Crabgrass is a common problem in the typical lawn. Crabgrass is an annual grass that germinates once soil temperature reaches 55 to 60 degrees Fahrenheit for seven to 10 consecutive days. It grows all summer and produces seed that will germinate the following season. The first frost typically kills it to the ground. A few different approaches prove to be effective against crabgrass--pre-emergent herbicides and post-emergent herbicides. Pre-emergent herbicides prevent the crabgrass seed from germinating while post-emergent herbicides kill the plant once it has grown. One must take care though, as certain grasses can be killed by crabgrass post-emergent herbicide--St. Augustine and centipede grasses are two of those. If you have these cultivars, you will have to manually remove the crabgrass from the lawn.
Apply a pre-emergent crabgrass herbicide in early spring before your soil temperature reaches 55 degrees Fahrenheit. Look for products that contain dithiopyr, ethofumesate, oxadiazon, pendimethalin, prodiamine or trifluralin. Scotts Halts is one such crabgrass preventer. Follow directions indicated on the packaging and apply with a broadcast spreader.
Control already germinated crabgrass with a post-emergent herbicide. Look for one that contains the chemical MSMA or quinclorac. Weed-B-Gon with crabgrass preventer is an example of this type of product. Screw the bottle onto your garden hose end and spray over the entire yard. Make sure to read the directions to see if it can be used on your cultivar of grass. St. Augustine and centipede are two cultivars that can be damaged by this chemical.
Remove the crabgrass manually. This method is the safest alternative if you have a cultivar of grass that is sensitive to the chemicals that kill crabgrass. Take a serrated knife or v-shaped weeding tool and slice into the root of the crabgrass plant. Pull up and discard. Repeat for every crabgrass plant in your lawn.