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This study was conducted to determine the critical period of weed competition in wheat under different tillage systems during 2011-2012. The experiment comprised of two factors including tillage and weed control period. The tillage treatments were conventional, minimum and zero tillage in main plots and weed control period were weedy check, weed competition for 20, 40, and 60 days after germination and weed free throughout the growing season in sub plots. The experiment was laid out in randomized complete block design with split plot arrangement having three replications with a net plot size of 6 m x 2.2 m. Data regarding weeds, yield and yield components was recorded following the standard procedures. The agronomic parameters plant height, number of productive tillers, number of grain per spike, 1000-grain weight, biological and grain yield showed significant results under zero tillage along with 20 days competition period. The results showed that zero tillage suppressed total weed density and total weed dry weight up to 59 % and 38 % respectively and increase the yield up to 6 % over conventional tillage. The results of weed control periods showed that weed control after 20 DAE suppress the weed density and dry weight up to 76 % and 95 % respectively and increase the grain yield up to 34 % over weedy check. [ABSTRACT FROM AUTHOR]