Sweet potato is either left unweeded or weeded lately in southern Ethiopia. The study was conducted to evaluate the effect of canopy structure, plant density and weeding frequency on weed infestation and tuber yield during 2002and 2003 Three sweet potato varieties with different growth habit [‘TIS 1499’,’TIS 2498’ and ‘Koka 6’], four plant densities [5, 7, 10, and 12.5 plants m-2], and two weeding frequencies [Weeding once, 30-40 days after sprout (DAS) (W1), and twice 30-40 and 70 DAS (W2)] were laid out in factorial arrangement in randomized complete block design with three replications.The major weeds were broadleaf, grass and sedge. Weed density in 2002 was 54.5% less while weeding ‘TIS 1499’ and ‘Koka 6’ twice reduced weeds by 31.9 and 31.2%, respectively, but no significant variation in ‘TIS 2498’. The dry weed biomass in ‘TIS 2498’ and ‘Koka 6’ was 48.3 and 29.2% less, respectively. The yield in 2002 was 30.8% higher whereas the yields of ‘TIS 1499’ and ‘TIS 2498’ were not significant in both years. Weeding twice significantly produced 68.9% more yield of ‘TIS 1499’, but no significant variation between weeding practices in other varieties. The yields of ‘TIS 1499’ and ‘Koka 6’ within a population of 7 to 10 plants m-2 were significantly high, but ‘TIS 2498’ showed no significant variation among plant densities. The cultivar with spreading growth reduced weed infestation and required only one weeding, while that with erect growth needed two weedings. Plant density of 7 to 12.5 plants m-2 can be used for cultivars with erect and intermediate growth. Growth with spreading canopy can be used as means to reduce weed infestation that saves farmers’ time and labor. Breeders can thus focus in developing cultivars with spreading canopy with high yield.
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