INTEGRATION OF Allium cepa AQUEOUS EXTRACTS AND FARMYARD MANURES IN THE CONTROL OF Aphis fabae AND Tetranychus evansi INFESTING Solanum nigrum CULTIVARS IN WESTERN KENYA

Abstract

The black nightshade, Solanum nigrum Linnaeus (Solanaceae), is a widely distributed tropical plant used as a nutritive vegetable and herbal medicine in East Africa. This plant expresses high levels of secondary metabolites such as steroidal glycoalkaloids (SGA) and phytoalexins, which offer protection against pests and microbial pathogens. However, insect pests especially the black bean aphid Aphis fabae Linnaeus (Homoptera, Aphididae) and the red spider mite Tetranychus evansi Linnaeus. (Acarina, Tetranychidae), have become a major problem for S. nigrum Linnaeus, especially the improved cultivars with less bitterness that are being adopted in western Kenya. The effects of A. fabae Linnaeus are aggravated by attendant ants that protect them while cleaning their sugary secretions. The current research evaluated the potential of onion (Allium cepa Linnaeus) extracts and farmyard manures in the integrated control of A. fabae Linnaeus and T. evansi Linnaeus infesting three S. nigrum Linnaeus cultivars in western Kenya. The field study was conducted within Masinde Muliro University of Science and Technology farm, in Kakamega County, western Kenya. The experiment was a randomized block design of 8 blocks of 3.6 m x 4 m with 9 plots represented by rows of 20 plants. Two cultivars of S. nigrum var. scabrum Linnaeus and one cultivar of S. nigrum var. nigrum Linnaeus were used. Extracts were prepared using a Detergent water method. Cattle and chicken manure were obtained from the University farm and left to mature and dry naturally in a shade before being crushed to fine particles. Field investigations included pest population build up, pest enumeration, plant height, leaf deformations and biomass. Sampling was done once every week on plants in situ one day after spraying with the onion extracts and numbers counted. Data was analyzed using SAS version 9.1. The number of aphids was highest in cultivar B (Solanum nigrum var. nigrum Linnaeus). Plants grown with cattle manure grew better than those grown with chicken manure or without manure. Pest populations were high in plants grown with chicken manure, especially cultivar B, showing a preference that occurs during the presence of non-preferred hosts. Four attendant ant specie, Dolichoderus mariae, Formica glarialis, Formica padelifulva and Camponotus sp protected aphids from predators. Application of onion extracts reduced pest populations, and cultivars F and M tended to have the best effect.