A field experiment was conducted for two consecutive cropping seasons (2013 and 2014) to estimate effect of weed interference period on transplanted tomato (Lycopersicon esculentum M.) in Guder West Shewa, Ethiopia. The experiment consisted of 14 treatments laid out in RCBD with three replications. From the total weed species, 81.81% were broadleaved weeds whereas 9.09 and 9.1% were sedges and grass weeds, respectively. During 2014 cropping season of the total weed flora, 83.3% were broad leaved weeds, 8.33 and 8.33% were sedges and grass weeds, respectively. Two years pooled data revealed that, density, weed dry biomass, tomato yield and relative yield loss were observed in all the two years. The lowest weed density was recorded in plot kept weed free, plot harvest (0.0 and 0.0 m-2) whereas the highest was recorded in no-weeded up to harvest (146.51, 161.33 m-2) in 2013 and 2014, respectively. Similarly, lowest (0.0, 0.0 gm-2) dry weight of weeds was recorded in weed free, whereas the highest was recorded in no-weeded up to harvest (1127.2, 1093.2 gm-2) in 2013 and 2014, respectively. The highest yield (32.04, 29.57 tons ha-1) was recorded in weed free plot which is not statistically significant with weed free up to 90 days after transplanting (DAT) (28.336, 31.511 tons ha-1) and no-weeded up to 15 DAT (29.894, 27.484 tons ha-1), whereas the lowest (4.00, 2.59 tons ha-1) was recorded from no-weeded up to harvest, respectively. Uninterrupted weed growth caused a reduction of (87.5, 90.8%), in tomato yield as compared to complete weed free in 2013 and 2014, respectively.
Key words: Weed interference period, tomato yield, weed growth, yield loss.