Effects of Bio-rational Insecticides on Diamondback Moth (Plutella xylostella L.) and Cabbage Aphid (Brevicoryne brassicae L.) on Cabbage

Abstract

Background: Cabbage is a subsistence crop for smallholder farmers in Ethiopia. Diamondback moths and cabbage aphids are among the devastating insects that cause yield losses of 90% and 30%. Objective: The aim was to test the efficacy of the bio-rational insecticides against diamondback moth and cabbage aphids, and their effect on cabbage yield and yield loss. Methods: A field experiment was conducted at the Gumsalasa micro dam with furrow irrigation during 2019/20 in Northern Ethiopia. Treatments were arranged in RCB design and replicated thrice. The experiment included five bio-rational insecticides; (R. obtusifolius), (P. dodecandra), (N. glauca), (T. minuta), (A. indica), Karate 5% EC (standard test), and control. Results: Phytolacca dodecandra aqueous leaf extract showed inspiring results, reducing diamondback moth larvae to 0.13 and aphid colonies to 0.16, 48 hours after the 4th spraying, leading to a higher (40.28 t ha-1) fresh cabbage yield followed by A.indica, which had reduced the invasion of diamondback moth and aphid colonies to 0.20 and 0.40 and the yield was recorded as 27.69 t ha-1 compared with 2.46 and 5.53 diamondback moth and aphid colonies, and 23.86 t ha-1 cabbage yield in the control group. Similarly, aqueous extracts of P. dodecandra showed a commendable yield (68.82%) increment over the control, and an estimated yield loss of 40.76% was recorded from the control plots due to the tested insect pests. Conclusion: This study concludes that foliar extracts of P. dodecandra can be used as an alternative management option to replace synthetic insecticides and thereby maintain food security.