Controle de plantas daninhas em soja com herbicidas pré-emergentes sob condições de cerrado

The effects of cyanazine 2-{[4-chloro-6-(ethylamino)-s-triazin-2-yl] amino} -2-methylpropionitrile), metolachlor (2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-l-methylethyl) acetamide), metribuzin (4-amino-6-tert-buthyl-3-methylthio-astriazin-5 (4H) one) and cinmethylin (7-oxabicicle (2, 2, 1) heptane, 1-methyl-4-(1-methylethyl)-2-(2-methyl-phenylmethoxy)-exo) on soybean (Glycine max (L.) Merr.) weed control were evaluated. Cyanazine applied, either alone or in mixture with cinmethylin was injurious to the crop by a concentration-dependent phytotoxicity. The inicial stand was reduced by cyanazine at 0,75 kg/ha + cinmethylin at 0,42 kg/ha and cyanazine at 1,00 kg/ha + cinmethylin at 0,42 kg/ha. The lowest final stands were observed with cyanazine at 1.00 kg/ha + cinmethylin at 0,42 kg/ha. Cyanazine + metolachlor reduced the phytotoxic effect caused by cyanazine. Eleusine indica and Richardia Brasiliensis were well controlled by all herbicides up to 30 days after application. From that date on, the higher rates of cyanazine were applied, the less control of those weeds were obtained. Alternanthera ficoidea was well controlled by cyanazine, cinmethylin, and metolachlor up to 30 days after application. Ageratum conyzoides was controlled by herbicides tested up to 30 d.a.a. Commelina sp was controled by cyanazine + cinmethylin, cyanazine + metolachlor, and by metolachlor up to 30 d.a.a. Foram avaliados os efeitos de cyanazine (2-{[4-cloro-6-(etilamino)-s-triazin-2-il] amino}-2-metilpropionitrila), metolachlor (2-cloro-N-(2-etil-6-metilfenil)-N-(2-metoxi-1-metiletil) acetamida), metribuzin (4-amino-6-tert-butil-3-metiltio-1,2,4-triazina-5(4H)ona) e cinmethylin (7-oxabiciclo-(2,2,1) heptano 1-metil-4-(1-metiletil)-2-metil-fenilmetoxi)-exo), para o controle de plantas daninhas em soja (Glycinemax (L.) Merr.). Cyanazine e a mistura cyanazine + cinmethylin apresentaram tendências de fitotoxicidade para a cultura em função da dose. O estande inicial foi reduzido pelas misturas de cyanazine a 0,75 kg/ha + cinmethylin a 0,42 kg/ha e cyanazine a 1,00 kg/ha + cinmethylin a 0,42 kg/ha e em menor intensidade pelo cinmethylin a 0,42 kg/ha. Os menores estandes finais foram observados com cyanazine + cinmethylin a 1,0 kg/ha + 0,42 kg/ha. A mistura de cyanazine + metolachlor diminuiu o efeito fitotóxico da cyanazine. O capim-pé-de-galinha (Eleusine indica) e a poaia (Richardia brasiliensis) foram eficientemente controlados por todos os herbicidas testados, aos 30 dias após a aplicação. A partir desta data, doses mais altas de cyanazine mostraram-se menos eficientes. O apaga-fogo (Alternanthera ficoidea) foi controlado por cyanazine, cinmethylin e metolachlor até aos 30 dias. O controle do mentastro (Ageratum conyzoides) foi conseguido por todos os herbicidas testados. A trapoeraba (Commelina sp) foi eficientemente controlada pelas misturas de cyanazine + cinmethylin e metolachlor e pelo metolachlor aplicado isoladamente, até aos 30 dias após a aplicação (d.a.a.).