This study introduces a unifying concept combining the theory of critical density and critical period of weed infestation. It is hypothesized that these two periods are interdependent, rather than fixed values. The hypothesis is based on studies of interference between Solanum americanum and the tomato crop. Multiple regression models were applied to the results of five field trials. The independent variables were density and number of days of weed and culture cohabitation. Applying the Tolerance Level (TL) to the graphic representation (2D) of the equations estimated from multiple non-linear models allowed answering the following question: how long does a particular infestation of Solanum americanum remain without causing injury to the tomato crop? It was also possible to conclude that the variation of control costs and crop prices changes the TL values, concomitantly changing the time allowable for the presence of Solanum americanum in the tomato crop, without causing yield loss.
multiple competition model; tolerance level; weed interference
