Efficacy of homemade botanical insecticides against diamondback moth (Plutella xylostella) and cabbage aphids (Brevicoryne brassicae) on Brassica crops

Abstract

The growing need for accessible alternatives to synthetic insecticides has renewed interest in farmer-made botanical formulations for pest management. This study evaluated the efficacy of selected homemade botanical insecticides against diamondback moth (Plutella xylostella) and cabbage aphid (Brevicoryne brassicae) on cabbage (Brassica oleracea var. capitata) and kale (B. oleracea var. acephala) under laboratory and semi-field conditions. Three homemade formulations were assessed: a one-day-old multi-plant extract with neem (Azadirachta indica; PE + N), a one-day-old extract without neem (PE), and a fourteen-day-old, fermented extract without neem (PE14). These were compared with three commercial botanical products. In replicated leaf- and plant-based bioassays, neem-based treatments (PE + N and Nimbecidine) consistently caused higher pest mortality than non-neem formulations. Both treatments achieved over 50% mortality of P. xylostella and B. brassicae at higher concentrations, with shorter median lethal times (LT50) and lower median lethal concentrations (LC50). Formulations without neem remained below the 50% mortality threshold under most conditions. Efficacy was lower under semi-field conditions than in laboratory assays, reflecting environmental influences on botanical stability. These findings demonstrate that neem-based homemade botanicals derived from farmer practices can provide pest suppression comparable to commercial biopesticides under controlled and semi-field conditions. While variability in efficacy and lack of formulation standardization remain challenges, such botanicals represent a promising complementary option within integrated pest management strategies for smallholder farming systems.