Sunflower Broomrape ( Orobanche cumana Wallr.) and Weeds in Sunflower Crops with Minimized Tillage in a Steppe Ecotype Crop Rotation

Abstract An important reserve for increasing the productivity of agricultural production is a scientifically based crop structure and the use of rational crop rotations, which implement the optimal ratio of agroecological standards. The aim of the research was to determine the influence of elements of agrotechnical measures, in particular, the saturation of crop rotations with sunflower, soil tillage system on the number and species composition of various agrobiological groups of weeds in sunflower crops, including the weed parasite sunflower broomrape ( Orobanche cumana Wallr.). Weed control measures and the spread of the parasitic weed sunflower broomrape in sunflower crops have been carried out according to the methods generally accepted in agriculture and weed science. The scheme of the experiment included crop rotations with saturation in the structure of sunflower sowing of 12.5, 20, 25, 33.3, 50, 100% and three systems of basic tillage: moldboard plowing, disc tillage, and no-tillage. As a result of the research, it has been found that the systems of disc tillage and no-tillage cause an increase in the number of weeds in sunflower crops compared to the moldboard plowing by 1.3–1.5 times. On average, over the years of research, the abundance of weeds in the plots when using disk tools was 10.4–15.1 pcs./m 2 , moldboard plowing was 7.1–12.4 pcs./m 2 , and before harvesting was 2.6–5.2 and 4.1–12.4 pcs./m 2 . The highest degree of sunflower broomrape damage has been observed in 2-fields crop rotation (winter wheat—sunflower) and permanent sunflower cultivation, as 16.0–32.4% of affected sunflower plants have been observed here. The intensity of sunflower broomrape damage to sunflower plants was higher in the moldboard plowing system and amounted to 1.2–8.3 pcs./per plant, which exceeded disc tillage and no-tillage by 1.2–1.6 times. The maximum seed yield of 2.92–2.95 t/ha has been obtained in 8- and 5-fields rotations with the use of moldboard plowing. The lowest yields of sunflower seeds were in short-rotation crop rotations with a sunflower saturation of 50% in the structure of sown areas and permanent cultivation and amounted to: moldboard plowing—1.75–2.21 t/ha, disk tillage—1.57–2.01 t/ha, and no-tillage—1.49–1.95 t/ha. Given the urgency of supplying the global market with sunflower oil, in the future it is necessary to increase the concentration of sunflower in the structure of sown areas to 30-40% through the system of basic tillage, selection of resistant hybrids, and use of herbicides.