Effect of Intercropping Collard with Beans or Onions on Aphid Populations and Yields of Collard Under High Altitude Conditions in Kenya

Abstract

Collard (Brassica oleracea var,acephala D, C) is an important source of income to many small-scale farmers in Kenya and constitutes part of the diet of many Kenyans especially in urban areas, Successful production of collard is however, constrained by several pests, with aphids (Brevicoryne brassicae and Myzus persicae) being among the major pests. Control of aphids has mainly been by chemical sprays, which has tended to result in pest resistance and pollution to the environment. This study was therefore, an attempt to look into alternative and environmentally friendly ways of controlling aphids in collard. To achieve this, two studies were conducted in Kenya to determine the effects of intercropping and nitrogen fertilization on aphid population on collard and the yield response of the crop to these practices. The experimental design used was a split plot arranged in a randomized complete block design with three replications. Nitrogen levels (0,145,289, and 361 kg N/ha) comprised the main plots while cropping regimes (collard intercropped with 'onions (Allium cepa L), collard intercropped with beans (Phaseolus vulgaris L), monocrop collard sprayed with 'Bulldock' and unsprayed monocrop collard formed the subplots. Intercropping collard with either beans or onions significantly lowered aphid population on collard compared to unsprayed monocrop collard, Overall, the lowest aphid population was recorded in insecticide sprayed nionocrop collard during the first season of the study. In the second season, aphid populations recorded in sprayed collard plots were not significantly 'different from those recorded in collard - bean intercrop, Nitrogen fertilization increased aphid population on collard plants but did not have any significant effect on leaf vegetable yields. Intercropping increased food output per unit area of land, measured by Land Equivalent Ratios. In both seasons, nitrogen fertilization did not significantly affect collard, bean or onion yields. Considering the potential risks associated with frequent use of synthetic insecticides and high doses of nitrogen in crop production, these results indidicate that intercropping collard and beans or onions and use of low nitrogen rates can be effectifively used to suppress aphid populations in collard.

Keywords: Allium cepa., Brassica oleracea, Brevicoryne brassicae, Inlercropping, IPM, LER, Myzus persicae, Nitrogen fertilizer, Phaseolus vulgaris

Tanzania J.Agric.Sc, (2606) VoI.7 No.2, 57- 66