Phytosociological surveys are basis for weed management in agricultural crops. We aimed in this study to survey weed within a cassava cultivation field in the city of Vitória da Conquista, Southwestern Bahia, Brazil. The crop was grown for 18 months (from January 2013 to July 2014), with samples at 35, 70 and 105 days after planting (first year cultivation), and at 350, 385 and 420 days after planting (second year cultivation). Sampling was performed according to inventory square method, in which a 0.25 m2 iron frame is thrown randomly on the cropland. Then, weed within this metal square area are cut at ground level, identified, quantified and afterwards placed into an oven at 65°C during 72 h to obtain dry mass of each species. Evaluated phytosociological parameters were frequency, relative frequency, density, relative density, abundance, relative abundance and importance value index. The main identified families in the survey were Malvaceae, Asteraceae and Poaceae. In total, it was assessed 14 families, 32 genera and 38 species of weeds. The highest importance value index was found for Sida rhombifolia, Cynodon dactylon and Brachiaria plantaginea. Regarding dry mass, Panicum maximum, B. plantaginea and S. rhombifolia had the largest values. It was concluded that weed control methods must focus on species and consider reinfestations in the second crop year.
Key words: Manihot esculenta Crantz, infesting community, competition, weed-competition.
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