T. Barakova*

Agricultural Academy, Field Crop Institute, 6200, Chirpan, Bulgaria

(Manuscript received 2 June 2023; accepted for publication 23 June 2024)

Abstract. The research was conducted during the period 2020-2022 in the experimental field of the Field Crops Institute – Chirpan, Bulgaria. In a three-factor field experiment, the effect of the vegetation-applied herbicide Envoke, containing 75% trifloxysulforon-sodium, was tested on two cotton cultivars. Factor A includes the three years of the study. Factor B includes the cotton cultivars Chirpan-539 and Helius. Factor C includes the herbicide Envoke, applied in 3 rates – 10 g ha-1, 15 g ha-1, 20 g ha-1, once and two times during the 4-5 leaf and budding stages of cotton. The aim of the trial was to study the selectivity and stability of the effects of the three different rates of the herbicide Envoke on cotton under different weather conditions. It has been found that the vegetation-applied herbicide Envoke, applied in the three rates, once and two times during the 4-5 leaf and budding stages of cotton, does not have a phytotoxic effect on the crop and is selective to the two cultivars – Chirpan-539 and Helius. The highest yields in both cotton cultivars were obtained with the two-time application of the herbicide Envoke during the 4-5 leaf and budding stages. Technologically, the most valuable are all variants with the herbicide Envoke for the cultivar Chirpan-539 and the variants with the herbicide Envoke in rates of 15 g ha-1 and 20 g ha-1 for the cultivar Helius. These variants combine high yield values and high stability of this indicator in different years. The untreated controls in the two cotton cultivars were the only ones that received negative evaluations. This is due to the high number of weeds and sunflower volunteers.