Goatheads, also known as puncture vine (Tribulus terrestris), are notorious for their sharp, woody seed pods. This noxious weed is often encountered as a painful reminder of a walk or the cause of a flat bicycle tire. Its ability to thrive in harsh conditions and effective seed dispersal mechanism have made it a pervasive problem across many continents. Understanding the plant’s biology is the first step toward effective management.
Identifying Puncture Vine
This annual, broadleaf plant belongs to the caltrop family. It grows low to the ground, forming dense, mat-like patches that radiate outward from a central taproot. Its stems and leaves are covered with fine, soft hairs.
The leaves are compound, finely divided into multiple pairs of smaller, fern-like leaflets. The plant produces small, five-petaled, lemon-yellow flowers, typically blooming from spring through fall. Though the flowers are inconspicuous, the fruit that follows is the source of the plant’s infamous reputation.
The fruit is a small, hard burr that breaks apart into five wedge-shaped nutlets, each containing several seeds. Each nutlet possesses two to four tough, sharp spines, giving the entire cluster a shape distinctly resembling a goat’s head or a medieval caltrop weapon. Native to Southern Eurasia and Africa, this species has successfully spread to become a worldwide invasive weed.
Physical Hazards and Invasive Spread
The mature, woody burrs produced by the puncture vine are responsible for a range of physical hazards. The spines can penetrate thin shoe soles, cause painful injuries to bare feet, and easily pierce bicycle and vehicle tires. Pets are also susceptible, as the burrs frequently lodge in paw pads and fur, causing discomfort and potential infection.
Beyond mechanical injury, the foliage contains steroidal saponins, which can be toxic to grazing livestock, particularly sheep. This can lead to conditions like hepatogenous photosensitization. Toxicity is a concern in agricultural areas when the weed is consumed because more palatable forage is scarce.
The rigid, sharp structure of the burr is a highly effective dispersal mechanism, designed to hitchhike on anything that brushes past it. Seeds are transported long distances by sticking to vehicle tires, shoe treads, clothing, or the fur and hooves of animals. A single plant can produce hundreds of burrs, and the seeds within these hard casings can remain viable in the soil for at least seven years, ensuring a persistent seed bank.
Strategies for Control and Removal
Managing goathead populations requires a combination of mechanical, chemical, and preventative strategies implemented consistently over time. Manual removal is preferred for small infestations, but must be done before flowers mature into hardened burrs. To prevent regrowth, pull the plant, ensuring the central taproot is removed or severed below the soil line.
All pulled plant material, especially if burrs are present, must be placed into heavy-duty plastic bags and disposed of in the trash, not composted, to prevent seed spread. Heavy gloves and thick-soled shoes are strongly recommended when working in infested areas to protect against the spines. Tools like a stirrup hoe or a specialized rolling tool can also be used to scrape up plants and collect burrs from the soil surface.
Chemical control utilizes both pre-emergent and post-emergent herbicides for larger areas. Pre-emergent herbicides are designed to prevent seeds from sprouting and should be applied in early spring before the soil is warm enough for germination. Post-emergent treatments target growing plants and are most successful when applied to young seedlings before they produce mature burrs.
For long-term prevention, simple cultural practices can discourage the weed’s growth. Increasing the density of desired turf or ground cover can outcompete the low-growing puncture vine for sunlight and nutrients. Covering small infested areas with clear plastic sheeting during the summer, a technique called solarization, uses the sun’s heat to kill seeds and existing plants in the top few inches of the soil.