Goat head thorns (Tribulus terrestris), also called puncturevine, is an annual weed that presents a significant nuisance and hazard. It is notorious for producing hard, woody burrs armed with sharp, tack-like spines that resemble a goat’s head. These spines easily puncture bicycle tires, thin-soled shoes, and cause painful injuries to people and pets. Each plant is a prolific seed producer, generating between 300 and 5,000 seeds per season that can remain viable in the soil for several years. Effective control requires a sustained, multi-faceted approach due to its aggressive growth and long-term seed viability.
Immediate Physical Removal Techniques
The most direct way to gain immediate relief is through hands-on removal, focusing on eliminating the plant before it sets seed. Target plants when they are young and actively growing, ideally before the small yellow flowers appear and the spiny burrs develop. This prevents the plant from adding to the extensive seed bank already present in the soil.
Manual removal works best when the soil is moist, allowing the plant to be pulled out completely. The goal is to sever or remove the entire taproot by pulling the plant where all the stems meet at the central crown. If the plant is larger, a hoe or specialized weeding tool can cut the plant off just below the soil surface, which usually prevents re-sprouting.
After removing the plants, clear the area of any loose, fallen burrs, which can easily spread and germinate. Dragging old carpet, a towel, or burlap across the infested area is effective, allowing the spines to adhere to the material. For paved areas, a stiff broom or wet-dry vacuum can collect the loose seeds. All plant material and collected burrs must be sealed in a heavy-duty plastic bag and disposed of in the trash, never added to a compost pile, as the seeds survive composting.
Applying Herbicides for Elimination
Chemical control manages large infestations or treats areas where manual removal is impractical. Pre-emergent herbicides are preventative, designed to kill seeds as they begin to sprout in the soil. These products, often containing active ingredients like oryzalin, benefin, or trifluralin, should be applied in late winter or early spring before germination.
For plants that have already emerged, post-emergent herbicides are necessary, and effectiveness increases when plants are small and actively growing. Selective broadleaf weed killers, such as 2,4-D and dicamba, are effective against puncturevine and can be safely applied to established turfgrass. Non-selective herbicides like glyphosate will kill the puncturevine but must be used only as a spot treatment in non-turf areas, as they destroy nearly all other vegetation they contact.
When using any herbicide, follow the label instructions and consider adding a surfactant to the spray mixture, which helps the chemical adhere to the puncturevine’s small, hairy leaves. Applying the herbicide before the plant flowers and sets its seeds is crucial, as chemical treatments will not prevent mature burrs from sprouting next season. The repeated germination of seeds throughout the season means multiple applications may be necessary to gain control.
Preventing Future Infestations
Long-term control relies on altering the environment to make it inhospitable for puncturevine, which thrives in sunny, bare, and disturbed soil. The most sustainable strategy is to establish dense, competitive vegetation, such as turfgrass or ground covers, that shade the soil. This shading prevents annual weed seeds from germinating and outcompetes any seedlings that manage to sprout.
Physical barriers are another effective tool for prevention, particularly in garden beds or around walkways. Applying a thick layer of mulch, ideally three inches deep or more, blocks sunlight and significantly inhibits seed germination. Landscape fabric can also be utilized under gravel or mulch to create a barrier, though vigilance is required to remove any plants that root on top of the fabric.
In larger areas, biological control is available using two specific weevil species: Microlarinus lareynii (seed-feeding) and Microlarinus lypriformis (stem-mining). These weevils are most successful in large, non-irrigated infestations and can take several years to reduce the weed population. Consistent monitoring and spot-treatment of new seedlings remain necessary to ensure the weed does not regain a foothold.