Effectiveness of pesticidal plant extracts on field and post-harvest pests in Bambara groundnuts in Tanzania

Abstract

A randomized complete block design (RCBD) experiment was conducted to assess the effectiveness of Bidens pilosa, Lantana camara, Vernonia amygdalina, Tithonia diversifolia, Tephrosia vogelii and Lippia javanica against field pests of bambara groundnuts. The extracts were prepared by dissolving powder of the plants leaves at the concentration of 10% (w/v) in tap water containing 1% soap and left for 24 hours. Then, extracts were sprayed on 2 weeks seedlings of bambara groundnut and assessment of the abundance of insect pests and beneficial arthropods and plant damage was conducted weekly for 15 weeks. The results showed that pesticidal plants significantly (P ≤ 0.05) reduced the abundance of foliage beetles, aphids, mealybugs, red spider mites, and leafhoppers and caused significantly (P ≤ 0.05) less threat to ladybird, hoverfly, wasps and spiders. A storage experiment was conducted to assess the insecticidal effectiveness of B. pilosa, L. camara, T. vogelii, V. amygdalina, L. javanica, T. diversifolia and Croton dichogamus leaves powder on Callosobruchus maculatus. The pesticidal plants powder were admixed with grains at the dosage of 10% (w/w) and compared with actellic dust and untreated control. The experiment was monitored for 6 months. T. vogelii and actellic dust were the most effective treatments by killing 93.07 - 100% and 91.33 - 100% of bruchids respectively for 180 days of the study. Therefore, Tephrosia vogelii is recommended in controlling field and post-harvest pests in bambara groundnuts. Further research is recommended to assess the active compounds, mode of action and toxicity of T. vogelii and assess its effect on non-target organisms in bambara groundnuts.