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Abstract

A field experiment was conducted at the Demonstration Farm of the Faculty of Agricultural Sciences- El Selaim-University of Dongola- Sherg Elneel Unit, Dongola Locality, Northern State, Sudan, during two consecutive winter seasons of 2012/2013 and 2013/1014 to determine yield loss in sunflower (Helianthus annuus L.) due weeds and to identify the critical period for weed control. Sunflower, cultivar hysun 33, was sown on 24 November in both winter seasons. This research comprised 12 treatments which were arranged in randomized complete block design, with four replicates. The crop was kept weed-free for the first 2, 4, 6, 8 or 10 weeks after crop sowing and then left weedy till harvest or kept weedy for the same periods and then remained weed-free till harvest. Weed free and weedy treatments till harvest were included as controls for comparison. Broad-leaved weeds were predominant in the experimental site. The results revealed that sunflower seed yield progressively increased with the decrease of weed infestation period. Further, combined analysis of both winter seasons showed that unrestricted weeds interference significantly reduced both yield and yield components and the observed yield reductions was 51.87. Growth components were significantly reduced by weed competition under full season weed infestation treatment. Therefore, the critical period for weed control (C P WC) in sunflower according to this investigation was found to be between 2 to 8 weeks after planting.