Grass bur, or field sandbur, is an annual grassy weed that often pops up in lawns. Most homeowners notice the infestation when they step on one of its pesky burs. There are methods for killing the grass bur plant, but that is no solace to your bare feet if the burs are already in the grass. To get rid of grass burs on your lawn, spread an old blanket over the grass. Then step on it or drag it over the lawn. The grass burs will become embedded in the blanket's fibers. After several passes, most of the grass burs should be gone.
Wait them out. If you live in a climate with freezing winters, the first frost will kill the grass burs for you. And winter does a better job than most post-emergent grass bur herbicides at getting rid of this persistent weed. Follow up with a spring application of a pre-emergent herbicide, and you should be rid of the grass burs.
Spray the grass bur plants with a post-emergent herbicide labeled for use on grass burs and safe to use on the type of grass in your lawn. Follow the manufacturer's instructions when spraying (most require you to coat the grass bur plant's foliage just until the point of runoff). Re-spray the grass bur plants at the intervals indicated on the herbicide's packaging.
Treat your lawn with a granular or spray pre-emergent herbicide that targets grass burs and is labeled as safe to use on the grass in your lawn. Follow the manufacturer's instructions for application rates. Make your first application in February. Light infestations can be controlled with two applications administered at six-week intervals. To control a heavy infestation of grass bur seed, the horticultural experts at Texas A&M recommend following up with subsequent applications in May, July and September.
Water the lawn with one to two inches of water immediately after each application of pre-emergent herbicide.
Mow your lawn regularly. If any grass bur plants manage to sprout, they will likely be cut down before they can produce seed burs. Use a grass bag attachment to catch any seed burs that do crop up. Keep your lawn at the higher end of the height limit recommended for your grass variety. Taller grass is more resistant to infestation.