Babenko A. The Damage from Segetal Weeds and Optimization of Weeds Control of Sunflower Crops in the Right-Bank Forest Steppe of Ukraine

The thesis paper is devoted to the theoretical justification and improvement of existing and development of new complex measures and systems of weed control in sunflower crops. Among the factors that decrease sunflower productivity, weeds remain the most potent. Weeds that are present in the first 60 days after the emergence of the crop most influence the sunflower yield. This decrease was from 11 (the presence of weeds in the crops was 20 days after the crop germination) to 41 % (the presence of weeds in the crops was 60 days after the crop germination). There is an inverse linear correlation between the number of weeds in crops and the yield of sunflower seeds, the degree of which increases with the number of weeds, especially their mass. One of the criteria for the development and implementation of effective measures to protect sunflower crops from weeds is a critical period of competitive relationship, which depends on the level of weediness and biological characteristics of the crop, especially the duration of the vegetative period of the hybrid. The 35–40 days’ mark for mid-term hybrids is the critical moment of competitive relationships. Hence, sunflower crops should be clear of weeds from the beginning of emergence to the 60–70 day growing season. In the system of integrated weeds control a crucial role belongs to the rational tillage of the soil. In the total effect of the general system of soil tillage, the specific contribution of its individual units to the weed effect of the primary tillage is about 58 %, pre-sowing – 17, post-sowing – 25 %. In deep plowing, about 40 % of weed seeds are placed in a soil layer of 20–30 cm, 35 % in a layer of 10–20 and 25 % in a layer of 0–10 cm. After chiseling and disking at different depths from 46 to 50 % of the weed seeds are in the soil layer 0–10 cm and only 22 to 25 % in the layer 20–30 cm. In addition, various basic tillage systems affect the germination of weed seeds. Seeds selected for tillage have better germination in the direction of increasing the depth of its earning from the surface to the deeper layers. Conversely, the seeds selected in the spring before sunflower sowing has a better germination, which is located in the top (0–10 cm) soil layer. Such seeds are the source of the actual weediness of the fields. The lowest weeds in sunflower crops and the highest productivity were due to the deep chisel tillage of the soil against the background of combined protection of the crops. Under these conditions, the yield was 4.0 t/ha, the profitability level was 119 %, and the energy efficiency ratio was 2.40. At the same time, wet and cool winter with sharp fluctuations in temperature on the soil surface contributes to a significant reduction of potential weed-infested fields, moderately cool and dry winter – helps preserve stocks of weed seeds in the soil.