Weeds are unwanted plants which harm the crop. Weeds are necessary to remove from crop plants to increase the yield of the growing crop. For the removal of weeds, we need to know about their habitat, morphology, physiology and life cycle. The physiology of weeds helps to formulate herbicides to kill the weeds by blocking their physiological activities.  All these features help to identify and detect weeds. Herbicides are used according to the features, like aquatic or terrestrial. It is essential to know how to dispatch them in the most efficient manner.