Things You'll Need
Pressure sprayer or hose-end sprayer
Spectracide Weed Stop concentrate
If some weeds still look alive three weeks after a whole-lawn treatment, spot-treat the surviving weeds. Apply no more than two whole-lawn treatments per year.
If you use a hose-end sprayer, work from the farthest part of the lawn toward the part closest to the faucet to avoid walking on the newly sprayed grass.
Do not use Spectracide Weed Stop on Floratam variety of St. Augustinegrass in Florida.
Avoid getting the diluted or full-strength concentrate on the skin or eyes, and avoid inhaling the vapors or spray.
Wear protective eyewear, rubber gloves, a long-sleeve shirt, long pants, socks and shoes while using chemcials. Immediately after you're done, rinse off or dispose of the gloves, and wash your hands and clothing. Don't reuse measuring containers for food, and don't reuse the container the herbicide came in.
Choose a still day and spray carefully to avoid spray drifting onto fruits, vegetables, ornamentals or food for people or animals. The herbicide is toxic to fish and other aquatic life, so keep it away from ponds and other natural water.
Spectracide Weed Stop concentrate is a three-ingredient herbicide for killing broadleaf weeds in lawns. It contains the active ingredient 2,4-D along with mecoprop-p and dicamba. Because Spectracide Weed Stop targets broadleaf plants, it controls most common weeds while leaving grasses untouched. Use it in spring or fall, when weeds are small or germinating. Keep Spectracide Weed Stop away from ornamentals whose roots have spread into your lawn; the dicamba in the product may harm them. Note also that this herbicide kills white lawn clover (Trifolium repens), hardy in U.S. Department of Agriculture plant hardiness zones 3 through 10.
Determine the square footage of your lawn by measuring the approximate length and width with a tape measure or by pacing it out. To pace it out, measure the approximate length of one step from the heel of the left foot to the heel of the right foot, walk the distance counting your steps, then multiply by the length of one step. Multiply the length by the width of the lawn to calculate the total square feet.
Divide the total square feet by 250 to determine the amount of water and chemical needed. Different lawn grasses need different amounts, so follow the product's label directions. For example, each 250 square feet of St. Augustinegrass (Stenotaphrum secundatum), hardy in USDA zones 8 through 10, requires 1 tablespoon (1/2 fluid ounce) of Spectracide Weed Stop concentrate per 1 gallon of water. Bermudagrass (Cynodon dactylon), hardy in USDA zones 7 through 10, requires 4 teaspoons (2/3 fluid ounce) of product per 1 gallon of water. Zoysia grass (Zoysia japonica), hardy in USDA zones 5 through 10, needs 2 tablespoons (1 fluid ounce) of herbicide per 1 gallon of water. Add the appropriate amount of Spectracide Weed Stop concentrate to a pressure sprayer or to a hose-end sprayer's jar.
Add 1 gallon of water to the sprayer, along with the appropriate amount of the chemical, for every 250 square feet of lawn. Close the sprayer and shake it well to mix the solution thoroughly. If using a hose-end sprayer, put the product in the sprayer but don't add water. Set the hose-end dial to deliver the amount of concentrate per gallon needed for your lawn type, and attach the hose to your sprayer.
Set either kind of sprayer to produce small droplets rather than a fine mist. Spray the lawn on a calm day when the temperature is below 85 degrees Fahrenheit and the forecast predicts no rain for at least six hours. Cover the lawn evenly so that 1 gallon of the solution covers 250 square feet. Keep pets and people off the lawn until the spray dries.
Measure 2 tablespoons of Spectracide Weed Stop concentrate and add it to a pressure sprayer. Don't use a hose-end sprayer for spot treatments.
Add 1 gallon of water to the sprayer and mix well. Spray the weeds you want to kill with the herbicide solution until the leaves are wet.
Treat problem areas with additional spot treatments, as needed, until weeds are completely gone.
David Thompson began writing for eHow in 2009. He has written how-to articles on home improvement, carpentry, cabinet making and gardening.