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Item On-field assessment of critical period of weed interference in okra [abelmoschus esculentus (l.) moench] field in ibadan, a rainforest-savanna transition eco-zone of Nigeria(2009) Awodoyin ,R.O.; Olubode, O.S.The critical period of weed interference is defined as the period in the life cycle of a crop during which it must be kept free of weeds to prevent unacceptable yield losses. The critical period of weed interference in okra [Abelmoschus esculentus (L.) Moench] was determined in the field trials during two cropping seasons (2006 and 2007) in the crop garden of the Department of Crop Protection and Environmental Biology, University of Ibadan, Ibadan located in the rainforest-savanna transition ecological zone of Nigeria. The study, consisting of two sets of treatments was carried out in a randomized complete block design with three replicates. In the first set of treatments, the crop was kept free of weeds for the first 2, 4, 6 and 8 weeks after planting (WAP) and subsequently weeds were allowed to grow (weed-free then weedy, WF-WD) until harvest, to determine the growth stage at which emerging weeds would no longer reduce the crop yields. In the second set of treatments, weeds were permitted to grow with the crop for an increasing length of time as listed above and subsequently the plots remained weed-free (weedy then weed-free, WD-WF) to determine the period at which weeds emerging with the crop began to suppress the growth of the crop and reduce its yield. Seasonlong weed-free (WD-0-WF) and weedy (WF-0-WD) treatments served as checks to compare weed competition and yield losses with other treatments. Season-long weed interference with okra resulted in 42.3% and 33.3% reduction in plant height, 54.9% and 45.5% reduction in stem diameter and 71.2% and 79.5% reduction in okra shoot dry weight in 2006 and 2007, respectively. Weeds that interfered with okra from 2 WAP resulted in 79.8% and 72.5% fresh fruit yield reduction in 2006 and 2007 respectively, and weed interference with okra from 8 WAP resulted in 19.8% and 19.6% yield losses in 2006 and 2007, respectively. Thirty one (31) weed species were enumerated in the study area with dicotyledons being the most prevalent (80.7%). The most important of the weed species among the dicotyledons was SynedrellaItem Response of vigna unguiculata.(L.) Walp. and amaranthus cruentus (L.) Thell to interference from acalypha segetalis mull arg. on marginal lands in southwestern Nigeria(2001) Ogunyem, S.; Awodoyin, R. O; Osunkoya, O.O; Olubode, O.S.; Wewe, O.F.The role of each weeds depends on weed type, density and duration of association with the crop as well as competitive ability of the crop. In open garden experiments, the phenology of Acalypha segetalis, a common weed of arable and ruderal habitats in south western Nigeria, and its influence on the growth and performance of Vigna unguiculata and Amaranthus cruentus, were investigated in 1999 and 2000. Acalypha segetalis was found to be slow growing in the first four weeks of its life cycle but developed rapidly and vigorously afterwords. It produced and shed seeds within 10 weeks of growth. Vigna unguiculata, which is highly susceptible to weed infestation in the first four weeks of growth, did not suffer significant growth and yield reductions from the association with j4 ca/yp/ia segetalis. However, Amaranthus cruentus, which has similar growth habits with the weed, suffered significant reductions in growth and yield. Amaranthus suffered up to 42% marketable yield loss when grown with Acalypha. The early slow growth of Acalypha determines its competitive potential in arable cropping systems. Crops that establish fast and with superior early growth ability may not suffer adverse competitive repression with the weed.