Spring maize is becoming popular in Punjab state owing to its higher yield potential and is a new introduction. A field experiment was conducted at Punjab Agricultural University, Ludhiana with 12 treatments viz. crop kept weedy for 20, 30, 40, 50, 60 DAS, crop kept weed free for 20, 30, 40, 50, 60 DAS, weed free throughout and weedy check. The weed density showed a linear progression as the weedy interval was increased from 30 to 40 days, 40 to 50 days and 50 to 60 days. The results showed that yield attributes and grain yield declined with the increased duration of crop- weed interference period and increased with long weed free durations. Significant reduction in grain yield was recorded with increased weed infestation from 30 to 60 DAS, however, the differences observed between 20 and 30 days weedy were statistically at par. This suggested the tolerance of weed interference up to 30 days in spring maize. The 60 days weed free treatment resulted in grain yield statistically same with that of weed free throughout but significantly better from all other weed free duration treatments. This marked the end of critical period of crop-weed competition in spring maize. A significant negative linear correlation was observed for weed biomass and grain yield. The critical period of crop-weed competition in spring maize started at 30 DAS and ended at 60DAS. This period needs immediate attention for the adoption of weed control measure
