At ray floret opening, spray boric acid 0.2% (2 g per litre) on the flower head to improve seed set and filling. In the mid-flowering phase (58–60 days for long-duration and 45–48 days for short-duration varieties), improve pollination between 9 and 11 a.m. by gently rubbing the flower heads with a hand covered in soft cloth, or rubbing two flowers face to face. Keeping 5 bee hives per hectare also improves seed setting.
Pending expert review
Source
Crop Production Guide – Agriculture 2020 (Directorate of Agriculture, Tamil Nadu & Tamil Nadu Agricultural University (TNAU)), Sunflower – Boric acid; improving seed set, p. 219
