You only have a few products you can use for weed control. The most commonly used products are corn gluten meal, Fiesta and horticultural vinegar.
Corn Gluten Meal
Corn gluten meal can be used for weed control but it does not work on existing weeds. It has a nitrogen component and this acts like a fertilizer and this helps green up your lawn. Corn gluten meal works as a pre-emergent herbicide meaning if you spread it before the seeds germinate the amino acids in the corn gluten protein stop the seeds from germinating.
The major disadvantages of corn gluten meal as a weed control it can be expensive you have to apply a lot of the product; it can take time to build up levels so it inhibits weed seed germination(2 to 3 years). If you need to seed your lawn you have to wait a minimum 6 to 8 weeks before grass seed can be applied.
Fiesta (iron based herbicides)
Fiesta or the iron based weed controls are post emergent selective herbicides that work on broadleaf weeds. They are sprayed to the point of runoff on the weeds that are up and growing in your lawn. It kills off the top of the plant forcing the root to re-grow. It will kill small weeds in one application but it can take multiple applications to control larger weeds. It cannot be applied in hot weather as it will kill the turf as well when temperatures reach over 28 degrees Celsius.
Horticultural vinegar is a non selective weed control kills all weeds and grasses including lawn grasses so before careful spraying it around flower beds and lawns. It is mostly used to kills weeds on hard surfaces like sidewalks and patios.