Diquat and Glufosinate-Ammonium for Pre-Harvest Desiccation of Sunflower: Effects of Growth Stage on Seed Physiological Quality

Pre-harvest desiccation is widely used in sunflower (Helianthus annuus L.) production to accelerate harvest and improve crop management; however, comparative information on the effects of different desiccant herbicides applied at distinct phenological stages on seed physiological quality under Brazilian Cerrado conditions remains limited. This study evaluated the effects of glufosinate-ammonium and diquat applied at the R8 and R9 growth stages on the physiological quality of seeds from the sunflower hybrid BRS 323. A completely randomized design with five treatments and four replications was used. Seeds exhibited primary dormancy after harvest; therefore, initial viability was confirmed by the tetrazolium test, and physiological quality was assessed after 30 days of dry storage using germination, accelerated aging, electrical conductivity, seedling dry mass after accelerated aging, and field seedling emergence tests. Data were subjected to analysis of variance, Tukey’s test (p ≤ 0.05), and principal component analysis (PCA). All treatments produced seed lots with germination percentages above the 75% minimum standard required for sunflower seed commercialization in Brazil. Glufosinate-ammonium applied at R8 significantly reduced seed germination and vigor, whereas diquat applied at the same stage maintained high physiological performance comparable to that of the untreated control. Applications at R9 preserved seed physiological quality regardless of the herbicide. The first two principal components of the PCA jointly explained 63.2% of the total variation and supported the univariate findings. Pre-harvest desiccation proved to be a technically viable strategy for sunflower seed production, with applications at R9 providing the greatest preservation of seed vigor; when desiccation at R8 is required, diquat was superior to glufosinate-ammonium.