Barboi V. Optimization of Weed Control in Sunflower Crops Using the Express Technology under the Conditions of the Northern Steppe of Ukraine

The dissertation work is devoted to the scientific substantiation and improvement of the elements of the technology of post-emergence herbicide protection of sunflower by optimizing the consumption rates of the working solution and doses of the herbicides Express and Express Gold in the conditions of the Northern Steppe of Ukraine. The purpose of the dissertation research is to scientifically substantiate the optimal rates of application of post-emergence herbicides in sunflower crops using the "Express" technology and to establish a rational water consumption rate for the preparation of tank mixtures in order to increase the efficiency of weed control, productivity and economic efficiency of crop cultivation. The experimental part of the work was carried out during 2023–2025 in the production conditions of LLC "Agrofirma im. Gorky" of the Novomoskovsk district of the Dnipropetrovsk region. It was established that the use of herbicides extended the duration of the growing season of sunflower compared to the control by 12–19 days. The lengthening of interphase periods was a consequence of the improvement of plant growth conditions as a result of the effective elimination of competition from weeds. According to such ideas, plants formed a more developed assimilation apparatus, accumulated dry matter more intensively and ensured a more complete use of natural environmental resources. The positive effect of post-emergence herbicide protection on the growth of sunflower plants was proven. The maximum increase in plant height (6.9% relative to the control) was obtained with a two-time application of the Express herbicide at a rate of 25+25 g/ha at a working solution consumption of − 200 l/ha. Reducing the working solution consumption to 100 l/ha practically did not worsen biometric indicators, while the use of 50 l/ha led to less intensive plant growth. At the same time, increasing the herbicide rates above the optimal ones did not provide additional advantages and in some cases was accompanied by a slight decrease in biometric indicators. It was found that the use of herbicide protection had a positive effect on the formation of the main elements of the crop structure. The weight of 1000 seeds increased by 13.6–16.3% compared to the control, with the best indicators provided by the options with the use of a working solution in a volume of 100–200 l/ha. Improving plant growth conditions after effective weed suppression contributed to a more complete seed filling and an increase in its fullness. A significant effect of herbicide protection technology on seed moisture before harvesting was also found. The lowest value of this indicator - 5.70% was obtained with a two-time application of the Express herbicide at a rate of 25+25 g/ha at a working solution consumption of 100 l/ha. This indicates a more uniform ripening of plants and acceleration of the processes of moisture release by seeds. According to the results of three-year studies, it was determined that the optimal consumption of the working solution for post-emergence application of herbicides is 100–200 l/ha. It was under these conditions that the most complete implementation of the herbicidal action was achieved, favorable conditions for the growth and development of the crop were created, and the maximum level of productivity was formed. The highest yield of sunflower seeds - 3.81 t/ha - was obtained with a two-time application of the Express Gold herbicide at a rate of 20+20 g/ha at a consumption of the working solution of 100 l/ha. At the same time, it was established that the use of 50 l/ha of the working solution under certain technological schemes also provided a sufficiently high level of yield and can be recommended in case of a shortage of water resources. It was established that the oil yield was determined by a complex combination of yield and oil content of the seeds. On average, for 2023–2025, in the control variant, it was 1.36 t/ha, while the use of post-emergence herbicides increased it to 1.56–2.05 t/ha. The maximum oil yield was achieved with a two-time application of the Express Gold herbicide at a rate of 20+20 g/ha, which combined high yield with an increased oil content in seeds. The highest economic efficiency was achieved by the use of the Express Gold herbicide at a rate of 20+20 g/ha at a working solution consumption of 100 l/ha. This variant yielded the maximum yield of 3.81 t/ha, the lowest cost of production of 9720 UAH/t, the highest conditional net income of 73450 UAH/ha, and the highest level of profitability of 198%.