How to Kill Weeds in a Pasture But Not the Grass

Obtain a selective weed killer for the pasture. Since you want to kill the weeds and keep the grass, you need an herbicide that selects the unwanted weeds and won't harm the grass. An herbicide that contains 2,4-D is recommended by the Oklahoma State University Extension service. If the weeds are more than 6 inches high, it is also recommended that you purchase an herbicide that has either picloram or dicamba mixed with the 2,4-D.

Fill a large tractor-pulled tank sprayer with the herbicide and water. A mixture of 4 lbs. of chemicals to 1 gallon of water works well. If you do not have a sprayer, rent one from an equipment rental company.

Pull the tractor to one corner of the pasture. Spray the herbicide evenly over the area by moving the nozzle back and forth. Once this section of the pasture is coated, move the tractor to a new section. Repeat until the entire grass area is treated.

Wait a week to see if all the weeds die. If some still exist, reapply to kill the rest. Once you have killed the weeds, overseed with new grass to fill in the empty spots. A thick grass covering is less likely to have weeds.