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Striga hermonthica (Scrophulariaceae) is one of the greatest scourges of food crops in semi-arid areas in Africa. To improve the efficiency of a chemical treatment using 2,4-D, the dynamics of flowering together with the embryology of S. hermonthica were studied on untreated and treated plants growing in field conditions. It was established that the flowering period lasts 21 to 25 days. Embryogenesis, conforming to the Capsella type, shows a key step, i.e. the hypophysis initiation, occurring 7 to 10 days after the opening of the flower. Treatments applied before this step destroy the embryos whereas later treatments are ineffective. The best results are obtained with two or three low doses of 2,4-D, the first one being applied at the beginning of the flowering period and the others at an interval of 10 to 12 days. However, to convince smallholders of the effectiveness of the method, an important campaign of information and training is necessary.