Pre–emergence herbicides kill weeds before emergence from soil. It prevents the germination of seeds by inhibiting a key enzyme. The herbicide is used to prevent grasses from growing in order not to compete for nutrient and other resources required by the plant. Pre-emergent herbicides are used before planting or a day after planting is done. They are best applied when the temperature is low preferably in the morning. The herbicide is applied to the soil majorly by spraying.