Crabgrass is often thought of as a nasty weed that commonly grows in turf grass, such as St. Augustine grass. However, some lawn owners benefit from the crabgrass in order to feed cattle and to add small amounts of greenery to soil that is full of animal waste. Since crabgrass is an annual weed, it takes much control, such as pre-emergent and post-emergent herbicide applications. It's important to reapply herbicide as often as needed to stop growth and germination of the crabgrass seeds. The best thing to do once you notice unsightly crabgrass in your lawn is to act immediately and to control the weed before each season. However, if you have dead crabgrass in your lawn, you should still apply herbicide treatments to prevent the weeds from growing again.
Mow your grass down to at least 2 1/2 inches, but no shorter. Before removing the dead crabgrass you must make sure your lawn is mowed but not cut too short.
Examine the dead crabgrass and the area around the crabgrass to make sure that other portions of your grass are not dead. If you can't directly identify the cause of the dead crabgrass, remove it immediately so that no disease spreads.
Remove the dead crabgrass by hand or by using a small shovel. Make sure to wear latex gloves if you are removing the dead weeds by hand. Use a shovel if the grass is deep into the soil or if there are any roots stuck in the soil.
Fertilize the grass in early September and the middle of November to help prevent the crabgrass from growing back again. Use at least 2 lbs. nitrogen fertilizer per every 1,000 square feet.
Apply a pre-emergent herbicide during the beginning of April. Follow the instructions on the container to make sure not to disrupt other areas of the lawn or growing seedlings. Common pre-emergent herbicides include Benefin, Oxadiazon and Dithiopyr.