Broad-leaved Lawn Weeds Most Objectionable
Fortunately broad-leaved weeds are generally controllable with the 2-4-D group of chemicals commonly found in the "Weed and Feed" type of fertilizers. These weed killers are absorbed through the leaves. The weed dies slowly, twisting and curling. Since the material affects the roots as well as the tops, there is seldom any re-sprouting. Used properly, grass is not affected but take caution, this is not so with other landscape plants, see below. Follow the manufacturer's directions exactly, different products may have different actions. Use the amount recommended, don't guess or use the spreader settings for a different product..
Make certain that this material gets on the leaves and stays there. Sometimes granular weed killers do not stick well to foliage; you may have better results if you spread them when the leaves are moist with dew or after irrigating for a few minutes. DO NOT WATER IT IN! This type of product is a fertilizer pellet coated with an herbicide. It needs to stick to the weed leaf until the coating is absorbed by the plant, a process that may take 24 hours. Putting it on or into the ground allows the fertilizer to do its thing, but the weed killer will not function there, it has to be applied to the leaf..
Sprays are also available and generally stick better than dry materials, but even sprays may work better if you add a pinch of detergent to the solution. The detergent acts as a wetting agent- that is, it "makes the water wetter" so that it spreads and is absorbed more easily.
CAUTION: This stuff is a hazard to your health. 2,4-D weed killers must be used exactly as recommended in the instructions that come with the product. If you use too little you may not kill the weeds. If you use too much you can damage the grass and soil. Some products, both liquid and granular, tend to vaporize, and these vapors can injure or kill garden plants at surprising distances away. Most manufacturers of weed killers for home gardens use "low-volatile' formulas in their products.
Containers (such as sprayers) that have been used for liquid 2,4-D and even related materials such as Monsanto's Roundup are best not used for applying fertilizers, insecticides, etc. They are difficult to clean completely of the plant killer, and even tiny amounts can damage some plants.
Be considerate of your neighbors and the environment. Over-applied fertilizer/herbicide will end up in the storm drain (which flows to the nearest creek, not the sewer plant). That's quite toxic for the creek's inhabitants and you may find a citation in your mailbox.
One more time; follow the directions on the package. They are not put there to cover someone's liability, they are there to help you get a nice-looking lawn because the manufacturer wants you as a repeat customer.