Don’t attack the weed, kill the seed. A pre-emergent weed killer applied in the spring and fall will help eliminate most weeds before the weed emerges by killing the weed seeds.
Fall weed controls the winter annuals which germinate in autumn or winter, then bloom in winter or spring. Some of the most common winter annuals are chickweed, deadnettle, hairy bittercress, wild mustard, prickly lettuce, annual bluegrass, etc.
You would need to know what type of weed(s) you want to eliminate in order
to pick a product that is going to be effective on your weed(s). There are 2 types of weeds leaves broadleaf and grassy; the same herbicide may not be effective on both types of weeds. It would be best if you check with your local nursery and inquire what type of weed control is recommended. If you are using an organic product such as our Maize Weed Preventer, it can be applied to any type of grass and used in any state.
Many weed killers may have a specific timing or temperature requirements. Fall weed control is usually done in early October.It is also very important to know what type of grass you have, not every product is 
safe for all types of grasses.
Remember, to read the entire label of whatever product you choose and follow the instructions for applying. Do not increase the recommended dosage, thinking this will help to kill more of the weeds or kill them quicker. Instead you could end up killing your lawn.