Influence of weeding regime and neem seed extract on the population of insect pests and yield of cabbage in the Guinea savannah zone

摘要

This experiment was conducted during the 2005 and 2006 cropping seasons at the research field of the Faculty of Agriculture, University for Development Studies, on Nyankpala campus near Tamale in the Guinea savannah zone of Ghana. The objectives of the study were to determine the influence of weeding regime and application of neem seed extract (NSE) on insect pest populations and yield of cabbage. The experiment was a 3 x 5 factorial laid out in randomized complete block design with three replications. The treatments consisted of: hoe weeding every 2 or 3 weeks and unweeded control combined with applications of NSE at 2% (w/v), 5% and 10%, and Karate 2.5 EC (Lambda cyhalothrin) and water-treated control. The results indicated the occurrence of broadleaves, grasses, sedges and shrubs in order of dominance as weed species. Insect species prevalent included grasshoppers (Zonocerus variegatus [L.]), crickets (Gryllus spp.), caterpillars of diamondback moth (Plutella xylostella L.), cabbage webworm (Hellula undalis F.), and flea beetles (Phyllotreta cruciferae [Goeze]). Snails (Helix pomatia L.) were the other prevalent pests recorded. Weed biomass was affected only by weeding regime and was highest on control plots followed by plots weeded every 3 weeks and every 2 weeks, respectively. Weeding regime significantly affected the populations of insect pests on cabbage. Hoeing every 2 or 3 weeks lowered pest populations with consequent stability in plant population and increased cabbage yield more than the control plots. The 10% NSE was highly effective and gave better protection to cabbage plants against pest damage than the 5% NSE, Karate, 2% NSE and water-treated control with corresponding increase in yield and cosmetic beauty of cabbage heads. Overall however, between 5% - 10% NSE can be used as an alternative to the synthetic insecticide Karate to control insect pests of cabbage. Also, weeding every 3 weeks was adequate to avoid yield loss due to weed competition.