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

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%.

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.

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.

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.

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.