Grass burs, grassburs or sand burs (Cenchrus echinatus L.) are low-growing annual or perennial weeds that thrive in poor soils with low fertilization levels. The weed is most often found in dry, sandy soils but can be found in all soil types if conditions are favorable. The distinguishing feature of the grass bur plant is its spiny, hard seed heads that cling to skin and clothing. When a lawn is infested, the seed heads are pervasive and make enjoying the lawn nearly impossible. The best way to kill grass burs is to use a combination of methods.
Treat the lawn in late spring with a weed killer appropriate for your lawn and the type of turf grass you are growing. The weed killer should specifically state that it is for the control of sand bur or grass bur on the label. The label must also clearly state that it is appropriate for the type of grass you are growing; for example, Bermudagrass or St. Augustine grass. Don't guess or take someone's word on whether it is safe for your type of lawn grass. It must say it is safe on the label. Use only as directed. Overuse of herbicides can kill your lawn and ornamental plants, including trees.
Contact your local county extension office and find out the correct procedure to take a soil sample from your lawn and where to send the soil sample. Before sending the soil sample to the processing lab, you must write on the instructions what type of grass you are growing. The reason you take a soil sample is so you can find out all the amendments you need to add to your soil so the grass is as healthy as possible. Healthy turf grass will crowd out the grass burs before they can take over. A healthy lawn prevents the return of grass burs.
Add all recommended soil amendments to the lawn. If the soil test recommends several applications of the amendments during the season, be sure to add all amendments. It is important to follow the directions from the soil test carefully.
Reseed or re-sod any bare patches of ground where the grass burs may begin to grow. Grass burs will take every opportunity to infest a lawn, including growing in any area where there is no other grass.
Mow the grass at a height that is 50 percent higher than normal to allow the grass to grow thickly and shade out the low-growing grass bur. Mowing at a height of 3 to 4 inches is best for grass bur control.
Water deeply every seven to 10 days unless there is at least 1 inch of rain during that period. Watering deeply means watering so the ground is wet to a depth of 6 inches. Test with a sharp tool, such as a screwdriver, by pushing it into the soil and checking to see how deeply the water penetrated. Water deeply so the deeper grass roots can get to the water, while the top of the soil, where the shallow-rooted grass burs are located, stay dry. Watering that soaks only the top 1 or 2 inches of soil encourages grass bur growth.