Goat head stickers are the hard, spiny seed pods of a weed, often encountered as a painful surprise on bare feet or bicycle tires. These sharp nuisances are a widespread problem, particularly in dry and disturbed areas globally. The small, tack-like burs are designed for travel, easily hitching a ride on shoes, vehicle tires, or animal fur. Dealing with this pest requires understanding its unique life cycle and employing specific control methods to prevent its sharp seeds from spreading further.
The Plant Behind the Sticker
The plant responsible for these stickers is known scientifically as Tribulus terrestris, a species that has earned a host of descriptive common names, including Puncture Vine, Caltrop, and Devil’s-Weed. This invasive species is native to warm temperate and tropical regions of the Old World, but has since spread globally. The plant thrives in poor, sandy, or compacted soils, often colonizing roadsides, waste areas, and neglected lawns.
Tribulus terrestris is a low-growing, mat-forming summer annual, though it can behave as a perennial in warmer climates. Its slender stems radiate outward from a central taproot, trailing along the ground for up to a meter. The plant produces small, inconspicuous yellow flowers, which are soon replaced by the developing fruit that represents the true problem.
Anatomy and Impact of the Sticker
The structure commonly called a goat head sticker is the mature fruit of the plant, a hard, woody capsule that splits apart upon drying. This capsule fragments into five distinct, wedge-shaped segments known as nutlets. Each nutlet is heavily armed, typically bearing two or more rigid, horn-like spines that can measure up to a quarter of an inch long.
These projections give the fruit its common name because the shape of the nutlet resembles a goat’s head with horns. The function of this spiky design is seed dispersal, allowing the burs to readily hook onto anything passing by. The hardened spines easily puncture thin rubber, causing flat bicycle tires, and inflicting painful injuries to bare human or animal feet.
The nutlets also become deeply embedded in pet fur and paws, leading to discomfort and potential infection. The stickers can contaminate agricultural products like hay and wool, reducing their value. The spines are durable and remain a hazard long after the plant has died, as the seeds within the burs can remain viable in the soil for several years.
Strategies for Eradication
Controlling this weed requires a multi-faceted approach, and timing is the most important factor for success.
Manual and Cultural Control
Manual or physical removal is effective for small infestations, but it must be done before the plant sets seed. Plants should be carefully dug out, ensuring the central taproot is removed entirely, which is easiest when the plant is young. Once removed, the entire plant, especially any mature burs, must be disposed of properly, such as by bagging and placing them in the trash for deep burial, rather than composting. For areas already covered in stickers, specialized tools like a prickle roller or a stiff rake can be used to collect the burrs from the soil surface. Cultural control involves deeply watering an area to encourage a flush of seed germination, allowing the young seedlings to be removed before they can produce their own stickers.
Chemical Control
For larger areas, chemical control offers a practical solution, often involving both pre-emergent and post-emergent herbicides. Pre-emergent herbicides are applied in late winter or early spring before the seeds germinate, creating a chemical barrier to block the summer-growing weed from emerging. Post-emergent products like glyphosate or 2,4-D amine can be used to kill actively growing seedlings. Application is most successful when the plants are still small and have not yet produced flowers or fruit. Repeated applications are necessary throughout the summer growing season, as new seeds will germinate following successive rain events.