The experiments were conducted in 2009-2011 in the experimental field of the Department of Agriculture and Herboligy of the Agricultural University – Plovdiv. The biological efficacy of three foliar systemic selective herbicides was studied as well as their influence on the yield of two varieties of medium-early potatoes. The studied herbicides were as follows: propakvizafop (Azhil 100 EC in a dose 200 ml/dka), kvizalofpo-P-etyl (Targa Super 5 EC in a dose 300 ml/dka) and fluazifop-P-butyl (Fuzilad forte in a dose 130 ml/dka). Azhil 100 EC in a dose 200 ml/dka (a.s.propakvizafop) showed the highest biological efficiency destroying on the average 99.74% of Johnson grass from seeds and from rhizomes. The best effect on the yield of potatoes was manifested by propakvizafop, increasing the yield of the Sante cultivar by 132.0 kg/dka.