The old adage "A good offense is the best defense" couldn't be more true when battling weeds. Weeds are the inevitable enemy and will take over your yard if nothing is done to stop them. A single weed may be capable of dropping hundreds or thousands of seeds, where they can last decades just waiting for the right conditions to take root. Pre emergent herbicides are chemicals that prevent the germinating weeds from establishing in your yard without doing any harm to the surrounding established plants. These herbicides control weeds by inhibiting cell division in the young root system. The failure of the root system to develop results in the death of the young seedling weed shortly after germination.