Crabgrass is an annual grass that grows in many home lawns. The grass resembles the shell of a crab by growing in a wide, dense mat. Crabgrass exists in seed form in many lawns. It can be prevented by keeping established grass mowed to a height that will not allow the seeds to germinate. Once crabgrass germinates in the lawn, your lawn care focus should switch from preventing seed germination to controlling the grass before it can form seed heads and spread new seed to your lawn.
Select a chemical crabgrass killer that contains monosodium methanearsonate for your lawn. Monosodium methanearsonate is marketed specifically as a spray for killing crabgrass.
Water your lawn so the soil is damp to a 3-inch depth before applying monosodium methanearsonate. Water amounts will vary depending on your soil structure. Sandy soil will require less water than clay soil.
Spread a plastic drop cloth around the crab grass to prevent getting monosodium methanearsonate on surrounding grass. Monosodium methanearsonate will kill desirable grass as well as crabgrass.
Wear protective clothing when working with monosodium methanearsonate, including long sleeves, long pants, closed-toe shoes, gloves and breathing protection.
Spray monosodium methanearsonate over crabgrass until the plant is saturated with the chemical.
Remove drop cloth and discard it. Shower immediately after spraying monosodium methanearsonate.