Comparative efficacy of post-emergence herbicides in soybean in central Uganda

Abstract

In Uganda, farmers depend on hand weeding to manage weeds in soybean fields and this has restricted the expansion of soybean production area. Labour shortages, particularly during the critical crop-weed competition period, and inclement weather conditions lead to delayed weeding, which is ultimately costly, and ineffective. The use of postemergence herbicides is an attractive alternative for weed control in soybean because it provides faster, cheaper, and effective weed control in soybeans but there is limited information about the efficacy of postemergence herbicides in controlling weed species in Uganda and their effects on soybean performance. The experiment studied three postemergence herbicides i.e. Imazamox 40g/l SL, Imazamox 35.0% + 35.0% Imezethapyr, and Quizalofop p-ethyl 35 gr/lt + Fomesafen 125g/l, against controls of hand weeding using a hoe and no weeding. The treatments were laid out in a split-plot design with six replicates where the main blocks were the herbicides, and the subplots were soybean varieties. The weed species recorded during the study include; Cynodon dactylon, Cyperus rotundus, Digitaria abyssinica Bidens pilosa Panicum maximum, Oxalis latifolia, Commelina Banghalensis, Mimosa pudica. Rottboellia exaltata, Galinsoga parviflora, and Elusine indica. Out of the three postemergence herbicides, Quizalofop p-ethyl 35 gr/lt + Fomesafen 125g was the most effective in terms of weed control in soybean and its effect remains until crop harvest. Imazamox 35.0% + 35.0% Imezethapyr was better than Imazamox 40g/l SL in terms of weed suppression in soybean, however, a single application of these two post-emergence herbicides is not effective in controlling weeds in soybean throughout the growth period. A single hand weeding at 21 DAS is not effective in controlling weeds in soybean. There is no post-emergence herbicide that provided total weed control of all the weed species observed in the field.