Tiempos de aplicacion de oxyfluorfen y halosulfuron-methyl y su control de malezas en cebollas (Allium cepa L.)

Three field experiments were conducted to evaluate phytoxicity and efficacy of weed control of oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl) benzene] and halosulfuron-methyl [[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonylaminosulfonyl]-3-chloro-1-methyl-1- H-pyrazole-4-carboxylate] in onion (Allium cepa L.) crops at the Agricultural Experimental Station of Lajas from 2002 to 2003. In the first experiment, early applications of oxyfluorfen at 0.13 and 0.27 kg ia/ha at the 5, 10 and 15 days after onion emergence (DAE) caused less phytoxicity than simultaneous applications of halosulfuron-methyl at 0.027 and 0.054 kg ia/ha. Ten days after each application (DAA) the best weed control was obtained with the oxyfluorfen treatment at 15 DAE, however, twenty days later weed density was significantly reduced with the application at 5 DAE. Both rates of halosulfuron-methyl were deficient in general weed control and highly phytotoxic, regardless of application timing. In the second experiment, intermediate applications (20, 25 and 30 DAE) of halosulfuron-methyl at 0.013 y 0.027 kg ia/ha caused from moderate to severe damage to onion and were deficient in weed control. Compared with handweeded check, both rates of halosulfuron-methyl reduced onion yield and bulb number. Damage from halosulfuron-methyl was confirmed under greenhouse conditions, where it also caused reduction in fresh and dry weight of onion plants. In the third field experiment, the applications of halosulfuron-methyl at 35 DAE to plots previously treated with oxyfluorfen at 5, 10 and 15 DAE, caused severe damage to onion. In relation to weed control, the best combination for both herbicides was the application of oxyfluorfen at 10 DAE followed by halosulfuron-methyl at 35 DAE. Halosulfuron-methyl application resulted highly phytotoxic, reducing onion yield; for this reason the potential use in this crop must be dismissed.