Yield of sunflower hybrids depending on doses of insurance herbicides in the Steppe of Ukraine

Abstract

The study was aimed to quantify how varying doses of post-emergence herbicides affect the yields sunflower hybrids ‘Neoma’ (Clearfield) and ‘Biloba CLP’ (Clearfield Plus) under arid conditions in the Steppe of Ukraine. The field experiments had a split-plot design and were conducted in the experimental field of the State Institution “Institute of Grain Crops” of NAAS (Vasylivka, Dnipropetrovska Oblast) in 2022–2024. The treatments included a control (mechanical weeding) and post-emergence applications of Неliantex (0.045–0.090 L/ha) and Pulsar Flex (1.6–3.2 L/ha). The yield clearly depended on herbicide dose and hybrid. The excessive Неliantex dose (0.090 L/ha) caused a sharp yield reduction of 31–38 % associated with decreased thousand-kernel weight (TKW), test weight, and oil content, indicating delayed seed filling under phytotoxic stress. In contrast, Pulsar Flex 1.6 L/ha maintained or slightly increased yield (+5 % for hyb. ‘Biloba CLP’) without visible phytotoxicity, demonstrating its selective tolerance threshold. Higher Pulsar Flex doses (2.4–3.2 L/ha) led to partial seed filling inhibition and a moderate yield decline (6–9 %), confirming the importance of adherence to the  recommended dose. Correlation and regression analyses identified TKW as the dominant yield determinant (r = 0.82–0.88; p < 0.01), while oil content showed a moderate relationship (r = 0.48–0.61). Coefficient of determination (R² = 0.58–0.66) confirmed that herbicide-induced variation in TKW accounted for more than 60 % of total yield fluctuations. These findings clarify the physiological mechanism of yield loss through seed-filling disruption rather than plant density or head number changes. The study justified a data-driven recommendation to apply Pulsar Flex at 1.6 L/ha as a safe, selective rate, while avoiding Heliantex 0.090 L/ha due to high phytotoxicity risk and yield reduction.