica and N. tabacum were most effective in reducing FAW attack and maize ear rot infection. Given their effectiveness , it is imperative these extracts are included in an Integrated Pest Management Program for FAW.