Existing crabgrass can be extremely difficult to remove from lawns and gardens. The small seeds from the annual grass can be carried to different locations by sticking to shoes or garden equipment. After the grass is established, it thrives in hot and sunny locations. The small seed heads quickly develop to carry on the life cycle of the grass. Consulting your local agricultural extension service will help you in determining the best method, as some areas around the country may ban the use of certain herbicides.
Use a recommended pre-emergent herbicide spray when the crabgrass is at a young plant stage. Mix the herbicide according to the manufacturer's or extension service's guidelines. Failure to follow the mixing instructions may cause the spray to be ineffective or kill other plants from a too-strong solution. Exercise caution when using these products. as sprays may drift into areas and kill other plants.
Apply pre-emergent granules with a spreader according to the instructions on the herbicide container. Granules allow you to directly apply the material onto the ground and decreases the chance for cross-contamination to other plants.
Find corn gluten meal at your local feed or mill store. See the Reference article from the University of Illinois, The Green Line Corn gluten meal is an organic method of controlling crabgrass. Research has shown that typically 50 percent to 60 percent of crabgrass can be controlled in the first year by an application of 20 pounds per 1,000 square feet. This material must be applied over a period of years to completely eradicate the crabgrass.
Use a weed torch and burn the individual plants as they emerge from the ground. Although quite labor intensive, the use of weed torches are effective in killing specific plants. The flame from the weed torch is directed onto the plant and burns it back to the ground level. This method may be impractical for areas that have a severe infestation of crabgrass.