Easy Ways to Kill Johnson Grass

Mowing

• Repeated close mowing can kill Johnson grass seedlings and reduce their seeds, according to the University of Illinois. Reducing Johnson grass seeds is extremely important, because they are coated with an inhibitor that prevents their germination until the inhibitor has been leached. This often means that seeds can remain on the ground for years. Set your mower's blades to 1 1/2 inches and mow the area. Avoid leaving the Johnson grass clippings on the lawn or placing them in the compost.

Glyphosate

• Glyphosate is an effective herbicide used on Johnson grass. Your herbicide must contain at least 41 percent glyphosate in order for the product to be effective, according to Dr. Carl Whitcomb of Lacebark Research Farm. Use 2 gallons of glyphosate per 25 gallons of water. Wait to spray your Johnson grass until it is free of any dust, so that the glyphosate can penetrate the grass blades. Spray the herbicide on a dry day. When spraying, avoid applying too much glyphosate, to prevent it dripping off the Johnson grass and landing on preferred grass. The herbicide will kill off anything it comes into contact with.

Pre-Emergent Herbicide

• Spray a pre-emergent herbicide on the lawn area in the spring to prevent Johnson grass seeds from germinating. Use a pre-emergent herbicide that contains trifluralin as an active ingredient. Apply the pre-emergent herbicide early in the growing season, such as right after the last frost. Water the pre-emergent herbicide in, so that it creates a barrier over the soil. You can also apply a pre-emergent herbicide in the morning when afternoon showers are expected.

Hand Pulling

• Hand pulling grass can reduce your Johnson grass population. You can either hand pull weeds after a rain or irrigate the area, so that the soil is soft. To pull out the Johnson grass, tug at the weed until the root system is loosened and lifts through the ground. For stubborn weeds, dig up the weeds by placing a shovel a few inches from their base and at a depth of 6 inches to push the roots through the soil.