Integrated Management of the Diamondback Moth, Plutella xylostella (L) (Lepidoptera:Plutellidae) and the Cabbage Budworm, Hellula undalis (F.) (Lepidoptera:Pyralidae) on Cabbage in Ghana

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Vegetables constitute an important component of the diet of Ghanaians. However, particularly to cabbage, pests and diseases are the militating factors against the industry. A survey was conducted in 1993 to gather baseline information on cabbage production and constraints to develop safe management practices to combat insect pest problems on the crop. A limited study was also conducted on the biology of Plutella xylosfella in the laboratory for basic information to develop an integrated control programme. Bioassays were conducted in the laboratory to determine promising candidate extracts of neem seed, garlic bulb, dry tobacco, tomato leaves and Chromolaena odorata leaves in controffing P. xylostella and Hellula undalis. Other pesticides evaluated included Dipel 2x (a biopesticide) and Karate, Lambda cyhalothrin (a chemical insecticide) and Omo (a detergent). Field efficacy trials were subsequently conducted on neem seed, garlic bulb and dry tobacco leaf extracts in addition to Omo solution Dipel 2x and Karate. Intercropping cabbages with onions, tomatoes, M. spicata and C. odorata were also evaluated for their efficacy in controlling cabbage pests on the field. The survey revealed that production of cabbage is done in all the 10 administrative regions of the country but less important in the Upper West and Western regions. Cabbage production was noted to be increasing, however, pests and diseases were forces to reckon with particularly in the Greater Accra, Ashanti and Central Regions. About 8 different cabbage varieties are grown in the country. Cabbage is produced all the year round on mainly rented lands in the urban centres. Indications are that apart from transplanting nursed seeds, direct planting of the seeds is also practiced. Notwithstanding, the latter method has a problem of poor crop establishment. Major constraints identified included insect pests namely; P. xylostella and H. undalis, land acquisition and marketing. P. xylostella has become resistant to all available chemical insecticides in the Country since 1990 (Joseph Amengor, 1993, Unpublished) and about 80% of pesticides used to control pests on cabbage are chemical insecticides. Twenty chemical insecticides were noted for use in controlling cabbage pests, most of which are unrecommended. Bioassay results obtained on plant extracts and other solutions indicated that extracts of neem seed, garlic bulb ‘and dry tobacco leaves and solutions of Omo hold promise in controlling P. xylostella and H. undalis on cabbage. Field efficacy trials on promising plant extracts and solutions effectively controlled H. undalis on cabbage at weekly application. The results did not show any significant differences between weekly and two weekly applications in controlling P. xylostella using the plant extracts and solutions at the 5% level of significance. P. xylostella can be effectively controlled when cabbage is intercropped with onions, M. spicata and tomato. However, in intercropping, there is the need to control H. undalis with pesticides up to six weeks after transplanting. Both Karate and Dipel 2x were effective in mitigating the problem of H. undalis in the intercropping experiments and both are recommended. Biological studies on P. xy1ostella showed that the insect can complete a life cycle in 14.3 days and can go through 26 generations in a year. The use of plant extracts and intercropping cabbages with onion, tomato and M. spicata hold promise in controlling P. xjlostella and H. undalis in Ghana.
A thesis submitted to the Board of Postgraduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfilment of the requirement for the award of the Degree of Master of Philosophy, 1997