Z. Petrova*, G. Sabev

1Department of Agrotechnology, Dobrudzha Agricultural Institute, 9520 General Toshevo, Bulgaria

Abstract. The aim of this investigation was to determine the effect of the date of introduction of herbicides on the infestation with weeds. The experiments were carried out during 2012 – 2013 at Dobrudzha Agricultural Institute (DAI). The following herbicides were used: Derby super VG (33 g/ha), Palace 75WG + oil (250 + 1000 g/ml/ha), Granstar 75DF (15 g/ha), Lintur 70VG (150 g/ha), Husar Max OD (1000 ml/ha), Secator OD (100 ml/ha), Mustang 306, 25 CK (800 ml/ha) from the group of sulphonylureas with various modes of activity. The preparations were introduced at three phenophases of winter common wheat cultivar Aglika (29, 32 and 37 according to the scale of Zadoks). The herbicide effect was determined by a quantitative weight method and evaluated by the EWRS scale. The results from the obtained data showed that Derby super VG, Luntur 70VG, Secator OD and Mustang 306, 25 CK had the highest effect when introduced at phenophases 29 of wheat growth (the efficiency varied from 95 % to 100 %). With the later dates of herbicide application and the later growth stages of weeds, a tendency towards lower efficiency was observed.