For those of you who are still pulling up weeds
Because there are so many different types, let's go over the different descriptions of these chemicals called herbicides. Emergence refers to whether the herbicide can target the weeds before they've broken through the soil or not. Those can are call pre-emergent and are good to use against annuals. Annuals are weeds that grow for a season. Those that cannot and must wait for the weed to peak up through the dirt are called post-emergent. Post-emergent herbicides can be easily sprayed onto plants or soil. They won't, however be effective with the underground weeds as they break down quickly in the soil. Selectivity refers to the spectrum that the herbicide attacks. Selective weed killers will only kill their target weeds like dandelions. Nonselectives, however, will attack all plant life that it comes into contact with. These are ideal for when clearing an area when you plan on re-planting as farmers will switch up their crops. Persistence refers to the time of effectiveness. Nonselectives, discussed above, that kill all plant life and prevent re-growth are deemed very persistent. Those that do not fight re-growth are considered nonpersistent. Nonpersistent herbicides break down more quickly and often require more frequent application. Contact refers to the way a substance kills weeds. If it kills a weed right after application, it's considered a contact killer. It is important to understand, though, that only the plants and only the parts of the plant that come into contact with the chemicals will die. On the flip side of that, herbicides that are absorbed through the plant and can travel to other parts or other plants are called translocated. In addition to the different types, there are different forms of weed killers. Some are liquids, most often concentrates, that can be used as a spray. Most of these will be contact killers. It is important that you use caution when spraying as it is easy to spray non-target plants. Others are granules or salts that are scattered throughout the yard or garden by hand or broadcaster (as you would when seeding a yard) and are structured to withstand harsh weather. There are even organic herbicides. Whatever you choose, be sure to read all labels for proper usage.