Effects of an intercrop on the insect pests, yield, and quality of cabbage

Abstract

A field experiment to investigate the effects of crop diversity on the insect pests and yield of cabbage, Brassica oleracea var. capitata, was carried out at Lincoln College, Canterbury. All treatments were based on a standard cabbage plant spacing of 50 cm within rows and 100 cm between rows. Treatment 1 remained untreated; Treatment 2 was sprayed with 1.0 kg/ha Bacillus thuringiensis (Thuricide HP) at fortnightly intervals; Treatment 3 was intercropped with dill (Anethum graveolens); Treatment 4 was cabbage planted between standard rows, i.e., double the density in Treatment 1. Regular monitoring showed fewer white butterfly (Pieris rapae L.) eggs were laid on cabbages planted at the higher density and fewer alate cabbage aphids (Brevicoryne brassicae L.), occurred on plants intercropped with dill. Diamondback moth (Plutella xylostella L.) was not a prevalent pest. Applications of Bacillus thuringiensis resulted in improved cabbage quality but not increased yields. Lowest ‘per plant’ yields occurred at the higher plant density, but overall this treatment produced the highest yield per plot. Yield differences appeared to be largely a result of plant competition effects rather than insect feeding injury. © 1988 Taylor and Francis Group, LLC.