A field trial was carried out in Eldorado do Sul, RS, during the 1994/95 growing season to evaluate Alexandergrass (Brachiaria plantaginea (Linck ) Hitchc ) control, that occurred with na average population of 95 plants/m2. The herbicide used was clethodim at full-rate (120g/ha) and at half-rate (60g/ha). The tested cultivar was RS-7 Jacuí and it was use d a complete randomized blocks design with four replicates. The treatments were applied at 14, 21, 28, and 35 days after soybean emergence (DAE) . Hand hoeing treatments were included, and started at the same date of herbicide applications. A weeded check was kept during all crop cycle. Control evaluations were visualy performed in three opportunities using percentual scale. The levels of Alexandergrass control got with full herbicide rate were equival ents when clethodim was applied at the three first times. Its efficiency ranged from 95 to 98% at the last evaluation. Half herbicide rate showed si mil ar trends at the la st eval uation, although at lower levels, ranging from 85 to 95% control for the three first application times. Alexandergrass control was only fair when clethodim was applied at 35 DAE at either rate. Grain yield did not show differences between treatments except for weedy check; nevertheless, all of them supplanted the weeded treatment with increments ranging from 73 to 105%. This trial allows to conclude that it is possible to use half-rate of clethodim to control Alexandergrass in soybean, being the application done preferably until the fourth week after soybean emergence .
Glycine max; postemergence herbicide; interference; Brachiaria plantaginea