Weeds: Less Popular Than The Nick Nolte Film

Weeds are mainly an issue if you have weakened turf. Healthy turfgrass will outcompete weeds for space. Generally speaking, when turfgrass is stressed due to improper irrigation or mowing height, weeds will move into those weakened areas. The best remedy to keep the weeds out is to maintain proper mowing height and proper irrigation.
However, there are times when something happens such as a broken sprinkler head or accidently cutting the lawn too low and weeds invade the weaker areas. This may call for chemical control if hand pulling is not an option.
Most lawns in FL are going to be St Augustine, Zoysia, Bermuda, Bahia, or Centipede grass. Herbicides need to be selected based on the type of grass you have and the type of weeds you are dealing with. Most selective herbicides are going to target broadleaf weeds, sedges/kylinga, or grassy weeds. Familiarize yourself with the label before purchasing any herbicide regardless of what anyone has told you. Too many homeowners listen to bad advice given by people who have not studied the subject or who are only familiar with certain types of grasses. It is extremely important that caution is used and the label is followed in selecting an herbicide for your lawn. Using the wrong herbicide or even the correct herbicide at the wrong rate can easily destroy the lawn you are working hard to improve.
If weeds do manage to invade your lawn due to some stressor weakening the turf and an application of an herbicide is necessary, make sure that the cause of the turfgrass stress has been addressed. It makes little sense to apply an herbicide to deal with weeds when the irrigation system is not functioning properly or your mowing height is too low. Correct the cause and then use an herbicide if necessary.
Also remember that weeds have a life cycle. Unwanted plants in turf are either annuals, bi-annuals, or perennials. This means that typically speaking, weeds will germinate in late winter or early Spring and then die in late Fall or Winter. Before the weed dies, it will drop its seed which will then germinate once temperatures reach a certain point. Now there are some weeds that spread through the rhizomes or roots, but most broadleaf, sedge-type, and grassy weeds spread through the distribution of their seeds.
Once you are able to identify the main weeds that are a problem in your lawn, you can select an herbicide and treat based on the life cycle of the weed. For example, if it is late Summer or Fall, the weed is already full grown and may be much more difficult to control (such as crabgrass, goosegrass, doveweed, etc). Knowing that the weed is at the end of its lifecycle and has already dropped its seed, the best strategy will be to preempt the weed outbreak in the late Winter or early Spring. This will involve the use of what is called a “Pre emergent Herbicide.”
Pre Emergent Herbicides are chemicals which act as a barrier between the soil and the seed to prevent or curtail germination. These chemicals are to be applied prior to seed germination in the Spring. They typically last in the soil long enough to prevent seed germination or prevent the root of the weed from getting a foothold into the soil.
A good approach would involve the combination of both Pre and Post Emergent herbicides or one herbicide with both properties such as Atrazine or Dithiopyr. If you had a weed outbreak in your lawn, then apply a pre emergent herbicide in the late Winter/early Spring time of year before the seeds are able to germinate. Then if you happen to see weeds germinate in Spring, follow up with a post emergent herbicide while the weeds are still small enough to control. Once the weed is fully mature, it is much more difficult to control.
As already mentioned, prevention is key. Keep your lawn mowed at the proper height and irrigate as needed. When you avoid stressing the turf with improper irrigation and improper mowing height, you increase the likelihood of a weed infestation.