Critical Period of Weed Competition in Spring Sunflower (Helianthus annuus L.)

Weed-crop compelition was studied to determine the critical period in sunflower (Helianthus annuus L.) during spring seasons of 1996 and 1997 at the Research Farm of Indian Agricultural Research Instilute, New Delhi Heliotropium eichwaldi, Melilotus indica, Chenopodium album and Cyperus rotundus were the dominant weed species associated with the crop. H. eichwaldi was the most predominating weed. Seed yield loss increased with the increase in the duration of competition and maximum loss (25.7%) occurred due to full season competition. Seed yield of sunflower increased significantly with the increase in initial duration of weed-free condition. Critical period of weed competition was found to be 25 to 43 days after sowing.