7. Effect of intercropping and soil amendment on the population dynamics of major pests and natural enemies of white cabbage

Abstract

Cabbage is an important exotic vegetable widely grown in Ghana. Despite its importance, cabbage production is constrained by insect pests attack, with the diamondback moth (DBM), Plutella xylostella L. and the Indian mustard aphid, Lipaphis erysimi pseudobrassicae (Davis) as the most important. A field trial was conducted at the Soil and Irrigation Research Centre, Kpong, in Ghana, during the major and minor rainy seasons of 2013 to study the effect of intercropping and soil amendment on the incidence of these key pests, their natural enemies and the yield of crop. The field was laid out as a split-plot design with soil amendment (biochar from rice husk, poultry manure and their combination) as the main plot and cropping system (sole cabbage, sole onion and cabbage-onion intercrop) as sub-plots. Multiple head formation was higher in sole cabbage plots than cabbage intercropped with onion. Similarly, sole cabbage plots supported a higher number of DBM larvae than cabbage intercropped with onion. Cabbage planted on soils without amendment, generally supported a fewer number of DBM larvae and natural enemies than the amended soils. The effect of the different treatments on the aphids population was not significant. The intercrop had the highest number of beneficial insects. The effect of soil amendment on the yield of cabbage and onion was significant with poultry manure plots recording the highest yield. The effect of cropping system was also significant on the yield of onion, with sole onion obtaining higher yields than onion intercropped with cabbage. The use of soil amendment also significantly improved the soil chemical and physical properties. Intercropping and soil amendment, therefore, have a lot of potential in sustainable vegetable production.