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The biology and competitive ability of African bonebract, Sclerocarpus africanus Jacq are less understood in the tropics. Studies were conducted in the roof-top garden (7o27.0301N; 3o53.8251E; 222 m asl] of the Department of Crop Protection and Environmental Biology, University of Ibadan, Ibadan in the dry forest-savanna transition ecological zone of Nigeria to understand its biology of germination and growth, and its critical period of interference in okra [Abelmoschus esculentus (L.) Moench] and cowpea [Vigna unguiculata (L.) Walp] in completely randomized design experiments in 2008. Effect of boiling water treatments at durations 0, 5, 10, 15, 20, 30, 40, 50 and 60 seconds on germination were investigated. Growth and biomass accumulation over 12 weeks were studied in two trials. The critical period of weed interference was studied in two sets of treatments. In one set of treatments, S. africanus was permitted to grow with okra or cowpea for the first 2, 4, 6, 8 and 10 weeks after planting (WAP) and subsequently free of the weed till final harvest at 12 WAP [weedy-weedfree, wd-wf]. In the second set of treatments, the seedlings of S. africanus were introduced to the crops from 2, 4, 6, 8 and 10 WAP to interfere with the crop till 12 WAP [weedfreeweedy, wf-wd]. Weedfree and weedy treatments served as checks. Seeds of S. africanus had low germination rateof about 13%. Boiling water treatment for 5 seconds reduced germination to about 10%, and treatments from 10 seconds and above resulted in zero germination. Within 12 weeks of growth, S. africanus had attained a height of 45.9 ± 0.2 cm and 60.3 ± 2.9 cm in the first and second trial, respectively. It had total dry matter accumulation of 16.7 ± 0.7 g and 16.73 ± 0.03 g in the first and second trial, respectively. It produced flowers within 10 weeks of growth and had started to form seeds at 12 weeks when the study was terminated. Interference of the weed with okra for 10 WAP resulted in 65.5% fruit yield reduction and interference throughout resulted in 65.9% yield reduction. Interference with cowpea for 10 WAP and throughout resulted in 30.6% and 47.9% respectively. To prevent >10% yield loss S. africanus must be removed on okra plot at 2-6 WAP and on cowpea plot at 2-4 WAP. Results indicated that S. africanus emerging after 6 WAP and 4 WAP did not reduce yield in okra and cowpea, respectively.
Keywords: Competition, cowpea, germination, okra, phenology