Vivekananda Parvatiya Krishi Anusandhan Sansthan (ICAR), Almora-263 601 (Uttaranchal), India.
A set of 12 treatments comprising weedy and weed-free conditions upto 40, 60, 80, 100, 120 days after sowing and harvest was evaluated at the Experimental Farm, Hawalbagh of VPKAS (ICAR), Almora during 1999 and 2000 to find out critical period of crop-weed competition in spring rice. Weed competition index increased with increase in duration of weedy condition ranging from 11.1 to 97.4 during 1999 and 20.9 to 86.5 during 2000. On the other hand, increase in weed-free period for different duration from sowing to 120 DAS decreased weed competition index to 6.1 from 83.9 during 1999 and to 4.6 from 68.6 during 2000. Weed-free condition beyond 120 days had no significant effect on grain yield over full season weed-free condition. The critical duration of weed-crop competition was observed to be between 40–120 days after seeding.
