Weeds are considered as one of the serious pests of crops causing huge economic losses to countries annually. This menace can be controlled after knowing the damage on the base of density and duration. There is no need for controlling weeds for duration untill which weeds do not pose economic loss. But when weeds start to cause economic loss in crop fields it becomes compulsory to know duration within which the weeds cause maximum damage. it is only then that a judicious plan for weed control can be devised.