Pre-emergent is a weed control that prevents weed germination. It is applied to areas before weeds start to grow. The effect of pre-emergent is a prevention, not a controller of existing weeds. A pre-emergent program allows a layer to chemicals to stop weed growth. Although pre-emergent is very effective, it does not prevent 100% of weed germination. It is still applied to an external environment, which can not be controlled from all angles.
