The experiments were carried out in the period 2005-2007 in the experimental fields of the Agricultu University – Plovdiv. The conventional hybrid PR64 A83 of Pioneer Company was sown. The traditional for the crop agrotechnical practices were appiied for growing the sunflower. Four soil—acting herbicides were the object of the experiment. For control of the weeds that were not killed by the herbicides, three different types of inter-row tiltage were applied in the separate variants – without inter-row hoeing, one inter-row hoeing and two inter-row tillages – hoeing and earthening up, respectively. The experiment was carried out under non-irrigation conditions.
The effect of the studied factors – soil-acting herbicides and soil tillage – on the specific diversity of weeds and the weed infestation rate in the sunflower plantation were followed out in dynamics. Significant differences in herbicide efficiency and in yields were reported in the separate years, which were mainly due to the differences in the amount and distribution of rainfalls in the experimental years.