Two field experiments were carried out in grower's fields of the Bebedouro Irrigation Project, in Petrolina, PE, in order to study the performance of several herbicides in controlling weeds on transplanted onion crop and the crop tolerance. The treatments were arranged in a randomized complete block design with 3 replications, in a sandy red -yellow Latosol, of low clay and organic matter values. In the experiment I, oxadiazon (1.00 kg/h a), pent imethalin (1.25 kg/h a) and napropamide (1.50 kg/ ha) were applied in pre -emergence, two days aft er transplanting; oxyfluorfen (0.24 and 0.48 kg/h a) in early post emergence, ten days after transplanting; oxadiazon (1.00 kg/ha), oxadiazon (1.00 kg/h a) + ammonium sulphat e (5.00 kg/h a), bentazon (0,72 kg/h a), acifluorfen-sodium (0.32 kg/h a), dinoseb acetate (1.50 kg/h a), setoxydim (0.23 kg/ ha), alloxydim -sodium (1.12kg/ha ), diclofop-methyl (0.72 kg/h a) , and bentazon (0.72 kg/ha) + sethoxydim (0.23 kg/h a), 14 days after transplanting. In the experiment II, oxadiazon (1.00 kg/h a), oxyfluorfen (0.48 and 0.96 kg/h a), and napropamide (1.50 and 3,00 kg/h a) were applied two days after transplanting; oxyf luorfen (0.48 and 0.96 kg/h a), bentazon (0.72 and 1.44 kg/h a), acifluorfen-sodium (0.27 and 0.54 kg/h a), dinoseb acetate (1.50 and 3.00 kg/h a), and bentazon (0.72 kg/h a) + sethoxydim (0.23 kg/h a), 14 days after transplanting. In evaluations made 20 and 34 days after transplanting, respectively in the experiment I and II, high levels of weed control by oxadiazon and oxyflurfen herbicides were observed. Among other treat ments, acifluorfen -sodium was outs tanding in controlling broad leave weeds and sethoxydin, alloxydim-sodium, napropamide, pendimethalin and bentazon + sethoxydim mixture in grass control. In experiment II, dinoseb and mainly napropamide affected the develop ment of the onion crop and caused yield reductions.
onion; her icide; weeds; chemical control