Dallisgrass (Papalum dilatatum Poir.) is a warm-season, invasive grassy weed native to South America. It was originally brought to the United States in the 19th century to be used as a forage grass. In the 21st century, it is most often encountered when it sprouts up in unsightly clumps in home lawns. Its growing season is longer than most species of turf grass. which gives it the upper hand in the invasion. The best way to kill dallisgrass for good is to apply a combination of chemical, cultural and physical control methods over several seasons.
Dig up dallisgrass clumps with a trowel. This removal strategy works best on young plants and areas with only mild to moderate infestations. When removing large, mature clumps of dallisgrass, be sure to remove their entire root systems. Even small root pieces are able to regenerate. Monitor your lawn for several subsequent seasons and re-dig any re-emerging dallisgrass clumps as soon as you spot them.
Spread a 3-inch layer of organic mulch over garden beds after you dig up the dallisgrass clumps. The mulch will kill any seedlings that sprout.
Kill widespread infestations of dallisgrass by spraying the offending clumps with herbicide. Choose a selective post-emergent herbicide prescribed for use on dallisgrass. Follow the manufacturer's instructions for application rates and methods. Spray in the summer when the dallisgrass is actively growing. It will often be necessary to retreat the weeds at regular intervals (dictated by the herbicide's manufacturer) throughout the growing season and for a few subsequent seasons. Do not water the grass for 24 hours after applying the herbicide.
Treat your lawn with a selective pre-emergent dallisgrass herbicide to prevent the seed in your lawn from germinating. Follow the manufacturer's instructions for application rates and amounts. Apply the herbicide in late winter or early spring--just before the dallisgrass is scheduled to germinate. Water the lawn with 1/2 inch of water immediately after applying the herbicide.