Weed Management in sorghum (Sorghum bicolor (L.) Moench

Abstract

The present study was conducted at Agadi farm, Arab Sudanese Blue Nile Agriculture Company (ASBNACO), in seasons 2009/2010 and 2010/011 during July to December. The objectives of the study were to determine the critical period for weed/crop interference and to determine activity and selectivity of some of the herbicides (atrazine, S-metolachlor and 2, 4-D) in use for weed control in sorghum. Predominant weed species in Agadi farm; constituting 52-64% of early season weed flora, were the broadleaved Merremia emarginata, Desmodium dichotomum (Klein.) DC, Vernonia pauciflora (DC.) Hiern, and Sonchus cornutus (Hochst.ex.Oliv & Hiern). Dinebra retroflexa, Brachiaria eruciformis, Penmisctum mosumra Hocnst Aschess and Ischaemum afrum (Desr.) Choisy were the dominant grassy weeds. The study showed that sorghum growth and grain yield increased with the weed free period (r = 0.91) and decreased with weedy period (r = 0.83). Unrestricted weed growth, irrespective of season and location, reduced all crops growth parameters. Crop stand, head length, head volume and grain yield were reduced by 52, 34, 14 and 49%, respectively. The onset of the critical period for weed/crop interference was at 2 WAS and termination was 8-10 weeks. All herbicide treatments reduced weed infestation, curtailed weed growth and significantly reduced weed biomass and increased crop growth and yield. The pre-emergence herbicides atrazine at 0.25 and 0.35 kg a . i. fed -1 and S-metolachlor at 0.384 and 0.48 kg a . i. fed-1 and tank mixtures of atrazine with S-metolachlor (0.2 and 0.25) kg a . i. fed-1 resulted in good to excellent control (73-84%) of the broadleaved weeds early in the season, however, moderate to good control (56-78%) was achieved late in the season. Control of grassy weeds by metolachlor was good to excellent (77-88%) early in the season, but moderate to satisfactory (59-63%) late in the season. The man hours required for clean weeding were 60.8 hr. fed-1. The herbicides reduced the man-hours for supplementary weeding. The time required for supplementary weeding of atrazine at (0.25 and 0.35 kg a . i. fed-1 ), S-metolachlor at 0.288 and 0.48 kg a . i. fed -1 and 2, 4-D at(0.16, 24 and 0.32 kg a . e. fed -1) were 36-46% of that required for clean weeding. 2, 4-D at 0.16-0.32 kg a . e. fed-1 resulted in moderate to good control (64-77%) of the broadleaved weeds early in the season, however, excellent control (84-89%) was achieved late in the season. 6 Control of grassy weeds by 2, 4-D was only moderate to satisfactory (52- 68%) throughout the season. S-metolachlor at 0.48 kg a. i. fed -1 tank mixed with atrazine at 0.2 and 0.25 kg a . i. fed-1 resulted in moderate to excellent control (69-93%) of grassy weeds early in the season, but late in the season only moderate to good control (56-79%) was maintained. Atrazine at 0.15 and 0.2 kg a . i. fed-1 in tank mixtures with 2, 4-D effected moderate to good activity (56-73%) of both grassy and broadleaved weeds early in the season, however late in the season moderate to excellent (61- 94%) control was achieved. All herbicides improved sorghum growth in comparison to the unweeded control, crop stand increased by 4-48, head length by 1-23, head volume by 1-15 and grain yield by 12- 48%. It is appearent that in Agadi, when no-till technique has been adapted for crop production, losses due to weeds are considerable. The critical period of weed interference for sorghum was between 4 and 8 weeks after sowing. Over the two years studies grain yield comparable to the weeded control was attained when the herbicides (atrazine at 0.25 kg a . i. fed -1 and 2, 4-D at 0.32 kg a . e. fed-1) were supplemented by hand weeding