RESEARCH ARTICLE Comparison of the effect of market crop wastes and chemical soil fertility amendments on insect pests, natural enemies and yield of Brassica oleracea J. Karungi 1 , S. Kyamanywa 1 & B. Ekbom 2 1 Department of Crop Science, Makerere University, Kampala, Uganda 2 Department of Entomology, Swedish University of Agricultural Sciences, Uppsala, Sweden Keywords Brevicoryne brassicae; diamondback moth; integrated pest management; Myzus persicae; organic fertilisers. Correspondence J. Karungi, Department of Crop Science, Makerere University, PO Box 7062, Kampala, Uganda. Email: jkarungi@agric.mak.ac.ug; jkarungitumu@yahoo.com Received: 16 January 2006; revised version accepted: 5 May 2006. doi:10.1111/j.1744-7348.2006.00068.x Abstract Field studies were conducted over three growing seasons during 2 years to assess the relative effect of market crop waste (MCW)-derived soil fertility amendments and conventional fertiliser (NPK) on tritrophic relations as well as yield performance of white cabbage. A randomised complete block design with four treatments and a control replicated four times was used. Treatments were (a) MCW compost incorporated in the soil, (b) uncomposted MCW incor- porated in the soil, (c) uncomposted MCW applied as surface mulch, (d) a conventional chemical fertiliser (NPK) incorporated in the soil and (e) the untreated control. Results indicated that relative to NPK-amended plants, MCW-amended cabbage performed better in plant growth parameters as well as yield, despite having sustained aphid and Plutella xylostella infestations that could be as much as double as those in the NPK treatment. Natural enemy occurrence followed the trend of host insect infestations. The average yield performance and net financial benefits from MCW-compost-amended plants were three-fold as that of NPK-amended plants. Soil analysis results indicated an advantage in soil quality accruing from the MCW amendments. This study, therefore, provides documentation for the utilisation of MCW, pre- viously handled as garbage to be disposed of, as a key component in inte- grated management of insect pests and depleted soils in crop production in sub-Saharan Africa and beyond. Introduction Cabbage, Brassica oleracea var. capitata L. (Brassicaceae), has gained popularity as a cash crop among periurban farmers in Uganda as evidenced by a 30% increase in land under production in recent years (Ssonko et al., 2005). Cabbage production has, however, only increased by 23%, indicating an overall decline in productivity (Ssonko et al., 2005). The major constraints are soil nutrient depletion and the ravages from insect pests and diseases. In East Africa, the most damaging pests of cab- bage include aphids [Brevicoryne brassicae L. and Myzus persicae (Sulzer) – Homoptera: Aphididae] and the dia- mondback moth (Plutella xylostella (L.) – Lepidoptera: Plutellidae) (Nyambo & Pekker, 1995). Dependence on chemical pesticides to control these pests, P. xylostella in particular, has led to increased production costs, and contributed to development of resistance to pesticides and loss of beneficial insects (Leibee & Savage, 1992). The problem of fertility decline in sub-Saharan Africa has been brought about by insufficient replacement of soil nutrients removed in harvests (Smaling, 1993), and this has been identified as the leading biophysical cause of food insecurity (Sanchez et al., 1997). It is imperative that the insect pests and soil nutrient depletion con- straints are investigated together to develop an inte- grated management strategy. Ironically, fertiliser amendments may be needed to combat pest infestations as there is evidence that organic fertilisers decrease herbivorous insect populations (Eigenbrode & Pimental, 1988; Phelan et al., 1995). In Uganda, periurban vege- table growers could utilise market crop wastes (MCW), Annals of Applied Biology ISSN 0003-4746 Ann Appl Biol 149 (2006) 103–109 ª 2006 The Authors Journal compilation ª 2006 Association of Applied Biologists 103