The grass bur, also known as sandbur or sandspur (Cenchrus species), is an annual weed that invades lawns and turf areas. This plant is identifiable by its sharp, spiny seed heads, which are difficult to remove from skin, clothing, and pet fur. Effective control relies on understanding its life cycle and timing interventions accurately. Successful management requires targeting both the current infestation and the seeds waiting in the soil.
Understanding the Grass Burr Life Cycle
Grass burrs are warm-season annual weeds, completing their life cycle within one growing season, though seeds remain viable for years. Germination begins when soil temperatures consistently reach 52 to 55 degrees Fahrenheit, typically in late spring or early summer. The weed grows throughout the summer, often unnoticed until it matures and produces spiky seed heads in mid-to-late summer. Since each burr contains several seeds, the primary goal of management is to kill the plant before it can reproduce and reseed the area.
Eradication Using Herbicides
Chemical control is the most direct method for combating grass burrs, divided into two strategies based on the plant’s life stage. The most efficient method is pre-emergent control, which involves applying a barrier to the soil before seeds germinate. Common active ingredients include prodiamine, pendimethalin, and dithiopyr. These herbicides must be applied in early spring, coinciding with the 52-55°F soil temperature window, and then watered into the soil to activate the chemical barrier.
A second application of pre-emergent herbicide is often necessary six to eight weeks after the first to ensure continuous protection throughout the extended germination period. This preventative approach is more successful than trying to eliminate mature plants later in the season. Post-emergent control targets grass burrs that have already sprouted and are actively growing. This method is less effective once the plants have matured and begun to produce hardened seed heads.
For existing plants, selective post-emergent herbicides containing active ingredients like quinclorac or MSMA (where legally available for turf use) can be used. These chemicals work best when applied to young, actively growing weeds, typically before the burrs form. Since grass burrs are a type of grass weed, choosing a selective product is necessary to kill the burr without damaging the surrounding turfgrass. Multiple applications may be needed to fully control a widespread infestation.
Non-Chemical Removal and Management Techniques
For small infestations or for those who prefer to avoid commercial chemicals, non-chemical methods offer a viable alternative, though they require intensive labor. Manual removal is effective for individual plants or small patches, but requires digging deep enough to remove the entire root system. Spot treatments can use household solutions such as horticultural vinegar, which contains a higher percentage of acetic acid than standard kitchen vinegar.
A vinegar solution works as a non-selective, contact herbicide, dehydrating and killing any plant tissue it touches, including desirable turfgrass. It should be applied directly to the weed on a warm, sunny day and is reserved for small, isolated plants or areas of bare ground. For large, heavily infested areas, soil solarization is an intensive non-chemical approach. This involves covering the area with clear plastic sheeting during the hottest months. The trapped solar heat sterilizes the top layer of soil, killing the seeds and existing plants below.
Preventing Future Infestations
Long-term success depends less on immediate eradication and more on improving the overall health of the lawn. Grass burrs are opportunistic weeds that thrive in thin, stressed turf and disturbed, sandy soils. The most effective cultural practice is increasing the density of the turfgrass, which shades the soil and crowds out weed seedlings.
Mowing at the correct height is important, as taller grass blades create more shade, discouraging germination. Addressing soil deficiencies through soil testing and amendments, such as proper fertilization, promotes a vigorous stand of grass that resists weed invasion. Adopting deep, infrequent watering practices encourages deep turfgrass roots, making the lawn more resilient and creating a drier surface soil layer that is less favorable for germination.