Efficacy of plant extracts for reducing larval populations of the diamondback moth, Plutella xylostella L.(Lepidoptera: Yponomeutidae) and cabbage webworm, Crocidolomia binotalis Zeller(Lepidoptera: Pyralidae), and evaluation of cabbage damage.

Abstract

The efficacy of four plant extracts, Alpinia galanga Sw. (Zingiberaceae), Amomum cardamomum Auct. (Zingiberaceae), Cyperus rotundus L. (Cyperaceae), and Gomphrena globosa L. (Amaranthaceae) were evaluated against the diamondback moth, Plutella xylostella L. and the cabbage webworm Crocidolomia binotalis Zeller larvae on cultivated cabbage. Treatments with 0.5% A. galanga and G. globosa extracts significantly reduced P. xylostella larval density, and the percentage of infested plants, proving to be more effective than a standard insecticide Decis7 2.5EC (deltamethrin). Moreover, G. globosa significantly reduced the intensity of cabbage damage caused by P. xylostella. Treatment with 0.5% A. cardamomum extract reduced the percentage of P. xylostella-infested plants and the intensity of cabbage damage. However, the plant extracts did not effectively reduce C. binotalis larval density, the percentage of infested plants or the intensity of cabbage damage. Phytotoxic effects on cabbage plants were not observed in any extract treatment.