Efficacy of imazethapyr and chlorimuron-ethyl in pre-sowing applications on soybean crop.
A study was carried out in Rio Verde, Goias, Brazil, during 2003/04 to evaluate the efficacy of the herbicides imazethapyr and chlorimuron-ethyl [chlorimuron] under pre-sowing conditions in soyabean crop. Weed control before sowing and emergence reduction during the crop season were evaluated. The experiment was established in the soyabean field cultivated under no tillage. Four herbicide treatments: glyphosate (1.62 kg ha-1); glyphosate (1.62 kg ha-1)+imazethapyr (100 g ha-1); glyphosate (1.62 kg ha-1)+chlorimuron-ethyl (10 g ha-1); and glyphosate (1.62 kg ha-1)+chlorimuron-ethyl (20 g ha-1) were combined with 4 application intervals between herbicide application and sowing time (0, 1, 3 and 7 days). The cultivar MG/BR 46 (Conquista) with rows spaced at 0.50 m was used as the control, with no herbicide application. The addition of imazethapyr (100 g ha-1) and chlorimuron-ethyl (10 or 20 g ha-1) to glyphosate did not improve weed control nor decreased late re-growth of the following species: Digitaria insularis, Tridax procumbens and Leptochloa filiformis. Three days was the minimum interval in which the 3 species were not injured by the mechanical sowing process. The herbicide treatments did not affect the number of emerged plants of the following species: Sida santaremensis, D. insularis, Eleusine indica, Chamaesyce hirta, Bidens pilosa and Senna obtusifolia [Cassia obtusifolia]. Only Alternanthera tenella [A. ficoidea] had its emergence rate decreased by herbicide addition to glyphosate, showing pre-sowing efficiency. All the herbicide treatments during pre-sowing increased the soyabean yield compared to the control. Herbicide addition to glyphosate did not increase the yield.