During the field study 20 weed species were registered and determined in seedling alfalfa and 36 weed species in established alfalfa. Efficacy of herbicides in seedling alfalfa was ranged of 94.0% (imazethapyr) to 97.5% (imazamox-1.2 L/ha) in 2006, and 95.0% (imazethapyr) to 98.7% (imazamox-1.2 L/ha) in 2007, respectively. Efficacy of herbicides in established alfalfa was ranged of 91.8% (pronamide) to 98.4% (metribuzin-1.0 kg/ha) in 2007, 93.1% (imazetapyr) to 97.3% (metribuzin-1.0 kg/ha) in 2008 and 92.1% (imazetapyr) to 97.3% (metribuzin-1.0 kg/ha) in 2009, respectively. In the end of alfalfa exploitation period, a greenhouse experiment was conducted to detect the soil residues of metribuzin, imazethapyr and pronamide applied in established alfalfa stand by a bioassay using wheat. Detection of herbicide residues was determined from soil samples collected from depths of 0-5, 5-10, 10-20 and 20-30 cm. Most of the herbicides did not significantly affected plant density, height and fresh weight of wheat plants in any soil depth. Exceptions was pronamide, which significantly reduced wheat plant density, height and fresh weight of wheat at 10-20 and 20-30 cm depth.