Controlling weeds involves more than spraying a weed killer or herbicide. There are several types of weeds and several types of herbicides.
Weeds can be either broad-leaved or grasses.
Within each of these two types, weeds may be annual or perennial. Total vegetation killers kill any type of vegetation they land on. When the weeds are young and actively growing they absorb the herbicide readily, giving good control. Such herbicides must be applied before seeds germinate. Perennial grasses are controlled with total vegetation killers.