Field experiments were conducted to determine the critical period for weedcontrol (CPWC) in nongrafted ‘Amelia’ and Amelia grafted onto ‘Maxifort’tomato rootstock grown in plasticulture. The establishment treatments (EST)consisted of two seedlings each of common purslane, large crabgrass, andyellow nutsedge transplanted at 1, 2, 3, 4, 5, 6, and 12 wk after tomatotransplanting (WAT) and remained until tomato harvest to simulate weedsemerging at different times. The removal treatments (REM) consisted of thesame weeds transplanted on the day of tomato transplanting and removed at 2,3, 4, 5, 6, 8, and 12 WAT to simulate weeds controlled at different times.The beginning and end of the CPWC, based on a 5% yield loss of marketabletomato, was determined by fitting log-logistic and Gompertz models to therelative yield data representing REM and EST, respectively. In both graftedand nongrafted tomato, plant aboveground dry biomass increased asestablishment of weeds was delayed and tomato plant biomass decreased whenremoval of weeds was delayed. For a given time of weed removal andestablishment, grafted tomato plants produced higher biomass thannongrafted. The delay in establishment and removal of weeds resulted in weedbiomass decrease and increase of the same magnitude, respectively,regardless of transplant type. The predicted CPWC was from 2.2 to 4.5 WAT ingrafted tomato and from 3.3 to 5.8 WAT in nongrafted tomato. The length (2.3or 2.5 wk) of the CPWC in fresh market tomato was not affected by grafting;however, the CPWC management began and ended 1 wk earlier in grafted tomatothan in nongrafted tomato.